JP2000332546A - Photodetecting amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the photodetecting amplifier circuit which can reduce the noise in a high-frequency area. SOLUTION: The photodetecting amplifier circuit has a 1st preamplifier A1 where a photodetector element PD1 is connected and which has a feedback circuit constituted by connecting a 1st gate resistance Rf1 and a 1st phase compensating capacitor Cf1 in parallel, a 2nd preamplifier A2 having a feedback circuit constituted by connecting a 2nd gain resistance Rf2 and a 2nd phase compensating capacity Cf2 in parallel, and a differential amplifier A3 which obtains the difference in output voltage between the 1st preamplifier A1 and 2nd preamplifier A2, and the 2nd phase compensating capacitor Cf2 is made larger than the 1st phase compensating capacitor Cf1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light-receiving amplifier circuit for an optical pickup used for a CD-ROM driver or the like.

[0002]

2. Description of the Related Art Recently, with the increase in speed of CD-ROM drivers and the like, low noise has been required in light receiving amplifier circuits that require high-speed response.

As shown in FIG. 4, a conventional light-receiving amplifier circuit for an optical pickup used for a CD-ROM driver or the like is connected to a light-receiving element PD91 such as a photodiode, and has a first gain resistor Rf91 and a first gain resistor Rf91. A first preamplifier A91 having a feedback circuit in which phase compensation capacitors Cf91 are connected in parallel, and a second preamplifier having a feedback circuit in which a second gain resistor Rf92 and a second phase compensation capacitor Cf92 are connected in parallel A92, and a differential amplifier A93 for obtaining a difference between the output voltages of the first preamplifier A91 and the second preamplifier A92, and the first preamplifier A91 is connected via a resistor R93. The second preamplifier A92 is connected to the non-inverting input terminal of the dynamic amplifier A93, and the second preamplifier A92 is connected to the inverting input terminal of the differential amplifier A93 via a resistor R94.
Further, a reference voltage Vref is applied to a non-inverting input terminal of the differential amplifier A93 via a resistor R95.

[0004] Here, the first phase compensation capacitance Cf91 and the second phase compensation capacitance Cf92 are set to the same value, and the AC characteristics of the first preamplifier A91 and the second preamplifier A92 match. By doing so, an amplifier insensitive to common-mode noise such as power supply line noise has been configured.

That is, Rf91 = Rf92, Cf91 = C
At the time of f92, the first pre-amplifier A91 and the second pre-amplifier A92 amplify noise with the same amplification factor and output the same noise voltage. At this time, the differential amplifier A93
Does not amplify the noise component even if the same noise voltage is input, and thus is insensitive to common-mode noise such as power supply line noise.

[0006]

In the conventional light receiving amplifier circuit shown in FIG. 4, the phase compensation capacitance Cf91 of the first preamplifier A91 and the phase compensation capacitance Cf92 of the second preamplifier A92 are set to be the same. are doing. First preamplifier A9
1 is a high-speed amplifier capable of responding up to about several tens of MHz, so that the second preamplifier A92 is also a similar high-speed amplifier, and generates noise up to a high-frequency region.

The differential amplifier A93 is a first preamplifier A
The difference between the output voltage of the first pre-amplifier A91 and that of the first pre-amplifier A91
And the noises generated by the second preamplifier A92 are independent and arbitrarily generated. Therefore, in the differential amplifier A93, the noise generated in the first preamplifier A91 and the noise generated in the second preamplifier A92 are independently amplified.

Therefore, if the noise generated in the differential amplifier A93 is neglected, the output of the differential amplifier A93 is
The noise obtained by adding the noise generated by the first preamplifier A91 and the noise generated by the second preamplifier A92 is further amplified by the differential amplifier A93, and large noise up to a high frequency region is generated.

An object of the present invention is to solve such a problem of the prior art, and an object of the present invention is to provide a light receiving amplifier circuit capable of reducing noise in a high frequency region.

