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Re: new polymer caps

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Am 04.09.25 um 19:26 schrieb john larkin:
> https://www.mouser.com/c/?marcom=113518709
> 
> Interesting. Replacement for tantalums but low ESR.
> 
> 470uF 2VDC 9mOhm would be a good bypass for an FPGA core supply.
> 
> I'll get a few and TDR them, estimate inductance.

Be careful with "DC" current through polymer caps.

I once built a low noise amplifier that had to do without
feedback for stability reasons, There was a negative real
part of the input resistance, even in the circuit from AOE3.

CS stage, cascode, opamp, feedback to the sources so that
may look like CS but it is no longer CS.

To get at least a stable o/p I fed the sources from a
fixed current mirror and bypassed the sources with
large electrolytics with fb removed.
That was a *bad* idea. The circuit seems to show every
electron that defects through the electrolytics.
Oscon Polymer was worst by far: a 1/(f**2) corner at
a few KHz and so much noise that the 89441A went into
clipping. That's not 1/f!!!

Nippon Chemical ALU was way better but the only thing that
worked in a usable way was a AVX wet slug tantalum for €100,
Sprague wanted twice that. 1/f**2 corner at 10 Hz.

stability problem with feedback:
< 
https://www.flickr.com/photos/137684711@N07/52419417337/in/datetaken/ 
    >
The green s11 plot leaves the unit circle ---> not stable at these
frequencies.

Same thing in LTspice:
< 
https://www.flickr.com/photos/137684711@N07/52419417337/in/datetaken/ 
                    >
3 GHz CFB amplifiers can keep that stable (TI) but they drown
everything in 1/f noise, even with 40 dB of amplification
in front of them.

------
flickr gets worse by the week. The now limit pic size to just
a bit more than stamp size for free accounts. I'll have to
soup up my web site.  :-(

Cheers, Gerhard.

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new polymer  caps john larkin <jl@glen--canyon.com> - 2025-09-04 10:26 -0700
  Re: new polymer  caps "Edward Rawde" <invalid@invalid.invalid> - 2025-09-04 13:58 -0400
    Re: new polymer caps John R Walliker <jrwalliker@gmail.com> - 2025-09-04 19:15 +0100
      Re: new polymer caps John Robertson <jrr@flippers.com> - 2025-09-04 13:26 -0700
        Re: new polymer caps liz@poppyrecords.invalid.invalid (Liz Tuddenham) - 2025-09-05 08:43 +0100
          Re: new polymer caps Joe Gwinn <joegwinn@comcast.net> - 2025-09-05 08:42 -0400
            Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-05 23:24 +1000
              Re: new polymer caps Jeff Layman <Jeff@invalid.invalid> - 2025-09-06 08:19 +0100
                Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-06 18:15 +1000
                Re: new polymer caps JM <sunaecoNoChoppedPork@gmail.com> - 2025-09-06 20:18 +0100
                Re: new polymer caps Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2025-09-06 17:46 +0000
                Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-07 14:38 +1000
        Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 08:01 -0700
  Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-04 20:13 +0200
    Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-04 20:25 +0200
      Re: new polymer caps Jeroen Belleman <jeroen@nospam.please> - 2025-09-05 00:14 +0200
    Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 08:12 -0700
      Re: new polymer caps Gerhard Hoffmann <dk4xp@arcor.de> - 2025-09-05 19:23 +0200
        Re: new polymer caps john larkin <jl@glen--canyon.com> - 2025-09-05 13:53 -0700
          Re: new polymer caps Bill Sloman <bill.sloman@ieee.org> - 2025-09-07 02:35 +1000

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