AMIS-720233 Datasheet, PDF (6/12 Pages) AMI SEMICONDUCTOR – Contact Image Sensor

AMIS-720233-B: Contact Image Sensor
Data Sheet
Figure 5 shows a simply circuit that provides the cleanest technique in processing the video output. It integrates all the currents from
each pixel element onto a capacitor (CAP). Then the CAP is reset to zero volts by activating the shunt switch (SW) and connecting the
video line to ground prior to accessing the following pixel element. Simultaneous to SW activation, the pixel element storage is reset to
the dark level, hence initialized for the new pixel integration process. Since this process sums the switch edges and signal current
pulses onto the CAP, it minimizes the switching patterns on the video pixels. The summed charges stored in the CAP produces a pixel
voltage with amplitude proportional to the charge from the current pulse. Since switching energies are high frequencies components,
they tend to integrate to a 0 value and the remainder adds a constant value to the dark level. The signal pixels Vp(n) is referenced to
the dark level as it is seen in Figure 6, which depicts the typical pixel waveform.
Figure 6: Single Pixel Video Output
To measure these device’s parameters the value of the CAP is set to 100pf. This value includes the stray capacitance of the video line.
The value of RIN in the amplifier circuit is set to infinity before it is removed and accordingly, the amplifier gain is one, therefore serving
as a buffer amplifier, EL2044, AD8051 or its equivalent, to isolate the video line.
Since the output is specified with a light exposure, the video output is specified with a fixed exposure. However, exposure is a function
of power and time, Exp = Light power x the tint, as well as its color. Accordingly, the AMIS-720233-B is measured with a Yellow-Green
LED light source. See Figure 7.
Note: The value of 100pf is selected because the typical PCB layout of an A6 length module has a video line capacitance, including the
stray, in the order of 100pf. The A6 length CIS module uses 13 sensor chips. See Figure 9.
AMI Semiconductor –May 06, M-20567-001
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