A two-chip, 4-MHz, microelectromechanical reference oscillator

The paper describes a 4-MHz temperature compensated reference oscillator based on a capacitive silicon micro-mechanical resonator. The design of the resonator has been optimized to offer large quality factors (22000), while maintaining tunability in excess of 3000 ppm for fine tuning and temperature compensation. Oscillations are sustained with a CMOS amplifier and temperature compensation is performed with a novel resonator bias generator. When interfaced with the bias circuit, the oscillator exhibits a temperature drift of 380 ppm over a 90°C range, a 6 times improvement in stability over an uncompensated oscillator. The sustaining amplifier and compensation circuitry were fabricated in a 2P3M 0.5 μm CMOS process. The oscillator is designed to prototype highly stable, low phase-noise reference oscillators integrated at the chip or package level.