Current-voltage transforming circuit employing limiter circuit

This application claims to benefit of Korean Patent Application No. 2003-0061480, filed Sep. 29, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

1. Field of the Invention

The present invention relates to a current-voltage transforming (converting and amplifying) circuit employing a limiter circuit unit used with a photo detector integrated circuit, and more particularly, to a photo detector integrated circuit having a current-voltage transforming (converting and amplifying) circuit employing a limiter circuit unit detecting a current flowing through the current-voltage transforming circuit to generate a limiter current to the current-voltage transforming circuit, thereby preventing saturation of the current-voltage transforming circuit occurring when a high optical power is supplied to the photo detector integrated circuit during a writing operation of writing data on a recording medium, such as a CD-RW, in a disc recording and/or reading apparatus.

2. Description of the Related Art

Generally, an. optical pickup apparatus recording information on and/or reading information from a recording medium, such as a CD-RW, includes a photo detector integrated circuit (PDIC) detecting an optical beam reflected from an optical recording medium, such as an optical disc, containing information by a laser beam generated from a laser diode.

In a recordable CD, such as the CD-RW, a writing operation is performed by projecting the laser beam having a high power on a surface of the CD to form a pit on the surface of the CD. When an excessive power of the laser beam is supplied to the PDIC during the writing operation, a great amount of current generates to cause a current-voltage transforming (converting and/or amplifying) circuit of the PDIC to be saturated, thereby distorting an over-response characteristic of the current-voltage transforming circuit of the PDIC.

FIG. 1 is a view showing a conventional current-voltage transforming (converting and/or amplifying) circuit having a limiter circuit in a photo detector integrated circuit.

A photo detector (PD) current I PD is generated by carriers generated from a photo detector (PD) 12 to which an input laser beam is reflected. The PD current I PD pulls a feedback (FD) current I f from an output buffer G 3 , the FD current I f generates a voltage difference on both ends of the feedback resistor when flowing through the feedback resistor having a resistance of R f , and the PD current I PD is converted into a voltage signal V OUT of V OUT =I f ×R f .

A differential amplifier G 1 , an emitter follower G 2 , and the output buffer G 3 constitutes a trans-impedance amplifier 10 . If an excessive optical signal is inputted into the PD 12 , the trans-impedance amplifier 10 is saturated to be out of an operational range. Due to this saturation of the trans-impedance amplifier 10 , when the FD current I f increases, the output voltage V OUT is no longer increased, an amplification speed of the current-voltage transforming circuit becomes slow even in response to a small amount of an input signal, and an excessive response characteristic of the current-voltage transforming circuit is distorted.

Referring to FIG. 1 , an emitter of a transistor Q 1 is connected to an output terminal of the emitter follower G 2 to detect an output of the emitter follower G 2 . When an output voltage of the emitter follower G 2 is greater than a predetermined value of V LMT +V BE , the transistor Q is turned on so that the limiter current I LMT is allowed to flow through the current-voltage transforming circuit. At a terminal T in , I PD =I f +I LMT . Even if the PD current I PD is excessively increased, the FD current I f is no longer increased, and the trans-impedance amplifier 10 is not saturated but continues to operate.

As described above, in order to prevent the current-voltage transforming circuit from being saturated, an output voltage of the trans-impedance amplifier 10 is detected. When the output voltage is greater than a predetermined voltage, the limiter current I LMT is allowed to flow through the trans-impedance amplifier 10 so as to prevent the trans-impedance amplifier from being saturated.

In Japanese patent publication no.: 10-188315, disclosed on Jul. 21, 1998, an output voltage of a current-voltage transforming circuit is detected to allow a limiter current to flow into the current-voltage transforming circuit when the output voltage is greater than a predetermined value, so that saturation of the current-voltage transforming circuit is prevented.

