Integrable tunable filter circuit comprising a set of BAW resonators

摘要

A tunable filter circuit having inputs IN1-IN2 and outputs OUT1-OUT2, comprising at least a primary four-pole circuit including in cascade: a first varactor having a first electrode connected to IN1 and a second electrode; a first inductive resistor connected between the second electrode of the varactor and input IN2, a secondary four-pole circuit comprising four BAW resonators. First and second of these resonators have a first electrode connected to a first input of the secondary four-pole circuit and a second electrode connected to first and second outputs of the secondary four-pole circuit, respectively. Similarly, third and fourth of these resonators have a first electrode connected to a second input of the secondary four-pole circuit and a second electrode connected to the second and first outputs of the secondary four-pole circuit, respectively. The circuit further comprises a second inductive resistor connected in parallel to the first and second outputs of the secondary four-pole circuit and a second varactor having a first electrode connected to the first output of the secondary four-pole circuit and a second electrode for connecting a second primary four-pole circuit having the same structure. This allows realization of a particularly effective tunable filter circuit with only four inductive resistors.