JP4347178B2 - Gain switching amplifier, light receiving amplifier element and optical pickup element using the same - Google Patents

Description

  The present invention relates to a gain switching amplifier that switches a gain by a saturation switch, and more particularly to a gain switching amplifier that is used for a light receiving amplifier element and an optical pickup element of an apparatus capable of reproducing and / or recording an optical disk.

  In a writable CD or DVD drive mainly used as a personal computer device, the light intensity of the laser (LD) power that is larger than that at the time of reproduction is irradiated to the disk at the time of writing. Even in the element, a large light input occurs. In order to cope with the difference in optical input level between writing and reproduction, a method of switching gains corresponding to writing / reproduction is adopted in the light receiving amplifier element (for example, Patent Document 1). Conventionally, the gain ratio of a plurality of rear-stage amplifiers (large / small gain) is small, and the circuit configuration of the front-stage amplifier is as shown in FIG.

  The configuration of the pre-stage amplifier in FIG. 5 will be described. The pre-amplifier includes a photodiode PD that is a photoelectric conversion element that performs photoelectric conversion of received light, and amplifies and outputs the photoelectric conversion signal. The gain can be switched in two ways, large and small, by saturation switches respectively provided on the reference voltage input path and the feedback loop. The reference voltage Vref is input to the non-inverting input terminal of the operational amplifier 101 via a parallel circuit of a gain resistor RfH and a series circuit of a transistor Q1 as a saturation switch and a gain resistor RfL. The inverting input terminal is connected to the cathode of the photodiode PD and to the feedback circuit of the output voltage of the amplifier. The anode of the photodiode is grounded. The feedback circuit is constituted by a parallel circuit of a gain resistor RfH and a series circuit of a transistor Q2 as a saturation switch and a gain resistor RfL. When setting the large gain, the transistors Q1 and Q2 are in the OFF state, and only the gain resistor RfH is used as the gain resistor. On the other hand, when setting a small gain, the transistors Q1 and Q2 are turned on, and a parallel connection resistance of the gain resistance RfH and the gain resistance RfL is used as the gain resistance. Since the transistors Q1 and Q2 as the saturation switches operate in the saturation region when they are in the ON state, a slight ON resistance is inserted in series with the gain resistance RfL. The transistors Q1 and Q2 are PNP transistors. A reference voltage Vref is applied to the emitter of the transistor Q1, and a feedback voltage Vout2 described later is applied to the emitter of the transistor Q2.

  ON / OFF of the transistors Q1 and Q2 is controlled by a circuit including a constant current source I1, a switch SW, and transistors Q3, Q4, and Q5. Transistor Q3, transistor Q4, and transistor Q5 are NPN type transistors and constitute a current mirror circuit. The constant current source I1 is connected in series to the collector of the transistor Q3 via the switch SW. The collector of the transistor Q4 is connected to the base of the transistor Q1, and the emitter of the transistor Q5 is connected to the base of the transistor Q2. The emitters of the transistors Q3, Q4, and Q5 are grounded.

  When the transistors Q1 and Q2 are turned off, the switch SW is turned off. At this time, the base current does not flow through the transistors Q1 and Q2. When the transistors Q1 and Q2 are turned on, the switch SW is turned on. At this time, the current of the constant current source I1 flows through the current mirror to the bases of the transistors Q1 and Q2, respectively.

