Electronic Temperature Compensation of Lateral Bulk Acoustic Resonator Reference Oscillators Using Enhanced Series Tuning Technique

This paper reports on the demonstration of series tuning for lateral micromechanical oscillators and its application for electronic temperature compensation of piezoelectric lateral bulk acoustic resonator (LBAR) micromechanical oscillators. Two aluminum nitride-on-silicon (AlN-on-Si) piezoelectric LBARs, one operating at 427 MHz (R
_m
≈180 Ω, Q
_unloaded
≈ 1400) and the other operating at 541 MHz (R
_m
≈ 55 Ω, Q
_unloaded
≈ 3000) are interfaced with a 13 mW three-stage tunable TIA implemented in 0.18 μm 1P6M CMOS process to sustain the oscillation. Recognizing the impact on the frequency tuning range due to the body capacitances appearing in parallel with the ports of the resonator, the TIA uses parasitic cancellation techniques to neutralize this effect and boost the tuning range of 427 MHz and 541 MHz oscillators, by as much as 12× to 810 ppm and 1,530 ppm, respectively, with negligible impact on the phase noise performance. The shunt parasitic capacitor is either resonated out with an active inductor or is cancelled out by using a single-terminal negative capacitor of equal value. However, the oscillator that uses negative capacitance parasitic cancellation yields larger tuning. This extended tuning range is used for temperature compensation. A 2 mW bandgap-based temperature compensation circuit which uses second-order parabolic approximation is fabricated on the same chip. Using this temperature compensation circuit has lowered the overall frequency drift of a 427 MHz tunable oscillator using negative capacitance cancellation from ±390 ppm to ±35 ppm in the -10°C to 70°C temperature range. The phase noise of this oscillator reaches -82 dBc/Hz at 1 kHz offset. The total phase noise variation for offset frequencies below 10 kHz is under 5 dB within the specified tuning range, and the best phase noise floor is under -147 dBc/Hz . Due to the higher Q and lower insertion loss of the resonating tank, the 541 MHz oscillator achieves -86 dBc/Hz at 1 kHz offset, and lower phase noise floor of -158 dBc/Hz.