JP2006345459A - Amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain necessary circuit gain and frequency characteristics while reducing the number of circuit elements in a two-stage amplifier circuit, and to reduce the cost.
An amplifier circuit according to the present invention is an amplifier circuit including a detector that detects an input signal, and a feedback amplifier circuit that is connected to the detector and amplifies an output current thereof. A voltage dividing resistor provided between an output of the circuit and a reference potential; one end of the voltage dividing resistor is connected to the output side; and a resistance of the feedback amplifier circuit is connected to a dividing point of the voltage dividing resistor. The other end of the voltage dividing resistor is connected to the input of the feedback amplifier circuit.
With the configuration described above, the number of circuit elements can be reduced, the necessary circuit gain and frequency characteristics can be obtained, and the cost can be reduced.
[Selection] Figure 1

Description

    The present invention relates to an amplifier circuit for amplifying a voltage of an output current output from a photodetector, and more specifically, is used for an optical pickup device using a laser element having two or more types of light having different wavelengths.

    Optical discs such as DVD and CD are widely used as media for recording music, video, data information, etc., and optical pickup devices have been developed for reproducing information recorded on the media or recording on the media. It was. In addition, with the spread of DVD in recent years, it is possible to use both DVD and CD, and further to reduce the cost of the optical pickup device, which is compatible with two wavelengths of λ = 650 nm for DVD and λ = 780 nm for CD. There is a need for a light receiving element for pickup.

    FIG. 6 shows a schematic diagram of an optical pickup device compatible with a two-wavelength laser having a two-wavelength laser chip. The optical pickup device shown in FIG. 6 includes a two-wavelength laser 7, a prism 8, a condenser lens 9, a light receiving element IC chip 10, and a photodiode 11 included in the light receiving element IC chip 10. The two-wavelength laser 7 can output (emit) two types of light of 650 nm for DVD and 780 nm for CD.

    Laser light 12 emitted from the two-wavelength laser 7 passes through the prism 8 and the condenser lens 9 and is irradiated to the disk 13 that is a medium. The reflected laser light 14 is applied to the photodiode 11 included in the light receiving element IC chip 10 via the condenser lens 9 and the prism 8. Since the emission point position of each wavelength light of the laser light 12 emitted by the two-wavelength laser 7 is different, the reflected light irradiation position to the photodiode 11 included in the light receiving element IC is different. Therefore, a photodiode shape and an amplifier circuit corresponding to each reflected laser beam 14 are required.

    FIG. 7 is an enlarged view of the surface of the light receiving element IC chip 10 corresponding to the two-wavelength laser. The two-wavelength laser compatible photodiode is composed of ten photodiodes. A1 to A4, E and F are used for CD (λ = 780 nm), and a1 to a4 are used for DVD (λ = 650 nm). In each of the CD and DVD, the photodiodes A1 to A4 and a1 to a4 receive information signal light and focus signal light. The photodiodes E and F are used for tracking adjustment. As a result, an amplifier circuit connected to each of the photodiodes A1 to A4 and a1 to a4 is required, and it is necessary to switch the amplifier circuit according to the CD and the DVD.

    FIG. 8 shows a block diagram of a conventional amplifier circuit compatible with a two-wavelength laser, and FIG. 9 shows a circuit diagram of a conventional amplifier circuit compatible with a two-wavelength laser. In FIG. 8, an amplifier circuit connected to the photodiode a1-A1 is taken as an example, and an amplifier circuit having the same configuration is required for each of the photodiodes a2-A2, a3-A3, and a4-A4. . The photodiodes a1 and A1 are respectively connected to the first stage amplifier circuits AMP1 and AMP2 controlled by the selection signal, and the output signals of the first stage amplifier circuits AMP1 and AMP2 are amplified by the amplifier circuit AMP3 connected to the subsequent stage. In FIG. 9, the amplifier circuit AMP1 of FIG. 8 is a differential circuit 2 composed of transistors Q1 and Q2, a constant current circuit I1, transistors Q5 and Q6, an active circuit 1 composed of resistors R7 and R8, a gain resistor R1, and a phase compensation capacitor. It is composed of C1. Similarly, in FIG. 9, the amplifier circuit AMP2 of FIG. 8 includes a differential circuit 3 composed of transistors Q3 and Q4, a constant current circuit I2, transistors Q5 and Q6, an active circuit 1 composed of resistors R7 and R8, a gain resistor R2, and a phase. It is composed of a compensation capacitor C2. R5 and R6 in FIGS. 8 and 9 are resistors for offset adjustment. Further, in FIG. 9, the amplifier circuit AMP3 of FIG. 8 is a differential circuit 6 composed of transistors Q8 and Q9, a constant current circuit I4, transistors Q10 and Q11, an active circuit 5 composed of resistors R9 and R10, gain resistors R3 and R4, phase The compensation capacitor C3 is used. The active circuit 1 is shared by the amplifier circuits AMP1 and AMP2, and the light receiving element IC chip cost can be reduced by reducing the number of circuit elements.

