Driver for N-channel VFET output stage of power amplifier
AssigneeMitek Corp., Inc.
InventorJohn J. Pleitz
Life of this patent
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Abstract
An input driver stage for an audio power amplifier wherein the amplifier incorporates only N-channel VFETs in the output stage, the invention locks the currents in second stage (via a closed loop) which is directly connected to the VFET output stage thus allowing precise open loop predictive temperature compensated programming of the quiescent operating point of the VFET output stage into an acceptable linear area of operation--without fettering the amplifiers inherent straight forwardness OF implementation or the amplifiers excellent signal amplification characteristics.
Claims19
The input stage of an audio amplifier for use with an output stage having first and second N-channel VFET, the amplifier receiving an audio input signal on an input line and producing an output signal on an output line, the amplifier also providing positive and negative DC voltage sources, each VFET having a gate terminal, the input stage comprising:
- a differential amplifier receiving both the audio input signal and the output signal and generating difference signals at first and second nodes;
- a current conveyor stage including first and second conveying junction transistors having base, emitter and collector terminals;
- a mirror stage including first and second mirror junction transistors having base, emitter and collector terminals;
- and
- first, second, and third biasing resistors;
- wherein the bases of the first and second conveying transistors are connected to the differential amplifier at the first and second nodes respectively, the emitters of the first and second conveying transistors are connected to the bases of the first and second mirror transistors respectively and to the positive DC voltage source through the first biasing resistor, the emitters of the first and second mirror transistors are connected to the positive DC voltage source, the collector of the first conveying transistor is connected to the output line through the second biasing resistor, the collector of the second conveying transistor is connected to the negative DC voltage source through the third biasing resistor, and the collectors of the first and second conveying transistors are connected to the gate terminals of the first and second VFETs respectively;
- whereby, the first and second mirror transistors lock an emitter to collector current through each of the first and second conveying transistors so as to program gate voltages at the VFET gate terminals into a desired region despite temperature changes.
An input stage of a audio amplifier for use with an output stage having first and second N-channel WETs, the amplifier receiving an audio input signal on an input line and producing an output signal on an output line, each VFET having a gate terminal, the input stage comprising:
- a plurality of junction transistors including first and second conveying junction transistors having collector terminals connected to the gate terminals of the first and second VFETs respectively;
- first and second biasing resistors connected to the first and second junction transistor collector terminals respectively;
- and
- means responsive to the temperature of the VFETs for automatically locking the collector to emitter currents through the first and second conveying junction transistors into a desired range thereby locking the potential drop across the first and second biasing resistors so as to bias first and second gate voltages at the gate terminals into desired operating regions despite varying temperature.
Dependencies are inferred from the claim text.