JP3155191B2 - Low light measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weak light measuring device and a weak light measuring method suitable for measuring extremely weak scattered light.

[0002]

2. Description of the Related Art Ultra-low light detection technology is expected to be applied to a wide range of fields such as biology, medical field, and astronomy field, and the development of high-sensitivity light receiving elements for realizing this is being pursued. Conventionally, to detect extremely weak light, a photomultiplier tube (PM
T) has been used, but the quantum efficiency is as small as several percent or less, and since it is an electron tube, its dimensions are large, and there are many applications that require cooling, but it is difficult to cool it to below minus 80 degrees. Was.

[0003] For these reasons, recently, it has become important to develop a semiconductor light receiving element capable of easily achieving a quantum efficiency of about 90%. On the other hand, for example, in an application for detecting extremely weak light emitted from a living body, the living body light source does not emit light only in a specific direction, but emits light in all directions from its surface. For this reason, it is not possible to condense light with a lens. Therefore, it is preferable to use a large-diameter light receiving element of, for example, several tens of millimeters in order to increase sensitivity. In such a light receiving element, a considerable current (dark current) flows even when light is not detected due to imperfections of the element. In order to reduce this dark current and at the same time reduce the effects of background light, cooling of the elements and devices is performed. Even under the current situation where such measures are taken, the characteristics have not yet reached sufficient to detect weak light from a living body with sufficient accuracy. In addition, compound semiconductors such as GaAs, InGaAs, and InP are often used for detecting light having an emission wavelength of 0.5 to 1.7 μm, but at the present stage, the diameter is about 10 mmφ even in the world. No element having a maximum receiving diameter of the maximum was manufactured.

As described above, the development of the light receiving element itself is important, but on the other hand, it is also important to devise a circuit for maximizing the performance of the light receiving element. 2. Description of the Related Art Conventionally, a high-resistance type light-receiving circuit and a charge storage type light-receiving circuit are known as light-receiving circuits that measure incident light incident on the semiconductor light-receiving element using the semiconductor light-receiving element.

FIG. 12 is a principle circuit diagram (a) of a high resistance type light receiving circuit, its equivalent circuit diagram (b), and a diagram (c) showing its characteristics. The high-resistance type light receiving circuit is employed in many optical receivers including optical communication, and here only the basic part is shown. As shown in FIG. 12A, a high resistance (here, 100M) is connected in series with a photodiode (here, PIN photodiode) 1.
Ω), and a bias voltage is applied to both ends of the load resistors 2 in opposite directions to the photodiodes by a bias power supply 3. Then, t = 0 (sec)
It is assumed that a predetermined amount of light is incident on the photodiode 1 and a constant current of iT flows through this circuit.

The equivalent circuit at this time is represented as shown in FIG. That is, the photodiode 1 is connected to the resistor 1
a and the junction capacitance 1b.
The load resistor 2 is connected in parallel to the (resistor 1a and the junction capacitor 1b), and a constant current iT flows from the constant current source 3 'to the parallel circuit starting from t = 0. At this time, the voltage (output voltage V _out ) between both ends of the parallel circuit changes as shown in the graph of FIG. The output voltage V _out is mainly determined by the resistance value of the load resistor 2 and the flowing current iT. Therefore, by measuring the output voltage V _out after rising, the amount of light incident on the photodiode 1 is measured.

Although this high-resistance type light receiving circuit has an advantage that it has superior responsiveness as compared with the charge storage type light receiving circuit described below, it also has the disadvantage that the load resistance generates thermal noise and is susceptible to noise. have. FIG. 13 is a principle circuit diagram (a) of the charge storage type light receiving circuit, its equivalent circuit diagram (b), and a diagram (c) showing its characteristics. FIG.
The difference from the high-resistance type light receiving circuit shown in FIG.

