System architecture of an RF-DAC based multistandard transmitter

Abstract

In this paper the system concept of a radiofrequency digital-to-analog converter (RF-DAC) based multistandard transmitter is presented. The RF-DAC combines DA converter and up-conversion mixer in a single building block. Thereby, the analog baseband blocks are eliminated and replaced by easily reconfigurable digital blocks. Requirements on the digital and mixed-signal blocks are discussed. Spurious emissions are a major issue of this ‘direct digital modulator’. This is especially true for multiradio devices with several receivers running simultaneously and in close proximity to the transmitter. Therefore, a maximum emission limit is formulated and especially critical frequency bands are identified. Several techniques for reducing the spurious emissions are discussed and performance requirements for an LTE transmitter and its main building block are found. System simulations demonstrate the feasibility of the concept.