GS3281 datasheet(17/97 Pages) SEMTECH

17 / 97 page

GS3281

Final Data Sheet

Rev.7

PDS-061453

January 2019

17 of 97

Semtech

Proprietary & Confidential

www.semtech.com

By default at power up or after system reset, the trace equalizer is configured to

compensate for up to 3" of 7-mil stripline in FR4 material at high frequencies.

Note: If using input trace lengths longer than 5", use an upstream launch swing of

~800mVppd

4.2.2 Carrier Detect, and Loss of Signal

The trace equalizer input has a highly configurable Carrier Detection mechanism that

allows the system designer to optimize the sensitivity and hysteresis of the Carrier

Detection mechanism to meet specific system requirements.

Default settings should satisfy most applications; however, designers can modify the

following three parameters to customize the trace equalizer's carrier detection for their

application:

•

CFG_TREQ0_CD_BOOST

•

CFG_TREQ0_CD_ASSERT_THRESH

•

CFG_TREQ0_CD_DEASSERT_THRESH

The trace equalizer Carrier Detect is reported by status parameter STAT_PRI_CD in

The first CD control parameter is CFG_TREQ0_CD_BOOST in register 0x1E. This

parameter determines the method and therefore the level of equalization to be used on

the input signal routed to the Carrier Detection sub-block. The default value is 0b, which

maximizes the level of equalization. Alternatively, the designer can choose to have this

signal equalized at the same level as the main signal routed to the CDR by setting

CFG_TREQ0_CD_BOOST to 1b. The setting of this parameter has no impact on the main

signal routed to the CDR.

The last two CD control parameters can be found in register 0x1F. Parameters

CFG_TREQ0_CD_ASSERT_THRESH and CFG_TRE0Q_CD_DEASSERT_THRESH set

the Carrier Detect assert and de-assert thresholds to the input signal, which also defines

the hysteresis of CD signal.

The default values of CFG_TREQ0_CD_ASSERT_THRESH and

CFG_TREQ0_CD_DEASSERT_THRESH are is 4d and 3d respectively. With the default

settings, the minimum launch swing needed to assert the carrier detect is 200mV and it

will be de-asserted when the signal level falls below 150mV.

The STAT_PRI_CD (Carrier Detect) parameter will be set to 0b and the LOS will be set to

1b whenever a new signal at the input does not exceed the assert threshold, or an

existing signal falls below the de-assert threshold. The result is that the device will not

indicate lock, and the outputs will mute (assuming Mute on LOS is left to its default value

in the CONTROL_OUTPUT_MUTE register (0x49). See Section 4.7.5 for more details.

Given a differential input trace with 17dB of insertion loss at 1.485GHz and

CFG_TREQ0_CD_BOOST = 0b, Figure 4-2 illustrates the relationship between launch

swing voltage, and minimum threshold setting to assert or de-asset Carrier Detect at all

rates up to threshold setting at 2.97Gb/s.

GS3281 Datasheet(PDF) 17 Page - Semtech Corporation

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