In this charge storage type light receiving circuit, a load capacitance (here, 3 pF) 4 is connected in series with the photodiode 1 instead of the load resistor 2 shown in FIG.
Therefore, when the constant current iT flows after the time point of t = 0, as shown in FIG. 13C, the output voltage V _out has a value much larger than that of the high-resistance type light receiving circuit. In the case of this charge storage type, mainly the load capacitance 4 and the junction capacitance 1b,
The rising speed of the output voltage _Vout is determined by the current value iT. Therefore, in the charge storage type, the integrated voltage is observed at a time after a predetermined measurement time has elapsed since t = 0, so that the photodiode 1 Is measured. In the case of the charge storage type light receiving circuit, the responsiveness is inferior to that of the high resistance type light receiving circuit, but the pulse noise is averaged over time, which is advantageous for measuring weak light.

FIG. 14 is a circuit diagram showing a configuration example of a weak light detection circuit employing a charge storage type light receiving circuit. A dual junction FET 21 composed of two junction FETs 21a and 21b having uniform characteristics;
Two resistors 22 connected between the respective sources of the junction FETs 21 a and 21 b and the ground line 5.
The differential amplifier 20 is constituted by a and 22b. The drains of these two junction FETs 21a and 21b are connected to each other, a power supply 6 is arranged between the drain and the ground line 5, and a predetermined power supply voltage (here, 5V) is applied.

Further, between the gate of the junction FET 21a, which is one of the signal input terminals 20a of the differential amplifier 20, and the ground line 5, the PIN is arranged such that the gate side is a cathode and the ground line 5 side is an anode.
The photodiode 1 is connected. Also, this PI
A MOSFET 7 is connected in parallel with the N photodiode 1. The MOSFET 7 has a role of a switch for short-circuiting between the anode and the cathode of the PIN photodiode 1. When a reset signal is input to the gate of the MOSFET 7, the PIN photodiode 1 is short-circuited, and the measurement start time At t = 0, the reset signal is released, and after the time t = 0, the reset signal is transmitted through the optical filter 8 and P
The photocurrent caused by the signal light incident on the IN photodiode 1 is input to one first signal input terminal 20 a of the differential amplifier 20. Further, a predetermined reference signal is input to the gate of the junction FET 21b, which is the other second signal input terminal 20b of the differential amplifier 20. In the differential amplifier 20, two signal input terminals 20a,
The difference between the two signals input from 20b is amplified and output. This output signal is input to, for example, a next-stage differential amplifier (not shown) and further amplified.

The weak light detection circuit shown in FIG.
Although the load capacitance for storing the photocurrent generated in the IN photodiode 1 is not shown, the PIN photodiode 1
(Junction capacitance 1b shown in FIG. 13), MOSFE
T7 drain-source capacitance, junction FET
The gate-source capacitance 21a corresponds to the load capacitance 4 (including the junction capacitance 1b) shown in FIG.

FIG. 15 shows a plurality of PIN photodiodes 1 shown in FIG.
FIG. 16 is a circuit diagram showing a weak light detection circuit composed of three PIN photodiodes 1a, 1b, and 1c. FIG. 16 shows a plurality (three in this case) of PIN photodiodes 1 shown in FIG. PIN photodiode 1a,
FIG. 3 is a circuit diagram showing a weak detection circuit constituted by 1b and 1c.

As shown in FIG. 15 and FIG.
When N photodiodes are connected in series or in parallel with each other, pulse noise generated uncorrelatedly in the PIN photodiode with respect to the signal light and the background light input to each PIN photodiode in the same phase becomes relatively small, S /
N (signal-to-noise ratio) is improved, which is advantageous for detecting weak light. Whether a plurality of PIN photodiodes are connected in series or in parallel depends on the nature of the signal light (high output and
The short-time signal changes depending on the low output / long time signal.

[0014]

A very weak signal light emitted from an object to be measured, such as a biological sample, is incident on the PIN photodiode 1, but from the object to be measured, only the signal light is emitted. However, background light is also emitted due to heat radiation, and the background light also enters the PIN photodiode 1. Even if an optical filter 8 is provided on the front surface of the PIN photodiode 1 so that only the light of the wavelength component of the signal light is incident on the PIN photodiode 1, the background light due to heat radiation is spread over a wide wavelength region, and the background light Among them, the wavelength component that is the same as the wavelength of the signal light passes through the optical filter 8 together with the signal light and enters the PIN photodiode 1. At this time, there is no problem if the intensity of the signal light is sufficiently higher than the intensity of the background light that cannot be completely removed by the optical filter 8, but, for example, if the extremely weak light emitted from the biological sample is used as the signal light, There is a problem that the signal light is buried even in the background light transmitted through the optical filter 8, and the signal light cannot be measured with sufficient accuracy.

