A cascode crystal oscillator suitable for integrated circuits

In this paper, we propose a new structure for the cascode crystal oscillator which is suitable for integrated circuit realization. The cascode crystal oscillator is composed of a Colpitts crystal oscillator and a base-common buffer amplifier. In the proposed cascode crystal oscillator, the buffer amplifier is biased by a temperature-independent voltage source and the bypass capacitor of the buffer amplifier is eliminated. Both the Colpitts oscillator and the buffer amplifier use the common divider resistors. We have evaluated the performance of the proposed cascode crystal oscillator by simulation and experiment, and estimated the required circuit area as an integrated circuit design. Fifty-percent reduction of the start-up time and thirty eight percent reduction of the area have been achieved. The frequency stability verses power supply and load impedance is comparable to that of a typical cascode crystal oscillator. SSB phase noise is also comparable to that of the conventional cascode crystal oscillator despite the increased number of transistors used. From these results, we have confirmed that the proposed cascode crystal oscillator is useful and suitable for integrated circuits.