Square wave signal frequency comparison circuit - uses logic, integration, and D-A circuits for oscillator frequency control

摘要

A frequency comparison circuit for the determination of which of two square wave signals has the higher frequency regulation of an oscillator. The oscillator frequency is compared with an almost equal frequency. A difference between the two frequencies triggers a counter which regulates the oscillator frequency via digital-to-analogue convertor. Two NOR circuits (L1, L2) are supplied with the reference frequency (a). The first NOR circuit is also supplied with a signal (b) having twice the frequency of the oscillator (G) output signal (c), and its output is connected to the counter (Z) input via a first integrator (I1). The second NOR circuit (L2) is also supplied with the oscillator output (c) and frequency doubled signal (D), and its output (e) is connected to the counter reset input (g) via a second integrator (I2).