Re: [SI-LIST] : Re: Guard banding

D. C. Sessions (dc.sessions@tempe.vlsi.com)
Wed, 12 Nov 1997 12:54:45 -0700

Robert Voelker wrote:
>
> Hi,
>
> Another approach to reduce crosstalk between lines of a bus is to
> transpose the conductors every so often along the length of the bus.
> Basically, this prevents two conductors from being nearest neighbors
> for the entire length of the bus. This approach is effective
> if not all of the lines are switching simultaneously, such as in
> a control bus. An added benefit is that there is less propagation
> delay skew than in an ordinary parallel bus.
>
> The technique is described in "Transposing Conductors in Signal Buses
> to Reduce Nearest-Neighbor Crosstalk," R. H. Voelker, IEEE Trans.
> Microwave Thoery Tech., vol. 43, no.5, pp. 1095-1099, May 1995.

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.

-- 
D. C. Sessions
dc.sessions@tempe.vlsi.com