The output stage 21 of the preceding amplifier includes a feedback loop section 21a having a transistor Q23 and an indirect output section 21b having a transistor Q24. The output terminal of the operational amplifier 101 is connected to the base of a PNP transistor Q21 and the base of an NPN transistor Q22. The active load of the transistor Q21 is provided with a constant current source I2 on the emitter side, and the active load of the transistor Q22 is provided with a constant current source I3 on the emitter side. The collector of the transistor Q21 is grounded, and the collector of the transistor Q22 is connected to the power supply VCC. When the pre-stage amplifier operates with a small gain, the transistor Q21 operates, and its emitter follower output is input to the bases of the NPN transistors Q23 and Q24. The collectors of the transistors Q23 and Q24 are connected to the power supply VCC, and the emitter of the transistor Q24 is connected to the output terminal OUT of the preceding amplifier. The emitter follower output of the transistor Q24 is output as an output voltage Vout1 from the output terminal OUT to the subsequent amplifier, and the emitter follower output of the transistor Q23 is applied as a feedback voltage Vout2 to the feedback circuit. Further, when the pre-stage amplifier operates at a large gain, the transistor Q21 operates on the low output voltage side, and the transistor Q22 operates on the high output voltage side. The operation of the transistor Q21 is the same as when the gain is small. When the transistor Q22 operates, the emitter follower output of the transistor Q22 is input to the bases of the PNP transistors Q25 and Q26. The emitter of the transistor Q25 is connected to the emitter of the transistor Q23, and the emitter of the transistor Q26 is connected to the output terminal OUT. The collectors of the transistors Q25 and Q26 are grounded. The emitter follower output of the transistor Q26 is output from the output terminal to the subsequent amplifier as the output voltage Vout1, and the emitter follower output of the transistor Q25 is applied to the feedback circuit as the feedback voltage Vout2.
Japanese Patent Laid-Open No. 8-154023 (published on June 11, 1996)

  Increasing the laser power is indispensable for increasing the writing speed. To avoid saturation of multiple photoreceiver amplifiers with different gains at the time of writing, multiple subsequent amplifiers (large / small gain) Gain ratio increases. When the gain of the rear-stage amplifier increases, an output offset due to the switch current of the front-stage amplifier that switches the gain by the saturation switch becomes a problem.

  Specifically, in the pre-stage amplifier described with reference to FIG. 5, the output voltage Vout1 = feedback voltage Vout2 is ideal. However, in order to turn on the transistors Q1 and Q2 during the small gain operation, The control current is obtained by shunting from the feedback loop current. As a result, the base current of the transistor Q2 is drawn from the emitter of the transistor Q23. Therefore, the emitter current of the transistor Q23 and the emitter current of the transistor Q24 are the same even when there is no load / no signal when no output amplifier is connected to the output terminal OUT and no optical signal is input to the photodiode. Not equal. As a result, the output voltage Vout1 is not equal to the feedback voltage Vout2, and an output offset occurs. Therefore, during the small gain operation of the pre-stage amplifier, the output offset of the pre-stage amplifier tends to cause a saturation problem of the post-stage amplifier when performing amplification with a large gain by the post-stage amplifier.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a gain switching amplifier capable of compensating for an output offset in a configuration in which a gain is switched by a saturation switch, a light receiving amplifier element using the same, and An optical pickup device is provided.

  In order to solve the above problems, the gain switching amplifier according to the present invention switches the gain by saturation switches respectively provided on the input path and the feedback loop of the reference voltage of the operational amplifier, and outputs from the indirect output section of the output stage. In a gain switching amplifier that outputs a voltage and shunts a current used for the control current of the saturation switch on the feedback loop from the feedback loop section of the output stage from the current of the feedback loop, the current used for the control current and A current source for extracting the same current from the indirect output unit is provided.

  According to the above invention, the same current as that supplied for the control current from the feedback loop unit can be extracted from the indirect output unit by the current source. Therefore, when there is no load / no signal, the same current flows in the indirect output section of the output stage as in the feedback loop section of the output stage, so that the offset between the output voltage and the feedback voltage can be compensated.

  As a result, it is possible to provide a gain switching amplifier capable of compensating for the output offset in the configuration in which the gain is switched by the saturation switch.

  In order to solve the above problem, the gain switching amplifier according to the present invention includes a first current control element that allows the control current to flow, and the current source includes a second current mirror that forms a current mirror with the first current control element. The current control element is characterized by that.

