The video signal chain is located in the Analog Electronics Box. The CCD video outputs are processed by four independent preamps, after which the analog signals are multiplexed to reduce chip count. A single amplifier and event detection chain is used. This consists of a post amp, a double correlated sample processor, and a sample and hold circuit. An Analog-to-Digital Converter (ADC) performs a fast 12 bit A/D conversion. This analog signal chain is shown in Figure 23.
Figure 23: Schematic diagram of the video signal chain.
The A/D converter (a Crystal CS5012A) digitizes both the
science data and our housekeeping data.
The signal chain output signal is inverted, with an analog
voltage range of 0 to -5 V.
The Crystal ADC has an input range of 
(0x00) to 
V
(0xFF).
In order to accommodate the signal chain levels, the ADC board
contains a level shifter that inverts the input signal and
subtracts 2.5 V.
The digital output of the ADC is buffered by a FIFO for
further processing by the digital electronics.
The CCD camera, especially the analog signal chain, is extremely
sensitive to low level electronic noise and is designed to be as separate
as possible from the rest of the payload electronics.
Careful attention to grounding and to potential noise sources
is essential for the achievement of low noise performance.
For this reason, the noise-sensitive electronics are powered by their
own DC supplies, and critical cables are twisted and shielded.
The analog (
15V) and digital (+5V) returns are grounded
to the chassis in the CCD camera electronics to minimize noise on the
return lines.
The grounding philosophy adopted for these signals is to use massively
parallel returns, rather than single point grounds, in order to minimize
inductive coupling, which is
the dominant mode of noise transmission at the video frequencies
present in the CCD clock drivers.
The data from the camera are processed in the digital electronics section. This processing consists of event recognition and T/M framing. These are described below.