Level shift circuit for transmitting signal from leading edge to trailing edge of input signal

This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. P2001-386703, filed on Dec. 19, 2001; the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a level shift circuit converting a signal level between two circuits supplied by different power sources respectively.

2. Description of the Related Art

A level shift circuit 200 shown in FIG. 1A is used to convert a signal of amplitude Va received from a circuit 201 to a signal of amplitude Vb supplied to a circuit 204 . The level shift circuit 200 consists of an inverter 202 , and an inverter 203 having an input terminal connected to an output terminal of the inverter 202 . The voltage Va is supplied to the circuit 201 and to the inverter 202 from a power source VCC 1 . The voltage Vb is supplied to the inverter 203 and to the circuit 204 from a power source VCC 2 .

When the voltage of an input signal Vin transmitted from the circuit 201 becomes larger than a threshold voltage Vth(a) of the inverter 202 , the output voltage V 1 of the inverter 202 starts increasing. When the output voltage V 1 of the inverter 202 becomes smaller than a threshold voltage Vth(b) of the inverter 203 , the output signal Vout supplied from an output terminal of the inverter 203 starts increasing. The output signal Vout is supplied to the circuit 204 . However, the threshold voltage Vth(b) of the inverter 203 is different from the threshold voltage Vth(a) of the inverter 202 , because the inverters 202 and 203 are supplied with different voltages Va and Vb. In other words, a trailing edge of the output signal Vout is delayed, because the threshold voltage Vth(b) is different from the threshold voltage Vth(a). As shown in FIG. 1B, a low level period TBoff of the output signal Vout is longer than a high level period TBon. In other words, a duty of the output signal Vout is different from a duty of the input signal Vin.

In a aspect of the present invention, a level shift circuit encompasses a first transmission circuit configured to transmit a leading edge of an input signal, a second transmission circuit configured to transmit a trailing edge of the input signal, and a composite circuit configured to generate an output signal by synthesizing the leading edge and the trailing edge.

FIG. 1A is a circuit diagram of a level shift circuit according to a related art;

FIG. 1B is a diagram for describing an operational timing of a level shift circuit according to the related art;

FIG. 2 is a circuit diagram of a level shift circuit according to a first embodiment of the present invention;

FIG. 3 is a diagram for describing the operational timing of the level shift circuit according to the first embodiment of the present invention;

FIG. 4 is a circuit diagram of a level shift circuit according to a second embodiment of the present invention;

FIG. 5 is a circuit diagram of a level shift circuit according to a third embodiment of the present invention;

FIG. 6 is a circuit diagram of a level shift circuit according to a fourth embodiment of the present invention;

FIG. 7 is a circuit diagram of a level shift circuit according to a fifth embodiment of the present invention;

FIG. 8 is a circuit diagram of a level shift circuit according to a sixth embodiment of the present invention;

FIG. 9 is a circuit diagram of a level shift circuit according to a seventh embodiment of the present invention;

FIG. 10 is a circuit diagram of a level shift circuit according to a eighth embodiment of the present invention;

FIG. 11 is a circuit diagram of a level shift circuit according to a ninth embodiment of the present invention;

Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that the same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and description of the same or similar parts and elements will be omitted or simplified. In the following descriptions, numerous specific details are set forth such as specific signal values, etc. to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention with unnecessary detail. In the following description, the word “connect” defines a state in which first and second elements are electrically connected to each other without regard to whether or not there is a physical connection between the elements.

First Embodiment

As shown in FIG. 2, a level shift circuit 10 a according to a first embodiment of the present invention encompasses, a first transmission circuit 1 configured to transmit a leading edge of an input signal Vin, a second transmission circuit 2 configured to transmit a trailing edge of the input signal Vin, and a composite circuit 3 configured to generate an output signal Vout by synthesizing the leading edge and the trailing edge. The first transmission circuit 1 includes a nMOS transistor N 1 having a gate terminal connected to a signal input terminal 50 , a drain terminal connected to a first high voltage power supply VCC 1 , a back gate terminal connected to a low voltage power supply VSS, and a source terminal connected to an input side of the composite circuit 3 .

The second transmission circuit 2 includes a first transmission inverter I 1 having an input terminal connected to the signal input terminal 50 , a high voltage power supply terminal connected to the first high voltage power supply VCC 1 , a low voltage power supply terminal connected to the low voltage power supply VSS, and a second transmission inverter I 2 having input terminal connected to an output terminal of a first transmission inverter I 1 , a high voltage power supply terminal connected to the second high voltage power supply VCC 2 , a low voltage power supply terminal connected to the low voltage power supply VSS.

