Digital architecture for direct digital-to-RF converters

This paper presents a novel technique for direct conversion of digital complex time series into radio frequency (RF) band. Most of the operations in this method are implemented by software and/or digital circuits. The proposed method is composed of some signal processing procedures, some switching circuits, a phase shifter (all-digital phase-locked loop), and an analog RF filter. The switching technique, which is used for a joint amplitude and phase modulation, makes the method highly power efficient. The signal processing procedure results in a highly linear converter and shapes the power spectrum of the output in order to satisfy the required power masking properties in a given application. The all-digital phase-locked loop or the phase shifter along with some simple digital circuits control the switching times of the output. The complex input sequence is first converted into phase and amplitude after over-sampling using a CORDIC processor. The phase sequence controls the amplitude and phase of a six-step waveform which has three levels at the output, i.e., zero and +/- A(t), where +/- A(t) is controlled by the amplitude sequence. In this paper, the theoretical and some practical aspects of the proposed technique are presented.