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.