Abstract
This work explores frequency tuning capabilities through the application of internal phase feedback configuration on a multi-port (e.g., 4 ports in this implementation) thin-film piezoelectric-on-silicon (TPoS) oscillator, which can be operated in various vibrating modes. The characterization in this work involves resonators in both bulk extensional (high frequency) and flexural (low frequency) modes to feature different tuning range. A lock-in amplifier with PLL is employed to enable oscillation for the resonator (i.e., main oscillation loop) by using one side of its electrodes while simultaneously generating internal phase-delayed feedback with variable magnitude onto the resonator electrodes at opposite side. With this technique, the AlN TPoS oscillator in its flexural mode features a decent frequency tuning range of 3,786 ppm over a full 2π phase change. Moreover, considering operation of a phase change through a non-periodical 2π transformation, the tuning range can be further extended to 6,774 ppm. This technique has shown a great potential in applications of frequency control, wireless communication, filter design, tunable oscillators, and sensor fields that need a precise frequency matching, such as mode-match MEMS gyroscopes.