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From: firstname.lastname@example.org (Steve Pepper)
Subject: Re: Comb/Harmonic Generators
Date: 12 Dec 2002 10:54:33 -0800
NNTP-Posting-Date: 12 Dec 2002 18:54:33 GMT
email@example.com (Vance) wrote in message news:...
> > Downconverting to an IF is interesting. What is the IF frequency and
> > bandwidth? And why is this better than straight sampling to DC? Is it due to
> > the difficulty of obtaining stable signals at 100 GHz?
> > The 100 GHz sampling bandwidth is interesting, since it would improve
> > acquisition of 10 GHz logic signals from Motorola GigaCom ECL, which is my
> > main interest. Also, I would expect your modules to be considerably less
> > expensive than the HP or TEK samplers.
> > Since your sampler can run at 10 Gs/sec, is downconverting to an IF still
> > necessary?
> > Mike
> OK, I gotta bring in some horsepower! I'll get one of our guys to
> respond, Mike. Or, you can drop me an email at firstname.lastname@example.org.
Hi Mike. Vance asked me to try to answer your questions. First let me
introduce myself: I'm Steve Pepper, Sr Design Eng. with Picosecond
Pulse Labs. I'm a co-designer of the sampler and NLTL components,
working with Agoston and others in Beaverton, OR.
First, your calculation of the RMS voltage noise of a 50 Ohm resistor
in 100 GHz BW is correct. Vance's slide rule might need a tune-up
The 3 mV RMS noise Vance quoted is the input-referred noise for the
combined sampler and IF charge amp operated in "sample-resolved" mode,
in which individual samples are pulse-resolved and digitized the way a
conventional sampling scope operates. I'm not sure "Noise Figure" is
the appropriate metric to use in this case, but the input-referred 3
mV RMS noise can be used to calculate the "minimum resolvable signal"
that you were looking for, when the sampler is operated in this mode.
Another way of operating the sampler, "downconversion mode" is
more like a conventional harmonic mixer. The sampler is strobed at an
LO frequency that is higher than the (baseband) IF bandwidth, and
individual samples are not resolved. Instead, many samples are
averaged together within the IF bandwidth. Without going into a lot of
detail, suffice to say the the noise and conversion loss depend on the
RF/IF bandwith ratio and the LO frequency (sample rate). The advantage
of operating in this mode (downconversion to baseband) is lower noise
and conversion loss. The IF bandwidth of the sampler described on the
web site is DC to about 1 GHz. We have other designs with a range of
RF and IF bandwidths.
I believe you answered your own comment on the need for dynamic
range when you referred to 10 Gb/s logic signals. These are
volt-level signals with fast edges, and the edge speed will be
degraded by the rise-time of the acquisition system.
P.S. If you enjoy reading patents, you can get a lot of detail on
our sampler design from our US patent applications: 20020167373 and
20020145484, which were recently published.
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