JP2735543B2 - Photoelectric conversion device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention switches a plurality of photodiodes,
The present invention relates to a photoelectric conversion device capable of detecting the amount of light applied to each photodiode as a short-circuit current. [Prior Art] FIG. 5 shows an example of a conventional photoelectric conversion device for detecting a short-circuit current of a plurality of photodiodes, wherein the short-circuit current of the plurality of photodiodes is switched by an N-ch (N-channel) MOS transistor. In the figure, reference numerals 3 and 4 denote photodiodes whose cathodes are interconnected, and 1-1 and 1-2 denote NchMs that short-circuit the photodiodes 3 and 4.
OS transistors, 2-1 and 2-2 are N-ch MOS transistors for switching the short-circuit currents of the photodiodes 3 and 4, 8 are diodes for converting the short-circuit currents of the photodiodes 3 and 4 to voltages, and 7 is a switch for the switches 3 and 4. An operational amplifier for determining the voltage of the cathode, 6 is a power supply for determining the non-inverting input voltage of the operational amplifier 7, and 9-1 and 9-2 control on / off of the N-ch MOS transistors 1-1 and 1-2. 11-1 and 11-2 are inverters for inverting the control signal input to these control terminals, and 10 is an output terminal for outputting a photoelectrically converted voltage. FIG. 6 shows the NchMOS transistors 2-1 and 2-1 of FIG.
2 shows a circuit obtained by replacing 2-2 with a PNP transistor. Next, the operation will be described. The short-circuit current generated in the photodiodes 3 and 4 flows from the output of the operational amplifier 7 through the diode 8, and a voltage is generated at both poles of the diode 8 by logarithmically compressing the short-circuit current of the photodiode. The operational amplifier 7 is negatively fed back by the diode 8,
Since the cathode electrodes of the photodiodes 3 and 4 have the same potential as the voltage of the power supply 6, the output terminal 10 has a voltage obtained by logarithmically compressing the short-circuit current of the photodiode by the diode 8 and the power supply 6.
The sum of the voltage and the voltage is output. Here, the control terminal 9-
When the signal 1 is H and the signal 9-2 is L, the N-chMOS
Transistor 1-1 is on, N-ch MOS transistor 1
-2 is off, N-ch MOS transistor 2-1 is off, N
The -ch MOS transistor 2-2 is turned on, only the short-circuit current generated by the photodiode 4 flows through the diode 8, and the short-circuit current is output as the sum of the logarithmically compressed voltage and the power supply 6 voltage. Output to terminal 10. When the signal of the control terminal 9-1 is L and the signal of the control terminal 9-2 is H, the N-ch MOS transistor 1-1 is off, and the N-ch M
The OS transistor 1-2 is turned on, the N-ch MOS transistor 2-1 is turned on, and the N-ch MOS transistor 2-2 is turned off. Only the short-circuit current generated by the photodiode 3 flows through the diode 8, and the output The terminal 10 outputs the sum of the voltage obtained by logarithmically compressing the short-circuit current generated in the photodiode 3 by the diode 8 and the voltage of the power supply 6. [Problems to be Solved by the Invention] In such a conventional photoelectric conversion device, the voltage of the back gate of the MOS transistor used as an element for switching the short-circuit current of the plurality of photodiodes is given by the power supply voltage. In addition, the leakage current between the back gate and the source, drain, and channel is large, and this leakage current causes an error in light conversion output. Especially,
This error was large when the short-circuit current of the photodiode was small. The present invention has been made to solve the above-described problems, and has as its object to obtain a photoelectric conversion device capable of performing high-precision photoelectric conversion even when a short-circuit current generated in a photodiode is small. [Means for Solving the Problems] The photoelectric conversion device according to the present invention is configured such that the voltage of the back gate of the MOS transistor that switches the short-circuit current of the plurality of photodiodes is set to ± the potential of the cathode electrode connected to the photodiodes. The potential is set to a potential within 1 V, or a potential within ± 1 V of the potential of the anode electrode when the anode electrodes of the photodiodes are interconnected. [Operation] In the present invention, by setting the potential of the back gate of the MOS transistor that switches the short-circuit current of the plurality of photodiodes to a potential within ± 1 V of the potential of the cathode (anode) electrode connected to the photodiodes,
The leakage current between the back gate, the source, the drain, and the channel of the MOS transistor that switches the short-circuit current can be reduced, and highly accurate photoelectric conversion can be performed. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a photoelectric conversion device according to an embodiment of the first invention of the present application. In the drawing, reference numerals 3 and 4 denote photodiodes having cathodes connected to each other, and 1-1 and 1-2 denote photodiodes.
N-chMOS transistors for short-circuiting 3 and 4; 2-1 and 2-2 are N-chMOS for switching short-circuit current of photodiodes 3 and 4.
