JPH10115552A - Optical detector and solid-state image sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical detector by which light is detected while a good SN ratio is ensured even when the greater part of the output current of a light-receiving element is occupied by a dark-current component. SOLUTION: A photoelectric conversion element 110 which receives light to be measured and a dummy photoelectric conversion element 120 whose dark- current characteristic is nearly identical to that of the photoelectric conversion element and which is shielded from light are arranged side. First, the mean value of dark currents generated by the dummy photoelectric conversion element 120 at a point of time close to a measuring pint of time is removed by a dark- current removal circuit 400, and the ratio of a dark-current component to a signal-current component is improved. In addition, an estimated residual-dark- current component in which a residual dark-current component is found in an adjacent point of time in terms of time is subtracted by a difference computing circuit 500, and a signal component is extracted. Therefore, while a good SN ratio is ensured, the signal component is extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector for measuring the intensity of light to be measured.

[0002]

2. Description of the Related Art For measuring the intensity of light to be measured, a semiconductor light receiving element such as a photodiode which generates a charge corresponding to the amount of received light of the light to be measured and outputs it as a current signal is frequently used. In measuring the amount of received light with high accuracy using such a light receiving element, the dark current of the light receiving element always poses a problem, and a method of reducing or removing the dark current according to the type of the light receiving element has been proposed.

[0003] As a proposed method, the dark current is
There is a method of cooling the light receiving element by paying attention to the fact that it is reduced when the operating temperature of the light receiving element is lowered (hereinafter referred to as conventional method 1). In addition, a dummy light receiving element that is shielded from light is provided, the dark current of the light receiving element that receives the light to be measured is evaluated, and the output current of the dummy light receiving element is calculated from the output current of the light receiving element that receives the light to be measured. A method of obtaining a current signal according to the intensity of the light to be measured by subtraction has been proposed (hereinafter, a method has been proposed).
Conventional method 2).

[0004]

In the conventional photodetector, the dark current component is reduced by the above-described method, and therefore, has the following problems.

[0005] In the conventional method 1, since it is necessary to provide a cooling unit for cooling the light receiving element, the photodetector becomes large-scale. Furthermore, when the dark current is reduced by cooling, it often occurs that a sufficient SN ratio cannot be secured when the light to be measured is weak.

In the conventional method 2, a certain SN ratio can be secured when the amount of current (hereinafter also referred to as signal current amount) generated by the reception of the light to be measured is substantially equal to the amount of dark current. The signal current amount is overwhelmingly smaller than the dark current amount,
For example, in the case of an InGaAs photodiode, it is impossible to secure a good SN ratio.

The present invention has been made in view of the above, and provides a photodetector capable of ensuring a good SN ratio even when a dark current component occupies most of the output current of a light receiving element. The purpose is to do.

Further, the present invention provides a solid-state imaging device capable of securing an excellent SN ratio and capturing an incident light image even when a dark current component occupies most of the output current of a light receiving element corresponding to a pixel. It is intended to provide a device.

[0009]

According to a first aspect of the present invention, there is provided a photodetector, comprising: (a) a first photoelectric conversion element for generating a charge corresponding to the intensity of incident light to be measured and outputting it as a current signal;
(B) a second photoelectric conversion element which has substantially the same dark current characteristics as the first photoelectric conversion element and is shielded from light;
When the light detection instruction signal is significant, the current signal output from the first photoelectric conversion element is input. When the light detection instruction signal is insignificant, the dark current output from the second photoelectric conversion element is input. An integration circuit for receiving a signal and integrating the first capacitance element connected between the input and output terminals in accordance with the integration instruction signal; and (d) inputting a dark current signal output from the second photoelectric conversion element. A dark current elimination circuit for obtaining an approximately average value of the dark current, and removing the approximately average value of the dark current from the current signal input to the integration circuit in response to the dark current elimination instruction signal; Input the output signal, and according to the subtraction instruction signal,
The first value of the output signal of the integration circuit after integrating the dark current signal from which the substantially average value of the dark current has been removed by the integration circuit for a predetermined time is retained, and the substantially average value of the dark current is removed for a predetermined time. A difference operation circuit that outputs a signal corresponding to a difference between a second value and a first value of an output signal of the integration circuit after integrating the current signal from the first photoelectric conversion element by the integration circuit; , (F) a timing generation circuit for outputting a light detection instruction signal, an integration instruction signal, a dark current removal instruction signal, and a subtraction instruction signal.

