[SI-LIST] Re: Crosstalk
- From: steve weir <weirsi@xxxxxxxxxx>
- To: zc@xxxxxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 16 Mar 2006 16:44:26 -0800
Zhenggang,
1. When two signals couple together, a wave front in one may be
supported or opposed by a wavefront in the other. When they oppose,
the timing "pushes out". When they support each other, the timing
"pulls in". This alters the effective flight time.
2. See above. Eric Bogatin has a nice description of this in his
book, "Signal Integrity Simplified".
3. Crosstalk is a distortion. I am hard pressed to think of when it
could be useful since the distortion changes depending on what each
coupled signal is up to. But in synchronous busses, on data lines it
can be well tolerated. It can be a big problem when it gets into
signals that are asynchronous or need to be out of phase.
Steve.
At 03:10 PM 3/16/2006, zc@xxxxxxxxxxx wrote:
>Dear All:
>
>Below is a discussion in the list before. I don't understand some of the
>ideas in it. Hope some experts can give me some explains.
>
>"Crosstalk in a bus isn't necessarily a bad thing. Large busses are limited
>by simultaneous switching delays (limited current in the chip supply
>inductors) into line impedances. Near-end crosstalk under SSO effectively
>raises the line impedance and reduces the SSO delay, compensating in part
>for the SSO and keeping timing more consistent."
>
>1. What's simultaneous switching delays ? why Large busses are limited by
>simultaneous switching delays ?
>
>2. Why near-end crosstalk under SSO effectively raises the line impedance?
>How raised line impedance reduces the SSO delay? Why raised line impedance
>can compensate in part for the SSO and keeping timing more consistent?
>
>3. Under what situations, the crosstalk is useful?
>
>Thanks in advance. Your sincere help is highly appreciated.
>
>Zhenggang
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>Zhenggang Cheng
>Ph.D Candidate
>Electrical and Computer Engineering Dept
>Duke University
>130 Hudson Hall, POBox 90291
>Durham, NC, 27708
>919-660-5232(O) 919-218-5520(H)
>
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