[SOLVED] How to measure 1/f noise close to DC

[eigenroot]

I am trying to measure low-frequency noise such as 1/f noise spectrum from a material.

I saw some people applied a DC current source, took the voltage across the material and amplified it with a preamp before it went into a FFT spectrum analyzer.

But the problem is the noise is relatively small compared to the DC component, and the amplifier can easily get overloaded by the DC offset before amplifying the noise to a reasonable level. But if I use a DC block, the low cut-off frequency is still not low enough. For 1/f noise, I would like to measure down to 1 Hz. Can anyone suggest a way of doing it? Thanks.

 

[jiripolivka]

You can use an oscilloscope with an amplifier. This instrument does run from DC to some frequency limit. The advantage is that if the noise is clipped, you can see it and reduce gain. Modern oscilloscopes have FFT modules to see the spectrum.
Most opamp manufacturers publish noise characteristics by noise records over time. This is also done with such scope.

If you still have magnitude problems at DC, you can use a logarithmic amplifier. This also works from DC.

 

[godfreyl]

But if I use a DC block, the low cut-off frequency is still not low enough.

You can make the cut-off frequency low enough, e.g. 0.1 Hz.

Alternatively, you could add a variable DC offset after the first stage of amplification, to allow you to set it back close to zero.

 

[eigenroot]

You can make the cut-off frequency low enough, e.g. 0.1 Hz.

Alternatively, you could add a variable DC offset after the first stage of amplification, to allow you to set it back close to zero.

I think this answer solves the problem.