
AD9923A
VERTICAL TIMING EXAMPLE
To better understand how the AD9923A vertical timing
generation is used, consider the example CCD timing chart
in Figure 52. It illustrates a CCD using a general three-field
readout technique. As described in the Complete Field:
Combining V-Sequences section, each readout field should
be divided into separate regions to perform each step of the
readout. The sequence change position (SCP) registers deter-
mine the line boundaries for each region. Then, the VSEQSEL
registers assign a V-sequence to each region. Each V-sequence
contains specific timing information required for each region:
XV1 to XV6 pulses (using VPAT groups), HBLK/CLPOB timing,
and VSG patterns for the SG active lines.
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The example shown in Figure 52 requires four regions, labeled
Region 0, Region 1, Region 2, and Region 3, for each of the
three fields. Because the AD9923A allows many individual
fields to be programmed, Field 0, Field 1, and Field 2 can be
created to meet the requirements of this timing example. In this
example, the four regions for each field are very similar, but the
individual registers for each field allow flexibility to accommodate
more complex timing requirements.
Region 0
Region 0 is a high speed vertical shift region. Sweep mode can
be used to generate this timing operation, with the desired
number of high speed vertical pulses needed to clear any charge
from the vertical registers of the CCD.
Region 1
Region 1 consists of two lines and uses standard, single line,
vertical shift timing. The timing of this region is the same as the
timing of Region 3.
Region 2
Region 2 is the sensor gate line, where the VSG pulses transfer
the image into the vertical CCD registers. This region might
require use of the second V-pattern group for the SG active line.
Region 3
Region 3 also uses the standard, single line, vertical shift timing,
the same timing used in Region 1. In summary, four regions are
required in each of the three fields.
The timing for Region 1 and Region 3 is essentially the same,
reducing the complexity of the register programming. Other
registers, such as the MODE register, shutter control registers
(that is, TRIGGER, and the registers to control the SUBCK,
VSUB, MSHUT, and STROBE outputs), and the AFE gain
registers, VGAGAIN and CDSGAIN, must be used during the
readout operation. These registers are explained in the MODE
Register and Variable Gain Amplifier sections.