In the photodetector according to the first aspect, first, the current signal output terminal of the second photoelectric conversion element and the current signal input terminal of the integration circuit are connected, and the integration instruction signal is made insignificant, and the integration circuit is connected. Operate in the non-integration mode, make the dark current removal instruction signal insignificant, and input the dark current signal output from the second photoelectric conversion element to the dark current removal circuit. The dark current elimination circuit obtains a substantially average value of the dark current signal until the dark current elimination instruction signal becomes significant based on the input dark current signal and the output signal from the integration circuit during the non-integration operation.

Next, the dark current removal signal is regarded as significant, and the current signal flowing into the current signal input terminal of the integration circuit is calculated as follows.
A dark current removing circuit continuously removes a substantially average value of the obtained dark current.

In this state, the integration instruction signal is made significant, and
A current signal obtained by removing a substantially average value of a dark current from a current signal output from the second photoelectric conversion element is input to an integration circuit for a predetermined time and integrated, and charge is accumulated in the first capacitance element. After a lapse of a predetermined time, the subtraction instruction signal is temporarily made significant, and the integration result of the integration circuit at that time is held in the difference calculation circuit.

After that, the electric charge accumulated in the first capacitive element is reset, the light detection instruction signal is made significant, and the current signal output terminal of the first photoelectric conversion element is connected to the current input terminal of the integrating circuit. . Then, a current signal obtained by removing a substantially average value of a dark current from the current signal output from the first photoelectric conversion element is input to an integrating circuit for a predetermined time and integrated, and the electric charge is stored in the first capacitive element. I do. After a lapse of a predetermined time, the subtraction instruction signal is temporarily made significant, and the integration result of the integration circuit at that time is notified to the difference calculation circuit.

The difference calculation circuit that has received the notification calculates the integration result corresponding to only the previously held dark current component and the integration result corresponding to the sum of the signal component and the dark current component notified this time. Is calculated and output.

Thus, in the photodetector according to the first aspect, even though most of the output current signal from the photoelectric conversion element is a dark current component, first, most of the dark current component is detected at a point in time that is close in time. After removing the approximated average value of the obtained dark current to improve the ratio between the dark current component and the signal current component, the remaining dark current component is further obtained at a time closer in time. Since the signal component is extracted by subtracting the estimated residual dark current component, a good S / N ratio is secured and the signal component is extracted. By measuring the signal components extracted in this way, the received light intensity of the light to be measured is accurately measured.

According to a second aspect of the present invention, there is provided the photodetector according to the first aspect, wherein (i) the first photoelectric conversion element and the second
Is a photodiode whose cathode terminal is set to the reference potential, and (ii) the integration circuit outputs a current signal output from the first photoelectric conversion element and an output signal from the second photoelectric conversion element. An operational amplifier having a negative input terminal for inputting a dark current signal and a positive input terminal set to a reference potential is provided.

The dark current generated in the photodiode as the photoelectric conversion element increases as the bias voltage applied between the cathode terminal and the anode terminal increases.

According to a second aspect of the present invention, the cathode terminal of the photodiode serving as the photoelectric conversion element is set to the reference potential, and the anode terminal serving as the current signal output terminal is integrated with the reference potential in an imaginary short state. Since it is connected to the negative input terminal of the operational amplifier of the circuit, the bias voltage applied between the cathode terminal and the anode terminal can be reduced to the limit. Therefore, the absolute amount of the generated dark current is reduced. As a result, the SN ratio of the extracted signal component is improved.