  According to the above invention, since the second current control element is made the current source by the current mirror configuration including the first current control element and the second current control element, the current source is saturated on the feedback loop. There is an effect that a current equal to the control current of the switch can flow.

  In order to solve the above problem, the gain switching amplifier according to the present invention includes a parasitic element that supplies a current that merges with the control current as a part of the control current, and for the current of the current source, A differential current obtained by subtracting the current flowing through the parasitic element from the control current is extracted from the indirect output unit as the same current as the current used for the control current.

  According to the above invention, since the differential current is extracted from the indirect output unit, it is possible to extract a current equal to the current extracted from the feedback loop unit.

  In order to solve the above problem, the gain switching amplifier of the present invention switches the gain by a saturation switch, outputs an output voltage from the indirect output unit of the output stage, and outputs the output voltage from the feedback loop unit of the output stage. In a gain switching amplifier that shunts a current used for a control current of a saturation switch from a current of the feedback loop, a first current control element that flows the control current, and a second current that constitutes a current mirror with the first current control element Current control element, and the current flowing by the second current control element is more on the feedback destination side than the point of outputting the feedback voltage of the feedback loop section of the output stage, and the saturation on the feedback loop It is characterized by flowing into a specific point that is closer to the feedback source than the switch.

  According to the above invention, the current flowing into the specific point is equal to the current that has been conventionally drawn out from the feedback loop unit, so that the current that flows through the feedback loop unit and the current that flows through the indirect output unit when there is no load and no signal. And are equal to zero. Thereby, the offset between the output voltage and the feedback voltage can be compensated.

  As a result, it is possible to provide a gain switching amplifier capable of compensating for the output offset in the configuration in which the gain is switched by the saturation switch.

  In order to solve the above problems, a gain switching amplifier according to the present invention includes a third current control element through which a current flowing by the second current control element flows, and a third current control element and a current mirror that constitute the current mirror. 4 current control elements, and a current flowing by the second current control element is allowed to flow from the fourth current control element to the specific point.

  According to the above invention, since the differential current is caused to flow into the specific point by the current mirror composed of the third current control element and the fourth current control element, the specific point is conventionally drawn out from the feedback loop unit. The effect is that a current equal to the current can be flown.

  In order to solve the above problem, the gain switching amplifier of the present invention switches the gain by a saturation switch, outputs an output voltage from the indirect output unit of the output stage, and outputs the output voltage from the feedback loop unit of the output stage. In a gain switching amplifier that shunts a current used for a control current of a saturation switch from a current of the feedback loop, a first current control element that flows the control current, and a second current that constitutes a current mirror with the first current control element Current control element, and the saturation switch includes a parasitic element that flows a current that merges with the control current as a part of the control current, and flows from the current that flows by the second current control element by the parasitic element. The difference current obtained by subtracting the current is on the feedback destination side and before the point at which the feedback voltage of the feedback loop unit of the output stage is output. It is characterized by pouring a certain point as a feedback source side than the saturation switch on the feedback loop.

  According to the above invention, when the saturation switch includes a parasitic element, the current that flows into the specific point is equal to the current that is conventionally drawn from the feedback loop unit. The current flowing through the feedback loop section and the current flowing through the indirect output section are equal to zero. Thereby, the offset between the output voltage and the feedback voltage can be compensated.

  As a result, it is possible to provide a gain switching amplifier capable of compensating for the output offset in the configuration in which the gain is switched by the saturation switch.

  In order to solve the above problem, a gain switching amplifier according to the present invention includes a third current control element that flows the differential current, and a fourth current control element that forms a current mirror with the third current control element. And the differential current is allowed to flow from the fourth current control element to the specific point.

  According to the above invention, since the differential current is caused to flow into the specific point by the current mirror composed of the third current control element and the fourth current control element, the specific point is conventionally drawn out from the feedback loop unit. The effect is that a current equal to the current can be flown.

