Circuit for measurement of instantaneous frequency

This paper describes a circuit that measures the instantaneous frequency of a pulse train applied to the input. Analog outputs are provided that are linearly proportional to the interval between successive pulses and to the reciprocal of that same interval. The design is based upon well-established operational amplifier circuits and can be built with readily available components. The range over which the circuit operated can be changed by the selection of a single resistor, and the initial calibration requires the adjustment of only three components.