JP2000182263A - Photo-detecting device, and device for detecting quantum wobbling level of light beam and wobbling of light intensity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect light with a high sensitivity, low noise and at high speed by current-voltage conversion after current amplification by an operational amplifier having a current amplifying part in a feedback loop. SOLUTION: To convert a current signal converted by a photo-electric converting element into a voltage signal, the current signal is inputted to an inversion input terminal 2a of an operational amplifier 2. This inversion input terminal 2a is connected with an output terminal 2c of the operational amplifier 2 via a current amplifier 3, and forms a feedback loop. Non-inversion input terminal 2b is grounded. For the current amplifier 3, a Darlington connection connecting two transistors 3a, 3b in series is used, and current-voltage conversion is operated via a resister R1 put in series with the collectors of both transistors 3a, 3b. Here, the operational amplifier is preferred to be of FET input, that is excellent in having low input equivalent current noise, and has a large effect in an S/N when amplifying the current of the operational amplifier input part with a large amplification factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed, high-sensitivity, low-noise photodetector, a quantum fluctuation level detector of a light beam, and a light intensity fluctuation detector applied to a high-precision optical measurement device and the like. .

[0002]

2. Description of the Related Art As a conventional photodetector, FIGS.
1 is known. In the device illustrated in FIG. 8, when light energy hν strikes the photodiode 100, a photoelectromotive force is generated, and a weak current is generated. The photoelectrically converted current is directly subjected to current-voltage conversion (IV conversion) using the resistor 101. In this technique, there is a problem that the response speed is reduced when trying to increase the gain (amplification rate).

[0003] The device shown in FIG.
The current photoelectrically converted by 0 is subjected to IV conversion using an operational amplifier (op-amp) 102. A resistor 103 is negatively connected to the operational amplifier 102 in order to stabilize the operation of the circuit. The gain of current-voltage conversion is determined by the resistor 103. The use of such an operational amplifier results in a faster response speed than the device shown in FIG. 8, but there is a problem of noise (operational amplifier noise and thermal noise) and response degradation at a high gain. These noises are caused by voltage fluctuations due to free electron motion and thermal motion.

The device shown in FIG. 10 uses a transistor as a current amplifying means. An NPN junction transistor 106, an NPN junction transistor 107 and a PN
The P-junction transistor 108 is used in a connected form. The current is amplified by this transistor, and it is subjected to IV conversion through a resistor 109 to obtain an output voltage. In this device, there is a problem of response deterioration due to the input impedance of the current amplifier.

The device shown in FIG. 11 is a device for measuring light fluctuation. The DC component is directly subjected to IV conversion by a resistor 110, and the AC component is passed through a capacitor 111 to an operational amplifier 11.
This is a technique of flowing to the 3 side and performing IV conversion with a resistor 112.
In this device, thermal noise (current component) of a resistor receiving a direct current (DC) is superimposed on an alternating current (AC), and the problem of noise is large. Further, there is a problem that the frequency is cut off at a frequency determined by the resistor 110 and the capacitor 111, and fluctuation of low frequency cannot be measured.

[0006]

Therefore, the first aspect of the present invention
It is an object of the present invention to provide a photodetector capable of detecting light with high sensitivity and high speed with low noise.

A second object of the present invention is to provide a light beam quantum fluctuation level detecting device capable of detecting light quantum fluctuations in a wide band at high speed.

A third object of the present invention is to provide a light intensity fluctuation detecting device capable of detecting light intensity fluctuation with high accuracy.

[0009]

Means for Solving the Problems A first method for solving the above problems is described below.
The present invention relates to a photodetector that amplifies a photocurrent generated from a photoelectric conversion element and then converts the photocurrent into a voltage signal, wherein the current is amplified by an operational amplifier having a current amplifying unit in a negative feedback loop, and then the current-voltage conversion is performed. A photodetector characterized in that:

In a preferred embodiment, (1) the current amplifying section is a transistor, more preferably, the transistor is Darlington connection, (2) the operational amplifier is an FET input, and (3) current-voltage conversion. The method is that a resistor is provided in series with the collector of the transistor. (4) The method of current-voltage conversion is that the current-voltage conversion circuit is composed of an operational amplifier having the transistor collector as a negative input. .

