| 摘要 |
PROBLEM TO BE SOLVED: To provide a frequency synthesizer where a VCO with an excellent C/N characteristic and a wide output frequency range is integrated as an IC at a low cost. SOLUTION: The frequency synthesizer is provided with a prescaler 2 and a counter 3 that output a frequency division signal of an output of the VCO 1, a reference frequency divider 5 that frequency-divides the frequency of a reference signal source 4, a frequency adjustment means 9 that detects a frequency error of an output signal between the counter 3 and the reference frequency divider 5 and provides the output of a signal to switch capacitance or resistance of a resonance circuit of the VCO 1 depending on the result of detection, and a bias control means that applies an optical voltage V1 to a control voltage terminal of the VCO 1 at the operation of the frequency adjustment means 9 to bring the output signal of a charge pump 7 to a high impedance state. Since the resonance frequency of the resonance circuit is changed in response to the actual oscillated frequency of the VCO 1, the VCO 1 is phase- locked at a desired frequency. Furthermore, since the VCO can be integrated as an IC, the VCO can be miniaturized at a low cost. |
