JP2009038648A - Light receiving amplifier circuit for optical pickup, and optical pickup device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately operate a light receiving amplifier circuit for optical pickup by minimizing its power consumption. <P>SOLUTION: This light receiving amplifier circuit 1 for optical pickup is provided with: a light receiving element 2 converting a light receiving signal to an electric signal; an amplifier circuit 3 amplifying the converted electric signal; an output circuit 5 for outputting the electric signal amplified by the amplifier circuit 3; a feedback circuit 4 feeding back the output signal of the amplifier circuit 3 to the input of the amplifier circuit; and a variable bias circuit 7. The variable bias circuit 7 generates a reference bias current, transmits a bias current for the output circuit according to the reference bias current to the output circuit 5, and transmits a bias current for the amplifier circuit according to the reference bias current to the amplifier circuit 3. The variable bias circuit 7 has a switch circuit composed of a resistor and a switch, and increases/decreases the reference bias current by turning on/off the switch circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light receiving amplifier circuit for detecting an optical signal used in an apparatus capable of reproducing and / or recording on an optical disk medium.

  In recent years, a plurality of formats such as CD, DVD, and BD have been developed for optical disc media (hereinafter simply referred to as media) for the purpose of increasing the recording capacity. Accordingly, the optical disk drive is required to support media of different formats.

  The optical disk drive includes an optical pickup device, and the optical pickup device includes a laser diode and a light receiving amplifier IC. Laser light output from the laser diode is irradiated onto the optical disc through a collimator lens, a beam splitter, and an objective lens. The reflected light from the optical disk is irradiated to the light receiving amplifier IC through the objective lens, the beam splitter, and the spot lens.

  As an example of the wavelength of the laser beam output from the laser diode, the wavelength of the infrared laser beam used for reading the CD data is 780 nm, the wavelength of the infrared laser beam used for reading the DVD data is 650 nm, and for reading the data of BD. The wavelength of the blue laser light used is 405 nm.

  The light receiving amplifier IC in the optical pickup device includes a light receiving amplifier circuit, reproduces an information signal from an incident optical signal, creates a signal for tracking and focusing servo, and includes a signal processing circuit and a control circuit (not shown). Output to the subsequent circuit.

  In a recordable CD or DVD drive mainly used as a peripheral device of a personal computer, a larger laser power and a larger amount of laser light are output from the LD and irradiated onto the disc at the time of recording than at the time of reproduction. The light receiving amplifier circuit to which the reflected light from the disk is input also has a large light input. In order to cope with the difference in optical input level between recording and reproduction, the light receiving amplifier circuit employs a method of switching gains corresponding to recording / reproduction. At the time of recording on the medium by the optical pickup device, the medium composition is changed by irradiating the medium with a large amount of laser light to change the reflectance. At the time of recording, it is necessary to simultaneously control a large amount of laser light and read a small amplitude reproduction signal, so the light receiving amplifier circuit generates a large amplitude pulse signal generated by the large amount of laser light. Is required to converge quickly, that is, to shorten the settling time.

  FIG. 9 is a block diagram of a conventional light receiving amplifier circuit 101 for an optical pickup. The optical pickup light receiving amplifier circuit 101 includes a photodiode (PD) 102 which is a light receiving element, an amplifier circuit 103, a feedback circuit 104, an output circuit 105, an output terminal 106, and a bias circuit 107.

  The amplifier circuit 103 converts the current signal from the photodiode 102 into a voltage signal. The feedback circuit 104 includes a feedback resistor, and feeds back an output signal of the amplifier circuit 103 that feeds back an output signal of the amplifier circuit 3 to an input of the amplifier circuit 3. The output circuit 105 outputs the output signal of the amplifier circuit 103 to the outside via the output terminal 106.

  In the bias circuit 107, a transistor (not shown) included in the amplifier circuit 103 and the output circuit 105 is used at a correct operating point, and a bias current necessary for the amplifier circuit 103 and the output circuit 105 to operate normally is supplied to the amplifier circuit 103. And is designed to be supplied to the output circuit 105. The amplifier circuit 103 is a circuit that converts the current signal converted by the photodiode 102 into a voltage signal, and uses a current-voltage amplifier circuit. The output circuit 105 has an output drive capability (current supply capability) that has a low impedance and can secure a dynamic range so that the converted voltage signal is not affected by the load resistor RL and the load capacitance CL connected to the output terminal 106. )is required.

  The output circuit 105 is connected to a load capacitance CL such as an LSI input capacitance connected through an output terminal 106 or a parasitic capacitance of a flexible cable. When the light receiving amplifier circuit 101 outputs a pulse signal having a large amplitude, the light receiving amplifier circuit 101 supplies an output current Ios from the output circuit 105 that raises the voltage generated at both ends of the load capacitor CL and the load resistor RL to the output voltage Vo.

FIG. 10 is an explanatory diagram for the settling time. The convergence time when the large-amplitude pulse signal falls and rises is called settling time. As described above, at the time of recording on the medium, it is necessary to both control the amount of laser light and to read a reproduction signal with a small amplitude, and thus the light receiving amplifier circuit is required to have a response as fast as possible. For this reason, it is necessary to shorten the settling time as much as possible. The settling time depends on the voltage change amount (slew rate) dVo / dt per unit time and the convergence characteristic of the voltage change, that is, the ringing characteristic. The slew rate, which is one determinant of settling time, is considered to be the speed at which the load capacitance CL is charged by the output current Ios. DVo / dt = Iosm / CL
It is represented by Here, Iosm represents the maximum output current Ios that can be output by the light receiving amplifier circuit, that is, the maximum output current, and is also called an output drive current. In order to obtain the pulse response characteristic of the light receiving amplifier circuit corresponding to the load capacity CL at the time of recording on the medium by the optical pickup device, it is necessary to increase the ability to output the output drive current Iosm, that is, the output drive ability as much as possible. . However, since the power consumption of the light receiving amplifier circuit is increased by increasing the output drive capability, it is necessary to design the power consumption so as not to become too large.

  Ringing characteristics, which are another determinant of settling time, depend on the phase margin of the amplifier circuit. FIG. 11 shows a Bode diagram of the open loop gain and phase of the amplifier circuit. The increase / decrease in the phase margin of the amplifier circuit due to the gain of the feedback circuit connected to the amplifier circuit will be described with reference to FIG.

  It is assumed that the frequency characteristic when there is no feedback circuit is the frequency characteristic 108 of the open loop gain of the amplifier circuit indicated by a solid line. The frequency characteristic 108 has frequency poles P1, P2 and P3. When the frequency of the signal input to the amplifier circuit becomes higher than the pole P1, the open loop gain is -6 dB / octave, and after the pole P2, it is -12 dB / octave. After the pole P3, it decreases with an inclination of −18 dB / octave. The phase of the amplifier circuit at this time is −45 ° at the pole P1, −135 ° at the pole P2, and −225 ° at the pole P3.

  Phase obtained by adding 180 ° to the phase at the intersection frequency between the gain of the feedback circuit and the frequency characteristics of the open loop gain of the amplifier circuit when feedback is applied to the amplifier circuit by a feedback circuit composed of a feedback resistor and a switch It is said that there is room.

  In FIG. 11, the phase margin at the intersection frequency fx between the feedback circuit gain G and the open loop gain frequency characteristic 108 is Φ. When the gain of the feedback circuit is increased to G1, the intersection frequency is reduced to f1, and the phase margin is increased to Φ1. Conversely, when the gain of the feedback circuit is lowered and G2, the intersection frequency is increased to f2 and the phase margin is decreased to Φ2.

