0.7–1.8 GHz digital polar transmitter using a watt-class CMOS power amplifier and digital pulse width modulation with spurious signal reduction

A polar transmitter driven by digital input signals for envelope and phase is demonstrated, using a switched output resonator to achieve multiband operation. A new digital pulse width modulation algorithm is also shown to partially suppress spurious signals associated with the digital input envelope signal. The transmitter consists of a current-mode class-D power amplifier (CMCD PA), together with a buck converter with a dead-time generator for improved efficiency. The CMCD PA was tuned by switched capacitors that can handle up to 9V, and was measured to have 30-31 dBm output power with 31-35% drain efficiency under single-tone testing. The proposed spurious signal reduction technique works to partially suppress the quantization noise without increasing power consumption. Overall efficiencies of 27.1 / 25.6% were obtained at 30.2 / 28.9 dBm CW output powers and 850 / 1750 MHz carrier frequencies respectively. Spur suppression of 9-10 dB peak was achieved when the proposed algorithm was applied to WCDMA modulation.