JPH07226631A - Optical signal detection circuit - Google Patents

Abstract

PURPOSE:To suppress input impedance low, to prevent speediness from being degraded and to provide high trans impedance by feeding back the output voltage of an initial stage amplifier for converting the output current signals of a photodetector to voltage signals through a circuit provided with an active element to an input side. CONSTITUTION:Optical signals are converted into current signals in the photodetector 11 and converted into voltage signals and amplified by the initial stage amplifier 12. The output signal voltage is outputted to a terminal 15, divided by resistors 16 and 17 and fed back through a feedback part 19 and the resistor 20 to the input terminal 13 of the initial stage amplifier 12. In this case, the feedback part 19 is constituted of an amplifier provided with input impedance sufficiently higher than the parallel value of the resistors 16 and 17. By turning the feedback part 19 to the active element in such a manner, the input impedance of the initial stage amplifier 12 is suppressed low, the degradation of response characteristics by the time constant of an input circuit is prevented, the speediness is not degraded, the high trans impedance is obtained and speeding-up and gain raising are simultaneously realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal detecting circuit used for an optical pickup of an optical disk device, an optical receiver for optical communication, an optical sensor, etc. and detecting an optical signal as a voltage signal.

[0002]

2. Description of the Related Art Conventionally, an optical signal detection circuit converts an optical input signal into a current signal by a photodetector 1 as shown in FIG. 12 and converts this current signal into a voltage signal by a first stage amplifier 2 to invert it, for example. Amplify. The first stage amplifier 2 has a feedback resistor 3 connected between an output terminal and an inverting input terminal. This optical signal detection circuit is used for optical signal detection in an optical pickup, an optical receiver for optical communication, an optical sensor, etc. used for reading an information signal of an optical disc in an optical disc device.

Japanese Laid-Open Patent Publication No. 1-238208 discloses a transimpedance type amplifier in which an emitter follower circuit is connected to a grounded emitter circuit, and the output of the emitter follower circuit is fed back to a base terminal of the grounded emitter circuit via a resistor. In a light receiving circuit composed of a circuit and a light receiving element, the cathode of the light receiving element is connected to the base input terminal of the grounded emitter circuit, and the load resistance _RL of the grounded emitter circuit and the ground resistance of the emitter follower circuit are connected. R _E
And between the current amplification factor h _FE of the transistors constituting the emitter follower circuit, an optical receiving circuit characterized by comprising R _L «h _FE R _E relation is configured to stand by is described.

In Japanese Unexamined Patent Publication No. 1-264313, a transformer in which an emitter follower circuit is connected to the collector of a grounded-emitter circuit, and the output of the emitter follower circuit is fed back to a base input terminal of the grounded-emitter circuit through a resistor. An impedance type amplifier circuit, a light receiving element having a cathode connected to the base input terminal of the grounded-emitter circuit, and a constant current circuit connected so that the emitter follower circuit operates with a constant emitter current. The constant current value I _o of the circuit, the current amplification factor h _{FE of} the transistor used in the grounded-emitter circuit, the load resistance _{RL of} the grounded-emitter circuit, the base-emitter voltage V _{BE4 of} the transistor used in the emitter follower circuit, and the constant current source are set. Emitter resistance of the emitter follower circuit when the emitter follower circuit is configured without using _E, and _{I O ≦ h FE / (R} L + h FE · R E) × (V CC -V BE4) the relationship light receiver, characterized in that is configured to establish between the supply voltage V _CC The circuit is described.

Japanese Patent Laid-Open No. 2-278906 discloses a light receiving element that receives an optical signal and converts it into an electric signal, a first resistor, a first transistor and a first resistor which are inserted in series between a power supply terminal and a ground terminal. A second CMOS transistor, which connects the base of the first transistor to the anode of the light receiving element, and is inserted in series between the power supply terminal and the ground terminal, and the base is the first A third transistor connected to the collector of the transistor, a level shift circuit, and a second resistor, and the connection node of the level shift circuit and the second resistor is connected to the base of the first transistor via a feedback resistor. A preamplifier including a second-stage amplifier circuit, an input terminal of which is connected to the connection node of the level shift circuit and the second resistor, and an output terminal of which is connected to an output terminal. And a AGC control amplifier having an input terminal connected to an output terminal of the AGC circuit and an output terminal connected to a control voltage input terminal of the AGC circuit and a gate of the second MOS transistor. An optical receiver circuit is described.

[0006]

With the high speed transfer and high speed reading of file data, an optical pickup has been developed to increase the speed of a photodetector of an optical signal detection circuit used for detecting an optical signal and a first stage amplifier used in the vicinity thereof.・ High gain has become important. However, there is a contradictory relationship between the increase in speed and the increase in gain, and it is difficult to realize them at the same time.

On the other hand, the first-stage amplifier that converts the current signal from the photodetector into a voltage signal in the optical signal detection circuit has a high resistance in the high frequency range and a high impedance on the input terminal side, and therefore has a high resistance. Although it is desired to obtain a high voltage gain all at once by applying feedback via the, it is difficult to obtain high impedance by performing feedback at a high speed and through a high resistance due to band limitation due to the capacitance of the input terminal. This is because only passive elements are inserted in the feedback circuit of the first stage amplifier, and in order to increase the gain of the first stage amplifier, the resistance between the output side and the input side of the first stage amplifier must be increased. This is because the impedance at the connection point between the output terminal of the photodetector having a function as a current source and the first-stage amplifier could not be lowered sufficiently.

For example, as shown in FIG.
Due to the input capacitance on the inverting input terminal side, the inter-terminal capacitance of the photodetector 1 and the time constant formed by the feedback resistor 3, the operating speed becomes slow even if the first-stage amplifier 2 itself is at high speed.
This makes the value of the feedback resistor 3 small and the first stage amplifier 2
However, it has been difficult to sufficiently extend the band of the optical signal detection circuit to the high frequency band of the first-stage amplifier 2 only by the passive element that constitutes the feedback circuit of the first-stage amplifier 2.

