Efficiency Enhancement of Sigma–Delta Modulator Based Transmitters Using Multi-Level Quantizers

Abstract

This paper is concerned with the performance of first- and second- order sigma---delta modulator (ΣΔM) based transmitters with an Orthogonal Frequency Division Modulation (OFDM) signal and Code Division Multiplexing Access (CDMA) signal. In particular, the WorldWide Interoperability for Microwave Access (WiMAX) and Interim Standard 95 (IS-95) down link signals have been used for this study as test signals. The simulation and experimental results showed that the performances of the ΣΔM for both signals are improved by increasing the number of quantization levels and the order of the ΣΔM circuit. A ΣΔ modulator based transmitter using a switching mode power amplifier was developed and built for validation purposes. It is found that the increase of the quantization level of the ΣΔ modulator from 2 to 5 leads to a substantial improvement in the measured power efficiency of the transmitter from 5% to 42%. This improvement in efficiency is in good agreement with simulated and measured results obtained using simulink and FPGA board respectively.