| 摘要 |
The circuit comprises an area dividing circuit for dividing the screen of a monitor into a number of areas, selecting an area to be evaluated as designated by a microcomputer, and providing a control signal; a band pass filter filtering desired frequency bandwidths of an analogue luminance signal in the selected area; an A/D converter converting the filtered luminance signals; a circuit integrating and storing the digital luminance signals, and outputting it when the video field period is complete; and the microcomputer comparing the filtered signals, controlling the band pass filter to output the corresponding frequency bandwidth analogue luminance signal, controlling the area dividing circuit to provide the control signal, and controlling the automatic focus moter in response to the stored integrated digital luminance signals output by the circuit. The focus circuit performs accurate and automatic focusing by converting the analog luminance signal into the digital signal and evaluating the integrated value of the digital luminance signal.
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