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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 at the switching frequency attenuating the output ripple voltage to less than 12 . 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 W with 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 .
Date of Publication: Dec. 2007