GB1350102A - Demodulator - Google Patents

Abstract

1350102 Pulse modulation systems T T FJ€LLBRANT 22 Nov 1971 [23 Nov 1970] 54211/71 Heading H4L A signal (dotted line Fig. 2a) which has been sampled at periodically varying intervals is demodulated by adding to it in circuit 1 a signal 12 representing the missing samples e required to make up a uniformly sampled signal f, and filtering the result at 2. Amplifier 3 produces the output U. If the notional uniform sampling signal shown at f has a period T, the varying sample periods of input a may be for example nT, (n+1)T, nT, &c., so that a generally lower (varying) sample frequency can be used for a given maximum frequency ¢T of the signal being sampled. The missing samples e may be generated in Fig. 1 by applying the demodulated output b to a uniform rate sampler 4 and to a variable rate sampler 5 whose rate varies in the same way as the sample rate of the input a. A subtractor at 6 derives e. The filter 2 may be an analogue or gate-and-store type, and timing for the sampler 4 is controlled either by a clock or by the input signal. Alternatively (Fig. 3, not shown) the output U is fed to one sampler 7 which samples at the missing sample times. In another embodiment (Fig. 4, not shown) a plurality of adding circuit is used, each receiving the input signal a through successive delays (J), and the missing samples each being derived by a filter 2 amplifier 3 and a missing sample generator (7), as in the Fig. 3 embodiment, but in this ease with the filter 2 being connected to the output of the previous adder circuit, or in the case of the first stage, the filter receiving the input signal a at 1. If a digital filter (F, Fig. 5, not shown) is used, the missing samples are generated by a gate circuit (G) operated at appropriate periods.