    For example, when used for DVD, the constant current circuit I1 is operated by the selection signal in FIG. 9 and the I2 is not operated, so that the differential circuit 2 is in an operating state and the differential circuit 3 is in a non-operating state. . The photocurrent Ia1 generated by the signal light applied to the photodiode a1 is subjected to current-voltage conversion by the gain resistor R1 and amplified by the subsequent amplifier circuit AMP3. In this case, the output voltage V1 of the amplifier circuit output terminal Vo is expressed by the following equation.

V1 = Ia1 * R1 * (R3 + R4) / R3
In this case, the amplification gain Z1 is as follows.

Z1 = R1 × (R3 + R4) / R3
Next, sensitivity characteristics, noise characteristics, and frequency characteristics, which are important items as an amplifier circuit used in the optical pickup device, will be described.

    The sensitivity characteristic of the amplifier circuit in the optical pickup device is expressed by the output voltage V1 / photodiode incident light quantity.

The noise characteristic (level) Vn of the amplifier circuit output when the shot noise of the transistor connected to the photodiode is Ni and the thermal noise of R1 is Nr is:
Vn = √ (Ni ² + Nr ² ) × (R3 + R4) / R3
It becomes.

    The frequency characteristic is a term expressing the sensitivity characteristic in an AC manner, and the circuit gain greatly affects the gain resistance R1 of the amplifier circuit in the first stage, and the time constant is expressed by the following equation.

fc = 1 / (2πR1 × C1)
The characteristics of the amplifier circuit are determined by R1, R2, and R3. The noise characteristic is deteriorated by increasing the amplification factor (R3 + R4) / R3 of the amplifier circuit connected to the subsequent stage, and the frequency characteristic is amplified in the first stage. It can be seen that this is a characteristic item that decreases as the gain resistance R1 of the circuit is increased.

    Actually, in the conventional amplifier circuit, in consideration of the signal current value generated by the photodiode, the signal value to be output, and the semiconductor manufacturing conditions of the IC, a total gain of 80 kΩ is required for the first stage amplifier circuit and the subsequent stage amplifier circuit. In the amplifier circuit, the gain / resistance (R3 + R4) / R3 = 2 times of the amplifier circuit in the first stage and the gain resistance (R3 + R4) / R3 = 2 times in the first stage of the amplifier circuit are excellent. The required frequency characteristic fc = 60 MHz is achieved.

As described above, in the optical pickup device using the two-wavelength laser, cost reduction has become an important issue, and the laser has been integrated into one chip and optical components have been shared. In particular, in the optical pickup device used for DVD-PLAYER, the cost reduction competition has been intensified with the spread, and in the amplifier circuit, the circuit elements are reduced to reduce the cost. As a solution to these problems, Japanese Patent Laid-Open No. 2001-202646 is disclosed.
JP 2001-202646 A

    However, Japanese Patent Laid-Open No. 2001-202646 switches the photodiode input to a single gain resistor and is not suitable for adjusting the gain according to the incident light wavelength. Furthermore, it is expected that it is difficult to obtain a frequency characteristic fc = 30 to 60 MHz for DVD with a single stage amplification circuit having a high gain. Although it can be achieved by adopting a fine high-speed process, it is not intended for cost reduction.

    In recent years, it has been required to reduce the number of circuit elements for further cost reduction.