The present invention has been made in view of the above circumstances, and as described above, even if the signal light is weak enough to be buried in the background light component in the same wavelength region, the weak light capable of measuring the signal light can be measured. It is an object of the present invention to provide a measuring device and a method for measuring weak light using the weak light measuring device.

[0016]

According to a first aspect of the present invention, there is provided a low-light-level measuring apparatus comprising: (1-1) two signal input terminals having two signal input terminals; A differential amplifier that amplifies the difference between two signals and outputs the amplified signal. (1-2) Each of the two signal input terminals of the differential amplifier that are connected in the same direction when viewed from each of the two signal input terminals 2 with photodiode
And two light receiving circuits.

According to a second embodiment of the present invention, there is provided a low-light level measuring apparatus according to the present invention, comprising: (2-1) two signal input terminals having a difference between two signals input from the two signal input terminals. Amplifier that amplifies and outputs the signal. (2-2) One of the two signal input terminals of the differential amplifier is connected to one of the two signal input terminals in opposite directions as viewed from the one of the signal input terminals. And a light receiving circuit having two diodes.

Here, in the first and second weak light measuring devices according to the present invention, the light receiving circuit accumulates electric charge flowing through a photodiode provided in the light receiving circuit and is generated by the accumulation of the electric charge. It is preferably a charge storage type light receiving circuit that transmits a voltage to a signal input terminal of a differential amplifier circuit. This is because a charge storage type that is resistant to noise is advantageous for measuring weak light.

As the photodiode, a PIN photodiode can be typically preferably used because of its high light receiving sensitivity. When a PIN photodiode is used as the photodiode, it is preferable that the light receiving circuit includes a bias circuit that applies a reverse bias voltage to the photodiode provided in the light receiving circuit. This is because, when a reverse bias is applied to the PIN photodiode, a depletion layer in which the p-type impurity and the n-type impurity hardly exist is formed in the i-layer, and the sensitivity to incident light is further increased.

Each of the photodiodes may be composed of a plurality of photodiodes connected in series with each other, or may be composed of a plurality of photodiodes connected in parallel with each other. . In these cases, the S / N (signal-to-noise ratio) is improved as described above. In addition, it is preferable that an optical filter for guiding light having a desired wavelength to the photodiode and removing light having a wavelength other than the desired wavelength be provided on the front side of the light receiving surface of the photodiode. This is because it is preferable that signal light having as high an S / N ratio as possible is incident on the photodiode.

Further, in the first and second weak light measuring devices according to the present invention, the light receiving circuit and the differential amplifier are housed in a container whose inside is cooled. A light having a desired wavelength among incident lights to be incident on a photodiode provided in a light receiving circuit housed in the container is made incident, and light having a wavelength other than the desired wavelength among the incident lights is not absorbed or absorbed. It is preferred to have an entrance window with a reflective optical filter. As described above, by cooling the photodiode or the like, the dark current can be reduced, and light reception with good S / N can be performed.

Further, in the first and second weak light measuring devices of the present invention, the light receiving circuit, the differential amplifier, and the optical filter are housed in a container whose inside is cooled. It is preferable to have an entrance window through which light of a desired wavelength, which is at least the wavelength of a signal, of the incident light to be incident from the outside of the container toward the optical filter accommodated in the container. Instead of using an optical filter for the entrance window, or using an optical filter for the entrance window, storing the optical filter inside the container and cooling the optical filter itself, the heat radiation generated from the optical filter itself This is because the background light can be reduced.

