Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2001-12-17
2004-11-23
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140AG
Reexamination Certificate
active
06822212
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photoelectric converter for receiving light impinging on an original image and reflected therefrom and for converting the light into an electric signal. In particular, the present invention relates to a linear image sensor suitable for an image reading apparatus such as a facsimile and an image scanner.
FIG. 6
shows a circuit diagram of an image sensor IC used in a conventional image reading apparatus, and
FIG. 7
shows a timing chart. The image sensor is described in Japanese Patent Application Laid-open No. Hei 10-051164.
An N-type region of a photodiode
101
is connected to a positive power source voltage terminal VDD, and a P-type region of the photodiode
101
is connected to a drain of a reset switch
102
and a gate of a source follower amplifier
103
. A source of the reset switch
102
is supplied with a reference voltage VREF
1
. A source of the source follower amplifier
103
, which is an output terminal, is connected to a reading switch
105
and a constant current source
104
. A gate of the constant current source
104
is supplied with a constant voltage of a reference voltage VREFA, the drain is grounded, and the source is connected with VDD. The drain of the reading switch
105
is connected with the source of the source follower amplifier
103
and the source of the reading switch
105
is connected with a common signal line
106
. Elements in a frame of a photoelectric conversion block An shown in
FIG. 6
are provided in a number corresponding to pixels. The photoelectric block An represents a photoelectric block in an n-th bit.
The common signal line
106
is input to an inversion terminal of an operational amplifier
109
through a resistor
110
and is grounded by a capacitor
108
. An output terminal of the operational amplifier
109
is connected to an output terminal
116
through a chip selecting switch
112
and a capacitor
113
. The common signal line
106
is connected to a signal line reset switch
107
, and a source of the signal line reset switch
107
is supplied with a reference voltage VREF
2
. A resistor
111
is connected between an output terminal of the operational amplifier
109
and the inversion terminal thereof. A non-inversion terminal of the operational amplifier
109
is fixed at a constant voltage VREF
3
. The operational amplifier
109
, and the resistors
110
and
111
constitute an inversion amplifier D.
An output terminal
116
of an image sensor is connected to a drain of a MOS transistor
114
, and a source of the MOS transistor
114
is supplied with a reference voltage VREF
4
. The output terminal
116
of the image sensor is also connected to a capacitor
115
such as a parasitic capacitor. The capacitors
113
and
115
, and the MOS transistor
114
constitute a clamping circuit C.
In the image sensor with the above-mentioned configuration, after light is reflected from the original image and received, electric charge accumulates on the photodiode, producing a light signal voltage. The light signal voltage is then read from the photodiode and the photodiode is reset. In another step, a reference voltage is read, and a difference between the light signal voltage and the reference voltage is obtained. Therefore, reset noise contained in the reference voltage is different from that in the light signal voltage. More specifically, reset noise at different timings is compared, so that random noise is rather large. Furthermore, since the read of a reference voltage, reset of a photodiode, and read of a light signal voltage are conducted successively in each bit, high-speed read is difficult.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a photoelectric converter that realizes high-speed read while reducing random noise.
In order to solve the above-mentioned problem of the prior art, a photoelectric converter includes charge transfer circuit between an output terminal of photoelectric converter and an input terminal of an amplifier, the input terminal of the amplifier being connected to a reset circuit, wherein after accumulation of a light signal of the photoelectric converter, a reference signal held at the input terminal of the amplifier is read from the output terminal of the amplifier, the charge transfer circuit is turned on to transfer light signal charge of the photoelectric converter to the input terminal of the amplifier, after the charge transfer circuit is turned off, a light signal held at the input terminal of the amplifier is read from the output terminal of the amplifier as a light signal, the charge transfer circuit and the reset circuit are turned on to reset the output terminal of the photoelectric converter and the input terminal of the amplifier, and after the reset circuit is turned off, the charge transfer circuit is turned off, whereby subsequent accumulation of a light signal is conducted.
Alternatively, a photoelectric converter includes charge transfer circuit between an output terminal of photoelectric converter and an input terminal of amplifier, the output terminal of the photoelectric converter being connected to a reset circuit, wherein after accumulation of a light signal of the photoelectric converter, a reference signal held at the input terminal of the amplifier is read from the output terminal of the amplifier, the charge transfer circuit is turned on to transfer light signal charge of the photoelectric converter to the input terminal of the amplifier, after the charge transfer circuit is turned off, a light signal held at the input terminal of the amplifier is read from the output terminal of the amplifier as a light signal, the charge transfer circuit and the reset circuit are turned on to reset the output terminal of the photoelectric converter and the input terminal of the amplifier, and after the reset means is turned off, the charge transfer circuit is turned off, whereby subsequent accumulation of a light signal is conducted.
Alternatively, there is provided a photoelectric converter for outputting a reference signal and a light signal from a photoelectric converting portion through an amplifier, wherein the reference signal is transferred to reference signal holding circuit through reference signal transfer circuit, the light signal is transferred to light signal holding circuit through light signal transfer circuit, the reference signal holding circuit is connected to an input terminal of a second amplifier through second reference signal transfer circuit, the light signal holding circuit is connected to an input terminal of the second amplifier through second light signal transfer circuit, during a signal reading period, the second light signal transfer circuit is turned onto transfer the light signal held at the light signal holding circuit to the input terminal of the second amplifier, a light signal output is read from an output terminal of the second amplifier, after the second light signal transfer circuit is turned off or at the same time when the second light signal transfer circuit is turned off, the second reference signal transfer circuit is turned on to transfer the reference signal held at the reference signal holding circuit to the input terminal of the second amplifier, and a reference signal output is read from the output terminal of the second amplifier.
According to the above-mentioned reading method, a reference voltage and a light signal voltage containing the same OFF noise of a reset switch are read successively. Therefore, if a difference between the voltages is amplified, a photoelectric converter in which not only fixed pattern noise but also random noise is small can be obtained. Furthermore, since a reference voltage and a light signal voltage can be temporary read to separate capacitors, simultaneously with respect to all the bits, this operation can be made slower. Thus, the area of a circuit to be read can be decreased. Furthermore, a light signal voltage and a reference voltage are read from the capacitor successive
Brinks Hofer Gilson & Lione
Luu Thanh X.
Seiko Instruments Inc.
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