An amplifier circuit of the present invention is an amplifier circuit comprising a detector that detects an input signal, and a feedback amplifier circuit that is connected to the detector and amplifies the output current thereof.
A voltage dividing resistor provided between an output of the amplifier circuit and a reference potential; one end of the voltage dividing resistor is connected to the output side; and a resistance of the feedback amplifier circuit is provided at a dividing point of the voltage dividing resistor. The other end of the voltage dividing resistor is connected to the input of the feedback amplifier circuit.

    Further, the detector in the amplifier circuit of the present invention is a detector corresponding to light input.

    The voltage dividing resistor in the amplifier circuit of the present invention is characterized in that the gain of the amplifier circuit can be adjusted by changing the position of the dividing point.

The amplifier circuit of the present invention includes a plurality of detectors that detect an input signal, and a feedback amplifier circuit that is connected to the detector and amplifies the output current of the detector. One of them is an amplifier circuit that is enabled,
A voltage dividing resistor provided between an output of the amplifier circuit and a reference potential; one end of the voltage dividing resistor is connected to the output side; and a resistance of the feedback amplifier circuit is provided at a dividing point of the voltage dividing resistor. The other end of the voltage dividing resistor is connected to the input of the feedback amplifier circuit.

    A plurality of detectors in the amplifier circuit of the present invention are detectors corresponding to different light inputs.

    The amplifier circuit of the present invention is characterized in that it is a first feedback amplifier circuit having a resistance matched to the first light and a second feedback amplifier circuit having a resistance matched to the second light. .

    The amplifier circuit of the present invention includes first and second voltage dividing resistors to which resistors of the first and second feedback amplifier circuits are respectively connected, and the resistance values of the first and second voltage dividing resistors are set. It is characterized by making it different.

    In the amplifier circuit according to the present invention, a selection switch (any one of an NPN transistor, a PNP transistor, and an emitter follower circuit) that operates in response to a selection signal and enables one of the first and second voltage dividing resistors. ) Is provided between the output of the amplifier circuit and a reference potential.

    In a two-stage amplifier circuit, the required circuit gain and frequency characteristics can be obtained while reducing the number of circuit elements, which can contribute to cost reduction.

(Embodiment 1)
FIG. 1 is a circuit diagram according to Embodiment 1 of the present invention. In FIG. 1A, the amplifier circuit includes a differential circuit 2 to which a DVD optical signal receiving photodiode a1 as a first detector is connected and a CD optical signal receiving photodiode A1 as a second detector. The differential circuit 2 includes transistors Q1 and Q2, and the differential circuit 3 includes transistors Q3 and Q4. The differential circuits 2 and 3 include constant current circuits I1 and I2, respectively. Is connected. The differential circuit 2 and the differential circuit 3 are configured to share the active circuit 1 including the PNP transistors Q5 and Q6 and the resistors R7 and R8, and the output circuit 4 including the transistor Q7 and the constant current circuit I3. Yes. The circuit gain resistor R1 for DVD and the circuit gain resistor R2 for CD are connected to the dividing point of the voltage dividing resistors R13, R14 connected to the amplifier output Vo terminal and the reference potential Vs terminal. The voltage dividing resistor R13 is a voltage dividing resistor provided on the reference potential side from the dividing point, and the voltage dividing resistor R14 is a voltage dividing resistor provided on the amplifier circuit output side from the dividing point. Thus, a feedback resistor is formed by the voltage dividing resistor R14 and the gain resistor R1 or R2, and the configuration shown in FIG. Further, phase adjusting capacitors C1 and C2 are connected in parallel to the gain resistors R1 and R2. Further, R5 and R6 are provided as offset adjusting resistors. By operating the constant current circuit I1 or I2 in accordance with the selection signal, the differential circuits 2 and 3 are switched to select either the DVD mode or the CD mode.

    As described above, the amplifier circuit in the pickup device requires frequency characteristics suitable for high gain. For this reason, in order to increase the gain of the amplifier circuit, it is necessary to make the gain resistor R1 or R2 have a large resistance value. However, in order to obtain a suitable frequency characteristic as described above, it is necessary to reduce the resistance value of the gain resistor R1 or R2. For this reason, in the conventional circuit, the gain resistance of the first stage is set to 30 to 40 kΩ, and a double gain is obtained by the amplifier circuit of the subsequent stage, and the desired characteristics are achieved with the frequency characteristics.

