Resonator filter with variable tuning
First Claim
1. A duplex filter formed by a plurality of resonators electromagnetically coupled together, wherein a first of the resonators, positioned first in the direction of travel of an input signal, is a resonant frequency-adjustable resonator controlled by separate first and second control signals, the filter being controllable between a first state effected by the first control signal in which its passband is narrowed to a first bandwidth in a first frequency range and a second state effected by the second control signal in which its narrowed passband is moved to a second frequency range.
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Accused Products
Abstract
An advantageous embodiment of the invention is the filter of the receiver branch of the duplex filter in a multi-channel radio transmitter/receiver having reception and transmission bands composed of plural radio-frequency channels. In the first state of the filter, when the radio transmitter/receiver is only receiving radio signals, the width of the pass band of the filter corresponds to said reception band. In the second state, in which the radio transmitter/receiver additionally transmits radio signals, the pass band of the filter is switched by current control to cover only part of the reception band. By constructing the filter in the manner proposed it is possible to use current control in the first resonator in the filter of the receiver branch. Because of its power consumption current control is otherwise unsuitable for use in e.g. the duplex filter of a portable radio-telephone.
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Citations
11 Claims
- 1. A duplex filter formed by a plurality of resonators electromagnetically coupled together, wherein a first of the resonators, positioned first in the direction of travel of an input signal, is a resonant frequency-adjustable resonator controlled by separate first and second control signals, the filter being controllable between a first state effected by the first control signal in which its passband is narrowed to a first bandwidth in a first frequency range and a second state effected by the second control signal in which its narrowed passband is moved to a second frequency range.
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10. A duplex filter with a receiver branch and a transmitter branch for a frequency division duplex telephone transceiver, the duplex filter including a variable filter in its receiver branch, the variable filter comprising:
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i) at least first and second resonators electromagnetically coupled to each other and forming a bandpass filter arrangement; and ii) control circuitry coupled to the first and second resonators to control the bandwidth of the receiver branch in response to .separate first and second control signals by controlling the coupling between the first and second resonators, said first control signal causing said control circuitry to effect a narrowing of the passband to a first bandwidth in a first frequency range and said second control signal causing said control circuitry to effect a move of the narrowed passband to a second frequency range.
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11. A method of tuning a duplex filter having a transmitter branch and a receiver branch with first and second resonators whose electromagnetic coupling to each other is controlled by control signals to form a variable receiver bandpass filter arrangement, the method comprising the steps of:
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(a) applying a first voltage control signal to at least the first resonator to narrow the bandwidth of the bandpass filter to a first bandwidth in a first frequency range; and (b) applying a separate second voltage control signal to at least the first resonator to move the narrowed bandwidth to a second frequency range.
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Specification