A Polyphase Multipath Technique for Software Defined Radio Transmitters

Abstract—Transmitter circuits using large signal swings and hard-switched mixers are power-efficient, but also produce unwante harmonics and sidebands, which are commonly removed using dedicated filters. This paper presents a polyphase multipath technique to relax or eliminate filters by canceling a multitude of harmonics and sidebands. Using this technique, a wideband and flexible power upconverter with a clean output spectrum is realized in 0.13- m CMOS, aiming at a software-defined radio application. Prototype chips operate from DC to 2.4 GHz with spurs smaller than 40 dBc up to the 17th harmonic (18-path mode) or 5th harmonic (6-path mode) of the transmit frequency, without tuning or calibration. The transmitter delivers 8 mW of power to a 100- load (2.54 Vpp-di voltage swing) and the complete chip consumes 228 mW from a 1.2-V supply. It uses no filters, but only digital circuits and mixers.