The current-voltage transforming circuit disclosed in the above Japanese publication includes a first amplifier, a second amplifier, and an output buffer. An emitter of a transistor is connected to receive an output of the second amplifier, and the transistor is turned on to generate the limiter current I LT when the output of the second amplifier is greater than V REF +V BE , that is, V 0 >V REF +V BE . Therefore, a feed back current I f is no longer increased even if a current I PH flowing through a photo detector is increased, so that the saturation of the current-voltage transforming circuit is prevented.

The above conventional current-voltage transforming circuit and the Japanese patent publication disclose that a current is compensated by detecting a voltage, and the Japanese patent publication discloses that the emitter of the transistor is connected to the second amplifier to perform a switching operation on the limiter current I LT as well as to control the output voltage V 0 to be below V REF +V BE .

However, the circuit having a PNP type transistor is designed to limit a maximum value of a predetermined terminal voltage controlled according to a characteristic of the PNP type transistor, and the circuit having an NPN type transistor is designed to limit a minimum value of the predetermined terminal voltage controlled according to the characteristic of the NPN transistor.

In the above patent publication, since the maximum value of the output voltage V 0 is controlled to below V REF +V BE , that is, the maximum value of the output voltage V 0 is limited below V REF +V BE , circuit elements should not be the NPN type transistor but the PNP type transistor. Accordingly, a current-voltage transforming circuit disclosed in the above patent publication should include the PNP type transistor, which has a lower gain than the NPN type transistor. Therefore, it is disadvantageous that the gain is lowered, and a speed becomes slow.

In order to solve the above problems, it is needed to develop an improved current-voltage transforming (converting and/or amplifying) circuit which does not limit the output voltage of the amplifier, which constitutes the current-voltage transforming circuit, to a predetermined value regardless of the NPN type transistor and the PNP type transistor, and dose not lower the gain and the speed.

In order to solve the above and/or other problems, it is an aspect of the present invention to provide a current-voltage transforming (converting and amplifying) circuit using a limiter current to prevent saturation in the current-voltage transforming (converting and amplifying) circuit used with a photo detector integrated circuit.

It is another aspect of the present invention to provide a current-voltage transforming circuit used with a photo detector integrated circuit to detect a current rather than a voltage of the current-voltage transforming circuit to generate a limiter current flowing into the current-voltage transforming circuit.

It is another aspect of the present invention to provide a current-voltage transforming circuit used with a photo detector integrated circuit to include a current detecting limiter unit switching a limiter current by detecting a current.

It is another aspect of the present invention to provide a current-voltage transforming circuit used with a photo detector integrated circuit to includes at least one NPN type transistor which is not limited to a maximum value or a minimum value, to detect a current to switch a limiter current, thereby improving a gain as well as a speed.

It is another aspect of the present invention to provide a current-voltage transforming circuit used with a photo detector integrated circuit to include a current detecting limiter unit in which a turn-on point of a limiter current is controlled by a user.

It is another aspect of the present invention to provide a current-voltage transforming circuit used with a photo detector integrated circuit to detect a current of the current-voltage transforming circuit to generate a limiter current to prevent saturation of the current-voltage transforming circuit, thereby improving characteristics, such as an over-response characteristic, of an RF wave of the current-voltage transforming circuit.

It is another aspect of the present invention to provide a disc recording and/or reading apparatus having a current-voltage transforming circuit.

Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.

To achieve the above and/or other aspects, there is provided a current-voltage transforming circuit used with a photo detector integrated circuit, the current-voltage transforming circuit including a photo detector to detect a photo signal (laser beam signal) to generate a photo current, an amplifier to amplify the photo current, which corresponds to the photo signal, an emitter follower to receive an output of the amplifier, an output buffer to receive an output of the emitter follower, a current detecting limiter unit having an input terminal and an output terminal and turned on to generate a limiter current when the detected current outputted from the amplifier is greater than a predetermined current, and a feedback resistor connected between the photo detector and an output terminal of the output buffer.

To achieve the above and/or other aspects, there is provided a disc recording and/or reading apparatus having a current-voltage transforming circuit of a photo detector integrated circuit, the disc recording and/or reading apparatus including a photo detector generating a photo current in response to a photo signal inputted into the photo detector, a trans-impedance amplifier converting and amplifying the photo current to generate an output voltage, and generating first and second currents, and a current detecting limiter generating a limiter current in response to the first and second currents so that the trans-impedance amplifier is prevented.

