AD9974BBCZ datasheet(22/52 Pages) AD

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AD9974

Rev. A | Page 22 of 52

HBLK Mode 1 Operation

Enable multiple repeats of the HBLK signal by setting

HBLK_MODE to 1. In this mode, the HBLK pattern can be

generated using a different set of registers: HBLKSTART,

HBLKEND, HBLKLEN, and HBLKREP, along with the six

toggle positions (see Figure 28).

Separate toggle positions are available for even and odd lines.

If alternation is not needed, load the same values into the registers

for even (HBLKTOGE) and odd (HBLKTOGO) lines.

Generating HBLK Line Alternation

HBLK Mode 0 and HBLK Mode 1 provide the ability to

alternate different HBLK toggle positions on even and odd

lines. Separate toggle positions are available for even and odd

lines. If even/odd line alternation is not required, load the same

values into the registers for even (HBLKTOGE) and odd

(HBLKTOGO) lines.

Increasing H-Clock Width During HBLK

HBLK Mode 0 and HBLK Mode 1 allow the H1 to H4 pulse

width to be increased during the HBLK interval. As shown in

Figure 29, the H-clock frequency can be reduced by a factor of

1/2, 1/4, 1/6, 1/8, 1/10, 1/12, and so on, up to 1/30. To enable this

feature, the HCLK_WIDTH register (Address 0x34[7:4]) is set to

a value between 1 and 15. When this register is set to 0, the wide

HCLK feature is disabled. The reduced frequency occurs only for

H1 to H4 pulses that are located within the HBLK area.

The HCLK_WIDTH register is generally used in conjunction

with special HBLK patterns to generate vertical and horizontal

mixing in the CCD.

Note that the wide HCLK feature is available only in HBLK Mode 0

and HBLK Mode 1, not in HBLK Mode 2.

Table 13. HCLK Width Register

Length (Bits)

Description

HCLK_WIDTH

Controls H1 to H4 width during HBLK as a fraction of pixel rate.

0 = same frequency as pixel rate.

1 = 1/2 pixel frequency, that is, doubles the HCLK pulse width.

2 = 1/4 pixel frequency.

3 = 1/6 pixel frequency.

4 = 1/8 pixel frequency.

5 = 1/10 pixel frequency.

…

15 = 1/30 pixel frequency.

HBLK

H-BLANK REPEATING PATTERN IS CREATED USING HBLKLEN AND HBLKREP REGISTERS.

H1/H3

H2/H4

HBLKSTART HBLKTOGE1

HBLKTOGE2

HBLKEND

HBLKTOGE3

HBLKTOGE4

HBLKLEN

HBLKREP NUMBER 1

HBLKREP NUMBER 2

HBLKREP NUMBER 3

HBLKREP = 3

Figure 28. HBLK Repeating Pattern Using HBLKMODE = 1

HBLK

H-CLOCK FREQUENCY CAN BE REDUCED DURING HBLK BY 1/2 (AS SHOWN),

1/4, 1/6, 1/8, 1/10, 1/12, AND SO ON, UP TO 1/30 USING HBLKWIDTH REGISTER.

H1/H3

H2/H4

1/FPIX

2 × (1/FPIX)

Figure 29. Generating Wide H-Clock Pulses During HBLK Interval

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