Linear frequency tuning of SAW resonators

Linear, voltage-frequency tuning of SAW resonators with 500-p.p.m. tuning range using conventional, abrupt-junction varactor diodes is shown to be possible. The technique implemented uses varactor diode parallel inductance to provide a linear reactance vs. voltage network, which is effectively connected in series with the resonator motional impedance. Typical tuning ranges are significantly larger than those achievable using the phase-shifter approach, and are on the order of 300-500 p.p.m. for the 320-MHz resonator used. Experimental measurements indicate no resultant degradation in oscillator short-term frequency stability when a low flicker noise-sustaining stage is utilized. The achievable degree of tuning will allow nonovenized, phase-locked, and/or temperature-compensated oscillator operation over a wide temperature range. Low-distortion, oscillator-signal FM modulation is also possible