Temperature-compensated crystal oscillators

This review paper describes the basic principle of temperature-compensated quartz oscillators (TCXOs) which are employed extensively in both industrial and consumer electronics. A brief history of quartz oscillators and artificial quartz crystals is given at the beginning followed by a discussion on the recent applications of TCXOs. Direct and indirect methods for compensating the effects of temperature on oscillation frequency in temperature-compensated crystal oscillators which consume low power and are miniature are then described. In the directly temperature-compensated crystal oscillators, temperature compensation networks (TCNs) can be either of the serial type or of the parallel type. In this paper, the function of a TCN is described using a parallel-type network as an example. In the indirectly temperature-compensated crystal oscillators, the functions of a TCN are discussed separately in high, intermediate and low-temperature regions. Digitally controlled temperature-compensated crystal oscillators are also included in this paper as the high-precision temperature-compensated crystal oscillators. Some outstanding issues in TCXOs are discussed, and a new type of TCXOs have been proposed to overcome the shortcomings of conventional TCXOs.