Is the QA the right tool for this measurement?


Excuse my ignorance but I am looking for a tool to characterize the following system and am wondering if the QA would do the job?

I would like to characterize the spurious signals (60Hz, switching noise and noise floor, etc) of a constant current amplifier which drives an inductor. I would like to do this with the input to the amplifier shorted and just look at what the amplifier is putting out in that condition. I have access to a current monitor which represents the output current of the amplifier. The amplifier has a bandwidth of less than 10KHz. An oscilloscope with FFT is just not giving me the resolution I am looking for.

I guess what I am asking is will this work without sweeping the input to the amplifier?

Thanks in advance

It should depending on how low a level you need to see your noise. Last night I measured the noise of a 250w/8ohms power amp of mine- built circa 1981- with the inputs terminated and the loads were 4ohm. This is what I got- hope it helps

Hi @3LionsCT, in addition to @VAR’s data point, there’s some more data on measurements of supplies at the link below. It’s a 3 part series looking at the noise output of various LDOs. Part one uses the QA350 DVM, and parts 2 and 3 focus on the QA401 audio analyzer. The current QA403 analyzer is quite a bit better than the QA401. But you can also add a low-noise pre-amp if you really need scrub down into the noise. You could hit RMS readings (20 kHz BW) of -125 dBV with a low-noise pre, which is about ~600 nV or so.

The LDO test at the links below included an LT3042, which is super low noise LDO and I think still unmatched, and it’s around the limit of the setup.

Thanks for the feedback. That looks exactly like what I need to do.

Now I just have to wait for them to come back into production…

I will check out the article

Thanks Matt!