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

[Bob Camp]

Hi

For a phase noise test set with the amp located at the mixer
output, you need good noise at a 1,10,100Hz sort of test point. 

The current mode stuff is great for things like distribution amps 
or for buffers driving the mixer. Indeed, a buffer into the mixer
is a pretty good idea. 

Bob

> On Feb 24, 2023, at 2:39 PM, Lux, Jim via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> 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 4817A   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.
> 
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