| 摘要 |
PURPOSE:To improve C/N of a DDS circuit by providing a CPU to operate a DDS (Direct Digital Synthesizer) circuit, a D/A converter and an electronic variable tuning circuit externally to the DDS circuit. CONSTITUTION:A frequency setting data 21 is inputted to a DDS 1 from a CPU 2 and an output of the DDS 1 is fed to a load through an electronic variable tuning circuit 4. The 2nd frequency setting data 22 is inputted from the CPU 2 so that the tuning frequency of the variable tuning circuit 4 is changed in tracking with the output frequency of the DDS 1 and a D/A converter 3 converts the signal into a control voltage 31a or a control current 31b, which is fed to the electronic variable tuning circuit 4 thereby setting the tuning frequency electronically. Thus, the C/N of the output wave restricting the dynamic range is improved. |
