Description Number

Amplifier having an active current source

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.

5,710,522 Patent number 5,710,522

Amplifier with gain stages coupled for differential error correction.

Abstract: An amplifier 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. Balanced amplified outputs are produced from either balanced or unbalanced inputs, and distortion and noise components are produced in common on both outputs for differential cancellation. Complementary-symmetry and power amplifier versions of the basic single-ended line-level amplifier are also provided.

5,376,899 Patent number 5,376,899

Efficient high fidelity audio power amplifier.

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. The cascode configuration can employ either a common drain or a common source connection for the gain transistor(s). The current source(s) reduce bias current through the cascode transistor(s) and thereby reduce power dissipation as the cascode transistor(s) holds the voltage drop across the gain transistor(s) relatively constant.

5,343,166 Patent number 5,343,166

Active low frequency acoustic resonance suppressor.

Abstract: An electrically active sound wave attenuation apparatus mounted in an upright, free-standing housing for eliminating unwanted reflected waves in a room. The housing is intended to be placed in a location where undesired wave patterns, such as standing waves, are formed in order to offset or cancel such conditions. These conditions are offset by generating an acoustic signal which is the inverse of pressure waves at a particular location. The pressure waves are sensed by a module, including a microphone which generates a corresponding electrical signal. This signal is sent to an electrical circuit where an inverse signal is created which is then transmitted to a loudspeaker. The loudspeaker output is directed toward the location where the standing wave would be formed. The loudspeaker output nulls local acoustic waves so that no standing waves are formed. the housing may incorporate two acoustically isolates modules with resonance attenuating qualities, one at each end of the structure.

4,899,387 Patent number 4,899,387

Opto-isolated bias circuit for operating push-pull amplifiers in class A and class AB modes.

Abstract: A high fidelity audio amplifier of the push-pull complementary symmetry type, featuring a feedback circuit with a bias sensing element connected to the output terminals of the output transistors. The feedback circuit includes a photoemitting element in optical communication with a photoconductive element which determines the relative voltage difference of the input terminals of the complementary symmetry output transistors.

4,752,745 Patent number 4,752,745

Constant voltage - constant current high fidelity amplifier.

Abstract: A transistor amplifier in which collector to emitter voltages and currents are kept constant, particularly in the power output stages of the amplifying devices for minimizing distortion due to changes in the transistor beta, the essential form of distortion in amplifiers. High fidelity low power output current from a cascoded transistor amplifier is fed through a load to a second, high power, amplifier having constant current and less than unity gain, with an output summed with the output of the first amplifier such that the output of the first low power amplifier is the signal bearing portion and the output of the second amplifier serves as a current bootstrap, increasing the effective impedance of the load as seen by the first amplifier.

4,107,619 Patent number 4,107,619

Active bias circuit for operating push-pull amplifiers in class A mode.

Abstract: A transistor audio amplifier of the Class AB complementary symmetry type is biased with a new bias circuit to keep both transistors on during all normal signal conditions. The bias circuit includes a pair of series connected VBE Multipliers with an interconnection between the two multipliers receiving signal feedback from the amplifier output such that the Multipliers can bias both complementary transistors on for all normal signal operating conditions.

3,995,228 Patent number 3,995,228
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