The present invention solves the above problems and provides an optical signal detection circuit which can suppress the impedance of the input terminal of the first-stage amplifier to a low level and can obtain a high transimpedance without deteriorating the high speed. The purpose is to

[0010]

In order to achieve the above object, the invention according to claim 1 is a photodetector for converting an optical input signal into a current signal, and an input terminal at one connection point of the photodetector. In the optical signal detection circuit having a first-stage amplifier to which a feedback terminal is connected, a feedback circuit unit including a feedback amplifier that divides the output voltage of the first-stage amplifier at a fixed ratio and outputs the feedback voltage, and a feedback circuit unit of the feedback circuit unit. The feedback resistor is connected between the output terminal and the feedback terminal of the first stage amplifier.

According to a second aspect of the present invention, in the optical signal detection circuit according to the first aspect, the first-stage amplifier is a differential amplifier in which an inverting input terminal and a feedback terminal are connected to one connection point of the photodetector. The feedback circuit section divides the output voltage of the first-stage amplifier, and the non-inverting amplifier provided between the output side of the voltage division circuit and the feedback resistor. Is to have.

According to a third aspect of the present invention, in the optical signal detection circuit according to the first aspect, the first stage amplifier is a differential amplifier in which a non-inverting input terminal and a feedback terminal are connected to one connection point of the photodetector. And a feedback circuit section in which the feedback circuit section divides the output voltage of the first-stage amplifier, and an inverting amplifier provided between the output side of the voltage division circuit and the feedback resistor. And have.

According to a fourth aspect of the present invention, in the optical signal detection circuit according to the first aspect, the resistance value of the feedback resistor is set to the inter-terminal capacitance of the photo detector and the capacitance of the input terminal of the first stage amplifier. The resistance value is set such that the bandwidth based on the time constant formed by the sum and the feedback resistance value of the first-stage amplifier exceeds at least the band of the first-stage amplifier.

According to a fifth aspect of the present invention, in the optical signal detection circuit according to the first aspect, the feedback circuit section is a voltage divider composed of two resistors for dividing the output voltage of the first-stage amplifier at a constant ratio. A feedback amplifier to which the output of the voltage division circuit is input, and a bandwidth based on the time constant formed by the input capacitance of the feedback amplifier and the parallel resistance value of the two resistors is at least the feedback. It is set to exceed the band of the amplifier for.

According to a sixth aspect of the present invention, in the optical signal detection circuit according to the second aspect, the non-inverting amplifier is an emitter follower.

According to a seventh aspect of the present invention, in the optical signal detection circuit according to the sixth aspect, the transistor has the same characteristics as the transistor forming the emitter follower, and the emitter is connected to the non-inverting terminal of the differential amplifier. In addition, the transistor is connected to the negative power source side via a resistor, the ground potential is applied to the base, and the collector is connected to the positive power source side.

According to an eighth aspect of the present invention, in the optical signal detection circuit according to the first aspect, the feedback amplifier is formed by using a transistor forming a grounded-emitter attenuation amplifier, and the emitter and the power supply side of the transistor are connected to each other. The value of the first resistor connected between the first and second resistors is set to be at least larger than the value of the second resistor connected between the collector of the transistor and the power supply side.

According to a ninth aspect of the present invention, in the optical signal detection circuit according to the eighth aspect, the power source is provided through a resistor having the same characteristics as the transistor and the emitter having the same resistance value as the first resistor. Connected to the power supply side through a resistor having the same resistance value as the second resistor and a collector connected to the inverting terminal of the feedback amplifier by applying a ground potential to the base. It is equipped with a transistor.

[0019]

According to the first aspect of the invention, the optical input signal is converted into a current signal by the photodetector, and this current signal is converted into a voltage signal by the first stage amplifier. The output voltage of the first-stage amplifier is divided and output at a constant ratio by the feedback circuit section including the feedback amplifier, and the output of this feedback circuit section is fed back to the feedback terminal of the first-stage amplifier via the feedback resistor.

According to a second aspect of the present invention, in the optical signal detection circuit according to the first aspect, the first stage amplifier composed of an inverting amplifier composed of a differential amplifier converts a current signal from the photodetector into a voltage signal, The feedback circuit section divides the output voltage of the first-stage amplifier by the voltage dividing circuit, performs non-inverting amplification by the non-inverting amplifier, and then feeds it back to the feedback terminal of the first-stage amplifier via the feedback resistor.

According to a third aspect of the present invention, in the optical signal detection circuit according to the first aspect, the first stage amplifier composed of a non-inverting amplifier made of a differential amplifier converts a current signal from the photodetector into a voltage signal. The feedback circuit section divides the output voltage of the first-stage amplifier by the voltage divider circuit, inverts and amplifies it by the inverting amplifier, and then feeds it back to the feedback terminal of the first-stage amplifier via the feedback resistor.

According to a fourth aspect of the invention, in the optical signal detection circuit according to the first aspect, the sum of the inter-terminal capacitance of the photodetector and the capacitance of the input terminal of the first stage amplifier and the feedback resistance value of the first stage amplifier are formed. The bandwidth based on the time constant exceeds at least the bandwidth of the first stage amplifier.

According to a fifth aspect of the invention, in the optical signal detection circuit according to the first aspect, the feedback circuit section divides the output voltage of the first-stage amplifier by a voltage dividing circuit composed of two resistors at a fixed ratio. It is fed back to the feedback terminal of the first-stage amplifier via the feedback amplifier and the feedback resistor, and the bandwidth based on the time constant formed by the input capacitance of the feedback amplifier and the parallel resistance value of the two resistors is at least that of the feedback amplifier. Exceeds bandwidth.

According to a sixth aspect of the present invention, in the optical signal detection circuit according to the second aspect, the output voltage of the first-stage amplifier is divided by the voltage dividing circuit at a constant ratio, and the non-inverting amplifier and the feedback resistor are formed of emitter followers. Is fed back to the feedback terminal of the first stage amplifier via.

