Extremely low phase noise UHF oscillators utilizing high-overtone, bulk acoustic resonators

High-overtone, bulk acoustic resonators (HBAR) that exhibit 9-dB insertion loss and loaded Q values of 80000 at 640 MHz with out-of-phase resonances occurring every 2.5 MHz have been designed. These resonators have been used as ovenized frequency control elements in very low phase noise oscillators. The oscillator sustaining stage circuitry incorporates low 1/f noise, modular RF amplifiers, Schottky-diode ALC, and a miniature two-pole helical filter for suppression of HBAR adjacent resonant responses. Measurement of oscillator output signal flicker-of-frequency noise confirms that levels of short-term frequency stability characterized by Sy(100 Hz)=5×10 ²⁶ have been obtained. The sustaining stage circuit contribution to resulting oscillator flicker-of-frequency noise is 7 to 10 dB below that due to the resonators themselves