| 摘要 |
PURPOSE:To attenuate an undesired wave having a multiple of an output frequency even when the range of the output frequency is wide by providing a band pass filter generating a control signal in response to an output frequency variable data and using the control signal to extract the output frequency of a voltage controlled oscillator. CONSTITUTION:An output data of a ROM 8 is inputted to a digital analog converter 9, where the data is converted into a DC voltage. The DC voltage biases the voltage variable filter 11 via a buffer amplifier 10. In the case of biasing the voltage filter, a data is written in advance in a prescribed memory area of a ROM 8 so that the center frequency passing through the voltage variable filter 11 is an output frequency fout. Since the pass band of the voltage variable filter 11 is changed corresponding to the conversion of the output frequency fout, a desired output frequency is outputted but, an undesired wave, especially, the undesired wave having a multiple of the output frequency is blocked by the attenuation region of the voltage variable filter 11 and not outputted. |
