Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2000-05-02
2002-06-25
Kim, Robert H. (Department: 2882)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
Reexamination Certificate
active
06410900
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a solid-state image sensor and a method of driving the same, and more particularly to a MOS-type solid-state image sensor having a function of detecting movement, and method of driving the same.
2. Description of the Related Art
A MOS-type solid-state image sensor including a plurality of pixels each having a photoelectric converter and arranged in a two-dimensional array is sometimes designed to have a function of detecting movement. Such a MOS-type solid-state image sensor not only converts a scene detected by a sensor array, into an electric signal, but also detects movement of something in a scene detected by a sensor array, and transmits a signal accordingly. In the specification, such a MOS-type solid-state image sensor having a function of detecting movement is hereinafter called a movement-sensor.
A conventional solid-state image sensor not having a function of detecting movement is explained hereinbelow with reference to
FIGS. 1 and 2
.
FIG. 1
is a block diagram of a conventional MOS-type solid-state image sensor, and
FIG. 2
is a circuit diagram of a pixel constituting a sensor array which is a part of the MOS-type solid-state image sensor illustrated in FIG.
1
.
As illustrated in
FIG. 1
, a conventional MOS-type solid-state image sensor is comprised of a sensor array
801
including a plurality of pixels arranged in an array, each pixel converting a light into an electric signal in accordance with brightness of an image, a scanning circuit
802
which scans electric signals converted by the pixels, a X-scanning circuit
803
which scans the electric signals converted by the pixels, and a plurality of line memories
804
each temporarily accumulating the electric signals.
The sensor array
801
is defined by a plurality of pixels arranged in a two-dimensional array. Each of the pixels is designed to include a photoelectric transfer diode. An image projected on the sensor array
801
is converted into an electric signal by the pixels.
The Y-scanning circuit
802
transmits Y-scanning signals
807
to thereby make access to the pixels row by row in the sensor array
801
from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array
801
are concurrently read out as row signals
805
.
These row signals
805
are accumulated in the line memories
804
. Each of the line memories
804
is comprised of a switched capacitor, for instance. Since row signals are generally analog signals, they can be accumulated in switched capacitors by the number equal to the number of pixels existing in a row.
The X-scanning circuit
803
transmits X-scanning signals
808
to the line memories
804
to thereby make successive access to the row signals accumulated therein, and transmits an output signal
806
.
As illustrated in
FIG. 2
, a pixel which carries out photoelectric transfer is comprised of a photodiode
901
, a first n-MOSFET
902
including a gate electrically connected to a bias terminal
905
, a drain electrically connected to a source voltage VDD and a source electrically connected to the photodiode
901
, a second n-MOSFET
903
including a gate electrically connected to the photodiode
901
, a source electrically connected to the source voltage VDD and a drain, and a third n-MOSFET
904
including a gate electrically connected to a terminal
906
through which a signal is input, a source electrically connected to the drain of the second transistor
903
and a drain electrically connected to a output line
907
.
The photodiode
901
is kept biased by the first n-MOSFET
902
, and hence, keeps producing photoelectric current. A bias voltage is applied to the first n-MOSFET
902
through the bias terminal
905
. A voltage at the drain of the first n-MOSFET
902
is output at a low impedance through the second n-MOSFET
903
.
The third n-MOSFET
904
acts as a switch. When the third n-MOSFET
904
makes access to a pixel, the third n-MOSFET
904
is turned on by the Y-scanning circuit
802
through the terminal
906
. When the third n-MOSFET
902
is caused to be turned on, a pixel output signal is transmitted through the output line
907
.
The conventional solid-state image sensor has such a structure as mentioned above, and operates in the above-mentioned way. If a movement sensor is designed based on the above-mentioned conventional solid-state image sensor, the movement sensor would have such a structure as mentioned below.
FIG. 3
is a block diagram of a conventional movement sensor having a structure designed based on the structure of the solid-state image sensor illustrated in FIG.
1
. The movement sensor illustrated in
FIG. 3
is comprised of a sensor array
1001
including a plurality of pixels arranged in a matrix array, each pixel converting a light into an electric signal in accordance with brightness of an image, a Y-scanning circuit
1002
which scans electric signals converted by the pixels, a X-scanning circuit
1003
which scans the electric signals converted by the pixels, a plurality of line memories
1004
each temporarily accumulating the electric signals, and a plurality of differential circuits
1007
electrically connected between the line memories
1004
and the X-scanning circuit
1003
.
In brief, the movement sensor additionally includes the differential circuit
1007
in comparison to the solid-state image sensor illustrated in FIG.
1
.
The Y-scanning circuit
1002
transmits Y-scanning signals
1009
to the sensor array
1001
to thereby make access to the pixels row by row in the sensor array
1001
from an uppermost row to a lowermost row. As a result, signals in each of rows in the sensor array
1001
are concurrently read out as first row signals
1005
. These first row signals
1005
are accumulated in the line memories
1004
.
Then, the Y-scanning circuit
1002
makes access again to the pixel row which has been previously accessed. As a result, signals in the row are read out as second row signals
1008
, which are accumulated in the line memories
1004
. The line memories
1004
separately transmits the first and second row signals a
1005
and
1008
to the differential circuits
1007
. The differential circuits
1007
calculates a difference between the first and second row signals
1005
and
1008
. The calculation is concurrently carried out for all the first and second row signals
1005
and
1008
transmitted from a pixel row.
The movement sensor illustrated in
FIG. 3
includes the differential circuits
1007
by the number equal to the number of pixels in a row in the sensor array
1001
.
Output signals transmitted from the differential circuits
1007
, each indicating a difference between the first and second row signals
1005
and
1008
, are successively read out in accordance with X-scanning signals
1010
transmitted by the X-scanning circuit
1003
. The thus read-out output signals are transmitted from the X-scanning circuit
1003
as output signals
1006
.
In the above-mentioned movement sensor, since signals are read out twice from the same pixel row at a certain interval and a difference between the signals is calculated, the differential circuits
1007
transmit non-zero output signals for pixels in which a light intensity varies. When the differential circuits
1007
transmits such non-zero output signals, it is deemed that movement has occurred in the sensor array
1001
.
It should be noted that the movement sensor illustrated in
FIG. 3
does never spoil functions of the conventional solid-state image sensor illustrated in FIG.
1
. Accordingly, the movement sensor can act as a solid-state image sensor. When the movement sensor acts as a solid-state image sensor, the Y-scanning circuit
1002
successively makes access to pixels row by row in the sensor array
1001
, and signals which were read out from each of rows are output through the differential circuits
1007
.
A movement sensor such as the above-mentioned one is detailed is described, for instance, in 1995 IEEE International Solid-State Circ
NEC Corporation
Yun Jurie
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