During the last 10-20 years wireless communications revolutionized the way people communicate. Currently the mobile phone is the most prominent symbol for our modern communications style. One of the most critical building blocks in any mobile phone is the radio frequency (RF) transceiver, which, in the transmitter, transfers the digital information into an electromagnetic wave to be transmitted, while the receiver extracts the digital information out of the received electromagnetic wave.

RF transceivers for wireless communications below 6 GHz were almost purely analog components around 15 years ago. Today these RF transceivers are fabricated in complementary Metal-Oxide-Semiconductor (CMOS) technology. This allows to integrate circuits for performing powerful digital signal processing (DSP) tasks, but come at the cost of poor analog/RF performance. The ongoing technology scaling, i.e. the shrinkage of the transistor dimensions below 14/16 nm leads to RF and analog performance degradation. Two common strategies have been established to deal with limited analog performance: First, the possibility to perform DSP on the RF transceiver chip enabled the use of many digital pre- and post-compensation algorithms, which try to correct for degradation effects due to the limited analog/RF performance. Examples are digital predistortion, I/Q-mismatch compensation, or on-chip self-interference cancellation. The second strategy tries to replace formerly analog building blocks in the RF transceiver with fully digital ones, so that the potential of semiconductor technology scaling can be fully exploited. The operation principle of such digital building blocks usually makes use of the switching performance of the transistors, which, in nm-CMOS technology, is superior to their analog performance. Examples for this strategy are the all-digital phase-locked loop, the RF-Digital-to-Analog converter or the digital power amplifier. This second strategy also lead to new architectural concepts for RF transmitters like the polar or the multiphase transmitter.

Based on a 20+ years history in digital assisted RF transceivers, our current research in this area is performed within the Christian Doppler Laboratory for Digitally Assisted RF Transceivers for Future Mobile Communications which we operate together with our academic partners, the Institute for Signal processing and the Institute for Integrated Circuits at the Johannes Kepler University and our company partner DMCE Danube Mobile Communications Engineering, a subsidiary of Intel.