| 摘要 |
A voltage controlled Colpitts type crystal oscillator includes a first crystal and a transistor coupled to the first crystal to provide positive feedback for generating an output oscillatory signal. A variable capacitance is coupled to the first crystal for producing a change in a frequency of the oscillatory signal when a corresponding change in the variable capacitance occurs. A first inductance is coupled in a resonant circuit that includes the variable capacitance and the first crystal having a value selected to provide a pulling range of at least 0.4% with respect to the frequency of the oscillatory signal. In one embodiment of the invention, a second crystal is coupled to the first crystal and included in the resonant circuit. An energy dissipating impedance is coupled in the resonant circuit to the first crystal for decreasing a Q characteristic of the first crystal to increase the pulling range of the oscillator. The first inductance separates the second crystal from each of the first crystal and the energy dissipating impedance to decrease an effect of the energy dissipating impedance on a Q characteristic of the second crystal.
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