XOR Gate FM Quadrature Detector

The circuit demodulates a frequency-modulated signal using an Exclusive OR (XOR) gate and an RLC phase-shifting network. The RLC network creates a phase shift that is a function of frequency. At FM carrier frequency the phase shift is 90°, as the frequency varies the phase shift varies from 0° to 180°. The original signal and the phase-shifted signal from the RLC network are applied to an Exclusive OR (XOR) gate to produce digital pulses with widths which are a function of the phase difference between the two input signals. By filtering these pulses the information signal can be satisfactorily recovered. Notes: The circuit is in initial form, the values of resistances, inductance, capacitances, and frequencies were chosen so that a working circuit, adequate for simulation, can be quickly built. Further modifications are needed for the circuit to be used in real-world application. The component values of the RLC phase-shifting network need to be scaled. The filter at the output of the Exclusive OR (XOR) gate is a cascaded two identical RC low-pass sections, this may not necessarily be the form of the filter. Also, as the filter is a low-pass type a dc component is present at the final output.