Television IF filter constructed in accordance with the surface wave principle

Abstract

A television IF filter constructed in accordance with the surface wave principle comprises an input transducer and two output transducers constructed in interdigital form, the output transducers being arranged symmetrically with respect to the input transducers upon a piezo-electric substrate. An input transducer comprises a main section and a subsidiary section. The main and subsidiary sections are electrically and mechanically connected in parallel, the main section being tuned to the center of the television IF frequency and having a variable overlapping range of the transducer teeth corresponding to a function y = sin x/x. The resonant frequency of the subsidiary section is tuned in such a manner that a step in the filter curve at the sound frequency, looking like staircase is produced. The output transducers also have a main section and a subsidiary section, respectively, whose respective resonant frequencies are tuned to that of the input transducer section which is associated therewith. The main and subsidiary sections of the output transducers are electrically connected in parallel and the output transducers are connected in series. The overlapping range of the teeth of the main subsidiary sections of the output transducers is constant and the length of the teeth of the subsidiary sections are shortened, as compared with those of the main sections, in accordance with the level difference at the sound and picture carrier frequency, respectively of the transmission curve. The filter produces an asymmetric frequency curve corresponding to the standard curve of a television IF filter with the help of the interdigital transducers having constant tooth spacings. The symmetrical arrangement of the output transducers with respect to the transmission converter compensates capacitive cross talk and the level step of the filter curve at the sound frequency is produced by transducer structures whose tooth length is shortened in correspondence with the desired level difference.

Dependencies are inferred from the claim text.