A digital bandpass delta-sigma modulator for class-S power amplifiers is presented. In comparison to a 2-level modulator coding efficiency can be increased by 10% over a large input power range with a 3-level modulator. Scaling the quantizer thresholds offers a trade-off between coding efficiency and signal-to-noise ratio. The bandpass modulator architecture allows twofold interleaving. A constraint on the quantizer thresholds and the feedback values reduces the effective operand word width in the feedback loop to the 5 most significant bits. Pipelining of the less significant bits leads to a short critical path. Interleaving and pipelining promise fast operation and thus a high maximum signal frequency.
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