According to another aspect of the present invention, the trans-impedance amplifier includes an amplifier amplifying the photo current received from the photo detector, an emitter follower coupled to the amplifier, an output buffer coupled to the emitter to generate the output voltage, and a feedback resistor coupled between the output buffer and the amplifier so that the photo current is converted into the output voltage.

According to another aspect of the present invention, the first and second currents are generated from one of a first junction between the amplifier and the emitter follower, a second junction between the emitter follower and the output buffer, and an output terminal of the output buffer.

According to another aspect of the present invention, the limiter current is outputted to one of a junction between the output buffer and the amplifier and a reference potential.

According to another aspect of the present invention, the first and second currents are different from each other.

According to another aspect of the present invention, the current detecting limiter unit outputs one of the first and second currents as the limiter current when the other one of the first and second currents is greater than a predetermined reference value.

These and/or other advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a view showing a conventional current-voltage transforming circuit having a limiter circuit in a photo detector integrated circuit;

FIG. 2 is a view showing a current-voltage transforming circuit having a limiter circuit used with a photo detector integrated circuit according to an embodiment of the present invention;

FIG. 3 is a circuit diagram showing a current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 2 ;

FIG. 4 is a circuit diagram showing a differential amplifier and an emitter follower of a trans-impedance amplifier, and the current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 2 ;

FIG. 5 is a block diagram showing a current-voltage transforming circuit having a limiter circuit used with a photo detector integrated circuit according to another embodiment of the present invention;

FIG. 6 is a block diagram showing a current-voltage transforming circuit having a limiter circuit used with the photo detector integrated circuit according to another embodiment of the present invention;

FIG. 7 is a circuit diagram showing a current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 6 ;

FIG. 8 is a circuit diagram showing another current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 6 ;

FIG. 9 is a circuit diagram showing another current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 6 ;

FIG. 10 is a block diagram showing a current-voltage transforming circuit having a limiter circuit used with the photo detector integrated circuit according to another embodiment of the present invention;

FIG. 11 is a circuit diagram showing a current-detecting limiter unit of the current-voltage transforming circuit shown in FIG. 10 ;

FIG. 12 is a circuit diagram showing another current-detecting limiter unit using a PNP type transistor having a high amplification constant β in the current-voltage transforming circuit shown in FIG. 10 ; and

FIG. 13 is a view showing an over-response characteristic of an output of the current-voltage transforming circuit according to an optical strength of a laser beam (light) inputted to the current-voltage transforming circuit employing the current-detecting limiter unit.

Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by reference to the figures.

FIG. 2 is a view showing a current-voltage transforming circuit 10 having a current detecting limiter unit 11 used with a photo detector integrated circuit according to an embodiment of the present invention.

A photo detector 12 generates a photo current I PD in response to a photo signal, such as laser beam (light), inputted to the photo detector 12 . The photo current I PD pulls a feedback (FB) current I f from an output buffer G 3 . When the FD current I f flows through a feedback resistor having a resistance of R f , a voltage difference is generated between both ends of the feed back resistor so that the FD current I f is converted into a voltage signal, that is, an output voltage V OUT , V OUT =I f ×R f . As described above, A photo diode which can generate the photo current I PD in response to the optical signal (laser beam or light) inputted to the photo diode, can be used as the photo detector 12 .

A differential amplifier G 1 , an emitter follower G 2 , and the output buffer G 3 constitute a trans-impedance amplifier 10 to transmit an input impedance as an output.

When the photo signal is too intense during a writing operation of writing information on a recording medium, such as a CD-RW, in a disc recording and/or reading apparatus, the trans-impedance amplifier 10 becomes saturated to be out of an operation range. Due to this, the output voltage V OUT is not increased even if the FD current I f increases, thereby decreasing a speed of an amplifier in response to a small amount of the photo signal and distorting an over-response characteristic of the amplifier.

