Frequency conversion system

TLDR: In this article, the authors present an approach to rapidly and accurately convert the frequency of an input signal into a voltage proportional to the frequency, which is the input signal to a sample and hold circuit.

Abstract: In many dynamic control systems, there is a need to rapidly and accurately convert the frequency of an input signal into a voltage proportional thereto. At a preselected time in a cycle of an input signal, a plurality of capacitors are charged to a reset level. After a fixed delay from the preselected time, each of the charged capacitors begins to discharge at a rate determined by the value of an RC network to generate a voltage signal that decays exponentially. The exponentially decaying voltage for each of the plurality of capacitors are summed together to produce a voltage that varies inversely with frequency. This voltage is the input signal to a sample and hold circuit. At the completion of one cycle of the input signal, the value of the voltage that varies inversely with frequency is read and stored as a voltage representative of the frequency of the input signal. Higher voltages correspond to fast frequency signals and lower voltages correspond to slow frequency signals. Conversion of a frequency takes place upon completion of a sampled cycle.