According to a seventh aspect of the invention, in the optical signal detection circuit according to the sixth aspect, the transistor having the same characteristics as the transistor forming the emitter follower applies a bias voltage from the emitter to the non-inverting terminal of the differential amplifier. , Cancels the offset due to the transistor that constitutes the emitter follower.

According to an eighth aspect of the present invention, in the optical signal detection circuit according to the first aspect, the feedback amplifier configured by using the transistor forming the grounded-emitter attenuation amplifier is configured by connecting the emitter of the transistor and the power supply side. The value of the first resistance connected between them is set to be larger than the value of the second resistance connected between at least the collector of the transistor and the power supply side, and the output voltage of the first-stage amplifier is divided and amplified before feedback. It returns to the feedback terminal of the first-stage amplifier through the resistor for use.

According to a ninth aspect of the invention, in the optical signal detection circuit of the eighth aspect, the transistor having the same characteristics as the transistor forming the feedback amplifier applies a bias voltage from the collector to the inverting terminal of the differential amplifier. , Cancels the offset due to the transistor that constitutes the feedback amplifier.

[0028]

FIG. 1 shows a first embodiment of the present invention. This first
The embodiment is an embodiment of the invention according to claim 1, and is an example of an optical signal detection circuit with an inverting output type first stage amplifier. The cathode of the photodetector 11 is connected to the power supply, and the anode is connected to the inverting input terminal 13 and the feedback terminal 14 of the first-stage amplifier 12. Two resistors 16 and 17 forming a voltage dividing circuit are connected in series between the output terminal 15 of the first-stage amplifier 12 and the ground, and an active portion is provided between the connection point 18 of the resistors 16 and 17 and the feedback terminal 14. A feedback unit 19 having an element and a feedback resistor 20 are connected in series. The voltage dividing circuit composed of the resistors 16 and 17 and the feedback section 19 constitute a feedback circuit section,
The feedback unit 19 is configured by using a feedback amplifier having an input impedance sufficiently higher than the parallel resistance value of the resistors 16 and 17.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the first stage amplifier 12, and inverted and amplified. The output signal voltage of the first-stage amplifier 12 is taken out from the output terminal 15, and is divided at a constant ratio by the resistors 16 and 17, and is fed back to the feedback section 19 and the feedback resistor 2.
It is fed back to the inverting input terminal 13 of the first stage amplifier 12 via 0.

As described above, in the first embodiment, the first stage amplifier 1
Since the feedback section 19 in the feedback circuit of No. 2 has an active element, the impedance of the input terminal of the first-stage amplifier 12 is suppressed to be low, and the resistance value of the feedback circuit in the first-stage amplifier 12 and the capacitance of the input terminal 13 of the first-stage amplifier 12 By preventing the deterioration of the responsiveness due to the constant, it is possible to obtain a high transimpedance without deteriorating the high-speed property, and it is possible to simultaneously realize a high speed and a high gain (high transimpedance).

That is, the voltage appearing at the output terminal 15 of the first stage amplifier 12 is divided by the two resistors 16 and 17, and the output is used as a feedback amplifier having an input impedance sufficiently higher than the parallel resistance value of the resistors 16 and 17. Since the impedance is converted by the feedback unit 19 configured as described above and is fed back to the inverting input terminal 13 of the first stage amplifier 12 via the feedback resistor 20,
The feedback resistor 20 is connected to the feedback unit 19 having a low output impedance.
Can be driven by. Therefore, when the feedback resistor 20 is directly connected to the output terminal 15 of the first-stage amplifier 12, it is difficult to realize high transimpedance and high speed at the same time.
The feedback amount can be reduced by the voltage division ratio of 17, and the gain can be increased without lowering the band.
It is possible to realize a wideband first-stage amplifier that can obtain a high transimpedance that is a voltage division ratio of the resistances 16 and 17 times the resistance value of 0.

FIG. 2 shows a second embodiment of the present invention. The second embodiment is an embodiment of the invention described in claims 1, 2, 4, and 5, and in the first embodiment, the first stage amplifier 12 is constituted by an inverting amplifier 21 composed of a differential amplifier, and a feedback section is provided. 19 is composed of a feedback amplifier 22 and resistors 23 and 24. The feedback amplifier 22 is composed of a non-inverting amplifier composed of a differential amplifier. The non-inverting amplifier 22 has its non-inverting input terminal connected to the connection point 18 of the resistors 16 and 17 and its output terminal connected to the feedback terminal 14 via the feedback resistor 20, and between the inverting input terminal and the output terminal. The resistor 23 is connected and the inverting input terminal is grounded via the resistor 24. The inverting amplifier 21 has an inverting input terminal grounded and a non-inverting input terminal connected to the feedback terminal 14 and the anode of the photodetector 11.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the differential amplifier 21, and inverted and amplified. The output signal voltage of the differential amplifier 21 is taken out from the output terminal 15, divided at a constant ratio by the resistors 16 and 17 and non-inverted and amplified by the non-inverting amplifier 22, and then the first stage amplifier via the feedback resistor 20. 1
It is fed back to the second inverting input terminal 13.

In the second embodiment, the response of the amplifier system is deteriorated due to the time constant formed by the feedback resistance of the first-stage amplifier, the input capacitance of the first-stage amplifier and the sum of the capacitances of the photodetectors in the optical signal detection circuit. Is valid and meets the following conditions. Feedback resistor of first stage amplifier 21 (feedback resistor 20
Frequency R _c (= R × C) formed by the sum (C = C _i + C _PD ) of the input capacitance C _i of the first stage amplifier 21 and the capacitance C _PD of the photodetector 11 (C = C _i + C _PD ). = 1 / 2π
τ) is set to be larger than the band of the first stage amplifier 21. That is, the input resistance of the first stage amplifier 21 and the photodetector 1
Since the capacitance of 1 is fixed, the resistance value of the feedback resistor 20 is set so that the frequency f _c determined by the time constant τ (= R × C) is larger than the band of the first stage amplifier 21. Thus, the feedback resistor 2 for realizing a wide-band first-stage amplifier with high transimpedance is obtained from the sum of the capacitance of the input terminal of the first-stage amplifier 21 and the capacitance between the terminals of the photodetector 11.
It is possible to select the resistance value of 0 and determine the required characteristics of the first-stage amplifier accordingly.

