AD9923ABBCZ datasheet(48/88 Pages) AD

48 / 88 page

AD9923A

Rev. 0 | Page 48 of 88

SUBCK: Suppression

Normally, the SUBCK begins pulsing on the line following the

sensor gate line (VSG). Some CCDs require suppressing the

SUBCK pulse for one or more lines following the VSG line. The

SUBCKSUPPRESS register enables such suppression.

Readout After Exposure

After the exposure, the readout of the CCD data occurs, beginning

with the sensor gate (VSG) operation. By default, the AD9923A

generates VSG pulses in every field. When only a single exposure

and readout frame are needed, as is the case in the CCD preview

mode, the VSG and SUBCK pulses can operate in every field.

However, often during readout, the SUBCK output must be

suppressed until the readout is complete. The READOUTNUM

to continue the suppression of SUBCK. READOUTNUM can be

programmed for 0 to 7 fields, and should be preprogrammed at

startup, not at the same time as the exposure write. A typical

interlaced CCD frame readout mode generally requires two fields

of SUBCK suppression (READOUTNUM = 2) during readout.

A three-field, six-phase CCD requires three fields of SUBCK

suppression after the readout begins (READOUTNUM = 3).

If SUBCK output is required to initiate backup during the last field

of readout, program the READOUTNUM register to one less

than the total number of CCD readout fields. Similar to the

exposure operation, the readout operation must be triggered

using the TRIGGER register.

SUBCK: Additional Masking

The SUBCKMASK register (Address 0x65) allows more complex

SUBCK masking. If SUBCKMASK = 1, it starts masking the

SUBCK at the next VD edge. If SUBCKMASK = 2, it enables

users to select the internal SHUT3 signal and create a custom

SUBCK masking pattern that spans several fields.

When generating an exposure by using the TRIGGER register,

as previously described in the Readout After Exposure section,

the AD9923A outputs the SUBCK and VSG signals on every

field by default. This works well for continuous, single field

exposure and readout operations, such as those in the CCD live

preview mode. However, if the CCD requires a longer exposure

time, or if multiple readout fields are needed, the TRIGGER

sequences.

Typically, the exposure and readout bits in the TRIGGER register

are used together. This initiates a complete exposure-plus-readout

operation. After the exposure, the readout occurs automatically.

The values in the EXPOSURE and READOUTNUM registers

determine the length of each operation.

It is possible to independently trigger the readout operation

without triggering the exposure operation. This causes the readout

to occur at the next VD, and the SUBCK output is suppressed

according to the value set in the READOUTNUM register.

The TRIGGER register also controls the SHUT and VSUB signals.

Each signal is individually controlled, but dependent on the

triggering of the exposure and readout operations. See Figure 71

for a complete example of triggering the exposure and readout

operations.

Alternatively, it is possible to manually control the exposure and

readout operations by carefully updating the SUBCKSUPPRESS

and VSG masking registers upon every VD field. As described in

the following sections, it is possible to have partial or full manual

control of the shutter signals. This allows greater flexibility in

generating custom exposure/readout/shutter signal timing.

AD9923ABBCZ Datasheet(PDF) 48 Page - Analog Devices

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