True Series Resonance Oscillator using Active Shunt Capacitance Cancellation

A true series resonance oscillator has been developed for use with a wide-range of 1-port resonance-based sensors and devices. The oscillator effectively removes the shunt capacitance Co, allowing the true series resonance to be monitored, providing the optimum sensitivity across a wide range of frequencies (i.e. kilohertz to gigahertz), shunt capacitances, and quality factors (Q) for the first time. It is well-known that non-zero shunt capacitance alters the impedance by shifting the location of the impedance minimum and the zero-phase crossing while causing significant impedance distortion. We have developed an active shunt capacitance cancelling oscillator (ASSCO) that removes any shunt capacitance across the resonator by supplying the circuit an equal “dummy” capacitance using a cancelling current. The oscillator does not require automatic gain control (AGC) and the resonator can be grounded to reduce parasitic contributions.