AD9633 datasheet(28/42 Pages) AD

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Data Sheet

AD9633

Rev. B | Page 27 of 41

DIGITAL OUTPUTS AND TIMING

The AD9633 differential outputs conform to the ANSI-644 LVDS

standard on default power-up. This can be changed to a low power,

reduced signal option (similar to the IEEE 1596.3 standard) via the

SPI. The LVDS driver current is derived on chip and sets the

output current at each output equal to a nominal 3.5 mA. A 100 Ω

differential termination resistor placed at the LVDS receiver

inputs results in a nominal 350 mV swing (or 700 mV p-p

differential) at the receiver.

When operating in reduced range mode, the output current is

reduced to 2 mA. This results in a 200 mV swing (or 400 mV p-p

differential) across a 100 Ω termination at the receiver.

The AD9633 LVDS outputs facilitate interfacing with LVDS

receivers in custom ASICs and FPGAs for superior switching

performance in noisy environments. Single point-to-point net

topologies are recommended with a 100 Ω termination resistor

placed as close to the receiver as possible. If there is no far-end

receiver termination or there is poor differential trace routing,

timing errors may result. To avoid such timing errors, it is

recommended that the trace length be less than 24 inches and

that the differential output traces be close together and at equal

lengths. An example of the FCO and data stream with proper

trace length and position is shown in Figure 69. Figure 70 shows

the LVDS output timing example in reduced range mode.

D0 500mV/DIV

D1 500mV/DIV

DCO 500mV/DIV

FCO 500mV/DIV

4ns/DIV

Figure 69. AD9633-125, LVDS Output Timing Example in ANSI-644 Mode

(Default)

D0 400mV/DIV

D1 400mV/DIV

DCO 400mV/DIV

FCO 400mV/DIV

4ns/DIV

Figure 70. AD9633-125, LVDS Output Timing Example in Reduced Range Mode

An example of the LVDS output using the ANSI-644 standard

(default) data eye and a time interval error (TIE) jitter histogram

with trace lengths less than 24 inches on standard FR-4 material is

shown in Figure 71.

5.5k

4.5k

5.0k

4.0k

0.5k

1.0k

1.5k

2.0k

2.5k

3.0k

3.5k

350ps

400ps

500ps

450ps

550ps

600ps

650ps

700ps

500

400

300

200

100

–500

–400

–300

–200

–100

–1.0ns

–0.5ns

0ns

0.5ns

1.0ns

EYE: ALL BITS

ULS: 8000/300062

Figure 71. Data Eye for LVDS Outputs in ANSI-644 Mode with Trace Lengths

Less than 24 Inches on Standard FR-4 Material, External 100 Ω Far-End

Termination Only

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