AD9991_15 Datasheet, PDF (20/60 Pages) Analog Devices – 10-Bit CCD Signal Processor with Precision Timing Generator

AD9991
Generating Line Alternation for V-Sequence and HBLK
During low resolution readout, some CCDs require a different
number of vertical clocks on alternate lines. The AD9991 can
support this by using the VPATREPO and VPATREPE regis-
ters. This allows a different number of VPAT repetitions to be
programmed on odd and even lines. Note that only the number
of repeats can be different in odd and even lines, but the VPAT
group remains the same.
Additionally, the HBLK signal can also be alternated for odd
and even lines. When the HBLKALT register is set high, the
HBLK TOG1 and TOG2 positions will be used on odd lines,
while the TOG3–TOG6 positions will be used on even lines.
This allows the HBLK interval to be adjusted on odd and even
lines if needed.
Figure 19 shows an example of VPAT repetition alternation and
HBLK alternation used together. It is also possible to use VPAT
and HBLK alternation separately.
Second V-Pattern Group during VSG Active Line
Most CCDs require additional vertical timing during the sensor
gate line. The AD9991 supports the option to output a second
V-pattern group for V1–V6 during the line when the sensor gates
VSG1–VSG5 are active. Figure 20 shows a typical VSG line,
which includes two separate sets of V-pattern groups for V1–V6.
The V-pattern group at the start of the VSG line is selected in the
same manner as the other regions, using the appropriate VSE-
QSEL register. The second V-pattern group, unique to the VSG
line, is selected using the VPATSECOND register, located with
the Field registers. The start position of the second VPAT group
uses the VPATLEN register from the selected VPAT registers.
Because the VPATLEN register is used as the start position and
not as the VPAT length, it is not possible to program multiple
repetitions for the second VPAT group.
HD
VPATREPO = 2
V1
V2
VPATREPE = 5
VPATREPO = 2
V6
HBLK
TOG1
TOG2
TOG3
TOG4
TOG1
TOG2
NOTES
1. THE NUMBER OF REPEATS FOR THE V-PATTERN GROUP MAY BE ALTERNATED ON ODD AND EVEN LINES.
2. THE HBLK TOGGLE POSITIONS MAY BE ALTERNATED BETWEEN ODD AND EVEN LINES IN ORDER TO GENERATE DIFFERENT HBLK PATTERNS FOR ODD/EVEN LINES.
Figure 19. Odd/Even Line Alternation of VPAT Repetitions and HBLK Toggle Positions
HD
VSG
V1
V2
START POSITION FOR 2ND VPAT GROUP
USES VPATLEN REGISTER
V6
2ND VPAT GROUP
Figure 20. Example of Second VPAT Group during Sensor Gate Line
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