CHRONTEL
CH5101A
201-0000-033 Rev 1.0, 6/2/99
7
Functional Description
The CH5101 accepts a light input to a photosensitive array, and produces a digital video stream in response.
The
internal functions performed are:
•
Scanning of the photodiode array into a serial data stream.
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Programmable gain sample and hold with programmable offset.
•
Digitization of data stream.
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Programmable gamma correction.
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Interpolate/Decimate data to desired resolution
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Formatting of the data stream for the desired type of output.
•
Automatic Shutter, Gain and Black Setting.
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Timing signal generation.
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Bus control.
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Power up control of key register bits
Scanning of the photodiode array:
The CH5101 serializes the data captured in the photo array, and outputs one pixel of data each clock period. The
first row is output a programmable number of lines after the leading edge of the vertical sync output. After the
entire row has been output, the next row will be addressed and output. Correlated double sampling techniques are
used during readout to reduce fixed pattern noise. After this transfer is complete, pixel data is serially sent to the
programmable gain amplifier and then to an A/D converter.
Programmable gain sample and hold:
The programmable gain is divided into two sections. The first gain block is controlled by PGSH[2:0] and the sec-
ond by the ADFS control. ADFS can be treated as the MSB of the gain control, and a plot of gain versus control set-
ting is shown below. The programmable gain section also provides a bias adjustment, under the control of the an
chip DAC. When the ASBE bit is a one (default) this DAC value is determined automatically, via a feedback loop
which monitors the A/D output signal. When the ASBE bit is a zero, the DAC can be controlled via BCLMP[7:0].
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GaindB
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Gain
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