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Noise measurement with spectrum analyzer

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Palpurul

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Hello,
I need to make noise measurement for low noise differential amplifier that I'm trying to build and I want to characterize its noise spectrum from kHz region to about 20 MHz and the minimum noise density that I need to measure is about 100nV/sqrt(HZ). I also have a Low noise preamp with gain of 20dB that can be helpful in my measurement. I want to be able to produce noise density vs. frequency graph like they show in the opamp datasheets, just like the picture below.

Opera Anlık Görüntü_2018-03-27_110332_www.analog.com.png

I might have access to RSA503 spectrum analyzer in a few weeks. My question is how reliable is noise measurement with spectrum analyzers at that frequency range? RSA503 has really low noise floor and great amplitude accuracy. What are some of the things that I need to be aware of? Is there a better measurement technique for noise measurement at that frequency range?

Any reading recommendation about this subject is appreciated.
 

Like other RF spectrum analyzers, RSA503 has lower frequency limit of 9 kHz. If you really don't want to know about 1/f noise corner and respective noise level, the instrument can be used. Most people would use a FFT analyzer instead.

If the DUT has some gain, no additional LNA required. A signal generator and attenuator for gain calibration should be at hand.
 
Thanks for your response FvM,
Is it better to use FFT analyzer for this measurement? 100nV/sqrt(Hz) is the output noise of my DUT, so it's the amplified input referred noise of my DUT. I want to make accurate measurements is there anything that I should know before I start this measurement? Is there a better technique or equipment for noise measurement at this frequency range?
 

Do you have a well calibrated Noise Source at that frequency ??

I don't think that Spectrum Analyzer is appropriate for Noise Measurements -especially for around 20MHz-
 
Do you have a well calibrated Noise Source at that frequency ??

No I don't have a calibrated noise source. What to look for in a spectrum analyzer when measuring noise?

I don't think that Spectrum Analyzer is appropriate for Noise Measurements -especially for around 20MHz-

Is it because of the larger noise floor at lower frequency? What to look for in a spectrum analyzer for better noise meausurement? I thought It was appropriate because of its amplitude accuracy is superior to many spectrum analyzers in the market. Am I in the wrong way?
 

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