| 摘要 |
PROBLEM TO BE SOLVED: To provide a broadband VCO(voltage controlled oscillator) which stabilizes output amplitude and reduces phase noise. SOLUTION: This VCO 9 is provided with a fixed collector bias current source 21, a variable collector bias voltage circuit 20 and a voltage tuned resonant circuit 22. The circuit 20 detects collector output amplitude of a transistor 10, changes collector bias voltage by using integration value of difference of reference voltage 25 and controls to make output amplitude constant. Also, because the collector bias voltage is maintained constant by the fixed collector bias current source, the operation point of the transistor 10 maintains a constant relation to emitter disconnection of the transistor 10. Consequently, collector voltage is made sufficiently high according to the fixed collector bias current in each tuning voltage and initialization value of the voltage 25 and bias is controlled so that certain instantaneous current may be zero, i.e., a state just before the occurrence of emitter disconnection. |
