On Friday, March 20, 2015 at 7:48:22 PM UTC-4, John Larkin wrote:
> On Fri, 20 Mar 2015 16:04:17 -0700 (PDT), George Herold
> <gherold@teachspin.com> wrote:
>
> >On Friday, March 20, 2015 at 2:28:25 PM UTC-4, John Larkin wrote:
> >> On Thu, 19 Mar 2015 19:45:19 -0700 (PDT), George Herold
> >> <gherold@teachspin.com> wrote:
> >>
> >> >On Thursday, March 19, 2015 at 9:33:52 PM UTC-4, Winfield Hill wrote:
> >> >> John Larkin wrote...
> >> >> >
> >> >> > High-value (like, 100M) thickfilms seem to have excess noise. Metal
> >> >> > films are hard to find at those values, but are much quieter.
> >> >>
> >> >> Yes. The "excess noise" I've observed is usually highly voltage dependent,
> >> >> proportional to voltage, etc. It may be non-existent at low voltages, like
> >> >> under 10V, but severe above 50 to 100V to 1kV. And it can vary dramatically
> >> >> from part to part. E.e., made some +/-2KV amplifiers, with sub 1ppm noise
> >> >> levels, and 20% of the 10kV feedback resistors were very noisy and had to be
> >> >> replaced.
> >> >>
> >> >> But troublesome FET transistor noise may not have classic 1/f characteristics at
> >> >> all, e.g., "telegraph noise" and "popcorn noise" are not strictly 1/f. Let's
> >> >> talk after you've digested our measurements and the discussion in Chapter 8.
> >> >> The book is being shipped as we speak. My order is in.
> >> >>
> >> >>
> >> >> --
> >> >> Thanks,
> >> >> - Win
> >> >
> >> >Excellent! I look forward to the discussion once
> >> >my piece of the 40 tons arrives.
> >> >I wonder if the voltage dependence is a surface
> >> >thing. (could be the outer surface or some
> >> >layer underneath.)
> >> >
> >> >George H.
> >>
> >> All resistors have the same Johnson noise at zero volts. Some, not
> >> metal films, have shot noise with current flowing, which is simple
> >> electron arrival statistics.
> >>
> >> I conjecture that some nonmetallic resistors, like cermets, may have
> >> shot noise when biased. They also have excess, 1/f ish, noise, maybe
> >> from their polycrystaline confused nature. Tiny temperature variations
> >> must play heck with a grainy cermet-like structure.
> >
> >I've never seen excess shot noise in resistors..
> >(excess noise that is white in frequency.)
> >but I haven't looked hard either.
> >According to Landauer a resistor should reduce the shot noise
> >as 1/N, where N is the number of scattering events
> >as a "single electron pulse" travels the length of the resistor.
> >
> >I'm not sure how to think about "scattering events"
> >and 10 ns pulses.
>
> 10 ns is still pretty slow.
Well just a number out of the air... well typical PMT pulse width,
that's more than one electron of course.
>
>
> >>
> >> I've done a little testing on high-ohm resistors, but just enough to
> >> get me through a project. I needed 100 Mohms and wound up using two
> >> Dale custom-ordered 50M axials in series in mid-air, hopping over some
> >> surface-mount parts. Cermets were awful. This is fairly difficult
> >> stuff to measure, but would be a good student project or something.
> >
> >I wired up my LTC6090 HV opamps today. Fired it up on the test bench.
> >no smoke, but all I saw noise-wise, was first the room lights, and then
> >60Hz, with cross-over spikies from the linear supply.... I wanted to
> >go watch the UB bulls play in the "big dance".* So I'll have,
> >to put it in the box tomorrow...(Monday) Measuring noise can be hard.
> >I sometime wonder how I ever made things work in the past....
> >
> >George H.
> >
> > *UB lost, we trailed the entire game, tied it up with ~3:00 to go,
> >and then lost. Still it was a great emotional ride for me.
> >+1, I hope Bobby Hurley stays and we go back.
> >(intellectually sports makes no sense at all,
> >for me, it's all about the emotion.)
> >
>
> Was that basketball? I never understood that game. It seems to be a
> bunch of guys with endocrine problems, running back and forth all
> night. Looks chaotic to me.
Yeah, I played it a lot when younger, which helps..
Team sports are fun.
I wish I still had good knees,
I hate running, but running after some ball is different.
(I'm trying to win!)
Basketball, soccer, tennis, volleyball...
I still play ping-pong, a pretty small ball,
and not much running.
George H.
>
>
>
>
> --
>
> John Larkin Highland Technology, Inc
> picosecond timing precision measurement
>
> jlarkin att highlandtechnology dott com
> http://www.highlandtechnology.com