Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
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Subject: Re: Aylward, Engelhardt: Noise in a transient sim?
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Date: Wed, 23 Oct 2002 12:01:54 +0100
NNTP-Posting-Date: Wed, 23 Oct 2002 12:02:00 BST
"Mike Monett" wrote in message
> "Kevin Aylward" wrote in message
> > This whole think is so daft it amazing. You can't get something for
> > nothing. This should be obvious to anyone. The idea that a signal
> > *truly* be random enough such that it has a *true* (noise) BW of
> > and that this random signal can be detected if it is as small as
> > i.e. 0.01nv/sqrthz is nonsense.
> > Kevin Aylward
> Kevin, I don't know how you got so far off track. I'm talking about
> sampling a repetitive waveform, the same as a conventional Tek or HP
> sampling scope.
I know ypou are.
>The signal is any waveform that can be viewed on a
> conventional scope, including eye patterns. The signal can be anything
> from dc to 7GHz, although dc is somewhat difficult due to thermal
> drift. Even so, the binary sampler is far better than a diode sampling
No problem here. I am taking issue with the claim that the signal has a
(noise) BW of 7GHz. It most certainly does not.
> Conventional sampling scopes have so much noise it is difficult to
> measure signals below 1mV. With the binary sampler, detecting a 10uV
> signal is easy, 1uV is difficult, and below 1uV looks unreachable at
> the moment. This is far better performance than can be obtained with
> conventional sampling technology.
> Does this help?
Ahmm.. I understand all of this very well indeed, this is all very
elementary. However, it seems that the subtleties I am pointing out are
not really being appreciated.
Yes, the signal can vary from DC to 7 GHz, but this is *not* the same as
saying that the signal has a *BW* of 7Ghz. The signal is not varying in
a continuous manner, such that while it is varying, you are extracting
its information content. You are sampling a fixed repetitive signal,
therefore it has a very limited BW, therefore you can filter out the
noise without filtering out the signal.
In summary, you are not measuring a 1uv, 7 GHz BW signal, you are
measuring a signal that varies from DC to 7Ghz, that has a very limited
BW. You are confusing signal frequency, with signal BW, they are not the
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