  In the gain switching amplifier of the present invention, in order to solve the above problem, the saturation switch on the input path of the reference voltage is controlled with a control current equal to the saturation switch on the feedback loop, and the saturation switch on the input path of the reference voltage The saturation switch includes a parasitic element that flows a current that merges with the control current as a part of the control current of the saturation switch, and current that flows through the parasitic element included in the saturation switch on a reference voltage input path is generated by a current mirror. Thus, the differential current is generated by using the current flowing through the parasitic element of the saturation switch on the feedback loop.

  According to the above invention, there is an effect that the current flowing through the parasitic element included in the saturation switch on the input path of the reference voltage can be obtained by the current mirror and the differential current can be generated.

  In order to solve the above problems, the light receiving amplifier element of the present invention is characterized in that the gain switching amplifier is provided as an amplifier that amplifies a photoelectric conversion signal of the photoelectric conversion element.

  According to said invention, there exists an effect that the light receiving amplifier element which can compensate an output offset using the structure which switches a gain with a saturation switch can be provided.

  In order to solve the above problems, the light receiving amplifier element of the present invention is characterized in that the gain switching amplifier is provided as a pre-stage amplifier and further a post-stage amplifier.

  According to the above invention, even if the gain ratio of the subsequent amplifier is large, the output offset of the small-amplifier front amplifier is compensated, so that there is an effect that the subsequent amplifier does not saturate.

  In order to solve the above problems, an optical pickup element of the present invention comprises the light receiving amplifier element and receives light from a recording / reproducing light source of an optical recording / reproducing medium.

  According to said invention, there exists an effect that the optical pick-up element which can compensate an output offset using the structure which switches a gain with a saturation switch can be provided.

  As described above, the gain switching amplifier according to the present invention includes the current source for extracting the same current as the current used for the control current from the indirect output unit.

  Further, as described above, the gain switching amplifier according to the present invention includes the first current control element that allows the control current to flow, and the second current control element that forms a current mirror with the first current control element. The current flowing by the second current control element is on the feedback destination side from the point of outputting the feedback voltage of the feedback loop portion of the output stage, and on the feedback source side than the saturation switch on the feedback loop. Pour into a specific point.

  As a result, it is possible to provide a gain switching amplifier capable of compensating for the output offset in the configuration in which the gain is switched by the saturation switch.

(Embodiment 1)
An embodiment of the present invention will be described below with reference to FIGS. Unless otherwise specified, members having the same functions as those in FIG. 5 are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 1 shows a circuit configuration of a gain switching amplifier 31 according to the present embodiment. The gain switching amplifier 31 is assumed to be configured as a light receiving amplifier element by connecting a plurality of amplifiers in the subsequent stage as a front stage amplifier, but the gain switching amplifier 31 can also be formed as a light receiving amplifier element.

  The gain switching amplifier 31 further includes transistors Q6, Q7, and Q8 in the configuration of FIG. The transistor Q6 is an NPN type transistor, and its base is connected to the bases of the transistors Q3 to Q5, and forms a current mirror with the transistors Q3 to Q5. Therefore, the transistor Q6 operates as a current source that supplies a current equal to the control current of the transistor Q2.

  The collector of the transistor Q6 is connected to the output terminal OUT and the collector of the transistor Q8. Transistors Q7 and Q8 are PNP transistors and constitute a current mirror. Here, the transistor Q1 which is a saturation switch on the input path of the reference voltage Vref is a vertical transistor, and a parasitic transistor (parasitic element) Q1 'is formed therein as shown in FIG. The parasitic transistor Q1 'is an NPN type transistor, the base is connected to the collector of the transistor Q1, and the emitter is connected to the base of the transistor Q1. The collector potential of the parasitic transistor Q1 'is called an epi potential. The collector of the transistor Q7 is connected to the collector of the parasitic transistor Q1 '. The base of the transistor Q7 is connected to its own collector and to the base of the transistor Q8. The emitters of the transistors Q7 and Q8 are connected to the power supply VCC.

