Microcontroller-based temperature compensation scheme for two-port SAW oscillators

We present a surface acoustic wave (SAW) two-port oscillator extended by a feed-forward control circuit, the goal of which is to suppress the effects of the SAW resonator temperature characteristics on the oscillator output frequency. The control circuit consists of a temperature sensor near the SAW resonator the output signal of which is fed to the analog-to-digital converter (ADC) input of a microcontroller. An algorithm implemented on the microcontroller combines the information on the actual temperature and the temperature behavior of all oscillator components (known from previous measurement campaigns) to determine a compensation signal. The latter is fed to a phase shifter inserted in the oscillator feedback loop such that any temperature-induced changes in the round-trip phase shift of the oscillator loop are counteracted. An improvement factor in the frequency stability of 4.4 was demonstrated in the temperature range from 0 to 60 degrees C and can be further improved to a value of at least 10.