| 摘要 |
PURPOSE:To obtain an AD converter with high accuracy at a high speed by providing a means correcting the gain of an amplifier into two within the blanking period of a video signal. CONSTITUTION:When the blanking period of a picture signal comes, a switch 6 is connected to a ground potential, the electric charge of a capacitor 22 is discharged, and since the MOS resistor is large, the output of the amplifier 1 is larger than a full scale voltage (VFS). While the switch 24 is kept closing when the output of the amplifier 1 is larger than the voltage VFS and charges the capacitor 22 via a resistor 25 from the bias power supply 26. As the voltage of the capacitor 22 rises, the MOS TR is going to be turned on, the output voltage of the amplifier 1 is lowered and the moment it is smaller than the voltage VFS, the output of the comparator 23 is inverted, a switch 24 is turned off and the gate voltage is kept constant for a prescribed time. Since the output is VFS with respect to the input of the voltage difference VFS/2, the gain of the amplifier is kept just twice.
|
