Performance comparison of RF class-D amplifier with Neoteric modulator and bandpass sigma-delta modulator

Abstract

The performance of RF class-D amplification with Neoteric modulator and bandpass sigma-delta (ΣΔ) modulator are studied and compared. The modulators encode the source signal into a binary level pulse train, and broaden the application of class-D amplifiers to include signals with time-varying envelopes. Their performance are directly linked to the power efficiency and linearity of the overall amplifier. The modulators are evaluated in terms of two important parameters, coding efficiency and average transition frequency. Tested at 800MHz with a 5MHz W-CDMA signal having a 10.6dB peak-to-average ratio and a class-D amplifier constructed using GaAs FET devices, it is found that the amplifier achieves a power efficiency of 21% with Neoteric modulator, compared to an efficiency of 11% with bandpass ΣΔ modulator, while with comparable level spectral growth of around −45dBc. The better power efficiency obtained with Neoteric modulator is due to its higher coding efficiency of 11.4% versus 5.8% for the bandpass ΣΔ modulator.