The auxiliary envelope tracking RF power amplifier system
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Abstract
The advancement of the mobile communication industry increases the need
for RF power amplifier (RFPA) to be more efficient and linear. The communication
network that is shifting towards smaller micro-cell or nano-cell network has also
motivated the design of the RF power amplifier to be simple, compact and cost
efficient. In this research work, a novel technique for efficiency and linearity
improvement of the RFPA is presented. A simplistic approach in the technique called
‘Auxiliary Envelope Tracking' (AET) system has promoted the design for small and
straightforward AET tracking generator, a key component in the system. The use of
low cost components in the AET tracking generator has made the technique
commercially attractive.
The AET technique proposes a separation in generating DC and AC
components of the AET signal that biases the drain of the RFPA. The separation
eases the generation of the signals resulting in low power consumption that leads to
efficiency improvement. The investigation of the gain characteristic of gallium
nitride (GaN) RFPA has shown an important RFPA attribute where the gain varied
substantially as the drain voltage increases. By using the AET technique, the gain
characteristic is harnessed to get linearity improvement.
In order to validate the technique, AET measurement systems for two-carrier
and WCDMA signals were developed and experimented. A special Class AB RFPA
is designed and implemented to use dedicatedly for this investigation. In two-carrier
signal measurement, a tracking generator is developed that consists of an envelope
amplifier (EA) and a diplexer. The RFPA and the tracking generator are then
combined to be an integrated AET block. In order to accommodate the high peak-toaverage
ratio (PAR) and high bandwidth WCDMA signal, a broadband RF
transformer was designed as part of the AET tracking generator to replace the
diplexer.
The two-carrier and WCDMA signals measurement results have proven that
the AET technique is a valid technique for efficiency and linearity improvement. The
improvements were achieved with simple, compact and cost-effective
implementation