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1. 发明授权

US5856760A Overdrive protection clamp scheme for feedback amplifiers 失效
标题翻译：反馈放大器的过驱保护钳位方案
公开(公告)号：US5856760A
公开(公告)日：1999-01-05
申请号：US745070
申请日：1996-11-07
申请人： Khanh Lam , Lloyd F. Linder , Carrie C. Lo , Tim M. Ng , Kelvin T. Tran
发明人： Khanh Lam , Lloyd F. Linder , Carrie C. Lo , Tim M. Ng , Kelvin T. Tran
IPC分类号： H03F1/52 , H03F3/30
CPC分类号： H03F1/52 , H03F3/3076 , H03F2200/372
摘要： A low-noise, low-distortion clamping scheme includes a bootstrapped voltage clamp and an R.sub.gm current clamp that provide superior overdrive protection when used together in a Class-AB feedback amplifier. The bootstrapped voltage clamp includes a transistor that is connected to a circuit node to be clamped. The transistor's base is bootstrapped to the node to maintain a constant V.sub.be when not clamping, to reduce the adverse effects of the junction capacitance C.sub.je which would normally vary with the node voltage and distort the signal at the node. Two such clamps provide positive and negative voltage limiting. The R.sub.gm current clamp is used in the input stage of a Class-AB feedback amplifier to limit the current through the resistor R.sub.gm that interconnects the current inputs of two transconductance amplifiers whenever the voltage drop across R.sub.gm increases to an unacceptable level. The clamp uses a dependent current source whose output current increases with the magnitude of the current flowing through R.sub.gm and prevents that current from exceeding a predetermined limit. When not clamping, the clamp has a very small effect on the amplifier's input stage. Two R.sub.gm current clamps are typically used to limit current flowing in either direction through R.sub.gm.
摘要翻译：低噪声，低失真钳位方案包括一个自举电压钳位电路和一个Rgm电流钳位电路，可在AB类反馈放大器中一起使用时提供卓越的过驱动保护。自举电压钳包括连接到要钳位的电路节点的晶体管。晶体管的基极被引导到节点，以在不夹持时保持恒定的Vbe，以减少结电容Cje的不利影响，其通常随着节点电压而变化并且使节点处的信号失真。两个这样的夹具提供正和负电压限制。 Rgm电流钳位用于AB类反馈放大器的输入级，以限制通过电阻Rgm的电流，每当跨过Rgm的电压降到不可接受的电平时，互连两个跨导放大器的电流输入。钳位使用依赖电流源，其输出电流随流过Rgm的电流的大小而增加，并防止该电流超过预定极限。当不夹紧时，夹具对放大器的输入级具有非常小的影响。通常使用两个Rgm电流钳来限制在任一方向流过Rgm的电流。

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