| 摘要 |
PURPOSE:To reduce the drawing time, by switching the frequency control of a voltage controlled oscillator from an exponential function control to a primary functional control, when an input signal goes to a given frequency error. CONSTITUTION:The frequency error between an input signal frequency and the reference frequency from an oscillator 2 is outputted from a frequency discriminator 1 and frequency-divided at 3 and inputted to a control circuit 5, and the high/low information of error is inputted to a reversible counter 4. When the frequency error is greater, a switch 10 inputs the output of the frequency divider 3 to the counter 4, which controls a voltage control oscillator 7 with the signal having D/A- converted at 6 the value obtained by performing up-or down-count according to the amplitude of the error, and the signal from an oscillator 7 is inputted to the discriminator 1 via a feedback 8. When the error reaches a given value, the circuit 5 detects it and switches the switch 10 to a pulse generator 9. The generator 9 produces the pulse of a given period, operates the counter 4 toward error decrease, and the output frequency of the oscillator 7 is changed in primary-functionally. When the error reaches a given value, the circuit 5 stops the operation of the counter 4. |
