XRD9818 Datasheet, PDF (9/28 Pages) Exar Corporation – 3-CHANNEL 16-BIT LINEAR CCD/CIS SENSOR SIGNAL PROCESSOR

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XRD9818
3-CHANNEL 16-BIT LINEAR CCD/CIS SENSOR SIGNAL PROCESSOR
REV. 1.0.1
PRODUCT DESCRIPTION
1.0 INTRODUCTION
The XRD9818 contains all of the circuitry required to create a complete 3-channel signal processor/digitizer for
use in CCD/CIS imaging systems. It can be configured to operate in a 3-CH rotating (RGB), 2-CH rotating
(RG, GR, GB or BR), or a 1-CH fixed (R, G or B) mode.
Each channel includes a correlated-double-sampler/sample-hold (CDS/SH), channel offset adjustment and
programmable gain amplifier (PGA). After signal conditioning the channel outputs are multiplexed and digitized
by a 16-bit A/D converter.
The XRD9818 has selectable 8-bit (byte) or 4-bit (nibble) data output modes. The ADCLK runs up to 12MHz in
the 8-bit data output mode or 24MHz in the 4-bit data output mode.
In order to maximize flexibility, the specific operating mode is programmable through internal configuration
registers. In addition, the offset and gain of each channel can be independently programmed through separate
offset and gain registers. The configuration, offset and gain register information is loaded through a 3-pin serial
interface.
2.0 MODES OF OPERATION
2.1 3-CH CCD Mode
In 3-CH mode the XRD9818 simultaneously samples the red, green and blue channel inputs. The CDS
extracts the video information which corresponds to the difference between the sample black reference and
video level for each pixel. The black reference level is sampled on the falling edge of BSAMP and the video
level is sampled on the falling edge of VSAMP. This information is then level shifted and gained up according to
the contents of the Offset and PGA registers respectively. The data is then sequentially converted (Red →
Green → Blue) by a 16-bit A/D converter.
In CCD mode, each channel input is sampled with respect to the CMN- input. This provides a sudo-differential
input. Typically the CMN- input is connected to the CCD ground through a capacitor. This coupling capacitor
should be at least 3 times the capacitor value used to couple the RED+, GRN+ and BLU+ inputs.
The timing for this mode is shown in Figure 15.
2.2 2-CH CCD Mode
The 2-CH mode operates identically to the 3-CH CCD mode except that only 2 channels are actively used to
process CCD output signals. The two channels to be used and the order in which they process data is
determined from the configuration of the Input-Mux/Channel-Select bits (CH[2:0]) located in the Mode 1
register. There are four possible 2-CH configurations, RG, GR, GB and BR. To conserve power that channel
not being utilized is powered down.
The timing for this mode is shown in Figure 16.
2.3 1-CH CCD Mode
The 1-CH mode operates identically to the 3-CH or 2-CH CCD modes except that the channel sampled is fixed
to only one input. The channel selection is set by the Input-Mux/Channel-Select bits (CH[2:0]) located in the
Mode 1 register. There are three possible one channel modes: R, G or B. The channels not being used will be
powered down to conserve power.
The timing for this mode is shown in Figure 17.
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