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: Sat, 26 Oct 2002 10:09:18 +0100
NNTP-Posting-Date: Sat, 26 Oct 2002 10:09:20 BST
"Mike Monett" wrote in message
> "Kevin Aylward" wrote in message
> > > Kevin, I don't know how you got so far off track. I'm talking
> > > sampling a repetitive waveform, the same as a conventional Tek or
> > > sampling scope.
> > I know you are.
> > >The signal is any waveform that can be viewed on a
> > > conventional scope, including eye patterns. The signal can be
> > > from dc to 7GHz, although dc is somewhat difficult due to thermal
> > > drift. Even so, the binary sampler is far better than a diode
> > > bridge.
> > >
> > No problem here. I am taking issue with the claim that the signal
> > (noise) BW of 7GHz. It most certainly does not.
> What's your problem. The instantaneous bandwidth and noise bandwidth
> are the same.
I was pointing out the fact that the true signal BW, *is* the signal
noise BW. This should indicate quite clearly, that a claim of
0.01nv/sqrth over a BW of 7Ghz, is quite nonsense. Why you don't see
this is pretty amazing really.
> > > Conventional sampling scopes have so much noise it is difficult to
> > > measure signals below 1mV. With the binary sampler, detecting a
> > > signal is easy, 1uV is difficult, and below 1uV looks unreachable
> > > the moment. This is far better performance than can be obtained
> > > 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
> > not really being appreciated.
> That is a good possibility. I have the feeling you are inventing
> definitions to suit your arguments. These definitions change depending
> on your position. Give me some equations that express your viewpoint,
> then we can discuss.
I have explained quite clearly, *accepted* facts of signal processing. A
pure repetitive signal has zero information BW. Its that simple.
> > Yes, the signal can vary from DC to 7 GHz, but this is *not* the
> > saying that the signal has a *BW* of 7Ghz. The signal is not
> > a continuous manner, such that while it is varying, you are
> > 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.
> Not exactly. The signal risetime defines the bandwidth needed to
> preserve the frequency components.
Technically, its the shape of the pulse.
>All I need to know is the
> fundamental frequency, then I can give you the waveshape which means
> the harmonic content and phase relationship. The same as any
> conventional sampling system is defined.
You just don't seem to *want* to understand, the distinction between a
repetitive signal and a random signal. A repetitive signal has no BW.
End of story.
Look, if *any* signal is on continuously, I can just keep on sampling it
whenever I like, say once every second even. Ultimately, I can build up
what that signal looks like, no matter what ever what its base frequency
is. This is what the sampling theorem *means*. I can sample at a rate of
twice a signals *BW* to recover it. Furthermore, I have explained, such
a method how you can do this, i.e. with multiple multipliers.
> > 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
> > BW. You are confusing signal frequency, with signal BW, they are not
> > same.
> No, Kevin. Any sampling scope has a defined bandwidth. I am using the
> same definition.
Unfortunately, a novice understanding/definition of BW from scope
vendors manuals targeted at technicians, is not sufficient to explain
the more advanced concepts required in signal processing.
I explained to you what *real* BW meant. Your making the classic mistake
equivalent to "how come I can sample a 100Mhz centred signal at a 10khz.
The reason is that the sampling theorem is with regards to BW, not
signal frequency. You are still confusing the two. A 7Ghz signal, does
*not* necessarily, in fact it rarely does, take up 7Ghz of BW. Its that
> Thank you for realizing the binary sampler has performance advantages
> that cannot be achieved with current sampling technology.
> Since there is no new information or insight in this thread, there is
> little need to continue this discussion.
I agree, unfortunately, you are a bit out of your theoretical depth. You
need to take a decent course on signals and information theory. I have
tried to explain to you where you are mistaken, but rather then
understand the *accepted* theory behind it, you deny it in ignorance.
Its your loss.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.