AD9942

Rev. A | Page 21 of 36

H DRIVER AND RG OUTPUTS

In addition to the programmable timing positions, the AD9942

features on-chip output drivers for the RG_X and H1X to H4X

outputs. These drivers are powerful enough to drive the CCD

inputs directly. The H-driver and RG-driver currents can be

adjusted for optimum rise and fall time into a particular load by

using the DRVCONTROL register (Address 0x62). The

DRVCONTROL register is divided into five 3-bit values, each

adjustable in 4.1 mA increments. The minimum setting of 0 is

equal to off, or three-state, and the maximum setting of 7 is

equal to 30.1 mA.

As shown in Figure 18, the H2X/H4X outputs are inverses of

H1X. The internal propagation delay resulting from the signal

inversion is less than l ns, which is significantly less than the

typical rise time driving the CCD load. This results in a

H1X/H2X crossover voltage at approximately 50% of the output

swing. The crossover voltage is not programmable.

DIGITAL DATA OUTPUTS

The AD9942 data output phase is programmable using the

DOUTPHASE register (Address 0x64). Any edge from 0 to 47

can be programmed, as shown in Figure 19. The pipeline delay

for the digital data output is shown in Figure 20.

FIXED CROSSOVER VOLTAGE

H1X/H3X

H2X/H4X

H2X/H4X

H1X/H3X

Figure 18. H-Clock Inverse Phase Relationship

NOTES

1. DIGITAL OUTPUT DATA (DOUT) PHASE IS ADJUSTABLE WITH RESPECT TO THE PIXEL PERIOD.

2. WITHIN ONE CLOCK PERIOD, THE DATA TRANSITION CAN BE PROGRAMMED TO ANY OF THE 48 LOCATIONS.

P[0]

P[48] = P[0]

CLI_X

1 PIXEL PERIOD

P[12]

P[24]

P[36]

DOUT

Figure 19. Digital Output Phase Adjustment

0123

4567

89

10

11

12

14

15

012

3

H-COUNTER

RESET

VD_X

NOTES

1. INTERNAL H COUNTER IS RESET SEVEN CLI_X CYCLES AFTER THE HD_X FALLING EDGE (WHEN USING VDHDEDGE = 0).

2. TYPICAL TIMING RELATIONSHIP: CLI_X RISING EDGE IS COINCIDENT WITH HD_X FALLING EDGE.

HD_X

CLI_X

XX

XX

X

X

X

H COUNTER

(PIXEL COUNTER)

XX

X

Figure 20. Pipeline Delay for Channel A and Channel B Digital Data Output