Two-phase frequency-conversion type spectrum analyzer for low-frequency noise measurement

An improved analog spectrum analyzer, which is suitable for noise analysis at very low frequencies, is presented. It is composed of two multipliers, two squarers, a summation circuit, and an integrator. This analyzer has half the value of the statistical error compared with that of the conventional analog analyzer. The design principle, actual circuit, and examples of the measured noise spectra at 0.05–1000 Hz are given. Certain specific measurement errors are also discussed theoretically.