AMIS-720341 Datasheet, PDF (5/16 Pages) AMI SEMICONDUCTOR – Contact Image Sensor

AMIS-720341-A: Contact Image Sensor
Data Sheet
5.0 Signal Conversion Circuit
Figure 5 is an example of the charge conversion that is used in the CIS modules. It is usually bonded on the same PCB on which the
image sensors are bonded. In applications where cost is an important factor, this simple circuit provides the cleanest technique in
processing the video output. It integrates all the currents from each pixel element onto a capacitor (CAP). It also sums the energy of the
switch edge along with the signal current pulses, minimizing the switching patterns on the video pixels. The summed charges stored on
the CAP produce a pixel voltage. This voltage amplitude is proportional to the charge from the current pulse and the value of the CAP.
Figure 5: Video Output Test and Application Circuit
Since switching energies are components with high frequencies, they tend to integrate to a 0 value and the remainder adds a constant
value to offset the dark level. After the pixel is integrated, the CAP is reset to 0V by activating the shunt switch, SW, that connects the
video line to ground prior to accessing the following pixel element. Figure 6, which depicts a typical pixel voltage waveform, shows that
the shunt time is controlled with CP. SW activation and the reset to the dark reference level of the pixel element storage occur
simultaneously, initializing the pixel for its integration process cycle. The signal pixels Vp(n) is referenced to its dark level as seen in
Figure 6.
Figure 6: Single Pixel Video Output
AMI Semiconductor – May 06, M-20570-001
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