JPH0451774B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a photodetection device that amplifies and outputs only signal light of the photocurrent photoelectrically converted by a photoelectric conversion element such as a photodiode. Regarding.

[Conventional technology]

In general, in a photodetection device consisting of a photoelectric conversion element such as a photodiode and an amplifier that converts and amplifies the photocurrent photoelectrically converted by the photoelectric conversion element, the signal light to be detected is simultaneously detected.
When disturbance light such as sunlight is incident on a photoelectric conversion element, it is necessary to amplify and output only the photocurrent caused by the signal light.

In particular, when the signal light is AC modulated light or pulse modulated light and the disturbance light is DC light or light with a frequency considerably lower than the frequency of the signal light, in the amplifier circuit, the DC component and the By removing low frequency components, only the photocurrent caused by the signal light can be extracted and output.

FIGS. 3 and 4 are configuration diagrams of this type of conventional photodetecting device.

The photodetection device shown in FIG. 3 includes a photoelectric conversion element 50 such as a photodiode, an amplifier 51 that converts and amplifies the photocurrent photoelectrically converted by the photoelectric conversion element 50, and is connected in series to the output terminal of the amplifier 51. A coupling capacitor 52 is connected to the coupling capacitor 52.

In the photodetector having the configuration shown in FIG. 3, an AC voltage component due to the signal light from the amplifier 51, a DC voltage component due to the disturbance light, and a low frequency voltage component are input to the coupling capacitor 52. Since only the AC voltage component caused by the disturbance light is passed through and output, the voltage component caused by the disturbance light can be removed.

Further, the voltage detection device shown in FIG. 4 includes a photoelectric conversion element 5
0, an amplifier 51 that converts and amplifies the photocurrent photoelectrically converted by the photoelectric conversion element 50,
A low-pass filter 62 passes a DC voltage component and a low-frequency voltage component of the output voltage from the amplifier 51, and a voltage-current converter converts the DC voltage component and low-frequency voltage component from the low-pass filter 62 and inputs negative feedback to the amplifier 51. It is equipped with an amplifier 63 for

In the voltage detection device shown in FIG. 4, the DC voltage component and low frequency voltage component due to the disturbance light from the amplifier 51 are input as negative feedback to the amplifier 51 via the low-pass filter 62 and the amplifier 63, so that the output of the amplifier 51 is DC voltage components and low frequency voltage components caused by disturbance light can be removed from the voltage.

[Problem that the invention seeks to solve]

However, in the photodetector shown in FIG. 3, the amplifier 51 outputs both the AC voltage component due to the signal light, the DC voltage component due to the disturbance light, and the low frequency voltage component, and then the coupling capacitor 52 outputs the DC voltage component. Since the low-frequency voltage component is removed, when the amount of disturbance light is large, a photocurrent exceeding the dynamic range of the amplifier 51 is applied to the amplifier 51, and the output characteristics of the amplifier 51 become saturated, causing the output to decrease. A situation occurs in which the alternating current voltage component due to the signal light contained therein disappears. For this purpose, the amplifier 5
It is necessary to make the dynamic range of the input current relatively large with respect to the gain. In other words, it is necessary to keep the gain small relative to the output dynamic range of the amplifier 51. However, if the gain of the amplifier 51 is reduced, although it is possible to prevent the output characteristics of the amplifier 55 from becoming saturated when the amount of disturbance light is large, the gain for the AC voltage component due to the signal light is also reduced, which improves the sensitivity. There is a problem in that this must be further amplified at a stage subsequent to the amplifier 51 in order to achieve this.

Further, in the photodetecting device shown in FIG. 4, since the DC voltage component and the low frequency voltage component are negatively fed back to the input of the amplifier 51, the input to the amplifier 51 is substantially only the AC voltage component due to the signal light. As a result, even when the amount of disturbance light is large, the amplifier 51 does not become saturated, and a large dynamic range can be achieved with respect to the disturbance light without reducing the gain of the amplifier 51. However, in the photodetection device shown in FIG. 4, a large capacitance capacitor is required for the low-pass filter 62 for negative feedback, and furthermore, it is difficult to always operate the circuit stably due to negative feedback. There was a problem.

An object of the present invention is to provide a photodetection device that is capable of stably and highly sensitively outputting only signal light of the photocurrent photoelectrically converted by a photoelectric conversion element.

