Linearization Transmitter Using Asynchronous Sigma Delta Modulation for UMTS Handsets

 It is crucial for the spectral-efficient communication systems, associated with the sophisticated digital modulation formats to be able to handle the RF signal containing a probably very large variation of the envelope magnitude. The aim of this work is to build an optimal transmitter linearization architecture suitable to achieve a highly linear transmission and to be highly power efficient. In this paper we propose a new linearization technique combining a switched-mode RF power amplifier (PA) with an envelope-modulated dynamic voltage supply, an asynchronous sigma delta modulator (ASDM) and a low-Q RF bandpass filter to achieve a highly efficient linear transmitter. The system has been investigated by using system-level behavior modeling of the ACLR test bench. It also compares the linearity with the well-known Envelope Elimination and Restoration (EER) technique. The simulation results show that the Adjacent Channel Leakage Power Ratio (ACLR) of the proposed system can be achieved significantly beyond the requirement of the UMTS handsets, by increasing the inherent self-oscillation frequency of the ASDM modulator. Moreover, the highly linear ASDM can compensate the errors caused by the envelope modulation, which makes the system very useful to overcome the envelope processing limitation of EER transmitter so that an optimal transmitter, realized in an available technology can fulfill the required ACLR by the UMTS. Keywords transmitter, power amplifier, asynchronous sigma delta, linearization, UMTS