  As the phase margin increases, a more excellent ringing characteristic, that is, a pulse response characteristic with smaller ringing can be obtained. When the phase margin is further increased, a pulse response characteristic in which no ringing occurs can be obtained. Since the bias current input from the outside to the amplifier circuit by the bias circuit or the like changes the open loop frequency characteristics of the amplifier circuit, the phase margin can be adjusted by adjusting the bias current.

FIG. 12 shows a conventional bias circuit 109. For simplicity, the transistor will be described below with a current amplification factor hfe = ∞ and an early voltage VA = ∞. With the application of the + side power supply voltage Vcc, a current flows through the resistor Ra, the NPN transistor Q1, the NPN transistor Q2, and the NPN transistor Q3, and the base-emitter voltage VBE generated in the NPN transistor Q3 is applied to the resistor R1. By applying a voltage to the resistor R1,
I1 = VBE / R1 (2)
Current flows to the NPN transistor Q4, and further flows to the PNP transistor Q5 in which the collector is connected to the NPN transistor Q4.

Since the PNP transistor Q5 and the PNP transistor Q6 constitute a current mirror circuit, Ibias = I1 · (R2 / R3) (3)
Current flows through the PNP transistor Q6. Further, the current Ibias also flows through the NPN transistor Q7 whose collector is connected to the PNP transistor Q6. This current Ibias becomes a reference bias current in the bias circuit. The reference bias current Ibias serves as a reference for the bias current flowing through the amplifier circuit and the output circuit.

The NPN transistor Q8 and the NPN transistor Q9 constitute a current mirror circuit with the NPN transistor Q7, and Iamp = Ibias (R4 / R5) (4)
Io = Ibias · (R4 / R6) (5)
Current flows. Iamp is set as an amplifier circuit bias current, and Io is set as an output circuit bias current.

  As described above, since the bias current supplied from the conventional bias circuit 109 shown in FIG. 12 is constant, the light receiving amplifier circuit using the conventional bias circuit 109 has constant output current and power consumption. Therefore, in the light receiving amplifier circuit including the conventional bias circuit 109, when the output current is increased to cope with the load capacity, the power consumption is increased at the same time.

  In contrast, a bias circuit is disclosed that includes a bias circuit that can change the bias current supplied to the amplifier circuit, thereby reducing current consumption and power consumption of the amplifier circuit. For example, in Patent Document 1, as a bias circuit in which a bias current is variable, an amplifier that limits a bias current by lowering a bias voltage of a current source that supplies a bias current input to an amplifier circuit during a mute operation. A power saving circuit for reducing the current consumption of the power is disclosed.

The conventional bias circuit 109 supplies both the bias current for the amplifier circuit and the bias current for the output circuit with one bias circuit, whereas Patent Document 2 discloses that the bias circuit for the amplifier circuit and the output circuit for the output circuit are supplied. A light receiving amplifier element that can supply a bias current for an amplifier circuit and a bias current for an output circuit by having a bias circuit is disclosed.
JP-A-8-18347 (published on January 19, 1996) JP 2006-203704 A (published August 3, 2006)

  The magnitude of the load capacitance connected to the output of the light receiving amplifier circuit varies depending on the subsequent circuit connected to the light receiving amplifier circuit and the flexible cable used for connection between the light receiving amplifier circuit and the subsequent circuit. In order to cope with this change, the gain of the internal amplifier circuit is set larger in the light receiving amplifier circuit. As a result, the maximum output current that can be output by the light receiving amplifier circuit is set larger. In other words, the output drive capability of the light receiving amplifier circuit is set high. Therefore, the output current of the light receiving amplifier circuit becomes large regardless of reproduction / recording. Therefore, the power consumption of the light receiving amplifier circuit increases, and the problem remains that it is contrary to energy saving.

  Further, the optical pickup device needs a multistage gain switching function in order to support various formats such as ROM, R, and RW of the optical disk. Therefore, the optical pickup device includes a high gain feedback circuit used at the time of reproduction and a low gain feedback circuit used at the time of recording. By switching between these feedback circuits, a large amplitude at the time of reading and recording a small amplitude reproduction signal is obtained. This makes it possible to control the amount of laser light.

  When the gain of the feedback circuit is high at the time of reproduction, it is required to reproduce at a higher frequency (high speed) than when there is no feedback circuit by making the frequency characteristic better than the frequency characteristic of the open loop gain. If the gain of the feedback circuit is low during recording, it is required to perform both reproduction and recording by improving the pulse response characteristics, that is, by shortening the settling time.

  However, the conventional light receiving amplifier circuit with a multistage gain switching function switches the feedback circuit connected to the common amplifier circuit during recording and during reproduction. Therefore, the frequency characteristics of the open loop gain cannot be changed.

  Therefore, unless an amplifier circuit capable of high-speed response is used that has a frequency characteristic of an open loop gain with a high intersection frequency when the gain during playback is high, the frequency decreases and the response speeds up when the gain is high. I can't. Furthermore, when the amplifier circuit described here is used, the intersection frequency when the gain is low is further increased and the phase margin is further decreased, and therefore ringing is more likely to occur.

  Similarly, the phase margin when the gain is low is small and stable unless the gain is low, unless an amplifier circuit with an open loop gain frequency characteristic is used that has a large phase margin when the pulse signal does not ring at all. And ringing is likely to occur. That is, excellent ringing characteristics cannot be obtained. Furthermore, when the amplifier circuit described here is used, the intersection frequency when the gain is high becomes low, so that high-speed response is impossible.

  As described above, it is difficult for the conventional light receiving amplifier circuit with a multistage gain switching function to achieve both high speed response when the gain is high and obtaining excellent ringing characteristics when the gain is low.

  The present invention has been made in view of the above-described conventional problems, and its purpose is to provide a light-receiving amplifier circuit for an optical pickup that can operate properly while minimizing power consumption according to the application, and An object of the present invention is to provide an optical pickup device using the same.

  A light receiving amplifier circuit for an optical pickup according to the present invention includes a light receiving element that converts a received light signal into an electric signal, an amplifier circuit that amplifies the converted electric signal, and an electric signal that is amplified by the amplifier circuit. An output circuit; a feedback circuit that feeds back an output signal of the amplifier circuit to an input of the amplifier circuit; a reference bias current generation circuit that generates a reference bias current; and an output circuit bias current corresponding to the reference bias current. A bias circuit having a current mirror circuit for supplying a bias current for an amplifier circuit corresponding to the reference bias current to the amplifier circuit while supplying the output circuit to the output circuit. Corresponds to the reference bias current and the resistance of the current path of the current flowing inside the reference bias current generation circuit. Characterized in that it has a resistance value variable circuit for changing the value.

  According to the invention, in the recording / reproducing mode of the optical pickup device using the light receiving amplifier circuit for the optical pickup, the resistance bias variable circuit included in the bias circuit corresponds to the reference bias current and generates the reference bias current. By changing the resistance value of the current path of the current flowing inside the circuit, the reference bias current can be increased or decreased, and the output circuit bias current and the amplifier circuit bias current can be increased or decreased. Therefore, the output current output from the output circuit of the optical pickup light receiving amplifier circuit can be reduced as much as possible according to the application, and the power consumption of the optical pickup light receiving amplifier circuit can be minimized.