Similarly, the resistance values R ₁ and R of the resistors 16 and 17 are
₂ is a band of the feedback amplifier 22 that is determined by the resistance value (parallel resistance value = R ₁ // R ₂ ) when the resistors 16 and 17 are considered to be in parallel and the time constant formed by the input capacitance of the feedback amplifier 22. It is set to be higher than the band. As a result, a foothold for determining the resistance values of the resistors 16 and 17 can be obtained, and the characteristics of the first-stage amplifier necessary for widening the band can be determined.

In the second embodiment, as in the first embodiment, the impedance of the input terminal of the first stage amplifier 21 can be suppressed to a low level, high transimpedance can be obtained without deteriorating the high speed performance, and the optical signal can be obtained. It is possible to realize a wide band first stage amplifier with high transimpedance that can obtain an inverted output for

FIG. 3 shows a third embodiment of the present invention. The third embodiment is an embodiment of the invention described in claims 1, 3, 4, and 5, and in the first embodiment, the first-stage amplifier 12 is constituted by a non-inverting amplifier 25 composed of a differential amplifier and is fed back. The section 19 is configured by a feedback amplifier 26 including an inverting amplifier and resistors 27 and 28. The inverting input terminal of the inverting amplifier 26 is a resistor 1 via a resistor 28.
6, 17 is connected to the connection point 18 and the output terminal is connected to the feedback terminal 14 via the feedback resistor 20. The resistor 27 is connected between the inverting input terminal and the output terminal to ground the inverting input terminal. It The inverting input terminal of the differential amplifier 25 is grounded, and the non-inverting input terminal 13 is connected to the feedback terminal 14 and the anode of the photodetector 11.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the differential amplifier 25, and non-inverted and amplified. The output signal voltage of the differential amplifier 25 is
While being taken out from the output terminal 15, it is divided at a constant ratio by the resistors 16 and 17 and is inverted and amplified by the inverting amplifier 26, and then is fed through the feedback resistor 20 to the first stage amplifier 12.
Is fed back to the inverting input terminal 13.

The third embodiment satisfies the following conditions similarly to the second embodiment. That is, the sum of the feedback resistance (resistance value of the feedback resistor 20) R of the first-stage amplifier 25, the input capacitance C _i of the first-stage amplifier 25, and the capacitance C _PD of the photodetector 11 (C = C _i
The frequency f _c (= 1 / 2πτ) determined by the time constant τ (= R × C) formed by + C _PD is set to be larger than the band of the first stage amplifier 25. That is, since the input resistance of the first stage amplifier 25 and the capacitance of the photodetector 11 are determined, the resistance value of the feedback resistor 20 has a frequency f _c determined by the time constant τ (= R × C) from the band of the first stage amplifier 25. It is set to be large. Similarly, the resistance values R ₁ and R of the resistors 16 and 17
₂ is a band of the feedback amplifier 26 that is determined by the resistance value (parallel resistance value = R ₁ // R ₂ ) when the resistors 16 and 17 are considered to be in parallel and the time constant formed by the input capacitance of the feedback amplifier 26. It is set to be higher than the band.

In the third embodiment, similarly to the first embodiment, the impedance of the input terminal of the first stage amplifier 25 can be suppressed to a low level, high transimpedance can be obtained without deteriorating the high speed, and the optical signal can be obtained. It is possible to realize a wide-band first-stage amplifier with high transimpedance that can obtain a non-inverted output. In each of the above embodiments, the photodetector 11 is used.
A current signal was input to the first stage amplifier from the anode side of
A current signal may be input from the cathode side of the photodetector 11 to the first-stage amplifier to connect the anode side of the photodetector 11 to a negative power source. The feedback amplifiers 22 and 26 are
Although the differential amplifier is used, a transistor may be used instead of the differential amplifier.

4 to 11 show the respective embodiments of the present invention in which the feedback amplifier is composed of transistors without using a differential amplifier. FIG. 4 shows a fourth embodiment of the present invention in which a feedback amplifier is constructed by an emitter follower using NPN type transistors. This fourth embodiment is characterized by claims 1, 2, 4, 5, and 6.
It is an embodiment of the invention described, in the second embodiment,
The feedback amplifier is composed of an emitter follower using an NPN transistor 29. This transistor 29
The base is connected to the connection point 18 of the resistors 16 and 17, the collector is connected to the positive power source + Vs, the emitter is connected to the negative power source −Vs via the emitter resistor 30, and the feedback is performed via the feedback resistor 20. It is connected to the terminal 14. The inverting amplifier 21 has a positive power supply terminal connected to the positive power supply + Vs and a negative power supply terminal connected to the negative power supply −Vs, and the photodetector 11
Is connected to the positive power source + Vs.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the differential amplifier 21, and inverted and amplified. The output signal voltage of the differential amplifier 21 is taken out from the output terminal 15, divided at a constant ratio by the resistors 16 and 17, non-inverted and amplified by the emitter follower using the transistor 29, and then passed through the feedback resistor 20. Is fed back to the inverting input terminal 13 of the first stage amplifier 12.

As is well known, in the emitter follower, the input impedance is about β times as large as the emitter resistance, and _β≈100 is obtained if a transistor with a high frequency f _t at which the current amplification factor h _FE is 1 is used. A high input impedance can be expected, and a low output impedance of about an emitter resistance is obtained, which satisfies the above conditions well.

