8/10/2019 cmos, analog , design-16
1/368 2005 IEEE International Solid-State Circuits Conference
0-7803-8904-2/05/$20.00 2005 IEEE.
ISSCC 2005 / SESSION 3 / BACKPLANE TRANSCEIVERS / 3.5
3.5 A 6.25Gb/s Binary Adaptive DFE
with First Post-Cursor Tap Cancellationfor Serial Backplane
Communications
Robert Payne, Bhavesh Bhakta, Sridhar Ramaswamy, Song Wu,John
Powers, Paul Landman, Ulvi Erdogan, Ah-Lyan Yee,Richard Gu, Lin Wu,
Yiqun Xie, Bharat Parthasarathy, Keith Brouse,Wahed Mohammed,
Keerthi Heragu, Vikas Gupta, Lisa Dyson,Wai Lee
Texas Instruments, Dallas, TX
As backplane data rates scale to 6.25Gb/s and beyond,
trans-ceivers must communicate in legacy systems originally
designedfor lower data rates. These cost-conscious system channels
typ-ically include >30 of FR-4 trace and several board
connectorsand signal vias, resulting in received signal eyes closed
by ISI,crosstalk noise, and reflections [1]. Previous solutions to
limitedchannel bandwidths use transmitter pre-emphasis (or
de-emphasis) to boost the relative transmit amplitude of
high-fre-quency data, linear filters to boost high frequencies at
the receiv-er, or multi-level signaling solutions such as PAM-4 to
fully uti-lize the available bandwidth. While effective for
equalizing iso-
lated channels, transmitter de-emphasis can also
increasecrosstalk, resulting in a decreased system SNR. Linear
filterscan flatten the channel response, but noise is amplified as
wellas the desired signal making them unsuitable for some
legacybackplanes with significant high-frequency crosstalk.
AlthoughPAM-4 reduces the required bandwidth, no signaling
standardsexist and the impact of reflections on PAM-4 solutions can
beworse compared to binary signaling [2].
DFEs can overcome these limitations. In a DFE, prior data
deci-sions are multiplied by tap weights equaling the magnitude
ofthe ISI and subtracted from the received signal, eliminating
ISIfrom subsequent bits. When correct decisions are made,
thepost-cursor channel response is equalized without boosting
high-frequency crosstalk. A half-baud rate adaptive DFE with
directfirst post-cursor tap cancellation suitable for legacy
backplanes
is presented in this paper. In particular, systems require: 1)
4post-cursor taps to equalize up to 20dB of channel loss
at3.125GHz, yielding BER
