Patent ID: 7492242

Claim:
A tunable filter circuit having first and second inputs and first and second outputs, the filter circuit comprising: at least one primary four-pole circuit including, in cascade: a first varactor having a first electrode coupled to said first input and a second electrode; a first inductive resistor having a first electrode coupled to the second electrode of said first varactor and having a second electrode coupled to said second input; a secondary four-pole circuit having first, second, third and fourth bulk acoustic wave (BAW)-type resonators, said secondary four-pole circuit having first and second inputs and first and second outputs, said first and second resonators having a first electrode coupled to said first input of the secondary four-pole circuit and a second electrode coupled to said first output and said second output of said secondary four-pole circuit, respectively; said third and fourth resonators having a first electrode coupled to said second input of said secondary four-pole circuit and a second electrode coupled to said second output and said first output of the secondary four-pole circuit, respectively; a second inductive resistor having a first electrode coupled to said first output of said secondary four-pole circuit and having a second electrode coupled to the second output of said secondary four-pole circuit; and a second varactor having a first electrode coupled to the first output of said secondary four-pole circuit, and a second electrode.