  A light receiving amplifier circuit for an optical pickup according to the present invention includes a light receiving element that converts a received light signal into an electric signal, an amplifier circuit that amplifies the converted electric signal, and an electric signal that is amplified by the amplifier circuit. An output circuit; a feedback circuit that feeds back an output signal of the amplifier circuit to an input of the amplifier circuit; a reference bias current generation circuit that generates a reference bias current; and an output circuit bias current corresponding to the reference bias current. A bias circuit having a current mirror circuit for supplying a bias current for an amplifier circuit corresponding to the reference bias current to the amplifier circuit while supplying the output circuit to the output circuit. Includes a first resistance value variable circuit that changes a resistance value of a current path through which the bias current for the output circuit flows, and Characterized in that a second resistance variable circuit for changing a resistance value of the current path amplifier circuit bias current flows.

  According to the invention, the bias circuit changes the resistance value of the current path through which the bias current for the amplifier circuit changes, and the first resistance variable circuit for changing the resistance value of the current path through which the bias current for the output circuit flows. A second resistance value variable circuit, and the first resistance value variable circuit and the second resistance value variable circuit have a function of increasing or decreasing the output circuit bias current and the amplifier circuit bias current, respectively. Thus, it is possible to set a bias current required for speeding up the response during reproduction and improving the pulse response characteristics during recording in each of the amplifier circuit and the output circuit.

  In the light receiving amplifier circuit for an optical pickup, the bias circuit may further include a third resistance value variable circuit that changes a resistance value of a current path through which the reference bias current flows.

  The third resistance value variable circuit can increase or decrease both the reference bias current and the amplifier circuit bias current by increasing or decreasing the reference bias current, and can reduce both the reference bias current and the output circuit bias current. Since it can be increased or decreased simultaneously, the bias current for the amplifier circuit and the bias current for the output circuit can be finely adjusted.

  In the light receiving amplifier circuit for an optical pickup, the feedback circuit switches the gain of the feedback circuit by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit. The bias circuit may increase or decrease the reference bias current in response to switching of the gain of the feedback circuit.

  Accordingly, an appropriate bias current corresponding to each mode such as recording and reproduction is set by increasing / decreasing the bias current input to the amplifier circuit and the output circuit in response to switching of the gain of the feedback circuit. In addition, the performance of the optical pickup device using the light receiving amplifier circuit for the optical pickup can be improved, and the power consumption can be reduced as much as possible.

  In the optical pickup light receiving amplifier circuit, the bias circuit may flow a large amount of the reference bias current when the gain of the feedback circuit is low.

  Accordingly, since the optical pip-up device is in the recording mode when the gain of the feedback circuit is low, the pulse slew rate is increased by increasing the output current of the optical pickup light receiving amplifier circuit in the recording mode. By shortening the settling time, the pulse response characteristics in the recording mode can be improved.

  In the light receiving amplifier circuit for an optical pickup, the feedback circuit switches the gain of the feedback circuit by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit. The bias circuit has a constant bias current for the amplifier circuit, the bias current for the output circuit is small when the feedback resistance is large and the gain of the feedback circuit is high, the feedback circuit is small, and the gain of the feedback circuit is low. Sometimes the output circuit bias current may be increased.

  Accordingly, the output current of the amplifier circuit is not increased or decreased, only the output current of the output circuit is increased or decreased, and the output current of the light receiving amplifier circuit for the optical pickup can be increased or decreased without changing the characteristics of the amplifier circuit. Therefore, when the gain in the recording mode is lower than that in the reproduction mode, the phase margin is made larger than when the output current of both the amplifier circuit and the output circuit is increased, and the increase in pulse ringing and oscillation of the amplifier circuit are avoided. The output current of the light receiving amplifier circuit for optical pickup can be increased.

  In the light receiving amplifier circuit for an optical pickup, the feedback circuit switches the gain of the feedback circuit by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit. The bias circuit has a large bias current for the amplifier circuit and a small bias current for the output circuit when the feedback resistance is large and the gain of the feedback circuit is high, and the feedback circuit gain is small. When the voltage is low, the bias current for the amplifier circuit may be reduced and the bias current for the output circuit may be increased.

  As a result, in the playback mode where the gain is higher than that of the recording mode, the response speed is increased by increasing the bias current for the amplifier circuit to increase the response frequency, and the output current of the light receiving amplifier circuit is decreased by reducing the output current. Electric power can be reduced. When the gain in the recording mode is low, the pulse current is reduced by increasing the bias current for the amplifier circuit to increase the phase margin, and the pulse slew rate is increased by increasing the output current of the light receiving amplifier circuit. Can be improved to improve the pulse response characteristics.

  In the light receiving amplifier circuit for optical pickup, the current mirror circuit included in the bias circuit is a circuit in which the base of the bipolar transistor is biased by a reference voltage source that is a collector-GND voltage, and a resistor is connected to the emitter. A switch circuit including a resistor and a MOS transistor may be provided in parallel with the connected resistor.

  Thus, since the current value supplied to the outside by the current mirror circuit is determined, a light receiving amplifier circuit can be created as an integrated circuit by using a MOS transistor for the switch circuit and can be electrically controlled. .

  In the light receiving amplifier circuit for an optical pickup, the resistance connected to the emitter of the bipolar transistor included in the current mirror circuit is switched, and the input terminal connected to the gate terminal of the MOS transistor for increasing or decreasing the current flowing in the current mirror circuit It may be provided outside the bias circuit.

  Thus, by changing the voltage applied to the gate terminal via the input terminal, that is, the gate voltage, the value of the ON resistance of the MOS transistor can be changed, and the bias current can be adjusted in an analog manner.

  Since the optical pickup device of the present invention includes any one of the above-described light receiving amplifier circuits for optical pickups, it can operate appropriately while minimizing power consumption according to the application.

  As described above, the light receiving amplifier circuit for an optical pickup of the present invention and the optical pickup device using the same are a light receiving element that converts a light receiving signal into an electric signal, an amplifier circuit that amplifies the converted electric signal, and An output circuit for outputting the electric signal amplified by the amplifier circuit, a feedback circuit for feeding back the output signal of the amplifier circuit to the input of the amplifier circuit, a reference bias current generating circuit for generating a reference bias current, and A bias circuit having a current mirror circuit that supplies the output circuit bias current according to the reference bias current to the output circuit, and supplies the amplifier circuit bias current according to the reference bias current to the amplifier circuit; A light-receiving amplifier circuit for an optical pickup, wherein the bias circuit corresponds to the reference bias current, and Those having a resistance value variable circuit for varying the resistance of the current path of the current flowing in the internal bias current generating circuit.

  Therefore, there is an effect of providing a light receiving amplifier circuit for an optical pickup that can appropriately operate while minimizing power consumption according to the application, and an optical pickup device using the same.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram of a light receiving amplifier circuit 1 for an optical pickup according to the present invention. A light receiving amplifier circuit 1 for optical pickup includes a light receiving element (PD) 2, an amplifier circuit 3, a feedback circuit 4, an output circuit 5, an output terminal 6, a variable bias circuit 7, a logic circuit 8, and a switch switching signal input terminal 9. Is done.

  The light receiving element 2, the amplifier circuit 3, the feedback circuit 4, the output circuit 5, and the output terminal 6 correspond to the light receiving element 102, the amplifier circuit 103, the feedback circuit 104, and the output corresponding to the conventional light receiving amplifier circuit 101 (see FIG. 12), respectively. The circuit 105 and the output terminal 106 have the same function. Therefore, the description thereof is omitted here.

  The variable bias circuit 7 generates a reference bias current, and transmits an output circuit bias current corresponding to the reference bias current to the output circuit 5 by an internal current mirror circuit, while an amplifier corresponding to the reference bias current. The circuit bias current is transmitted to the amplifier circuit 3.

