> On Thu, 16 Nov 2023, John Larkin wrote:
>
>> You can buy opamps with noise less than 1 fA/rthz.
>
> The AD549 has a promising current noise. I must experiment because of is
> undocumented voltage noise at the frequencies I want.
>
If you post a bit more about what you're actually trying to measure, we
can probably be more help.
A TIA with 4 pA/sqrt(Hz) noise, 100 kHz bandwidth, and 10**9 ohms
transimpedance will have an output noise floor of
E_N ~ 4e-12*1e9*sqrt(1e5 * pi/2) = 1.6 Vrms.
[The pi/2 is the ratio of the noise bandwidth of a 1-pole rolloff
(1/4RC) to its 3-dB bandwidth (1/2piRC).]
Viewed on an oscilloscope, that'll look like a 6-V wide stripe down the
middle of the display, with outliers up to +-5V at least.
Not exactly your state-of-the art low noise amplifier!
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Jean-Pierre Coulon●November 16, 20232023-11-16
On Thu, 16 Nov 2023, John Larkin wrote:
> You can buy opamps with noise less than 1 fA/rthz.
The AD549 has a promising current noise. I must experiment because of is
undocumented voltage noise at the frequencies I want.
--
Jean-Pierre Coulon
Reply by John Larkin●November 16, 20232023-11-16
On Thu, 16 Nov 2023 16:26:52 +0100, Jean-Pierre Coulon
<coulon@cacas.pam.oca.eu> wrote: