US Patent 7755423 Sigma delta class D power amplifier and method thereof

A sigma delta class D power amplifier includes a loop filter, a quantizer, and an output stage. The quantizer is coupled to the loop filter and quantifies an error signal according to levels of two reference signals to output a pair of mean signals, wherein different logic combinations of the mean signals belong to one of three quantum states. The output stage is coupled to the quantizer and outputs a corresponding output signal according to the different quantum states to drive a load, wherein a driving current of the output signal belongs to one of the three driving states which include at least a steady state with no current of a power amplifier.