[0010]

According to the present invention, there is provided a light-receiving amplifier circuit having a first front end having a feedback circuit connected to a light-receiving element and having a first gain resistor and a first phase compensation capacitor connected in parallel. An amplifier, a second preamplifier having a feedback circuit in which a second gain resistor and a second phase compensation capacitor are connected in parallel, and output voltages of the first preamplifier and the second preamplifier. A differential amplifier for taking a difference, wherein the second phase compensation capacitance is larger than the first phase compensation capacitance,
Thereby, the above object is achieved.

[0011] A second light receiving element having the same characteristics as the light receiving element may be provided in a light-shielded state on the input side of the second preamplifier.

Preferably, the time constant of the second preamplifier is about 0.21 μsec or more.

[0013] Preferably, the second phase compensation capacitance is about 7 pF or more.

The second phase compensation capacitance may be a capacitance of an insulating layer.

The second phase compensation capacitor has a structure in which an insulating layer is sandwiched between a metal layer and a semiconductor layer. The metal layer is connected to the input side of the second preamplifier, and the semiconductor layer is connected to the second preamplifier. It may be configured to be connected to the output side of the second preamplifier.

The operation of the present invention will be described below.

According to the above configuration, the first preamplifier having the feedback circuit in which the light receiving element is connected and the first gain resistor and the first phase compensation capacitor are connected in parallel, and the second gain resistor A second preamplifier having a feedback circuit in which a feedback circuit and a second phase compensation capacitor are connected in parallel, and a differential amplifier for obtaining a difference between output voltages of the first preamplifier and the second preamplifier. Since the second phase compensation capacitance is larger than the first phase compensation capacitance in the light receiving amplifier circuit having
The responsiveness of the preamplifier is lower than the responsiveness of the first preamplifier, and the noise in the high frequency region generated by the second preamplifier is reduced.

In this case, the AC characteristics of the first preamplifier and the second preamplifier become inconsistent, and there is a concern that the first preamplifier and the second preamplifier are weak against common-mode noise such as power supply line noise. In the ROM pickup circuit, since a bypass capacitor for removing noise is connected between the power supply line and the ground, the above-mentioned common-mode noise is removed by this capacitor, so that the problem of power supply line noise can be avoided.

More specifically, in the second preamplifier, the second gain resistor Rf2 and the phase compensating capacitor C
An integration circuit is formed by a feedback circuit in which f2 is connected in parallel. Similarly, in the first preamplifier, an integration circuit is formed by a feedback circuit in which a first gain resistor Rf1 and a phase compensation capacitor Cf1 are connected in parallel. Then, the high-frequency cutoff frequency fc2 of the second preamplifier is 1 / (2π
Rf2 · Cf2), and the high cutoff frequency fc1 of the first preamplifier is 1 / (2π · Rf1 · Cf1).
Is determined.

Under the conditions of Cf2> Cf1 and Rf1 = Rf2, the relationship of the above equations is 1 / (2π · Rf2 · Cf
2) <1 / (2π · Rf1 · Cf1).

That is, the high cutoff frequency fc2 of the second preamplifier is made lower than the high cutoff frequency fc1 of the first preamplifier, and the responsiveness of the second preamplifier is lowered. It is also possible to reduce the noise in the high frequency region that has occurred in the preamplifier.

If a second light receiving element having the same characteristics as the light receiving element is provided in a light-shielded state on the input side of the second preamplifier, the same leak current as that of the light receiving element occurs in the second light receiving element. Therefore, by using this, it is possible to offset the influence of the leak current of the light receiving element which increases at high temperatures.

In the reproduction of a CD-ROM, in particular,
Since noise in a high-frequency region of 0 KHz or more becomes a problem, if the time constant of the second preamplifier is set to about 0.21 μsec or more, it is possible to reduce noise at a frequency of 700 kHz or more. .

