Patent ID: 8665038

Claim:
A filtering circuit, comprising: first, second, and third cascade connected quadripoles, each quadripole having a series branch that includes a first acoustic resonator and a parallel branch that includes a second acoustic resonator, the first acoustic resonator having a series resonance frequency that is approximately equal to a parallel resonance frequency of the second acoustic resonator, the parallel branch of the first quadripole including a first parallel circuit in series with the second acoustic resonator of the first quadripole, the first parallel circuit including a first capacitance and a first switching transistor coupled in parallel with the first capacitance and structured to short-circuit the first capacitance; and a digital control bus coupled to the switching transistor and structured to convey a control voltage to the switching transistor, wherein: the second quadripole includes a second parallel circuit in series with the second acoustic resonator of the second quadripole, the second parallel circuit including a second capacitance and a second switching transistor coupled in parallel with the second capacitance and coupled to the digital bus to receive the control voltage and structured to short-circuit the second capacitance; and the first and second switching transistors are structured to tune the filtering circuit.