Re: [SI-LIST] : Ferrites on power leads

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From: Vinu Arumugham (vinu@cisco.com)
Date: Tue Aug 01 2000 - 13:28:58 PDT


Depends on the which circuit the power pin is supplying. If the power pin
supplies the internal PLL of a clock device, I would expect the output to be
affected through a non-linear process. If the power pin supplies the clock
output (TTL/LVTTL type) buffer, I would expect it to be linear addition.

Vinu

Ray Anderson wrote:

> Isn't the primary effect of noise ingress on the clock signal a bit
> different when the path of the ingress is via a power pin as opposed
> to via an output trace.
>
> If the noise gets into an oscillator or synthesizer via the power
> supply there is potential for the noise to modulate the circuitry
> both in amplitude and frequency/phase with the result on the output signal
> being some sort of degradation by some non-linear process.
>
> In the case of clock signal contamination when the impinging noise is
> picked up by a clock distribution transmission line, I'd be more inclined
> to expect a linear addition of the noise to the clock signal. The reverse
> isolation of the output driver serves to isolate the internal oscillator or
> synthesizer circuitry somewhat from effects of noise on the output line.
>
> Of course this is a lot of hand-waving theorizing because each case is
> a bit different, but in general I'd expect noise arriving via the
> power supply path to be more damaging as it's potential for inducing
> jitter and timing problems would be greater than the noise added
> more or less linearly by output trace contamination.
>
> These comments are anecdotal based on many years of designing
> communications oscillators and synthesizers for satcom applications,
> but I think the same end effect follows. Comments ?? Anyone know of any
> studies on the effects of clock degradation caused by different paths
> of noise ingress ?
>
> -Ray
>
> >
> > Ellis,
> >
> > Noise on the power pin of a device usually perturbs the output signal.
> > Such a perturbation may be significant, especially if the output is a
> > clock signal. In this context, if radiated noise impinging on traces is
> > a concern, my point was that the clock quality is affected more by the
> > noise picked up by the clock trace , than by the noise picked up by the
> > power trace of the clock driver.
> >
> > Thanks,
> > Vinu
> >
>
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