Ladder filter and method for producing conjugately matched impedance
AssigneeMotorola, Inc.
InventorThomas S. Hickernell
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Abstract
A bandpass filter and a method for making a bandpass ladder filter having a center frequency, a first port and a second port. The method has steps of providing a first L network having a first connection, a second connection and an inductive impedance at the center frequency and providing a second L network having a first connection, a second connection and a capacitive impedance at the center frequency. The method further has steps of coupling the first connection of the first L network to the first port, coupling the first connection of the second L network to the second connection of the first L network and coupling the second connection of the second L network to the second port.
Claims21
A method for making a bandpass ladder filter including a center frequency, a first port and a second port, said method comprising steps of:
- providing a first L network including a first connection, a second connection and a net inductive impedance at the center frequency of the bandpass filter;
- providing a second L network including a first connection, a second connection and a net capacitive impedance at the center frequency of the bandpass filter;
- coupling the first connection of the first L network to the first port;
- coupling the first connection of the second L network to the second connection of the first L network;
- and
- coupling the second connection of the second L network to the second port, wherein including the inductive impedance of the first L network and the capacitive impedance of the second L network provides conjugate impedance matching between the L networks at the center frequency of the bandpass filter.
A bandpass ladder filter including a center frequency, a first port and a second port, said bandpass ladder filter comprising:
- a first L network including a first connection, a second connection and an net inductive impedance at said center frequency of said bandpass ladder filter;
- and
- a second L network including a first connection, a second connection and a net capacitive impedance at said center frequency, said first connection of said first L network coupled to said first port, said first connection of said second L network coupled to said second connection of said first L network, and said second connection of said second L network is coupled to said second port, wherein including the inductive impedance of the first L network at said center frequency of said bandpass ladder filter and a capacitive impedance of the second L network at said center frequency of said bandpass ladder filter provides conjugate impedance matching between said first and second L networks at said center frequency of said bandpass ladder filter.
In a radio, a bandpass ladder filter including a center frequency, a first port and a second port, said filter comprising:
- a substrate comprising a piezoelectric material having an electromechanical coupling coefficient;
- a first resonator including a first terminal, a second terminal, a first resonant frequency and a first antiresonant frequency, said first resonator disposed on said substrate, said first terminal coupled to said first port;
- a second resonator including a first terminal, a second terminal, a second resonant frequency and a second antiresonant frequency, said second resonator disposed on said substrate, said first terminal of said second resonator coupled to said second terminal of said first resonator and said second terminal of said second resonator coupled to ground to form a first L network including an net inductive impedance at said center frequency of said bandpass ladder filter;
- a third resonator including a first terminal, a second terminal, a third resonant frequency and a third antiresonant frequency, said third resonator disposed on said substrate, said first terminal of said third resonator coupled to said second terminal of said first resonator, said second terminal of said third resonator coupled to said second port;
- and
- a fourth resonator including a first terminal, a second terminal, a second resonant frequency and a second antiresonant frequency, said fourth resonator disposed on said substrate, said first terminal of said fourth resonator coupled to said second terminal of said third resonator and said second terminal of said fourth resonator coupled to ground, said third and fourth resonators comprising a second L network including a net capacitive impedance at said center frequency of said bandpass ladder filter, said capacitive impedance substantially canceling said inductive impedance at said center frequency of said bandpass ladder filter.
Dependencies are inferred from the claim text.