  When the transistor Q1 is in the ON state, since the transistor Q1 is saturated, the collector potential and the emitter potential are substantially equal. Therefore, the base-emitter voltage of the transistor Q1 is substantially the base-emitter voltage of the transistor Q1 ', turning on the transistor Q1'. In this case, the control current (base current) of the transistor Q1 is supplied not only from the emitter of the transistor Q1, but also through the parasitic transistor Q1 'by the epi potential.

  Further, like the transistor Q1, the transistor Q2 is a vertical transistor and has a parasitic transistor (parasitic element) similar to that shown in FIG. The collector of the parasitic transistor of the transistor Q2 is connected to the power supply VCC.

  In the transistor Q1, the base current is a control current. This control current is a current that flows from the emitter to the base, that is, a current that is shunted from the current of the feedback loop and used as the control current. The 'emitter current (approximately equal to the collector current) is the combined current. Thus, the current flowing through the parasitic transistor Q1 'becomes a part of the control current of the transistor Q1. Similarly, in the transistor Q2, the base current is a control current, and this control current is combined with the current flowing from the emitter into the base and the emitter current of the parasitic transistor (substantially equal to the collector current) due to the epi potential. Current. Thus, the current flowing through the parasitic transistor Q1 'becomes a part of the control current of the transistor Q2. The current flowing through the parasitic transistor Q1 'of the transistor Q1 is equal to the current flowing through the parasitic transistor of the transistor Q2.

  Next, the operation of the gain switching amplifier 31 having the above configuration will be described.

  The gain switching of the amplifier is performed by a switch SW, and the switch SW is in an OFF state at a large gain. When the switch SW is turned off, no current flows through the transistor Q3. Therefore, no current flows through the transistors Q4, Q5, and Q6 that constitute the current mirror with the transistor Q3, and the gain resistance value becomes the value of the gain resistance RfH. When the gain is small, the switch SW is turned on, a current flows through the transistor Q3, and an equivalent current flows through the transistor Q3 and the transistors Q4, Q5, and Q6 constituting the current mirror. Then, when the transistors Q1 and Q2 are turned on, the gain resistance value becomes a parallel combined resistance of the gain resistance RfH and the series resistance composed of the gain resistance RfL and the ON resistance of the transistors Q1 and Q2. At this time, the current of the transistor Q5, that is, the control current of the transistor Q2, is supplied from the transistor Q23 and the parasitic transistor of the transistor Q2.

  The output stage 21 of the amplifier includes a feedback loop section 21a including a transistor Q23 and an indirect output section 21b including a transistor Q24. Since the transistor Q6 does not exist in the related art, the transistor Q23 can be used even when there is no load and no signal. Thus, the emitter current value of the transistor Q24 and the emitter current value of the transistor Q24 are different, and the base-emitter voltage Vbe of the transistor Q23 and the base-emitter voltage Vbe of the transistor Q24 are different. Therefore, the emitter potential of the transistor Q23 and the emitter potential of the transistor Q24 are different from each other, causing an offset.

  Therefore, in the present embodiment, in order to correct such an offset, by providing the transistor Q6, a current equivalent to the current of the transistor Q5 is drawn from the emitter of the transistor Q24. The transistor (first current control element) Q5 controls the control current of the transistor Q2, and the transistor (second current control element) Q6 forms a current mirror with the transistor Q5, so that it is pulled out from the indirect output unit 21b. The current used for the current is controlled to be equal to the control current. Since the transistor Q5 and the transistor Q6 constitute such a current mirror, when there is no current mirror composed of the transistors Q7 and Q8, the current flowing from the output terminal OUT toward the collector of the transistor Q6 is the transistor Q5. Is equal to the current. Accordingly, the emitter current of the transistor Q23 and the emitter current of the transistor Q24, that is, the current flowing through the indirect output portion 21b are substantially equal, and the emitter potential of the transistor Q23 and the emitter potential of the transistor Q24 are equal, thereby compensating for the offset.