[Means for solving problems]

The present invention includes a first photoelectric conversion element, a first photoelectric conversion element, a first current-voltage conversion amplification means that converts a photocurrent from the first photoelectric conversion element into a voltage and multiplies it, a second photoelectric conversion element, which has a frequency bandwidth narrower than the frequency bandwidth of the first current-voltage conversion amplification means, and responds to a low-frequency photocurrent from the second photoelectric conversion element and converts it into a current; and a second current-voltage conversion amplification means for converting and amplifying the output voltage from the second current-voltage conversion amplification means, and converting the output voltage from the second current-voltage conversion amplification means into a current with a predetermined gain to input the current to the first current-voltage conversion amplification means. voltage-current conversion amplification means applied to the terminal, and the current from the voltage-current conversion amplification means is
The above photodetecting device is characterized in that the photocurrent flows into the input terminal of the first current-voltage conversion and amplification means in a direction that cancels out the photocurrent from the first photoelectric conversion element. This improves the problems of the prior art.

[Effect]

In the present invention, the photocurrent output from the first photoelectric conversion element due to incident light is converted into a voltage by the first current-voltage conversion and amplification means, amplified, and output. By the way, the present invention further includes a second photoelectric conversion element, a second current-voltage conversion amplification means that converts the photocurrent from the second photoelectric conversion element into a voltage and amplifies it, and a second current-voltage conversion element. and voltage-current conversion means for converting the output voltage from the amplification means into a current and applying the current to the input terminal of the first current-voltage conversion amplification means. This second current-voltage conversion amplification means has a frequency bandwidth narrower than that of the first current-voltage conversion amplification means, and responds only to the low-frequency photocurrent from the second photoelectric conversion element. , the voltage output from the second current-voltage conversion amplification means is only due to disturbance light among the light incident on the second photoelectric conversion element, and this is converted into the first current through the voltage-current conversion means. - The photocurrent flows into the voltage conversion and amplification means in a direction that cancels out the photocurrent from the first photoelectric conversion element. This reduces the DC voltage component and low frequency component due to disturbance light among the photocurrent flowing into the first current-voltage conversion amplification means,
Even without setting the gain of the first current-voltage conversion amplification means small, the AC component of the signal light can be output with good sensitivity from the first current-voltage conversion amplification means.

Note that the light-receiving area of the second photoelectric conversion element is made smaller than the light-receiving area of the first photoelectric conversion element, and the gain by the second current-voltage conversion amplification means and the voltage-current conversion means is When set to be almost the same as the light receiving area ratio of the photoelectric conversion element, the first current -
At the input end of the voltage conversion and amplification means, the DC component and low frequency component due to disturbance light are completely canceled out.
The alternating current component of the signal light can be output with even higher sensitivity. Furthermore, the dynamic range of the second current-voltage conversion amplification means with respect to the amount of light incident on the second photoelectric conversion element is the dynamic range of the first current-voltage conversion amplification means with respect to the amount of light incident on the first photoelectric conversion element. By setting it larger than the range, the first current -
Only the alternating current component of the signal light can be output with good sensitivity and accuracy without saturating the voltage conversion and amplification means.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram of an embodiment of a photodetecting device according to the present invention.

The photodetector shown in FIG. 1 includes two photoelectric conversion elements 1 and 2, and current-voltage conversion amplification means 3 and 4 that convert photocurrents photoelectrically converted by the photoelectric conversion elements 1 and 2 into voltages, respectively. , a resistor 5 connecting the output end of the current-voltage conversion amplification means 4 and the input end of the current-voltage conversion amplification means 3.

The photoelectric conversion elements 1 and 2 each consist of a photodiode, and if the light-receiving areas of the photoelectric conversion elements 1 and 2 are A and B, respectively, the light-receiving areas are A and B.
is configured to satisfy the relationship A/B>1...(1).

The current-voltage conversion amplification means 3 includes a high-gain inverting amplifier 6 and a feedback resistor 7 that feeds back the output of the inverting amplifier 6 to its input side. It consists of an inverting amplifier 8, a feedback resistor 9 and a feedback capacitor 10 that feed back the output of the inverting amplifier 6 to its input side. The DC current-voltage conversion gain in the current-voltage conversion amplification means 3 and 4 is determined by the resistance values R _F1 and R _F2 of the feedback resistors 7 and 9, respectively. That is, the gains of the current-voltage conversion amplification means 3 and 4 are R _F1 and R _F2 , respectively.
Further, the current-voltage conversion amplification means 4 has a feedback capacitance 1
0, but the capacitance value of this feedback capacitor 10 is
Due to C _F , the cutoff frequency f ₀ of the current-voltage conversion amplification means 4 becomes f ₀ =1/2πC _F R _F2 ...(2), and as shown in FIG. The bandwidth f ₂ of 4 is considerably smaller than the bandwidth f ₁ of the current-voltage conversion amplification means 3.

A resistor 5 connecting the output end of the current-voltage conversion amplification means 4 and the input end of the current-voltage conversion amplification means 3
is for converting the output voltage from the current-voltage conversion amplification means 4 into a current and applying it to the input of the current-voltage conversion amplification means 3, and functions as a voltage-current converter. Note that when the resistance value of this resistor 5 is R _C , the voltage-current conversion gain due to this resistor 5 is 1/R _C .

