This work presents a lowpass ∆Σ based transmitter frontend suitable for software defined radios (SDRs). ∆Σ modulation is utilised to generate an RF signal suitable for driving highly efficient switchingmode 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 ∆Σ modulator based transmitter frontends for SDR applications. The circuit design in a 90 nm 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.Index Terms-Field-programmable gate array (FPGA), lowpass (LP) delta-sigma (DS), RF transmitter, software defined radio (SDR).