  The variable bias circuit 7 has a switch circuit composed of a resistor and a switch inside, and the switch circuit is turned on or off by bias current switching signals S1 to S5 given from the logic circuit 8, so that the variable bias circuit The resistance value of the resistor connected in parallel with the switch circuit 7 is increased or decreased. The logic circuit 8 receives a switch switching signal S0 which is a digital signal of HI (+ side power supply voltage Vcc) or Lo (− side power supply voltage GND) from the switch switching signal input terminal 9, whereby the bias current switching signal S1. ~ S5 are generated and transmitted to the variable bias circuit 7. Thus, only the reference bias current, the amplifier circuit bias current and the reference bias current, or the output circuit bias current and the reference bias current are increased or decreased. Based on the increase or decrease of these currents, the amplifier circuit 3 and The bias current flowing through the output circuit 5 can be increased or decreased. Further, the variable bias circuit 7 allows a large amount of the reference bias current to flow when the gain of the feedback circuit 4 is low. A specific example of the bias circuit used for the variable bias circuit 7 will be described later.

  Therefore, by reducing the bias current flowing through the amplifier circuit 3 and the output circuit 5 as much as possible according to the use of the light receiving amplifier circuit 1 for the optical pickup, the output current of the light receiving amplifier circuit 1 for the optical pickup is reduced, and the light receiving for the optical pickup is performed. The power consumption of the amplifier circuit 1 can be minimized.

  FIG. 2 shows a block diagram of another light receiving amplifier circuit 10 for optical pickup according to the present invention. Similar to the optical pickup light receiving amplifier circuit 1, the optical pickup light receiving amplifier circuit 10 includes a light receiving element 2, an amplifier circuit 3, a feedback circuit 4, an output circuit 5, an output terminal 6, a logic circuit 8, and a switch switching signal input terminal 9. In addition, an amplifier circuit bias circuit 11 and an output circuit bias circuit 12 are provided. The output circuit bias circuit 12 is connected to the logic circuit 8, and the logic circuit 8 is connected to the switch switching signal input terminal 9.

  In the light receiving amplifier circuit 1 for the optical pickup shown in FIG. 1, since the bias current increases and decreases simultaneously in both the amplifier circuit 3 and the output circuit 5, the frequency characteristics of the open loop gain of the amplifier circuit 3 and the light receiving amplifier circuit 1 of the optical pickup 1 In some cases, the output current changes at the same time, and the ringing characteristic of the pulse response characteristic changes.

  2, the amplifier circuit bias circuit 11 uses the bias circuit 109 shown in FIG. 12, and only the output circuit bias circuit 12 is a variable bias circuit. As a result, the bias current for the amplifier circuit is kept constant, the bias current for the output circuit is reduced when the feedback resistor is large and the gain of the feedback circuit 4 is high, and the output circuit bias is low when the feedback resistor is small and the gain of the feedback circuit 4 is low. Only the output drive capability can be increased or decreased without increasing the bias current and changing the characteristics of the amplifier circuit 3. Therefore, when the gain in the recording mode is lower than that in the reproduction mode, the phase margin is made larger than when the output currents of both the amplifier circuit 3 and the output circuit 5 are increased, and an increase in pulse ringing and oscillation of the amplifier circuit 3 are avoided. Thus, the output current of the optical pickup light receiving amplifier circuit 10 output from the output terminal 6 can be increased.

  FIG. 3 shows a bias circuit 15 with a bias current switching function of the present invention. The bias circuit 15 with a bias current switching function can be used for the variable bias circuit 7 in FIG. 1 and the output circuit bias circuit 12 in FIG. The bias circuit 15 with a bias current switching function has a configuration in which a resistor Rsw1, a switch SW1, a resistor Rsw2, and a switch SW2 are added to the conventional bias circuit 109 shown in FIG. The resistor Rsw1 and the switch SW1 are connected in series to form the switch circuit 16, and the switch circuit 16 and the resistor R1 are connected in parallel. Similarly, the resistor Rsw2 and the switch SW2 are connected in series to form the switch circuit 17, and the switch circuit 17 and the resistor R2 are connected in parallel. The switch SW1 is a switch that is turned on by a Hi signal and turned off by a Lo signal. For example, an N-channel MOS transistor is used. The switch SW2 is a switch that is turned on by a Lo signal and turned off by a Hi signal. For example, a P-channel MOS transistor is used.

  The reference bias current generation circuit 18 is a circuit that generates a reference bias current Ibias, and includes NPN transistors Q1 to Q4, PNP transistors Q5 and Q6, resistors R1 to R3, and switch circuits 16 and 17. The reference bias current generation circuit 18 is surrounded by an alternate long and short dash line in FIG. The reference bias current generation circuit 18 is a circuit that supplies the reference bias current Ibias from the collector of the PNP transistor Q6 to the collector of the NPN transistor Q7.

When the logic circuit 8 to which the switch switching signal S0 is input from the switch switching signal input terminal 9 receives the bias current switching signal S1 that is Hi and the bias current switching signal S2 that is Lo, the switch SW1 and the switch SW2 are Both are turned on. In this case, a current flows through the resistor Ra, the NPN transistor Q1, the NPN transistor Q2, and the NPN transistor Q3 as the power supply voltage Vcc is applied, and the base-emitter voltage VBE generated in the NPN transistor Q3 is applied to the combined resistor R1 // Rsw1. The Since the base-emitter voltage VBE is applied to the combined resistance R1 // Rsw1, I1 = I1_on
= VBE / (R1 // Rsw1)
= I1_off · (1 + R1 / Rsw1) (6)
Current flows to the NPN transistor Q4, and further flows to the PNP transistor Q5 in which the collector is connected to the NPN transistor Q4. Here, I1_on is a current that flows through the NPN transistor Q4 and the PNP transistor Q5 when the switch SW1 is in the ON state. I1_off is a current that flows through the NPN transistor Q4 and the PNP transistor Q5 when the switch SW1 is in the OFF state.
I1_off = VBE / R1 (7)
It becomes.

Since the PNP transistor Q5 and the PNP transistor Q6 constitute a current mirror circuit, Ibias = Ibias_on
= I1. ((R2 // Rsw2) / R3)
= Ibias_off · (Rsw2 / (Rsw2 + R2)) (8)
Current flows through the PNP transistor Q6. Further, the current Ibias_on also flows through the NPN transistor Q7 whose collector is connected to the PNP transistor Q6. Here, Ibias_on is a current that flows through the PNP transistor Q6 and the NPN transistor Q7 when the switch SW2 is in the ON state. Ibias_off is a current that flows through the PNP transistor Q6 and the NPN transistor Q7 when the switch SW2 is in the OFF state.
Ibias_off = I1 · (R2 / R3) (9)
It becomes.

That is, the current I1_on flowing through the NPN transistor Q4 and the PNP transistor Q5 when the switch SW1 is in the ON state is increased to (1 + R1 / Rsw1) times the current I1_off flowing through the NPN transistor Q4 and the PNP transistor Q5 when the switch SW1 is in the OFF state. The Similarly, the current Ibias_on that flows through the PNP transistor Q6 and the NPN transistor Q7 when the switch SW2 is in the ON state is (Rsw2 / (Rsw2 + R2)) with respect to the current Ibias_off that flows through the PNP transistor Q6 and the NPN transistor Q7 when the switch SW2 is in the OFF state. Doubled. At this time, the current values of the bias current Iamp for the amplifier circuit and the bias current Io for the output current circuit increase or decrease at the same ratio as the conventional bias circuit 109 of FIG. That is, Iamp = Ibias · (R4 / R5) (4)
Io = Ibias · (R4 / R6) (5)
It becomes.