The differential amplifier G 1 outputs an output calculated by multiplying a difference between two input signals inputted into input terminals of the differential amplifier G 1 by a predetermined gain. In the differential amplifier G 1 , a gain may be ideally an indefinite gain, and an input voltage of at least one of the inputs is 0. However, the gain is actually a definite gain, and the input voltage is not actually 0. Therefore, a non-inverter input of the differential amplifier 10 is connected to the feedback resistor to make the input voltage 0. Instead of the differential amplifier G 1 as shown in FIG. 2 , another type of an amplifier receiving a voltage generated according to the photo current generated from the photo detector 12 can be used.

In the emitter follower or a collector-common amplifier G 2 , an input is inputted into a base of the emitter follower G 2 , and an output is obtained from an emitter of the emitter follower G 2 . The emitter follower G 2 maintains a voltage gain when an input resistance is far greater than an output resistance, while outputting the input as the output. Since a gain between the base and the emitter of the emitter follower G 2 is almost 1, the emitter follower G 2 outputs the input of the base through the emitter as the output.

The output buffer G 3 maintains a current gain to output an input as an output when an input impedance is far greater than an output impedance. A gain of the output buffer G 3 is the same as the emitter follower G 2 .

The feedback resistance R f of the feedback resistor functions such that the photo current I PD generated from the photo detector 12 and inputted as an input of the trans-impedance amplifier 10 is converted into an output voltage V OUT as an output of the trans-impedance amplifier 10 .

The current detecting limiter unit 11 receives an output current I SENSE of the differential amplifier G 1 of the trans-impedance amplifier 10 as an input, and is turned on when the output current I SENSE is greater than a predetermined value to transmit a current I LMTIN as a current I LMTOUT to a terminal T in , a junction between the photo detector 12 and the differential amplifier G 1 .

Since the photo current I PD is I f +I LMTIN , the feedback current I f is controlled not to be increased over a predetermined value since the current I LMTIN is inputted to the terminal T in as a current I LMTOUT even if the photo current I PD is excessively increased in response to an increase of the intense (excess) photo signal I PD , thereby preventing the saturation of the trans-impedance amplifier 10 .

FIG. 3 is a circuit diagram showing the current-detecting limiter unit 11 of the current-voltage transforming circuit 10 shown in FIG. 2 .

The current-detecting limiter unit 11 includes first, second, and third terminals for currents I SENSE , I LMTIN , and I LMTOUT , respectively. First and second resistors R 1 and R 2 are connected between the first transistor Q 1 and a second transistor Q 2 and between the first resistor R 1 and a reference potential (voltage) signal V REF or a ground, respectively. When the current I SENSE I is supplied from the differential amplifier G 1 to the current-detecting limiter unit 11 through the first terminal, a current I 1 flows through the first transistor Q 1 . If an amplification coefficient of the first transistor Q 1 is β, the current I 1 is calculated by the following formula.

I 1=β× I SENSE

A base voltage V b2 of the second transistor Q 2 is calculated by the following formula.

V b2 =I 1× R 2

When V b2 >V REF +V beq2 , which is about 0.7V, the second transistor Q 2 is turned on to activate the current-detecting limiter unit 11 to output the current I LMTOUT to the terminal T in . Here, the voltage V beq2 is a voltage between a base and an emitter of the second transistor Q 2 . Therefore, the trans-impedance amplifier 10 is not saturated even if the photo current I PD is increased generated from the photo detector 12 during the writing operation of writing the information on the recording medium, such as the CD-RW, etc, in the disc recording and/or reading apparatus.

FIG. 4 is a circuit diagram showing operations of the differential amplifier G 1 and the emitter follower G 2 of the trans-impedance amplifier 10 , and the current detecting limiter unit 11 of the current-voltage transforming circuit shown in FIG. 2 .

The differential amplifier G 1 includes third, fourth, fifth, sixth, seventh transistors Q 3 , Q 4 , Q 5 , Q 6 , and Q 7 to output a value calculated by multiplying a difference between a signal PDIN and a reference potential VREF inputted through respective terminals by a predetermined gain.

