To provide an adequate signal integrity to a power amplifier (PA), we propose a digital system for the degradation at the transmitter path, and it is implemented on a field-programmable gate array (FPGA) board. The proposed system offers the following features: A M-ary quadrature amplitude modulation (QAM) digital signal generation and in-phase/quadrature (IQ) imbalance mitigation, and by default, it performs as a predistortion model extraction from PA-measured data. The simulations and tests provided are performed to effectively verify the PA linearity by using 256-QAM signals. The nonlinearities are predicted as a reliable solution for linearizing the PA from measurements of AM/AM and AM/PM conversion curves. The performance is evaluated in terms of linearity, computation complexity, and FPGA hardware synthesis according to a dependability compliance of digital signal processing. Finally, the model is validated with input/output data observations to linearize the model with a fitting normalized mean squared error (NMSE) of around -35 dB, a spurious free dynamic range of 40 dBm, and an adjacent channel power ratio reduction by -20 dBm, for a class-AB broadband radio frequency PA GaN HEMT of 10 W working at 2.34 GHz.
|Journal||International Journal of Circuit Theory and Applications|
|State||Accepted/In press - 1 Jan 2020|
- digital predistortion
- IQ imbalance estimation
- power amplifiers
- quadrature modulation
- RF circuits