Low power consumption data transmission circuit and method, and liquid crystal display apparatus using the same

The present invention relates to a data transmission circuit and method in which data is transmitted and a liquid crystal display apparatus in which display data is transmitted and the transmitted data is displayed on a liquid crystal panel.

As the conventional data transmission circuit is known, for example, a data transmission circuit provided with an input/output interface called GTL (Gunning Transceiver Logic) or CTT (Center Tapped Termination), as disclosed by Nikkei Electronics, No. 556, Jun. 8, 1992, pp. 133 to 144 published by Nikkei BP-Sha.

In the conventional liquid crystal display apparatus, an inputted video signal is converted by a liquid crystal controller into a display data signal for input to a liquid crystal data driver. This display data signal is supplied to the liquid crystal data driver by use of a data transmission circuit as mentioned above. The liquid crystal data driver generates a liquid crystal driving voltage from the supplied display data signal and outputs the generated liquid crystal driving voltage to a liquid crystal panel, thereby effecting the display of an image. For example, in a liquid crystal display apparatus providing display with RGB×64 gradation levels (64 gradation levels for each of R, G and B) and 260 thousands of colors, display data generated by a liquid crystal controller is connected to a plurality of liquid crystal data drivers by a (RGB×6=18)-bit data bus so that the display data is transferred to each liquid crystal data driver to effect display, as disclosed by the article 23.2 in SID (SOCIETY FOR INFORMATION DISPLAY) INTERNATIONAL SYMPOSIUM DIGEST OF TECHNICAL PAPERS VOLUME XXV, 1994.

However, an apparatus such as a liquid crystal display apparatus using the conventional data transmission circuit has the problem of large power consumption. More particularly, as an output circuit of the data transfer circuit is used, for example, a CMOS circuit as an output circuit which transmits data represented by the voltage amplitude value of a power supply voltage, or an open drain circuit or push-pull circuit as a transmission bus in which a line is terminated. In the case where the CMOS circuit is used, a driving current flows when a bit value of output data (for example, display data) is changed. Thereby, an electric power is consumed. Thus, a possible method considered in order to reduce the power consumption is to cause the change in bit value of output data to be not made as much as possible. In the CMOS circuit, there is a fear that an operation following input data becomes insufficient as the speed of input data is higher.

On the other hand, in the open drain circuit or push-pull circuit as a transmission bus in which a line is terminated, a sufficient operation is enabled even for high-speed input data but a steady current flows irrespective of an input signal. Namely, in the case where the open drain circuit is used, a driving current does not flow unless output data has a high level. However, if the output data has a low level, a driving current flows. Thus, a possible method considered in order to reduce the power consumption is to cause the output data to be provided with a high level. Also, in the case where the push-pull circuit is used, a driving current flows with power consumption irrespective of whether the level of output data is high or low. Thus, a possible method considered in order to reduce the power consumption is to cause the output of a termination voltage level.

In recent years, the image resolving power of a liquid crystal panel has been improved with the larger size of the liquid crystal panel. Therewith, the amount of display data to be transmitted to the liquid crystal panel within a unit time is increased. Accordingly, there is the problem that the power consumption of the transmission circuit is increased more and more.

Accordingly, an object of the present invention is to provide a data transmission circuit and method in which a reduction in power consumption is enabled and a liquid crystal display apparatus which uses such data transmission circuit or method.

To attain the above object, a data transmission circuit according to one aspect of the present invention has a transmitter section sequentially inputted with n-bit parallel data (n: an integer) and a receiver section connected to the transmitter section through a transmission line, in which the n-bit parallel data is transmitted from the transmitter section to the receiver section through the transmission line. The transmitter section is provided with a first holding circuit for storing, the n-bit parallel data inputted to the transmitter section, by plural sets the number of which is not more than 2 m (m: an integer satisfying m<n), judgement means for judging whether or not the present n-bit parallel data inputted to the transmitter section is identical to any one of the plural sets of n-bit parallel data stored in the first holding circuit, thereby outputting a first result of judgement in the case where the identification to any one of the plural sets is determined and a second result of judgement in the case where the identification to none of the plural sets is determined, hold position information output means for outputting information with m or less bits indicative of a hold position of the one set of n-bit parallel data in a second holding circuit in the case where the first result of judgement is outputted by the judgement means, and first output means for transmitting the hold position information to the receiver section through the transmission line in the case where the first result of judgement is outputted by the judgement means while transmitting, the present n-bit parallel data inputted to the transmitter section, to the receiver section through the transmission line in the case where the second result of judgement is outputted by the judgement means. In the case where the second result of judgement is outputted by the judgement means, the first holding circuit is inputted and stored with the present n-bit parallel data inputted to the transmitter section. The receiver section is provided with the second holding circuit for storing the same plural sets of n-bit parallel data as the first holding circuit, and second output means for reading, in the case where the hold position information is received through the transmission line, the one set of n-bit parallel data from the second holding circuit in accordance with the hold position information and outputting the read data from the receiver section while storing, in the case where the present n-bit parallel data is received through the transmission line, the received present n-bit parallel data into the second holding circuit and outputting the data from the receiver section.

Thus, in the present invention, in the case where the present n-bit parallel data inputted to the transmitter section is identical to any one of the plural sets of n-bit parallel data stored in the first holding circuit, information with m or less bits indicative of a hold position of the one set of n-bit parallel data in the second holding circuit is transmitted. Therefore, it is possible to make a reduction in power consumption as compared with the case where one set of n-bit parallel data is transmitted.

In an example of the present invention, each of the first and second output circuits is a circuit (for example, a CMOS circuit) for transmitting the n-bit parallel data in which data is represented by the voltage amplitude value of a power supply voltage and the first output circuit has a data holding circuit (for example, a latch circuit. In the case where the second result of judgement is outputted by the judgement means, (n−m)-bit parallel data in the present n-bit parallel data inputted to the transmitter section is transmitted from the first output circuit to the receiver section through the transmission line while the present (n−m)-bit parallel data is stored into the data holding circuit. In the case where the first result of judgement is outputted by the judgement means, that (n−m)-bit parallel data immediately before the output of the first result of judgement which is stored in the data holding circuit, is transmitted from the first output circuit to the receiver section through the transmission line.

With such a construction, in the case where the first result of judgement is outputted, the bit value of output data is not changed and hence a driving current does not flow, thereby making it possible to reduce the power consumption as compared with the prior art.

In an example of the present invention, the transmission line is connected to a termination voltage through a terminating resistor. In the case where the second result of judgement is outputted by the judgement means, the first and second output circuits transmit an output with a low level and an output with a high level to the receiver section through the transmission line in accordance with (n−m)-bit parallel data of the present n-bit parallel data inputted to the transmitter section 100 . In the case where the first result of judgement is outputted by the judgement means, the first and second output circuits transmit an output with a termination voltage level or an output with a high level to the receiver section through the transmission line.

In an example of the present invention, the first and second output circuits are open drain circuits, the above-mentioned output with a low level is a voltage level between a ground voltage and the termination voltage level, and the above-mentioned output with a high level is the termination voltage level. In the case where the first result of judgement is outputted by the judgement means, the output with a high level is transmitted to the receiver section through the transmission line. With such a construction, in the case where the first result of judgement is outputted, a steady current does not flow. Thereby, it is possible to reduce the power consumption as compared with the prior art.

In another example of the present invention, the first and second output circuits are push-pull circuits, the above-mentioned output with a low level is a voltage level between the ground voltage and the termination voltage level, and the above-mentioned output with a high level is a level between a power supply voltage of the first output section and the termination voltage level. In the case where the first result of judgement is outputted by the judgement means, the output with the termination voltage level is transmitted to the receiver section through the transmission line. With such a construction, in the case where the first result of judgement is outputted, a steady current does not flow. Thereby, it is possible to reduce the power consumption as compared with the prior art.

