I have some fundamental questions about noise in op amps.

1. How does Analog Devices know that an op amp has noise?

I.e. how does AD determine or measure that any given op amp has a certain amount of voltage or current noise?

2. What does noise data look like?

I.e. Is it frequency domain just like in datasheets (e.g. nV/rtHz per log10 freq), is it a time-domain waveform for which RMS is calculated?

3. I am wondering what noise is. Are the current, voltage noises of an op amp aperiodic, Gaussian waveforms (with zero mean and standard deviation equal to their RMS values)? Do they appear in reality as a small fluctuating voltage on highly sensitive voltmeters or instruments?

Thank you,

Daniel

HI Daniel,

There are two types of noise associated in amplifiers in general: 1/f noise or flicker noise and wideband noise. The flicker noise dominates the low frequency noise and it is increases as the frequency decreases. At high frequency, the broadband noise dominates and it is typically flat and constant.

This noise can easily be measured using the spectrum analyzer (nV/rtHz) and oscilloscope for peak to peak voltage noise usually at lower frequency ranging from from 0.1Hz to 10Hz. The distribution of noise is Gaussian. Please refer to this mini tutorial for more detailed discussion about noise of the opamp.

Here is the link: http://www.analog.com/media/en/training-seminars/tutorials/MT-048.pdf

Let me know if you need anything else.

Best regards,

Emman