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Feedforward 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 a detailed exposition of feedforward error nulling techniques is presented, and a recent commercial design is analyzed with an illustration of significant modifications. The paper thus consists of: 1) a brief history of error feedforward, 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 Black's feedforward configuration and how it relates to more recent circuit concepts such as Macdonald's active error feedback, Sandman's error takeoff, Walker's "current dumping," and several new topologies; 3) an illustration of the only commercially available error feedforward circuit, the Quad "current dumping" amplifier; 4) significant modifications to the latter scheme using practical amplifiers, and generalizations of the bridge system incorporated in this concept; 5) an incorporation of error correction into class-D switching amplifiers with resulting relaxed design criteria.
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