JPH0690083B2 - Bias automatic variable metering circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic bias variable photometry circuit for performing precision photometry using a photodiode.

Conventional technology When performing precision photometry using a photovoltaic type photoelectric conversion element such as a silicon photodiode, it is necessary to receive the output current of the element with a low input impedance and amplify it in order to maintain the linearity of the photocurrent output. Generally, a current-voltage converter using an operational amplifier as shown in FIG. 2 is used.

Photodiodes (particularly silicon photodiodes) have a wide dynamic range and a relatively fast response speed, but when the upper limit of the linearity of photoelectric conversion is desired to be further extended or the response speed is desired to be further increased, FIG. The method of applying a reverse bias voltage is widely used. The reverse bias voltage is also used when it is desired to bring the internal quantum efficiency of the photodiode close to 100%. In the circuit of FIG. 3, in general, the upper limit of linearity is raised to some extent according to the reverse bias voltage as shown in FIG. 4, so that precise photometry can be performed in a higher output current range.

Problems to be Solved by the Invention However, in the conventional photoelectric conversion circuit applying the reverse bias voltage as shown in FIG. 3, the response speed and the linearity are improved, but in exchange for this, the application of the reverse bias voltage is applied. Therefore, there is a problem that the noise component of the photodiode increases and the S / N ratio deteriorates.

FIG. 5 shows the relationship between the noise voltage and the reverse bias voltage of a typical silicon photodiode. When the reverse bias voltage exceeds a certain level, the noise starts to increase rapidly.
After that, noise tends to increase as the bias voltage increases. Therefore, when the reverse bias voltage is applied, there is a disadvantage that the measurement of weak light is extremely disadvantageous and the upper limit of the measurement range is increased. Therefore, in a precision photometer using a photodiode having an extremely wide measurement range, it is necessary to intermittently or adjust the reverse bias voltage according to the intensity level of incident light in order to maintain the highest measurement accuracy.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and provides an automatic bias variable photometry circuit that can maximize the measurement range of a photodiode and bring out the highest measurement accuracy for an arbitrary intensity level of incident light. With the goal.

Means for Solving the Problems In order to achieve the above object, the present invention provides a measurement circuit that receives a photodiode and an output current from one terminal of the photodiode, and receives a positive (negative) current with respect to a positive (negative) input current. ) And a current-voltage converter whose polarity is set so as to output the output voltage, the output of the current-voltage converter is connected to the other terminal of the photodiode.

Action The current-voltage converter receives the output current from one terminal of the photodiode with a low impedance, amplifies it and outputs it by converting it into a voltage, and by connecting this output to the other terminal of the photodiode, It serves to apply the output voltage of the current-to-voltage converter as a reverse bias of the photodiode. Due to this action, the present invention
A reverse bias voltage proportional to the output current of the photodiode is applied to the photodiode, and the reverse bias voltage is automatically adjusted to an optimum level according to the intensity level of incident light.

Embodiment FIG. 1 shows a circuit configuration of an automatic bias variable photometry circuit in an embodiment of the present invention. In FIG.
Reference numeral 1 is a silicon photodiode, and 2 and 3 are operational amplifiers.

Hereinafter, regarding the bias automatic variable photometry circuit of the present embodiment,
The operation will be described.

In FIG. 1, the silicon photodiode 1 has its anode connected to the inverting input terminal of the operational amplifier 2 and its cathode connected to the output terminal of the operational amplifier 3. When light is incident on the silicon photodiode 1, holes are collected at the anode, so that a positive output current flows out from the anode and is input to the operational amplifier 2. The operational amplifier 2 constitutes a current-voltage converter together with the resistor R ₁ , and a voltage proportional to the input current is output from the output terminal. This voltage has a negative polarity with respect to the positive input current because the operational amplifier 2 operates in the inverting mode. In order to apply a reverse bias to the silicon photodiode 1, it is necessary to apply a positive voltage to the cathode because the anode has a zero potential (virtual ground). Therefore, the polarity of the output voltage of the current-voltage converter is inverted by the inverting amplifier composed of the operational amplifier 3 and the resistors R ₂ and R ₃ to obtain a positive output voltage, and this voltage is applied to the cathode of the silicon photodiode 1. It is applied to act as a reverse bias. The amplification degree of the inverting amplifier 3 is determined by the resistances R ₂ and R ₃ , but it is determined so that the reverse bias voltage has an effective level in the region where the linearity of the silicon photodiode 1 begins to break down. This reverse bias voltage changes in proportion to the magnitude of the output current, that is, the intensity level of the incident light. Therefore, when measuring weak light, that is, in the region where there is no problem in linearity and noise voltage is a problem, the reverse bias voltage becomes almost zero, operating under the highest S / N ratio condition, and strong intensity. When measuring light, that is, in the region where S / N ratio is not a problem but linearity is a problem, extend the upper limit of linearity by applying a sufficient bias voltage to achieve a wider measurement range. You can

As described above, the bias automatic variable photometric circuit of the present invention is
The output of the current-voltage converter that receives the output current of the photodiode is fed back to the photodiode and acts as a reverse bias, so that the reverse bias voltage of the photodiode is automatically adjusted to the optimum level according to the intensity level of the incident light. It has a great practical effect, such as being able to realize the function to perform, and greatly expanding the measurement range of a precision photometer using a photodiode.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a bias automatic variable photometry circuit in one embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example of a general photoelectric conversion circuit for photodiodes, and FIG. 3 is the photoelectric conversion of FIG. FIG. 4 is a circuit diagram showing a conventional example of a photoelectric conversion circuit used to improve some of the characteristics of the circuit, FIG. 4 is a graph showing the relationship between the reverse bias voltage and the linearity of a typical silicon photodiode, and FIG. It is a graph which shows the relation between the reverse bias voltage of a typical silicon photodiode, and a noise voltage. 1 ... Silicon photodiode, 2 ... Operational amplifier, 3
…… Operational amplifier.

Claims (1)

[Claims] 1. A current-voltage converter in which a polarity is set so as to receive an output current from a photodiode and one terminal of the photodiode and output a positive (negative) output voltage with respect to a positive (negative) input current. And a bias automatic variable photometric circuit in which the output of the current-voltage converter is connected to the other terminal of the photodiode.