Virtex-5 RocketIO GTP Transceiver User Guide
125
UG196 (v1.3) May 25, 2007
RX Termination and Equalization
R
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
Clock Domain
Description
MGTRXN0
MGTRXN1
MGTRXP0
MGTRXP1
In
(Pad)
RX Serial Clock
RXN and RXP are the differential complements of each other forming
a differential receiver input pair. These ports represent pads, so their
locations must be constrained (see
), and
they must be brought to the top level of the design.
RXENEQB0
RXENEQB1
In
Async
Active-Low port for enabling linear receive equalization:
0
: Receiver equalization is enabled
1
: Receiver equalization is disabled
RXEQMIX0[1:0]
RXEQMIX1[1:0]
In
Async
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
01
: 62.5% wideband, 37.5% high-pass
10
: 75% wideband, 25% high-pass
11
: 37.5% wideband, 62.5% high-pass
RXEQPOLE0[3:0]
RXEQPOLE1[3:0]
In
Async
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%
1010
: -25.0%
1011
: -37.5%
1100
: +12.5%
1101
: +25.0%
1110
: +37.5%
1111
: +50.0%
Содержание Virtex-5 RocketIO GTP
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Страница 312: ...312 www xilinx com Virtex 5 RocketIO GTP Transceiver User Guide UG196 v1 3 May 25 2007 Appendix E Low Latency Design R...