I have done this and it works great; the breakpoint between the chopper amplifier and the low noise amplifier can be adjusted to combine the wideband noise from the low noise amplifier and the 1/f noise and drift of the chopper amplifier.
Jim Williams wrote a couple of different application notes where this was used with both integrated and discrete amplifiers. On Sat, 15 Oct 2016 00:53:25 +0200, you wrote: >... > >The low frequency range is what we usually call the 1/f region, >although the long term stability also belongs to it. But unlike >the long term region you don't have to sacrifice a virgin to >get decent measurment data. Jim William's appnote[1] has lots of >details how to measure noise in this region. There are slightly >more modern circuits by Todd Owen/Amit Patel[2] and Gerhard Hoffmann[3]. >I recently stumbled over a similar amplifier by Enrico Rubiola >and Franck Lardet-Vieudrin[4]. Both [4] and [5] explain why for >low impedance sources (like power supplies) a BJT input stage >would be a better choice than jFETs and also cover the influence >of temperature on the measurement. [6] gives some additional info >on how to design the differential input stage. > >I wonder how an active offset voltage cancelation scheme for >the differential pair input stage using one of the chopper stabilized >opamps (eg LTC2057) would change the temperature dependence and long >term stability (aka 1/f^a noise) of the circuit, but I have not seen >any measurements of a system like this yet. > >... _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.