MEMS based oscillator for UHF applications with automatic amplitude control

This paper presents a MEMS based oscillator with automatic amplitude control. Previously demonstrated ring shape anchored contour mode disk resonator is evaluated and some of its analytical aspects are extracted as well as its equivalent electrical circuit for further transistor level simulations. Due to 180° phase change of the resonator, the sustaining amplifier should provide another 180° phase for oscillation build up. As will be shown, the motional resistance of the resonator, which determines the minimum required gain of the circuit, is very high and conventional techniques could not provide such a gain in UHF frequencies. This paper proposes a trans-impedance amplifier satisfying mentioned conditions just at the required frequency. In this case, traditional Automatic Amplitude Control (AAC) method could not be applied and therefore this paper presents a novel AAC circuitry and technique. The overall circuit including bias circuitry consumes 1128 μW from 1.8 V power supply implemented in 0.18 μm standard CMOS technology.