Acoustic resonators may rely on resonance of materials, such as piezoelectric materials, to provide electrical signals, and as a result resonators may be able to provide signals with stable frequencies and predicable temperature characteristics. Accordingly, resonators are regularly used to implement electrical frequency control applications, such as clock signal generation in digital circuits, frequency stabilization in wireless devices, and signal filtering. Typically, resonators are configured to resonate at a frequency known as a center frequency. The center frequency of a resonator is predominantly determined based on factors such as the physical dimensions of the resonator and materials used to make it. Manufacturing variations in the thickness and other dimensions of the material used to make the resonator often result in poor center frequency accuracy, however.
In order to compensate for these errors, center frequencies may be passively tuned by coupling resonators to reactive circuit components, such as capacitors and inductors. In this manner, center frequencies may be increased or decreased such that a desired center frequency is achieved. Tuning center frequencies in this manner, however, can lead to increases in motional impedance of the resonator and/or degradation in overall performance. For example, tuning center frequencies may accelerate the rate at which center frequencies drift over time. Moreover, passively tuning center frequencies may provide a limited range over which tuning center frequencies may be tuned.