Rx Termination And Equalization; Overview; Ports And Attributes - Xilinx Virtex-5 RocketIO GTP User Manual

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RX Termination and Equalization

Overview

The first stage of the RX datapath in each GTP transceiver is the RX current mode logic
(CML) receiver. This block determines the value of the incoming high-speed differential
signal.
At high speeds, error-free data reception requires good signal integrity. The CML receiver
includes circuits to allow the termination of the channel to be optimized for the best
possible signal integrity.
The receiver also features an RX equalization circuit that allows it to compensate for high-
frequency losses in the channel, improving the quality of the received signal. This circuit
can be tuned to meet the specific requirements of the physical channel used in the design.

Ports and Attributes

The combination of the wideband signal and its high-pass filtered derivative compensates
for the low-pass characteristic of the transmission line on the board. The parameters of the
mixing ratio and the pole of the high-pass filter are described in
Table 7-1: RX Termination and Equalization Ports
Port Dir
MGTRXN0
MGTRXN1
In
(Pad)
MGTRXP0
MGTRXP1
RXENEQB0
In
RXENEQB1
RXEQMIX0[1:0]
In
RXEQMIX1[1:0]
RXEQPOLE0[3:0]
In
RXEQPOLE1[3:0]
Virtex-5 RocketIO GTP Transceiver User Guide
UG196 (v1.3) May 25, 2007
Clock Domain
RXN and RXP are the differential complements of each other forming
a differential receiver input pair. These ports represent pads, so their
RX Serial Clock
locations must be constrained (see
they must be brought to the top level of the design.
Active-Low port for enabling linear receive equalization:
Async 0: Receiver equalization is enabled
1: Receiver equalization is disabled
This port controls the wideband/high-pass mix ratio for the RX
equalization circuit. The following ratios are available:
00: 50% wideband, 50% high-pass
Async
01: 62.5% wideband, 37.5% high-pass
10: 75% wideband, 25% high-pass
11: 37.5% wideband, 62.5% high-pass
This port controls the location of the pole in the RX equalizer high-pass
filter. Adjusting this value shifts the threshold for rejecting low-
frequency signals. The following settings are available:
0xxx: Filter pole depends on resistor calibration
1000: 0% nominal pole
1001: -12.5%
Async
1010: -25.0%
1011: -37.5%
1100: +12.5%
1101: +25.0%
1110: +37.5%
1111: +50.0%
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RX Termination and Equalization
Table 7-1.
Description
Chapter 4, "Implementation"), and
125