  In the case of the configuration of FIG. 1, the control current of the transistor Q2 is not only supplied from the transistor Q23, but is also supplied from the parasitic transistor of the transistor Q2 by the epi potential, so that a current equivalent to the current of the transistor Q5 is obtained. When the transistor Q24 is pulled out, the current supplied from the transistor Q23 is pulled out by the amount supplied from the parasitic transistor of the transistor Q2. Therefore, in this embodiment, in order to further correct this current value, the current flowing through the parasitic transistor Q1 ′ of the transistor Q1 based on the epi potential is returned by the current mirror composed of the transistors Q7 and Q8 and supplied to the transistor Q6. is doing. As a result, the current flowing through the indirect output portion 21b is a differential current obtained by subtracting the current flowing through the parasitic transistor Q1 'from the current flowing through the transistor Q6, that is, the current flowing through the parasitic transistor of the transistor Q2. As a result, the current drawn by the transistor Q5 from the epi potential of the transistor Q2 is corrected.

  If no parasitic transistor is formed in the transistor Q2, the transistor Q6 draws the same current as the control current of the transistor Q2 from the transistor Q22 without providing a current mirror composed of the transistors Q7 and Q8. The emitter potential of the transistor Q23 and the emitter potential of the transistor Q24 become equal, and the offset is compensated.

Further, in the light receiving amplifier element configured by using the gain switching amplifier 31 of the present embodiment for the preceding amplifier and further connecting the succeeding amplifier, the preceding amplifier having a small gain even if the gain ratio of the succeeding amplifier is large. Since the output offset is compensated for, the subsequent amplifier does not saturate.
(Embodiment 2)
Another embodiment of the present invention will be described below with reference to FIG. Unless otherwise specified, members having the same functions as those shown in FIGS. 1, 2, and 5 are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 3 shows a circuit configuration of the gain switching amplifier 32 according to the present embodiment. The gain switching amplifier 31 is assumed to be configured as a light receiving amplifier element by connecting a plurality of amplifiers in the subsequent stage as a front stage amplifier, but the gain switching amplifier 31 can also be formed as a light receiving amplifier element.

  The gain switching amplifier 32 further includes transistors Q7, Q8, Q9, and Q10 in the configuration shown in FIG. The transistors Q9 and Q10 are PNP type transistors, and their bases are connected to each other to form a current mirror. The emitters of the transistors Q9 and Q10 are connected to the power supply VCC. The collector of the transistor Q9 is connected to its own base and to the collectors of the transistors Q6 and Q8. The collector of the transistor Q10 is connected on the feedback loop to a specific point M that is closer to the feedback destination than the point of outputting the feedback voltage Vout2 and closer to the feedback source than the transistor Q2.

  Next, the operation of the gain switching amplifier 31 having the above configuration will be described.

  The amplifier gain switching is as described with reference to FIGS. When the gain is small, conventionally, as described above, the emitter potential of the transistor Q23 and the emitter potential of the transistor Q24 are different, and an offset occurs. In order to correct such an offset, the present embodiment includes the transistors Q9 and Q10 in order to supply a current equivalent to that of the transistor Q5 from other than the transistor Q23. The transistor (third current control element) Q9 and the transistor (fourth current control element) Q10 constitute a current mirror. The transistor Q9 controls a current transmitted to the transistor Q10. The current flowing into the point M is controlled. Further, the transistor (first current control element) Q5 and the transistor (second current control element) Q6 constitute a current mirror, the transistor Q5 controls the control current of the transistor Q2, and the transistor Q6 is the transistor Q9. The current used for the current passed through is controlled to be equal to the control current. By providing such a current mirror composed of the transistors Q1 and Q2 and a current mirror composed of the transistors Q9 and Q10, when there is no current mirror composed of the transistors Q7 and Q8, the current of the transistor Q5 A current equivalent to that flows through the transistor Q10 and flows into the specific point M. Therefore, since this current becomes the base current of the transistor Q2, no emitter current flows through the transistor Q23 when there is no load and no signal. Accordingly, since the emitter current of the transistor Q23 and the emitter current of the transistor Q24 are equal at zero, the emitter potentials of the transistors Q23 and Q24 are equal, and the offset is compensated.

