TC237 Datasheet, PDF (9/15 Pages) Texas Instruments – 680- × 500-pixel ccd image sensor

TC237
680- × 500-PIXEL CCD IMAGE SENSOR
SOCS044B – JUNE 1994 – REVISED JUNE 1996
serial registers
The storage-area gate and serial gate(s) are used to transfer the charge line by line from the storage area into
the serial register(s). Depending on the readout mode, one or both serial registers is used. If both are used, the
registers are read out in parallel.
readout and video processing
After transfer into the serial register(s), the pixels are clocked out and sensed by a charge-detection node. The
node must be reset to a reference level before the next pixel is placed onto the detection node. The timing for
the serial-register readout, which includes the external pixel clamp and sample-and-hold signals needed to
implement correlated double sampling, is shown in Figure 7. As the charge is transferred onto the detection
node, the potential of this node changes in proportion to the amount of signal received. The change is sensed
by an MOS transistor and, after proper buffering, the signal is supplied to the output terminal of the image sensor.
The buffer amplifier converts charge into a video signal. Figure 8 shows the circuit diagram of the
charge-detection node and output amplifier. The detection nodes and amplifiers are placed a short distance
away from the edge of the storage area; therefore, each serial register contains 4 dummy elements that are used
to span the distance between the serial registers and the amplifiers.
SRG
RST
OUT
S/H
PCMP
Figure 7. Serial-Readout and Video-Processing Timing
VREF
QR
Q1
Q2
ADB
Reset
CCD Channel
VOUT
Figure 8. Output Amplifier and Charge-Detection Node
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