A comprehensive analysis of transfer-function measurement based on maximum-length sequences (MLS) is presented. MLS methods employ efficient cross correlations between input and output to recover the periodic impulse response (PIR) of the system being measured. For perfectly linear noiseless systems, the PIR so obtained is shown to be identical to the system`s response to a simple periodic square pulse. In the face of external noise and nonlinearities, the MLS approach is shown to be as robust as time-delay spectrometry (TDS). Like TDS, MLS methods are also capable of rejecting or selecting nonlinear (distortion) components when measuring weakly nonlinear systems. An MLS coherence function is defined that is not unlike the conference function usually associated with dual-channel FFT analyzers. Finally, a new low-cost instrument based on the IBM-PC makes MLS measurements generally available and affordable.
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