FIG. 1 is a block diagram showing the overall construction of a liquid crystal display apparatus according to an embodiment of the present invention;

FIG. 2 is a circuit diagram showing the construction of a transceiver circuit used in a data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 3 is a circuit diagram showing the construction of a holding circuit used in the transceiver circuit of the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIGS. 4A to 4 J are charts for explaining the operation of the holding circuit used in the transceiver circuit of the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 5 is a circuit diagram showing the construction of a receiver circuit used in the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 6 is a circuit diagram showing the construction of an output circuit and an input circuit used in the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 7 is a diagram for explaining the operation of an output circuit and an input circuit used in the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 8 is a circuit diagram showing the construction of an output circuit and an input circuit used in the data transmission circuit of the liquid crystal apparatus according to the embodiment of the present invention;

FIG. 9 is a circuit diagram showing the construction of an output circuit and an input circuit used in a data transmission circuit of a liquid crystal apparatus according to a second embodiment of the present invention;

FIG. 10 is a diagram for explaining the operation of the output circuit and the input circuit used in the data transmission circuit of the liquid crystal apparatus according to the second embodiment of the present invention;

FIGS. 11A to 11 E are charts for explaining the operation of a holding circuit used in a transceiver circuit of the data transmission circuit of the liquid crystal apparatus according to the second embodiment of the present invention;

FIG. 12 is a circuit diagram showing the construction of an output circuit and an input circuit used in the data transmission circuit of the liquid crystal apparatus according to the second embodiment of the present invention;

FIG. 13 is a circuit diagram showing the construction of an output circuit and an input circuit used in a data transmission circuit of a liquid crystal apparatus according to a third embodiment of the present invention;

FIG. 14 is a diagram for explaining the operation of the output circuit and the input circuit used in the data transmission circuit of the liquid crystal apparatus according to the third embodiment of the present invention;

FIGS. 15A to 15 E are charts for explaining the operation of a holding circuit used in a transceiver circuit of the data transmission circuit of the liquid crystal apparatus according to the third embodiment of the present invention; and

FIG. 16 is a circuit diagram showing the construction of an output circuit and an input circuit used in the data transmission circuit of the liquid crystal apparatus according to the third embodiment of the present invention.

Data transmission circuits according to embodiments of the present invention will now be described in reference to the accompanying drawings.

First, the description using FIGS. 1 to 8 will be made in conjunction with an example of the construction of a liquid crystal display apparatus to which a data transmission circuit according to an embodiment of the present invention is applied. The data transmission circuit according to the present invention is applicable to another apparatus.

A data transmission circuit according to one aspect of the present invention has the following construction.

Namely, the data transmission circuit has a transmitter section (for example, a transceiver circuit 100 ) sequentially inputted with n-bit parallel data (n: an integer, for example, 24 ) and a receiver section (for example, receiver circuits 200 ) connected to the transmitter section through a transmission line. The n-bit parallel data is transmitted from the transmitter section to the receiver section through the transmission line. The transmitter section is provided with a first holding circuit ( 110 ) for storing, n-bit parallel data inputted to the transmitter section, by plural sets (for example, 8 kinds) the number of which is not more than 2 m (m: an integer satisfying m<n), a judgement unit (for example, comparators CP 0 to CP 7 , an OR circuit 130 , a latch circuit 145 and RE) for judging whether or not the present n-bit parallel data inputted to the transmitter section is identical to any one of the plural sets of n-bit parallel data stored in the first holding circuit and outputting a first result of judgement (RE) in the case where the identification is determined and a second result of judgement (RE) in the case where the non-identification is determined, a hold position information output unit (for example, an encoder 120 and a latch circuit 140 ) for outputting information with m or less bits indicative of a hold position of the one set of n-bit parallel data in a second holding circuit ( 210 ) in the case where the first result of judgement is outputted by the judgement unit, and a first output unit (for example, a selection circuit 150 and output circuits 160 A and 160 B) for transmitting the hold position information to the receiver section through the transmission line in the case where the first result of judgement is outputted by the judgement unit while transmitting, the present n-bit parallel data inputted to the transmitter section, to the receiver section through the transmission line in the case where the second result of judgement is outputted by the judgement unit. In the case where the second result of judgement is outputted by the judgement unit, the first holding circuit is inputted and stored with the present n-bit parallel data inputted to the transmitter section. The receiver section is provided with the second holding circuit ( 210 ) for storing the same plural sets of n-bit parallel data as the first holding circuit, and a second output unit (for example, input circuits 220 A to 220 C, latch circuits 230 and 235 , and a selection circuit 240 ) for reading, in the case where the hold position information is received through the transmission line, the one set of n-bit parallel data from the second holding circuit in accordance with the hold position information and outputting the read data from the receiver section while storing, in the case where the present n-bit parallel data is received through the transmission line, the received present n-bit parallel data into the second holding circuit and outputting the data from the receiver section.

First, an example of the overall construction of the liquid crystal display apparatus in the present embodiment will be described using FIG. 1 . In each embodiment described in the following, an example of n-bit parallel data (n: an integer) inputted to a transmitter section (for example, a transceiver circuit 100 ) is display data of 24 bits with 8 bits for each of R, G and B (for example, display with 256 gradation levels and 16,777,216 colors). However, the present invention is applicable irrespective of the number of bits or is also applicable to the case of parallel data the number of bits of which is other than 24. In the present invention, such n-bit parallel data is transmitted, as one set of display data, that is, display data for one pixel, to the receiver circuit serially or sequentially every one pixel.

The liquid crystal display apparatus according to the present embodiment is composed of a liquid crystal controller 1000 , a data driver 2000 , a scan driver 3000 and a liquid crystal panel 4000 . The liquid crystal controller 1000 , the data driver 2000 and the scan driver 3000 are connected by a transmission line L.

The liquid crystal controller 1000 is inputted with a display signal DISP transferred from a system device. On the basis of the inputted display signal DISP, the liquid crystal controller 1000 generates display data DATA to be displayed on the liquid crystal panel 4000 . A transceiver circuit 100 generates transmit display data T-DATA, a display data transmission clock T-CLK, a horizontal synchronizing signal H-SYNC, a vertical synchronizing signal V-SYNC and a register validation signal RE on the basis of inputted display data I-DATA and outputs them to the data driver 2000 and the scan driver 3000 . The details of the transceiver circuit 100 will be described later on by use of FIG. 2 . The transmit display data T-DATA is transmitted on a data bus which is a 24-bit parallel bus. The horizontal synchronizing signal H-SYNC is a synchronizing signal indicating the timing of the data driver 2000 which will be described later on. The vertical synchronizing signal V-SYNC is a synchronizing signal indicating the timing of the scan driver 3000 which will be described later on. The register validation signal RE is newly provided in the present embodiment and the details thereof will be described later on by use of FIG. 2 .

The data driver 2000 sequentially takes in the transmit display data T-DATA every one pixel on the basis of the transmission clock T-CLK, the horizontal synchronizing signal H-SYNC and the register validation signal RE transmitted from the transceiver circuit 100 of the liquid crystal controller 1000 to generate a liquid crystal driving voltage corresponding to the display data. The data driver 2000 is generally composed of a plurality of data drivers 2000 A, 2000 B, - - - , and 2000 N which are provided corresponding to the resolving power of the liquid crystal panel 4000 . The respective data drivers 2000 A, 2000 B, - - - , and 2000 N are provided with receiver circuits 200 A, 200 B, - - - , and 200 N which sequentially take in the transmit display data T-DATA every one pixel on the basis of the transmission clock T-CLK, the horizontal synchronizing signal H-SYNC and the register validation signal RE to generate output display data O-DATA. The detailed construction of the receiver circuit ( 200 A, 200 B, - - - , 200 N) will be described later on by use of FIG. 5 .

The scan driver 3000 generates a sequential selection signal for the liquid crystal panel 4000 on the basis of the inputted vertical synchronizing signal V-SYNC.

A data transmission circuit is formed by the transceiver circuit 100 , the receiver circuits 200 and the transmission line L which connects both the circuits. Display data of RGB×8 bits or 24 bits in total is transmitted from the transceiver circuit 100 to the receiver circuits 200 A, 200 B, - - - , and 200 N, serially every one pixel, through the data bus in the transmission line L.

Next, an example of the construction of the transceiver circuit 100 used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment will be described using FIG. 2 .

The transceiver circuit 100 is composed of a holding circuit 110 , 2 m (for example, m=3) or less (for example, eight) comparators CP 0 , CP 2 , - - - and CP 7 , an encoder 120 , an OR circuit 130 , latch circuits 140 and 145 , a selection circuit 150 , and output circuits 160 A, 160 B, 160 C and 160 D.

