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This review paper describes the basic principle of temperaturecompensated 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 temperaturecompensated crystal oscillators which consume low power and are miniature are then described.In the directly temperaturecompensated 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 temperaturecompensated crystal oscillators, the functions of a TCN are discussed separately in hgh, intermediate and low-temperature regions. Digitally controlled temperature-compensated crystal oscillators are also included in this paper as the highprecision 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.

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A change of the oscillation frequency of an oscillator has commonly been achieved by changing the load capacitance of a crystal oscillator. Since the frequency changes nonlinearly with load capacitance, the rate of the frequency change varies with load capacitance. Therefore, when the frequency change through aging effects and/or due to the change in load capacitance occurs in TCXOs and VCTCXOs, the frequency shift must be compensated. However, the amount of compensation would be different before and after its adjustment. This paper describes a newly developed two‐port crystal resonator. This resonator has two independent load capacitances so that the frequency response and the oscillation frequency shift due to a temperature and/or capacitance fluctuation can be compensated independently. This function cannot be achieved in a conventional oscillator which has only one load capacitance. A formula to calculate the rate of a frequency change due to temperature and capacitance fluctuation has been derived by using the equivalent circuit of the two‐port crystal oscillator. The calculated value was found to be in good agreement with experimental result by taking into account stray capacitance. Therefore, this formula is useful for designing a two‐port crystal oscillator.