The composite circuit 3 includes a first composite inverter I 3 and a second composite inverter I 4 . The first composite inverter I 3 has an input terminal connected to output sides of the first transmission circuit 1 and the second transmission circuit 2 , a high voltage power supply terminal connected to the second high voltage power supply VCC 2 , and a low voltage power supply terminal connected to the low voltage power supply VSS. The second composite inverter I 4 has an input terminal connected to an output terminal of the first composite inverter I 3 , a high voltage power supply terminal connected to the second high voltage power supply VCC 2 , a low voltage power supply terminal connected to the low voltage power supply VSS, and an output terminal connected to a signal output terminal 51 .

Operation of the level shift circuit 10 a according to the first embodiment of the present invention is described using the timing chart shown in FIG. 3 .

(A) At time t 1 , as shown in FIG. 3 ( a ), the voltage of the input signal Vin supplied to the signal input terminal 50 starts increasing from a low level to a high level.

(B) At time t 2 when the voltage of the input signal Vin becomes larger than a threshold voltage VthN of the nMOS transistor N 1 , the nMOS transistor N 1 turns on. As shown in FIG. 3 ( d ), when the nMOS transistor N 1 turns on, a second voltage V 2 supplied from the nMOS transistor N 1 starts increasing. In other words, the first transmission circuit 1 transmits the leading edge of the input signal Vin to the input side of the composite circuit 3 . The input side of the composite circuit 3 is the input terminal of the first composite inverter I 3 .

(C) At time t 3 when the voltage of the input signal Vin becomes larger than the threshold voltage Vth(a) of the first transmission inverter I 1 , as shown in FIG. 3 ( b ), the first voltage V 1 supplied from the first transmission inverter I 1 starts decreasing.

(D) At time t 4 when the second voltage V 2 becomes larger than the threshold voltage Vth(b) of the first composite inverter I 3 , as shown in FIG. 3 ( e ), a third voltage V 3 supplied from the first composite inverter I 3 starts decreasing.

(E) At time t 5 when the third voltage V 3 becomes smaller than the threshold voltage Vth(b) of the second composite inverter I 4 , as shown in FIG. 3 ( e ), the output signal Vout supplied from the second composite inverter I 4 starts increasing.

(F) At time t 6 , the voltage of the input signal Vin reaches a high level. The high level voltage of the input signal Vin is defined as the voltage Va supplied from the first high voltage power supply VCC 1 .

(G) At time t 9 when the voltage of the input signal Vin starts decreasing from the high level to a low level.

(H) At time t 10 when the voltage of the input signal Vin becomes smaller than the threshold voltage Vth(a) of the first transmission inverter I 1 , as shown in FIG. 3 ( b ), the first voltage V 1 supplied from the first transmission inverter I 1 starts increasing.

(I) At time t 11 when the first voltage V 1 becomes larger than the threshold voltage Vth(b) of the second transmission inverter I 2 , as shown in FIG. 3 ( d ), the second voltage V 2 supplied from the second transmission inverter I 2 starts decreasing.

(J) At time t 12 when the second voltage V 2 becomes smaller than the threshold voltage Vth(b) of the first composite inverter I 3 , as shown in FIG. 3 ( e ), the third voltage V 3 supplied from the first composite inverter I 3 starts increasing.

(K) At time t 13 when the third voltage V 3 becomes larger than the threshold voltage Vth(b) of the second composite inverter I 4 , as shown in FIG. 3 ( f ), the output signal Vout supplied from the second composite inverter I 4 starts decreasing.

On the other hand, by the level shift circuit 200 according to a related art, at time t 7 when the first voltage V 1 becomes larger than the threshold voltage Vth(b) of the inverter 203 shown in FIG. 1A, the output signal Vout supplied from the inverter 203 starts increasing. At time t 8 , the output signal Vout arrives at the high level.

With the level shift circuit 10 a according to the first embodiment of the present invention, a delay time of a leading edge generated by the level shift circuit 200 becomes small. As stated above, the first transmission circuit 1 transmits a leading edge faster so that the duty of the output signal Vout can be controlled.

Second Embodiment

As shown in FIG. 4, in the first transmission circuit 1 used as part of a level shift circuit 10 b according to a second embodiment, the nMOS transistor N 1 shown in FIG. 2 is replaced with a pMOS transistor P 1 . The first transmission circuit 1 includes the pMOS transistor P 1 and a first pMOS transistor P 2 . The pMOS transistor P 1 has a gate terminal connected to the output terminal of the first transmission inverter I 1 , and a source terminal connected to the first high voltage power supply VCC 1 . The first pMOS transistor P 2 used as a diode-connected between a drain terminal of the pMOS transistor P 1 and the first input side of the composite circuit 3 . The first pMOS transistor P 2 has a drain terminal and a gate terminal connected to the first input side of composite circuit 3 , and a source terminal connected to the drain terminal of the pMOS transistor P 1 . Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

In the first transmission circuit 1 used in the level shift circuit 10 b according to the second embodiment of the present invention, the voltage of the input signal Vin supplied from the signal input terminal 50 starts increasing from a low level to a high level. When the voltage of the input signal Vin becomes larger than the threshold voltage Vth(a) of the first transmission inverter I 1 , the first voltage V 1 supplied from the first transmission inverter I 1 starts decreasing from the high level to the low level. When the first voltage V 1 supplied from the first transmission inverter I 1 becomes smaller than the threshold voltage VthP of the pMOS transistor P 1 , the pMOS transistor P 1 turns on. When the pMOS transistor P 1 turns on, a leading edge of the input signal Vin is transmitted to the input side of the first composite circuit 3 .

