Simulation indicates that the required C value depends on the transformer turns ratios and the RC product sets the notch frequency.
Large signal modulation of the transistor parameters results in a distorted signal at the base when a large signal is applied to the output. the RC product is around 4ns for a simulated 2N3904 for a reverse isolation notch at 10MHz. The value if C is a multiple (dependent on transformer turns ratio) of Ccb. Bruce > On 14 January 2020 at 09:01 Claudio Girardi via time-nuts > <time-nuts@lists.febo.com mailto:time-nuts@lists.febo.com > wrote: > > > Some years ago I played a little with that buffer circuit and found out > that the isolation up to a few MHz can be improved a little with an RC > feedback network between base and collector. > I cannot find my notes right now, IIRC from the output the circuit can be > seen as a sort of bridge where one can balance the various impedances for > minimum feedback. > Enclosed is a graph for the measured gain and isolation for that circuit, > using a 2N3904 (!), for several configurations - > without the RC feedback, with an RC combination giving some overall > improvement in S12 and with some values that gave a sharp null at 10 MHz. > > Claudio > > > > Il 13 gennaio 2020 alle 18.27 Jeffrey Pawlan <paw...@runbox.com > mailto:paw...@runbox.com > ha scritto: > > > > > > Many years ago I did a study of Norton amplifiers and optimized for > > IP3 > > using non-linear circuit simulation tools. I published a two part > > article in RF Design Magazine which covered the amplifier itself as > > well > > as the non-linear model for the BJT. My use for the Norton > > amplifier did > > not require high isolation so I spent little tile on that aspect. I > > am > > friends with the co-inventor of the original and the author of the > > subsequent patents. His name is Allen Podell. The webpage you > > included > > speculated that the reverse isolation degradation at high > > frequencies > > was owing to the layout or the transformer. Although those are > > contributors, the simulation showed high frequencies had poorer s12 > > so > > it is expected. > > > > If high isolation is what you need, then as written on this list, > > there > > are ICs which can provide this much better than a single stage > > amplifier. They do suffer from more residual noise however. > > > > Jeffrey Pawlan > > > > > > _______________________________________________ > > time-nuts mailing list -- time-nuts@lists.febo.com > > mailto:time-nuts@lists.febo.com > > To unsubscribe, go to > > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions > > there._______________________________________________ > > > > > time-nuts mailing list -- time-nuts@lists.febo.com > > mailto:time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