The signal is VREF is inputted into a base of the third transistor Q 3 , and the signal PDIN is inputted into a base of the fourth transistor Q 4 . Referring to FIGS. 2 and 4 , the base of the third transistor Q 3 corresponds to a non-inverting terminal of the differential amplifier G 1 to receive the reference potential VREF, and the base of the fourth transistor Q 4 corresponds to an inverting terminal of the differential amplifier G 1 .

When the signal PDIN is inputted to the differential amplifier G 1 as an input, the current I SENSE is transmitted to the base of the first transistor Q 1 of the current detecting limiter unit 11 through a junction between a collector of the sixth transistor Q 6 and a collector of the seventh transistor Q 7 .

In the current detecting limiter unit 11 , the current I SENSE is increased when the current of the signal PDIN is increased. Accordingly, the current I 1 is increased, and a voltage between the first and second resistor R 1 and R 2 , that is, the base voltage V b2 , is increased. When V b2 >V REF +V beq2 (about 0.7V), the second transistor Q 2 is turned on to supply the limiter current I LMT to the terminal T in . When an input current of the trans-impedance amplifier 10 is increased since the limiter current I LMT flows to the terminal T in , the saturation of the trans-impedance amplifier 10 is prevented since the feedback current I f is limited. The current detecting limiter unit 11 is biased due to a constant current source 18 . An output of the emitter of the emitter follower G 2 is transmitted to the output buffer G 3 .

The third, fourth, fifth, sixth, seventh transistors Q 3 , Q 4 , Q 5 , Q 6 , and Q 7 of the differential amplifier G 1 correspond to a pair of differential transistors Q 3 and Q 4 , active loads Q 5 and Q 6 , and a Wilson current mirror Q 7 , respectively.

The third and fourth transistor Q 3 and Q 4 are connected through collectors thereof and are biased by the constant current source 18 .

A bias 1 and a bias 2 are supplied to correspond to a current source and an active load of the third and fourth transistors Q 3 and Q 4 , respectively. The bias 1 is supplied to the seventh transistor Q 7 , and the bias 2 is supplied to the fifth and sixth transistor Q 5 and Q 6 .

The seventh transistor Q 7 corresponding to the bias 1 includes the Wilson current mirror having a PNP type transistor and excluding a self-biased circuit, and functions as the active load and the current source of the third and fourth transistor Q 3 and Q 4 .

Since gains of the sixth and seventh transistor Q 6 and Q 7 is proportional to respective output impedances R 0 , that is, G=g m ×Ro, a larger gain can be obtained according to a larger output impedances of the sixth and seventh transistor Q 6 and Q 7 .

FIG. 5 is a block diagram showing another current-voltage transforming circuit 10 and another current detecting limiter unit 11 used with the photo detector integrated circuit according to another embodiment of the present invention.

As shown in FIGS. 2 and 5 , the photo detector 12 generates the photo current I PD in response to the photo signal, such as the laser beam (light), inputted to the photo detector 12 . The photo current I PD pulls the feedback (FB) current I f from the output buffer G 3 . When the FD current I f flows through the feedback resistor having the resistance of R f , the voltage difference is generated between the both ends of the feed back resistor so that the FD current I f is converted into the voltage signal, that is, the output voltage V OUT , V OUT =I f ×R f . The converted output voltage is outputted through the differential amplifier G 1 , the emitter follower G 2 , and the output buffer G 3 . The structures of the differential amplifier G 1 , the emitter follower G 2 , and the output buffer G 3 are the same as shown in FIG. 4 .

In this embodiment shown in FIG. 5 , the limiter current I LMT is transmitted to the terminal Tin from an output terminal of the output buffer G 3 rather than an output terminal of the emitter follower G 2 of FIG. 2 according to the current I SENSE . When the limiter current I LMT flows into an input terminal of the trans-impedance amplifier 10 , the feedback current I f of the trans-impedance amplifier 10 is limited to prevent the saturation of the trans-impedance amplifier 10 . An effect of the prevention of the saturation in the trans-impedance amplifier 10 shown in FIG, 5 is the same as the trans-impedance amplifier 10 shown in FIG. 2 .

