A 2 W CMOS Hybrid Switching Amplitude Modulator for EDGE Polar Transmitters

Abstract

This paper presents a hybrid switching amplitude modulator for class-E2 EDGE polar transmitters. To achieve both high efficiency and high speed, it consists of a wideband buffered linear amplifier as a voltage source and a PWM switching amplifier with a 2 MHz switching frequency as a dependent current source. The linear amplifier with a novel class-AB topology has a high current-driving capability of approximately 300 mA with a bandwidth wider than 10 MHz. It can also operate on four quadrants with very low output impedance of about 200 m at the switching frequency attenuating the output ripple voltage to less than 12 mVpp. A feedforward path, a PWM control, and a third-order ripple filter are used to reduce the current burden of the linear amplifier. The output voltage of the hybrid modulator ranges from 0.4 to 3 V for a 3.5 V supply. It can drive an RF power amplifier with an equivalent impedance of 4 up to a maximum output power of 2.25 Wwith a maximum efficiency of 88.3%. The chip has been fabricated in a 0.35 m CMOS process and occupies an area of 4.7 mm2.