GB1260347A - Demodulators - Google Patents

Abstract

1,260,347. Detector circuits. BRITISH BROADCASTING CORP.. 12 Aug., 1970 [17 Sept., 1969], No. 45905/69. Heading H3Q. A demodulator comprises an envelope detector and multiplying means connected in series between an input and output, and a phase detector connected between the input and the multiplying means, which is arranged to multiply the signal in the series circuit by a sinusoidal function of the output of the phase detector, or by an approximation thereto. The arrangement is particularly suitable for demodulating amplitude-modulated carriers with asymmetrical sidebands. In one embodiment, the signal to be demodulated is fed from terminal 10, Fig. 1 to envelope detector 11, the output of which is fed to multiplier 16 and also to subtraction circuit 17. Signal from terminal 10 is also fed via limiter 12 to a phase discriminator comprising frequency discriminator 13 and integrator 14, the output of which is squared in squarer 15 and forms the second input to multiplier 16. The output from multiplier 16 forms the second input to subtraction circuit 17, in which it is subtracted from the input from envelope detector 11. In a second embodiment, the incoming signal is applied directly to the multiplier and subtraction circuit, and the envelope detector is connected between the latter and the output terminal (Fig. 2, not shown). In a further embodiment, the integrator 14, Fig. 3 provides two outputs of opposite polarity, to each of which is added a constant voltage in unit 22, the two outputs of which are applied, together with the output from envelope detector 11, to multiplier 23.