A second invention for solving the above-mentioned problem is to provide two photoelectric conversion elements which separately receive two light beams split by a beam splitter, and to provide a current of each of the photoelectrically converted by the two photoelectric conversion elements. A circuit for obtaining a difference current;
An optical beam quantum fluctuation level detecting device, comprising: a circuit for amplifying a current by an operational amplifier having a current amplifying unit in a negative feedback loop and thereafter performing a current-voltage conversion.

[0012] As a preferred embodiment of the present invention, (1)
The current amplifying unit is composed of two current amplifying units capable of amplifying positive and negative currents, (2) the current amplifying unit is a transistor, more preferably, the transistor is a Darlington connection, and (3) the operational amplifier is an FET. (4) the current-voltage conversion method is a resistor provided in series with the collector of the transistor, and (5) the current
-The voltage conversion method is a current-voltage conversion circuit composed of an operational amplifier having a negative input to the collector of the transistor.

According to a third aspect of the present invention, there is provided a photodetector having a current amplifying unit directly connected to a photoelectric conversion element, wherein a change in a potential difference between two output terminals of the photoelectric conversion element when light is incident is described. A photodetector having a voltage control unit that operates so as to eliminate the photodetector.

According to a fourth aspect of the present invention, a means for obtaining a difference current between a photocurrent generated from a photoelectric conversion element and a current generated from a constant current generator, and means for performing current-voltage conversion by an operational amplifier are provided. It is a light intensity fluctuation detection device characterized by having, as a preferred embodiment, the constant current generator is connected to a constant voltage source with a resistance higher than the differential resistance of the PN junction of the light emitting element to be detected. is there.

[0015]

Embodiments of the present invention will be described below.

According to a first aspect of the present invention, there is provided a photodetector for amplifying a photocurrent generated from a photoelectric conversion element and thereafter converting the photocurrent into a voltage signal. , And, if necessary, an “operational amplifier”), and then perform current-voltage conversion. A preferred embodiment is shown in FIGS.

In FIG. 1, reference numeral 1 denotes a photoelectric conversion element;
When the light energy hν is received by the photoelectric conversion element 1, it is converted into a weak photocurrent (current signal). Although a photodiode is used as the photoelectric conversion element 1 in this embodiment, an avalanche photodiode, a photoelectric tube, or the like may be used. In the following description, an example using a photodiode will be described.

The current signal converted by the photoelectric conversion element 1 is
It is input to an inverting input terminal (negative terminal) 2a of the operational amplifier 2 for conversion into a voltage signal. The inverting input terminal 2a is connected to the output terminal 2c of the operational amplifier 2 via the current amplifier 3 to form a negative feedback loop. The non-inverting input terminal 2b is grounded.

In the present embodiment, a transistor is used as the current amplifier 3 as the simplest configuration, and a Darlington connection in which two such transistors 3a and 3b are connected in series is employed. In the illustrated example, the output terminal 2c of the operational amplifier 2 is connected to the emitter of the transistor 3a.

By employing the Darlington connection as described above, the degree of current amplification can be increased.

The collectors of the transistors 3a and 3b are provided with a resistor R1 in series. The output voltage is obtained. That is, the resistor R1 provided in series with the collectors of the transistors 3a and 3b is employed as a current-voltage conversion method.

FIG. 2 shows an embodiment of FIG. 1 in which a resistor R2 is provided in a negative feedback loop of an operational amplifier 4 provided separately in place of the output by the resistor R1, and an output voltage is obtained from an output terminal 4c. It is. A diode D1 is provided on the base side of the transistor so that it can be connected to the operational amplifier 4 at an appropriate potential. In this manner, transistor 3
Signals from the collectors a and 3b are input to the inverting input terminal 4a. The non-inverting input terminal 4b is grounded. The embodiment shown in FIG. 2 employs an IV conversion circuit composed of an operational amplifier 4 having negative inputs to the collectors c1 and c2 of the transistors to perform current-voltage conversion.

In the example shown in FIG. 2, two PNP-junction transistors are connected. However, the present invention is not limited to this.
NPN connected in Darlington as shown in FIG.
An embodiment using the junction transistors 3c and 3d may be used. Alternatively, as shown in FIG.
An embodiment in which NPN junction transistors 3f and 3g connected in parallel may be used.

In the embodiment shown in FIGS.
Preferably, it is an ET input. This configuration is excellent in that the input equivalent current noise is small as compared with the transistor input, and this configuration in which the current of the operational amplifier input section is amplified with a large amplification factor has a great effect in terms of the S / N ratio.

