| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently remove the distortion of detection output by means of an overmodulation wave by comparing the detection output signal of a detection circuit with the DC voltage of a prescribed value and controlling the operation of a phase comparison circuit in accordance with the compared result. SOLUTION: The input signal S1 which is amplitude-modulated by the carrier of the prescribed frequency is branched into two. One is supplied to the detection circuit 11 and the other is supplied to a PLL(phase locked loop) circuit 12. The PLL circuit 12 reproduces the carrier included in the input signal S1 and it is composed of a phase comparison circuit 13, a loop filter circuit 14 and a voltage control oscillation circuit 15. A comparator 16 is provided and potential Vref against the carrier '0' (modulation degree 100%) is set to be a threshold and it is compared with a detection output signal S5. The operation of the phase comparison circuit 13 is controlled based on the compared result. Thus, influence against the phase inversion part of control voltage (output signal S3 from loop filter circuit 14) to the voltage control oscillation circuit 15 can be eliminated. Consequently, distortion occurred in detection output by the overmodulation wave can sufficiently be removed. |
