AMIS-720233 Datasheet, PDF (5/12 Pages) AMI SEMICONDUCTOR – Contact Image Sensor

AMIS-720233-B: Contact Image Sensor
Data Sheet
5.0 Output Circuit of the Image Sensor
The video signal from each photo-site is connected to a common video line on the sensor. Each photo-site is composed of a
phototransistor with a series MOS switch connecting its emitter to a common video line. The video line is connected to the pad labeled
IOUT. The photo-sensing element is the base of the phototransistor where it detects and converts the light energy to proportional
charges and stores it in its base capacitance. When the MOS switch is activated, the emitter is connected to the video line and acts as
source follower, producing an impulse current proportional to the stored charges in the base. This current is a discrete-time analog
signal output called the video pixel. Accordingly, the video pixel is proportional to the light energy impinging in the neighborhood of its
photo-sites. Figure 4, shows the output structure of four photo-sites out of 64. The multiplexing MOS switch in each photo-site
terminates into the output pad, IOUT, through a common video line. The shift register sequentially accesses each photo-site by a
activating the MOS switch. As they are accessed, a sequence of video pixels is sent to the IOUT where they are processed with an
external signal conversion circuit.
5.1 Signal Conversion Circuit
Figure 4: Video Pixel Output Structures
Figure 5: Video Output Test and Application Circuit
AMI Semiconductor –May 06, M-20567-001
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