High effective Q CMOS crystal oscillator design

According to a narrowing of frequency bandwidth in communication systems, high C/N crystal oscillators are required. In this report, a design method of high effective Q CMOS crystal oscillators is proposed to achieve high C/N characteristics. The method is achieved by inserting a series capacitance between the output terminal of CMOS and the /spl pi/-shaped feedback circuit. An example of design shows that the dissipation of the active circuit facing the crystal resonator can he reduced by a factor 1/25 and the effective Q can be increased by a factor 7. Thus the effectiveness of the design method has been shown. It is concluded that the present method is useful for achieving high C/N CMOS crystal oscillators.