DS25BR400

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SNLS230I – MAY 2006 – REVISED FEBRUARY 2013

To compensate for the high frequency losses incurred during signal transmission in cables and backplanes the

DS25BR400 employs input and output signal conditioning. Each input stage has a fixed equalizer and all output

drivers have four selectable steps of de-emphasis to reduce deterministic jitter on the serial link. All the CML

output drivers have 50

impedance.

Table 2. Logic Table for Loopback Controls

LB0

Loopback Function

0

Enable loopback from IB_0± to OA_0±.

1 (default)

Normal mode. Loopback disabled.

LB1

Loopback Function

0

Enable loopback from IB_1± to OA_1±.

1 (default)

Normal mode. Loopback disabled.

LB2

Loopback Function

0

Enable loopback from IB_2± to OA_2±.

1 (default)

Normal mode. Loopback disabled.

LB3

Loopback Function

0

Enable loopback from IB_3± to OA_3±.

1 (default)

Normal mode. Loopback disabled.

Table 3. De-Emphasis Controls

PreA_[1:0]

De-Emphasis in dB (VODPE/VODB)

(VODPE)

0 0

1200

1200

0

0 1

1200

850

−3

1 0

1200

600

−6

1 1 (Default)

1200

426

−9

PreB_[1:0]

De-Emphasis in dB (VODPE/VODB)

(VODPE)

0 0

1200

1200

0

0 1

1200

850

−3

1 0

1200

600

−6

1 1 (Default)

1200

426

−9

Output De-Emphasis

De-emphasis is the conditioning function for use in compensating against backplane transmission loss. The

DS25BR400 provides four steps of de-emphasis ranging from 0,

−3, −6 and −9 dB, user-selectable dependent

on the loss profile of the backplane. Figure 2 shows a driver de-emphasis waveform. The de-emphasis duration

is nominal 200 ps, corresponding to 50% bit-width at 2.5 Gbps. The de-emphasis levels of switch-side and line-

side can be individually programmed.

Copyright © 2006–2013, Texas Instruments Incorporated

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