REV. 0

AD9848/AD9849

–20–

H-Driver and RG Outputs

In addition to the programmable timing positions, the AD9848/

AD9849 features on-chip output drivers for the RG and H1–H4

outputs. These drivers are powerful enough to directly drive the

CCD inputs. The H-driver current can be adjusted for optimum

rise/fall time into a particular load by using the DRV registers. The

RG drive current is adjustable using the RGDRV register. Each

3-bit DRV register is adjustable in 3.5 mA increments, with the

minimum setting of 0 equal to OFF or three-state, and the maxi-

mum setting of 7 equal to 24.5 mA.

As shown in Figure 7, the H2/H4 outputs are inverses of H1/

H3. 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 H1/H2

crossover voltage at approximately 50% of the output swing.

The crossover voltage is not programmable.

Digital Data Outputs

The AD9848/AD9849 data output phase is programmable

using the DOUTPHASE register. Any edge from 0 to 47 may

be programmed, as shown in Figure 8.

P[0]

PIXEL

PERIOD

RG

H1/H3

RGf[12]

P[48] = P[0]

Hf[24]

SHP[28]

CCD SIGNAL

P[24]

P[12]

P[36]

Hr[0]

RGr[0]

SHD[48]

NOTES

1. ALL SIGNAL EDGES ARE FULLY PROGRAMMABLE TO ANY OF THE 48 POSITIONS WITHIN ONE PIXEL PERIOD.

2. DEFAULT POSITIONS FOR EACH SIGNAL ARE SHOWN ABOVE.

POSITION

Figure 6. High-Speed Clock Default and Programmable Locations

Table II. H1–H4, RG, SHP, SHD Timing Parameters

Register Name

Length

Range

Description

POL

1b

High/Low

Polarity Control for H1, H3, and RG (0 = No Inversion, 1 = Inversion)

POSLOC

6b

0–47 Edge Location

Positive Edge Location for H1, H3, and RG

Sample Location for SHP, SHD

NEGLOC

6b

0–47 Edge Location

Negative Edge Location for H1, H3, and RG

DRV

3b

0–7 Current Steps

Drive Current for H1–H4 and RG Outputs (3.5 mA Per Step)

Table III. Precision Timing Edge Locations

Quadrant

Edge Location (Decimal)

Register Value (Decimal)

Register Value (Binary)

I

0 to 11

0 to 11

000000 to 001011

II

12 to 23

16 to 27

010000 to 011011

III

24 to 35

32 to 43

100000 to 101011

IV

36 to 47

48 to 59

110000 to 111011