According to a third aspect of the present invention, in the photodetector of the first aspect, the dark current elimination circuit comprises: (i) a source terminal connected to a current signal input terminal of the integration circuit; And (ii) a second capacitance element having a gate terminal connected to the first terminal and a second terminal set to the reference potential, (Iii) a first switch element having a gate terminal connected to the first terminal and a second terminal connected to the output terminal of the integration circuit, and opening and closing in response to a dark current removal instruction signal; It is characterized by having.

According to a third aspect of the present invention, in removing the substantially average value of the dark current, the dark current signal from the second photoelectric conversion element is input to the source terminal of the field effect transistor, and the dark current removal instruction is issued. An output signal of the integrating circuit at the time of non-integrating operation is input to the gate terminal of the field-effect transistor and the first terminal of the second capacitive element via the first switch element that closes when the signal is insignificant. As a result, the potential of the amount corresponding to the substantially average value of the dark current signal from the second photoelectric conversion element during the period when the dark current removal instruction signal is insignificant is set to the first terminal of the second capacitor, that is, The current generated at the gate terminal of the field effect transistor is removed from the current signal flowing into the current signal input terminal of the integrating circuit via the field effect transistor.

When the dark current removal instruction signal is significant, a potential value corresponding to a substantially average value of the previous dark current signal from the second photoelectric conversion element is applied to the first terminal of the second capacitor. Will be retained. Therefore, when the dark current removal instruction signal is significant, the substantially average value of the dark current when the previous dark current removal instruction signal is insignificant continues, and the current signal flowing into the current signal input terminal of the integration circuit. Removed from

According to a fourth aspect of the present invention, in the photodetector of the first aspect, (i) the first terminal is connected to the current output terminal of the first photoelectric conversion element, and the second terminal is connected to the current output terminal of the first photoelectric conversion element. A second switch element connected to the current input terminal of the integration circuit and closing when the light detection instruction signal is significant; (ii) a first switch element;
(Iii) a first terminal is connected to the current output terminal of the photoelectric conversion element, the second terminal is set to the reference potential, and the third switch element is closed when the light detection instruction signal is insignificant; ) The first output terminal of the second photoelectric conversion element is
And a second switch connected to the current input terminal of the integration circuit, the fourth switch element closing when the light detection instruction signal is insignificant, and (iv) a second photoelectric conversion element. A first terminal is connected to the current output terminal, a second terminal is set to the reference potential, and a fifth switch element that closes when the light detection instruction signal is significant is provided by a current signal path setting unit. It is further characterized by being provided.

In the photodetector according to the fourth aspect, the second switch element and the fourth switch element are exclusively closed, so that
The current signal output terminal of the first photoelectric conversion element and the current signal output terminal of the second photoelectric conversion element are exclusively connected to the current signal input terminal of the integration circuit. Further, while the second switch element and the third switch element are exclusively closed, the fourth switch element is closed.
Since the switch element and the fifth switch element are exclusively closed, the voltage applied between the cathode terminal and the anode terminal while the current signal output terminal is not connected to the current signal input terminal of the integration circuit is It is zero, and all generated charges are discharged to the reference potential. Therefore, only the charges generated when the current signal output terminal is connected to the current signal input terminal of the integration circuit are output to the integration circuit.

According to a fifth aspect of the present invention, the light to be measured is infrared light, and the photoelectric conversion element is a photodiode made of InGaAs.

The photoelectric conversion element has an infrared sensitivity.
In a photodiode made of GaAs, most of the output current signal is a dark current component. Therefore, it is particularly preferable to adopt the configuration of the photodetector of the first aspect.

According to a sixth aspect of the present invention, there is provided a solid-state imaging device, wherein the photodetectors of the first aspect are arranged one-dimensionally or two-dimensionally.

