Surface-acoustic-wave filter for channel selection system of television receiver

In a channel selection system for a television receiver, a comb filter device for program channel detection comprising

• a surface-acoustic-wave composite filter formed in a piezoelectric substrate,
• said composite surface-acoustic-wave filter comprising:
• common input means for receiving a local oscillation signal from a tuner;
• a plurality of spaced input transducers which are electrically coupled together to said input means and responsive to an applied local oscillation signal corresponding to program channel components for generating surface acoustic waves respectively along isolated and parallel wave-propagation paths on said piezoelectric substrate, the respective input transducers having maximum response in respective channel bands of a predetermined number into which different program channels are correspondingly grouped in sequence of channel frequency magnitude;
• a plurality of pairs of output transducers, each pair of output transducers being located in a corresponding wave-propagation path relative to the corresponding one of said input transducers on one side thereof for developing output signals in response to the generated surface acoustic wave from said corresponding input transducer,
• said output transducer pair, individually including first and second output transducers electrically connected with each other and physically spaced from said corresponding input transducer with different distances such that the reciprocal of the difference between delay times of output signals from the first and second output transducers is equal to a divisor of a channel spacing in a corresponding channel band;
• and
• common output means coupled in common to said plurality of pairs of output transducers for deriving an output of the composite filter.

A one-chip acoustic surface-wave, wide-band responsive, comb filter formed in a piezoelectric substrate for use in a VHF/UHF television channel selection system comprising:

• first and second acoustic surface wave filter means responsive to local oscillator frequencies corresponding to a low band and a high band of a VHF program band, respectively,
• third and fourth acoustic surface-wave filter means responsive to local oscillator frequencies corresponding to a low band and a high band of a UHF program band, respectively,
• each filter means comprising an input transducer having maximum response in a corresponding allotted channel band for converting a local oscillator output into an acoustic surface wave, and a pair of output transducers whose outputs are additively coupled to develop an output signal of the filter means and located only on one side of said input transducer along a wave-propagation path on the substrate surface to establish a desired comb filter characteristic, the respective spacings of the pair output transducers from the input transducers being different such that the reciprocal of a differential delay time between electrical signals from the pair output transducers is equal to a divisor of a channel spacing in the corresponding channel band,
• said first and second filter means being connected in parallel and adapted to receive a local oscillator signal of a VHF tuner, and
• said third and fourth filter means being connected in parallel and adapted to receive a local oscillator signal of a UHF tuner.

A surface-acoustic-wave filter for a channel selection system of an electronic receiver comprising:

• a piezoelectric substrate;
• a plurality of surface-acoustic-wave comb filter means formed integrally on one face of said substrate, and having different center frequencies with respect to allotted filter bandwidth to cover a VHF/UHF local oscillator frequency range to thereby exhibit a wide-band comb filter characteristic as a whole,
• each comb filter means comprising:
• first, second and third electroacoustic transducers for converting electrical signals into surface-acoustic-waves or vice versa, said first and second transducers being electrically directly coupled and physically spaced, and aligned along a surface-acoustic-wave propagation path on the substrate on one side of said third transducer with different distances therefrom, the respective spacings of said first and second transducers from said third transducer being such that the reciprocal of a differential delay time between output signals of the filter means due to the spacing between the first and second transducers is equal to a divisor of a channel spacing in a corresponding channel band,
• one of said directly-coupled first and second transducers and said third transducer being supplied with a local oscillator output, while the other providing an output of the filter;
• and
• input and output terminal means formed on the substrate for coupling at least two of said comb filter means in parallel connection.