In the first and second weak light measuring devices according to the present invention, the relative position of the photodiode with respect to the incident light incident on the photodiode is determined by:
It is preferable to include a position changing unit that alternates between the photodiodes. This is because an error due to a variation in the photodiode, a light receiving circuit including the photodiode, or the like can be suppressed by performing the measurement while changing the position.

Further, the first method for measuring weak light according to the present invention, which achieves the above object, has a first weak light measuring apparatus according to the present invention, that is, having two input signal terminals, A differential amplifier that amplifies and outputs a difference between two input signals, and is connected to each of two signal input terminals of the differential amplifier in the same direction as viewed from each of the two signal input terminals. A weak light measuring device provided with two light receiving circuits having respective photodiodes. The first light and the second light emitted from the measured object and the reference object, respectively, having different emission levels of predetermined signal light from each other. Is simultaneously incident on each photodiode of the two light receiving circuits.

Further, a second weak light measuring device of the present invention for achieving the above object has a second weak light measuring device of the present invention, that is, having two input signal terminals and having two input signal terminals. A differential amplifier that amplifies and outputs a difference between two input signals, and a signal input terminal of one of the two signal input terminals of the differential amplifier as viewed from the one signal input terminal. A weak light measuring device including a light receiving circuit having two diodes connected in opposite directions to each other is prepared, and first and second light emitting levels of a predetermined signal light emitted from the measured object and the reference object, respectively, are different from each other. The light and the second light are simultaneously incident on each of the two photodiodes of the light receiving circuit.

Here, typically, the measured object itself emits a signal light to be measured and emits a background by heat radiation of a predetermined light amount (predetermined temperature). Is selected from materials whose background light emission level due to thermal radiation is equal to that of the object to be measured, and which does not emit signal light. Here, in the first and second methods for measuring weak light of the present invention, it is preferable that the photodiode to which the first light is incident and the photodiode to which the second light is incident are alternately changed. . This is to reduce errors due to variations in photodiodes and the like.

[0027]

Embodiments of the present invention will be described below. FIG. 1 is a circuit diagram showing a first example of a weak light measurement circuit incorporated in an embodiment of the weak light measurement device of the present invention. Differences from the above-described conventional example (see FIGS. 18 and 19) will be described.

In the weak detection circuit shown in FIG.
Is disposed between the drains of the junction FETs 21a and 21b and the negative power supply line 51,
The resistors 12a and 22b are connected to the junction FET 21a,
It is arranged between 21b and the minus power supply line 51. A dual junction FET 21 is constituted by the junction FETs 21a and 21b.

The second signal input terminal 20b of the differential amplifier 20 also has a PI when viewed from the second signal input terminal 20b and a PI when viewed from the first signal input terminal 20a.
P should be the same as the direction of N photodiode 1
IN photodiode 11 is connected, and this PI
A MOSFET 71 is connected in parallel with the N photodiode 11. This MOSFET 71 is a MOSFET
7, a reset signal is input at the same timing. An optical filter 81 is provided on the front surface of the PIN photodiode 11. The optical filter 81 has the same characteristics as the optical filter 8 and receives a background light emitted from a reference body (described later), and transmits the same wavelength component of the background light as the wavelength of the signal light. Then, the light enters the PIN photodiode 11. The weak light detection circuit shown in FIG. 1 is provided with two PIN photodiodes 1 and 11, and the PIN photodiode 1 has both the background light and the signal light emitted from the object to be measured, and the PIN photodiode. Only the background light emitted from the reference body is made incident on the photodiode 11 and the difference between them is amplified and output by the differential amplifier 20, so that the influence of the background light is canceled even if the background light exists. Thus, only the signal light can be measured with high sensitivity.

FIG. 2 is a diagram showing the result of measuring the terminal voltage of the PIN photodiode while cooling it. In the weak light detection circuit shown in FIG. 1, a bias voltage is not positively applied to the PIN photodiodes 1 and 11;
When cooled to K, a voltage of about 0.7 V is generated.
The IN photodiode is biased to enable higher sensitivity operation. Alternatively, as described later, even when a bias voltage is positively applied, a bias voltage is set in consideration of a cooling temperature and a terminal voltage generated at the cooling temperature.