FIG. 6 is a block diagram showing another current-voltage transforming circuit 10 and another current detecting limiter unit 11 - 1 used with the photo detector integrated circuit according to another embodiment of the present invention.

As shown in FIGS. 2 and 6 , the current I SENSE flows from an output terminal of the differential amplifier G 1 to the current detecting limiter unit 11 - 1 , and the current detecting limiter unit 11 - 1 generates the limiter current I LMT when the current I SENSE is greater than a predetermined value, so that saturation of the current-voltage transforming circuit 10 is prevented by limiting the feedback current I f of the current-voltage transforming circuit 10 .

In FIG. 6 , an output terminal of the current detecting limiter unit 11 - 1 is connected to the ground or another reference potential rather than the terminal T in which is shown in FIG. 2 .

FIG. 7 is a circuit diagram showing the current-detecting limiter unit 11 - 1 of the current-voltage transforming circuit shown in FIG. 6 ;

The current I SENSE flows through the differential amplifier G 1 , and then the first transistor Q 1 is turned on. If the amplification coefficient of the first transistor Q 1 is β, the current I 1 is calculated by the following formula.

I 1=β× I SENSE

The base voltage V b2 of the second transistor Q 2 is calculated by the following formula.

V b2 =I 1× R 2

When V b2 >V REF +V beq2 , which is about 0.7V, the second transistor Q 2 is turned on to activate the current-detecting limiter unit 11 to generate the current I LMTOUT . Here, the voltage V beq2 is a voltage between a base and an emitter of the second transistor Q 2 , and the voltage V REF is a reference voltage inputted into a non-inverter terminal of the differential amplifier G 1 . Therefore, the trans-impedance amplifier 10 is not saturated even if the photo current I PD is increased generated from the photo detector 12 during the writing operation of writing the information on the recording medium in the disc recording and/or reading apparatus. The structure of the current detecting limiter unit 11 - 1 according to this embodiment of the present invention shown in FIG. 6 is the same as the current detecting limiter unit 11 of FIG. 3 . However, the only difference between the current detecting limiter unit 11 and the current detecting limiter unit 11 - 1 is that the output terminal of the current detecting limiter unit 11 - 1 , that is, an emitter of the second transistor Q 2 , is connected to the ground or the potential so that the limiter current I LMT flows through the ground or the reference potential.

FIG. 8 is a circuit diagram showing another current detecting limiter unit 11 - 2 of the current-voltage transforming circuit shown in FIG. 6 . the current detecting limiter unit 11 - 2 can be used in the current-voltage transforming circuit shown in FIGS. 2 and 5 .

The current detecting limiter unit 11 - 2 of FIG. 8 is a combination of the current detecting limiter unit 11 of FIG. 3 and the current detecting limiter unit 11 - 1 of FIG. 7 . The current I SENSE is supplied from the differential amplifier G 1 , the current I 1 flows through the first transistor Q 1 . If the amplification coefficient of the first transistor Q 1 is β, the current I 1 is calculated by the following formula.

I 1=β× I SENSE

A base voltage V b2 of the second transistor Q 2 and a base voltage V b3 of an eighth transistor Q 8 are respectively calculated by the following formula.

V b2 (= V b3 )= I 1× R 2

When V b2 (V b3 )>V REF +V beq2 (=V beq3 ) (about 0.7V), the second and eighth transistors Q 2 and Q 8 are turned on to activate the current detecting limiter unit 11 - 2 to generate the current I LMT . The current I LMTIN flows through the second and eighth transistors Q 2 and Q 8 as the currents I LMTOUT1 and I LMTOUT2 , respectively. The current I LMTOUT1 flows through the ground, and the current I LMTOUT2 flows into the terminal T in . Accordingly, the feedback current I f of the trans-impedance amplifier 10 is limited to prevent, the saturation. Here, V beq2 and V beq3 are emitter-base voltages of the second and eighth transistors Q 2 and Q 8 , and the voltage V REF is a reference voltage inputted into a non-inverter terminal of the differential amplifier G 1 .