In the fourth embodiment, a feedback amplifier can be realized by using one transistor 29 instead of the differential amplifier, and a feedback amplifier having a high input impedance and a low output impedance having a high-speed response of an emitter follower is realized. A high-performance inverting first-stage amplifier that can easily form an active circuit and obtain a high gain of a value obtained by multiplying the resistance value of the feedback resistor 20 by the ratio of the emitter resistance and the collector resistance of the transistor 29 without lowering the band. Can be realized.

FIG. 5 shows a fifth embodiment of the present invention in which a feedback amplifier is constituted by an emitter follower using a PNP type transistor. This fifth embodiment is characterized by claims 1, 2, and
4 is an embodiment of the invention described in 4, 5 and 6, and in the second embodiment, the feedback amplifier is composed of an emitter follower using a PNP type transistor 31. In this transistor 31, the base is connected to the connection point 18 of the resistors 16 and 17, the collector is connected to the negative power source −Vs, the emitter is connected to the positive power source + Vs via the emitter resistor 32, and the feedback resistor 20 is connected. It is connected to the feedback terminal 14 via the. The inverting amplifier 21 has its positive power supply terminal connected to the positive power supply + Vs, its negative power supply terminal connected to the negative power supply -Vs, and the cathode of the photodetector 11 connected to the positive power supply + Vs.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the differential amplifier 21, and inverted and amplified. The output signal voltage of the differential amplifier 21 is taken out from the output terminal 15, divided by resistors 16 and 17 at a constant ratio, non-inverted and amplified by an emitter follower using a transistor 31, and then passed through a feedback resistor 20. Is fed back to the inverting input terminal 13 of the first stage amplifier 12.

In the fifth embodiment, similarly to the fourth embodiment, the above-described conditions are well satisfied, and like the fourth embodiment, a high-performance inverting first-stage amplifier which can obtain a high gain without dropping the band is realized. it can. Although the current signal is input from the anode side of the photodetector 11 to the first-stage amplifier in the fourth and fifth embodiments, the current signal is input from the cathode side of the photodetector 11 to the first-stage amplifier. You may make it connect the anode side of 11 to a power supply.

In the fourth and fifth embodiments, a bias voltage is required between the base and emitter of the transistors 29 and 31, so that the inverting input of the inverting amplifier 21 from the transistors 29 and 31 via the feedback resistor 20. The reference potential of the output voltage fed back to the terminal differs from the potential of the non-inverting input terminal of the inverting amplifier 21 to cause offset. FIG. 6 shows a sixth embodiment of the present invention in which the offset is eliminated. The sixth embodiment is defined by claims 1, 2, 4, 5, 6, 7
It is an embodiment of the invention described, in the fourth embodiment,
An offset compensation circuit is provided. The offset compensation circuit is composed of a bias circuit including an offset compensation transistor 33 and a resistor 34 for canceling an offset.

In the transistor 33, the base is grounded, the collector is connected to the positive power source + Vs, and the emitter is the resistor 3
It is connected to the negative power source −Vs via 4 and the non-inverting input terminal of the inverting amplifier 21. Transistor 33
Is designed to have the same characteristics as the transistor 29, and the resistor 34 having the same resistance value as the resistor 30 is used.

Therefore, when the optical signal is not input to the photodetector 11 and the output current of the photodetector 11 becomes zero, assuming that there is no offset of the inverting amplifier 21 itself, the output voltage of the inverting amplifier 21 is The bias potential applied from the emitter of the transistor 33 to the non-inverting input terminal of the inverting amplifier 21 is almost the same, and the offset generated by the transistor 29 of the feedback circuit is applied from the emitter of the transistor 33 to the non-inverting input terminal of the inverting amplifier 21. The offset is compensated by being canceled by the applied bias potential.

FIG. 7 shows a seventh embodiment of the present invention in which the offset is eliminated as in the sixth embodiment. The seventh embodiment is an embodiment of the invention described in claims 1, 2, 4, 5, 6, and 7, and in the fifth embodiment, an offset compensation circuit is provided. The offset compensation circuit is composed of a bias circuit including an offset compensation transistor 35 and a resistor 36 for canceling the offset.

The base of the transistor 35 is grounded, the collector is connected to the negative power source -Vs, and the emitter is the resistor 3
It is connected to the positive power source + Vs via 6 and is also connected to the non-inverting input terminal of the inverting amplifier 21. Transistor 35
Is designed to have the same characteristics as the transistor 31, and the resistor 36 having the same resistance value as the resistor 32 is used. In the photodetector 11, the cathode is connected to the inverting input terminal of the inverting amplifier 21 and the anode is the negative power source −.
It is connected to Vs, converts an optical signal into a current signal, and inputs it to the inverting input terminal of the inverting amplifier 21.

When an optical signal is not input to the photodetector 11 and the output current of the photodetector 11 becomes zero, assuming that there is no offset of the inverting amplifier 21 itself, the output voltage of the inverting amplifier 21 is the transistor 35. Is almost the same as the bias potential applied to the non-inverting input terminal of the inverting amplifier 21 from the emitter of, and the offset generated by the transistor 31 of the feedback circuit is applied from the emitter of the transistor 35 to the non-inverting input terminal of the inverting amplifier 21. The offset is compensated by being canceled by the bias potential.

In the sixth and seventh embodiments, since the bases of the transistors 29 and 31 for applying the ground potential when the optical signal is not input are grounded via the resistor 17, strictly speaking, the optical signal is When not input, the base potentials of the transistors 29 and 31 and the transistors 33 and 35
However, since the resistance value of the ground-side resistor 17 is sufficiently smaller than that of the resistor 16, there is almost no problem.

