A new mode of Class D amplification
Cowett, Philip M.
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With the current trend in electronics toward microminiaturization, there is a need for a more efficient method of power amplification. Class D operation, in which the output transistors are either cut off or saturated and, hence, dissipate very little power, is one method of satisfying this need. This paper presents a study of a new mode of Class D amplification. In a conventional Class D amplifier, one transistor is always on and one transistor is always off. In a New Mode Class D amplifier both transistors are off most of the time, reducing unwanted dissipation in the output transistors, filter and load. The output of a New Mode amplifier consists of positive and negative trains of width-modulated pulses. For a positive-going output, the positive pulses increase in width while the negative ones disappear. While the New Mode is theoretically capable of distortion performance as good as or better than the conventional mode, problems in filtering the output prevent it from obtaining this performance. These problems are caused by the infinite impedance presented to the filter during the time when both transistors are off. However, the addition of negative feedback and a "damping" resistor to the filter reduce distortion to a level tolerable in most applications. The New Mode of Class D amplification proved to be slightly more efficient than the conventional mode, and considerably more efficient than Class B amplification.
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