FIG. 3 is a structural diagram of a weak light measuring device including the weak light measuring circuit shown in FIG. The PIN photodiodes 1, 11, the differential amplifier 20, and the optical filters 8, 81 are housed in a container 100, and the inside of the container 100 is cooled down to, for example, 50K. This container 100
Has an entrance window 101. In addition, this container 100
Another container 110 is located at a position facing the entrance window 101 of FIG.
In the container 110, a living body sample, for example, a white blood cell, an object to be measured 120 made of an aqueous solution of a drug or the like that stimulates the white blood cell, and a dummy reference body 130 are arranged. The measured object 120 emits signal light from stimulated white blood cells in addition to background light due to thermal radiation. On the other hand, in the temperature environment composed of the reference body 130, it is placed in the same environment as the measured body 120, and emits background light having the same spectral distribution and the same light level as the background light emitted from the measured body 120. However, the reference body 130 does not include white blood cells in this example, and does not emit signal light.

An emission window 111 made of an optical material that transmits signal light and background light is formed at the bottom of the container 110, and the signal light and the background light emitted from the body 120 to be measured are transmitted through the container 110. Through the exit window 111 of the container 100, enters the container 100 from the entrance window 101 of the container 100, and the optical filter 8 allows the signal light to pass through as it is and the background light allows only the wavelength component equal to the wavelength of the signal light to pass through. Incident on the PIN photodiode 1. On the other hand, reference body 13
The background light emitted from 0 exits from the exit window 111 and enters from the entrance window 101, and only the wavelength component equal to the wavelength of the signal light is transmitted by the optical filter 81 and enters the PIN photodiode 11. Each photocurrent is generated in each of the photodiodes 1 and 11 by the respective incident light of the PIN photodiodes 1 and 11, and a signal corresponding to a difference between signals due to the respective photocurrents is output from the differential amplifier 20.

Here, the container 100 or the weak light detection circuit (at least the PIN photodiodes 1, 11) accommodated in the container 100 is rotated to alternately change the arrangement positions of the PIN photodiodes 1, 11 or Even if the positions of the PIN photodiodes 1 and 11 are fixed, the signal light and the reference light emitted from the measured object 120 are incident on the PIN photodiode 11 and emitted from the reference body 130 by rotating the container 110. When the obtained background light is incident on the PIN photodiode 1, errors due to variations in the PIN photodiodes 1, 11 and the like are cancelled, and more accurate measurement can be performed.

Here, the exit window 111 and the entrance window 10 are used.
1 is described on the assumption that the filter does not play a role not only for the signal light but also for the background light and is transparent,
An optical filter may be provided as the exit window 111 or the entrance window 101 so as to cut back light as much as possible. At this time, the background light is sufficiently cut by the optical filter provided as the exit window 111 or the entrance window 101, and the background light due to the heat radiation emitted from the exit window 111 or the entrance window 101 itself does not cause a problem. For example, the optical filters 8 and 81 shown in FIG. 3 may be omitted.

Hereinafter, various examples of the weak light measurement circuit that can be used in the present invention will be described. 4 and 5 are circuit diagrams showing a second example and a third example of the weak light measurement circuit. FIG.
In the circuit example shown in FIG. 1, the PIN photodiodes 1 and 11 in the circuit example shown in FIG. 1 are each composed of a plurality of (three in this case) PIN photodiodes 1 connected in series.
a, 1b, 1c; 11a, 11b, 11c. In the circuit example shown in FIG. 5, a plurality of PIN photodiodes 1 and 11 in the circuit example shown in FIG. (Three each) PIN photodiodes 1a, 1b, 1c; 11a, 11b, 11c. As described above, when a plurality of PIN photodiodes are connected in series or in parallel, the S / N ratio is improved, and it becomes possible to measure the weak light with higher accuracy.

FIG. 6 is a circuit diagram showing a fourth example of the weak light measuring circuit. Compared with the circuit example shown in FIG. 1, bias power supplies 31 and 32 are added. When the bias power supplies 31 and 32 are provided and a reverse bias power supply is added to the PIN photodiodes 1 and 11, a pure i-layer (depletion layer) is formed and measurement with higher sensitivity becomes possible.

