A 10 MHz Bandwidth, 2 mV Ripple PA Regulator for CDMA Transmitters

A combined class-AB and switch-mode regulator based supply modulator with a master-slave architecture achieving wide bandwidth and low ripple is presented. Low frequency content of the envelope waveform is provided by a synchronous-rectifier based switch-mode power supply while high frequency content is provided by a rail-to-rail class-AB amplifier. A wide range, low loss output current sensing circuit is used at the class-AB amplifier output, canceling the ripple due to switch-mode power supply and extending overall modulator bandwidth. The proposed regulator is designed and fabricated on a 0.35 mum CMOS process. The combined regulator achieves a maximum efficiency of 82% and an IMD3 of 65 dBc at 10 MHz for 16 dBm output power. The regulator achieves a frequency range up to 10 MHz with less than 0.2% envelope tracking error, making this PA regulator suitable for CDMA applications.