Caractérisation et linéarisation d'amplificateur de puissance RF par prédistorsion numérique dans un contexte d'appareils mobiles

Abstract

The linearization of power amplifier has long been a topic of study. Most studies are centered on its use for base station power amplifiers. However, there is a lack of literature regarding its use in the context of power amplifiers with lower consumption, especially in the context of mobile devices such as cell phones and tablets. A method for the generation of a predistorsion filter is developed and used in the design of a predistorsion bench for experimentation on RFIC PAs in the LACIME research lab. A polynomial NARMA model is used and its performances are compared to a first-order NMA model and a static model. The system is identified using the LMS algorithm and the full implementation of the predistorted signal generator is done using a software-defined radio (SDR). A PC is used in order to generate the baseband signal to transmit and also to generate the predistorsion filter with MATLAB. A power amplifier with low-power consumption is first biased in class A, then switched to class AB. This amplifier is then used to test the predistorsion algorithm. Finally, memory effects are added to the amplifier by putting a large choke inductor at the collector of the amplifier. These biasing conditions serve in the validation of the NARMA and NMA models. Results show an improvement in the linearity performance with every model used. A 9dB ACPR improvement is measured when a static polynomial predistorsion is used with maximum output power in class AB. Results also show that when efficiency is improved at the cost of linearity by changing the conduction angle in the power amplifier, linearity performances can then be improved with the predistorsion algorithm. The power and linearity performances of an amplifier are measured in predistorsionless class A and predistorted class AB. With 0.8dB more power at the output of the amplifier with class AB biasing, the power consumption, without accounting for the predistorsion circuit, is 145mW lower compared to predistorsionless class A and the ACPR (adjacent channel) levels are 3.7dB lower. A degradation of the performances in the alternate channel are however observed. The ACPR level in the alternate channel is 6.1dB higher in class AB than it was in predistorsionless class A. It can be concluded that there is a potential for predistorsion in the context of the linearization of power amplifiers meant for mobile devices such as cell phones and tablets. The techniques shown here can help to improve the overall quality of the communication systems in terms of power and efficiency-linearity trade-off.

Date	12 Apr 2017
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Nicolas Constantin (Supervisor)