A hardware spectrum analyzer starts at 9 kHz. It's so rare to find something that can analyze 1kHz and below.

If you meant a software PC spectrum analyzer. Which of them can view signals in microVolts?

No, I mean something like an Audio Precision. They can measure 20Hz to 90kHz to below -100dBm.

 

I'm a medical student.

1000 Hz is generated deep in the muscles and nerve centers.

Have you seen a Bioamplifier kit that can measure 1mV-10mV at 1000 Hz and less than 2 microVolt of noise? Such kit may have noises of hundreds of microVolt or even a milliVolt. Is it not? That is why I plan to buy a readily commercial one. But not easy to find a 1 channel of good noise profile.

Can some of you construct this kit for me? (Post #8)

A Medical Student??? In the information section you are listed as an electrical engineer. A bit of difference there.

 

A Medical Student??? In the information section you are listed as an electrical engineer. A bit of difference there.

Decades ago I took the electrical engineering course but failing so turn to medical field.

No, I mean something like an Audio Precision. They can measure 20Hz to 90kHz to below -100dBm.

Audio Precision may cost over $10,000. Why can't one just use a software spectrum analyzer? Also by using 1000X gain and getting an output like 8mV, can't this use to get the input referred noise of say 8uV?

 

Decades ago I took the electrical engineering course but failing so turn to medical field.



Audio Precision may cost over $10,000. Why can't one just use a software spectrum analyzer? Also by using 1000X gain and getting an output like 8mV, can't this use to get the input referred noise of say 8uV?

Because it is virtually impossible to get a quiet enough supply inside a computer.

 

Because it is virtually impossible to get a quiet enough supply inside a computer.

An external amplifier that will boost the 1 millivolt signal up to one volt with very low noise is about what is used in some ultrasound systems. So those amplifier ICs should be available. A low noise IC amplifier like that in a battery powered package could then drive the sound input of a PC with a signal well above the PC internal noise. The battery voltage will need to be what the amplifier requires because any voltage converter scheme will add lots of noise. quite a few very low noise ICs exist, none for sale at amazon or similar.

 

Because it is virtually impossible to get a quiet enough supply inside a computer.

How about just an ordinary oscilloscope?

A manufacturer told me he used oscilloscope to check for the 8mV output at 1000X gain so he figured the noise is 8uV referred to the input (this is using a 100 Ohm source impedance). The unit has frequency adjustments of 20Hz, 50Hz, 100Hz, 1000Hz, 5000Hz, 10,000Hz.

But since as one mentioned here a spectrum analyzer is the right tool to check for noises. How accurate is an ordinary oscilloscope compared to spectrum analyzer?

We know most spectrum analyzers (except the very expensive ones) have minimum 9kHz. But then the unit has a 10kHz setting. If he used spectrum analyzer, does the following relationship still hold?

Sqrt (10000Hz) = 100
Sqrt (100) = 10

So if the noise at 10,000 Hz is 8uV. Then the noise at 100Hz is 0.8uV (10 times less)?

I think he just used an ordinary oscilloscope which may be less accurate?

 

At this point I wonder if the noise anticipated is a specific frequency or simply a frequency band where signals are anticipated.

 

At this point I wonder if the noise anticipated is a specific frequency or simply a frequency band where signals are anticipated.

The manufacturer told me "The noise figure I gave was for broad-band, and we can't narrow it any more than that.". I figured he used the 10,000 Hz setting and he said used an oscilloscope. Can one simply say oscilloscope when one wanted to say spectrum analyzer?

As I asked in last message. Why need a spectrum analyzer to check for noises and not simply an oscilloscope. Please reply in that message instead. Thanks.

 

Many modern digital oscilloscopes have FFT function built-in.

If you want to measure down to 1μV without amplification, lookup 24-bit delta-sigma ADC, for example, Analog Devices MAX11200.

https://www.analog.com/media/en/technical-documentation/data-sheets/MAX11200-MAX11210.pdf

 

lookup 24-bit delta-sigma ADC

These are excellent for DC. Anything above about 10 Hz starts to get seriously attenuated.

This is what I meant by my first post, "how much time do you have?".

For slowly changing signals, trading time for S/N is the way to go.

 

Ah so, you are correct. Here is a 24-bit SAR ADC with 100dB SNR at 1.5Msps.

https://www.analog.com/media/en/technical-documentation/data-sheets/238024fa.pdf

 

Ah so, you are correct. Here is a 24-bit SAR ADC with 100dB SNR at 1.5Msps.

https://www.analog.com/media/en/technical-documentation/data-sheets/238024fa.pdf

Impressive: a 24 bit SAR with no missing codes.

And only $70 a pop.

 

Going back to an earlier post, it seems that you are looking to amplify a signal at about 1000 HZ, that would be just a few millivolts. And yet there is a big concern about noise that is a few microvolts. That noise would be about 60dB below the desired signal. And so far we have no hint as to what the frequency spectrum of the noise would be. Narrow band amplifiers at audio frequencies are not terribly complex, so it would not be so difficult to design an amplifier with suitable gain in the band from 900 hz to 1100hz, and less gain below and above that frequency range.
But if the noise is the same frequency as the signal that you are looking for it gets more challenging.
All circuits with current flow generate noise, but fortunately in most instances the noise is much less than the desired signal and so it can be ignored, or just compensated for.
It is also possible to create filters using more complex schemes that are very narrow, with a bandwidth of just a very few hertz, and very high rejection of everything outside that range.
And while an oscilloscope can provide a quite good measurement of noise amplitude, it will not provide the detailed frequency information about that noise.

SO RATHER THAN ASKING FOR SOLUTIONS ABOUT NOISE,, it makes much more sense to ask for help in measuring the amplitude of a signal at some frequency in the presence of signals at other frequencies. THAT seems to be what the goal is.