Resistor Noise—reviewing basics, plus a Fun Quiz

The noise performance of amplifier circuits is greatly affected by the Johnson noise of resistors—the source resistance and feedback resistors. Most everyone seems to know that resistors have noise but may be a bit foggy on some of the details. Here’s a bite-sized review in preparation for future discussions on amplifier noise:

Click Here to read on EDN magazine web site.

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  • If I take the result of the quiz right, doesn't it mean that the total open circuit noise voltage is independent of the resistor value and only the noise frequency bandwidth depends on the resistor value? You always have a stray parallel capacitance, even if it is infinite small?

  • Jens-Michael-- you are correct, assuming a constant stray capacitance, the total noise is independent of the resistor value. Higher value resistors have a higher noise density but the bandwidth rolls off at a lower frequency.