F-tile Architecture and PMA and FEC Direct PHY IP User Guide

ID 683872
Date 12/15/2021
Public

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2.3.1.1.1. FHT Transmitter Buffer and Phase Generator

The transmitter differential I/O buffer converts the serialized bit stream to an electrical signal suitable for transmission across a cable or PCB trace. The main cursor, pre-cursor taps, and post-cursor taps of the FFE circuit control the transmitter swing strength and shape the transmitter output waveform.

The transmitter buffer can be programmed to support the taps listed in the following table. Choose the frequency response of the filter to compensate for lane impairments such as intersymbol interference (ISI), crosstalk, frequency-dependent losses, and reflections.

Table 13.  FHT Transmitter PMA Equalizer Parameters for NRZ and PAM4 Modes

Parameter

(Cursor)

Description Rule

Increment and

Decrement Size

Minimum Default Maximum
C-3 Pre-cursor 3 -8 0 +7.75 0.25
C-2 Pre-cursor 2 -8 0 +7.75 0.25
C-1 Pre-cursor 1 -16 0 +15.5 0.5
C0 Main cursor 0 41.5 +41.5 7 0.5
C+1 Post-cursor 1 -16 0 +15.5 0.5
C+2 Post-cursor 2 -8 0 +7.75 0.25
C+3 Post-cursor 3 -8 0 +7.75 0.25
C+4 Post-cursor 4 -8 0 +7.75 0.25

For the most capable transmitter equalizer and best amplitude control, where ABS is the absolute value:

  • ABS(C-3) + ABS(C-2) + ABS(C-1) + C0 + ABS(C+1) + ABS(C+2) + ABS(C+3) + ABS(C+4) ≤ 41.5
  • ABS(C-3) + ABS(C-2) + ABS(C-1) +ABS(C+1) + ABS(C+2) + ABS(C+3) + ABS(C+4) ≤ C0
7 Provides the maximum TX output swing

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