Summary form only given, as follows. A lowpass (LP) ΔΣ based transmitter frontend suitable for software defined radios (SDR) is presented. ΔΣ modulation is utilised to generate an RF signal suitable for driving highly efficient switching-mode power amplifiers. The whole frontend is implemented in the digital domain up to the upconversion. Two implementations methods for LP-ΔΣ-modulator-based transmitter frontends are described. A circuit design in a 90 nm CMOS process and a discrete implementation utilizing a field-programmable gate array (FPGA) are discussed.