XRD9824

8

Rev. 2.00

THEORY OF OPERATION

CIS Configuration (Contact Image Sensor)

The XRD9824 has two configurations for CIS applications. 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

XRD9824 input.

Optically Shielded

Pixels

Valid Pixels

Adjust the offset of the CIS (-100 mV to 500 mV) by setting the internal registers of the XRD9824 to set the black

pixel value when the LEDs of the CIS are off. When the LEDs are on, use the XRD9824 Programmable Gain to

maximize the ADCs dynamic range. Figure 3 shows a typical application for a CIS with an offset of -100mV to

500mV.

Figure 2. Typical Output CIS Mode