AD9637 datasheet(24/40 Pages) AD

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AD9637

Data Sheet

Rev. 0 | Page 24 of 40

Figure 59 shows 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 of less than 24 inches

on standard FR-4 material.

0.5k

1.0k

1.5k

3.0k

2.5k

2.0k

300

200

100

–300

–200

–100

EYE: ALL BITS

ULS: 8000:448000

Figure 59. Data Eye for LVDS Outputs in ANSI-644 Mode with Trace Lengths

of Less Than 24 Inches on Standard FR-4, External 100 Ω Far-End

Termination Only

Figure 60 shows an example of trace lengths exceeding 24 inches

on standard FR-4 material. Note that the TIE jitter histogram

reflects the decrease of the data eye opening as the edge deviates

from the ideal position.

It is the responsibility of the user to determine if the waveforms

meet the timing budget of the design when the trace lengths exceed

24 inches. Additional SPI options allow the user to further increase

the internal termination (increasing the current) of all eight outputs

to drive longer trace lengths, which can be achieved by program-

ming Register 0x15. Even though this option produces sharper

rise and fall times on the data edges and is less prone to bit errors,

it also increases the power dissipation of the DRVDD supply.

0.5k

1.0k

1.5k

3.0k

2.5k

2.0k

300

200

100

–300

–200

–100

EYE: ALL BITS

ULS: 7000:448000

Figure 60. Data Eye for LVDS Outputs in ANSI-644 Mode with Trace Lengths

Greater Than 24 Inches on Standard FR-4, External 100 Ω Far Termination Only

The default format of the output data is twos complement. Table 10

shows an example of the output coding format. To change the

output data format to offset binary, see the Memory Map section.

Data from each ADC is serialized and provided on a separate

channel in DDR mode. The data rate for each serial stream is equal

to 12 bits times the sample clock rate, quantity divided by 2,

with a maximum of 480 Mbps (12 bits × 80 MSPS)/2 = 480 Mbps.

The lowest typical conversion rate is 10 MSPS. See the Memory

Map section for details on enabling this feature.

Table 10. Digital Output Coding

Input (V)

Condition (V)

Offset Binary Output Mode

Twos Complement Mode

VIN+ − VIN−

< −VREF − 0.5 LSB

0000 0000 0000

1000 0000 0000

VIN+ − VIN−

= −VREF

0000 0000 0000

1000 0000 0000

VIN+ − VIN−

= 0

1000 0000 0000

0000 0000 0000

VIN+ − VIN−

= +VREF − 1.0 LSB

1111 1111 1111

0111 1111 1111

VIN+ − VIN−

> +VREF − 0.5 LSB

1111 1111 1111

0111 1111 1111

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