The holding circuit 110 is sequentially inputted with the data transmission clock CLK and the input display data I-DATA which is parallel data having, for example, 24 bits with 8 bits for each of R,G and B. The holding circuit 110 sequentially holds plural sets of received input display data I-DATA in synchronism with the timing of the transmission clock CLK. Herein, the holding circuit 110 is constructed such that it holds eight sets of input display data I-DATA and the held input display data I-DATA turns into eight different kinds of data through an operation which will be described later on. The holding circuit 110 outputs the plural sets of held display data as data RD 0 , RD 1 , - - - and RD 7 . An example of the detailed construction of the holding circuit 110 will be described later on by use of FIG. 3 .

Respective first input terminals of the comparators CP 0 , CP 1 , - - - and CP 7 are inputted with the data RD 0 , RD 1 , - - - and RD 7 outputted by the holding circuit 110 and the other or second input terminals thereof are inputted with the input display data I-DATA. The comparator CP 0 , CP 1 , - - - or CP 7 compares the data RD 0 , RD 1 , - - - or RD 7 and the input display data I-DATA to output a coincidence signal AG 0 , AG 1 , - - - or AG 7 which takes one level (for example, high level) when both the data coincide with each other (that is, a signal indicative of a first result of judgement).

The coincidence signals AG 0 , AG 1 , - - - and AG 7 are inputted to the encoder 120 and the OR circuit 130 . The encoder 120 encodes the coincidence signals AG 0 , AG 1 , - - - and AG 7 of 8 bits into a 3-bit signal. For example, when the coincidence signal AG 0 takes a high level, an output signal of the encoder 120 (that is, hold position information) provides a 3-bit signal of “000”. When the coincidence signal AG 1 takes a high level, the output signal of the encoder 120 provides a 3-bit signal of “001”. When the coincidence signal AG 2 takes a high level, the output signal of the encoder 120 provides a 3-bit signal of “010”. The encoded 3-bit signal is latched by the 3-bit latch circuit 140 .

The OR circuit 130 produces a logical sum of the coincidence signals AG 0 , AG 1 , - - - and AG 7 to output a selection signal SEL which takes a high level when any one of the coincidence signals AG 0 , AG 1 , - - - and AG 7 takes a high level. The selection signal SEL is inputted to the holding circuit 110 and the latch circuit 145 . The selection signal SEL latched by the latch circuit 145 is inputted as a register validation signal RE to the output circuit 160 A, the selection circuit 150 and the output circuit 160 C.

In the present embodiment, present 24-bit input display data I-DATA inputted to the transceiver circuit 100 is divided into, for example, display data of 21 upper bits and display data of 3 lower bits. Another possible method of bit division may include the division into 21 lower bits and 3 upper bits or the extraction of any 3 bits from the 24-bit data.

In the case where the register coincidence signal RE takes, for example, a low level, that is, in the case where present input display data I-DATA inputted to the holding circuit 110 coincides with none of 8 kinds of display data (or in the case where a second result of judgement is obtained), the output circuit 160 A outputs the inputted 21-bit display data as it is. Also, the selection circuit 150 responds to the signal RE to select the 3-bit display data so that it is provided to the output circuit 160 B. Namely, the 24-bit input display data I-DATA is outputted as 21-bit transmit display data T-DATA( 21 ) from the output circuit 160 A and as 3-bit transmit display data T-DATA( 3 ) from the output circuit 160 B.

On the other hand, in the case where the register coincidence signal RE takes a high level, that is, in the case where present input display data I-DATA inputted to the holding circuit 110 coincides with any one of 8 kinds of display data (or in the case where the first result of judgement is obtained), the output circuit 160 A continues the output of 21-bit display data inputted preceding the present 21-bit display data. Also, the selection circuit 150 selects the output data of the encoder 120 latched by the latch circuit 140 (or hold position information) so that it is provided to the output circuit 160 B. Namely, only 3-bit encoded data is outputted as T-DATA( 3 ) from the output circuit 160 B.

Also, the register validation signal RE is outputted from the output circuit 160 C and the transmission clock CLK is outputted from the output circuit 160 D.

In FIG. 2, symbols ( 24 ), ( 21 ) and ( 3 ) applied to the transmission lines indicate 24-bit, 21-bit and 3-bit parallel data, respectively. Such denotation is similarly made in FIG. 3 and subsequent figures.

Now, an example of the construction of the holding circuit 110 used in the transceiver circuit 100 of the data transmission circuit of the liquid crystal display apparatus according to the present embodiment will be described using FIG. 3 .

The holding circuit 110 in the present embodiment is composed of a plurality of (for example, eight) 24-bit registers SR 0 , SR 1 , - - - and SR 7 , and eight selection circuits SL 0 , SL 1 , - - - and SR 7 . The registers SR 0 , SR 1 , - - - and SR 7 are connected in a 8-stage configuration to form a shift register.

The selection circuit SL 0 selects one of the input display data I-DATA and an output Q of the register SR 0 in accordance with the selection signal SEL to input the selected data to an input terminal D of the register SR 0 . In the case where the selection signal SEL takes a low level, the selection circuit SL 0 selects the input display data I-DATA so that the data is held by the register SR 0 . In the case where the selection signal SEL takes a high level, the selection circuit SL 0 selects data held in the register SR 0 so that the data is held again by the register SR 0 . The data held by the register SR 0 is outputted as data RD 0 .

The selection circuit SL 1 selects one of the output Q of the register SR 0 and an output Q of the register SR 1 in accordance with the selection signal SEL to input the selected data to an input terminal D of the register SR 1 . In the case where the selection signal SEL takes a low level, the selection circuit SL 0 selects the output Q of the register SR 0 so that the data is held by the register SR 1 . In the case where the selection signal SEL takes a high level, the selection circuit SL 0 selects data held in the register SR 1 so that the data is held again by the register SR 1 . The operations of the selection circuits SL 2 to SL 7 are similar to that of the selection circuit SL 1 .

Now, the operation of the holding circuit 110 for specific input display data I-DATA will be described using FIGS. 4A to 4 J together with FIG. 2 and FIG. 3 .

FIG. 4A shows transmission clock CLK, and FIG. 4B shows input display data I-DATA inputted in synchronism with the transmission clock CLK. Namely, in synchronism with the timings t 1 , t 2 , t 3 , t 4 , t 5 , - - - of the transmission clock CLK, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 2 ”, - - - are sequentially inputted as the input display data I-DATA to the holding circuit 110 of FIGS. 2 and 3.

At time t 1 , “Color 1 ” is held by the register SR 0 , as shown by FIG. 4D, and data RD 0 shown in FIG. 2 provides “Color 1 ”.

Next, when “Color 1 ” in the input display data is inputted to the holding circuit 110 at time t 2 , the comparator CP 0 shown in FIG. 2 outputs a coincidence signal AG 0 with a high level since the data RD 0 and the input display data I-DATA coincide with each other. Accordingly, a selection signal SEL outputted by the OR circuit 130 takes a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the register SR 0 are maintained, as shown at time t 2 in FIG. 4 D. Also, when the selection signal SEL takes the high level, a register validation signal RE turns into a high level, as shown in FIG. 4 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “000”. Therefore, the output circuit 160 B outputs “000”. Since this encoded data indicates the register SR 0 , there results in that data indicating “Reg 0 ” is outputted from the output circuit 160 B, as shown in FIG. 4 J. Also, when the register validation signal RE takes the high level, the output circuit 160 A maintains the preceding output. Therefore, the output circuit 160 A outputs the same “Color 1 ” as that at time t 1 , as shown in FIG. 4 I. The operations at times t 3 and t 4 are similar to that at time t 2 .

When “Color 2 ” is inputted as the input display data I-DATA to the holding circuit 110 at time t 5 , the output of the comparator CP 0 shown in FIG. 2 turns into a low level. Therefore, the selection signal SEL outputted by the OR circuit 130 turns into a low level. Accordingly, the selection circuit SL 0 shown in FIG. 3 selects the input data I-DATA and the selection circuit SL 1 selects the output of the register SR 0 . As a result, the register SR 0 holds “Color 2 ”, as shown in FIG. 4 D and the register SR 1 holds “Color 1 ” shifted from the register SR 0 , as shown in FIG. 4 E.

