Analysis and two proposed design methodologies for optimizing power efficiency of a class D amplifier output stage

In this paper, we analyze the power dissipation mechanisms and derive the overall power efficiency of a Class D output stage realized using the finger and waffle layouts. We propose two design methodologies to determine the aspect ratios of the transistors in the output stage for optimum power efficiency: (i) optimization to a single modulation index point, and (ii) optimization to a range of modulation indices. For the design of an output stage with optimum power efficiency (and small IC area), we recommend the waffle layout realization optimized to a range of modulation indices. The theoretical analysis and derivations are verified on the basis of computer simulations and measurements on fabricated prototype ICs.