It's Friday evening, time for some
Fun with TE!
Todays star of the show: a low noise preamplifier
It's set to a gain of 1000 and limits the bandwith from 1Hz to 30kHz. We see the output on the scope and dmm.
I'll adjust the timebase to show the noise best I can but leave the sensitivity the same.
Please excuse the shoddy camera work, still fighting with it a bit. Also, sorry for the big pictures Vince.
First let's check a LM399 based voltage reference:
Typical datasheet noise is 7µV, maxium 20µV in a bandwidth up to 10kHZ. We measure 33µV, but the circuit itself has some gain, the bandwidth is up to 30kHz and these are actually Czechoslovakian-made MAB399 clones - it's in the ballpark I'd say.
Next up, a reference based on a zener running at 5mA.
If it weren't for some kind of
evil wiggle it would be lower noise as expected for the higher current.
I'll have to come back to this and see where that comes from
Number three is a low noise voltage regulator based on
https://wenzel.com/documents/finesse.html Now that looks more like it!
Nice and well you might say, but how noisy is the supply you are powering this with?
Not exactly low noise, a linear supply based on LM723.
Now, what about that switching supply lurking below?
It's a switcher alright
But still only 2.5 times the noise of the linear one so not too shabby (it is without load though)