A base control Doherty power amplifier design for improved efficiency in GSM handsets

by Ferwalt, Darren W.

In cellular telephones, RF power amplifiers consume a significant part of the

total phone current. Reducing the average PA current will extend battery life. In

GSM systems the handset is commanded by the base station to transmit at power

levels lower than full power much of the time. A Doherty amplifier can be used to

improve efficiency at these lower power levels, providing a lower average PA current

when evaluated over the entire power range.

A Doherty amplifier is presented that uses the DC base voltage to control the

output power. The base control amplifier is first studied separately, then two such

amplifiers are combined to create a Doherty amplifier. An analysis of battery life

while the phone is on a call, or talk time, is then performed. Talk time for the base

control Doherty amplifier is compared to an ideal class B amplifier and to a Doherty

amplifier composed of two class B amplifiers. Finally a base control Doherty

amplifier is implemented at 30 MHz, both in simulation and hardware.