| 摘要 |
PURPOSE:To prevent the deterioration in the frequency characteristics and the increase in current consumption, by performing accurate clamping operation with a large input impedance. CONSTITUTION:In a clamp circuit formed with an inverting feedback system, a base of an NPN transistor (TR) Q21 is connected to an input terminal 14 of an operational amplifier 11. The emitter of this TRQ21 is grounded and the base is connected in common with the base of a substrate PNP TRQ22. TRs Q23, Q24, Q25 and a resistor R21 constitute a current mirror circuit and a TRQ26 and a resistor R22 forms an output circuit. The input impedance of this operational amplifier becomes larger through the cancellation of the base current of the TRQ22 and that of the TRQ21. Thus, the discharge time constant of charges of a capacitor C11 can be increased, allowing to perform accurate clamp operation. |
