Error Correction in Power Amplifiers
The engineering community is presently putting much effort into designing low distortion amplifiers with techniques more sophisticated than ordinary feedback. To guide this effort, we present a detailed exposition of feedforward error nulling techniques, and we analyze a recent commercial design, illustrating significant improvements. The paper thus consists of: 1) A brief history of feedforward error correction, why it was eclipsed by feedback, and why the time is now ripe to exploit its possibilities for total error nulling. 2) An analysis of Blacks' feedforward configuration and how it relates to more recent circuit concepts such as MacDonald's active error feedback, Sandman's error take-off, Walker's "current dumping," and Pass's "stasis" principle. 3) An illustration of the only commercially available feedforward circuit, the Quad "current dumping" amplifier. 4) Significant improvements of the latter scheme using practical amplifiers, and generalizations of the bridge system incorporated in this concept. 5) An incorporation of error correctioninto class D switching amplifiers with resulting relaxed design criteria.
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