AD9991 datasheet(28/60 Pages) AD

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AD9991

–28–

It is possible to independently trigger the readout operation

without triggering the exposure operation. This will cause the

readout to occur at the next VD, and the SUBCK output will be

suppressed according to the value of the READOUT register.

The TRIGGER register is also used to control the STROBE,

MSHUT, and VSUB signal transitions. Each of these signals are

individually controlled, although they will be dependent on the

triggering of the exposure and readout operation.

See Figure 32 for a complete example of triggering the exposure

and readout operations.

VSUB Control

The CCD readout bias (VSUB) can be programmed to accom-

modate different CCDs. Figure 29 shows two different modes

that are available. In Mode 0, VSUB goes active during the ﬁeld

of the last SUBCK when the exposure begins. The On position

(rising edge in Figure 29) is programmable to any line within

the ﬁeld. VSUB will remain active until the end of the image

readout. In Mode 1, the VSUB is not activated until the start of

the readout.

An additional function called VSUB KEEP-ON is also available.

When this bit is set high, the VSUB output will remain on (active)

even after the readout has ﬁnished. To disable the VSUB at a later

time, set this bit back to low.

MSHUT and STROBE Control

MSHUT and STROBE operation is shown in Figures 30, 31,

and 32. Table XII shows the register parameters for controlling

the MSHUT and STROBE outputs. The MSHUT output is

switched on with the MSHUTON registers, and will remain on

until the location speciﬁed in the MSHUTOFF registers. The

location of MSHUTOFF is fully programmable to anywhere

within the exposure period, using the FD (ﬁeld), LN (line), and

PX (pixel) registers. The STROBE pulse is deﬁned by the on and

SUBCK

VSUB OPERATION:

1. ACTIVE POLARITY IS POLARITY (ABOVE EXAMPLE IS VSUB ACTIVE HIGH).

2. ON POSITION IS PROGRAMMABLE. MODE 0 TURNS ON AT THE START OF EXPOSURE, MODE 1 TURNS ON AT THE START OF READOUT.

3. OFF POSITION OCCURS AT END OF READOUT.

4. OPTIONAL VSUB KEEP-ON MODE WILL LEAVE THE VSUB ACTIVE AT THE END OF READOUT.

EXP

VSG1

VSUB

READOUT

MODE 0

MODE 1

TRIGGER

VSUB

Figure 29. VSUB Programmability

SUBCK

MSHUT PROGRAMMABLE SETTINGS:

1. ACTIVE POLARITY.

2. ON POSITION IS VD UPDATED AND MAY BE SWITCHED ON AT ANY TIME.

3. OFF POSITION CAN BE PROGRAMMED ANYWHERE FROM THE FIELD OF LAST SUBCK UNTIL THE FIELD BEFORE READOUT.

EXP

VSG

MSHUT

TRIGGER

EXPOSURE

AND MSHUT

Figure 30. MSHUT Output Programmability

REV. 0

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