comparison of nrz, pr-2, and pr-4 signaling

Comparison of NRZ, PR-2, and PR-4 signaling

Presented by: Rob Brink

Contributors: Pervez Aziz

Qasim Chaudry

Adam Healey

Greg Sheets

IEEE P802.3ap Task Force2 March 15, 2005 (r1.0)

Scope and Purpose

� Operation over electrical backplanes at 10.3125Gb/s is investigated using NRZ, PR2, and PR4 signaling.

� A common equalizer architecture is used in all cases.

� Estimated BER, as well as voltage and timing margin at 1E-12, is reported.


Agenda

� Simulator Overview

• Link Model

• Transmitter Model

• Receiver Model

• Equalization Strategy

� Test Cases

� Sample Results

� Results Summary

Simulator Overview


Link Model

RXPackage

2

4

50

50

1

3

TXPackage

1

3

2

4

50

50Backplane

2

4

1

3

TP1 TP4

TX Package Model

Backplane Model

RX Package Model

Mellitz “Capacitor-Like” Model

As described in “Test Cases” section…

Mellitz “Capacitor-Like” Model


Crosstalk (1/2)

� For each crosstalk aggressor…

• The response to a PRBS-15 pattern (with an additional trailing “0”) is computed.

• This response is sampled at baud-spaced intervals at 16 offsets from 0 to (15/16)T in T/16 steps.

• At each offset, the amplitude distribution of sampled response is computed.

• The aggressor amplitude distribution is defined as the average of the amplitude distributions computed at each sample offset.


Crosstalk (2/2)

� The overall crosstalk distribution is defined as the convolution of the individual aggressor distributions.

� The effect of crosstalk on the eye is modeled as the convolution of the overall crosstalk distribution and amplitude distribution of the “thru” path at each sample phase.

� This methodology is has been previously described by Moore:

• http://ieee802.org/3/ap/public/channel_adhoc/moore_c1_0305.pdf

� Computed RMS and peak-peak crosstalk will be reported.


Transmitter Model

� Transmitter differential output voltage fixed at 800mVp-p.

� Transmit filter is Gaussian.• Rise Time (20-80%): 24 ps

� Transmitter output jitter• Duty Cycle Distortion: 0.05 UIp-p (even-odd)

• Deterministic Jitter: 0.10 UIp-p (sinusoidal)

• Random Jitter: 0.15 UIp-p (at 1E-15), 9.4mUIrms

� Parameters defined at package model input and do notinclude package parasitics.

• The impact of the package model is investigated in the next slide.


Transmitter Output at TP1

TXPackage

1

3

2

4

50

50

TP1

50

50

800 mV

p-p800 m

Vp-p

0.70 UIp-p at 1E-15


Receiver Model

� Receiver modeled as a single pole at 75% fbaud.

• Noise Bandwidth (Bn): 11.4 GHz

• Noise Figure: 18 dB

• sqrt( 4kTRBn ): 1.08 mVrms

� Receiver jitter:

• Random Jitter: 0.15 UIp-p (at 1E-15), 9.4 mUIrms

� No gain stages have been included in the receive path.

�∞

=0

2)( dffHBn


Equalization Strategy

� Transmitter Finite Impulse Response filter.

• 3 taps, T-spaced with “infinite” tap weight resolution.

� Receiver Decision Feedback Equalizer

• 5 taps, unconstrained with “infinite” tap weight resolution.

� Sequential adaptation

• Transmit FIR is adapted first, then the DFE.

� Sample phase chosen to minimize mean-squared error.

• T/32 resolution

Test Cases


Test Patterns

� Equalizer trained with PN-11 pattern with a trailing “0”.

� Equalizer settings are then frozen.

� Voltage and timing margin is estimated based on PN-15 pattern with a trailing “0”.

• Thru, NEXT, and FEXT channels share the same output amplitude (800 mVppd) and transmit FIR settings.

� Decision threshold set at the mid-point between nominal signal levels, as determined by the 1E-4 contour.

• Reported margins are twice the minimum distance from the sample phase (or threshold) to the BER contour of interest.


Channels Studied

� All Tyco Electronics channels

• Test Cases 1 through 7

• Note that the FEXT channels were included twice due to connector symmetry.

� Recommended subset of Intel channels

• Test Cases 8, 11, and 12 map to T1, T12, T20

• Test Cases 14, 17, and 18 map to B1, B12, B20

• Test Cases 20 and 24 map to M1, and M20

� Other channels not simulated due to a lack of time…

Sample Results


Disclaimer

� The following results are based on PRBS-11 pattern and are included for illustrative purposes.


NRZ Sample Results: Eye at Slicer InputTe

st C

ase

#1Te

st C

ase

#6


PR2 Sample Results: Eye at Slicer InputTe

st C

ase

#1Te

st C

ase

#6


PR4 Sample Results: Eye at Slicer InputTe

st C

ase

#1Te

st C

ase

#6

Results Summary


1.0E-361.0E-341.0E-321.0E-301.0E-281.0E-261.0E-241.0E-221.0E-201.0E-181.0E-161.0E-141.0E-121.0E-101.0E-081.0E-061.0E-041.0E-021.0E+00

0 5 10 15 20 25

Test Case

BE

R

NRZ

PR2

PR4

BER Estimates


Voltage and Timing Margin at 1E-12

Vertical Margin at 1E-12

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0 5 10 15 20 25

Test Case

Mar

gin

(V

p-p)

NRZ

PR2

Horizontal Margin at 1E-12

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0 5 10 15 20 25

Test Case

Mar

gin

(U

I p-p)

NRZ

PR2


Crosstalk Environment

RMS and Peak-Peak (at 1E-12) Crosstalk

0.0000

0.0200

0.0400

0.0600

0.0800

0.1000

0.1200

0.1400

0 5 10 15 20 25

Test Case

Pea

k-P

eak

Cro

ssta

lk (

V)

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

RM

S C

ross

talk

(V

) NRZ (p-p)

PR2 (p-p)

PR4 (p-p)

NRZ (rms)

PR2 (rms)

PR4 (rms)


Required FFE Boost

FFE Gain at (Symbol Rate)/2

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 5 10 15 20 25

Test Case

Gai

n (

dB

) NRZ

PR2

PR4


Conclusions (1/2)

� The target response for PR4 is a poor fit to the channel and therefore higher equalizer complexity is required to achieve acceptable performance.

� NRZ and PR2 both support 1E-12 operation over the Tyco channels.

• In general, PR2 requires considerably less boost to achieve this objective.

• In the majority of test cases studied, NRZ offered superior voltage and timing margin.


Conclusions (2/2)

� The Intel “T” channels were not supported by any of the signaling schemes studied with the chosen equalizer architecture.

� NRZ signaling may be feasible for select Intel “B” and “M” channels.

• Crosstalk is a significant impairment on these channels.

Backup


Relationship Between Crosstalk and Boost

RMS Crosstalk vs. FFE Boost

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0 5.0 10.0 15.0 20.0 25.0

FFE Gain at (Symbol Rate)/2

RM

S C

ross

talk

(V

)

NRZ (rms)

PR2 (rms)

PR4 (rms)

comparison of nrz, pr-2, and pr-4 signaling

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