In the solid-state image pickup device according to the present invention, a photodetector corresponding to pixels arranged one-dimensionally or two-dimensionally is provided.
, And a good S value is obtained for each pixel.
A suitable input image is captured with the N ratio secured.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a photodetector and a solid-state imaging device according to the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a configuration diagram of an embodiment of the photodetector of the present invention. As shown in FIG. 1, this photodetector includes (a) a photoelectric conversion element 110 which is a photodiode which generates a charge corresponding to the intensity of the incident light to be measured and outputs it as a current signal; A photoelectric conversion element 120 having substantially the same dark current characteristics as the conversion element 110 and being a light-shielded photodiode; and (c) an output current signal of the photoelectric conversion element 110 and the photoelectric conversion element 120.
And the light detection instruction signal φ1 and the light non-detection instruction signal φ2 are input. If the light detection instruction signal φ1 is significant according to the light detection instruction signal φ1 and the light non-detection instruction signal φ2, A current signal selection circuit 20 that outputs an output current signal of the photoelectric conversion element 110 and outputs an output current signal of the photoelectric conversion element 120 when the light detection instruction signal φ2 is significant.
0, and (d) a signal output from the current signal selection circuit 200 is input and integrated into the capacitive element 310 connected between the input and output terminals according to the integration instruction signal SM, and according to the reset instruction signal R1. And (e) a dark current signal output from the photoelectric conversion element 120, an average value of the dark current is calculated, and a dark current removal instruction signal RM is input. , A dark current removing circuit 400 for removing a substantially average value of dark current from the current signal input to the integrating circuit 300, and (f) the integrating circuit 30
After the output signal from 0 is input and the dark current signal from which the substantially average value of the dark current has been removed for a predetermined time T is integrated by the integrating circuit 300 in accordance with the subtraction instruction signal SB, the light detection instruction signal φ1 becomes significant. After the value V1 of the output signal of the integration circuit 300 immediately before becomes, the current signal from the photoelectric conversion element 110 from which the substantially average value of the dark current has been removed for a predetermined time T is integrated by the integration circuit 300, and then light detection is performed. A difference operation for outputting a signal corresponding to the difference between the value V2 and the value V1 of the output signal of the integration circuit 300 immediately after the instruction signal φ1 becomes insignificant, and resetting the held value according to the reset instruction signal R2. A circuit 500, and (g) a light detection instruction signal φ1,
Light non-detection instruction signal φ2, integration instruction signal SM, reset instruction signal R1, dark current removal instruction signal RM, subtraction instruction signal S
B, and a timing generation circuit 600 for outputting a reset instruction signal R2.

The photoelectric conversion element 110 and the photoelectric conversion element 120
This differs from the photoelectric conversion element 120 in that the photoelectric conversion element 120 is shielded from light by the light shielding material 121, but has substantially the same dark current characteristics. Such matching of the dark current characteristics can be achieved by forming the photoelectric conversion elements 110 and 120 in adjacent regions of the same substrate in the same step. In addition, as a light shielding material, Au
And Al can be suitably used.

Photoelectric conversion element 110 and photoelectric conversion element 1
As for 20, in the case of infrared measurement, a photodiode made of InGaAs can be suitably used. In the following description, it is assumed that the dark current component occupies most of the current signal output from the photoelectric conversion element 110.

As shown in FIG. 1, the cathode terminals of the photoelectric conversion elements 110 and 120 are grounded, and the photoelectric conversion elements 110 and 120 output current signals from the anode terminals.

In the current signal selection circuit 200, (i) the first terminal is connected to the current output terminal of the photoelectric conversion element 110, and the second terminal is connected to the current input terminal of the integration circuit 300. The 210 switch element which closes when the instruction signal φ1 is significant, and (ii) the first terminal is connected to the current output terminal of the photoelectric conversion element 110, the second terminal is grounded, and the light non-detection instruction signal φ2 Switch element 220 that closes when is significant, and (iii) photoelectric conversion element 1
A switch element 230 having a first terminal connected to the current output terminal 20 and a second terminal connected to the current input terminal of the integration circuit 300, and closing when the light non-detection instruction signal φ2 is significant; iv) a switching element 240 having a first terminal connected to the current output terminal of the photoelectric conversion element 120, a second terminal grounded, and closing when the light detection instruction signal φ1 is significant.