A transistor, 6 is a power supply for applying a potential to the anode electrodes of the photodiodes 3 and 4, 8 is a diode for converting a short-circuit current of the photodiodes 3 and 4 to a potential, and 7 is a potential for determining the potential of the cathode electrodes of the photodiodes 3 and 4. 9-1 and 9-2 are for turning on the N-ch MOS transistor.
A control terminal to which a signal for controlling off is input, 11-1, 11-
2 is an inverter for inverting a control signal input to the control terminal, 10 is an output terminal for outputting a photoelectrically converted potential, 5
Denotes N-ch MOS transistors 1-1, 1-2, 2-
This is a power supply for applying a potential to the back gates 1 and 2. Next, the operation and operation of this embodiment will be described. The operation of converting the short-circuit current generated by the photodiodes 3 and 4 into a voltage is the same as that of the conventional circuit.
The voltage of the back gate of S transistors 1-1, 1-2, 2-1 and 2-2 is ± 1 of the potential of the cathode electrodes of photodiodes 3 and 4.
Since the potential is within V, M
The potential difference between the source, drain and channel of the OS transistor and the back gate is within ± 1 V, and the leakage current between the source, drain and channel of the MOS transistor and the back gate can be made almost zero.
Therefore, almost all of the short-circuit current generated in the photodiodes 3 and 4 can flow to the diode 8 that performs voltage conversion, and high-precision photoelectric conversion can be performed. In the above embodiment, the circuit in which the cathode electrodes of the photodiodes are interconnected is shown. However, as shown in FIG. 2, the anode electrodes of the photodiodes are interconnected as shown in one embodiment of the second invention of the present application. And a switch for short-circuiting the photodiode and a switch for switching the short-circuit current of the photodiode are connected to P-.
It may be configured as a chMOS transistor. In the above embodiment, an N-ch MOS transistor is used as a switch for short-circuiting the photodiode and a switch for switching the short-circuit current of the photodiode.
A transmission gate composed of a transistor and a P-chMOS transistor may be used. In the other embodiments of the first and second inventions of the present application shown in FIGS. 3 and 4, this is constituted by PNP and NPN bipolar transistors, respectively. Furthermore, in the above embodiment, the number of photodiodes to be switched is one, but in the present invention, the number of photodiodes to be switched and detected is not particularly limited. [Effects of the Invention] As described above, according to the present invention, in a photoelectric conversion device in which a short-circuit current of a photodiode is switched by a MOS transistor, the back gate of the switched MOS transistor is set to a potential within ± 1 V of the cathode potential of the photodiode. Accordingly, there is an effect that a photoelectric conversion device capable of performing high-precision photoelectric conversion even in a region where the short-circuit current of the photodiode is small is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a photoelectric conversion device for switching and detecting a plurality of photodiodes according to an embodiment of the first invention of the present application, and FIG. 2 is a second invention of the present application. 3 and 4 are circuit diagrams of other embodiments of the first and second inventions of the present application, respectively, and FIGS. 5 and 6 are conventional circuit diagrams. FIG. 3 is a circuit diagram of an example. 1-1, 1-2, 2-1 and 2-2 are switches for switching each photodiode, 3 and 4 are photodiodes, 5 and 6 are power supplies, 7
Is an operational amplifier, and 8 is a diode.

Claims (1)

(57) [Claims] A plurality of photodiodes having their cathode electrodes interconnected; a first switch comprising a transistor connected between the anode electrode and the cathode electrode of each photodiode; and an interconnected cathode electrode of the photodiode being inverted. An operational amplifier connected to an input; a second switch composed of a transistor connected between a non-inverting input of the operational amplifier and an anode electrode of each of the photodiodes; an inverting input and an output of the operational amplifier And a power supply connected to the non-inverting input of the operational amplifier, wherein each of the plurality of the first and second switches is provided. Using a crab MOS transistor,
A photoelectric conversion device, wherein a back gate potential of the MOS transistor is set to a potential within ± 1 V of a non-inverting input potential of the operational amplifier. 2. A plurality of photodiodes having their anode electrodes interconnected; a first switch comprising a transistor connected between the anode electrode and the cathode electrode of each of the photodiodes; and an interconnected anode electrode of the photodiodes Is connected to the inverting input of the operational amplifier; a second switch including a transistor connected between the non-inverting input of the operational amplifier and the cathode electrode of each photodiode; and the inverting input of the operational amplifier And a power supply connected to the inverting input of the operational amplifier, wherein the plurality of first and second switches are provided. Using a MOS transistor for either,
A photoelectric conversion device, wherein a back gate potential of the MOS transistor is set to a potential within ± 1 V of a non-inverting input voltage of the operational amplifier.