[time-nuts] Re: +1/f of transistors

[Lux, Jim]

On 4/14/22 9:54 AM, ed breya wrote:
> The low noise opamps are indeed designed for the feature, and they 
> tell you about it, and how and why. The trade-offs are usually input 
> bias current being quite high (due to bigger or paralleled transistors 
> running at fairly high currents), and only good for a low resistance 
> environment. 


Actually not exactly - Parts like the OPA656 have about 6 nV/sqrt(Hz) 
voltage noise and tiny fA/sqrt(Hz) current noise, and are intended for 
use in high Z circuits.

The ADA4817 is about 4 nV/sqrt(Hz) and the OPA2810 (dual) and OPA810 
(single) are buffers with  6nV/Sqrt(Hz) and 5 fA/sqrt(hz). The AD8001 is 
a current feedback amp (normally for low Z) and is 2nV/sqrt(Hz), but 2 
pA/sqrt(Hz) on the non-inverting input, so a 1M input source will turn 
that into 2mV, which is pretty large. There's some folks who have 
combined a FET source follower with the AD8001.