Load-impedance and bias-network dependence of power amplifier with second harmonic injection

For the power amplifier (PA) used in code-division multiple-access cellular phones, the supply voltage is switched from around 1.5 to 3.5 V at the boundary transmission power of several decibels higher than 10 dBm using a DC-DC converter to improve operation efficiency. Recently, however, this boundary transmission power is being raised. We applied the second harmonic injection to reduce distortion and maximize the boundary transmission power under low supply voltage. This paper presents the design concept of the PA´s load impedance and bias network with second harmonic injection using Volterra-series analysis. We also present a design of the final stage of the PA under low supply voltage and show that the final stage has a drain efficiency of 53% at an output power of 21 dBm.