FIGS. 7 and 8 are circuit diagrams showing fifth and sixth examples of the weak light measuring circuit. Compared with the circuit example shown in FIG. 1, the bias power supplies 31 and 3 are similar to the circuit example shown in FIG.
2 and each of the PIN photodiodes 1 and 11, respectively, as in the circuit examples shown in FIGS.
A plurality of PIN photos 1a connected in series or in parallel,
1b, 1c; 11a, 11b, 11c.

Bias power supplies 31, 32; 31a, 31
b, 31c; action of arranging 32a, 32b, 32c, and replacing each PIN photodiode 1, 11 with a plurality of PIN photodiodes 1a, 1b, 1;
c; the effects of the configuration of 11a, 11b, and 11c are as described above, and redundant description will be omitted. FIG. 9 is a circuit diagram showing a seventh example of the weak light measurement circuit.

In this circuit example, one of the two signal input terminals 20a and 20b of the differential amplifier 20 is connected to the first signal input terminal 20a in a direction opposite to each other when viewed from the first signal input terminal 20a. Are connected to each other, and the other second signal input terminal 20b is configured to receive a reference signal.

In the circuit examples shown in FIGS. 1 and 4 to 8 described above, the PIN photodiode 1 which receives the background light and the signal light emitted from the measured object and the background light emitted from the reference body PIN photodiode 1 with incident light
1 are connected to different signal input terminals 20a and 20b, and the difference (background light cancellation) is performed by the differential amplifier 20, but in the circuit example shown in FIG. The background light component and the incident light of the PIN photodiode 11, that is, the background light, are canceled before being input to the differential amplifier 20, and only the signal component due to the signal light is input to the differential amplifier 20.

FIGS. 10 and 11 show an eighth example of the weak light measuring circuit.
FIG. 15 is a circuit diagram showing a ninth example. A plurality (three in this case) of PIN photodiodes 1a, connected in series (in the case of FIG. 10) or in parallel (in the case of FIG. 11), respectively.
1b, 1c; 11a, 11b, 11c.

As shown in these circuits, in the present invention, variously configured circuits can be employed.

[0043]

As described above, according to the present invention,
Weak signal light can be measured with high sensitivity while eliminating the influence of background light.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first example of a weak light measurement circuit incorporated in an embodiment of the weak light measurement device of the present invention.

FIG. 2 is a diagram showing a result of measuring a terminal voltage of a PIN photodiode while cooling the PIN photodiode.

FIG. 3 is a structural diagram of a weak light measuring device including the weak light measuring circuit shown in FIG. 1;

FIG. 4 is a circuit diagram showing a second example of the weak light measurement circuit.

FIG. 5 is a circuit diagram showing a third example of the weak light measurement circuit.

FIG. 6 is a circuit diagram showing a fourth example of the weak light measurement circuit.

FIG. 7 is a circuit diagram showing a fifth example of the weak light measurement circuit.

FIG. 8 is a circuit diagram showing a sixth example of the weak light measurement circuit.

FIG. 9 is a circuit diagram showing a seventh example of the weak light measurement circuit.

FIG. 10 is a circuit diagram illustrating an eighth example of the weak light measurement circuit.

FIG. 11 is a circuit diagram showing a ninth example of the weak light measurement circuit.

12A is a principle circuit diagram of a high-resistance type light receiving circuit, FIG. 12B is an equivalent circuit diagram thereof, and FIG. 12C is a diagram showing its characteristics.

13A is a principle circuit diagram of a charge storage type light receiving circuit, FIG. 13B is an equivalent circuit diagram thereof, and FIG. 13C is a diagram showing its characteristics.

FIG. 14 is a circuit diagram showing a configuration example of a weak light detection circuit employing a charge storage type light receiving circuit.

FIG. 15 shows a PIN photodiode 1 shown in FIG.
A plurality (three in this case) of PINs connected in series to each other
FIG. 3 is a circuit diagram illustrating a weak light detection circuit including photodiodes 1a, 1b, and 1c.

