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How to bias a CS mosfet

Positive feedback.

John

Reply to
John Larkin
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Oops! Got my OA inputs swapped! Redo:

o-----------------------------------o | | .-. .-. | | GND | | | | R | | | '-' --- '-' | --- | . . . | | ___ | | .-----'------|___|--------------o | | | | | ' | | |\| ||-+ |----|----|-\ ___ ||------|___|---------||-+ | -----|+/ | | |/| | | ' .-. .-. | | | | | | | | R '-' '-' | | | | === === GND GND (created by AACircuit v1.28.6 beta 04/19/05

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Reply to
John S

Thanks, John.

Reply to
John S

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Reply to
Ian Field 

--
Thanks! :-)

Version 4
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Reply to
John Fields

Thanks.

Okay, so it needs a little (.1uF) from OA output to inverting input.

Reply to
John S

BTW, it also needs some resistance between OA output and the FET gate so he can have a point to insert his signal.

Reply to
John S 

--
OK, I missed that part.

Thanks! :-)
Reply to
John Fields

JF and JT meet a lot of those criteria, but aren't likely to actually be dangerous. JT has threatened me with violence (and with car racing! Whatta man!) but I don't expect the old geeze will actually show up at my door and threaten me with his cane.

John

Reply to
John Larkin

I keep wondering which of the two would be most likely to shoot me in the back while I was unarmed had I been their side of the pond.

Reply to
Ian Field

That will complicate the loop dynamics some. And the DC servo clearly fights the signal, over some bandwidth range.

John

Reply to
John Larkin

What do you recommend to fix it?

John S

Reply to
John S

IMO an op-amp as a bias generator for a MOSFET is way OTT when a single BJT,

4 resistors and an electrolytic will do the job just fine.
Reply to
Ian Field

Can you post a schematic?

Reply to
John S

I wonder if you really mean: Is there any way to bias a mosfet CS

*using* source degeneration so that ....

If you mean using only source degeneration to achieve your goal, I'm not aware of any.

Reply to
John S

Its simple enough to describe - and I already did.

Reply to
Ian Field

Do you mean the common-base PNP thing?

John

Reply to
John Larkin 

--
Schematic, please?
Reply to
John Fields 

--
A picture is worth a thousand words, so why don't you just shut the
fuck up and post the picture?
Reply to
John Fields

"Old fart" has come to mean useless old fogey. It's like "crap" has come to mean "junk."

Get used to both terms.

John

Reply to
John Larkin

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