The negative feedback resistor that determines the gain of the first preamplifier and the second preamplifier requires a resistance of 30 KΩ or more, so that the second phase compensation capacitance is about 7 pF or more. By doing so, it is possible to reduce the above-mentioned noise at a frequency of 700 kHz or more.

If the second phase compensation capacitor is constituted by a capacitor formed by an insulating layer, noise such as popcorn noise generated when the second phase compensation capacitor is constituted by a junction capacitor does not occur. Can be achieved.

For example, in the light receiving amplifier circuit, the second phase compensation capacitor has a structure in which the insulating layer is sandwiched between a metal layer and a semiconductor layer, and the metal layer is formed of the second preamplifier. It can be configured to be connected to the input side and the semiconductor layer is connected to the output side of the second preamplifier.

[0027]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows a configuration example of a light receiving amplifier circuit according to a first embodiment of the present invention, in which a light receiving element PD1 is connected and a first gain resistor Rf1 is connected.
A first preamplifier A1 having a feedback circuit in which a first phase compensation capacitor Cf1 and a first phase compensation capacitor Cf1 are connected in parallel, and a second gain resistor Rf
2 and a first preamplifier A2 having a feedback circuit in which the second and second phase compensation capacitors Cf2 are connected in parallel.
1 and a differential amplifier A3 for obtaining a difference between the output voltages of the second preamplifier A2, and the second phase compensation capacitance Cf2 is set to be larger than the first phase compensation capacitance Cf1.

The first preamplifier A1 is connected to the non-inverting input terminal of the differential amplifier A3 via a resistor R3, and the second preamplifier A2 is connected to the inverting terminal of the differential amplifier A3 via a resistor R4. Connected to input terminal. Further, the differential amplifier A3
, A reference voltage Vref is applied via a resistor R5. The output of the differential amplifier A3 is fed back to the inverting input terminal of the differential amplifier A3 via the negative feedback resistor R6.

More specifically, as shown in FIG. 1, the output voltage of the first preamplifier A1 is fed back in parallel via the first gain resistor Rf1. The phase compensation capacitor Cf2 prevents the first preamplifier A1 from oscillating.

The light receiving element PD1 such as a photodiode is
The current output during light reception is defined as Ia, and the first preamplifier A
When the output voltage at the time of no signal of 1 is represented by Vd,
The output voltage V1 of the preamplifier A1 is represented by the following equation (1): V1 = Vd + Rf1 × Ia (1)

The second preamplifier A2 includes a light receiving element PD1
Has the same configuration as the first preamplifier A1 not connected, and satisfies the following equation (2): Rf1 = Rf2, Cf2> Cf1 (2)

In the second preamplifier A2, the second preamplifier A2 is the same as the first preamplifier A1 except that the capacitance of the phase compensation capacitor Cf2 is larger than the capacitance of Cf1. Therefore, the second preamplifier A2
And the first preamplifier A1 have the same characteristics except for the high-frequency response.

Therefore, the output voltage V2 of the second preamplifier A2 in the DC and low frequency regions is given by the following equation (3): V2 = V1 = Vd (3)

In the differential amplifier A3, a reference voltage Vref is applied to a non-inverting input terminal via a resistor R5.
The difference between the output voltage of the preamplifier A1 and the output voltage of the second preamplifier A2 is amplified.

In the differential amplifier A3, R3 = R4, R
When 5 = R6, the output voltage V3 is represented by the following equation (4): V3 = (R5 / R3) × (V1−V2) + Vref (4)

According to the above equations (1), (3) and (4), when the photocurrent Ia flows through the light receiving element PD1, the output voltage V3 of the differential amplifier A3 becomes the following equation (5). (R5 / R3) × (Rf1 × Ia) + Vref (5)

Next, the frequency response and noise of the amplifier will be described.

