AD9891 datasheet(24/58 Pages) AD

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REV. A

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AD9891/AD9895

Vertical Multiplier Mode

To generate very wide vertical timing pulses, a vertical region may

be configured into Multiplier Mode. This mode uses the vertical

sequence registers in a slightly different manner. Multiplier Mode

can be used to support unusual CCD timing requirements, such as

vertical pulses that are wider than a single HD line length.

The start polarity and toggle positions are still used in the same

manner as the standard sequence generation, but the length is

used differently. Instead of using the pixel counter (HD counter)

to specify the toggle position locations (VTPTOG1, 2, 3) of the

sequence, VTP length (VTPLEN) is multiplied by the

VTPTOG position to allow very long sequences to be generated.

To calculate the exact toggle position, counted in pixels after the

start position:

Multiplier Toggle Position VTPTOG VTPLEN

=×

Because the VTPTOG Register is multiplied by VTPLEN, the

resolution of the toggle position placement is reduced. If

VTPLEN = 4, the toggle position accuracy is now reduced to

4-pixel steps instead of single pixel steps. Table XII summarizes

how the Individual Vertical Sequence Registers are pro-

grammed for Multiplier Mode operation. Note that the bit

ranges for the VTPTOG and VTPREP Registers differ from the

normal operation shown in Table VII. In Multiplier Mode, the

VTPREP Register should always be programmed to the same

value as the highest toggle position register.

The example shown in Figure 27 illustrates this operation. The

first toggle position is 2 and the second toggle position is 9. In

Nonmultiplier Mode, this would cause the V-sequence to

toggle at pixel 2 and then pixel 9 within a single HD line. How-

ever, now toggle positions are multiplied by the VTPLEN = 4,

so the first toggle occurs at pixel count = 8, and the second toggle

occurs at pixel count = 36. Sweep Mode should be enabled to

allow the toggle positions to cross the HD line boundaries.

Frame Transfer CCD Mode

The AD9891/AD9895 may also be configured for use with frame

transfer CCDs. In Frame Transfer CCD (FTCCD) Mode,

an additional four vertical outputs are available for a total of

eight outputs (V1–V8). In this case, V1–V4 are used for clock-

ing the active image area, and V5–V8 are used for clocking the

storage area. In FTCCD Mode, the sequences assigned to the

V1–V4 outputs are duplicated at the V5–V8 outputs to allow the

storage area to be clocked along with the image area. Individual

masking of the V1–V4 and V5–V8 outputs allows for vertical

decimation techniques during transfer from the image to the

storage area. The additional outputs V5–V8 are available on four

of the sensor gate output pins, VSG1–VSG4. Figure 28 shows

an example of the eight V-clocks configured for use with a frame

transfer CCD.

V1–V4

VTPLEN

MULTIPLIER MODE VERTICAL SEQUENCE PROPERTIES:

1: START POLARITY (ABOVE: STARTPOL = 0)

2: 1ST, 2ND, AND 3RD TOGGLE POSITIONS (ABOVE: VTPTOG1 = 2, VTPTOG2 = 9)

3: LENGTH OF VTP COUNTER (ABOVE: VTPLEN = 4). THIS IS THE MINIMUM RESOLUTION FOR TOGGLE POSITION CHANGES.

4: TOGGLE POSITIONS OCCUR AT LOCATION EQUAL TO (VTPTOG

VTPLEN)

5: ENABLE SWEEP REGION ALLOWS THE COUNTERS TO CROSS THE HD BOUNDARIES

123412341234123412341234

START POSITION OF SEQUENCE IS INDIVIDUALLY PROGRAMMABLE FOR EACH V1–V4 OUTPUT

PIXELS

234

5678

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Figure 27. Example of Multiplier Region for Wide Vertical Pulse Timing

Table XII. Multiplier Mode and Sequence Register Parameters

Length

Range

Description

MULTI

HIGH/LOW

High Enables Multiplier Mode for Each Region 0–4

VTPPOL

HIGH/LOW

Starting Polarity of Vertical Transfer Pulse for Each Sequence 0–11

VTPTOG1

12b

0–4095 Pixel Location

First Toggle Position for Each Sequence 0–11

VTPTOG2

12b

0–4095 Pixel Location

Second Toggle Position for Each Sequence 0–11

VTPTOG3

12b

0–4095 Pixel Location

Third Toggle Position for Each Sequence 0–7

VTPLEN

10b

0–1023 Pixels

“Multiplier” Factor for Repetition Counter

VTPREP

12b

0–4096

Should Be Programmed to the Same Value as the Highest Toggle Position

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