From narrowband to wideband modeling of radio frequency power amplifiers

Correct modeling of radio frequency power amplifiers (RF PA) is difficult, as nonlinear characteristics are not only statics but also dynamics and strongly depend on input signal frequencies. Recent studies in PA behavioral model have shown the interest of structures based on memory polynomial functions with sparse delay taps between instantaneous and previous input signal. The extension of such structures is proposed in this work to achieve a measurement based wideband model of PA for digital wireless communication systems. The model uses Infinite Impulse Response filters which describe the frequency response of each nonlinearity order. The characterization of this new model structure includes direct calculation of polynomial parameters and delay taps with two-tone test for different frequencies and parameter estimation of equivalents filters in frequency domain using least mean square algorithm and Instrumental Variable method. The obtained architecture improves memory effect description and provides computational efficiency suitable for dynamic time-domain PA studies. This new approach is validated using a 1.85GHz RF PA from Advanced semiconductor business with various modulations such as two-tone test, WCDMA and WiMax signals.