In the second preamplifier A2, an integration circuit is formed by a feedback circuit in which a second gain resistor Rf2 and a phase compensating capacitor Cf2 are connected in parallel.
In the preamplifier A1, the feedback circuit in which the first gain resistor Rf1 and the phase compensation capacitor Cf1 are connected in parallel forms an integration circuit.

High frequency cutoff frequency f of second preamplifier A2
c2 is determined by the following equation (6): fc2 = 1 / (2π · Rf2 · Cf2) (6)

High frequency cutoff frequency f of first preamplifier A1
c1 is determined by the following equation (7): fc1 = 1 / (2π · Rf1 · Cf1) (7)

Cf2> Cf1, Rf shown in the above equation (2)
Under the condition of 1 = Rf2, the relationship between the above expressions (6) and (7) is expressed by the following expression (8): 1 / (2π · Rf2 · Cf2) <1 / (2π · Rf1 · Cf1) (8) ).

That is, the high cut-off frequency fc2 of the second preamplifier A2 is made lower than the high cutoff frequency fc1 of the first preamplifier A1, and the responsiveness of the second preamplifier A2 is reduced. In addition, the noise in the high frequency region generated by the second preamplifier A2 can be reduced.

(Embodiment 2) FIG. 2 shows a configuration example of a light receiving amplifier circuit according to Embodiment 2 of the present invention. The light receiving element PD1 is connected and a first gain resistor Rf1 is connected.
A first preamplifier A1 having a feedback circuit in which a first phase compensation capacitor Cf1 and a first phase compensation capacitor Cf1 are connected in parallel, and a second gain resistor Rf
2 and a second preamplifier A2 having a feedback circuit in which a second phase compensation capacitor Cf2 is connected in parallel, and the same characteristics as the light receiving element PD1 provided on the input side of the second preamplifier A2 in a light-shielded state. And a differential amplifier A3 for obtaining a difference between output voltages of the first preamplifier A1 and the second preamplifier A2, and a second phase compensation capacitor Cf2.
Is set to be larger than the first phase compensation capacitance Cf1.

The first preamplifier A1 is connected to a non-inverting input terminal of a differential amplifier A3 via a resistor R3, and the second preamplifier A2 is connected to an inverting terminal of the differential amplifier A3 via a resistor R4. Connected to input terminal. Further, the differential amplifier A3
, A reference voltage Vref is applied via a resistor R5. The output of the differential amplifier A3 is fed back to the inverting input terminal of the differential amplifier A3 via the negative feedback resistor R6.

That is, the light receiving amplifier circuit according to the second embodiment shown in FIG. 2 is different from the first embodiment in that the input terminal of the second preamplifier A2 is shielded from light by a wiring metal having the same structure as the photodiode PD1. The second embodiment is different from the first embodiment in that the second photodiode PD2 is connected, and the other configuration is the same as that in the first embodiment.

The photodiode has a large junction area P
Because of the N-junction, a large leakage current occurs at high temperatures.

For example, in the light receiving amplifier circuit according to the first embodiment shown in FIG. 1, let Ic be the leakage current at the time of no signal generated in the photodiode PD1, and let the output voltage of the first preamplifier A1 be Ic = 0. When Vdd is used, the output voltage V1 of the first preamplifier A1 is represented by the following equation (9): V1 = Vdd + Rf1 × Ic (9)

At this time, since the output voltage of the second preamplifier A2 is Vdd, the output voltage V3 of the differential amplifier A3 can be calculated from the above equation (4) by the following equation (10): V3 = (R5 / R3 ) × (Rf1 × Ic) + Vref (10)

Therefore, the leakage current Ic of the photodiode PD1 is converted and amplified by the IV, and appears in the output voltage V3. That is, the leak current Ic of the photodiode PD1 is handled in the same manner as the photocurrent at the time of receiving light, and causes a malfunction.

