An ultra-compact and low-power oven controlled crystal oscillator design for precision-timing applications

This thesis proposes and demonstrates an ultra-compact and low-power oven controlled crystal oscillator (OCXO) design for use in precision-timing applications. In the last decade, the rapid growth of wireless applications has led to an increasing demand for highly accurate and stable reference clock sources for data communication. Quartz crystal resonators are the most common devices used to generate frequencies in order to control and manage the systems. Among the various types of crystal oscillators, OCXOs have superior frequency stability. However, a typical OCXO package includes not only a metal block, but also multiple PCBs for the resonator, oscillator circuitry, and temperature sensitive components, the combination of which results in a large package size and a long warm-up time. An SC-cut crystal, which is considerably more expensive than an AT-cut crystal, is generally used as the resonator. In addition, power consumption of these OCXOs is very high. Despite the excellent frequency characteristics of OCXOs, these drawbacks prevent their use in small mobile or battery-powered devices.;To overcome the limitations of conventional OCXOs, we present a new design of miniature OCXO on a single CMOS chip. The object of this project is to design an ultra-compact and low-power precision OCXO. All the main components of an OCXO such as an oscillator, a temperature sensor, a heater, and temperature-control circuitry are integrated on a single CMOS chip. The OCXO package size can be reduced significantly with this design, since the resonator does not require a separate package and most of the circuitry is integrated on a single CMOS chip. Other characteristics such as power consumption and warm-up time are also improved.;Two different types of quartz resonators, an AT-cut Tab Mesa type quartz crystal and a frame enclosed resonator (FER) allowed the miniaturization of the OCXO structure. Neither of these two quartz resonator types requires a separate package inside the oven structure; therefore, they can each be directly integrated with the custom-designed CMOS chip. The miniature OCXO achieved a frequency stability of +/-0.35 ppm with an AT-cut Tab Mesa type quartz crystal in the temperature range of 0 °C to 60 °C. The maximum power consumption of this miniature OCXO was 1.2 W at start-up and 303 mW at steady state. The warm-up time to reach the steady state was 190 seconds. These results of the proposed design are better than or comparable to high-frequency commercial OCXOs. Polyimide flexible circuit boards and anisotropic conductive film bonding techniques were also investigated for further optimization.