FIG. 8 shows an eighth embodiment of the present invention. The eighth embodiment is an embodiment of the invention according to claims 1 and 8,
In the first embodiment, the first stage amplifier 12 is constituted by the non-inverting amplifier 38 which is a differential amplifier, and the feedback section 19 is constituted by an inverting amplifier which is a grounded-emitter attenuation amplifier. The type attenuation amplifier is a PNP type transistor 39 and resistors 40 and 41.
It is composed of

In the transistor 39, the base is connected to the output terminal of the first stage amplifier 38, and the emitter is the emitter resistor 4
0 is connected to the positive power supply + Vs, the collector is connected to the negative power supply −Vs via the collector resistor 41, and is connected to the feedback terminal 14 via the feedback resistor 20. The non-inverting amplifier 38 has a positive power supply terminal connected to the positive power supply + Vs, a negative power supply terminal connected to the negative power supply -Vs, an inverting input terminal grounded, and a non-inverting input terminal connected to the feedback terminal 14 and the photodetector. 11 connected to the anode.

The optical signal is converted into a current signal by the photodetector 11, converted into a voltage signal by the differential amplifier 38, and non-inverted and amplified. The output signal voltage of the differential amplifier 38 is
While being taken out from the output terminal 15, the signal is inverted and amplified by the transistor 39 constituting the grounded-emitter attenuation amplifier, and then fed back to the non-inverting input terminal 13 of the non-inverting amplifier 38 via the feedback resistor 20.

In the grounded-emitter attenuation amplifier, the input impedance is about β times that of the emitter resistance as in the case of the emitter follower, and a sufficiently high input impedance can be expected, and the output impedance has a resistance value higher than that of the emitter resistance 40. Collector resistance 4 set sufficiently small
A low resistance value of about 1 is obtained, which satisfies the above conditions well. The resistance value of the collector resistor 41 is the transistor 3
The time constant formed by the base-emitter capacitance of 9 does not affect the target band.

In the eighth embodiment, a feedback amplifier can be realized by using one transistor 39 instead of the differential amplifier, and the voltage dividing circuit by the resistors 16 and 17 is not necessary. Moreover, since the value of the collector resistance 41 of the transistor 39 can be set small, a high-speed response can be obtained even with the transistor 39 having a grounded emitter, and an active circuit including a feedback amplifier having high input impedance and low output impedance can be easily configured. It is possible to realize a high-performance non-inverting first-stage amplifier in which a high gain of a value obtained by multiplying the resistance value of the feedback resistor 20 by the ratio of the emitter resistance 40 and the collector resistance 41 of the transistor 39 can be obtained without lowering the band.

FIG. 9 shows a ninth embodiment of the present invention. The ninth embodiment is an embodiment of the invention according to claims 1 and 8,
In the eighth embodiment, instead of the PNP type transistor 39 and the resistors 40 and 41, an NPN type transistor 42 and resistors 43 and 44 which form a grounded-emitter attenuation amplifier are formed.
Is used. In the transistor 42, the base is connected to the output terminal of the first stage amplifier 38, the collector is connected to the positive power supply + Vs via the collector resistance 43, the emitter is connected to the negative power supply −Vs via the emitter resistance 44, and the feedback is provided. It is connected to the feedback terminal 14 via the resistor 20. The output signal voltage of the differential amplifier 38 is inverted and amplified by the transistor 42 forming the grounded-emitter attenuation amplifier, and then fed back to the non-inverting input terminal 13 of the non-inverting amplifier 38 via the feedback resistor 20. In the photodetector 11, the cathode is connected to the non-inverting input terminal of the non-inverting amplifier 38 and the anode is connected to the negative power source -Vs, and the optical signal is converted into a current signal to convert the non-inverting input of the non-inverting amplifier 38. Input to the terminal.

In the grounded-emitter attenuation amplifier using the transistor 42, the input impedance is about β times the emitter resistance as in the emitter follower, and a sufficiently high input impedance can be expected, and the output impedance is the collector resistance 43. In comparison, a low value such as the resistance value of the emitter resistor 44, whose resistance value is set to be sufficiently small, is obtained, and the above condition is satisfied well. Emitter resistor 44
Is set so that the time constant formed by the base-emitter capacitance of the transistor 42 does not affect the target band.

In the ninth embodiment, a feedback amplifier can be realized by using one transistor 42 instead of the differential amplifier, and the voltage dividing circuit by the resistors 16 and 17 is not required. In addition, since the value of the emitter resistance 44 of the transistor 42 can be set small, a high-speed response can be obtained even with the grounded-emitter transistor 42, and an active circuit including a feedback amplifier with high input impedance and low output impedance can be easily configured. It is possible to realize a high-performance non-inverting first-stage amplifier in which a high gain obtained by multiplying the resistance value of the feedback resistor 20 by the ratio of the emitter resistance 44 and the collector resistance 43 of the transistor 42 can be obtained without lowering the band.

In the sixth, eighth, and ninth embodiments, the current signal is input from the anode side of the photodetector 11 to the first-stage amplifier, but a current signal is input from the cathode side of the photodetector 11 to the first-stage amplifier. You may make it input a signal and connect the anode side of the photodetector 11 to a power supply.

In the eighth and ninth embodiments, since a bias voltage is required between the base and emitter of the transistors 39 and 42, the non-inversion of the first stage amplifier 38 is performed from the transistors 39 and 42 through the feedback resistor 20. The reference potential of the output voltage fed back to the input terminal differs from the potential of the non-inverting input terminal of the first stage amplifier 38, and an offset occurs. FIG. 10 shows a tenth embodiment of the present invention in which the offset is eliminated. The tenth embodiment is an embodiment of the invention described in claims 1, 8 and 9, and in the eighth embodiment, an offset compensation circuit is provided. The offset compensating circuit is composed of a bias circuit including an offset compensating PNP transistor 45 for canceling an offset and resistors 46 and 47.

In the transistor 45, the base is grounded, the emitter is connected to the positive power source + Vs via the emitter resistor 46, and the collector is the negative power source −via the collector resistor 47.
It is connected to Vs and also to the non-inverting input terminal of the non-inverting amplifier 38. Transistor 45 is transistor 3
9, the resistor 46 has the same resistance value as the resistor 40, and the resistor 47 has the same resistance value as the resistor 41.

