Evolution of Power Amplifiers for Mobile Phone Terminals from the 2nd Generation to the 5th Generation

SUMMARY Mobile phone systems continue to evolve from the 2nd generation, which began in the early 1990s, to the 5th generation, which is now in service. Along with this evolution, the power amplifier (PA) is also evolved. The characteristics required for PA are changing with each generation. In this paper, we will give an overview of the evolution of PAs from the 2nd generation mobile phones such as GSM (global system for mobile communications) to the 5th generation mobile phones that is often called NR (new radio), in particular, the circuit system. Specifically, the following five items will be described. (1) Ramp-up and ramp-down power control circuit corresponding to GSM, (2) Self-bias circuit technology for improving linearity that becomes important after W-CDMA (wideband code di- vision multiple access), (3) Power mode switching methods for improving e ffi ciency at low output power, (4) Power combining methods that have be- come important since LTE (long term evolution), and (5) Backo ff e ffi ciency improvement methods represented by ET (envelop tracking) and Doherty PA.