新形状GTカット水晶振動子を用いたCMOS発振回路の発振周波数特性

概要

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This paper describes oscillation frequency characteristics in a CMOS oscillator circuit using a new shape GT cut quartz crystal resonator. It is well-known that a new shape GT cut quartz crystal resonator manufactured by an etching process has more excellent frequency temperature behavior than the conventional GT plate manufactured by a mechanical process. However, as this GT resonator is a coupling resonator, its frequency temperature behavior varies with load capacitance C_L of the circuit. The object of this paper is to clarify the relationship of oscillation frequency and frequency temperature coefficients versus load capacitance C_L. The noteworthy features are summarized as follows: 1) Since the GT resonator has the phase difference of 180 degree between principal vibration and subvibration, coupling capacitance C_m has a negative value. As a result, the first order temperature coefficient α_+ decreases according to decrease of load capacitance C_L, because coupling factor Km becomes small. 2) The optimum load capacitance C_L gives a zero temperature coefficient for α_+. Therefore, it is shown that an oscillator circuit is obtained with frequency deviation less than 1 ppm over a wide temperature range of -30℃ to +70℃. 3) Oscillation frequency increases as load capacitance C_L decreases.
1991-06-20