Discrete fourier transform analysis for harmonic distortion and am/fm modulation in ate testing

The use of FFT versus DFT for signal analysis are compared in an automatic test system. For distortion and mod ulation analyses, where only a small number of spectral lines need to be computed, the DPT method is shown to be superior in flexibility and accuracy. It is shown that coherent sampling can be achioved in DFT distortion analysis by simple crossover detection without the use of windowing techniques. In AM/FM modulation analysis, the DFT program is used to recover all modula tion parameters from samples of the modulated signal without a demodulator. Frequency shift in DFT analysis to reduce leakage error from non-coherent sampling are also discussed.