Analysis And Measurement Of Intrinsic Noise In Op Amp Circuit
Part II: Introduction To Op Amp Noise
by Art Kay,
Senior Applications Engineer,
Texas Instruments Incorporated
An important characteristic of noise is its spectral density. Voltage noise spectral density is a measurement of root-mean-square (rms) noise voltage per square root Hertz (or commonly: nV/√Hz). Power spectral density is given in W/Hz. In the previous article we learned that the thermal noise of a resistor can be computed using Equation 2.1. This equation can be rearranged into a spectral density form. One important characteristic of this noise is that it has a flat spectral density plot (ie it has uniform energy at all frequencies). For this reason, thermal noise is sometimes called broadband noise. Op amps also have broadband noise associated with them. Broadband noise is defined as noise that has a flat spectral density plot.
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