AD9927 Analog Devices, AD9927 Datasheet - Page 42

• Manufacturer Part Number: AD9927
• Description: 14-Bit CCD Signal Processor
• Manufacturer: Analog Devices

AD9927
Sweep Mode Operation
The AD9927 contains an additional mode of vertical timing
operation called sweep mode. This mode is used to generate a
large number of repetitive pulses that span across multiple HD
lines. An example of where this mode is needed is at the start of
the CCD readout operation. At the end of the image exposure
before the image is transferred by the sensor gate pulses, the
vertical interline CCD registers should be free of all charge. This
can be accomplished by quickly shifting out any charge using a
long series of pulses from the vertical outputs. Depending on
the vertical resolution of the CCD, up to 3000 clock cycles
might be needed to shift the charge out of each vertical CCD
line. This operation spans across multiple HD line lengths.
Normally, the AD9927 vertical timing must be contained within
one HD line length, but when sweep mode is enabled, the HD
boundaries are ignored until the region is finished. To enable
sweep mode within any region, program the appropriate SWEEP
register to high.
XV1 TO XVN
XV1 TO XVN
VSG
HD
VD
VD
HD
FIELD SETTINGS:
1. SEQUENCE CHANGE POSITIONS (SCP0 TO SCP8) DEFINE EACH OF THE NINE AVAILABLE REGIONS IN THE FIELD.
2. SEQ0 TO SEQ8 SELECT THE DESIRED V-SEQUENCE FOR EACH REGION.
3. SGACTLINE1 REGISTER SELECTS WHICH HD LINE IN THE FIELD CONTAINS THE SENSOR GATE PULSE(S).
SCP0
REGION 0
SEQ0
LINE 0
REGION 0
SCP1
REGION 1
SEQ1
SGACTLINE1
LINE 1
Figure 50. Example of Sweep Region for High Speed Vertical Shift
SCP2
SCP1
Figure 49. Complete Field is Divided into Regions
REGION 2
SEQ2
LINE 2
SCP3
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REGION 3
SEQ3
REGION 1: SWEEP REGION
SCP4
Figure 50 shows an example of the sweep mode operation. The
number of vertical pulses needed depends on the vertical reso-
lution of the CCD. The toggle positions for the XV1 to XV24
signals are generated using the V-pattern registers (shown in
Table 13). A single pulse is created using the polarity and toggle
position registers. The number of repetitions is then programmed
to match the number of vertical shifts required by the CCD.
Repetitions are programmed into the V-sequence registers
(shown in Table 14) by using the VREP registers. This produces
a pulse train of the appropriate length. Normally, the pulse train
is truncated at the end of the HD line length, but when sweep
mode is enabled for this region, the HD boundaries are ignored.
In Figure 50, the sweep region occupies 23 HD lines. After the
sweep mode region is complete, normal sequence operation
resumes in the next region. When using sweep mode, be sure to
set the region boundaries (using the sequence change positions)
to the appropriate lines to prevent the sweep operation from
overlapping the next V-sequence.
REGION 4
SEQ4
SCP5
SCP8
REGION 8
SEQ8
LINE 24
SCP2
LINE 25
REGION 2