The invention relates to a device for demodulating an input signal containing information being conveyed by phase modulation of a carrier wave. A transmitter generates a signal controlling a phase variation in the carrier wave, for each symbol having N cycles, N being an integer strictly greater than 1. The phase variation stretches on the receiver side over n cycles, n being an integer greater than 1 and less than N. The device generates a single pulse for each symbol received suited to generate the leading edge of the pulse corresponding to the symbol considered after a constant duration from the moment the symbol considered starts; and generates the trailing edge of the pulse considered at a moment the phase shift corresponding to the symbol considered has to be measured. Conversion means generate an output signal with a voltage varying as a function of the duration of the pulse produced.