A new direct digital transmitter architecture for constant envelope modulation

Abstract

A high speed Direct Digital Synthesizer (DDS) based transmitter architecture is presented. The DDS driven by a Sigma Delta (Σ∆) locks by injection an LC-tank Oscillator on an upper harmonic. Moreover, the Injection Locked Oscillator (ILO) provides a band-pass filtering within its locking range which rejects out of band Σ∆ quantization noise. The DDS is detailed in order to explain how to design an output signal frequency close to the clock frequency. Then the architecture is modulated thanks to constant envelope modulation. Finally, ILO output is compared to high constraint mask such as GSM/DCS in order to simulate architecture capability.