    On the other hand, in the circuit of the present embodiment, the divided potential generated by the voltage dividing resistors R13 and R14 between the amplifier circuit output Vo end and the reference potential Vs end is fed back to the amplifier circuits AMP1 and AMP2 by the gain resistor R1 or R2. . FIG. 1B shows a block diagram of the circuit diagram shown in FIG. 1A, and FIG. 1C shows a portion used as a DVD amplifier circuit. In FIG. 1C, the following three expressions hold.

I14 = I13 + I1
Vo = R1 ・ I1 + R14 ・ I14
I1 ・ R1 = Vs + R13 ・ I13
Solving the output terminal voltage Vo from these three equations, Vo = I1 · R1 × (R13 + R14) / R13 + I1 · R14−Vs · R14 / R13
The second and third terms on the right side are sufficiently smaller than the first term on the right side and can be ignored. Therefore,
Vo = I1 · R1 × (R13 + R14) / R13
It becomes. The amplification gain Z2 is Z2 = R1 × (R13 + R14) / R13
It becomes. The same concept can be applied when used for CDs. As a result, the amplifier circuit configuration of the amplifier circuit can be made one stage, and at the same time, the same amplification gain and frequency characteristics as in the conventional example can be obtained. In addition, since the number of circuit elements is reduced, the area occupied by the elements can be reduced, and the cost can be reduced.

    Specifically, taking the DVD mode as an example, when the conventional circuit has a two-stage amplifier circuit configuration, the first stage gain resistance of 40 kΩ and the subsequent stage gain of 2 are required, whereas in this embodiment, R13 = R14 = 1 kΩ, the gain resistance R1 = 40 kΩ, which can be set to the same value as the gain resistance value of the first stage in the conventional two-stage amplifier circuit configuration, and the equivalent circuit characteristics can be obtained. In addition, it is possible to make a ratio with a small resistance value in the voltage dividing resistor, thereby reducing the area occupancy of the resistor element in the light receiving element and further reducing the cost.

    Further, by setting the resistance values for the DVD gain resistor R1 and the CD gain resistor R2 to the respective wavelengths, it is possible to obtain the desired sensitivity characteristics according to the mode.

    In this embodiment, an amplifier circuit corresponding to two lights is shown. However, the number of lights to be associated with the feedback amplifier circuit and the detector is prepared, and one light is supported, or three or more lights are supported. Is also possible.

    Further, in the present embodiment, an example is shown in which R13 = R14 = 1 kΩ and the same double gain as in the conventional post-stage amplifier circuit is obtained. However, if the values of R13 and R14 are changed to different values, an arbitrary gain value is obtained. It is possible to obtain

(Embodiment 2)
FIG. 2 is a circuit diagram according to Embodiment 2 of the present invention. The circuit in this embodiment is effective when a larger gain difference is required between the DVD mode and the CD mode.

    In FIG. 2, the amplifier circuit is connected to a differential circuit 2 to which a DVD optical signal receiving photodiode a1 as a first detector is connected and a CD optical signal receiving photodiode A1 as a second detector. The differential circuit 2 is composed of transistors Q1 and Q2, and the differential circuit 3 is composed of transistors Q3 and Q4. Constant current circuits I1 and I2 are connected to the differential circuits 2 and 3, respectively. ing. The differential circuit 2 and the differential circuit 3 are configured to share the active circuit 1 including the PNP transistors Q5 and Q6 and the resistors R7 and R8, and the output circuit 4 of the constant current circuit I3 and the transistor Q7. . The circuit gain resistor R1 for DVD is a circuit connected to the dividing point of the voltage dividing resistors R15 and R16 connected to the amplifier circuit output Vo end and the reference potential Vs end. Similarly, the CD circuit gain resistor R2 is connected to the dividing point of the voltage dividing resistors R17 and R18 connected to the amplifier circuit output Vo end and the reference potential Vs end. As a result, a voltage dividing resistor R16 and a gain resistor R1 are used for DVD, and a voltage dividing resistor R18 and R2 are used for CD to form a feedback resistor to form a feedback amplifier circuit. Further, phase adjusting capacitors C1 and C2 are connected in parallel to the gain resistors R1 and R2. Further, R5 and R6 are provided as offset adjusting resistors. The selection switches 1 and 2 are respectively provided between the voltage dividing resistor and the amplifier circuit output Vo terminal or the reference potential Vs terminal. The selection switches 1 and 2 are switched by the selection signal, and the constant current circuit I1 or I2 is switched. Is operated to switch between the differential circuits 2 and 3 to select either the DVD mode or the CD mode.

