| 摘要 |
PURPOSE:To obtain detecting characteristics which is excellent in its linearity, by providing a capacitor, a charging circuit and a discharging circuit, and controlling the charge and discharge to the capacitor. CONSTITUTION:A charging circuit is constituted of a transistor (TR) Q25, Q21, Q22, a resistance R21, a constant-current source 111 and a constant-voltage source 112, and a discharging circuit is constituted of TRQ23 and TRQ24, a constant- current source 113 and a constant-voltage 114. When a pulse signal S1 is in a high level, TRQ22 is turned off, and base voltage of TRQ25 becomes nearly output voltage V1 of the constant-voltage source 112. Voltage across a capacitor C21 becomes nearly V1-VBE instantaneously. On the other hand, when the pulse signal S1 is in a low level, TRQ22 is turned on, base voltage of TRQ25 becomes lower than voltage across the capacitor C21, and TRQ25 is turned off. When a horizontal synchronizing signal SH is in a low level, TRQ23 is turned on, and voltage across the capacitor C21 drops. On the other hand, when SH is in a high level, TRQ23 is turned off, the capacitor C21 becomes a floating state, and voltage before that time is held. |
