Quartz crystal oscillators with direct resonator heating

The authors describe a novel low-power, ovenized oscillator with the crystal heated directly by means of a thin-film resistive heater deposited on its surface. The only significant path for heat loss is through the resonator mounting ribbons and posts, and these, being long and thin, have quite high thermal resistance. Pulse duration modulation controls resonator heating current. Phase noise, Allan variance, and aging all appear unaffected by direct resonator heating. Frequency-temperature stability better than ±2.5×10^-8 from 0 to 70°C has been achieved using a third overtone 10.230-MHz SC-cut resonator with room-temperature power consumption of about 300 mW. Theoretical analysis shows substantial heating power reduction is possible by introducing additional thermal resistance in the form of a glass ring as part of the resonator mounting structure