At times t 6 to t 8 , the input display data I-DATA sequentially changes to “Color 3 ”, “Color 4 ” and “Color 5 ”, as shown in FIG. 4 B. Therefore, the registers SR 0 , SR 1 , SR 2 , SR 3 and SR 4 sequentially operate as a shift register in a manner similar to that in the operation described in conjunction with time t 5 so that they hold “Color 5 ”, “Color 4 ”, “Color 3 ”, “Color 2 ” and “Color 1 ”, respectively, at time t 8 .

Next, when “Color 2 ” in the input display data is inputted to the holding circuit 110 at time t 9 , “Color 2 ” is held in the register SR 3 at time t 9 , as shown in FIG. 4 G. Therefore, the comparator CP 3 shown in FIG. 2 outputs a coincidence signal AG 3 with a high level since both the data RD 3 and the input display data I-DATA coincide as “Color 2 ”. Accordingly, the selection signal SEL outputted by the OR circuit 130 turns into a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the registers SR 0 to SR 4 at time t 8 are maintained, as shown at time t 9 in FIGS. 4D to 4 H. Also, when the selection signal SEL takes the high level, the register validation signal RE turns into a high level, as shown in FIG. 4 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “011”. Therefore, the output circuit 160 B outputs “011”. Since this encoded data indicates the register SR 3 , there results in that data indicating “Reg 3 ” is outputted from the output circuit 160 B, as shown in FIG. 4 J. Also, when the register validation signal RE takes the high level, the output circuit 160 A maintains the preceding output. Therefore, the output circuit 160 A outputs the same “Color 5 ” as that at time t 8 , as shown in FIG. 4 I. Up to time t 14 , the same input display data I-DATA as that having already been held in the holding circuit 110 is inputted as “Color 3 ” at time t 10 , “Color 4 ” at time t 11 , - - - . Therefore, the operations at times t 10 to t 14 are similar to that at time t 9 . However, since the position of a register having the held data is different, 3-bit data indicating each register position is outputted, as shown in FIG. 4 J.

Namely, as shown in FIGS. 4I and 4J, in the case where the input display data I-DATA is the same as data held in the holding circuit 110 (as shown at times t 2 , t 3 , t 4 , t 9 , t 10 , t 11 , t 12 , t 13 and t 14 in FIGS. 4A to 4 J), the 21-bit data shown in FIG. 4J holds the preceding data and the display data can be transmitted using the 3-bit data. Namely, the transmission of 24-bit display data is performed with 3 bits.

Next, an example of the construction of the receiver circuit 200 used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment will be described using FIG. 5 .

The receiver circuit 200 is composed of a holding circuit 210 , input circuits 220 A, 220 B, 220 C and 220 D, latch circuits 230 and 235 , and a selection circuit 240 .

The input circuit 220 A is inputted with 21-bit transmit display data T-DATA( 21 ) outputted by the output circuit 160 A shown in FIG. 2 . The input circuit 220 B is inputted with 3-bit transmit display data T-DATA( 3 ) outputted by the output circuit 160 B shown in FIG. 2 . The transmit display data T-DATA( 21 ) and the transmit display data T-DATA( 3 ) are inputted as 24-display data T-DATA( 24 ) to the holding circuit 210 . Also, the transmit display data T-DATA( 3 ) is held by the latch circuit 230 .

The input circuit 220 C is inputted with a register validation signal RE outputted by the output circuit 160 C shown in FIG. 2 . The register validation signal RE is held by the latch circuit 235 while it is inputted as a selection signal SEL to the holding circuit 210 . The input circuit 220 D is inputted with a clock CLK outputted by the output circuit 160 D shown in FIG. 2 . The clock CLK is inputted as a synchronizing signal to the holding circuit 210 and the latch circuits 230 and 235 .

The holding circuit 210 is inputted with the data transmission clock CLK, the parallel transmit display data T-DATA of RGB×8 bits or 24 bits in total, and the selection signal SEL. The holding circuit 210 is constructed so that it sequentially holds, plural sets of input display data I-DATA inputted thereto, in synchronism with the timing of the transmission clock CLK. Herein, the holding circuit 210 is constructed such that it holds 2 m (for example, m=3) or less (for example, eight) sets of input display data (or n-bit parallel data) I-DATA and the held input display data I-DATA turns into eight different kinds of data through an operation which will be described later on. The holding circuit 210 outputs the plural sets of held display data as data RD 0 , RD 1 , - - - and RD 7 .

The construction of the holding circuit 210 is similar to that of the holding circuit 110 shown in FIG. 3 . Therefore, when the selection signal SEL has a low level, the holding circuit 210 operates as a 8-stage shift register which holds the inputted transmit display data T-DATA while sequentially shifting it. When the selection signal SEL turns into a high level, a value held at the preceding timing is held as it is. The holding circuit 110 and the holding circuit 120 are synchronized by the transmission clock CLK. Therefore, when data held by the 8 stages of registers SR 0 to SR 7 forming the holding circuit 110 changes as shown in FIGS. 4D to 4 H, the contents of the 8 stages of registers forming the holding circuit 210 have a similar change.

In the case where the register validation signal RE has a low level, the selection circuit 240 selects the output RD 0 of the holding circuit 210 and outputs it as output display data O-DATA. Since this output RD 0 corresponds to the output RD 0 shown in FIG. 3, it is data held by the register SR 0 . Accordingly, when the data of register SR 0 of the holding circuit 110 has a sequential change to “Color 2 ”, “Color 3 ”, “Color 4 ” and “Color 5 ”, as shown at times t 5 to t 8 in FIG. 4D, the output RD 0 of the holding circuit 210 has a similar sequential change to “Color 2 ”, “Color 3 ”, “Color 4 ” and “Color 5 ”.

On the other hand, in the case where the register validation signal RE has a high level, the selection circuit 240 selects data RD 0 , - - - or RD 7 indicated by a decoded value of 3-bit data held by the latch circuit 230 and outputs the selected data as output display data O-DATA. Since the output RD 0 , - - - or RD 7 of the holding circuit 210 corresponds to the output RD 0 , - - - or RD 7 shown in FIG. 3, it is data held by the register SR 0 , - - - or SR 7 . Accordingly, in the case where the 3-bit data held by the latch circuit 230 is “Reg 3 ”, as shown at time t 9 in FIG. 4J, a value held by the register SR 3 shown in FIG. 3, that is, the output data RD 3 of the holding circuit 210 is selected so that “Color 2 ” is outputted.

As mentioned in the foregoing, in the case where input display data I-DATA is the same as data held in the holding circuit 110 (as shown at times t 2 , t 3 , t 4 , t 9 , t 10 , t 11 , t 12 , t 13 and t 14 in FIGS. 4A to 4 J), 21-bit data shown in FIG. 4I holds the preceding data and the display data can be transmitted using 3-bit data. Namely, the transmission of 24-bit display data can be performed with 3 bits. On the other hand, the receiver circuit 200 can use data held by the holding circuit 210 to restore the transmitted 3-bit data into 24-bit data.

Next, the construction and operation of the output circuit 160 A and the input circuit 220 A used in the data transmission circuit of the liquid crystal apparatus according to the present embodiment will be described using FIGS. 6 and 7.

The output circuit 160 A is composed of switching circuits SW 1 and SW 2 of CMOS, a selection circuit 162 and a latch circuit 164 . The switching circuits SW 1 and SW 2 are connected in series between a power supply voltage VCC and a ground potential GND, and the gate of the switching circuit SW 1 has an inverted input.

Input data I-DATA is inputted to the selection circuit 162 and the latch circuit 164 . The latch circuit 164 holds the input data I-DATA and outputs it to the selection circuit 162 . The selection circuit 162 selects one of inputs in accordance with a register validation signal RE. When the register validation signal RE has a low level, the selection circuit 162 outputs the input data I-DATA to the switching circuits SW 1 and SW 2 as it is. When the register validation signal RE has a high level, the selection circuit 162 outputs, the input data I-DATA held by the latch circuit 164 , to the switching circuits SW 1 and SW 2 . With such a construction, the selection circuit 164 operates so that for example, as shown at time t 2 , t 3 or t 4 in FIG. 4I, the preceding display data “Color 1 ” is outputted as maintained.