FIG. 9 is a circuit diagram showing another current detecting limiter unit 11 - 3 of the current-voltage transforming circuit. The current detecting limiter unit 11 - 3 can be used in the current-voltage transforming circuit shown in FIGS. 2 and 5 .

In the current detecting limiter unit 11 - 3 according to this embodiment, the second resistor R 2 is replaced with a variable resistor VR to selectively adjust the amplitude of an output of the current detecting limiter unit 11 - 3 which can be used to limit the feedback current I f according to a user demand.

The base voltage V b2 of the second transistor Q 2 of FIG. 9 is calculated using the following formula.

V b2 =I 1× VR

When V b2 >V REF +V beq2 (about 0.7V), the second transistor Q 2 is turned on to activate the current detecting limiter unit 11 - 3 to generate the current I LMT . Here, V beq2 is the emitter-base voltage of the second transistor Q 2 , and the voltage V REF is a reference voltage inputted into the non-inverting terminal of the differential amplifier G 1 .According to this structure of the current detecting limiter unit 11 - 3 , the trans-impedance amplifier 10 is not saturated even if the photo current I PD is increased during the writing operation of writing the information on a recording medium, such as the CD-RW, in the disc recording and/or reading apparatus.

The second resistor R 2 of the current detecting limiter units 11 - 1 and 11 - 2 shown in FIGS. 7 and 8 , respectively, can be replaced with the variable resistor VR shown in FIG. 9 to selectively adjust the output of the current detecting limiter units 11 - 1 and 11 - 2 .

FIG. 10 is a block diagram showing a current-voltage transforming circuit 10 having a current detecting limiter unit 11 - 4 used with the photo detector integrated circuit according to another embodiment of the present invention. As opposed to previous embodiments, the current-voltage transforming circuit includes at least one PNP type transistor.

As shown in FIG. 10 , when the transistor elements are realized by the PNP type transistor, a current direction of the photo diode 12 is changed (reversed), and a direction of the current I LMT of the current detecting limiter unit 11 - 4 becomes changed (reversed).

FIG. 11 is a circuit diagram showing another current detecting limiter unit 11 - 4 of the current-voltage transforming circuit. The current detecting limiter unit 11 - 4 can be used in the current-voltage transforming circuit shown in FIGS. 2 and 5 .

The current I SENSE flows through the differential amplifier G 1 , and then the first transistor Q 1 is turned on. If the amplification coefficient of the first transistor Q 1 is β, the current I 1 is calculated by the following formula.

I 1=β× I SENSE

The base voltage V b2 of the second transistor Q 2 is calculated by the following formula.

V b2 =V CC −I 1× R 1

When V b2 <V CC −I 1 ×R 1 (about 0.7V), the second transistor Q 2 is turned on to activate the current detecting limiter unit 11 - 4 to generate the current I LMT . Here, the voltage V beq2 is a voltage between a base and an emitter of the second transistor Q 2 , and the voltage V REF is a reference voltage inputted into a non-inverter terminal of the differential amplifier G 1 . Therefore, the trans-impedance amplifier 10 is not saturated even if the photo current I PD is increased generated from the photo detector 12 during the writing operation of writing the information on the recording medium, such as the CD-RW, in the disc recording and/or reading apparatus.

It is possible that the output current I LMTOUT of the current detecting limit unit 11 - 4 of FIG. 11 is controlled to flow through the ground like as the current detecting limit unit shown in FIG. 7 . It is also possible that the output current I LMTOUT of the current detecting limit unit 11 - 4 of FIG. 11 is controlled to divide the output current into the current I LMTOUT1 and I LMTOUT2 to be transmitted to the ground and the terminal T in , respectively, like as the current detecting limit unit shown in FIG. 8 .