  In the case of the configuration of FIG. 2, the control current of the transistor Q2 is not only supplied from the transistor Q10 but also from the parasitic transistor of the transistor Q2, so that a current equivalent to the current of the transistor Q5 is supplied from the transistor Q10. When pulled out, the current drawn from the transistor Q23 in the conventional configuration is drawn more than the current supplied from the parasitic transistor of the transistor Q2. In order to correct this current value, the current flowing through the parasitic transistor Q1 'of the transistor Q1 is returned by the current mirror of the transistors Q7 and Q8 and supplied to the transistor Q6. As a result, the current flowing into the specific point M becomes a differential current obtained by subtracting the current flowing through the parasitic transistor Q1 'from the current flowing through the transistor Q6, that is, the current flowing through the parasitic transistor of the transistor Q2. As a result, the current drawn by the transistor Q5 from the epi potential of the transistor Q2 is corrected.

  If no parasitic transistor is formed in the transistor Q2, the current flowing through the transistor Q6, that is, the control current of the transistor Q2, ie, the control current of the transistor Q10 can be obtained without using the current mirror composed of the transistors Q7 and Q8. , The emitter potential of the transistor Q23 and the emitter potential of the transistor Q24 become equal, and the offset is compensated.

In addition, in the light receiving amplifier element configured by using the gain switching amplifier 32 of the present embodiment for the front-stage amplifier and further connecting the back-stage amplifier, the front-stage amplifier having a small gain even if the gain ratio of the back-stage amplifier is large. Since the output offset is compensated for, the subsequent amplifier does not saturate.
(Embodiment 3)
The following will describe still another embodiment of the present invention with reference to FIG.

  FIG. 4 is a diagram for explaining the optical system of the recording / reproducing apparatus 1 for the optical recording / reproducing medium. The recording / reproducing apparatus 1 includes a laser diode 3, collimator lenses 4 and 6, a beam splitter 5, an objective lens 7, a spot lens 8, a light receiving element 9, and optical pickup elements 10 and / or 11. These are incorporated in the optical pickup device. The optical pickup elements 10 and 11 of the optical pickup device are constituted by light receiving amplifier elements including the gain switching amplifiers 31 and 32 described in the first and second embodiments.

  Here, the laser light emitted from the laser diode 3 which is a light emitting element as a light source for recording and reproduction is converted into parallel light in the collimator lens 4, and the optical path is bent by 90 ° in the beam splitter 5, and then the collimator lens 6 and The optical disk 2 is irradiated through the objective lens 7. Then, the reflected light from the optical disk 2 passes through the beam splitter 5 from the objective lens 7 and the collimator lens 6, is condensed by the spot lens 8, and enters the light receiving element 9. The light receiving element 9 reproduces an information signal from the incident optical signal, creates a signal for tracking and focusing servo, and outputs the signal to a signal processing circuit and a control circuit (not shown). At the time of recording, the emitted light from the laser diode 3 is modulated corresponding to the data to be written.

