Advanced linear PA architectures for handset applications

Summary form only given. The handset PAs for advanced system, such as 4G and beyond, should handle signals with high PAPR. For amplification of the signals, efficiency of the PAs is degraded significantly due to the operation at a low power region. For the system application point, the PAs are required to have a multimode and multiband capability, also. These stringent requirements ask advanced design architectures of the PAs. These architectures are based on a highly efficient amplifier and try to maintain the high efficiency at a low power level. The representative architectures are ET technique, Doherty amplifier, class-S amplifier, LINC and some digital PAs. ET is the most popular architecture for the handset application since the ET PA is very flexible, suitable to the multimode and multiband operation, together with high efficiency. This technique can be applied easily to a low-high mode PA, also. One variation of the technique is an average power tracking (APT) amplifier, controlling VDC according to the average power level at a slow speed using a buck DC-DC converter. This PA is on the market, now. Doherty can provide a high efficiency for the application and there is a significant progress for the broad banding but the bandwidth is still limited. Recently, the performance of the LINC PA is improved significantly by increasing the power combining efficiency. The distortion is cancelled using DPD technique. The progress in LINC is mainly focused on the infrastructure application but it can be employed for handset PA also. As transistors are scaled down with higher speed, the digitally configured circuit can be applied for the RF signal amplification. The digital circuit is very flexible and can be used for multimode/multiband application but the performance is not up to the expectation, yet. For the digital amplification, the I-Q modulated signal is, normally, up-converted to a polar signal. The amplitude information is digitized at the base band speed or the RF frequency and is applied to the digital circuit. The digital bit signal can be amplified by the thermo coded cells, forming a digital amplifier. The digitizing can be done using sigma-delta modulator and the digitized bit can be applied to a PA, either as an input or as a bias voltage. The resulting amplifier is a class-S PA. The I-Q modulated signal can be directly up-converted while maintaining the digital bits using sampling technique and is applied to the thermo code cells. These digitally configured PAs are actively studied now and will progress continuous. These various advanced architectures for the next generation PA for handset application will be introduced in this talk.