In a photodetector having such a configuration, when light of the same amount of light, that is, signal light containing disturbance light, is simultaneously incident on the photoelectric conversion elements 1 and 2, the photoelectric conversion elements 1 and 2
2, photocurrents I ₁ and I ₂ flow through them, respectively. Since the light-receiving areas A and B of the photoelectric conversion elements 1 and 2 have the relationship shown in equation (1) above, the relationship between the photocurrents I ₁ and I ₂ is given by I ₁ =K, where k is a constant.・I ₂ ……(3) holds true. When the photocurrent _I2 is applied to the current-voltage conversion amplification means 4, the current-voltage conversion amplification means 4
The output voltage V ₀₂ of is V ₀₂ = −I ₂・R _F2 = −I ₁・R _F2 /k (4), and this output voltage V ₀₂ causes the current-voltage conversion amplification means 3 to pass through the resistor 5. The current I _C flowing into the input terminal of is I _C =V ₀₂ /R _C =-I ₁ ·R _F2 /(k·R _C ) (5). Now, the resistance value R _F2 of feedback resistor 9 and resistor 5
If the resistance value R _C is selected so as to satisfy the relationship R _F2 /R _C =k (6), then from equation (5), a The inflowing current I _C becomes I _C =-I ₁ ...(7), which cancels out the photocurrent I ₁ from the photoelectric conversion element 1 and makes the current flowing into the current-voltage conversion amplification means 3 zero. Can be done. However, if the currents are canceled in all bands, not only the DC component and low frequency component due to the disturbance light but also the AC component due to the signal light will be lost, so in this example, the feedback capacitance 1
0 cancels out only the DC component and low frequency component current due to disturbance light. That is, as shown in FIG. 2, the frequency band (bandwidth f ₁ ) of the current-voltage conversion amplification means 4 is made sufficiently lower than the frequency band (bandwidth f ₂ ) of the alternating current component due to the signal light by the feedback capacitor 10. If set, the output voltage V ₀₂ of the current-voltage conversion amplification means 4 does not include the AC component caused by the signal light, but only the DC component and low frequency component caused by the disturbance light, and therefore the current-voltage is converted through the resistor 5. The current I _C flowing into the conversion amplification means 3 also has a DC component,
As a result, only the direct current component and low frequency component of the photocurrent I ₁ from the photoelectric conversion element 1 can be substantially removed by the current I _C . In this way, only the alternating current component due to the signal light of the photocurrent _I1 is applied to the input terminal of the current-voltage conversion amplification means 3, so that the current -
The voltage conversion amplification means 3 can convert only the photocurrent caused by this signal light into a voltage with a gain R _F1 and output it without reducing the gain, so the sensitivity can be significantly improved compared to the conventional one. becomes possible.

Furthermore, in the photodetecting device shown in FIG. 1, the photoelectric conversion element 2, the current-voltage conversion amplification means 4, and the resistor 5 are not provided, and the current I _C from the resistor 5 is supplied to the input terminal of the current-voltage conversion amplification means 3. When the light is not allowed to flow in (that is, in a configuration similar to the conventional photodetecting device as shown in FIG. 3), the amount of light incident on the photoelectric conversion element 1 is equal to Limited by the saturated output voltage _VTH .

That is, the limit photocurrent I _1TH that allows the inverting amplifier 6 to operate without saturation is I _1TH =V _TH /R _F1 (8).

On the other hand, as in this embodiment, the photoconversion element 2 whose light-receiving area B is smaller than the light-receiving area A of the photoelectric conversion element 1 by 1/k, the current-voltage conversion amplification means 4, and the resistor 5 are used. When the current I _C from the resistor 5 is caused to flow into the input terminal of the current-voltage conversion amplification means 3, the dynamic range becomes significantly wider than when no current I _C is caused to flow therein. That is, when a current is caused to flow into the input terminal of the current-voltage conversion amplification means 3, the dynamic range is determined by the saturated output voltage of the inverting amplifier 8 of the current-voltage conversion amplification means 4. Assuming that the inverting amplifier 8 has the same saturation output voltage V _TH as the inverting amplifier 6, the limit photocurrent I _2TH that allows the inverting amplifier 8 to operate normally without saturating it is I _2TH = V _TH /R _F2 ... …(9) becomes. As can be seen by comparing equation (9) with equation (8), _the dynamic range of the current-voltage conversion amplification means 4 is smaller than that of the current-voltage conversion amplification means 3 alone _. )/(I _2TH・R _F2 ) =k・R _F1 /R _F2 ...(10) This will increase by a factor of 1. For example, feedback resistance value
Assuming that R _F1 and R _F2 are the same value, the current-voltage conversion amplification means 4 can allow k times the amount of light to enter until the saturated output voltage V _TH is reached. Therefore, the limit value of the light amount when the current I _C is not flowing is, for example, 1000 lux, but it is now possible to tolerate a light amount of 1000 k lux. As long as the output of the current-voltage conversion amplification means 4 is within the dynamic range, no DC component or low frequency component output due to disturbance light will appear in the current-voltage conversion amplification means 3. In this case, the dynamic range against disturbance light can be increased by K·R _F1 /R _F2 as a whole compared to when no current I _C is introduced.

