A Digital Instantaneous Frequency Meter

A basic instrument is described which produces a parallel digital output proportional to frequency once per cycle, i.e., instantaneously. This is achieved by means of a reciprocal time generator which continuously generates digitally the reciprocal of the time elapsed between successive incoming pulses and the output of which is sampled and held at the end of each cycle. The meter is a 12-bit instrument having an accuracy of ±1 count plus clock stability. An analog output and a digital readout can be readily obtained. The range of the instrument is from zero to fc × 2-12 Hz, where fc is the clock frequency in hertz. Thus the range can be varied by appropriate adjustment of fc. An additional circuit to provide an analog output proportional to rate of change of frequency, also on a cycle-to-cycle basis, is suggested.