    The selection switch here performs on / off control in conjunction with switching between the DVD and CD modes, but the operation is possible even when the selection switch is not provided. However, for example, when there is no selection switch in the constant current circuit I1 = on and constant current circuit I2 = off in the DVD mode, the CD voltage dividing resistors R17 and R18 are connected to the amplifier circuit output in the DVD mode operation. The resulting load resistance can be a cause of characteristic degradation. Therefore, by having the selection switch of this embodiment, it is possible to disconnect the resistance load and obtain good characteristics.

    Next, specific examples of the selection switch are shown in FIGS.

    In FIG. 3, NPN transistors Q8 and Q9 as selection switches are connected between the DVD voltage dividing resistor R15 and the reference potential, and between the CD voltage dividing resistor R17 and the reference potential. The function is achieved by turning the NPN transistor on / off in each mode. Further, by arranging the NPN transistors Q8 and Q9 at the above-described locations, the base current IbQ8 of the transistor Q8 or the base current IbQ9 of the transistor Q9 in each transistor on state flows in the reference potential direction through the emitter of each transistor. The voltage drop at the gain resistors R1 and R2 is not affected.

    In FIG. 4, PNP transistors Q10 and Q11 as selection switches are connected between the DVD voltage dividing resistor R16 and the amplifier circuit output terminal, and between the CD voltage dividing resistor R18 and the amplifier circuit output terminal. The function is achieved by turning the PNP transistor on / off in each mode. Further, by arranging the PNP transistors Q10 and Q11 at the above-described locations, the base current IbQ10 of the transistor Q10 or the base current IbQ11 of the transistor Q11 in each transistor on state flows from the output terminal, and the emitter and base of each transistor are connected. Therefore, there is no influence on the voltage drop at the gain resistors R1 and R2.

    As described above, by having the selection switches 1 and 2 having the NPN transistor or the PNP transistor in the above arrangement, it is possible to obtain good characteristics.

(Embodiment 3)
FIG. 5 is a circuit diagram according to Embodiment 3 of the present invention. When the selection switch in the above-described embodiment is controlled by a transistor switch, when the transistor is in an ON state, there is an ON resistance between the collector and the emitter of the transistor, which may affect the total resistance value. For example, in the DVD mode in FIG. 3, when the ON resistance of the NPN transistor Q8 is set to Rtr8on, the amplification circuit gain becomes Z3 below, and the circuit gain value accuracy may be lowered by the ON resistance of the transistor Q8.

DVD mode
Z3 = R1 × (R15 + Rtr8on + R16) / (R15 + Rtr8on)

    In FIG. 5, the selection switch includes a first emitter follower circuit (constituting constant current circuits I4 and I5 and transistors Q12 and Q13) for supplying a reference potential Vs connected between the voltage dividing resistor R15 and the reference potential Vs; The emitter follower circuit is constituted by a second emitter follower circuit (constituting constant current circuits I6 and I7 and transistors Q14 and Q15) for supplying a reference potential Vs connected between the voltage dividing resistor R17 and the reference potential Vs. By controlling with the selection signal, an effect equivalent to that of the selection switch described in the second embodiment can be obtained. Specifically, when operating in the DVD mode, the emitter follower circuit 1 is activated by the selection signal, and the emitter follower circuit 2 is deactivated, whereby the reference potential is supplied to the DVD voltage dividing resistor R15. Since the potential is not supplied to the CD voltage dividing resistor R17, the effect as a load is reduced by setting the open state.

    Therefore, by adopting a configuration in which the reference potential is supplied by the emitter follower circuit controlled by the selection signal, it is possible to avoid problems such as transistor on-resistance when the transistor switch is a selection switch.

