A temperature compensated 1 GHz STW oscillator

An improved temperature compensation technique, applied to a 1-GHz surface transverse wave (STW) oscillator using 36° rotated Y-cut quartz, is described. The parabolic temperature dependence is roughly compensated for by an analog circuit. A fine compensation is performed by simple digital circuitry keeping the total instability within ±1.4 p.p.m. over the temperature range of (-45. . .+75)°C. The key for achieving this stability is a novel combined mode resonator filter (CMRF) in the oscillator loop. This device features low loss, a fractional bandwidth of up to 0.2% and a smooth phase response over this bandwidth. Thus, excellent tuning of the oscillator over a range of 1.8 MHz is achieved. Since this is much more than is needed to compensate for the total temperature shift of ±180 p.p.m., compensation at multiple frequencies in the oscillator tuning range is possible