On 03/20/2015 07:04 PM, George Herold 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.Cermets and high value carbon comp resistors rely on the spreading resistance of minute contacts between grains--IOW the effective length of the resistor is much shorter than its physical length. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Apex HV opamp issues.
Started by ●March 13, 2015
Reply by ●March 23, 20152015-03-23