The integrator circuit 300 includes: (i) an operational amplifier 320 which receives the current signal output from the current signal selection circuit 200 from the negative input terminal 321 and has the positive input terminal 322 grounded; and (ii) an operational amplifier. A capacitive element 310 to which the negative input terminal 321 of the first capacitor 320 and the first terminal are connected;
(Iii) A switch element 330 that has a second terminal connected to the first terminal of the capacitive element 310 and a second terminal connected to the output terminal 323 of the operational amplifier 320, and that opens and closes in response to the integration instruction signal SM. And (iv) the operational amplifier 320
And a switch element 340 connected to the output terminal 323 of the operational amplifier 320 and connected to the negative input terminal 321 of the operational amplifier 320 to open and close in response to the reset instruction signal R1.

The dark current removing circuit 400 includes (i) a field effect transistor 410 having a source terminal connected to a current signal input terminal of the integrating circuit 300 and a drain terminal grounded, and (ii) a field effect transistor 410. The gate terminal of the capacitor 420 is connected to the first terminal, the second terminal is grounded, the capacitor 420 is connected to the first terminal, and (iii) the gate terminal of the field effect transistor 410 is connected to the first terminal. Is connected to the output terminal of the integration circuit 300, and includes a switch element 430 that opens and closes in response to the dark current removal instruction signal RM.

The difference calculation circuit 500 includes (i) the integration circuit 3
A switch element 510 that inputs the signal output from the first terminal 00 to the first terminal and opens and closes in response to the subtraction instruction signal SB;
(Ii) a capacitive element 520 for inputting a signal output from the second terminal of the switch element 510 to the first terminal;
i) the current signal output from the second terminal of the capacitive element 520 is input from the negative input terminal 531 and the positive input terminal 532 is grounded; and (iv) the negative input terminal 531 of the operational amplifier 530. And the first terminal are connected, and the second terminal is connected to the output terminal 533 of the operational amplifier 530. (v) The negative input terminal 531 of the operational amplifier 530 is connected to the first terminal. And a switch element 550 having a second terminal connected to the output terminal 533 of the operational amplifier 530 and opening and closing in response to the reset instruction signal R2.

The photodetector of this embodiment measures the amount of received light of the light to be measured as follows. FIG. 2 is a timing chart showing the operation of the photodetector of the present embodiment. In FIG. 2, the light detection instruction signal φ1, the light non-detection instruction signal φ2, the integration instruction signal SM, the reset instruction signal R1, the subtraction instruction signal SB, and the reset instruction signal R
2 is significant at a high level, each signal closes a switch element controlling opening and closing, and a low level is insignificant, each signal opens a switching element controlling opening and closing. On the other hand, the dark current elimination signal RM is insignificant at a high level, and the switch element 430 is closed, and is significant at a low level, and the switch element 430 is opened.

In the photodetector of this embodiment, first, the timing generation circuit 600 generates the photodetection instruction signal φ1, the integration instruction signal SM, the reset instruction signal R1, the dark current removal instruction signal RM, and the subtraction instruction signal SB. In addition to making it insignificant, the light non-detection instruction signal φ2 and the reset instruction signal R
2 is output as significant and set to the initial state. As a result, the switching elements 210 and 240 are opened, and the switching elements 220 and 230 are opened.
Is closed, the current signal output terminal of the photoelectric conversion element 110 is grounded, and the current signal output terminal of the photoelectric conversion element 120 is connected to the current signal input terminal of the integration circuit 300 and the source of the field effect transistor 410 of the dark current removal circuit 400. Connected to terminal. Further, since the switch element 430 is closed, the signal output terminal of the integration circuit 300 is connected to the gate terminal of the field effect transistor 410 and the first terminal of the capacitor 420. Further, the switch element 550 is closed.

