Auto focus circuit for video camera

An autofocus circuit for a video camera including a focusing motor for focusing, comprising:

• [a] high-pass filter [circuit] means to which a luminance signal of a video signal is applied [so that] for extracting a high frequency component higher than a predetermined frequency [is extracted] from said applied luminance signal,
• [an absolute value calculating circuit connected to said high-pass filter circuit for obtaining an absolute value of the output of said high-pass filter circuit,]
• [an] A-D converting [circuit] means operatively connected to said [absolute value calculating circuit] high-pass filter means for converting an analog [absolute value] output signal [provided] derived from said [absolute value calculating circuit to] high-pass filter means into a digital signal,
• [a] calculating [circuit] means connected to said A-D converting [circuit] means for adding the converted digital signal with a predetermined period cycle,
• [a] comparing [circuit] means connected to said calculating [circuit] means for comparing the output of calculation in one predetermined period and the output of calculation in [the predetermined period coming one] another predetermined period [ahead of said predetermined period], and
• [a] focusing motor control [circuit] means connected to said comparing [circuit] means for providing a signal for controlling the rotation of the focusing motor included in said video camera in the clockwise direction or in the counter-clockwise direction based on the output of said comparing [circuit] means .