All-Digital Outphasing Modulator for a Software-Defined Transmitter

An all-digital outphasing modulator to be used in a software-defined radio (SDR) transmitter is presented. A digitally-controlled oscillator (DCO) followed by two digital phase rotators (DPR) are the main building blocks. The DCO and DPRs are enclosed, respectively, by a phase-locked loop and two delay-locked loop. All functions, including filtering and calibration are performed in a digital signal processor (DSP). The chip was fabricated in a 90 nm CMOS process and tested for GSM and WCDMA. The total active area of the chip is 3 mm² . Semi-analog blocks (DCO core, DPR core and their buffers) and digital processor consume 30 mA and 25 mA, respectively. Current consumption of the phase-to-digital converter is 70 mA, which can be reduced to 30% by gating off the circuit during idle times.