Spectrum emission considerations for baseband-modeled CALLUM architectures

Linear transmitters based on combined analog locked loop universal modulator (CALLUM) architectures are attractive, as they promise both high efficiency and high linearity. To date, it has not been possible to analyze a CALLUM transmitter as a linear feedback network due to the nonlinear nature of the control equations governing it. The main purpose of this paper has been the derivation of a linearized model for the control equations, which enables the use of linear network theory in the study of CALLUM. In particular, it can be used to analyze the stability and maximize the bandwidth of the system. Simulation examples are presented on how three different CALLUM architectures behave for enhanced data rates for global system for mobile communications evolution and wide-band code-division multiple-access signals. In addition, we have considered the effects of loop time delay, which is the ultimate limiting factor for all feedback-based linear transmitter architectures, particularly for large bandwidths. Finally, it is shown how frequency compensation of the feedback loop improves insensitivity to the loop time delay