Re: Why do JFET/FET amps experience the miller effect? There isn't any feedback

"Stephen" <stephendeese@xxxxxxxxxxx> wrote in message news:1113322777.053497.318560@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
> Could someone explain why a self biasing JFET amp (for example:
> http://www.mission-technology.com/ELECLABS/images%5C21lb10_1.gif) would
> display the miller effect? There isn't any feedback, so there
> shouldn't be any miller effect.. right?
>
>>>From what I've read "The miller effect is the effective multiplication
> of a impedance across a negative gain device."
> http://www.odyseus.nildram.co.uk/RFIC_Theory_Files/Miller_Effect.pdf
>
> In Erno Boberly's great article "JFETS: The New Frontier Part I"
> (http://www.tkhifi.com/div/Erno_Borbely_fet_articel_1.pdf).. he
> mentions how the JFET amp can have this huge input capacitance with a
> large gain. But.. these amps don't have feedback... so why?


There is a capacitance between the FET drain and gate.
This arises due to the fact that the gate and channel are
separated by only a PN junction. That capacitance acts
as a feedback element. So your premise, "don't have
feedback", does not apply. (Your conclusions would
be sensible, otherwise.)

--
--Larry Brasfield
email: donotspam_larry_brasfield@xxxxxxxxxxx
Above views may belong only to me.


.

Relevant Pages
Quantcast