Electronics > Beginners
(pre-)amplifier to measure power supply noise
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exe:
Thank you very much, guys! I'll take suggestion into account and try to measure something.


--- Quote from: imo on April 07, 2019, 06:30:17 am ---Mind the "bandwidth" of an opamp is always a product of the closed loop Gain and the BW.

--- End quote ---

Good point, I had doubts about that as well. I started to look into the datasheet and it says "[two-stage architecture] This architecture results in a 3.5 MHz bandwidth at a gain of 2000 for an equivalent gain bandwidth product of 7 GHz.". I'm glad they are explicit about that :)
exe:

--- Quote from: imo on April 07, 2019, 06:30:17 am ---FYI - below is a 2 transistors Amplifier with 72.4dB (4190x) gain, with 135kHz bandwith (30Hz-135kHz). I bet with good noise params for your application.

--- End quote ---

Nice old-school! May be I'll start with that, before buying expensive AD devices :).
not1xor1:

--- Quote from: exe on April 07, 2019, 08:53:40 pm ---
--- Quote from: imo on April 07, 2019, 06:30:17 am ---FYI - below is a 2 transistors Amplifier with 72.4dB (4190x) gain, with 135kHz bandwith (30Hz-135kHz). I bet with good noise params for your application.

--- End quote ---

Nice old-school! May be I'll start with that, before buying expensive AD devices :).

--- End quote ---

That is a bad choice.
Those AD ICs are differential amplifiers. They would take care and get rid of all common mode noise while that simple 2 BJTs amplifier will show just EMI noise in your lab.
Look at "How to measure PSU noise and ripple" video and thread for more details.
Gerhard_dk4xp:
Quite a strong allegation. Show me a baseline at -190 dBV with your differential amplifier.
The EMI noise in my lab must be something different.

<       https://www.flickr.com/photos/137684711@N07/24354944411/in/album-72157662535945536/        >

noise density of some LEDs,   0 dB = 1 nV/rtHz, no cross correlation.

regards, Gerhard
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