Abstract: The present invention is a single-ended Class A gain stage amplifier consisting of an active current source. A feedback path from an output node of the amplifier senses the direction and magnitude of the current going through a load coupled to the output node. The feedback path varies the output of the active current source in accordance with the sensed load current. By so doing, the efficiency of the amplifier of the present invention can be doubled as compared to prior art amplifiers operating in Class A mode. In addition, the present invention amplifier exhibits lower signal distortion.

Abstract: An amplifier circuit having two identical inverting folded-cascode amplifier stages coupled together through a coupling resistor at the positive terminals of the respective stages. Each stage includes an input gain transistor whose gate forms the negative input terminal of the amplifier stage coupled to receive an input signal through an input resistor, whose source forms the positive input terminal of the amplifier stage, and whose drain is connected to the source of a level-shifting cascode transistor. Both transistors are supplied current from a constant current source also connected to the source of the level-shifting transistor. The drain of the level-shifting transistor forms an output terminal of the amplifier stage. Each stage feeds its amplifier output negatively to the positive input of the other stage, while at the same time feeding its distortion and noise contribution positively, via input gain transistor conduction, to the other stage.

Abstract: A power amplifier circuit having a cascode transistor configuration with at least one gain transistor biased for Class-A or Class-AB operation and at least one cascode transistor, and having at least one isolated high impedance current source connected across the gain transistor(s) to provide an alternate path for bias current other than through the cascode transistor(s). In a complementary symmetry embodiment of the amplifier, a bias voltage across the gates of the complementary gain transistors ensures Class-A (or -AB) operation, while either a single current source connected across both gain transistors or a pair of current sources, each connected across one gain transistor, provides the alternate bias current path. In a single-ended embodiment of the amplifier, a current sink to one of the power supply terminals assures forward bias for Class-A (or -AB) operation, and a single current source is connected across the sole gain transistor.