When the input data I-DATA has a low level, the switching circuit SW 1 is turned on and the switching circuit SW 2 is turned off, so that transmit data T-DATA outputted from the output circuit 160 A to the transmission line L takes a high level of the power supply voltage VCC at time tm, as shown in FIG. 7 . Also, when the input data I-DATA has a high level, the switching circuit SW 1 is turned off and the switching circuit SW 2 is turned on, so that the transmit data T-DATA outputted from the output circuit 160 A takes a low level of the ground potential GND at time tm+1, as shown in FIG. 7 .

In the present embodiment, in the case where data held in the holding circuit 110 is transmitted, as shown at times 8 and 9 in FIG. 4I, the preceding data is maintained. For example, consider times t 9 in FIG. 7 in which data has a high level at time t 8 . Namely, in this case, the conventional system operates so that the data turns into a low level at time t 9 , as shown by dotted line. In the present embodiment, however, the preceding data (or the high level) is held at time t 9 , as shown by solid line. In the output circuit including the CMOS circuit, a driving current flows at a data change point where the bit value of display data changes. Thereby, the power consumption is increased. However, in the present embodiment, an increase in power consumption is suppressed by causing no change in bit value so that a driving current does not flow.

As shown in FIG. 6, the input circuit 220 A is composed of switching circuits SW 3 and SW 4 which include, for example, CMOS. The switching circuits SW 3 and SW 4 are connected in series between a power supply voltage VCC and a ground potential GND, and the gate of the switching circuit SW 3 has an inverted input.

When transmit data T-DATA inputted through the transmission line L has a low level, the switching circuit SW 3 is turned on and the switching circuit SW 4 is turned off, so that transmit data T-DATA outputted from the input circuit 220 A takes a high level of the power supply voltage VCC. Also, when the transmit data T-DATA has a high level, the switching circuit SW 3 is turned off and the switching circuit SW 4 is turned on, so that the transmit data T-DATA outputted from the input circuit 220 A takes a low level of the ground potential GND.

Next, the construction and operation of the output circuits 160 B, 160 C and 160 D and the input circuits 220 B, 220 C and 220 D used in the data transmission circuit of the liquid crystal apparatus according to the present embodiment will be described using FIG. 8 .

The output circuit 160 B, 160 C or 160 D is composed of switching circuits SW 1 and SW 2 which include, for example, CMOS. The switching circuits Scald SW 2 are connected in series between a power supply voltage VCC and a ground potential GND, and the gate of the switching circuit SW 1 has an inverted input.

When input data I-DATA has a low level, the switching circuit SW 1 is turned on and the switching circuit SW 2 is turned off, so that transmit data T-DATA outputted from the output circuit 160 B, 160 C or 160 D to the transmission line L takes a high level of the power supply voltage VCC. Also, when the input data I-DATA has a high level, the switching circuit SW 1 is turned off and the switching circuit SW 2 is turned on, so that the transmit data T-DATA outputted from the output circuit 160 B, 160 C or 160 D takes a low level of the ground potential GND.

The input circuit 220 B, 220 C or 220 D is composed of switching circuits SW 3 and SW 4 of CMOS. The switching circuits SW 3 and SW 4 are connected in series between a power supply voltage VCC and a ground potential GND, and the gate of the switching circuit SW 3 has an inverted input.

When transmit data T-DATA inputted through the transmission line L has a low level, the switching circuit SW 3 is turned on and the switching circuit SW 4 is turned off, so that transmit data T-DATA outputted from the input circuit 220 B, 220 C or 220 D takes a high level of the power supply voltage VCC. Also, when the transmit data T-DATA has a high level, the switching circuit SW 3 is turned off and the switching circuit SW 4 is turned on, so that the transmit data T-DATA outputted from the input circuit 220 B, 220 C or 220 D takes a low level of the ground potential GND.

As described above, in the case where the transmission of the same data held in the holding circuit 110 of the transceiver circuit 100 is to be made in transmitting 24-bit display data (for example, as shown at times t 2 , t 3 , t 4 , t 9 , - - - , t 14 in FIGS. 4A to 4 J), the preceding data is held as 21-bit data, as shown in FIG. 4 I. Therefore, no change in bit value of display data of the output circuit is caused so that a driving current does not flow. Thereby, an increase in power consumption is suppressed. Information of data held in the holding circuit 110 is transmitted to the receiver circuit 200 by use of encoded 3-bit data. Therefore, the receiver circuit 200 can restore 24-bit display data by use of display data held in the holding circuit 210 of the receiver circuit 200 . Namely, there results in that the transmission of 24-bit data can performed with 3 bits.

In the present embodiment, a 1-bit transmit signal is newly added as the register validation signal and hence there is a corresponding increase in power consumption. However, since a power consumption corresponding to 21 bits can be reduced, it is possible to attain a reduction in power consumption as a whole.

In a liquid crystal display apparatus using display data of 24 bits with 8 bits for each of R, G and B, in the case where a word processor or table calculation software as general application software for OA use is displayed on a liquid crystal panel, 256 color modes are involved but the number of colors actually used for display is about 10 to 20. In such display of application software for OA use, it has been ascertained that a hit rate exceeding 90% is obtained even in the case where the same display data as the preceding display data is transmitted and the holding circuit 210 is formed by a 3-stage shift register (that is, three kinds of display data are held). Namely, though the holding circuit 210 is formed by the 8-stage shift register in the example shown in FIG. 3, it is possible to attain a reduction in power consumption even if the number of stages of the shift register is reduced corresponding to display data.

Thus, in the case where each of the first and second output circuits 160 A and 160 B is a circuit (for example, CMOS circuit) for transmitting the n-bit parallel data in which data is represented by the voltage amplitude value of a power supply voltage VCC, the first output circuit 160 A has a data holding circuit (for example, the latch circuit 164 ). In the case where the second result of judgement is outputted by the judgement unit (for example, the comparators CP 0 to CP 7 , the OR circuit 130 , the latch circuit 145 , and so forth), (n−m)bit (for example, 21-bit) parallel data in the present n-bit (for example, 24-bit) parallel data inputted to the transmitter section 100 is transmitted from the first output circuit to the receiver section 200 through the transmission line while the present (n−m)-bit parallel data is stored into the data holding circuit. In the case where the first result of judgement is outputted by the judgement unit, that (n−m)-bit parallel data immediately before the output of the first result of judgement which is stored in the data holding circuit, is transmitted from the first output circuit to the receiver section through the transmission line.

With such a construction, in the case where the first result of judgement is outputted, the bit value of output data is not changed and hence a driving current does not flow, thereby enabling a reduction in power consumption as compared with the prior art.

As described above, the present embodiment enables a reduction in power consumption of the data transmission circuit and the liquid crystal display apparatus.

Next, the construction and operation of a liquid crystal display apparatus using a data transmission circuit according to a second embodiment of the present invention will be described using FIGS. 9 to 12 .

The overall construction of the liquid crystal display apparatus in the second embodiment is similar to that of the apparatus shown in FIG. 1, the construction of a transceiver circuit 100 used in a data transmission circuit of the liquid crystal display apparatus is similar to that shown in FIG. 2, and the construction of a holding circuit 110 used in the transceiver 100 is similar to that shown in FIG. 3 . Also, the construction of a receiver circuit 200 used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment is similar to that shown in FIG. 5 .

In the present embodiment, the construction of an output circuit 160 and an input circuit 220 is particularly different. In connection with this, the present embodiment will now be described by use of FIGS. 9 to 12 .

In the present embodiment, the output circuit uses, for example, an open drain circuit with a line terminated by a terminating resistor. A differential circuit is used as the input circuit.

Now, the construction of the output circuit 160 A and the input circuit 220 A used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment will be described using FIGS. 9 and 10.

The output circuit 160 A is composed of a switching circuit SW 1 of CMOS, an inverting circuit INV and a NOR circuit NOR. The drain of the switching circuit SW 1 is connected to a termination voltage Vt through the impedance Z 0 of a transmission line L and a terminating resistor Rt, and the source thereof is connected to a ground potential GND. The termination voltage Vt is lower than a power supply voltage VCC.

The input circuit 220 A is composed of switching circuits SW 3 , SW 4 , SW 5 and SW 6 of CMOS, and a constant current source I. The switching circuits SW 3 and SW 4 are connected in series between the constant current source I and the ground potential GND, and the switching circuits SW 5 and SW 6 are connected in series between the constant current source I and the ground potential GND. An inverted input of the gate of the switching circuit SW 3 is inputted with transmit display data T-DATA and an inverted input of the gate of the switching circuit SW 5 is inputted with a reference voltage Vref so that a differential circuit is formed by the switching circuits SW 3 and SW 4 and the switching circuits SW 5 and SW 6 .