On the other hand, in the light receiving amplifier circuit according to the second embodiment shown in FIG. 2, the input terminal of the second preamplifier A2 is also shielded from light by a wiring metal having the same area and the same structure as the photodiode PD1. Second photodiode PD
When the leak current of the second photodiode PD2 is Id in this case, the output voltage V2 of the second preamplifier A2 is expressed by the following equation (11). V2 = Vdd + Rf2 × Id ··· -It is represented by (11).

Since the photodiodes having the same area and the same structure have the same leak current at the PN junction, Ic = Id
It is. Further, according to the above equation (2), Rf1 = Rf2.

As a result, from the above equations (9) and (11), V1 = V2, and the output voltage V3 of the differential amplifier A3 is obtained.
Is V3 = Vref, and the influence of the leak current of the photodiode PD1 can be eliminated.

(Embodiment 3) In the light receiving amplifier circuit according to Embodiment 3 of the present invention, the time constant of the second preamplifier A2 in Embodiment 1 shown in FIG. 1 or Embodiment 2 shown in FIG. The configuration is about 0.21 μsec or more.
Here, the time constant is represented by the product of the second gain resistance Rf2 and the second phase compensation capacitance Cf2.

For example, the second preamplifier A2 shown in FIG.
Generated in the second preamplifier A2
And the thermal noise generated by the second gain resistor Rf2.

In a light receiving amplifier circuit for an optical pickup used for a CD-ROM driver or the like, a small photocurrent I
The first gain resistor Rf1 for -V conversion is about 30K
Ω or more, the second gain resistor R
f2 also has the same value as the first gain resistor Rf1.

Since the thermal noise generated by the second gain resistor Rf2 is proportional to the square root of the resistance value, the thermal noise is larger than the shot noise generated by the second preamplifier A2.

Therefore, the noise generated by the second preamplifier A2 is dominated by the thermal noise generated by the second gain resistor Rf2.

The thermal noise Vn generated by the second gain resistor Rf2 is expressed by the following equation (12): Vn = (4k · Rf2 · T · Δf) ^1/2 (12)

Here, k: Boltzmann's constant, T: absolute temperature, Δf: bandwidth.

In a light receiving amplifier circuit for an optical pickup used for a CD-ROM driver or the like, about 700 KH
Since it is necessary to amplify signals of z or more, 700 kHz
It is necessary to reduce thermal noise in the above frequency bands.

In the second preamplifier A2 shown in FIG. 1, the second gain resistor Rf2 and the phase compensating capacitor C
An integration circuit composed of a feedback circuit in which f2 is connected in parallel is configured, and a noise V generated in the second preamplifier A2 is generated.
An is expressed by the following equation (13): Van = (4k · Rf2 · T · Δf) ^1/2 / (1 + j · ω · Rf2 · Cf2) (13)

Here, k: Boltzmann constant, T: absolute temperature, Δf: bandwidth, j: imaginary unit, and ω: angular frequency.

In the above equation (13), the time constant R
By setting f2 × Cf2 to 0.21 μsec or more, 7
It is possible to reduce the noise Van of the second preamplifier A2 generated in the high frequency region of 00 KHz or higher.

(Embodiment 4) The photoreceiver amplifier circuit according to Embodiment 4 of the present invention comprises the second phase compensation capacitor Cf in Embodiment 1 shown in FIG. 1 or Embodiment 2 shown in FIG.
2 is about 7 pF or more.

In a light-receiving amplifier circuit for an optical pickup used for a CD-ROM driver or the like, the first gain resistor Rf1 needs to use a resistor of 30 KΩ or more for IV conversion of a small photocurrent. Gain resistance Rf2
Also takes the same value as the first gain resistor Rf1.

With respect to the noise Van represented by the above equation (13), when Rf2 = 30 KΩ, Rf2 × Cf2 ≧ 0.2
In order to be 1 μsec, it is necessary to satisfy Cf2 ≧ 7 pF.

