| 摘要 |
PURPOSE:To eliminate the need for manual adjustment and also reduce the influence of ambient temperature, and to absorb the secular change, etc., of elements of a unit by adjusting the output of an amplifier which amplifies presence/absence information on an original previously and automatically by an AGC circuit. CONSTITUTION:The AGC circuit 30 consists of an FET 2, an amplifier 3, comparators 4-6, a capacitor 9, etc. Then, the capacitor 9 is charged and discharged to control the gate voltage of the FET 2. Consequently, the output corresponding to the presence/absence information on an original is obtained by comparing and deciding on the output variation of the amplifier 3 which occurs when the original 25 is absent through comparators 4 and 5. Thus, the output of the amplifier 3 is adjusted automatically by the AGC circuit 30 previously. Therefore, manual adjustment is not necessary, the influence of the ambient temperature is small, and the secular change, etc., of elements of the unit are absorbed. |
