Lowpass delta-sigma modulator with digital upconversion for switching-mode power amplifiers

This work presents a lowpass ΔΣ based transmitter frontend suitable for software defined radios (SDRs). ΔΣ modulation is utilised to generate an RF signal suitable for driving highly efficient switching-mode power amplifiers. The whole transmitter frontend is implemented in the digital domain up to the upconversion. Thus, high reconfigurability and flexibility necessary for SDR is achieved. This work presents two implementations methods for lowpass ΔΣ modulator based transmitter frontends for SDR applications. The circuit design in a 90nm CMOS process and a discrete implementation utilising a field programmable gate array (FPGA) are discussed. Feasibility of the concept is demonstrated by simulation for the integrated implementation and by measurements for the FPGA solution.