According to a second aspect of the present invention, there is provided a circuit for providing two photoelectric conversion elements for separately receiving two light beams split by a beam splitter and obtaining a difference current between currents photoelectrically converted by the two photoelectric conversion elements. A light beam quantum fluctuation level detection device characterized by having a circuit for current amplification by an operational amplifier having a current amplification unit in a negative feedback loop, and thereafter performing a current-voltage conversion. This is shown in FIG.

In FIG. 4, reference numeral 5 denotes a beam splitter. The configuration of the beam splitter is not particularly limited, as long as a light beam incident from a certain direction can be split into two beams having the same light amount. The two light beams split by the beam splitter 5 are received by respective photoelectric conversion elements (photodiodes) 6a and 6b, and are respectively photoelectrically converted.

In this embodiment, a circuit for obtaining a difference current between the currents converted by the photoelectric conversion elements 6a and 6b is provided. Since the same amount of the photocurrent generated by the photoelectric conversion elements 6a and 6b is passed from 6a to 6b connected in series, a difference current is obtained from the contact point between 6a and 6b.

The difference current obtained as described above is input to the inverting input terminal 8a of the operational amplifier 8 having the current amplifier 7 in the negative feedback loop, and the current is amplified.

The current amplifying section 7 preferably comprises two current amplifying sections capable of amplifying positive and negative currents. More preferably, the current amplifying section 7 is a transistor.
Furthermore, that the transistor is Darlington connection,
It is more preferable because the measurement can be performed with high sensitivity.

The operational amplifier 8 is an FET input,
This is preferable because it improves noise performance.

The current amplified as described above is then subjected to current-voltage conversion. In the illustrated embodiment, an IV conversion circuit comprising an operational amplifier 9 having a negative input to the collector of the transistor is used as the conversion method. Has been adopted. By employing such a circuit, it is possible to measure a fluctuation signal that changes to both positive and negative poles.

When the same amount of light is incident on the photoelectric conversion elements 6a, 6b, the minute difference current becomes the standard quantum fluctuation level of the light beam before splitting by the beam splitter. Since the configuration is such that amplification is performed as it is and then voltage conversion is performed, it is possible to provide a light beam quantum fluctuation level detection device capable of detecting light quantum fluctuations in a wide band and at high speed.

According to a third aspect of the present invention, in a photodetector having a current amplifying unit directly connected to a photoelectric conversion element, an operation is performed so as to eliminate a fluctuation in a potential difference between two output terminals of the photoelectric conversion element when light is incident. A photodetector comprising a voltage controller. A preferred embodiment of the present invention is shown in FIG.
And in FIG.

The device shown in FIG. 5 is different from the conventional device shown in FIG. 10 in that the non-inverting input terminal 12b of the operational amplifier 12 receives a potential fluctuating with the current signal converted by the photoelectric conversion element 10,
The output 12c of the operational amplifier 12 is controlled via the capacitor 11 so that both ends of the photoelectric conversion element fluctuate by the same displacement. This operates to eliminate the fluctuation of the potential difference between the two output terminals of the photoelectric conversion element at the time of light incidence, so that it is possible to prevent deterioration in responsiveness due to the parallel capacitance component of the photodiode, and to achieve high speed and high sensitivity. Light detection becomes possible.

The configuration of the Darlington-connected transistor circuit shown in FIG. 5 may be replaced with a plurality of transistor circuits provided in parallel as shown in FIG.

According to a fourth aspect of the present invention, there are provided means for obtaining a difference current between a photocurrent generated from a photoelectric conversion element and a current generated from a constant current generator, and means for performing current-voltage conversion by an operational amplifier. This is a light intensity fluctuation detecting device, and FIG. 7 shows a preferred embodiment.

In FIG. 7, reference numeral 13 denotes a constant current generating unit corresponding to a DC photocurrent of the photoelectric conversion element 14. The constant current generating unit 13 includes a PN of a light emitting element to be detected as a constant voltage source.
It is preferable to connect a resistor R4 higher than the differential resistance of the junction. The reason is that the noise of the constant current becomes a current noise smaller than the quantum fluctuation level of light emitted from the light emitting element, and a good S / N ratio can be obtained in measuring the quantum characteristics of light.

The photocurrent signal converted by the photoelectric conversion element 14 merges with the above-described constant current, cancels the photoelectrically converted DC component, and transmits the signal to the resistor R5 provided in the negative feedback loop of the operational amplifier 14. It is configured so that only the fluctuation amount of the beam intensity can be detected. In this configuration, the DC component of the photocurrent can be cut with a very low noise constant current, so that it is possible to detect light intensity fluctuation with high accuracy.

