Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2001-03-13
2003-01-28
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S2140RC, C250S2140AG, C250S214100, C257S443000, C257S291000, C348S294000, C348S300000
Reexamination Certificate
active
06512221
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the field of the CIS (Contact Image Sensor) technology, in particular, it concerns the manufacturing of a sensor chip and the assembly of a CIS module with a butting technique to form a sensor chip array.
BACKGROUND OF THE INVENTION
The prior art technique of butting for the assembly of a sensor array inside a CIS module is schematically illustrated in
FIG. 1
wherein a PCB (Printed Circuits Board)
100
is shown. Sensor chips
110
,
120
, . . . ,
190
were attached to the PCB
100
and butted to form a linear array. All the sensor chips
110
,
120
, . . . ,
190
were of the same design and were manufactured with the same process. That is, the pixel arrays (
1101
to
1109
), (
1201
to
1209
) and (
1901
to
1909
) were the same. Likewise, the mux (multiplexing) switch arrays (
1111
to
1119
) from chip
110
and (
1911
to
1919
) from chip
190
were the same. In each of the sensor chips
110
,
120
and
190
, each switch of the mux switch array was connected between a corresponding pixel and a single common line. For example, in chip
110
, the common line is designated as
1121
. In turn, the common line
1121
was connected to an output bonding pad
1132
. Other bonding pads,: like bonding pad
1131
in chip
110
, are shown with no connections on purpose, as they are not relevant to the current invention.
The output bonding pad
1132
from chip
110
and the other output bonding pads from the other chips were wire bonded to a common conductor stripe
1151
, which in turn was connected to an associated electronic block
1173
necessary for the proper functioning of the CIS module. The detail of the electronic block
1173
is not shown here as it is not relevant to the current invention. Additionally, if the pixel of the sensor array was of a photo-transistor type, the common conductor stripe
1151
was connected to a charge integrating capacitor
1161
and an input resistor
1162
, which in turn was connected to the non-inverting input terminal of an operational amplifier (OP)
1170
. However, if the pixel of the sensor array was of a photo-diode type, the charge integrating capacitor
1161
can be omitted from the circuitry. The output terminal
1171
of operational amplifier
1170
was connected to the electronic block
1173
for final output of the photo-signal from each pixel. A feedback resistor
1172
was connected between the output terminal
1171
and the inverting input terminal of the operational amplifier
1170
. A gain-control resistor
1175
was connected between the inverting input terminal of the operational amplifier
1170
and ground. The operational principle of the sensor array can be described as follows:
After a desired time period of exposure of the sensor array to an incident light, the generated light-signal from each pixel was read by applying a read signal pulse to turn on an individual switch of the mux switch array in sequential order from left to right of each chip. After the light-signal from the last pixel of the first chip
110
was read, the first pixel
1201
of the next butted chip
120
was read and so on until the reading of the light-signal from the last pixel
1909
of the last chip
190
to complete the reading of light-signal from the entire sensor array on the PCB
100
.
Next, the process of generation of the light-signal from a pixel and its readout is described in more detail. With the mux switch
1111
turned on, the charge integrating capacitor
1161
started to sense the light-signal from the first pixel
1101
by accumulating the photo-charge flowing from the first pixel. The light-signal from the first pixel
1101
of the first chip
110
was then amplified by the operational amplifier
1170
with a gain which was determined by the ratio of the feedback resistor
1172
to the gain-control resistor
1175
. The amplified light-signal from the first pixel
1101
appeared at the output terminal
1171
of the operational amplifier
1170
and was transferred to the outside system through the associated electronic block
1173
. After reading the light-signal from the first pixel
1101
of the first chip
110
, the stored photo-charge of the charge integrating capacitor
1161
was cleared by applying a reset signal pulse to turn on a reset switch
1181
which was a transistor connected across the charge integrating capacitor
1161
. The charge integrating capacitor
1161
was then ready to read the light-signal from the next pixel. Thus, a second read pulse was applied to turn on the second mux switch connecting the second pixel of the first chip
110
and the common conductor stripe
1121
. The aforementioned reading process of the light-signal from the first pixel
1101
was repeated to acquire the light-signal from the second pixel. This reading process was continued until every pixel of the first chip
110
was read. After the light-signal from the last pixel
1109
of the first chip
110
was read, the first pixel
1201
of the second chip
120
was read following the same procedure as described above. This reading process was continued on until the last pixel
1909
of the last chip
190
of the chip array to complete the reading of all the light-signals of the sensor array. Likewise, the dark-signal, which was the signal from the pixel with no light exposure, was read from each pixel of the sensor array with the same process as described above for the reading of the light-signal. Finally, the actual usable photo-signal from each pixel was computed as the corresponding light-signal minus the dark-signal for the subject pixel.
While this technique is simple, it suffers from a drawback of high assembly cost as many components, like a charge integrating capacitor
1161
, three resistors
1162
,
1172
,
1175
and an operational amplifier
1170
, are required to be assembled onto the PCB
100
. The result is increased cost of the CIS module.
In order to reduce the cost of the CIS module, an approach was taken to integrate the operational amplifier into the sensor chip. This is illustrated in FIG.
2
. From now on, the same component designation will be used in different figures whenever either the same component or a component with the same function is encountered. As shown, the sensor chip
200
now included additional components of a charge integrating capacitor
210
, a reset switch
281
, an operational amplifier
231
plus two resistors, a feedback-resistor
252
and a gain-control resistor
253
in contrast to the conventional sensor chips
110
,
120
, . . . ,
190
from FIG.
1
. An output bonding pad
1132
was provided for the output-terminal
251
of the operational amplifier
231
. Each operational amplifier functioned only while a light signal was read from the pixels within the same chip. Each chip had its own charge integrating capacitor for reading purposes. The pixel array (
1101
to
1109
) and the mux switch array (
1111
to
1119
) of the sensor chip
200
remained the same as those shown in FIG.
1
. An associated electronic block
259
was also shown for other electronic functions. Thus, just like the chip array
110
,
120
, . . .
190
from
FIG. 1
, many of these chips
200
with their respective on-chip operational amplifiers
231
were butted to form a sensor array of the desired length. The operational principle remained the same as described in
FIG. 1
except that each chip now has its own operational amplifier instead of a common operational amplifier being shared by the entire chip array. While the associated assembly cost of the CIS module was now reduced with the corresponding reduction of component counts, other problems were brought about by this approach. Firstly, the offset voltage of the operational amplifier was different from chip to chip. Additionally, the gain of the operational amplifier also varied slightly from chip to chip. This resulted in an undesirable non-uniformity of the dark signal level. Secondly, the required size of the charge integrating capacitor
210
was usually large. Consequently it was difficult if not imp
Wang Weng-Lyang
Yen Yung Chau
Allen Stephone B.
Chang Chi Ping
CMOS Sensor, Inc.
Glass Christopher W.
Pacific Law Group LLP
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