Saw notch filter for improving stop-band attenuation of a duplex filter
First Claim
1. A circuit for increasing a stop band attenuation, comprising a duplex filter having a pass band, said duplex filter having a transmit branch connected between an antenna and a transmit branch connection, and a receive branch connected between said antenna and a receive branch connection, said transmit branch and said receive branch each including respectively at least one resonator circuit operatively coupled between the antenna and corresponding branch connection;
- and a surface acoustic wave device having two terminals connected together at one and the same location of one of said transmit and receive branches for affecting said surface acoustic wave device to operate as a notch filter.
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Accused Products
Abstract
When the bandwidth of a duplex filter having a certain band-width, intended for a radio telephone, is increased by affecting the coupling between the resonator circuits, the stop band of the filter is at the same time deteriorated. According to the invention, the stop-band attenuation can be improved by coupling a surface-wave filter, coupled as a notch circuit, in parallel with one of the resonator circuits of the duplex filter.
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Citations
6 Claims
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1. A circuit for increasing a stop band attenuation, comprising a duplex filter having a pass band, said duplex filter having a transmit branch connected between an antenna and a transmit branch connection, and a receive branch connected between said antenna and a receive branch connection, said transmit branch and said receive branch each including respectively at least one resonator circuit operatively coupled between the antenna and corresponding branch connection;
- and a surface acoustic wave device having two terminals connected together at one and the same location of one of said transmit and receive branches for affecting said surface acoustic wave device to operate as a notch filter.
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2. A circuit for increasing a stop band attenuation, comprising a duplex filter having a pass band, said duplex filter having a transmit branch connected between an antenna and a transmit branch connection, and a receive branch connected between said antenna and a receive branch connection, said transmit branch and said receive branch each including respectively at least one resonator circuit operatively coupled between the antenna and corresponding branch connection;
- and a surface acoustic wave device having two terminals connected together at one and the same point location on one of said transmit and receive branches for affecting said surface acoustic wave device to operate as a notch filter.
- View Dependent Claims (3, 4, 5, 6)
Specification