  Note that both the switch circuit 16 and the switch circuit 17 are not necessarily provided, and only one of them may be provided as necessary.

  FIG. 4 shows another bias circuit 19 with a bias current switching function of the present invention. The bias circuit 19 with a bias current switching function can be used for the variable bias circuit 7 in FIG. 1 and the output circuit bias circuit 12 which is the variable bias circuit in FIG. 2, and the amplifier circuit bias current Iamp and the output circuit bias current. This is a bias circuit capable of increasing or decreasing Io.

  The bias circuit 19 with a bias current switching function has a configuration in which a resistor Rsw3, a switch SW3, a resistor Rsw4, a switch SW4, a resistor Rsw5, and a switch SW5 are added to the conventional bias circuit 109 shown in FIG. The switches SW3 to SW5 are switches that are turned on by a Hi signal and turned off by a Lo signal. For example, N-channel MOS transistors are used.

  The reference bias current generation circuit 20 is a circuit that generates a reference bias current Ibias, and includes NPN transistors Q1 to Q4, PNP transistors Q5 and Q6, and resistors R1 to R3. The reference bias current generation circuit 20 is surrounded by an alternate long and short dash line in FIG. The reference bias current generation circuit 20 is a circuit that supplies the reference bias current Ibias from the collector of the PNP transistor Q6 to the collector of the NPN transistor Q7.

  As shown in FIG. 4, in the bias circuit 19 with a bias current switching function, a resistor Rsw3 and a switch SW3 are connected in series to form a switch circuit 21, and the switch circuit 21 and the resistor R3 are connected in parallel. . Similarly, the resistor Rsw4 and the switch SW4 are connected in series to form the switch circuit 22, and the switch circuit 22 and the resistor R4 are connected in parallel. Further, the resistor Rsw5 and the switch SW5 are connected in series to form the switch circuit 23, and the switch circuit 23 and the resistor R5 are connected in parallel. The resistors R3, R4, and R5 are respectively connected to the emitters of the NPN transistor Q7, the NPN transistor Q8, and the NPN transistor Q9 that constitute the current mirror circuit.

  The reference bias current Ibias is obtained from the equation (3) as in the conventional bias circuit 109 of FIG.

When the bias current switching signal S3 which is Hi is input by the logic circuit 8 to which the switch switching signal S0 is input from the switch switching signal input terminal 9 and only the switch SW3 is ON, the amplifier circuit bias current Iamp is Iamp = Iamp_on3
= Ibias × (R3 // Rsw3 / R4)
= Iamp_off × (Rsw3 / (Rsw3 + R3)) (10)
It becomes. Here, Iamp_on3 is an amplifier circuit bias current Iamp that flows when the switch SW3 is in the ON state, and Iamp_off is an amplifier circuit bias current Iamp that flows when the switch SW3 to the switch SW5 is in the OFF state.
Iamp_off = Ibias × (R3 / R4) (11)
It becomes.

Furthermore, when the bias current switching signal S4 which is Hi is input and only the switch SW4 is ON,
Iamp = Iamp_on4
= Ibias × (R3 / R4 // Rsw4)
= Iamp_off × (1 + R3 / Rsw4) (12)
It becomes. Here, Iamp_on4 is an amplifier circuit bias current Iamp that flows when only the switch SW4 is in the ON state.
That is, the amplifier circuit bias current Iamp_on3 that flows when the switch SW3 is in the ON state decreases by (Rsw3 / (Rsw3 + R3)) times the amplifier circuit bias current Iamp_off that flows when the switches SW3 to SW5 are in the OFF state. Similarly, the bias current for amplifier circuit Iamp_on4 that flows when only the switch SW4 is in the ON state is the bias current for amplifier circuit that flows when the bias current switching signals S3 to S5 that are Lo are input and the switches SW3 to SW5 are in the OFF state. Increased to (1 + R3 / Rsw4) times Iamp_off. If both the switch SW3 and the switch SW4 are in the ON state, the amplifier circuit bias current Iamp is (Rsw3 / (Rsw3 + R4)) × (1 + R3) of the amplifier circuit bias current Iamp_off that flows when the switches SW3 to SW5 are in the OFF state. / Rsw4) times.

  The output circuit bias current Io can also be calculated in the same manner as the amplifier circuit bias current Iamp. That is, in the equations (10) to (12), the currents Iamp, Iamp_on3, Iamp_off and Iamp_on4 are replaced with the currents Io, Io_on3, Io_off and Io_on4, and the resistors R4 and Rsw4 are replaced with the resistors R5 and Rsw5 (10) to (10) to It can be calculated by substituting into equation (12).

  As described above, when the bias circuit 19 with a bias current switching function is used, bias currents required for speeding up the response during reproduction and improving the pulse response characteristics during recording are set in the amplifier circuit 3 and the output circuit 5, respectively. be able to. Also, the bias circuit 19 with a bias current switching function makes the reference bias current Ibias constant, and outputs the output circuit bias current Io or the amplifier circuit bias current Iamp supplied from the current mirror circuit included therein to the switch circuits 21 to 21. It can be increased or decreased by using the circuit 23. Furthermore, both the reference bias current Ibias and the amplifier circuit bias current Iamp can be increased or decreased, and both the reference bias current Ibias and the output circuit bias current Io can be increased or decreased simultaneously, so that the amplifier circuit bias current Iamp and the output circuit bias are increased. The current Io can be finely adjusted.

  FIG. 5 shows a block diagram of a light receiving amplifier circuit 24 for an optical pickup having a multistage gain switching function. The optical pickup light receiving amplifier circuit 24 includes a light receiving element 2, an amplifier circuit 3, an output circuit 5, an output terminal 6, and a switch switching signal input terminal 9 in the same manner as the optical pickup light receiving amplifier circuit 1. A circuit 25, a variable bias circuit 26, and a logic circuit 27 are provided.

  The feedback circuit 25 is configured by connecting a plurality of switch circuits in parallel for multi-stage gain switching. Each of the plurality of switch circuits is configured by connecting a feedback resistor and a switch in series. The feedback resistor has a different resistance value for each switch circuit, and when a switch circuit having a feedback resistor having a large resistance value is turned on, the gain of the feedback circuit 25 is increased. The feedback circuit 25 is connected to both ends of the amplifier circuit 3.

  The feedback circuit 25 makes only one switch circuit conductive by the gain switching signals S6 to SN transmitted from the logic circuit 27 to which the switch switching signal S0 is input from the switch switching signal input terminal 9. N is an integer greater than or equal to 7, and when the feedback circuit is composed of M switch circuits, N = M + 5. The gain of the feedback circuit 25 is switched by switching the feedback circuit by switching the switch circuit that is turned on by the feedback circuit.

  The variable bias circuit 26 uses the bias circuit 19 of FIG. 4 that can increase or decrease the reference bias current corresponding to the gain switching of the feedback circuit 25 and can increase or decrease the amplifier circuit bias current and the output circuit bias current, respectively. Accordingly, the variable bias circuit 26 receives the bias current switching signals S3 to S5 from the logic circuit 27.

  Since the output circuit 5 does not require a large amplitude pulse response characteristic when the gain is high, the output current is reduced, and when the gain is low, the output current is increased because a large amplitude pulse response characteristic is required.

  In the variable bias circuit 26, the gain of the feedback circuit 25 is switched by the gain switching signals S6 to SN, and at the same time, the bias current switching signals S3 to S5 are input and output from the variable bias circuit 26 to be output from the amplifier circuit 3 and the output circuit 5. Increase or decrease the bias current input to. For example, in the reproduction mode, a switch circuit having a large feedback resistance value is turned on by the gain switching signals S6 to SN to increase the gain of the feedback circuit 25, while the amplifier circuit bias current output from the variable bias circuit 26 is increased. Increase the output circuit bias current.

