EXTREMELY LOW PHASE NOISE UHF OSCILLATORS UTILIZING HIGH-OVERTONE, BULK-ACOUSTIC RESONATORS

High-overtone, bulk acoustic resonators (HBAR) have been designed that exhibit 9 dB insertion loss and loaded Q values of 80 000 at 640 MHz with out-of-phase resonances occurring every 2.5 MHz. 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, 2-pole, helical filter for suppression of HBAR adjacent resonant responses. Measurement of oscillator output signal flicker-of-frequency noise confirms that state-of-the-art levels of short-term frequency stability characterized by Sy(100 Hz) = 5 x 10(-26) [(100 Hz Pounds) = -120 dBc/Hz] have been obtained. Sustaining stage circuit contribution to resulting oscillator flicker-of-frequency noise is 7-10 dB below that due to the resonators themselves. At 16 dBm resonator drive, an oscillator output signal white phase noise floor level of -175 dBc/Hz is achieved.