Ultra-fast voltage comparators for transient waveform analysis

The time at which an input signal crosses the reference level of a voltage comparator can be used in the analog-to-digital conversion of fast single waveform transients. In such a converter, an array of identical comparators, properly biased, provides stop inputs to a picosecond-resolution multistop time digitizer. Each stop represents a point in the voltage-time reconstruction of the measured waveform. A number of state-of-the-art comparators, bipolar and GaAs, have been evaluated for this application to determine the differences in their time propagation as a function of the input signal overdrive and risetime. Normalized data are presented to assist in the correction of a digitizer's measurement errors. A picosecond time resolution measurement system used in the tests is described.>