[time-nuts] Re: Phase Noise Measurement {External}

[Lux, Jim]

On 2/24/23 7:57 AM, Jim Muehlberg via time-nuts wrote:
> Tobias,
>
> Maybe you have seen Charles Wenzel's "teclib.com" site.  Lots of fun 
> stuff there.  Including a design for a LNA for precisely what you want:
>
> http://techlib.com/files/lowamp.pdf
>
> I built this about 15 years ago.  There are probably better LN op amps 
> out there now.
>
> Take a look at this guy: (Marco Reps)
>
> https://youtu.be/XpbDMo8an5w
>
> He's a "voltnut", but that's OK.  We're all nuts.
>
> Oh, and certainly, you need to read Linear application note #124 by 
> Jim Williams.
>
> Good Luck!
>
> Jim 


There's a variety of very low noise current mode amplifiers, but they 
are challenging to keep stable, because they have enormous GBW products 
(1 GHz). And designing with current feedback is tricky - you need a 
certain Rin and Rfb, but they add Johnson noise.

example ADA4927 1.4nV/sqrt(Hz), 14 pA/sqrt(Hz) at G=28, 100kHz - 
estimating off the plot in the data sheet, the 1/f knee is around 10-20kHz

There's also the ADA 4817AÂ Â  4nV/sqrt(Hz) 2.5 fA/sqrt(Hz) - this one 
looks like it's 1/f is a bit lower.  It's also challenging in low gain 
applications.