  According to the above configuration, in the reproduction mode, the switch circuit having a large feedback resistance is turned on by the gain switching signals S6 to SN, the gain of the feedback circuit 25 is increased, and the bias current for the amplifier circuit output from the variable bias circuit 26 is obtained. And increase the crossover frequency by decreasing the output circuit bias current. As a result, the response speed can be increased and the power consumption can be reduced by reducing the output current of the light receiving amplifier circuit. In the recording mode, the switch circuit having a small feedback resistance value is turned on by the gain switching signals S6 to SN, the gain of the feedback circuit 25 is lowered, and the bias current for the amplifier circuit output from the variable bias circuit 26 is reduced. In addition, the output circuit bias current is increased to increase the output current of the optical pickup light receiving amplifier circuit 24. This reduces the ringing of pulses by increasing the phase margin, and increases the output current of the photoreceiver amplifier circuit to increase the pulse slew rate and shorten the settling time, improving the pulse response characteristics in the recording mode. I can do it.

  The optical pickup light receiving amplifier circuit 24 includes an amplifier circuit bias circuit 11 and an output circuit bias circuit 12 as shown in FIG. 2 in place of the variable bias circuit 26, whereby the amplifier circuit 3 or the output circuit 5 is provided. Each bias current can be switched. Also, the bias current of the amplifier circuit 3 or the output circuit 5 can be switched by using the variable bias circuit 26 to change the bias current 19 for the amplifier circuit and the bias current Io for the output circuit shown in FIG. Can do.

  FIG. 6 is a diagram for explaining changes in the frequency characteristics of the open loop gain due to increase / decrease in the bias current of the amplifier circuit. In the figure, the frequency characteristic 29 of the open loop gain of the amplifier circuit is the same as the frequency characteristic 108 of the open loop gain of the amplifier circuit in FIG. That is, the frequency characteristic 29 has frequency poles P1, P2 and P3, and when the frequency of the signal input to the amplifier circuit becomes higher than the pole P1, the open loop gain is -6 dB / octave, and -12 dB after the pole P2. / Octave, decreasing at -18 dB / octave slope after pole P3.

  In FIG. 6, by increasing the bias current of the amplifier circuit, the frequency characteristic 29 of the open loop gain of the amplifier circuit becomes the frequency characteristic indicated by reference numeral 30. As a result, the pole P1 having the first frequency in the frequency characteristic 29 of the open loop gain of the amplifier circuit moves to the pole P1 'having a higher frequency in the frequency characteristic 30, and the response becomes faster.

  If the bias current of the amplifier circuit is increased in a state where the gain of the feedback circuit is higher than the gain G2 at the time of recording and the gain G1 at the time of reproduction is increased, the intersection frequency is obtained from the intersection frequency f1 between the gain G1 and the frequency characteristic 29. The frequency becomes higher at the intersection frequency f2 between G1 and the frequency characteristic 30, and the response becomes faster.

  On the contrary, when the gain of the feedback circuit is the gain G2 at the time of recording and the bias current of the amplifier circuit is decreased and the frequency characteristic 30 is changed to the frequency characteristic 29, the intersection frequency is decreased from f3 to f4. The phase margin is increased, and ringing generated in the pulse can be reduced. Accordingly, the settling time is shortened and the pulse response characteristics are improved.

  As described above, the bias current input to the amplifier circuit 3 and the output circuit 5 is increased or decreased in response to the gain switching signal input to the feedback circuit 25 of the optical pickup light receiving amplifier circuit 24 with a multistage gain switching function. Therefore, it is possible to set an appropriate bias current corresponding to each mode such as recording and reproduction, improve the performance of the optical pickup device using the optical pickup light receiving amplifier circuit 24 with a multistage gain switching function, and reduce power consumption as much as possible. Can be reduced.

  FIG. 7A shows a circuit diagram using an N-channel MOS transistor 31 as the switch SW1, and FIG. 7B shows a circuit diagram using a P-channel MOS transistor 32 as the switch SW2. Since it is difficult to construct a mechanical switch circuit on an actual integrated circuit, the MOS transistor is operated as a switch by electrically turning it on and off.

  In the present embodiment, the current mirror circuit included in the bias circuit is a circuit in which the base of the bipolar transistor is biased by a reference voltage source that is a collector-GND voltage, and the current value is determined by connecting a resistor to the emitter. And a switch circuit including a resistor and a MOS transistor is provided in parallel with the resistor connected to the emitter.

  Therefore, by using a MOS transistor for the switch circuit, a light receiving amplifier circuit can be created as an integrated circuit and can be electrically controlled. The MOS transistor used in the switch circuit switches the resistance connected to the emitter of the bipolar transistor included in the current mirror circuit in the bias circuit, and increases or decreases the current flowing through the current mirror circuit.

  As an example of the switch circuit connected to the negative side power supply voltage (GND), the switch circuit 16 of FIG. 3 is shown, and as an example of the switch circuit connected to the positive side power supply voltage (Vcc), the switch circuit 17 of FIG. . An N channel MOS transistor 31 is used as the switch SW1 of the switch circuit 16, and a P channel MOS transistor 32 is used as the switch SW2 of the switch circuit 17.

  At this time, since there is the ON resistance of the MOS transistor, it is necessary to consider the ON resistance of the MOS transistor in the calculation formula of the current value. In the MOS transistor used in the switch circuit, the value of the ON resistance varies depending on the voltage applied to the gate terminal, that is, the gate voltage. The input terminal connected to the gate terminal is provided outside the bias circuit, the value of the ON resistance is changed by changing the gate voltage via the input terminal, and the adjustment of the bias current is controlled in an analog manner. Can do.

  FIG. 8 shows a schematic diagram of an optical system of an optical pickup device 33 using a light receiving amplifier IC 40 including the light receiving amplifier circuit for optical pickup described in the present embodiment. The optical pickup device 33 is mounted on an optical disk drive (not shown), and the optical disk 38 is reproduced or recorded by this optical disk drive.

  The optical pickup device 33 in FIG. 8 includes a plurality of semiconductor lasers, that is, laser diodes (LDs) 34 having different wavelengths in order to support a plurality of different formats, and outputs laser light corresponding to each medium. The laser diode 34 outputs laser beams having different laser powers during recording and during reproduction.

  Laser light output from the laser diode 34 is applied to the optical disk 38 via the collimator lens 35, the beam splitter 36, and the objective lens 37. The laser light reflected from the optical disk 38 is applied to a light receiving amplifier IC 40 including a light receiving amplifier circuit through an objective lens 37, a beam splitter 36, and a spot lens 39.

  The light receiving amplifier circuit for the optical pickup included in the light receiving amplifier IC 40 reproduces an information signal according to the laser light irradiated to the light receiving amplifier IC 40 and creates a signal for tracking and focusing servo. Output to a subsequent circuit such as a control circuit.

  A plurality of laser diodes 34 configured in the optical pickup device 33 are optically arranged with high accuracy. That is, the arrangement is made so that the reflected light from the optical disk 38 is irradiated to the light receiving amplifier IC 40 with high accuracy.

