To secure the satisfactory stability of a crystal oscillator for a long period with no occurrence of minute jumps of oscillation frequency by setting the base current of an oscillation transistor TR in an area where the oscillation frequency has a linear change against the change of the base current of the oscillation TR.
An oscillation circuit 2 using a TR is equal to a Colpitts crystal oscillation circuit, for example, and oscillates in the resonance frequency of a crystal vibrator 1. Then the DC voltage which is generated by a sweep voltage generator 3 and varies by the lapse of time is supplied to the base of the oscillation TR of the circuit 2 to sweep the oscillation. The base current of the oscillation TR is set in an area where the oscillation frequency has a linear change against the change of the base current. Therefore, the stable oscillation frequency is secured with no occurrence of librations even with an oscillator which uses a crystal vibrator that causes the librations at a certain crystal current level as long as the circuit constant is set to secure such a current level that never causes the librations.
SAITO MIKIO
KOUKI MOTOKAZU
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