Modeling and predistortion for digital transmitters based on delta-sigma and pulse-width modulation

Digital transmitters based on delta-sigma modulation (DSM) and pulse-width modulation (PWM) are very active research areas because of their potential for achieving better integrated, lower cost, and higher efficiency communication devices. To achieve the best output power and efficiency, it is critical to have accurate models of the nonlinear behaviors in these transmitters and the ability to apply nonlinearity compensation. Previous research efforts have been mostly focused on behavior modeling of this type of transmitters using bit sequences from the DSM/PWM. The resulting models have high complexity and computation cost. In this paper, we start from the passband Volterra model and derive a new baseband Volterra model for this type of transmitters. The effectiveness of the new model is demonstrated in simulations and in linearizing of a 45nm CMOS digital transmitter. For a 10 MHz LTE signal, DPD based on the new model achieved around 5 dB adjacent channel power ratio improvement, while DPD based on conventional models showed improvement less than 1 dB.