Are the EFC inputs all directly DC coupled to the varactor diodes making them high DC impedance?
I always thought they should bring the varactor or EFC ground out as a separate pin but I assume that since they do not, ground noise at least within the oscillator does not limit performance. In the past when I have had low frequency ground noise, I have either used an instrumentation amplifier at the load or used a high impedance current source with a load resistor to ground at the load. But I have difficulty imagining either being used to drive an EFC input because close proximity of the driving circuit allows it to use the oscillator ground as a single point ground. I wonder if there is anything to be learned by studying how the old varactor based (parametric) operational amplifiers were used. On Mon, 1 Aug 2016 16:32:35 -0400, you wrote: >Hi > >If you wire up all the possible circuits and check them all out the >answer is that big C / small R wins. Big R gets you into resistor noise issues >and stray pickup. > >Bob > >> On Aug 1, 2016, at 4:16 PM, David <davidwh...@gmail.com> wrote: >> >> This duplicates the problems encountered when trying to quantify low >> frequency noise from a voltage reference; it is difficult to make an >> low frequency high pass filter with lower noise than the lowest noise >> references and the capacitor is the problem. >> >> In Linear Technology Application Note 124, Jim Williams discusses the >> problems with electrolytic capacitors for this type of application. I >> have read that you *can* get away with aluminum electrolytics if you >> grade them for low leakage and low noise. The dielectric absorption >> is also a problem unless you can wait hours for best performance. >> >> What about the alternative of buffering the signal with a low noise >> low input bias current operational amplifier so that a large film >> capacitor can be used instead? Is the low frequency noise of a good >> operational amplifier still too much? What about a chopper stabilized >> amplifier without suitable output filter? _______________________________________________ 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.
