Digital Object Identifier 10.1109/MMM.2012.2226541 Mohammad Mojtaba Ebrahimi, Mohamed Helaoui, and Fadhel M. Ghannouchi Mohammad Mojtaba Ebrahimi (mm.ebrahimi@ucalgary.ca), Mohamed Helaoui (mhelaoui@ucalgary.ca), and Fadhel M. Ghannouchi (fghannou@ucalgary.ca) are with the iRadio Lab, Department of Electrical and Computer Engineering, University of Calgary, Calgary, Canada T2N1N4. Date of publication: 23 January 2013 Delta-Sigma- Based Transmitters P ower efficiency is one of the most important parameters in designing communication systems, especially battery- operated mobile terminals. In a typical transceiver, most of the power is dissipated in the power amplifier (PA) and consequently, it is very important to obtain the maximum efficiency from the PA. A PA operating in Class AB or B is at its maxi- mum efficiency when it is driven by its maximum allowable input power [1]. In practice, the input signal of the PA usually has a varying envelope, and to avoid distortion the PA should not be driven to more than its maximum input saturating power. Unfortunately, this peak power of the input signal happens at very short periods, and most of the time the signal power is around its average power, which is much smaller than its peak power, meaning that, often, the PA works at much lower efficiencies than its maximum efficiency. The power difference is defined as the peak to average power ratio (PAPR) of the signal. For example, for a signal with 12 dB PAPR, a Class B PA would be driven with 12 dB power back-off from its peak input power, and at this power back-off, the efficiency of the PA will degrade from 78.5% to around 20% [1]. Unfortunately, by moving to high throughput modulation schemes, for example, quadrature amplitude modula- tions (QAMs) such as 16-QAM and 64-QAM mean that more envelope variation is needed to encode the information, and, consequently, lower efficiency is achieved. One well-established solution to this problem is to shape the signal in such a way that all the information lies in the phase of the signal 68 January/February 2013 1527-3342/13/$31.00©2013IEEE