Tunable resonator for use in active-RC continuous-time filters

摘要

An integrated circuit (IC) resonator in which resonator parameters potentially affected by IC fabrication processes are correctable after fabrication. Resonance frequency tuning is effected by forming each feedback capacitor (C_1A,C_2A) in a pair of integrator circuits to include a variable capacitance device, such as a varactor diode (24). A tuning signal (V_tune-f) is applied to the varactor diode to adjust the total capacitance value and, therefore, the resonance frequency. Similarly, the quality (Q) factor of the resonator is adjusted by providing a variable capacitance in an RC (resistance-capacitance) network coupling the output of one of the integrator circuits to the input of the other. The variable capacitance in the RC network permits adjustment of phase in the event that the integrator circuits do not provide a desired 180° total phase shift.