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From: Mike Monett
X-Mailer: Mozilla 2.02 (Win16; I)
Subject: Re: Comb/Harmonic Generators
References: <3DF54583.49C9@Spam.Bots> <email@example.com> <3DF9B8A5.585A@Spam.Bots> <firstname.lastname@example.org>
Date: Fri, 13 Dec 2002 20:13:36 -0800
NNTP-Posting-Date: Fri, 13 Dec 2002 20:13:37 EST
Organization: Bell Sympatico
Steve Pepper wrote:
> Mike wrote:
> > With 10:1 attenuation in the test adapter, the sampler could see 12
> > to 35 mV p-p. With 3 mV rms noise in the sampler, the signal could
> > end up buried in noise
> This is where a high sample rate combined with averaging really helps.
> Commercial sampling scopes have a sample rate of 100 Ks/sec or less.
> At a mere 10 Ms/sec, you can average 100 samples in the time a
> commercial scope takes a single sample. This reduces the noise by
> sqrt(100), and you are down to 300 uV RMS. The only caveat is that
> your data pattern must repeat at 10 MHz minimum (< 100 nSec pattern
> This is essentially how "downconversion" works. The sampler is
> strobed synchronously with the data pattern, and the strobe timing is
> slowly "walked" through the data pattern, building up the waveform in
> "equivalent time". The RF waveform appears at the IF "time stretched"
> to the rate at which the strobe is advanced through the pattern. This
> is also sometimes called "sequential sampling".
300 uV rms is much more interesting. I'm familiar with sequential
sampling and sqrt(N). But it's not clear where and how the averaging
I've got Agoston's white paper on meauring the risetime, but it's in
Acrobat 4 and the images come out black in my Adobe 3.0 viewer. Do you
have any other papers that talk about it more?
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