Therefore, when the optical signal is not input to the photodetector 11 and the output current of the photodetector 11 becomes zero, assuming that there is no offset of the non-inverting amplifier 38 itself, the output of the non-inverting amplifier 38. Voltage is transistor 45
The bias potential applied to the inverting input terminal of the non-inverting amplifier 38 is substantially the same as the bias potential applied to the non-inverting amplifier 38, and the offset generated by the transistor 39 of the feedback circuit is the transistor 45.
The offset is compensated by being canceled by the bias potential applied from the collector to the inverting input terminal of the non-inverting amplifier 38.

FIG. 11 shows an eleventh embodiment of the present invention in which the offset is eliminated as in the tenth embodiment. The eleventh embodiment is an embodiment of the invention described in claims 1, 8 and 9, and an offset compensation circuit is provided in the ninth embodiment. This offset compensation circuit is composed of a bias circuit including an offset compensation NPN transistor 48 for canceling an offset and resistors 49 and 50.

In the transistor 48, the base is grounded, the collector is connected to the positive power source + Vs via the collector resistor 49, and the emitter is the negative power source −via the emitter resistor 50.
It is connected to Vs and also to the inverting input terminal of the non-inverting amplifier 38. Transistor 48 is transistor 42
It is designed so that the characteristics are the same, and the resistor 49 is the resistor 4
A resistor having the same resistance value as 3 is used, and a resistor 50 having the same resistance value as the resistor 44 is used.

When an optical signal is not input to the photodetector 11 and the output current of the photodetector 11 becomes zero, assuming that there is no offset of the non-inverting amplifier 38 itself, the output voltage of the non-inverting amplifier 38 is The bias potential applied from the collector of the transistor 48 to the inverting input terminal of the non-inverting amplifier 38 becomes almost the same as the bias potential of the transistor 4 of the feedback circuit.
The offset generated by 2 is canceled by the bias potential applied from the collector of the transistor 48 to the inverting input terminal of the non-inverting amplifier 38, and the offset is compensated. In addition, in the tenth and eleventh embodiments, the voltage dividing circuit including the resistors 16 and 17 is not used.
You may make it use the voltage division circuit which consists of resistors 16 and 17.

[0070]

As described above, according to the first aspect of the invention, a photodetector for converting an optical input signal into a current signal and an input terminal and a feedback terminal are connected to one connection point of the photodetector. In the optical signal detection circuit having the first stage amplifier
A feedback circuit unit including a feedback amplifier, which outputs the output voltage of the first-stage amplifier by dividing it at a constant ratio, and a feedback connected between the output terminal of the feedback circuit unit and the feedback terminal of the first-stage amplifier. , The impedance of the input terminal of the first-stage amplifier can be suppressed to a low level, and a high transimpedance can be obtained without degrading the high speed.

According to a second aspect of the invention, in the optical signal detection circuit of the first aspect, the first stage amplifier is a differential circuit in which an inverting input terminal and a feedback terminal are connected to one connection point of the photodetector. The feedback circuit section is configured by an inverting amplifier including an amplifier, and the feedback circuit section divides the output voltage of the first stage amplifier, and a non-inverting circuit provided between the output side of the voltage division circuit and the feedback resistor. Since it has an amplifier, it is possible to realize a high-impedance wideband first-stage amplifier that can obtain an inverted output for an optical signal.

According to a third aspect of the present invention, in the optical signal detection circuit of the first aspect, the first stage amplifier has a difference in which a non-inverting input terminal and a feedback terminal are connected to one connection point of the photodetector. The feedback circuit section is provided between the output side of the voltage division circuit and the feedback resistor, and the feedback circuit section is composed of a non-inverting amplifier composed of a dynamic amplifier and the feedback circuit section divides the output voltage of the first stage amplifier. Since it has an inverting amplifier, a high-transimpedance wideband first-stage amplifier that can obtain a non-inverting output for an optical signal can be realized.

According to the invention described in claim 4, in the optical signal detection circuit according to claim 1, the resistance value of the feedback resistor is set to the inter-terminal capacitance of the photo detector and the capacitance of the input terminal of the first stage amplifier. Since the bandwidth based on the time constant formed by the sum of the above and the feedback resistance value of the first stage amplifier exceeds the band of at least the first stage amplifier, the capacitance of the input terminal of the first stage amplifier and the light detection It is possible to select the resistance value of the feedback resistor to realize a wide-band first-stage amplifier with high transimpedance and to determine the required characteristics of the first-stage amplifier accordingly, from the sum of the capacitance between the terminals of the device.

According to the invention described in claim 5, in the optical signal detection circuit according to claim 1, the feedback circuit section is composed of two resistors for dividing the output voltage of the first-stage amplifier at a constant ratio. A voltage divider circuit and a feedback amplifier to which the output of the voltage divider circuit is input are provided, and the bandwidth based on the time constant formed by the input capacitance of the feedback amplifier and the parallel resistance value of the two resistors is at least. Since the setting is made so as to exceed the band of the feedback amplifier, a foothold for determining the resistance values of the two resistors can be obtained, and the characteristics of the first-stage amplifier necessary for widening the band can be determined.

According to the invention of claim 6, in the optical signal detection circuit of claim 2, since the non-inverting amplifier is an emitter follower, one amplifier is used instead of the differential amplifier for feedback amplifier. It is possible to easily realize an active circuit consisting of a feedback amplifier of high input impedance and low output impedance having a high-speed response of an emitter follower, and the resistance value of the feedback resistor is set to the emitter resistance and collector resistance of the transistor. It is possible to realize a high-performance inverting first-stage amplifier that can obtain a high gain of a value obtained by multiplying the ratio without lowering the band.

