Precision low frequency noise measurement

Techniques have been developed for conveniently making precision (1%) noise spectral density measurements in the 10/sup -3/-kHz to 35-Hz or higher range. Application interest is particularly in the area of amplifier l/f noise measurement. Measurements are made by overlap averaging of the fast Fourier transform (FFT) with analog preconditioning of the noise. Calibration of the measurements requires only a known sine wave signal source. The use of the FFT makes possible good statistical control of the measurement result. It was found in most cases that the longer the FFT, the better the results. It was shown that high-pass filtering of the data prior to digitization is required for accurate results. The biggest limitation to more accurate measurements, particularly at very low frequencies, is the time required to get a large sample size.<>