Digital signal processing techniques for RF power amplifiers mismatches compensation, linearization and energy efficiency improvement

Contact:

Prof. Pere Lluis Gilabert Pinal (plgilabert@tsc.upc.edu)
Prof. Gabriel Montoro López (gabriel.montoro@upc.edu)

Research topics:

Energy efficient architectures for RF amplification: Envelope Tracking (ET) and Envelope Elimination and Restoration (EE&R)

ET transmitters employ a linear RF PA and a supply modulation circuit (envelope amplifier - EA), where the supply voltage tracks the input signal envelope. While ET structures demand for the use of current source mode amplifying classes, in PT or EE&R structures, the RF transistor is driven hard in switched or saturation mode with a constant amplitude phase modulated signal. ET and EE&R may offer excellent average power efficiency values (above 50%) for high PAPR signals, being a polar transmitter able of theoretically providing the dreamed 100% efficiency figure. As in any engineering solution, system and circuit level sources of nonlinear distortion have to be kept under control. In the first group, the finite EA bandwidth and the differential delay between the amplitude and RF signal paths may be included. In the second group, special attention should be put into the AM-AM and AM-PM characteristics of the final bias (or load) modulated RF PA.

Digital baseband compensation techniques

Highly efficient transmitting architectures such as ET, EE&R, PT and LINC, demand for digital signal processing (DSP) compensation mechanisms to deal with nonlinear distortion, unbalances or mismatches arising in these kinds of transmitting schemes. These digital solutions may be addressed by properly exploiting the use of the digital processors already present in modern transmitter architectures. Regarding digital predistortion (DPD), novel DPD approaches deal with maximizing both the linearity and power efficiency of the whole transmitter, based on mathematical tools in the time domain, to either to explore the signal features either to accomplish the adaptive calibration process. For example, by using a set of specific waveforms, faster and more efficient training of the DPD function is obtained. Moreover, adaptive compensation mechanisms for time-alignment (including fractional delays), or amplitude and phase unbalances correction of the signals involved in these highly efficient transmitters (polar, outphased components) will be also considered since they are crucial to guarantee the correct performance of these advanced transmitter schemes.

Highlighted projects

Competitive projects:

• Soluciones de radio digital para sistemas de comunicaciones sostenibles y reconfigurables de próxima generación. (2015-2017)
• Soluciones de procesado digital de la señal para sistemas inalámbricos sostenibles y reconfigurables.(2012-2014)
• Técnicas digitales avanzadas para tecnologías emergentes en transmisores inalámbricos. (2009-2011)

Industry contracts:

• Digital predistortion and shaping strategies for Envelope Tracking power amplifiers for handsets. (2014-2015)
• CFR and DPD solutions for microwave wideband power amplifiers. (2012-2014)