Furthermore, the device of this embodiment does not have an overall negative feedback like the conventional device shown in FIG. It can be made to work.

In this way, the photodetector of this embodiment has a large dynamic range for disturbance light and a large current-voltage conversion gain for signal light as AC modulated light, so even if strong disturbance light is incident along with signal light, , it is possible to amplify only the optical signal from the signal light with high sensitivity, and this makes it possible to simplify the signal processing circuit connected to the latter stage of the current-voltage conversion amplification means 3, reducing the overall circuit scale. can do.

In addition, since the entire device can operate stably by not having negative feedback as a whole, the capacitance value C _F of the capacitor 10 may be set to a small value. ，
8. Resistors 7, 9 and signal processing circuit (not shown)
They can also be integrated into one monolithic IC.

Note that the current-voltage conversion amplification means 3 is based on equation (3) or
If the condition of equation (7) is satisfied, the DC component of the disturbance light,
Although it does not respond to low frequency components at _{all , the current} - It is also conceivable that the voltage conversion and amplification means 3 slightly responds to the DC component and low frequency component of the disturbance light. For this purpose, a coupling capacitor is connected in series between the current-voltage conversion amplification means 3 and a signal processing circuit (not shown) at the subsequent stage, and disturbance light that may be output from the current-voltage conversion amplification means 3 is connected in series. The slight DC component and low frequency component of the signal may be removed by a coupling capacitor and input to the subsequent signal processing circuit.

〔Effect of the invention〕

As explained above, according to the present invention, the second
a second current-voltage conversion amplification means that responds only to the low-frequency photocurrent from the photoelectric conversion element and converts it into a voltage; , this current is made to flow into the input terminal of the first current-voltage conversion amplification means in a direction that cancels out the photocurrent from the first photoelectric conversion element, so that in the first current-voltage conversion amplification means, Only the alternating current component of the signal light can be output in a stable state with high sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the photodetection device according to the present invention, FIG. 2 is a diagram showing the frequency response characteristics of the current-voltage conversion and amplification means, and FIGS. 3 and 4 are respectively related to conventional photodetection devices. FIG. 1, 2... Photoelectric conversion element, 3, 4... Current-voltage conversion amplification means, 5... Resistor, 6, 8... Inverting amplifier, 7, 9... Feedback resistor, 10... Feedback capacitor,
f ₀ ... Cutoff frequency, f ₁ , f ₂ ... Frequency bandwidth.

Claims (1)

[Claims] 1. A first photoelectric conversion element, a first current-voltage conversion amplification means that converts a photocurrent from the first photoelectric conversion element into a voltage and multiplies it, and a second photoelectric conversion element. a second photoelectric conversion element, which has a frequency bandwidth narrower than the frequency bandwidth of the first current-voltage conversion amplification means, and responds to a low-frequency photocurrent from the second photoelectric conversion element, converts it into a current, and amplifies it. a voltage that converts the output voltage from the second current-voltage conversion amplification means into a current with a predetermined gain and applies it to the input terminal of the first current-voltage conversion amplification means; current conversion amplification means, the current from the voltage-current conversion amplification means is directed to the input terminal of the first current-voltage conversion amplification means in a direction that cancels the photocurrent from the first photoelectric conversion element. A light detection device characterized in that the light detection device is configured to allow an inflow. 2. The second photoelectric conversion element has a light-receiving area smaller than the light-receiving area of the first photoelectric conversion element, and the gain by the second current-voltage conversion amplification means and the voltage-current conversion means is 2. The photodetecting device according to claim 1, wherein the light receiving area ratio of the first and second photoelectric conversion elements is set to be substantially the same. 3. The dynamic range of the second current-voltage conversion amplification means with respect to the amount of light incident on the second photoelectric conversion element is determined by the dynamic range from the voltage-current conversion means to the input terminal of the first current-voltage conversion amplification means. Claim 1, characterized in that the dynamic range of the first current-voltage conversion and amplification means is larger than the amount of light incident on the first photoelectric conversion element when no current flows in. 1
Photodetection device as described in Section.