XRD9825 Datasheet, PDF (8/33 Pages) Exar Corporation – 16-Bit Linear CIS/CCD Sensor Signal Processor with Serial Control

XRD9825
THEORY OF OPERATION
CIS Configuration (Contact Image Sensor)
The XRD9825 has two configurations for CIS applica-
tions. Each configuration is set by the control registers
accessed through the serial port.
Mode 1. DC Coupled
If the CIS does not have leading or trailing black pixels
as shown in Figure 2, then DC couple the CIS output to
the XRD9825 input.
Optically Shielded
Pixels
Valid Pixels
Figure 2. Typical Output CIS Mode
Adjust the offset of the CIS (-100 mV to 500 mV) by
setting the internal registers of the XRD9825 to set the
black pixel value when the LEDs of the CIS are off.
When the LEDs are on, use the XRD9825 Program-
mable Gain to maximize the ADCs dynamic range.
Figure 3, shows a typical application for a CIS with an
offset of -100mV to 500mV.
Rev. 1.00
8