When Rf2 ≧ 30 KΩ, Cf2 ≧ 7
In the case of pF, the high-frequency cutoff frequency fc2 of the integrating circuit composed of Rf2 and Cf2 is represented by the following equation (14): fc2 = 1 / (2π · Rf2 · Cf2) ≦ 700 kHz (14)

Therefore, it is possible to reduce the noise Van of the second preamplifier A2 generated in the high frequency region of 700 KHz or more.

(Embodiment 5) FIG. 3 shows a light-receiving amplifier circuit according to Embodiment 5 of the present invention as shown in FIGS.
2 shows a specific configuration example in which the second phase compensation capacitor Cf2 shown in FIG. 3 is a capacitor made of an insulating layer. The second phase compensation capacitor Cf2 is composed of an insulating layer 32 formed of a metal layer 33 and a semiconductor layer 3.
5, the metal layer 33 is connected to the input side of the second preamplifier A2, and the semiconductor layer 35 is connected to the output side of the second preamplifier A2.

More specifically, the second phase compensation capacitance Cf2
As shown in FIG. 3, the capacitor section is formed on a P-type semiconductor substrate 37 by forming an N-type semiconductor layer 36 having a low impurity concentration by an epitaxial layer, an N-type semiconductor layer 35 having a high impurity concentration,
It has a structure in which an insulating layer 32 made of a thin film such as a nitride film and an oxide film constituting a capacitor portion, and a metal layer 33 are sequentially laminated. The N-type semiconductor layer 36 includes a P-type isolation / diffusion layer 38,
By 39, the epitaxial layer of the capacitor portion is separated from other epitaxial layers, and the outside of the capacitor is covered with a thick protective film 31 such as an oxide film. The metal layer 33 constitutes one electrode of the capacitor portion, and a part of a region on the N-type semiconductor layer 35 having a high impurity concentration serving as the other electrode of the capacitor portion has an electrode outlet for forming an ohmic contact. 34 are provided.

The high impurity concentration N-type semiconductor layer 35 and the low impurity concentration N-type semiconductor layer 36 are electrically connected by the same N-type semiconductor, and the low impurity concentration N-type semiconductor layer 36 is connected to the P-type semiconductor substrate 37 and PN. Has a joint. Since the PN junction operates in the same manner as the photodiode in the light receiving element, the P type semiconductor substrate 37
A photocurrent is generated toward.

The electrode outlet 34 is connected to the second port shown in FIG.
When the photocurrent is Ib when connected to the input side of the preamplifier A2, the output voltage of the second preamplifier A2 is increased by Rf2 × Ib.

When the electrode outlet 34 is connected to the output of the second preamplifier A2, the second preamplifier A
2 has sufficient ability to supply the photocurrent Ib, so that the output voltage of the second preamplifier A2 can be prevented from rising due to the photocurrent Ib.

The light receiving amplifier circuit of the present invention is not limited to the specific configuration of each of the above embodiments.

[0076]

As described above, according to the light receiving amplifier circuit of the present invention, it is possible to reduce noise in a high frequency region.

More specifically, a first preamplifier having a feedback circuit to which a light receiving element is connected and a first gain resistor and a first phase compensation capacitor are connected in parallel; A second preamplifier having a feedback circuit in which two phase compensation capacitors are connected in parallel, and a differential amplifier for obtaining a difference between output voltages of the first preamplifier and the second preamplifier. In the amplifier circuit, since the second phase compensation capacitance is larger than the first phase compensation capacitance, the responsiveness of the second preamplifier is lower than the responsiveness of the first preamplifier. The noise in the high frequency region generated by the preamplifier is reduced.

If the second light receiving element having the same characteristics as the light receiving element is provided in a light-shielded state on the input side of the second preamplifier, the same leak current as that of the light receiving element occurs in the second light receiving element. Therefore, by using this, the influence of the leak current of the light receiving element which increases at high temperature can be canceled.