With the level shift circuit 10 b according to the second embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled. In addition, when the pMOS transistor P 1 turns on, the first pMOS transistor P 2 works as a diode. Therefore, the voltage of the output signal Vout does not exceeded the voltage Vb. But, the voltage Vb is defined as smaller than the voltage Va. In other words, if the pMOS transistor P 1 and the second transmission inverter I 2 supply a high level signal simultaneously, the first pMOS transistor P 2 can prevent flowing the current from the first high voltage power supply VCC 1 to the second high voltage power supply VCC 2 .

Third Embodiment

As shown in FIG. 5, in the first-transmission circuit 1 used as part of the level shift circuit 10 c according to the third embodiment, the pMOS transistor P 1 shown in FIG. 4 is replaced with a pMOS transistor P 3 . The first transmission circuit 1 includes the pMOS transistor P 3 . The pMOS transistor P 3 has a back gate terminal the first high voltage power supply VCC 1 , a drain terminal connected to the low voltage power supply VSS, and a source terminal connected to the first input side of composite circuit 3 . A back gate terminal of the pMOS transistor P 3 is connected to the first high voltage power supply VCC 1 . Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

With the level shift circuit 10 c according to the third embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled. Furthermore, when the first pMOS transistor P 2 shown in FIG. 4 is not present, the level shift circuit 10 c according to a third embodiment can prevent flowing the current from the first high voltage power supply VCC 1 to the second high voltage power supply VCC 2 .

Fourth Embodiment

As shown in FIG. 6, in the first transmission circuit 1 used as part of the level shift circuit 10 d according to a fourth embodiment, the nMOS transistor N 1 shown in FIG. 2 is replaced with a first nMOS transistor N 2 and a second nMOS transistor N 3 . The first transmission circuit 1 includes the first nMOS transistor N 2 , and the second nMOS transistor N 3 . The first nMOS transistor N 2 has a drain terminal connected to the first high voltage power supply VCC 1 , and a gate terminal connected to a inversion terminal of the second transmission circuit 2 . The second nMOS transistor N 3 has a drain terminal connected to a source terminal of the first nMOS transistor N 2 , a gate terminal connected to the input terminal 50 , and a source terminal connected to the low voltage power supply VSS. The gate terminal of the first nMOS transistor N 2 is connected to the output terminal of the first transmission inverter I 1 . The connection point of the first nMOS transistor N 2 and second nMOS transistor N 3 is connected to the output terminal of the first composite inverter I 3 . A back gate terminal of the first nMOS transistor N 2 is connected to the low voltage power supply VSS. The other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

In the first transmission circuit 1 used in the level shift circuit 10 d according to the fourth embodiment of the present invention, the first nMOS transistor N 2 and the second nMOS transistor N 3 turns on depending on the voltage level of the input signal Vin, alternately. When the first nMOS transistor N 2 turns on, a voltage Va is supplied to the input terminal of the second composite inverter I 4 . In other words, the leading edge of the input signal Vin is transmitted to the input side of the composite circuit 3 . When the second nMOS transistor N 3 turns on, the voltage of the input terminal of the second composite inverter I 4 becomes a voltage Vg of the low voltage power supply.

With the level shift circuit 10 d according to the fourth embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled.

Fifth Embodiment

As shown in FIG. 7, in the first transmission circuit 1 used as part of the level shift circuit 10 e according to a fifth embodiment, an inverter I 5 is added to the first transmission circuit 1 shown in FIG. 6 . The first transmission circuit 1 includes the first nMOS transistor N 2 , the second nMOS transistor N 3 , and the inverter I 5 . The first nMOS transistor N 2 has the drain terminal connected to the first high voltage power supply VCC 1 , and the gate terminal connected to the inversion terminal of the second transmission circuit 2 . The second nMOS transistor N 3 has the drain terminal connected to the source terminal of the first nMOS transistor N 2 , the gate terminal connected to input terminal 50 , and the source terminal connected to the low voltage power supply VSS. The inverter I 5 has an input terminal connected to a connection point with the first nMOS transistor N 2 and the second nMOS transistor N 3 , and an output terminal connected to the input side of the composite circuit 3 . The output terminal of the inverter I 5 is connected to the input terminal of the first composite inverter I 3 . Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