When the gate input of the switching circuit SW 3 has a low level, the switching circuit SW 3 is turned off so that no current flows in the transmission line L. Thereby, the potential of the transmission line L becomes equal to the termination voltage Vt, as shown at time tm in FIG. 10 . When the gate input of the switching circuit SW 3 turns into a high level, the switching circuit SW 3 is turned on so that a current flows in the transmission line L. Thereby, the potential of the transmission line L becomes lower than the termination voltage Vt by a voltage drop across the termination resistor Rt, as shown at time tm+1 in FIG. 10 .

Referring to FIG. 9, when a register validation signal RE has a low level, input display data I-DATA inputted to the inverting circuit INV is inputted to the gate of the switching circuit SW 1 as it is, since the input display data I-DATA is inverted by the inverting circuit INV and is thereafter inverted by the NOR circuit NOR. On the other hand, when the register validation signal RE turns into a high level, the output of the NOR circuit NOR takes a low level always irrespective of the level of the input display data I-DATA.

Now assume, for example, the case where transmit display data T-DATA has a high level H equal to the termination voltage Vt at time t 8 , as shown in FIG. 10 and that input display data I-DATA changes at time t 9 . In this case, the conventional system operates so that the transmit display data T-DATA turns into a low level L at time t 9 , as shown by dotted line. In the present embodiment, however, the register validation signal RE is turned into a high level at time t 9 so that the transmit display data T-DATA maintains the high level H equal to the termination voltage Vt, as shown by solid line. When the switching circuit SW 1 is placed in a turned-off condition, no driving current flows in the transmission line L. Thereby, it is possible to reduce the power consumption.

An example of display data transmitted in the present embodiment will now be described using FIGS. 11A to 11 E.

FIG. 11A shows a transmission clock CLK, and FIG. 11B shows 24-bit input display data I-DATA inputted in synchronism with the transmission clock CLK. Namely, in synchronism with the timings t 1 , t 2 , t 3 , t 4 , t 5 , - - - of the transmission clock CLK, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 2 ”, - - - are sequentially inputted as the input display data I-DATA to the holding circuit 110 shown in FIGS. 2 and 3.

At time t 1 , the register SR 0 shown in FIG. 3 holds “Color 1 ”, as shown by FIG. 11D, and the data RD 0 shown in FIG. 2 provides “Color 1 ”.

Next, when “Color 1 ” in the input display data is inputted to the holding circuit 110 at time t 2 , the comparator CP 0 shown in FIG. 2 outputs a coincidence signal AG 0 with a high level since the data RD 0 and the input display data I-DATA coincide with each other. Accordingly, a selection signal SEL outputted by the OR circuit 130 takes a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the register SR 0 are maintained, as shown at time t 2 in FIG. 4 D. Also, when the selection signal SEL takes the high level, a register validation signal RE turns into a high level, as shown in FIG. 11 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “000”. Therefore, the output circuit 160 B outputs “000”. Since this encoded data indicates the register SR 0 , there results in that data indicating “Reg 0 ” is outputted from the output circuit 160 B, as shown in FIG. 11 E. Also, when the register validation signal RE takes the high level, the switching circuit SW 1 of the output circuit 160 A shown in FIG. 9 is turned off so that a high level H is outputted, as shown in FIG. 11 D. The operations at times t 3 and t 4 are similar to that at time t 2 .

When “Color 2 ” is inputted as the input display data I-DATA to the holding circuit 110 at time t 5 , the output of the comparator CP 0 shown in FIG. 2 turns into a low level. Therefore, the selection signal SEL outputted by the OR circuit 130 turns into a low level. Accordingly, the selection circuit SL 0 shown in FIG. 3 selects the input data I-DATA and the selection circuit SL 1 selects the output of the register SR 0 . As a result, the register SR 0 holds “Color 2 ”, as shown in FIG. 4 D and the register SR 1 holds “Color 1 ” shifted from the register SR 0 , as shown in FIG. 4 E.

At times t 6 to t 8 , the input display data I-DATA sequentially changes to “Color 3 ”, “Color 4 ” and “Color 5 ”, as shown in FIG. 11 B. Therefore, the registers SR 0 , SR 1 , SR 2 , SR 3 and SR 4 sequentially operate as a shift register in a manner similar to that in the operation described in conjunction with time t 5 so that they hold “Color 5 ”, “Color 4 ”, “Color 3 ”, “Color 2 ” and “Color 1 ”, respectively, at time t 8 .

Next, when “Color 2 ” in the input display data is inputted to the holding circuit 110 at time t 9 , “Color 2 ” is held in the register SR 3 at time t 9 . Therefore, the comparator CP 3 shown in FIG. 2 outputs a coincidence signal AG 3 with a high level since both the data RD 3 and the input display data I-DATA coincide as “Color 2 ”. Accordingly, the selection signal SEL outputted by the OR circuit 130 turns into a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the registers SR 0 to SR 4 at time 8 are maintained. Also, when the selection signal SEL takes the high level, the register validation signal RE turns into a high level, as shown in FIG. 11 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “011”. Therefore, the output circuit 160 B outputs “011”. Since this encoded data indicates the register SR 3 , there results in that data indicating “Reg 3 ” is outputted from the output circuit 160 B, as shown in FIG. 11 E. Also, when the register validation signal RE takes the high level, the switching circuit SW 1 of the output circuit 160 A is turned off so that a high level H is outputted, as shown in FIG. 11 D.

Up to time t 14 , the same input display data I-DATA as that having already been held in the holding circuit 110 is inputted as “Color 3 ” at time t 10 , “Color 4 ” at time t 11 , - - - . Therefore, the operations at times t 10 to t 14 are similar to that at time t 9 . However, since the position of a register having the held data is different, 3-bit data indicating each register position is outputted, as shown in FIG. 11 E.

Namely, as shown in FIGS. 11D and 11E, in the case where the input display data I-DATA is the same as data held in the holding circuit 110 (as shown at times t 2 , t 3 , t 4 , t 9 , t 10 , t 11 , t 12 , t 13 and t 14 in FIGS. 11A to 11 E), the 21-bit data shown in FIG. 11D provides a high level output and the display data can be transmitted using the 3-bit data. Namely, the transmission of 24-bit display data is performed with 3 bits.

Next, the construction and operation of the output circuits 160 B, 160 C and 160 D and the input circuits 220 B, 220 C and 220 D used in the data transmission circuit of the liquid crystal apparatus according to the present embodiment will be described using FIG. 12 .

The output circuit 160 B, 160 C or 160 D is composed of switching circuits SW 1 and SW 2 of CMOS. The drain of the switching circuit SW 1 is connected to a termination voltage Vt through the impedance Z 0 of a transmission line L and a terminating resistor Rt, and the source thereof is connected to a ground potential GND. The termination voltage Vt is lower than a power supply voltage VCC.

Also, the input circuit 220 B, 220 C or 220 D is composed of switching circuits SW 3 , SW 4 , SW 5 and SW 6 of CMOS, and a constant current source I. The switching circuits SW 3 and SW 4 are connected in series between the constant current source I and the ground potential GND, and the switching circuits SW 5 and SW 6 are connected in series between the constant current source I and the ground potential GND. An inverted input of the gate of the switching circuit SW 3 is inputted with transmit display data T-DATA and an inverted input of the gate of the switching circuit SW 5 is inputted with a reference voltage Vref so that a differential circuit is formed by the switching circuits SW 3 and SW 4 and the switching circuits SW 5 and SW 6 .

When the gate input of the switching circuit SW 3 has a low level, the switching circuit SW 3 is turned off so that no current flows in the transmission line L. Thereby, the potential of the transmission line L becomes equal to the termination voltage Vt. When the gate input of the switching circuit SW 3 turns into a high level, the switching circuit SW 3 is turned on so that a current flows in the transmission line L. Thereby, the potential of the transmission line L becomes lower than the termination voltage Vt by a voltage drop across the termination resistor Rt.

