Computer Analysis of Colpitts Crystal Oscillator

In this paper, a novel analyzing method o f crystal oscillators is described. In an ordinary oscillator, such as colpitts oscillator, an oscillation can be achieved by connecting a crystal resonator to an active circuit having a capacitive reactance and a negative resistance . In the present method, the negative resistance and equivalent capacitance of the circuit are first calculated by use of a circuit simulation program based on nonlinear models of active devices. Then the oscillation frequency and its signal level are obtained for a specified crystal resonator. In this work calculations have been made on a colpitts oscillator widely used in the frequency range up to 3 0 MHz. The important design parameters of the oscillator, such as the l vel and the frequency dependences of both the equivalent capacitance and the negative resistance, the oscillation frequency and level and the oscillation frequency change due to the power supply voltage variation, have been calculated with satisfactory agreements with measurements. It is concluded from these results that this analyzing method is useful for the analysis and design of crystal oscillators.