Study of Power Amplifier Linearization

Abstract

Nowadays, different methods with non-constant envelop signal are implemented to meet limited channel bandwidth. As a consequence, the final stage of power amplifier must behave linearly over the whole dynamic range with desirable efficiency. Traditional methods based on 3rd order intermodulation distortion (IMD3) sweet spot use biasing adaption. However, they are limited by narrow dynamic range and might fail at higher output power level. In this project IMD3 sweet spot was studied. Biasing and harmonic termination effects on sweet spot were investigated. A novel adaptive source termination was proposed. ADS simulation, which uses a single state BJT amplifier working at 2.4GHz, has shown more than 20dB improvement for IMD3 at peak output power with a wider dynamic range. In the two tone test experiment, the same amplifier with 12.86dB gain was used. Its IMD3 can be well controlled below -44dBm throughout the whole output dynamic range by optimizing source harmonic termination at each input power level. Comparing with adaptive biasing method, 45dB improvement can be achieved at peak power. In addition, less than -50dBc adjacent channel power ratio (ACPR) over the whole dynamic range was got from two tone excitation. Under -40dBc and -50dBc ACPR requirement, boosted upper dynamic range with enhanced efficiency was realized in comparison with adaptive biasing method. The result demonstrated good linearity and dynamic range. With those desired features and simple design, the method, thus, is applicable.