As described above, the present embodiment is constructed so that the open drain circuit is used as the output circuit, the line is terminated by the terminating resistor and the differential circuit is used as the input circuit. With such a construction, even in the case where the turn of input display data into a low level causes a driving current to flow in the transmission line so that there results in power consumption, it is possible to reduce the power consumption of the data transmission circuit and the liquid crystal display apparatus in such a manner that when the same display data as the preceding data is to be transmitted, 21-bit data is brought into a high level while encoded display data information is transmitted using 3 bits.

Namely, the transmission line is connected to the termination voltage through the terminating resistor. In the case where the second result of judgement is outputted by the judgement unit (the comparators CP 0 to CP 7 , the OR circuit 130 , the latch circuit 145 , and so forth), the first and second output circuits 160 A and 160 B transmit an output with a low level and an output with a high level to the receiver section through the transmission line in accordance with (n−m)-bit (for example, 21-bit) parallel data of the present n-bit (for example, 24-bit) parallel data inputted to the transmitter section 100 . In the case where the first result of judgement is outputted by the judgement unit, the first and second output circuits 160 A and 160 B transmit an output with a termination voltage level or an output with a high level to the receiver section through the transmission line.

In an example of the present invention, in the case where the first and second output circuits are open drain circuits, as in the above-described second embodiment, the above-mentioned output with a low level is a voltage level between a ground voltage and the termination voltage level and the above-mentioned output with a high level is the termination voltage level. In the case where the first result of judgement is outputted by the judgement unit, the output with a high level is transmitted to the receiver section through the transmission line. With such a construction, in the case where the first result of judgement is outputted, a steady current does not flow. Thereby, it is possible to reduce the power consumption as compared with the prior art.

In another example of the present invention, in the case where the first and second output circuits are push-pull circuits, as in a third embodiment which will be described later on, the above-mentioned output with a low level is a voltage level between the ground voltage and the termination voltage level and the above-mentioned output with a high level is a level between a power supply voltage of the first output unit and the termination voltage level. In the case where the first result of judgement is outputted by the judgement unit, the output with the termination voltage level is transmitted to the receiver section through the transmission line. With such a construction, in the case where the first result of judgement is outputted, a steady current does not flow. Thereby, it is possible to reduce the power consumption as compared with the prior art.

Next, the construction and operation of a liquid crystal display apparatus using a data transmission circuit according to a third embodiment of the present invention will be described using FIGS. 13 to 16 .

The overall construction of the liquid crystal display apparatus in the third embodiment is similar to that of the apparatus shown in FIG. 1, the construction of a transceiver circuit 100 used in a data transmission circuit of the liquid crystal display apparatus is similar to that shown in FIG. 2, and the construction of a holding circuit 110 used in the transceiver 100 is similar to that shown in FIG. 3 . Also, the construction of a receiver circuit 200 used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment is similar to that shown in FIG. 5 .

In the present embodiment, the construction of an output circuit 160 and an input circuit 220 is particularly different. In connection with this, the present embodiment will now be described by use of FIGS. 13 to 16 .

In the present embodiment, a push-pull circuit is used as the output circuit with a line terminated by a terminating resistor and a differential circuit is used as the input circuit, thereby enabling a high-speed operation.

Now, the construction of the output circuit 160 A and the input circuit 220 A used in the data transmission circuit of the liquid crystal display apparatus according to the present embodiment will be described using FIGS. 13 and 14.

The output circuit 160 A is composed of switching circuits SW 1 of CMOS, an inverting circuit INV, a NOR circuit NOR and an OR circuit OR. The switching circuits SW 1 and SW 2 are connected in series between a power supply voltage VCC and a ground potential. Input display data I-DATA is inputted to one input terminal of the NOR circuit NOR through the inverting circuit INV and to one input terminal of the OR circuit OR. A register validation signal RE is inputted to the other input terminal of the NOR circuit NOR and the other input terminal of the OR circuit OR. An output of the NOR circuit NOR is inputted to the gate of the switching circuit SW 2 , and an output of the OR circuit OR is inputted to the gate of the switching circuit SW 1 .

A transmission line L is connected to a termination voltage Vt through a terminating resistor Rt. The termination voltage Vt is lower than the power supply voltage VCC.

Also, the input circuit 220 A is composed of switching circuits SW 3 , SW 4 , SW 5 and SW 6 of CMOS, and a constant current source I. The switching circuits SW 3 and SW 4 are connected in series between the power supply voltage VCC and the constant current source I, and the switching circuits SW 5 and SW 6 are connected in series between the power supply voltage VCC and the constant current source I. The gate of the switching circuit SW 4 is inputted with transmit display data T-DATA and the gate of the switching circuit SW 6 is inputted with the termination voltage Vt so that a differential circuit is formed by the switching circuits SW 3 and SW 4 and the switching circuits SW 5 and SW 6 .

When the switching circuit SW 1 is turned on and the switching circuit SW 2 is turned off, a current flows from the power supply voltage VCC toward the termination voltage Vt through the transmission line L and the terminating resistor Rt so that the potential of the transmission line L becomes higher than the termination voltage Vt by a value corresponding to the termination resistor, as shown at time tm in FIG. 14 . Also, when the switching circuit SW 1 is turned off and the switching circuit SW 2 is turned on, a current flows from the termination voltage Vt toward the ground potential GND through the terminating resistor Rt and the transmission line L so that the potential of the transmission line L becomes lower than the termination voltage Vt by a value corresponding to the termination resistor, as shown at time tm+1 in FIG. 14 .

Further, in the present embodiment, the switching circuit SW 1 and the switching circuit SW 2 are both turned off. At this time, a current flows in the transmission line L so that the the potential of the transmission line L becomes equal to the termination voltage Vt.

Referring to FIG. 13, when a register validation signal RE has a low level, input display data I-DATA is inputted to the gate of the switching circuit SW 2 through the inversion thereof by the inverting circuit INV and the subsequent inversion thereof by the NOR circuit NOR, that is, as it is while the input display data I-DATA is inputted to the switching circuit SW 1 in an inverted form. On the other hand, when the register validation signal RE turns into a high level, the output of the NOR circuit NOR takes a low level always irrespective of the level of the input display data I-DATA and the output of the OR circuit OR takes a high level, so that the switching circuits SW 1 and SW 2 are both turned off.

Now assume, for example, the case where transmit display data T-DATA has a high level H higher than the termination voltage Vt at time t 8 , as shown in FIG. 14 and that input display data I-DATA changes at time t 9 . In this case, the conventional system operates so that the transmit display data T-DATA turns into a low level L at time t 9 , as shown by dotted line. In the present embodiment, however, the register validation signal RE is turned into a high level at time t 9 so that the transmit display data T-DATA takes a voltage equal to the termination voltage Vt, as shown by solid line. When the switching circuits SW 1 and SW 2 are placed in a turned-off condition, no driving current flows in the transmission line L. Thereby, it is possible to reduce the power consumption.

An example of display data transmitted in the present embodiment will now be described using FIGS. 15A to 15 E.

FIG. 15A shows a transmission clock CLK, and FIG. 15B shows 24-bit input display data I-DATA inputted in synchronism with the transmission clock CLK. Namely, in synchronism with the timings t 1 , t 2 , t 3 , t 4 , t 5 , - - - of the transmission clock CLK, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 1 ”, “Color 2 ”, - - - are sequentially inputted to the holding circuit 110 shown in FIGS. 2 and 3.

At time t 1 , the register SR 0 shown in FIG. 3 holds “Color 1 ”, as shown by FIG. 15D, and the data RD 0 shown in FIG. 2 provides “Color 1 ”.

Next, when “Color 1 ” in the input display data is inputted to the holding circuit 110 at time t 2 , the comparator CP 0 shown in FIG. 2 outputs a coincidence signal AG 0 with a high level since the data RD 0 and the input display data I-DATA coincide with each other. Accordingly, a selection signal SEL outputted by the OR circuit 130 takes a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the register SR 0 are maintained, as shown at time t 2 in FIG. 4 D. Also, when the selection signal SE 1 takes the high level, a register validation signal RE turns into a high level, as shown in FIG. 15 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “000”. Therefore, the output circuit 160 B outputs “000”. Since this encoded data indicates the register SR 0 , there results in that data indicating “Reg 0 ” is outputted from the output circuit 160 B, as shown in FIG. 15 E. Also, when the register validation signal RE takes the high level, the switching circuits SW 1 and SW 2 of the output circuit 160 A shown in FIG. 13 are turned off so that the potential of the transmission line L takes the termination voltage Vt, as shown in FIG. 15 D. The operations at times t 3 and t 4 are similar to that at time t 2 .