Although each of the above-described inventions has been described as a device for detecting a photocurrent, their configurations can be applied to other sensors (for example, IC temperature sensors) having a small current output as they are.

[0040]

According to the present invention, a photodetector capable of detecting light with high sensitivity, high speed and low noise, a quantum fluctuation level detector for a light beam capable of detecting photon fluctuation in a wide band and high speed, and a light intensity fluctuation with high accuracy Can be provided.

[Brief description of the drawings]

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

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

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

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

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

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

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

FIG. 8 is a circuit diagram showing a conventional example.

FIG. 9 is a circuit diagram showing a conventional example.

FIG. 10 is a circuit diagram showing a conventional example.

FIG. 11 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1: photoelectric conversion element 2: operational amplifier 2a: inverted input terminal 2b: non-inverted input terminal 2c: output terminal 3: current amplifier 3a, 3b, 3c, 3d, 3e, 3f, 3g: transistor 4: operational amplifier 4c: Output terminal 4a: inverting input terminal 4b: non-inverting input terminal 5: beam splitter 6a, 6b: photoelectric conversion element 7: current amplifier 8: operational amplifier 8a: inverting input terminal 9: operational amplifier 10, 14: photoelectric conversion element 11 : Capacitor 12: Operational amplifier 12a: Inverting input terminal 12b: Non-inverting input terminal 13: Constant current generator 15: Operational amplifier D1: Diode R1, R2, R3, R4, R5: Resistance

Claims (16)

[Claims] 1. A photodetector for amplifying a photocurrent generated from a photoelectric conversion element and thereafter converting the photocurrent to a voltage signal.
A photodetector characterized in that current is amplified by an operational amplifier having a current amplifier in a negative feedback loop, and then current-voltage conversion is performed. 2. The photodetector according to claim 1, wherein the current amplifier is a transistor. 3. The photodetector according to claim 2, wherein the transistor has a Darlington connection. 4. The photodetector according to claim 1, wherein the operational amplifier is an FET input. 5. The photodetector according to claim 1, wherein the method of current-voltage conversion is a resistor provided in series with the collector of the transistor. 6. The current-voltage conversion circuit according to claim 1, wherein the current-voltage conversion method is a current-voltage conversion circuit comprising an operational amplifier having a negative input to the collector of the transistor.
5. The photodetector according to any one of 4. 7. A circuit for providing two photoelectric conversion elements for separately receiving two light beams split by a beam splitter and obtaining a difference current between currents photoelectrically converted by the two photoelectric conversion elements, and a negative feedback. An optical beam quantum fluctuation level detecting device, comprising: a circuit for amplifying a current by an operational amplifier having a current amplifying unit in a loop, and thereafter performing a current-voltage conversion. 8. A current amplifying unit capable of amplifying positive and negative currents.
8. The apparatus for detecting a quantum fluctuation level of a light beam according to claim 7, comprising two current amplifiers. 9. An apparatus for detecting a quantum fluctuation level of a light beam according to claim 7, wherein the current amplifier is a transistor. 10. An apparatus for detecting a quantum fluctuation level of a light beam according to claim 7, wherein the transistor has a Darlington connection. 11. An apparatus for detecting a quantum fluctuation level of a light beam according to claim 7, wherein the operational amplifier is an FET input. 12. An apparatus for detecting a quantum fluctuation level of a light beam according to claim 7, wherein the method of current-voltage conversion is a resistor provided in series with the collector of the transistor. 13. The current-voltage conversion circuit is a current-voltage conversion circuit comprising an operational amplifier having a negative input to the collector of the transistor.
12. The apparatus for detecting a quantum fluctuation level of a light beam according to any one of claims 11 to 11. 14. A photodetector having a current amplifying section directly connected to a photoelectric conversion element, wherein a voltage control section operable to eliminate a fluctuation in a potential difference between two output terminals of the photoelectric conversion element when light is incident. A photodetector, comprising: 15. A light intensity fluctuation detecting device, comprising: means for obtaining a difference current between a photocurrent generated from a photoelectric conversion element and a current generated from a constant current generating unit; and means for converting current to voltage by an operational amplifier. . 16. The light intensity fluctuation detecting device according to claim 15, wherein the constant current generator is connected to a constant voltage source with a resistance higher than a differential resistance of a PN junction of a light emitting element to be detected.