All-digital single-bit-output RF transmitters using homodyne sigma-delta modulation

Abstract

An all-digital RF transmitter architecture capable of driving directly a switching RF power amplifier and therefore without the need of a high-speed RF DAC is presented. Modulation is achieved by directly modulating a direct digital synthesizer (DDS) generated signal. The proposed architecture is based on single-bit sigma-delta modulation using the introduced homodyne band-pass filter topology, which allows for the adjustment of its central frequency without changing its coefficients. This is achieved by using variable frequency homodyne down- and up-conversion along with a low-pass filter with fixed coefficients. Furthermore, a multiplier-less homodyne filter topology is shown to be possible, greatly reducing the hardware requirements for its implementation. MATLAB simulation results are presented based on a 64-QAM modulation scheme demonstrating the capabilities of the proposed architecture.