| 摘要 |
PURPOSE:To attain high speed frequency changeover of the frequency synthesizer by sweeping out an output frequency of a direct digital synthesizer stepwise. CONSTITUTION:When input data kp to a data setting circuit 19 are changed into data Kq by the application of an external frequency changeover instruction, the data setting circuit 19 sends sequentially integers [k(p+1), k(p+2)...] existing between the data kp and the data Kq to a direct digital synthesizer 1 at a prescribed time interval. In this case, an output frequency of the direct digital synthesizer 1 is swept sequentially at a width of DELTAfr' as frp, fr(p+1), fr(p+2)... After the data kq are sent, the output frequency of the direct digital synthesizer 1 is frq and then the sweeping is finished. Then, a phase locked loop 8 is converged and reaches a steady-state and the output frequency of the frequency synthesizer reaches foq. In this case, the sweep width DELTAfr' is set to be less than the cut-off frequency of a loop filter. |
