| 摘要 |
PURPOSE:To accurately set the output frequency of a VCO at high speed by using the measuring frequency of the voltage controlled oscillator VCO, a set D/A converter input and a desired frequency so as to use a D/A converter input corresponding to the desired frequency set next with prediction. CONSTITUTION:A control circuit 110 applies operation by using the output frequency of the VCO 105 measured by a counter 109, the desired frequency setting value 101, the output of a register 103 and a value in a RAM 102 and the value of the RAM 102 is revised so that the output frequency of the VCO 105 is the desired frequency setting value 101. Further, as to the frequency not set by the interpolarion using the control circuit 110, it is registered on the table of the RAM 102. The operation above is repeated at every desired frequency setting value change to improve the accuracy of the table or the concerned equation to the RAM 102. Since the linearity error of a D/A converter 104 is corrected by the table or the equation in the RAM 102, it does not give any problem. |