In this state, the cathode terminal of the photoelectric conversion element 120 is grounded, and the anode terminal, which is the current signal output terminal, is connected to the ground level and the negative input terminal 321 of the operational amplifier 320 of the integration circuit 300 in an imaginary short state. , The bias voltage applied between the cathode terminal and the anode terminal is substantially reduced to the limit. Therefore, the absolute amount of the generated dark current is reduced.

When a dark current is generated in the photoelectric conversion element 120 in this state, the dark current flows through the field effect transistor 410. Then, a gate potential at which a substantially average value of the amount of dark current flows through the field effect transistor 410 is generated at the first terminal of the capacitor 420.

Next, the timing generation circuit 600 makes the dark current removal instruction signal RM significant. As a result, the gate potential corresponding to the approximate average value of the amount of dark current immediately before the dark current removal instruction signal RM is made significant is held at the first terminal of the capacitor 420. Thereafter, the dark current removal circuit 400 The approximate average value of the dark current amount is continuously extracted from the current flowing into the current signal input terminal of the circuit 300.

Subsequently, after the timing generation circuit 600 makes the integration instruction signal SM significant, the reset instruction signal R1
Is temporarily significant.

Thereafter, the photoelectric conversion element 1
A current signal obtained by removing a substantially average value of dark current from the current signal output from 20 is input to the integration circuit, and the inflowing charge is accumulated in the capacitor 310. The electric charge accumulated in the capacitor 310 is an integral value of a dark current time T that cannot be extracted by the dark current removing circuit 400.

Next, the timing generation circuit 600 sets the subtraction instruction signal SB to be temporarily significant, and
By temporarily closing the switch element 510 of 00, the output value V1 of the integration circuit 300 at that time is held in the capacitance element 520 of the difference calculation circuit 500.

Subsequently, the timing generation circuit 600 makes the light non-detection instruction signal φ2 insignificant, and makes the light detection instruction signal φ1 significant. As a result, the switching element 210
And the switch element 240 is closed, and the switch element 220 is closed.
And the switch element 230 are opened, and the photoelectric conversion element 1
The current signal output terminal 20 is grounded, and the current signal output terminal of the photoelectric conversion element 110 is connected to the current signal input terminal of the integration circuit 300 and the source terminal of the field effect transistor 410 of the dark current removal circuit 400.

In this state, the cathode terminal of the photoelectric conversion element 110 is grounded, and the anode terminal, which is the current signal output terminal, is connected to the ground level and the negative input terminal 321 of the operational amplifier 320 of the integration circuit 300 in an imaginary short state. To the photoelectric conversion element 120
As in the case of (1), the bias voltage applied between the cathode terminal and the anode terminal is reduced to the limit. Therefore, the same dark current generation condition as that of the photoelectric conversion element 120 is realized, and the absolute amount of the generated dark current is reduced.

Next, the reset instruction signal R1 is temporarily made significant, and the electric charge accumulated in the capacitor 310 is released.
After that, the photoelectric conversion element 110
A current signal obtained by removing a substantially average value of a dark current from the current signal output from is input to the integration circuit 300, and the inflowing charge is accumulated in the capacitor 310. The charge accumulated in the capacitor 310 is obtained by integrating the photoelectric conversion element 1 with the integrated value of the dark current that cannot be extracted by the dark current removing circuit 400 over time T.
Numeral 10 denotes the sum of the signal current corresponding to the received light to be measured and the integrated value over time T of the signal current.

The current signal obtained by removing the substantially average value of the dark current from the current signal output from the photoelectric conversion element 110 is the sum of the dark current component and the signal current component, but the dark current component occupies the entire current. The ratio is much lower than the ratio of the dark current component in the current signal output from the photoelectric conversion element 110.

The time T of the current signal obtained by removing the substantially average value of the dark current from the current signal output from the photoelectric conversion element 110
As a result of the integration over the range, the value V of the output signal of the integration circuit 300 is
2 is V2 = V1 ′ + V3 (1) where V1 ′ is a contribution value of a dark current component and V3 is a contribution value of a signal current component. As described above, since most of the dark current in the current signal at the time of output from the photoelectric conversion element 110 has been removed from the current signal to be integrated, V1 '>> V
The relationship of 3 does not hold.

