AD9807/AD9805
3-Channel SHA Operation
This mode of the AD9807/AD9805 enables 3-channel simulta-
neous sampling; it differs from the CDS sampling mode in that
the CDS functions are replaced with sample-and-hold amplifiers
(SHAs). CDSCLK1 becomes the sample-and-hold clock;
CDSCLK2 is tied to ground. The input is sampled on the
falling edge of CDSCLK1. The input signals must be either dc
coupled and level shifted, or dc restored prior to driving the
VINR, VING, and VINB pins of the AD9807/AD9805 (clamp
mode must be disabled). The input signal in this mode is
ground-referenced. The offsets of the three input channels are
modified by the values stored in the input offset registers. The
part does not invert the input signals prior to amplification by
the PGAs; the settings in the corresponding PGA Gain Registers
determine the gains of the PGAs. These outputs from the
PGAs are then routed through a high speed multiplexer to a
12-bit A/D converter (10-bit for AD9805) for digitization; the
multiplexer cycles between the red, green and then blue
channels. After digitization, the data is modified by the amount
indicated in the Odd and Even Offset Registers. A digital
subtracter allows additional pixel rate offset modification of
each color based on the values written to the OFFSET data bus.
Finally, a digital multiplier allows pixel rate gain modification
of each color based on the values written to the GAIN data bus.
Latency for the red, green and blue channels is 6 ADCCLK
cycles (9 cycles for the gain and offset bus; see Figure 13).
The STRTLN signal indicates the first red, green and blue
pixels in a scan line and the red channel is always the first pixel
digitized. The state of STRTLN is evaluated on the rising
edges of ADCCLK. When STRTLN is low, the internal
circuitry is reset on the next rising edge of ADCCLK; the
multiplexer is switched to the red channel and the odd/even
circuitry is configured to expect even pixels. After STRTLN
goes high, the first set of pixels is assumed to be even. Consecu-
tive sets of pixels (red, green and blue) are assumed to alternate
between odd and even pixel sets.
1-Channel Operation with CDS
values written to the GAIN data bus. Latency is 6 ADCCLK
cycles (7 cycles for the gain and offset bus; see Figure 14).
The state of STRTLN is evaluated on the rising edges of
ADCCLK. When STRTLN is low, the internal circuitry is
reset on the next rising edge of ADCCLK; the odd/even
circuitry is configured to expect an even pixel. After STRTLN
goes high, the first pixel is assumed to be even. Consecutive
pixels (red, green or blue) are assumed to alternate between odd
and even. The blue and green channels are recommended for
single channel operation to achieve the maximum sampling rate;
if using red, invert ADCCLK as shown in Figure 1d.
1-Channel SHA Operation
This mode of the AD9807/AD9805 enables single-channel, or
monochrome sampling; it differs from the CDS monochrome
sampling mode in that the CDS function is replaced with a
sample-and-hold amplifier (SHA). CDSCLK1 becomes the
sample-and-hold clock; CDSCLK2 is tied to ground. The
input is sampled on the falling edge of CDSCLK1. The input
waveform would typically be either dc coupled and level shifted,
or dc restored prior to driving either the VINR, VING and
VINB pins of the AD9807/AD9805 (clamp mode must be
disabled).
Bits 6 and 7 in the Configuration Register select the desired
input. The input signal in this mode is ground referenced. The
input signal is not inverted prior to amplification by the PGA;
the setting in the corresponding PGA Gain Register determines
the gain of the PGA. The offset of the input signal is modified
by the value stored in the input offset register. This signal is
then routed through a high speed multiplexer to a 12-bit A/D
converter (10-bit for AD9805) for digitization; the multiplexer
does not cycle in this mode. After digitization, the data is
modified by the amount indicated in the Odd and Even Offset
Registers. A digital subtracter allows additional pixel rate offset
modification of the signal based on the values written to the
OFFSET data bus. Finally, a digital multiplier allows pixel rate
gain modification of the signal based on the values written to the
GAIN data bus. Latency is 6 ADCCLK cycles (7 cycles for
gain and offset; see Figure 15).
The state of STRTLN is evaluated on the rising edges of
ADCCLK. When STRTLN is low, the internal circuitry is
reset on the next rising edge of ADCCLK; the odd/even
circuitry is configured to expect an even pixel. After STRTLN
goes high, the first pixel is assumed to be even. Consecutive
pixels (red, green or blue) are assumed to alternate between odd
and even. The blue and green channels are recommended for
single channel operation to achieve the maximum sampling rate;
if using red, invert ADCCLK as shown in Figure 1f.
2-Channel Bayer Mode Operation with CDS
This mode of the AD9807/AD9805 enables single-channel, or
monochrome, sampling. The CCD waveform is ac coupled to
either the VINR, VING, and VINB pin of the AD9807/AD9805
where it is biased at an appropriate voltage level using the on-
chip clamp; the input may alternatively be dc coupled if it has
already been appropriately level shifted. Bits 6 and 7 in the
Configuration Register select the desired input. The internal
CDS takes two samples of the incoming pixel data: the first
sample (CDSCLK1) is taken during the reset time while the
second sample (CDSCLK2) is taken during the video, or data,
portion of the input pixel. The offset of the input signal is
modified by the value stored in the input offset register. The
voltage
difference
of the reset level and video level is inverted and
amplified by the PGA; the setting in the corresponding PGA
Gain Register determines the gain of the PGA. The output
from the PGA is then routed through a high-speed multiplexer
to a 12-bit A/D converter (10-bit for AD9805) for digitization;
the multiplexer does not cycle in this mode. After digitization,
the data is modified by the amount indicated in the Odd and
Even Offset Registers. A digital subtracter allows additional
pixel rate offset modification of the signal based on the values
written to the OFFSET data bus. Finally, a digital multiplier
allows pixel rate gain modification of the signal based on the
This mode of the AD9807/AD9805 enables Bayer Mode. The
CCD waveform is ac coupled to both the VING and VINB pins
of the AD9807/AD9805 where it is biased at an appropriate
voltage level using the on-chip clamp; the input may alterna-
tively be dc coupled if it has already been appropriately level
shifted. The internal CDS takes two samples of the incoming
pixel data: the first sample (CDSCLK1) is taken during the
reset time while the second sample (CDSCLK2) is taken during
the video, or data, portion of the input pixel. The offset of the
input signal is modified by the value stored in the input offset
register. The voltage difference of the reset level and video level
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