circuit for removing a radio receiver interference in fm

摘要

1493870 Interference suppression; stereo systems PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 21 Feb 1975 [26 Feb 1974] 7357/75 Addition to 1279756 Headings H4L and H4R The invention of the parent Specification is modified in that the parallel resonant circuit in series with the storage capacitor, provided to reduce substantially the interference which would otherwise still be present in stereophonic reception, is replaced by a network 9 which, in conjunction with the storage capacitor 6 provides a ringing circuit resonant at the pilot tone frequency. The network 9 may comprise an inductor 11, or inductive reactance may be provided by an active, current amplifying, filter (15-18), Fig. 2 (not shown), or (15, 20-23), Fig. 3 (not shown). The circuitry (13, Fig. 2), or (19, Fig. 3), including the delay means 4, gate circuit 5, interference {rate of change} detector 7, pulse shaper 8 and buffer 12 may comprise an integrated circuit, receiving a signal from f.m. detector 3, itself fed via i.f. stage 2 from tuner 1. The non-inverting amplifier (15) may comprise two cascaded current mirrors.