Controlled coefficient adaptation in linearization of PA by modified baseband signal

This paper presents the linearization of RF Doherty amplifier by the baseband signals for linearization whose adjustable parameters are adapted on required values in automated process. The signal for linearization is generated by digitally processing of I and Q components of the useful baseband signal forming in that manner the adequate second-order nonlinear signal required for linearization. The signals for linearization modified in amplitude and phase in the baseband modulate the fundamental carrier second harmonic and modulated signals are injected at the input and output of the transistor into the carrier cell of the Doherty configuration. DSP should adjust the amplitude and phase of the baseband signals for linearization in order to supress the third- and fifth-order intermodulation products. Process of the linearization coefficient setting and adaptation is performed automatically by minimizing power of the intermodulation products. The linearization results and effects of the linearization parameter adjustment and adaptation are considered for quadrature amplitude modulated signals characterized with different bandwidth up to 30 MHz, as well as for WCDMA and OFDM digitally modulated signals.