When “Color 2 ” is inputted as the input display data I-DATA to the holding circuit 110 at time t 5 , the output of the comparator CP 0 shown in FIG. 2 turns into a low level. Therefore, the selection signal SEL outputted by the OR circuit 130 turns into a low level. Accordingly, the selection circuit SL 0 shown in FIG. 3 selects the input data I-DATA and the selection circuit SL 1 selects the output of the register SR 0 . As a result, the register SR 0 holds “Color 2 ”, as shown in FIG. 4 D and the register SR 1 holds “Color 1 ” shifted from the register SR 0 , as shown in FIG. 4 E.

At times t 6 to t 8 , the input display data I-DATA sequentially changes to “Color 3 ”, “Color 4 ” and “Color 5 ”, as shown in FIG. 15 B. Therefore, the registers SR 0 , SR 1 , SR 2 , SR 3 and SR 4 sequentially operate as a shift register in a manner similar to that in the operation described in conjunction with time t 5 so that they hold “Color 5 ”, “Color 4 ”, “Color 3 ”, “Color 2 ” and “Color 1 ”, respectively, at time t 8 .

Next, when “Color 2 ” in the input display data is inputted to the holding circuit 110 at time t 9 , “Color 2 ” is held in the register SR 3 at time t 9 . Therefore, the comparator CP 3 shown in FIG. 2 outputs a coincidence signal AG 3 with a high level since both the data RD 3 and the input display data I-DATA coincide as “Color 2 ”. Accordingly, the selection signal SEL outputted by the OR circuit 130 turns into a high level so that the selection circuits SL 0 to SL 7 shown in FIG. 3 select the outputs Q of the registers SR 0 to SR 7 , respectively. As a result, the held contents of the registers SR 0 to SR 4 at time 8 are maintained. Also, when the selection signal SEL takes the high level, the register validation signal RE turns into a high level, as shown in FIG. 15 C. Accordingly, the selection circuit 150 selects the output of the latch circuit 140 . Herein, the output of the encoder 120 takes “011”. Therefore, the output circuit 160 B outputs “011”. Since this encoded data indicates the register SR 3 , there results in that data indicating “Reg 3 ” is outputted from the output circuit 160 B, as shown in FIG. 15 E. Also, when the register validation signal RE takes the high level, the switching circuits SW 1 and SW 2 of the output circuit 160 A shown in FIG. 13 are turned off so that the potential of the transmission line L takes the termination voltage Vt, as shown in FIG. 15 D.

Up to time t 14 , the same input display data I-DATA as that having been held in the holding circuit 110 is inputted as “Color 3 ” at time t 10 , “Color 4 ” at time t 11 , - - - . Therefore, the operations at times t 10 to t 14 are similar to that at time t 9 . However, since the position of a register having the held data is different, 3-bit data indicating each register position is outputted, as shown in FIG. 15 E.

Namely, as shown in FIGS. 15D and 15E, in the case where the input display data I-DATA is the same as data held in the holding circuit 110 (as shown at times t 2 , t 3 , t 4 , t 9 , t 10 , t 11 , t 12 , t 13 and t 14 in FIGS. 15A to 15 E), the 21-bit data shown in FIG. 15D provides an output having the termination voltage Vt and the display data can be transmitted using the 3-bit data. Namely, the transmission of 24-bit display data is performed with 3 bits.

Next, the construction and operation of the output circuits 160 B, 160 C and 160 D and the input circuits 220 B, 220 C and 220 D used in the data transmission circuit of the liquid crystal apparatus according to the present embodiment will be described using FIG. 16 .

The output circuit 160 B, 160 C or 160 D is composed of switching circuits SW 1 and SW 2 of CMOS. The switching circuits SW 1 and SW 2 are connected in series between a power supply voltage VCC and a ground potential GND. Input display data I-DATA is inputted to the gate of the switching circuit SW 2 and an inverted input of the gate of the switching circuit SW 1 .

A transmission line L is connected to a termination voltage Vt through a terminating resistor Rt. The termination voltage Vt is lower than the power supply voltage VCC.

Also, the input circuit 220 B, 220 C or 220 D is composed of switching circuits SW 3 , SW 4 , SW 5 and SW 6 of CMOS, and a constant current source I. The switching circuits SW 3 and SW 4 are connected in series between and the power supply voltage VCC and the constant current source I, and the switching circuits SW 5 and SW 6 are connected in series between the power supply voltage VCC and the constant current source I. The gate of the switching circuit SW 4 is inputted with transmit display data T-DATA and the gate of the switching circuit SW 6 is inputted with the termination voltage Vt so that a differential circuit is formed by the switching circuits SW 3 and SW 4 and the switching circuits SW 5 and SW 6 .

When the switching circuit SW 1 is turned on and the switching circuit SW 2 is turned off, a current flows from the power supply voltage VCC toward the termination voltage Vt through the transmission line L and the terminating resistor Rt so that the potential of the transmission line L becomes higher than the termination voltage Vt by a value corresponding to the termination resistor. Also, when the switching circuit SW 1 is turned off and the switching circuit SW 2 is turned on, a current flows from the termination voltage Vt toward the ground potential GND through the terminating resistor Rt and the transmission line L so that the potential of the transmission line L becomes lower than the termination voltage Vt by a value corresponding to the termination resistor.

As described above, the present embodiment is constructed so that the push-pull circuit is used as the output circuit, the line is terminated by the terminating resistor and the differential circuit is used as the input circuit. With such a construction, even in the case where the turn of input display data into a high level or a low level causes a driving current to flow in the transmission line so that there results in power consumption, it is possible to reduce the power consumption of the data transmission circuit and the liquid crystal display apparatus in such a manner that when the same display data as the preceding data is to be transmitted, 21-bit data is brought into the termination voltage level while encoded display data information is transmitted using 3 bits.

Though each of the foregoing embodiments has been described in conjunction with the case where the number of stages of the shift register of the holding circuit 110 or 210 is eight, the number of stages is not limited to this value or can be set so that the power consumption becomes the minimum.

In the foregoing embodiments, n and m are respectively set to 24 and 3 for the holding circuit 110 storing, n-bit parallel data inputted to the transmitter section, by a plurality of sets thereof the number of which is 2 m or less than that (m: integer satisfying m<n). When m is set to be a larger number, there is increased a possibility that the present n-bit parallel data inputted to the transmitter section coincides with any one of the plural sets of n-bit parallel data. However, there is also increased that m-bit information transmitted at the time of coincidence which indicates a hold position in the holding circuit 210 . This is not preferable from the aspect of reduction in power consumption. In the present invention, therefore, m is set to a proper value from the aspect of the possibility of coincidence and the reduction in power consumption.

In each of the foregoing embodiments, the first and second holding circuits 110 and 210 are made the same in construction so that when the present n-bit parallel data inputted to the transmitter section coincides with one of the plural sets of n-bit parallel data stored in the first holding 110 , information indicating a hold position of that n-bit parallel data in the first holding circuit 110 is used as information indicating a hold position of the same n-bit parallel data in the second holding circuit 210 . However, there may be used a construction in which a data hold position in the first holding circuit 110 and a data hold position in the second holding circuit 210 are set such that they have a predetermined relationship and this relationship is, for example, stored in a memory such as a table or map at the receiver section 200 . With this construction, if information indicating a hold position in the first holding circuit 110 is transmitted to the receiver section 200 , it is possible to know the corresponding hold position in the second holding circuit 210 by use of the memory. Such a memory may be provided in the transmitter section 100 . In this case, information indicating a hold position in the first holding circuit 110 is converted into information indicating the corresponding hold position in the second holding circuit 210 at the transmitter section and is thereafter transmitted to the receiver section.

Though each of the foregoing embodiments has been described in conjunction with the transmission of data between the liquid crystal controller and the data driver, the present invention is not limited thereto. The present invention is applicable to a transceiver circuit or a receiver circuit which serially transmits display data or the like.

According to the present invention as described above, it is possible to reduce the power consumption of the data transmission circuit and the liquid crystal display apparatus.