| 摘要 |
PURPOSE:To keep a bit rate at a time to A/D convert a focus evaluating value in a necessary minimum by providing a subtracting means to obtain the differential value of a prescribed component per prescribed period and minimumizing the range of an analog signal inputted to an A/D converting means. CONSTITUTION:A sample and hold circuit 34 samples the output of a detector 32 according to the signal of a timing corresponding to the vertical synchronizing signal of a video signal and holds it for an IV period. A substracter 36 substracts the hold value of the sample and hold circuit 34 from the output voltage of a detector 32 and outputs the substracted voltage. An amplifier 38 amplifies the output voltage of the substracter 38 and impresses it to an A/D converter 40. An operation processing circuit 42 adds the output of the A/D converter 40 per IV, calculates the driving direction and the driving speed of a motor 24 and outputs them to a D/A converter 44. Thus, since a little bit number can be efficiently used and a digital value can be accurately reproduced, the accuracy of a down-hill control can be enough secured. |
