Sequential Digital Predistortion for Two-stage Envelope Tracking Power Amplifier

To improve the efficiency of the main power amplifier, the envelope tracking technique is widely used. However, due to the reduced gain of the main amplifier by the envelope tracking, the driving power of the drive amplifier requires to be larger and the amplifier should be optimized accordingly for an efficiency operation. In this letter, a two stage envelope tracking power amplifier is studied for the purpose. The envelope tracking technique is applied to both the drive and main power amplifiers to improve efficiency of the drive amplifier, which is usually operated at a low efficiency. The experimental results show that the efficiency of the total system is improved by 2.1% while the efficiency of the drive amplifier is increased by 8%. In addition, to overcome a serious non-linearity due to the dual envelope tracking operation, a new sequential digital predistortion architecture is proposed and using this architecture, the linearity specification of the long term evolution signal has been successfully satisfied.