[time-nuts] Norton amplifiers

[Claudio Girardi]

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 <pawlan at 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 at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: iso_buffer.png
Type: image/png
Size: 84116 bytes
Desc: not available
URL: <http://febo.com/pipermail/time-nuts_lists.febo.com/attachments/20200113/2513dc64/attachment.png>