  As described above, the light receiving amplifier circuits 1, 10, and 24 for the optical pickup according to the present invention include the light receiving element 2 that converts the received light signal into the electrical signal, the amplifier circuit 3 that amplifies the converted electrical signal, and the amplifier circuit 3. The output circuit 5 for outputting the electric signal amplified in step S3, the feedback circuit 4 for feeding back the output signal of the amplifier circuit 3 to the input of the amplifier circuit 3, and the reference bias current generation circuit 18 for generating the reference bias current Ibias. And a bias circuit having a current mirror circuit that supplies the output circuit bias current Io corresponding to the reference bias current Ibias to the output circuit 5 and supplies the amplifier circuit bias current Iamp corresponding to the reference bias current Ibias to the amplifier circuit 3. A light receiving amplifier circuit for an optical pickup comprising a circuit 15, wherein a current I1 flows through the bias circuit 15. Characterized in that it has a switch circuit 16 and 17 to change the resistance value of the channel.

  According to the above invention, in the recording / reproducing mode of the optical pickup device using the light receiving amplifier circuits 1, 10 and 24 for the optical pickup, it corresponds to the reference bias current Ibias of the switch circuits 16 and 17 included in the bias circuit 15, By changing the resistance value of the current path of the current I1 flowing inside the reference bias current generation circuit 18, the reference bias current Ibias can be increased or decreased, and the output circuit bias current Io and the amplifier circuit bias current Iamp can be increased or decreased. I can do it. Therefore, the output current output from the output circuit 5 of the light receiving amplifier circuit 1 for the optical pickup can be reduced as much as possible according to the application, and the power consumption of the light receiving amplifier circuits 1, 10 and 24 for the optical pickup can be minimized. it can.

  The light receiving amplifier circuit for an optical pickup according to the present invention outputs a light receiving element 2 for converting a light receiving signal into an electric signal, an amplifier circuit 3 for amplifying the converted electric signal, and an electric signal amplified by the amplifier circuit 3. Output circuit 5, feedback circuit 4 that feeds back the output signal of amplifier circuit 3 to the input of amplifier circuit 3, reference bias current generation circuit 20 that generates reference bias current Ibias, and output corresponding to reference bias current Ibias A bias circuit 19 having a current mirror circuit for supplying a bias current Iamp for the amplifier circuit to the amplifier circuit 3 while supplying the bias current Io for the circuit to the output circuit 5 and supplying the bias current Iamp for the amplifier circuit corresponding to the reference bias current Ibias. The bias circuit 19 is an amplifier circuit, and a resistance of a current path through which the output circuit bias current Io flows. A switch circuit 23 that increases / decreases the output circuit bias current Io by changing the output circuit, and a switch circuit 22 that increases / decreases the amplifier circuit bias current Iamp by changing the resistance value of the current path through which the amplifier circuit bias current Iamp flows. It is characterized by having.

  According to the above invention, the bias circuit 19 changes the resistance value of the current path through which the output circuit bias current Io flows, and the switch circuit changes the resistance value of the current path through which the amplifier circuit bias current Iamp flows. 22, and the switch circuit 23 and the switch circuit 22 have a function of increasing / decreasing the bias current Iamp for the amplifier circuit and the bias current Io for the output circuit, respectively, thereby increasing the response speed during reproduction and the pulse response during recording. The bias current required for improving the characteristics can be set for each of the amplifier circuit 3 and the output circuit 5.

  In the optical pickup light receiving amplifier circuits 1, 10, and 24, the bias circuit 19 may further include a switch circuit 21 that changes the resistance value of the current path through which the reference bias current Ibias flows.

  Since the switch circuit 21 increases or decreases the reference bias current Ibias, both the reference bias current Ibias and the amplifier circuit bias current Iamp can be increased or decreased, and both the reference bias current Ibias and the output circuit bias current Io can be increased or decreased simultaneously. The bias current Iamp for the amplifier circuit and the bias current Io for the output circuit can be finely adjusted.

  In the light receiving amplifier circuit 24 for the optical pickup, the feedback circuit 25 switches the gain of the feedback circuit 25 by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit 3. The bias circuit 15 may increase or decrease the reference bias current Ibias in response to the gain switching of the feedback circuit 25.

  Thus, in response to the switching of the gain of the feedback circuit 25, the bias current input to the amplifier circuit 3 and the output circuit 5 is increased or decreased to set an appropriate bias current corresponding to each mode such as recording and reproduction. In addition, the performance of the optical pickup device using the light receiving amplifier circuit 24 for the optical pickup can be improved, and the power consumption can be reduced as much as possible.

  In the optical pickup light receiving amplifier circuit 24, the bias circuit 15 may flow a large Ibias reference bias current when the gain of the feedback circuit 25 is low.

  Thus, since the optical pip-up device 33 is in the recording mode when the gain of the feedback circuit 25 is low, the pulse slew rate is increased by increasing the output current of the optical pickup light receiving amplifier circuit 24 in the recording mode. By shortening the settling time, the pulse response characteristics in the recording mode can be improved.

  In the light receiving amplifier circuit 24 for the optical pickup, the feedback circuit 25 switches the gain of the feedback circuit 25 by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit 3. The bias circuit 19 keeps the amplifier circuit bias current Iamp constant, and when the feedback resistance is large and the gain of the feedback circuit 25 is high, the output circuit bias current Io is small, and the feedback resistance is small and the gain of the feedback circuit 25 is low. Sometimes the output circuit bias current Io may be increased.

  As a result, the output current of the amplifier circuit 3 is not increased or decreased, only the output current of the output circuit 5 is increased or decreased, and the output current of the optical pickup light receiving amplifier circuit 24 can be increased or decreased without changing the characteristics of the amplifier circuit 3. Therefore, when the gain in the recording mode is lower than that in the reproduction mode, the phase margin is made larger than when the output currents of both the amplifier circuit 3 and the output circuit 5 are increased, and an increase in pulse ringing and oscillation of the amplifier circuit 3 are avoided. Thus, the output current of the light receiving amplifier circuit 24 for optical pickup can be increased.

  In the light receiving amplifier circuit 24 for the optical pickup, the feedback circuit 25 switches the gain of the feedback circuit 25 by switching one of a plurality of feedback resistors having different resistance values to be connected to the amplifier circuit 3. The bias circuit 19 increases the bias current Iamp for the amplifier circuit and decreases the bias current Io for the output circuit when the feedback resistance is large and the gain of the feedback circuit 25 is high, and the gain of the feedback circuit 25 is small because the feedback resistance is small. When the current is low, the bias current Iamp for the amplifier circuit may be decreased and the bias current Io for the output circuit may be increased.

  As a result, in the reproduction mode in which the gain is higher than that in the recording mode, the response speed is increased by increasing the bias current Iamp for the amplifier circuit to increase the response frequency, and the output current of the light receiving amplifier circuit 24 for the optical pickup is decreased. By doing so, power consumption can be reduced. When the gain of the recording mode is low, by reducing the bias current Iamp for the amplifier circuit and increasing the phase margin, the ringing of the pulse is reduced, and the output current of the light receiving amplifier circuit 24 for the optical pickup is increased. The pulse response characteristic can be improved by increasing the pulse slew rate.

  In the optical pickup light-receiving amplifier circuits 1, 10 and 24, the current mirror circuit included in the bias circuit 15 or 19 is biased by a reference voltage source whose bipolar transistor base is a collector-GND voltage, and a resistor is connected to the emitter. Thus, a current value is determined, and a switch circuit including a resistor and the MOS transistor 31 or 32 may be provided in parallel with the resistor connected to the emitter.

  Thus, since the value of the current I1 is determined, it is possible to create the light receiving amplifier circuits 1, 10 and 24 for the optical pickup as an integrated circuit by using the MOS transistors 31 or 32 for the switch circuits 16, 17 and 21 to 23. Can be controlled electrically.