By the way, as described above, the integration circuit corresponding to the integration over the time T of the current obtained by removing the substantially average value of the dark current amount from the dark current output from the photoelectric conversion element 120 having substantially the same dark current characteristics as described above. Since the output value of 300 is V1, V1 '≒ V1. Therefore, V2 = V1 + V3 (2) is a very good approximation. Hereinafter, this approximation will be adopted.

In parallel with the integration operation by the integration circuit 300 of the current signal obtained by removing the substantially average value of the dark current from the current signal output from the photoelectric conversion element 110, the reset instruction signal R2 is made insignificant and the switch element 550 is set. To release.

After integration of the current signal from which the average value has been removed,
The subtraction instruction signal SB is temporarily made significant, the switch element 510 of the difference calculation circuit 500 is temporarily closed, and the output value V2 of the integration circuit 300 is transmitted to the capacitance element 520. As a result, charges corresponding to the value V3 (= V2−V1) are accumulated in the capacitor 540, and the output value V3 is output as the output of the difference calculation circuit. From equation (2), the output value V3 reflects the amount of received light of the measurement target light.

As described above, since V1 >> V3 is not satisfied, the value V3 obtained by calculating the difference between the value V2 and the value V1 can be obtained by securing a good SN ratio and receiving the light to be measured. Reflects the quantity. Therefore, by sampling the value V3, the amount of received light of the light to be measured can be measured at a high SN ratio.

After sampling the value V3, the timing generation circuit 600 returns each signal to the initial state, and prepares for the next measurement.

That is, in the photodetector of this embodiment,
Even if most of the output current signal from the photoelectric conversion element is a dark current component, first, the dark current component and the signal current are removed by removing the approximate average value of the dark current obtained at a point in time that is close in time. After improving the ratio with the component, the signal component is extracted by subtracting the estimated residual dark current component obtained when the remaining dark current component is further closer in time, so that a good SN ratio is secured. To extract signal components. By measuring the signal components thus extracted, the received light intensity of the light to be measured can be accurately measured.

By arranging the photodetectors of this embodiment one-dimensionally or two-dimensionally and making each detector correspond to a pixel, the majority of the output current signal from the photoelectric conversion element is a dark current component. Even when such a photoelectric conversion element is used, it is possible to realize a one-dimensional or two-dimensional solid-state imaging element that executes a suitable input image capturing while securing a good SN ratio.

The present invention is not limited to the above embodiment, but can be modified. For example, even when the dark current component does not occupy most of the output current of the photoelectric conversion element, the photodetector of the present invention can be used, and the light reception amount of the light to be measured can be measured with extremely high accuracy. it can.

[0058]

As described above in detail, according to the photodetector of the present invention, the photoelectric conversion element for receiving the light to be measured, and the light-shielded dummy photoelectric conversion element having substantially the same dark current characteristic as the photoelectric converter. The conversion elements are juxtaposed, first, the average value of the dark current generated by the dummy photoelectric conversion element at the time point close to the measurement time point is removed, and the ratio between the dark current component and the signal current component is improved. Since the signal component is extracted by subtracting the estimated residual dark current component obtained when the remaining dark current component is further approached in time, the signal component is extracted while securing a good SN ratio. As a result, without using cooling, even when using a photoelectric conversion element in which most of the output current signal from the photoelectric conversion element is a dark current component,
It is possible to measure the amount of received light of the measurement target light while securing a good SN ratio.

Since the solid-state imaging device of the present invention employs the photodetector of the present invention in accordance with each pixel, the photoelectric conversion device in which most of the output current signal from the photoelectric conversion device is a dark current component. Even when an element is used, a suitable one-dimensional or two-dimensional imaging of an input image can be realized while securing the SN ratio.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photodetector according to an embodiment of the present invention.

