Noise can be composed of both environmental deterministic noise (e.g. spurious RF) and random thermal noise. This note focuses on random noise and its measurement. A perfect electronic device would perform its function and add no noise that wasn’t presented at it’s input. Practical devices add noise and therefore reduce the signal-to-noise ratio of their system. Noise factor is the ratio of noise power out to noise power in (output referred by Gain). And noise figure is noise factor in dB units. Of particular importance are devices in the early stages of amplified systems since their noise will be amplified in subsequent stages.

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