  In the optical pickup light receiving amplifier circuits 1, 10, and 24, the resistance connected to the emitter of the bipolar transistor included in the current mirror circuit is switched, and the MOS transistor 31 or 32 that increases or decreases the current flowing in the current mirror circuit is connected to the gate terminal. An input terminal to be connected may be provided outside the bias circuit 15 or 19.

  Thereby, by changing the voltage applied to the gate terminal via the input terminal, that is, the gate voltage, the value of the ON resistance of the MOS transistor 31 or 32 can be changed, and the bias current can be adjusted in an analog manner. it can.

  Since the optical pickup device 33 according to the present invention includes any one of the above-described light receiving amplifier circuits for optical pickup, it can operate appropriately with minimum power consumption according to the application.

  The light receiving amplifier circuit for an optical pickup of the present invention and the optical pickup device using the same can operate appropriately with minimum power consumption depending on the application, so that an optical disk drive mounted on a personal computer, etc. Can be suitably used.

1 is a block diagram of a light receiving amplifier circuit for an optical pickup according to an embodiment of the present invention. FIG. It is a block diagram of another light receiving amplifier circuit for an optical pickup according to an embodiment of the present invention. It is a circuit diagram of a bias circuit with a bias current switching function in the light receiving amplifier circuit for both optical pickups. It is a circuit diagram of another bias circuit with a bias current switching function in the light receiving amplifier circuit for both optical pickups. FIG. 10 is a block diagram of still another light receiving amplifier circuit for an optical pickup according to an embodiment of the present invention. It is a figure explaining the change of the frequency characteristic of an open loop gain by increase / decrease in the bias current of an amplifier circuit. FIG. 7A is a circuit diagram using an N-channel MOS transistor for the switch circuit, and FIG. 7B is a circuit diagram using a P-channel MOS transistor for the switch circuit. It is the schematic of the optical system of the optical pick-up apparatus which concerns on embodiment of this invention. It is a block diagram of a conventional light receiving amplifier circuit. It is explanatory drawing about settling time. It is a Bode diagram of an open loop gain and phase of an amplifier circuit. It is a circuit diagram of the conventional bias circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10, 24 Optical pick-up amplifier circuit for optical pick-up 2 Light receiving element 3 Amplifier circuit 4, 25 Feedback circuit 5 Output circuit 6 Output terminal 7, 26 Variable bias circuit 8, 27 Logic circuit 9 Switch switching signal input terminal 11 Bias for amplifier circuit Circuit 12 Bias circuit for output circuit 15, 19 Bias circuit 16, 17 Switch circuit (resistance value variable circuit)
18, 20 Reference bias current generation circuit 21-23 Switch circuit (third resistance value variable circuit, second resistance value variable circuit, first resistance value variable circuit)
29, 30 Frequency characteristics 31 N channel MOS transistor 32 P channel MOS transistor 33 Optical pickup device 34 Laser diode 35 Collimator lens 36 Beam splitter 37 Objective lens 38 Optical disc 39 Spot lens 40 Light receiving amplifier IC
CL Load capacitance G, G1, G2 Gain GND-side power supply voltage I1 current Iamp Bias current for amplifier circuit Ibias Reference bias current Io Bias current for output circuit Q1-Q4, Q7-Q9 NPN transistor Q5, Q6 PNP transistor R1-R5, Ra, Rsw1 to Rsw5 Resistance RL Load resistance S0 Switch switching signal S1 to S5 Bias current switching signal S6 to SN Gain switching signal SW1 to Sw5 to Switch Vcc + side power supply voltage Vo Output voltage f1, f2, fx Intersection frequency

Claims (10)

A light receiving element that converts the light reception signal into an electrical signal;
An amplifier circuit for amplifying the converted electrical signal;
An output circuit for outputting an electrical signal amplified by the amplifier circuit;
A feedback circuit that feeds back an output signal of the amplifier circuit to an input of the amplifier circuit;
A reference bias current generating circuit for generating a reference bias current, and supplying an output circuit bias current corresponding to the reference bias current to the output circuit, while supplying an amplifier circuit bias current corresponding to the reference bias current to the amplifier circuit A bias circuit having a current mirror circuit for supplying to a light receiving amplifier circuit for an optical pickup,
The bias circuit includes a resistance value variable circuit that corresponds to the reference bias current and changes a resistance value of a current path of a current flowing in the reference bias current generation circuit. Amplifier circuit. A light receiving element that converts the light reception signal into an electrical signal;
An amplifier circuit for amplifying the converted electrical signal;
An output circuit for outputting an electrical signal amplified by the amplifier circuit;
A feedback circuit that feeds back an output signal of the amplifier circuit to an input of the amplifier circuit;
A reference bias current generating circuit for generating a reference bias current, and supplying an output circuit bias current corresponding to the reference bias current to the output circuit, while supplying an amplifier circuit bias current corresponding to the reference bias current to the amplifier circuit A bias circuit having a current mirror circuit for supplying to a light receiving amplifier circuit for an optical pickup,
The bias circuit includes a first resistance value variable circuit that changes a resistance value of a current path through which the output circuit bias current flows, and a second resistance value variable that changes a resistance value of a current path through which the amplifier circuit bias current flows. And a light receiving amplifier circuit for an optical pickup.   3. The light receiving amplifier circuit for an optical pickup according to claim 2, wherein the bias circuit further includes a third resistance value variable circuit that changes a resistance value of a current path through which the reference bias current flows. The feedback circuit switches the gain of the feedback circuit by selecting one of a plurality of feedback resistors having different resistance values and switching the connection to the amplifier circuit,
2. The light receiving amplifier circuit for an optical pickup according to claim 1, wherein the bias circuit increases or decreases the reference bias current in response to switching of the gain of the feedback circuit.   5. The light receiving amplifier circuit for an optical pickup according to claim 1, wherein the bias circuit allows a large amount of the reference bias current to flow when the gain of the feedback circuit is low. The feedback circuit switches the gain of the feedback circuit by selecting one of a plurality of feedback resistors having different resistance values and switching the connection to the amplifier circuit,
The bias circuit has a constant bias current for the amplifier circuit, the bias current for the output circuit is small when the feedback resistance is large and the gain of the feedback circuit is high, and the bias current for the output circuit is small and the gain of the feedback circuit is low. 3. The light receiving amplifier circuit for an optical pickup according to claim 2, wherein the bias current for the output circuit is increased. The feedback circuit switches the gain of the feedback circuit by selecting one of a plurality of feedback resistors having different resistance values and switching the connection to the amplifier circuit,
The bias circuit has a large bias current for the amplifier circuit and a small bias current for the output circuit when the feedback resistance is large and the gain of the feedback circuit is high, and the feedback circuit gain is small and the gain of the feedback circuit is small. 3. The light receiving amplifier circuit for an optical pickup according to claim 2, wherein when the voltage is low, the bias current for the amplifier circuit is reduced and the bias current for the output circuit is increased.   The current mirror circuit included in the bias circuit is a circuit in which the base of the bipolar transistor is biased by a reference voltage source that is a collector-GND voltage, and a resistor is connected to the emitter. The resistor is connected in parallel with the resistor connected to the emitter. 8. A light receiving amplifier circuit for an optical pickup according to claim 1, further comprising a switch circuit including a MOS transistor and a MOS transistor.   The bias circuit includes an input terminal connected to a gate terminal of a MOS transistor that switches a resistor connected to an emitter of a bipolar transistor included in the current mirror circuit and increases or decreases a current flowing in the current mirror circuit. A light receiving amplifier circuit for an optical pickup according to claim 8.   An optical pickup device using the light receiving amplifier circuit for an optical pickup according to any one of claims 1 to 9.

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