    In the present embodiment, an amplifier circuit corresponding to two lights is shown. However, a feedback amplifier circuit, a detector, and the number of lights to be associated with a voltage dividing resistor are prepared, and three or more lights can be supported. .

    Further, instead of optical input, other sensor signals such as voice and temperature can be used.

It is a figure which shows the amplifier circuit concerning Embodiment 1 of this invention. It is a figure which shows the amplifier circuit concerning Embodiment 2 of this invention. It is an amplifier circuit diagram which shows the specific example of Embodiment 2 of this invention. It is an amplifier circuit diagram which shows the specific example of Embodiment 2 of this invention. It is a figure which shows the amplifier circuit concerning Embodiment 3 of this invention. It is an optical pick-up apparatus structure schematic diagram in a prior art. It is a surface enlarged view of a light receiving element IC chip. It is an amplifier circuit block diagram corresponding to a two-wavelength laser in the prior art. It is an amplifier circuit diagram corresponding to two-wavelength laser in the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Active circuit 2 Differential circuit 3 Differential circuit 4 Output circuit 5 Active circuit 6 Differential circuit 7 2 wavelength laser 8 Prism 9 Lens 10 Light receiving element IC chip 11 corresponding to 2 wavelength laser Photodiode 12 It is radiate | emitted from 2 wavelength laser 7 Laser light 13 Disc 14 Reflected laser light a1 to a4 Photodiode for DVD A1 to A4, E, F Photodiode for CD

Claims (12)

In an amplifier circuit comprising a detector for detecting an input signal, and a feedback amplifier circuit connected to the detector for amplifying the output current,
A voltage dividing resistor provided between an output of the amplifier circuit and a reference potential; one end of the voltage dividing resistor is connected to the output side; and a resistance of the feedback amplifier circuit is provided at a dividing point of the voltage dividing resistor. An amplifying circuit connected, wherein the other end of the voltage dividing resistor is connected to an input of the feedback amplifying circuit.     The amplifier circuit according to claim 1, wherein the detector is a detector corresponding to light input.     2. The amplifier circuit according to claim 1, wherein the voltage dividing resistor can adjust a gain of the amplifier circuit by changing a position of a division point. An amplifying circuit comprising a plurality of detectors for detecting an input signal and a feedback amplifying circuit connected to each detector for amplifying the output current, wherein one of the feedback amplifying circuits is enabled by a selection signal In
A voltage dividing resistor provided between an output of the amplifier circuit and a reference potential; one end of the voltage dividing resistor is connected to the output side; and a resistance of the feedback amplifier circuit is provided at a dividing point of the voltage dividing resistor. An amplifying circuit connected, wherein the other end of the voltage dividing resistor is connected to an input of the feedback amplifying circuit.     The amplifier circuit according to claim 4, wherein the plurality of detectors are detectors corresponding to different light inputs.     The amplifier circuit is a first feedback amplifier circuit having a resistance matched to the first light, and a second feedback amplifier circuit having a resistance matched to the second light. 5. The amplifier circuit according to 5.     The first and second voltage dividing resistors are connected to the resistors of the first and second feedback amplifier circuits, respectively, and the resistance values of the first and second voltage dividing resistors are different from each other. The amplifier circuit according to claim 6.     A selection switch that operates in response to the selection signal and enables one of the first and second voltage dividing resistors is provided between an output of the amplifier circuit and a reference potential. Item 8. The amplifier circuit according to Item 7.     The selection switch is provided between the other end of the voltage dividing resistor and a reference potential, and the selection switch is an NPN transistor controlled by a selection signal that enables one of the feedback amplifier circuits. The amplifier circuit according to claim 8.     The selection switch is provided once between the voltage dividing resistor and the output of the amplifier circuit, and the selection switch is a PNP transistor controlled by a selection signal that enables one of the feedback amplifier circuits. The amplifier circuit according to claim 8.     The selection switch is provided between the other end of the voltage dividing resistor and a reference potential, and the selection switch is an emitter follower circuit controlled by a selection signal that enables one of the feedback amplifier circuits. The amplifier circuit according to claim 8, characterized in that:     An optical pickup device comprising the amplifier circuit according to claim 1.

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