[SI-LIST] How to simulate worse case eye
- From: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 6 Mar 2009 16:21:17 -0700
Joel,
Since the pattern generation algorithm is proprietary, Hyperlynx (HL)
should be involved.
Then the flow becomes:
1. HSPICE is used to generate test response (e.g. step response at Rx).
2. This response is provided to HL, together with bit interval then HL
builds the pattern and saves it in a file.
3. In HSPICE you specify the source of type "PAT" and substitute the
patterns generated by HL, something like:
* vhi vlo del tr tf bit interval
vdatap 1 0 PAT (5 0 0 8e-12 8e-12 0.5e-9 a1 a2)
.pat a1=b01110000101010100101111101000101011101101001001
.pat a2=b10111010100010101010100111110100101000111100101
The source that you described is a PRBS of a given order (in your case
order = 7). This pattern contains all possible combinations built from 7
bits, but of course it cannot cover longer sub patterns. Worst case
pattern may contain up to hundreds of bits. That's why eye diagram
estimation made from PRBS 7 could be over-optimistic.
However, if your SERDES is supposed to work with encoding (e.g. 8b10b)
then PRBS of order 6 and higher will give you some illegal combinations
(e.g. 6 or more zeros or ones in a row). Because of that, your PRBS may
also give you too pessimistic prediction.
In fact, we even cannot say if PRBS 7 or whatever it is gives us too
pessimistic or too optimistic results.
Vladimir
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Joel Brown
Sent: Friday, March 06, 2009 4:35 PM
To: SI-LIST@xxxxxxxxxxxxx
Subject: [SI-LIST] How to simulate worse case eye
I was watching a webinar by Mentor on Hyperlynx and how they can quickly
generate a prbs pattern that results in a worse case eye diagram. They
said without this feature it could take days or even years of simulation
to do this. I do most of my simulation in hspice since most of my models
are based in Hspice.
Is there a way to do what Mentor is claiming in Hspice by generating a
certain pattern?
I have been using the following code for a prbs sequence:
vin inr vcm LFSR(0.1 -0.1 1n 5ps 5ps
+ 'data_rate' 1 [7,4,1] rout=0)
vinn innr vcm LFSR(-0.1 0.1 1n 5ps 5ps
+ 'data_rate' 1 [7,4,1] rout=0)
Thanks - Joel
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