The performance of a zero-crossing-based optical spectrum analyzer is presented. With the use of only a single comparator, the analyzer circuit detects one zero crossing per Nyquist interval with a location accuracy of 1 part in 256. The dynamic range of sampling is limited only by the supply voltages of the comparator and the noise arising from truncation errors associated with computation. The 512-component spectra of various interferogram inputs are directly computed by Newton's formula from the measured crossings. The single-channel spectrum analyzer with a preselectable Nyquist sampling interval setting is constructed with discrete transistor–transistor logic and analog components. The ultimate performance characteristics of the analyzer are set by the response capabilities of the electronic components used.
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