FIG. 2 is a timing chart illustrating the operation of the photodetector according to the embodiment of the present invention.

[Explanation of symbols]

110, 120: photoelectric conversion element, 121: light shielding material, 20
0: current signal selection circuit, 210, 220, 230, 24
0: switch element, 300: integrating circuit, 310: capacitive element, 320: operational amplifier, 330, 340: switch element, 400: dark current removing circuit, 410: field-effect transistor, 420: capacitive element, 430: switch element, 5
00: difference operation circuit, 510, 550: switch element,
530: Differential amplifier, 520, 540: Capacitance element, 60
0: timing generation circuit.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 5/335 H01L 31/10 G

Claims (6)

[Claims] A first photoelectric conversion element for generating an electric charge according to the intensity of the incident light to be measured and outputting the same as a current signal; and a dark current characteristic substantially equal to that of the first photoelectric conversion element. When the light-shielded second photoelectric conversion element and the light detection instruction signal are significant, the current signal output from the first photoelectric conversion element is input, and when the light detection instruction signal is insignificant, An integration circuit that inputs a dark current signal output from the second photoelectric conversion element and integrates the dark current signal into a first capacitance element connected between input and output terminals in accordance with an integration instruction signal; A dark current signal output from the photoelectric conversion element is input, and a substantially average value of the dark current is obtained, and a substantially average value of the dark current is calculated from a current signal input to the integration circuit according to a dark current removal instruction signal. A dark current elimination circuit for eliminating An output signal from the integrating circuit is input, and the dark current signal from which the substantially average value has been removed for a predetermined time is integrated by the integrating circuit according to a subtraction instruction signal. And a second output signal of the integration circuit after integrating the current signal from the first photoelectric conversion element from which the substantially average value has been removed over the predetermined time by the integration circuit while retaining the value of 1 A difference calculation circuit for outputting a signal corresponding to a difference between the first value and the first value; and a timing for outputting the light detection instruction signal, the integration instruction signal, the dark current removal instruction signal, and the subtraction instruction signal. A light detection device, comprising: a generation circuit. 2. The first photoelectric conversion element and the second photoelectric conversion element.
Is a photodiode having a cathode terminal set to a reference potential, and the integration circuit outputs a current signal output from the first photoelectric conversion element and an output current signal from the second photoelectric conversion element. The photodetector according to claim 1, further comprising an operational amplifier having a negative input terminal for inputting a dark current signal and a positive input terminal set to the reference potential. 3. The dark current elimination circuit includes: a field effect transistor having a source terminal connected to a current signal input terminal of the integration circuit and a drain terminal set to a reference potential; and a gate of the field effect transistor. A second capacitor having a terminal connected to the first terminal, a second terminal set to a reference potential, and a gate terminal of the field-effect transistor connected to the first terminal; The light detection device according to claim 1, further comprising: a first switch element connected to an output terminal of the integration circuit, and opened and closed in response to a dark current removal instruction signal. 4. A first terminal is connected to a current output terminal of the first photoelectric conversion element, and a second terminal is connected to a current input terminal of the integration circuit. And a second switch element that is closed in the case of: a first terminal is connected to a current output terminal of the first photoelectric conversion element, and a second terminal is set to the reference potential; Closed when is insignificant
A first terminal is connected to a current output terminal of the second photoelectric conversion element, a second terminal is connected to a current input terminal of the integration circuit, and the light detection instruction signal is A fourth switch element that is closed when significant, a first terminal connected to a current output terminal of the second photoelectric conversion element, a second terminal set to the reference potential, and the light detection instruction The light detection device according to claim 1, further comprising: a current signal selection circuit including: a fifth switch element that closes when the signal is significant. 5. The photodetector according to claim 1, wherein the light to be measured is infrared light, and the photoelectric conversion element is a photodiode made of InGaAs. 6. A solid-state imaging device, wherein the photodetectors according to claim 1 are arranged one-dimensionally or two-dimensionally.