[BP] how to evaluate signaling method
guys,
What i propose for signaling evaluation is an extension of
ideas i presented at the July meeting in Portland in the talk
"Receiver Testing Using Interference Tolerance Measurements".
The basic idea is to do a time domain simulation of the Tx,
channel, and Rx using a standard, generally available simulator.
To provide a simple and reproducible model of cross talk, a
sinusoidal interfering signal will be added at the input to the
receiver. The amplitude of the interfering signal will be
increased until the signal at the output of the Rx is deemed to
be no longer usable. The highest level of interference at which
the Rx provides a usable output will be called the interference
tolerance. If the interference tolerance is below a specified
(and perhaps signaling method dependent) value the simulated data
path is non-compliant. If the interference tolerance is above
the specified value, it is compliant and has a margin which is
equal to the difference between the simulated tolerance and the
spec. In general more margin is better.
This is the basic idea. Details which i suggest be adopted as
part of the method but which can be changed without altering the
basic idea include:
1. Use hspice as the simulator.
2. Model the transmitter as:
a. 1 or 2 piecewise linear (PWL) current sources:
i. 1 current source with NRZ encoded data for NRZ signaling.
ii. 1 current source with precoded data for duo-binary
signaling.
iii. 2 current sources with 1/3 and 2/3 NRZ amplitude with LSB
and MSB data respectively, for PAM4 signaling.
b. Rise times of PWL current sources set at about 30ps for NRX or
duo-binary or 60ps for PAM4
c. R,L,C network between current source and Tx pins to provide
reasonable return loss vs frequency
3. Include signaling method dependent Tx equalization in PWL current
source model. Control equalization with hspice parameters.
4. Include some modeled Tx Jitter in PWL current sources.
5. Use hspice S-parameter network modeling capabilities to model
channel.
6. Allow proprietary Rx models by Encryption.
7. Add interference signal at Rx with sinusoidal current source.
8. Allow for Rx input noise in the minimum interference tolerance spec.
9. Determine that the Rx provides a usable output by:
a. showing that data out of Rx gives the correct bits.
b. If Rx does not include re-clocking, show that output eye is
wide enough
c. If Rx does not include a limiting stage, show that the output
eye has enough amplitude.
10. Use 127 bit long PRBS pattern for data. Offset a few bits between
pattern for MSB and LSB to give PAM4 pattern or use shorter PRBS
pattern for LSB. Repeat PRBS pattern at least 4 times to allow
interference to "walk through" the data.
11. Test with more than one interfering rate. Interesting rates
should include:
a. For NRZ or PAM4, (1+.2/127)*(baud rate)/2
b. For duo-binary, (1+.2/127)*(baud rate)/4
charles
--
|--------------------------------------------------------------------|
| Charles Moore
| Agilent Technologies
| ASIC Products Division
| charles_moore@agilent.com
| (970) 288-4561
|--------------------------------------------------------------------|