FIG. 16 is a circuit diagram showing a weak detection circuit in which the PIN photodiode 1 is composed of a plurality (three in this case) of PIN photodiodes 1a, 1b, and 1c connected in parallel to each other.

[Explanation of symbols]

1, 1a, 1b, 1c, 11, 11a, 11b, 11c
PIN photodiode 7, 71 MOSFET 8, 81 Optical filter 20 Differential amplifier 20a First signal input terminal 20b Second signal input terminal 21 Dual junction FET 21a, 21b Junction FET 22a, 22b Resistance 31, 31a, 31b, 31c , 32,32a, 32
b, 32c Bias power supply 51 Negative power supply line 61 Power supply 100, 110 Container 101 Incident window 111 Exit window 120 DUT 130 Reference object

Continuation of front page (56) References JP-A-4-186127 (JP, A) JP-A-62-192635 (JP, A) JP-A-3-111724 (JP, A) JP-A-61-108931 (JP, A) JP-A-6-29567 (JP, A) Japanese Utility Model Application Laid-Open No. 61-195428 (JP, U) Japanese Utility Model Application Laid-open No. 62-155351 (JP, U) International Publication 90/8946 (WO, A1) International Publication 90 / 6597 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01J 1/16 G01J 1/42-1/46 G01N 21/00-21/01 G01N 21/17-21/74

Claims (10)

(57) [Claims] A differential amplifier having two signal input terminals for amplifying and outputting a difference between two signals input from the two signal input terminals; and a differential amplifier for each of two signal input terminals of the differential amplifier. , Said 2
Two light receiving circuits each having a photodiode connected to the same direction when viewed from each of the two signal input terminals and receiving each light emitted from the measured object and the reference body; and A weak light measuring device comprising a position changing means for alternately changing a relative position with respect to incident light incident on a photodiode between the photodiodes. 2. A differential amplifier having two signal input terminals and amplifying a difference between two signals input from the two signal input terminals and outputting the amplified signal, of the two signal input terminals of the differential amplifier A light receiving circuit having two photodiodes respectively connected to one of the signal input terminals in opposite directions as viewed from the one signal input terminal and receiving light emitted from the measured object and the reference body, respectively. And a position changing means for alternately changing the relative position of the photodiode with respect to the incident light incident on the photodiode between the photodiodes. 3. The light-receiving circuit is a charge-storage-type light-receiving circuit that accumulates a charge flowing through a photodiode provided in the light-receiving circuit and transmits a voltage generated by the accumulation of the charge to the signal input terminal. The weak light measuring device according to claim 1 or 2, wherein: 4. The weak light measuring device according to claim 1, wherein the photodiode is a PIN photodiode. 5. An apparatus according to claim 4, wherein said light receiving circuit includes a bias circuit for applying a reverse bias voltage to a photodiode provided in said light receiving circuit. 6. The weak light measuring device according to claim 1, wherein each of the photodiodes comprises a plurality of photodiodes connected in series. 7. The weak light measuring device according to claim 1, wherein each of the photodiodes comprises a plurality of photodiodes connected in parallel with each other. 8. An optical filter for guiding light having a desired wavelength to the photodiode and removing light having a wavelength other than the desired wavelength is provided on a front surface side of a light receiving surface of the photodiode. Item 6. The weak light measuring device according to item 1 or 2. 9. The light receiving circuit and the differential amplifier,
The inside is stored in a container to be cooled, and the container has a desired wavelength of incident light from the outside of the container, which is to be incident on the photodiode provided in the light receiving circuit stored in the container. The weak light measuring device according to claim 1 or 2, further comprising an incident window provided with an optical filter that receives light and absorbs or reflects light having a wavelength other than the desired wavelength out of the incident light. 10. The light receiving circuit, the differential amplifier, and the optical filter are housed in a container whose inside is cooled, and the container is directed from the outside of the container to the optical filter housed in the container. 9. The weak light measuring device according to claim 8, further comprising an incident window through which at least the light having the desired wavelength out of the incident light to be incident.