In reproducing a CD-ROM, in particular,
Since noise in a high-frequency region of 0 KHz or more becomes a problem, if the time constant of the second preamplifier is set to about 0.21 μsec or more, noise at frequencies of 700 kHz or more can be reduced.

The negative feedback resistor that determines the gain of the first preamplifier and the second preamplifier requires a resistance of 30 KΩ or more, so that the second phase compensation capacitance is about 7 pF or more. By doing so, it is possible to reduce the above-described noise at a frequency of 700 kHz or more.

When the second phase compensation capacitance is a capacitance constituted by an insulating layer, noise such as popcorn noise generated when the second phase compensation capacitance is constituted by a junction capacitance does not occur, so that noise can be reduced. Can be achieved.

For example, in the light receiving amplifier circuit, the second phase compensation capacitor has a structure in which the insulating layer is sandwiched between a metal layer and a semiconductor layer, and the metal layer is formed of the second preamplifier. It can be configured to be connected to the input side and the semiconductor layer is connected to the output side of the second preamplifier.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a light receiving amplifier circuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration example of a light receiving amplifier circuit according to a second embodiment of the present invention.

FIG. 3 shows the second phase compensation capacitor C shown in FIGS. 1 and 2 as the light receiving amplifier circuit according to the fifth embodiment of the present invention.
FIG. 9 is a cross-sectional view illustrating a specific configuration example when f2 is a capacitance by an insulating layer.

FIG. 4 is a block diagram illustrating a configuration example of a conventional light receiving amplifier circuit.

[Explanation of symbols]

 A1 First preamplifier A2 Second preamplifier A3 Differential amplifier Cf1 First phase compensation capacitance Cf2 Second phase compensation capacitance Rf1 First gain resistor Rf2 Second gain resistor PD1 Light receiving element PD2 Second Light receiving element 31 protective film 32 insulating layer 33 metal layer 34 electrode outlet 35 high impurity concentration N-type semiconductor layer 36 low impurity concentration N-type semiconductor layer 37 P-type semiconductor substrate 38, 39 P-type isolation diffusion layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4M118 AA05 AB10 BA02 BA06 CA03 DD10 FC05 5F049 MA02 NA04 NB08 RA06 UA04 UA06 UA20 5J090 AA01 AA56 CA41 FA19 HA19 HA25 HA29 HA44 HN06 KA02 KA25 MA11 MN04 NN12 QA02 A00 HA19 HA25 HA29 HA44 KA02 KA25 MA11 QA02 SA00 UL02

Claims (6)

[Claims] A first preamplifier having a feedback circuit in which a light receiving element is connected and a first gain resistor and a first phase compensation capacitor are connected in parallel; a second gain resistor and a second preamplifier; A second preamplifier having a feedback circuit in which phase compensation capacitors are connected in parallel; and a differential amplifier for obtaining a difference between output voltages of the first preamplifier and the second preamplifier. A light-receiving amplifier circuit in which the second phase compensation capacitance is larger than the first phase compensation capacitance. 2. The light-receiving amplifier circuit according to claim 1, wherein a second light-receiving element having the same characteristic as the light-receiving element is provided in a light-shielded state on an input side of the second preamplifier. 3. The time constant of said second preamplifier is about 0.5.
3. The light receiving amplifier circuit according to claim 1, wherein the light receiving amplifier circuit is at least 21 μsec. 4. The light-receiving amplifier circuit according to claim 1, wherein the second phase compensation capacitance is about 7 pF or more. 5. The light-receiving amplifier circuit according to claim 1, wherein said second phase compensation capacitance is a capacitance of an insulating layer. 6. The second phase compensation capacitor has a structure in which an insulating layer is sandwiched between a metal layer and a semiconductor layer, wherein the metal layer is connected to an input side of the second preamplifier; The light receiving amplifier circuit according to any one of claims 1 to 4, wherein is connected to an output side of the second preamplifier.