GS3241 datasheet(40/108 Pages) SEMTECH

40 / 108 page

GS3241

Final Data Sheet

Rev.2

PDS-061444

September 2017

40 of 108

Semtech

Proprietary & Confidential

www.semtech.com

If required, per-rate selection of the trace driver output group setting is possible by

setting CTRL_OUTPUT<n>_TRDR_PER_RATE = 1. Once set, the trace driver output

group will be determined by the rate to which the CDR is locked. For example, if the CDR

is locked to 3G, the following parameters will be used to control the output drivers.

 CFG_OUTPUT<n>_TD_3G_DRIVER_SWING

 CFG_OUTPUT<n>_TD_3G_PREEMPH_WIDTH

 CFG_OUTPUT<n>_TD_3G_PREEMPH_AMPL

 CFG_OUTPUT<n>_TD_3G_PREEMPH_PWRDWN

Note: If per-rate settings are being used, when the CDR is not locked, the trace driver will

use the Bypass trace driver output group settings.

4.7.4 Amplitude and Pre-Emphasis Control

The two output drivers offer very granular amplitude and pre-emphasis control. For

optimal loss compensation, both the pre-emphasis pulse amplitude and the

pre-emphasis pulse width can be independently configured on both output drivers.

This extra flexibility provides a mechanism to better shape the pre-emphasis gain to

match the frequency loss response of interconnect composed of trace, connector and

via losses. The swing and pre-emphasis can be independently configured for specific

data rates.

CFG_OUTPUT<n>_TD_SD_DRIVER_SWING (SD)

CFG_OUTPUT<n>_TD_HD_DRIVER_SWING (HD)

CFG_OUTPUT<n>_TD_3G_DRIVER_SWING (3G)

CFG_OUTPUT<n>_TD_BYPASS_DRIVER_SWING (Bypass)

The output pre-emphasis on the trace driver can be configured for the following four

rates:

CFG_OUTPUT<n>_TD_SD_PREEMPH_WIDTH (SD)

CFG_OUTPUT<n>_TD_SD_PREEMPH_AMPL (SD)

CFG_OUTPUT<n>_TD_HD_PREEMPH_WIDTH (HD)

CFG_OUTPUT<n>_TD_HD_PREEMPH_AMPL (HD)

CFG_OUTPUT<n>_TD_3G_PREEMPH_WIDTH (3G)

CFG_OUTPUT<n>_TD_3G_PREEMPH_AMPL (3G)

CFG_OUTPUT<n>_TD_BYPASS_PREEMPH_WIDTH (Bypass)

CFG_OUTPUT<n>_TD_BYPASS_PREEMPH_AMPL (Bypass)

The trace driver swing can be adjusted in ≈25mVpp increments. The default swing value

is 400Vppd into an external 100Ω differential load. Although an adequate swing and

pre-emphasis can be achieved with a 1.8V output supply, for long traces where

maximum output swing and pre-emphasis range is desired, it is recommended that the

device VCC_DDO output supply pin be connected to a 2.5V supply. The default

pre-emphasis settings provide minimal insertion loss compensation.

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