According to a seventh aspect of the invention, in the optical signal detection circuit of the sixth aspect, the transistor has the same characteristics as the transistor forming the emitter follower, and the emitter is a non-inverting terminal of the differential amplifier. Since it is equipped with a transistor that is connected to the negative power supply side through a resistor and whose base is grounded and the collector is connected to the positive power supply side, the offset that occurs in the transistor that constitutes the emitter follower Can be canceled.

According to an eighth aspect of the present invention, in the optical signal detection circuit of the first aspect, the feedback amplifier is formed by using a transistor forming a grounded-emitter attenuation amplifier, and the emitter and the power source of the transistor are used. Since the value of the first resistor connected to the power supply side is set to be larger than the value of the second resistor connected between the collector of the transistor and the power supply side, one differential resistor is used instead of the differential amplifier. A feedback amplifier can be realized by using a transistor, and a voltage dividing circuit by a resistor is not required. In addition, a transistor with a grounded emitter can also obtain a high-speed response, and an active circuit consisting of a feedback amplifier with high input impedance and low output impedance can be easily constructed, and the resistance value of the feedback resistor can be used as the emitter resistance and collector resistance of the transistor. It is possible to realize a high-performance non-inverting first-stage amplifier in which a high gain obtained by multiplying the ratio with is obtained without lowering the band.

According to a ninth aspect of the present invention, in the optical signal detection circuit of the eighth aspect, the resistor having the same characteristics as the transistor and the emitter having the same resistance value as the first resistor is provided. Is connected to the power supply side, the base is supplied with the ground potential, the collector is connected to the inverting terminal of the feedback amplifier, and the collector is connected to the power supply side via a resistor having the same resistance value as the second resistor. Since the integrated transistor is provided, it is possible to cancel the offset generated in the transistor forming the grounded-emitter attenuation amplifier.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a sixth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a seventh embodiment of the present invention.

FIG. 8 is a circuit diagram showing an eighth embodiment of the present invention.

FIG. 9 is a circuit diagram showing a ninth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a tenth embodiment of the present invention.

FIG. 11 is a circuit diagram showing an eleventh embodiment of the present invention.

FIG. 12 is a circuit diagram showing a conventional optical signal detection circuit.

[Explanation of symbols]

11 Photodetector 12 First Stage Amplifier 13 Input Terminal 14 Feedback Terminal 15 Output Terminal 16, 17, 23, 24, 27, 28, 30, 32, 3
4,36,40,41,43,44,46,47,4
9,50 Resistor 19 Feedback unit 20 Feedback resistors 21,22,25,26,38 Differential amplifier 29,31,33,35,39,42,45,48
Transistor

Claims (9)

[Claims] 1. An optical signal detection circuit having a photodetector for converting an optical input signal into a current signal, and an initial stage amplifier having an input terminal and a feedback terminal connected to one connection point of the photodetector. A feedback circuit unit including a feedback amplifier that divides the output voltage of the first-stage amplifier at a fixed ratio and outputs the feedback circuit, and a feedback circuit connected between the output terminal of the feedback circuit unit and the feedback terminal of the first-stage amplifier. An optical signal detection circuit comprising a resistor. 2. The optical signal detection circuit according to claim 1,
The first-stage amplifier is composed of an inverting amplifier composed of a differential amplifier in which an inverting input terminal and a feedback terminal are connected to one connection point of the photodetector, and the feedback circuit section divides the output voltage of the first-stage amplifier. An optical signal detection circuit having a voltage division circuit and a non-inverting amplifier provided between the output side of the voltage division circuit and the feedback resistor. 3. The optical signal detection circuit according to claim 1,
The first-stage amplifier is composed of a non-inverting amplifier composed of a differential amplifier in which a non-inverting input terminal and a feedback terminal are connected to one connection point of the photodetector, and the feedback circuit section outputs the output voltage of the first-stage amplifier. An optical signal detection circuit having a voltage dividing circuit for dividing voltage and an inverting amplifier provided between an output side of the voltage dividing circuit and the feedback resistor. 4. The optical signal detection circuit according to claim 1,
A bandwidth based on a time constant formed by a sum of the inter-terminal capacitance of the photodetector and the capacitance of the input terminal of the first stage amplifier and the feedback resistance value of the first stage amplifier is at least the bandwidth of the feedback resistor. An optical signal detection circuit that has a resistance value that exceeds the band of the first-stage amplifier. 5. The optical signal detection circuit according to claim 1,
The feedback circuit section includes a voltage divider circuit configured by two resistors that divide the output voltage of the first-stage amplifier at a constant ratio, and a feedback amplifier to which the output of the voltage divider circuit is input. An optical signal detection circuit, wherein a bandwidth based on a time constant formed by the input capacitance of the feedback amplifier and the parallel resistance value of the two resistors is set to exceed at least the bandwidth of the feedback amplifier. 6. The optical signal detection circuit according to claim 2,
An optical signal detection circuit, wherein the non-inverting amplifier comprises an emitter follower. 7. The optical signal detection circuit according to claim 6,
The emitter follower has the same characteristics as the transistor, the emitter is connected to the non-inverting terminal of the differential amplifier, and is also connected to the negative power source side via a resistor,
An optical signal detection circuit comprising a transistor whose base is connected to the ground potential and whose collector is connected to the positive power supply side. 8. The optical signal detection circuit according to claim 1,
The feedback amplifier is configured by using a transistor that forms a grounded-emitter attenuation amplifier, and the value of the first resistance connected between the emitter of the transistor and the power supply side is at least the collector of the transistor and the power supply side. An optical signal detection circuit characterized in that it is set to be larger than a value of a second resistor connected between the two. 9. The optical signal detection circuit according to claim 8,
The emitter is connected to the power supply side through a resistor having the same characteristics as the transistor and having the same resistance value as the first resistor, and a ground potential is given to the base to make the collector of the feedback amplifier. An optical signal detection circuit comprising a transistor connected to an inverting terminal and connected to a power supply side via a resistor having the same resistance value as the second resistor.