TLC8044 Datasheet, PDF (11/32 Pages) Texas Instruments – 12-BIT ANALOG-TO-DIGITAL INTERFACE FOR CHARGE-COUPLED DEVICE IMAGE SENSORS FOR SCANNERS

TLC8044
12-BIT ANALOG-TO-DIGITAL INTERFACE FOR
CHARGE-COUPLED DEVICE IMAGE SENSORS FOR SCANNERS
SLAS128 – JUNE 1997
PRINCIPLES OF OPERATION
general CCD system operation
CCD image sensor array output summary
Figure 8 shows a simplified CCD image sensor linear array system with typical CCD array inputs and outputs.
The inputs for the shift gate (SH), reset, and two-phase clock drive the array. An electronic charge proportional
to the light input is generated by a photo diode for each pixel of the array. The charge for each pixel is transferred
in parallel into the analog CCD shift register using the shift gate input and then shifted out serially using a
two-phase clock. At the CCD output (OS terminal), the array converts the charge for each pixel into a voltage
using a capacitor and source follower MOS transistor. The charge on this capacitor is reset for each pixel by
the reset pulse input. A typical output signal then includes a reset period, a dark period, and a period containing
video output for each pixel, as shown in Figure 9. This signal sits on a varying dc offset of typically 5 V and is
negative going for an increase in video output. An output (DOS terminal) also provides only the dc level from
the CCD array.
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