Abstract
We propose a twin-T-type quartz resonance circuit in which the null frequency can be changed by adjusting the applied voltage ratio. In the circuit construction, two sets of T-type circuits are used in which a quartz resonator is placed in the shunt branch and the output of each circuit settles in one terminal. The changeable frequency range exceeds the limit of the electromechanical coupling factor of the piezoelectric resonator used when the resonance frequency of a coil and a capacitor in the series branch of the twin-T-type circuit is set to almost the same value as the resonance frequency of the resonators used in the twin-T-type circuit.
