Photoelectric conversion integrated circuit device

Details Photoelectric conversion integrated circuit device Photoelectric conversion integrated circuit device

2000-02-15

2001-11-13

Munson, Gene M. (Department: 2811)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C257S461000

Reexamination Certificate

active

06316955

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a photoelectric conversion integrated circuit device provided with a light-sensing device that outputs a current signal in accordance with a light signal it receives and a current-to-voltage conversion circuit that outputs a voltage signal in accordance with a current signal it receives so as to convert, as a whole, a light signal into a voltage signal.
BACKGROUND ART
FIG. 4
shows a circuit block diagram of a conventional photoelectric conversion integrated circuit device that employs a photodiode as a light-sensing device. In this figure, reference numeral
1
′ represents a photodiode that outputs a current signal in accordance with a light signal it receives, reference numeral
2
represents a current-to-voltage conversion circuit (hereafter referred to as the “I/V conversion circuit”) that outputs a voltage in accordance with a current signal it receives, and reference numeral
3
represents a test circuit composed of a switching device
31
, a constant-current circuit
32
, and a switch driving circuit
33
.
To the input of the I/V conversion circuit
2
, the output (cathode) of the photodiode
1
′ is connected, and the constant-current circuit
32
provided within the test circuit
3
is also connected thereto through the switching device
31
. Thus, when the photodiode
1
′ senses a light signal L, or when the switching device
31
is turned on, a current flows from the I/V conversion circuit
2
to the photodiode
1
′ or to the switching device
31
, and a voltage corresponding to this current is fed out via a terminal T
o
. Within the I/V conversion circuit
2
, as shown in
FIG. 5
, a reference voltage Vref is applied to the non-inverting input terminal (+) of an operational amplifier via a terminal
21
through a resistor R
1
, and the cathode of the photodiode
1
′ is connected via a terminal
22
to the inverting input terminal (−) the operational amplifier. Between this inverting input terminal (−) and the output terminal T
o
, a resistor R
2
is connected. When an output current flows through the photodiode
1
′, the current I flows through the resistor R
2
, and thus a voltage I×R
2
appears at the output terminal T
o
.
In
FIG. 4
, the switch driving circuit
33
controls the on/off state of the switching device
31
; specifically, when the switch driving circuit
33
receives a predetermined voltage at its test pin T
T
, it turns on the switching device
31
.
In general, an integrated circuit device is subjected to a functioning check in its manufacturing process. In a functioning check of a photoelectric conversion integrated circuit device, it is desirable to shine light on the photodiode (light-sensing device)
1
′; however, in reality, it is difficult to shine a predetermined amount of light on the photodiode
1
′. For this reason, a functioning check is achieved by externally turning on the switching device
31
provided within the test circuit
3
so that the constant-current circuit
32
will cause the I/V conversion circuit
2
to output a predetermined amount of current as much as it outputs when a predetermined amount of light is shone on the photodiode
1
′.
Here, if there is a break at point A′ shown in
FIG. 4
in the wiring between the photodiode
1
′ and the I/V conversion circuit
2
, even if the photodiode
1
′ senses light, the I/V conversion circuit
2
outputs no current I; that is, the photoelectric conversion integrated circuit device is defective.
However, in the functioning check described above, unless there is a fault in the wiring between the I/V conversion circuit
2
and the test circuit
3
, the I/V conversion circuit
2
outputs a current, and therefore, unless any fault is found in other respects such as the characteristics of the I/V conversion circuit
2
, the photoelectric conversion integrated circuit device passes as acceptable.
In this way, with a conventional photoelectric conversion integrated circuit device, even if a functioning check is conducted in the manner described above, i.e. by feeding an input current to the I/V conversion circuit without shining light on the light-sensing device, it is impossible to detect a fault in the wiring between the photodiode
1
′ and the I/V conversion circuit
2
.
Disclosure of the Invention
An object of the present invention is to provide a photoelectric conversion integrated circuit device that allows detection of a fault in the wiring between a light-sensing device and an I/V conversion circuit even if an input current is fed to the I/V conversion circuit without shining light on the light-sensing device.
To achieve the above object, according to one aspect of the present invention, a photoelectric conversion integrated circuit device for converting a light signal into a voltage signal is provided with a light-sensing device that outputs a current in accordance with a light signal it receives, a current-to-voltage conversion circuit that outputs a voltage signal in accordance with a current signal it receives, and a test circuit that outputs a current in accordance with a drive signal fed from outside. In addition, a plurality of terminals are provided at the output of the light-sensing device, with one of the terminals connected to the current-to-voltage conversion circuit and at least one of the remainder of the terminals connected to the test circuit.
According to this configuration, the current exchanged between the I/V conversion circuit (current-to-voltage conversion circuit) and the test circuit always flows by way of the wiring between the light-sensing device and the I/V conversion circuit and by way of the output layer of the light-sensing device. If there is a fault such as a break in the wiring between the light-sensing device and the I/V conversion circuit, no input current can be fed to the I/V conversion circuit by the test circuit.
According to another aspect of the present invention, in the photoelectric conversion integrated circuit device described above, the temperature characteristic of the conversion efficiency of the current-to-voltage conversion circuit is reverse to the temperature characteristic of the output of the test circuit.
In general, even if the input current fed to the I/V conversion circuit is kept constant, its output varies with temperature. However, according to this configuration, the input current fed to the I/V conversion circuit by the test circuit varies in such a way as to cancel the variation of the output of the I/V conversion circuit. This makes it possible to keep the output free from influence of temperature variation and thus keep it substantially at a fixed level. Accordingly, it is possible to conduct a functioning check of the photoelectric conversion integrated circuit device with higher accuracy.
According to still another aspect of the present invention, in a photoelectric conversion integrated circuit device, a photodiode is composed of a semiconductor substrate and first and second terminals that are kept in contact with a first conducting layer formed within the substrate so as to exhibit conduction reverse to that of the substrate. In addition, a photodiode current flows from the first terminal to a second conducting layer, then to the first conducting layer, and then to the substrate, and a test current flows from the first terminal to the second conducting layer, and then to the second terminal.


REFERENCES:
patent: 4241358 (1980-12-01), Wade
patent: 5418396 (1995-05-01), Mita
patent: 5585731 (1996-12-01), Tsuchida et al.
patent: 5767538 (1998-06-01), Mullins et al.
patent: 63-13368 (1988-01-01), None

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