In the first transmission circuit 1 used in the level shift circuit 10 e according to the fifth embodiment of the present invention, the first nMOS transistor N 2 and the second nMOS transistor N 3 turn on depending on the voltage level of input signal Vin, alternately. When the first nMOS transistor N 2 turns on, a voltage Va is supplied to the input terminal of the inverter I 5 . In other words, the leading edge of the input signal Vin is transmitted to input side of the composite circuit 3 . When the second nMOS transistor N 3 turns on, the voltage supplied to the input terminal of the inverter I 5 becomes the voltage Vg of the low voltage power supply VSS. The leading edge of the input signal Vin is transmitted to the input terminal of the first composite inverter I 3 from the output terminal of the inverter I 5 .

With the level shift circuit 10 e according to the fifth embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled.

Sixth Embodiment

As shown in FIG. 8, in the first transmission circuit 1 used as part of a level shift circuit 10 f according to a sixth embodiment, a connection point of the gate terminal of the second nMOS transistor N 3 showed in FIG. 7 is replaced with a connection point of the gate terminal of the first nMOS transistor N 2 . The first transmission circuit 1 includes the first nMOS transistor N 2 and the second nMOS transistor N 3 and the inverter I 5 . The first nMOS transistor N 2 has the drain terminal connected to the first high voltage power supply VCC 1 , and the gate terminal connected to input terminal 50 . The second nMOS transistor N 3 has the drain terminal connected to the source terminal of the first nMOS transistor N 2 , the gate terminal connected to the inversion terminal of the second transmission circuit 2 , and the source terminal connected to low voltage power supply VSS. The inverter I 5 has the input terminal connected to the connection point with the first nMOS transistor N 2 and the second nMOS transistor N 3 , the output terminal connected to the first input terminal of composite circuit 3 . The output terminal of the inverter I 5 is connected to the output terminal of the first composite inverter I 3 . The other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

In the first transmission circuit 1 used in the level shift circuit 10 f according to the sixth embodiment of the present invention, the first nMOS transistor N 2 and the second nMOS transistor N 3 turn on depending on the level of input signal Vin, alternately. When the first nMOS transistor N 2 turns on, the first high supply voltage Va is supplied to the input terminal of the inverter I 5 . In other words, the leading edge of the input signal Vin is transmitted to composite circuit 3 . When the second nMOS transistor N 3 turns on, the voltage supplied to the input terminal of the inverter I 5 becomes the voltage Vg of the low voltage power supply VSS. The leading edge of the input signal Vin is transmitted to the output terminal of the first composite inverter I 3 from the output of the inverter I 5 .

With the level shift circuit 10 f according to the sixth embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled.

Seventh Embodiment

As shown in FIG. 9, in the first transmission circuit 1 used as part of the level shift circuit 10 g according to a seventh embodiment, the nMOS transistor N 1 shown in FIG. 2 is replaced with a pMOS transistor P 4 and an inverter I 6 . The first transmission circuit 1 includes the pMOS transistor P 4 and the inverter I 6 . The pMOS transistor P 4 has a source terminal connected to the first high voltage power supply VCC 1 , and a gate terminal connected to input terminal 50 . The inverter I 6 has an input terminal connected to a drain terminal of the pMOS transistor P 4 , and an output terminal connected to a first input terminal of composite circuit 3 . The output terminal of the inverter I 6 is connected to the input terminal of the second composite inverter I 4 . Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

With the level shift circuit 10 g according to the seventh embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled.

Eighth Embodiment

As shown in FIG. 10, in the first transmission circuit 1 used as part of the level shift 10 h circuit according to a eighth embodiment, the pMOS transistor P 4 shown in FIG. 9 is replaced with the pMOS transistor P 5 . The first transmission circuit 1 includes a pMOS transistor P 5 and an inverter I 7 . The pMOS transistor P 5 has a gate terminal connected to a inversion terminal of the second transmission circuit 2 , and a drain terminal connected to the low voltage power supply VSS. The inverter I 7 has an input terminal connected to a source terminal of the pMOS transistor P 5 , and the output terminal connected to the input side of the composite circuit 3 . Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

With the level shift circuit 10 g according to the eighth embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled.

Ninth Embodiment

As shown in FIG. 11, in the first transmission circuit 1 used as part of a level shift circuit 10 i according to a ninth embodiment, the composite circuit 3 shown in FIG. 2 is added to a plurality of inverters connected in series. Other aspects are substantially similar to the first embodiment, and accordingly, redundant description is omitted.

With the level shift circuit 10 i according to the ninth embodiment of the present invention, the delay time of the leading edge generated by the level shift circuit 200 becomes small. The duty of the output signal Vout can be controlled. Furthermore, the level shift circuit 10 i according to the ninth embodiment can adjust the duty of the output signal Vout.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.