FIG. 12 is a circuit diagram showing another current detecting limiter unit 11 - 5 of the current-voltage transforming circuit. The current detecting limiter unit 11 - 5 can be used in the current-voltage transforming circuit shown in FIGS. 2 and 5 .

The current detecting limiter unit 11 - 5 of FIG. 12 includes a ninth transistor Q 9 of the PNP type transistor, which is shown in the current detecting limiter unit 11 - 4 of FIG.11 , and a tenth transistor Q 10 of the NPN type transistor. A base terminal of the tenth transistor Q 10 is connected to a collector terminal of the ninth transistor Q 9 , a collector terminal of the tenth transistor Q 10 is connected to an emitter terminal of the ninth transistor Q 9 , and an emitter terminal of the tenth transistor Q 10 is an output terminal of the current detecting limiter unit 11 - 5 to output the current I LMTOUT .

The ninth and tenth transistors Q 9 an dQ 10 of FIG. 12 forms an equivalent circuit of the second transistor Q 2 of FIG. 11 to perform the same switching function as the second transistor Q 2 of FIG. 11 . However, a coupling state in which the tenth transistor Q 10 and the ninth transistor Q 9 having the same equivalent circuit as a single PNP type transistor, has a higher amplification coefficient β′ than the single PNP transistor since the amplification coefficient β′ is calculated by multiplying a second amplification coefficient β 2 of the ninth transistor Q 9 by a third amplification coefficient β 3 of the tenth transistor Q 10 .

In the PNP type transistor, the amplification coefficient β is lower to slow the speed compared to the NPN type transistor. The amplification coefficient β can be increased using a coupling structure of the PNP type transistor and the NPN type transistor as shown in FIG. 12 . Although the coupling structure of the PNP type transistor and the NPN type transistor includes the PNP type transistor, the coupling structure of the PNP type transistor and the NPN type transistor is used in the current-voltage transforming circuit having the amplification coefficient β greater than the circuit constituted of the PNP type transistor and same speed as the circuit constituted of the NPN type transistor.

FIG. 13 is a view showing an over-response characteristic of an output of the current-voltage transforming circuit according to an optical strength of a laser beam (light) inputted to the current-voltage transforming circuit employing the current-detecting limiter unit.

A graph 20 is the over-response characteristic of the output of the current-voltage transforming circuit according to the embodiments of the present invention, and another graph 21 is the over-response characteristic of the output of a conventional current-voltage transforming circuit which does not use the embodiments of the present invention.

In the conventional current-voltage transforming circuit, when the laser beam becomes being weakened, an output voltage indicated with a circular broken line of the graph 21 is lowered too much. However, in the current-voltage transforming circuit according to the embodiments of the present invention, a change of the output voltage is limited in a predetermined range as indicated with another circular broken line of graph 20 , thereby stabilizing the output voltage.

According to the current-voltage transforming circuit used with the PDIC, since the current is detected rather than the voltage of the trans-impedance amplifier, the saturation of the current-voltage transforming circuit can be prevented using the limiter current.

The current-voltage transforming circuit used with the PDIC is provided with NPN type transistor.

According to the current-voltage transforming circuit used with the PDIC, the current of the current detecting limiter unit can be switched by detecting the current of the current-voltage transforming circuit regardless of the maximum or minimum value of the voltage of the current-voltage transforming circuit, thereby obtaining an improved current-voltage transforming circuit used with the PDIC having the higher gain and speed.

According to the current-voltage transforming circuit used with the PDIC, a current turning-on point of the current detecting limiter unit can be adjusted by a user.

According to the current-voltage transforming circuit used with the PDIC, the limiter current flows through the trans-impedance amplifier to prevent the saturation of the trans-impedance amplifier, thereby improving the over-response characteristic of an RF wave as well as a signal to noise ratio in the current-voltage transforming circuit used with the PDIC.

According to the above embodiments of the present invention, the current-voltage transforming circuit used with the PDIC can be employed in the disc recording and/or reading apparatus.

Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principle and sprit of the invention, the scope of which is defined in the claims and their equivalent.