amplitude discriminator[′am·plə‚tüd dis′krim·ə‚nād·ər]
an apparatus that automatically selects electrical signals having an amplitude higher than a specific (threshold) value. Amplitude discriminators are used extensively in remote control and telemetry for separating a useful signal from noise and for investigating random processes by means of amplitude analyzers. In amplitude discriminators use is made of circuits or devices that have an amplitude characteristic with a sharply defined nonlinearity (discontinuity). Such characteristics are possessed by diodes (particularly the electronic vacuum type), some receiving amplifier tubes, and special electronic trigger circuits. The most widely used amplitude discriminator is a diode circuit that takes advantage of the discontinuity in its anode current characteristic. Depending on the cutoff voltage, which in such a circuit is equal to the discrimination threshold, the only signals that pass through the diode are those having an amplitude above the cutoff voltage. The accuracy of such an amplitude discriminator is conditioned by the stability of the diode characteristic. For reliable operation with low-amplitude signals preliminary amplification is used, and for the investigation of nanosecond pulses, special auxiliary circuits are employed to shape the signals. Trigger circuits used as amplitude discriminators permit pulses to be obtained at the output which have an amplitude and duration that is independent of the input signal shape.