Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2002-04-08
2004-05-04
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C348S310000
Reexamination Certificate
active
06730898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photoelectric converter that receives a light reflected from an original to which the light is irradiated, and converts the light into an electric signal, and more specifically to a linear image sensor suitable for an image reading device such as a facsimile or an image scanner.
2. Description of the Related Art
A circuit diagram of an image sensor IC used in a conventional image reading device is shown in
FIG. 4
, and a timing chart thereof is shown in FIG.
5
. The image sensor is disclosed in Japanese Patent Application Laid-open No. Hei 10-051164.
An n-type region of a photo diode
101
is connected to a positive supply voltage terminal VDD, and a p-type region 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 given a reference voltage VREF
1
. A source that is an output terminal of the source follower amplifier
103
is connected to a read switch
105
and a constant current source
104
. The gate of the constant current source
104
is given a constant voltage of a reference voltage VREFA. The number of elements disposed inside of a frame of a photoelectric conversion block An shown in
FIG. 4
is identical with the number of pixels, and the read switches
105
of the respective blocks are connected to a common signal line
106
. Note that the photoelectric conversion block An is indicative of a photoelectric conversion block of an n-th bit.
The common signal line
106
is inputted to an inverse terminal of an operational amplifier
109
through a resistor
110
, and an output terminal of the operational amplifier
109
is connected to an output terminal
116
through a chip select 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 given a reference voltage VREF
2
. A resistor
111
is connected between the output terminal and the inverse terminal of the operational amplifier
109
, and a non-inverse terminal of the operational amplifier
109
is fixed to a constant voltage VREF
3
. An inverse amplifier D is composed of the operational amplifier
109
, the resistor
110
and the resistor
111
.
An output terminal
116
of the image sensor is connected to a drain of the MOS transistor
114
, and a source of the MOS transistor
114
is given a reference voltage VREF
4
. Also, the output terminal
116
of the image sensor is also connected to a capacitor
115
such as a parasitic capacitor. A clamp circuit C is composed of the capacitor
113
, the capacitor
115
and the MOS transistor
114
.
However, in the image sensor of the above type, the photo diode is reset after an optical signal voltage is read subsequent to the completion of photocharge storage, and thereafter the reference voltage is read, and a difference between the optical signal voltage and the reference voltage is taken. This leads to such a problem that reset noises put on the reference voltage and the optical signal voltage are different from each other. That is, because the reset noises of the different timings are compared with each other, there arises a problem in that the random noises are large.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned problems inherent in the prior art, according to the present invention, there is provided a photoelectric converter in which: an output terminal of a photoelectric converter means is connected to input terminals of a reset means and an amplifying means; a charge transfer means is connected to an output terminal of the amplifying means; another terminal of the charge transfer means is connected to a capacitor and a gate of a source follower amplifier; a source of the source follower amplifier is connected to a channel select means; another terminal of the channel select means is connected to a common signal line; and the common signal line is connected to a current source, and the photoelectric converter is characterized in that: the channel select means is closed to read a reference voltage in the common signal line; the charge transfer means is closed to read signal charges in the capacitor; the charge transfer means is opened after the channel select means is opened; and the channel select means is closed to read a signal voltage in the common signal line; the reset means is closed to initialize the photoelectric conversion means; the charge transfer means is closed to read reference charges in the capacitor after the reset means is opened; and the charge transfer means is opens after the channel select means is opened.
Alternatively, the photoelectric converter according to the present invention is characterized in that: the channel select means is closed to read a reference voltage in the common signal line; the charge transfer means is closed to read signal charges in the capacitor; the charge transfer means is closed to read signal charges in the capacitor; the charge transfer means is opened to read a signal voltage in the common signal line; the reset means is closed to initialize the photoelectric conversion means; the charge transfer means is closed to read reference charges in the capacitor after the reset means is opened; and the channel select means is opened after the charge transfer means is opened.
Also, there is provided a photoelectric converter, in which: an output terminal of a photoelectric converter means is connected to input terminals of a reset means and a first amplifying means; a first charge transfer means is connected to an output terminal of the first amplifying means; another terminal of the first charge transfer means is connected to input terminals of a first capacitor and a second amplifying means; a second charge transfer means is connected to an output terminal of the second amplifying means; another terminal of the second charge transfer means is connected to input terminals of a second capacitor and a third amplifying means; a third charge transfer means is connected to an output terminal of the third amplifying means; another terminal of the third charge transfer means is connected to a third capacitor and a gate of a source follower amplifier; a source of the source follower amplifier is connected to a channel select means; another terminal of the channel select means is connected to a common signal line; and the common signal line is connected to a current source, characterized in that a following series of operations is repeated, in which: the second charge transfer means operates; subsequently, the first charge transfer means and the third charge transfer means operate; subsequently, the reset means and the second charge transfer means operate; subsequently, the first charge transfer means operates; subsequently, the channel select means operates; subsequently, the third charge transfer means operates; and subsequently, the channel select means operates.
According to this reading manner, since the reference voltage and the signal voltage containing the same off-noise of the reset switch are read in order, if a voltage difference is taken by using the correlated double sampling circuit or the like, a photoelectric converter small in the fixed pattern noise and the random noise can be obtained.
REFERENCES:
patent: 5233180 (1993-08-01), Tsuruta et al.
patent: 5900623 (1999-05-01), Tsang et al.
patent: 6054704 (2000-04-01), Pritchard et al.
patent: 6252462 (2001-06-01), Hoffman
patent: 6369853 (2002-04-01), Merrill et al.
patent: 6512544 (2003-01-01), Merrill et al.
Adams & Wilks
Lee Patrick J.
Porta David
Seiko Instruments Inc.
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