GS3590 datasheet(49/118 Pages) SEMTECH

49 / 118 page

GS3590

Final Data Sheet Rev.4



PDS-061414 September 2017

49 of 118

Semtech

Proprietary & Confidential

www.semtech.com

The output pre-emphasis on the Trace Driver can be configured for the following four

rates:

CFG_OUTPUT1_TD_SD_PREEMPH_WIDTH (SD)

CFG_OUTPUT1_TD_SD_PREEMPH_AMPL (SD)

CFG_OUTPUT1_TD_HD_PREEMPH_WIDTH (HD)

CFG_OUTPUT1_TD_HD_PREEMPH_AMPL (HD)

CFG_OUTPUT1_TD_3G_PREEMPH_WIDTH (3G)

CFG_OUTPUT1_TD_3G_PREEMPH_AMPL (3G)

CFG_OUTPUT1_TD_BYPASS_PREEMPH_WIDTH (Bypass)

CFG_OUTPUT1_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.

4.8.5.1 Pre-emphasis Optimization

The goal of pre-emphasis is to open the eye at the downstream receiver as much as

possible. This means minimizing ISI jitter while meeting sufficient inner eye amplitude

to meet a receiver's input sensitivity. The Cable Driver has the additional requirement to

meet the SMPTE output specification.

The GS3590 has a high level of precision for pre-emphasis control, which allows for fine

optimization of any loss channel. The default Cable Driver settings should meet SMPTE

output specification for most applications with short (1 to 2 inch) trace between the

GS3590 and the output BNC. However, the pre-emphasis values may be adjusted to

produce a better-looking eye. It is difficult to provide guidance regarding dB, as a 3G eye

diagram looks different depending on the video test equipment used. The designer

must optimize for their targets.

The only requirement of the Trace Driver pre-emphasis settings is to minimize ISI

introduced by a lossy link and maximize the eye opening at the receiver. The

pre-emphasis compensation of the GS3590 output channel is a two-step process. The

first step is to use the settings from Figure 4-12 to Figure 4-19 that best match the

insertion loss of the link in the application, while the second step is a fine optimization

procedure.

In most cases, where the downstream device has a CDR, the first step alone may meet

the design target. However, if the downstream device is a non-re-timed buffer or

crosspoint, it may be required to further optimize the settings to minimize the jitter

thereby maximizing the system jitter budget. To do this, please see the Fine

Optimization Procedure.

In the remainder of this section the following abbreviations are used for clarity:

DS = Driver Swing

PPA = Pre-emphasis Pulse Amplitude

PPW = Pre-emphasis Pulse Width

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