  In the optical system configured as described above, the optical pickup element 10 is provided at a position near the laser diode 3, and the optical pickup element 11 is provided at a position opposite to the laser diode 3 via the beam splitter 5. A part of the light emitted from the laser diode 3 is monitored by the optical pickup elements 10 and 11, and the output of the optical pickup elements 10 and 11 is fed back to the laser diode 3 so that the laser light intensity is optimized. Adjusted.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention can be suitably used for an optical pickup element of an optical recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram illustrating a configuration of a gain switching amplifier according to a first embodiment of the present invention. It is an equivalent circuit diagram which shows the structure of the parasitic transistor formed in a saturation switch. FIG. 7 is a circuit diagram illustrating a configuration of a gain switching amplifier according to a second embodiment of the present invention. FIG. 10 is a diagram illustrating a configuration of an optical system of a recording / reproducing apparatus for an optical recording medium according to a third embodiment of the present invention. It is a circuit diagram which shows the structure of the gain switching amplifier which switches a gain with the conventional saturation switch.

Explanation of symbols

31, 32 Gain switching amplifier (light receiving amplifier element)
10, 11 Optical pickup element 21 Output stage 21a Feedback loop section 21b Indirect output section Q1 Transistor (saturation switch)
Q2 transistor (saturation switch)
Q5 transistor (first current control element)
Q6 transistor (second current control element)
Q9 transistor (third current control element)
Q10 transistor (fourth current control element)
Q1 'parasitic transistor Vout1 output voltage Vout2 feedback voltage

Claims (8)

The gain is switched by saturation switches provided on the input path and the feedback loop of the reference voltage of the operational amplifier, the output voltage is output from the indirect output section of the output stage, and the feedback from the feedback loop section of the output stage In a gain switching amplifier that shunts the current used for the control current of the saturation switch on the loop from the current of the feedback loop,
A gain switching amplifier, comprising: a current source for drawing out the same current as the current used for the control current from the indirect output unit. A first current control element for flowing the control current;
The gain switching amplifier according to claim 1, wherein the current source is a second current control element that forms a current mirror with the first current control element. The saturation switch includes a parasitic element that flows a current that merges with the control current as part of the control current,
The differential current obtained by subtracting the current flowing through the parasitic element from the control current with respect to the current of the current source is extracted from the indirect output unit as the same current as the current used for the control current. Item 3. A gain switching amplifier according to item 1 or 2. The gain is switched by the saturation switch, the output voltage is output from the indirect output section of the output stage, and the current used for the control current of the saturation switch on the feedback loop from the feedback loop section of the output stage is shunted from the current of the feedback loop In the gain switching amplifier
A first current control element for flowing the control current; and a second current control element constituting a current mirror with the first current control element;
The saturation switch includes a parasitic element that flows a current that merges with the control current as part of the control current,
The difference current obtained by subtracting the current flowing through the parasitic element from the current flowing through the second current control element is closer to the feedback destination than the point of outputting the feedback voltage of the feedback loop section of the output stage, and the A gain switching amplifier characterized by flowing into a specific point on the feedback source side with respect to the saturation switch on the feedback loop. A third current control element for flowing the differential current;
A third current control element and a fourth current control element constituting a current mirror;
5. The gain switching amplifier according to claim 4 , wherein the differential current flows from the fourth current control element to the specific point. The saturation switch on the reference voltage input path is controlled with a control current equal to the saturation switch on the feedback loop;
The saturation switch on the input path of the reference voltage includes a parasitic element that flows a current that merges with the control current as a part of the control current of the saturation switch,
The current flowing through the parasitic element included in the saturation switch on the reference voltage input path is obtained by a current mirror and used as the current flowing through the parasitic element of the saturation switch on the feedback loop, thereby generating the differential current. gain switching amplifier according to any one of claims 3 to 5, characterized in that. Receiving amplifier element gain switching amplifier according to any one of claims 1 to 6, characterized in that it comprises as an amplifier for amplifying the photoelectric conversion signal of the photoelectric conversion element. 8. An optical pickup element comprising the light receiving amplifier element according to claim 7 , wherein the optical pickup element receives light from a recording / reproducing light source of an optical recording / reproducing medium.

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