Ultra broadband envelope tracking systems for 5G utilizing class-S supply voltage modulator
Final Report Abstract
The project addressed three topics: 1) A GaN power amplifier (HF-LV) for 26...28 GHz adapted for ET operation, 2) a digital modulator that modulates the supply voltage of the HF- LV according to the envelope of the signal, and 3) the integration of these two components into an envelope tracking (ET) system and its characterization. With regard to the MMIC power amplifier (HF-LV) one can state: • A coplanar HF-LV using 0.15µm GaN MMIC technology was realized at FBH, which delivers 2 W output power at 26 GHz. This is in line with the state-of-the-art for coplanar versions for frequencies above 25 GHz, but remains below the performance of microstrip versions. • For backoff operation, PAE is very low at 4% for 10 dB versus 11% for 0 dB. • This has a decisive influence on the potential for improvement by ET and Doherty concepts. In the project, an improvement of 2 percentage points from 1.7 % to 3.8 % was experimentally demonstrated with a static ET. • For Ka-band amplifiers with higher efficiencies, these values will increase accordingly, but a first estimate leads to improvements of only less than 10 percentage points even if 0 dB efficiencies reach 40 %. The digital modulator as the most critical component was investigated in particular detail: • As DC-DC converters do in general, the digital amplifiers based on the preliminary work show a degradation of efficiency at low output voltages (and thus low supply voltages of the PA). • Therefore, two other topologies based on the buck converter and boost converter were developed using FBH's 0.25 µm GaN technology. The boost converter could only be realized as hybrid circuit, because it requires powerful diodes, which were not available in a MMIC environment so far. Efficiencies in the 35...90 % range were achieved with the hybrid boost converter. • The demonstrated efficiencies are remarkable, especially in view of the parasitic effects caused by the design, but are not yet sufficient to realize an ET system in the K-band with convincing overall efficiency. With the components developed in the project, an ET system was set up and tested and its function demonstrated. Despite the use of a worldwide unique measurement set-up and a great deal of efforts, reliable broadband measurements with modulated signals proved to be a challenge and could not be carried out to the desired extent, so that the results had to be supplemented by extrapolations. Overall, three conclusions can be drawn from the results obtained: • The absolute improvement in power efficiency that can be reached by ET decreases with increasing frequency due to the deteriorating PAE values. This applies to the Doherty concept to a similar extent. The lower savings in DC power limit severely the power budget, which is available for additional components such as the modulator when using ET. • Envelope tracking with continuous modulation is of only limited use for larger bandwidths due to the low modulator efficiencies, even if digital approaches based on PWM are applied. Discrete modulation (class G), on the other hand, which only switches back and forth between different voltage values, promises better results and should be pursued. • Linearity becomes more important with increasing operating frequency, since with overall decreasing gains their voltage-related variation grows, which increases the linearization effort.
Publications
- "Switch-Type Modulators and PAs for Efficient Transmitters in the 5G Wireless Infrastructure," 2018 IEEE MTT-S International Microwave Workshop Series on 5G Hardware and System Technologies (IMWS-5G), 2018, pp. 1-3
N. Wolff, S. Chevtchenko, A. Wentzel, O. Bengtsson and W. Heinrich
(See online at https://doi.org/10.1109/IMWS-5G.2018.8484690) - “Highly Compact GaN-based All-Digital Transmitter Chain Including SPDT Switch for Massive MIMO,” in Proceedings of the 48th European Microwave Conference (EuMC) 2018, pp. 918 - 921, Madrid, Spain
F. Hühn, A. Wentzel, W. Heinrich
(See online at https://doi.org/10.23919/EuMC.2018.8541526) - “Versatility, Bandwidth and Efficiency: Digital GaN-Based Switch-Mode Supply Modulators,” in Proceedings of the 48th European Microwave Conference (EuMC) 2018, pp. 523 - 526, Madrid, Spain
F. Hühn, A. Wentzel, W. Heinrich
(See online at https://doi.org/10.23919/EUMC.2018.8541774) - “A Reconfigurable Modulator for Digital Outphasing Transmitters,” in IEEE MTT-S International Microwave Symposium Digest 2019, pp. 1480 – 1483, Boston, USA
F. Hühn, A. Wentzel, W. Heinrich
(See online at https://doi.org/10.1109/MWSYM.2019.8700817) - “Highly Compact GaN-based All-Digital Transmitter Chain Including SPDT T/Rx Switch for Massive MIMO Applications,” in International Journal of Microwave and Wireless Technologies, Vol. 11, Special Issue 7, pp. 609 - 617, April 2019
F. Hühn, A. Wentzel, W. Heinrich
(See online at https://doi.org/10.1017/S175907871900045X) - “Wideband GaN-based supply modulated power amplifier systems-aiming for 5G at mmW,” Workshop-Wideband Supply Modulated RF Power Amplifiers for Energy Efficient Wireless Communication Infrastructure – towards 5G, International Microwave Symposium, Boston, USA, 2019
O. Bengtsson, S. Paul, S. Preis, N. Wolff
- "High Efficiency, High Bandwidth Switch-Mode Envelope Tracking Supply Modulator," in 2020 IEEE/MTT-S International Microwave Symposium (IMS), Los Angeles, CA, USA, 2020, pp. 853-856
F. Hühn, F. Müller, L. Schellhase, W. Heinrich and A. Wentzel
(See online at https://doi.org/10.1109/IMS30576.2020.9223925) - “A highly efficient GHz switching GaN-based synchronous buck converter module,” in International Journal of Microwave and Wireless Technologies, vol. 12, no. 10, pp. 945–953, 2020
A. Wentzel, O. Hilt, J. Würfl, and W. Heinrich
(See online at https://doi.org/10.1017/S1759078720000380) - “Discrete level supply modulation with large dynamic wideband signals,” Workshop-High-efficiency linear power amplifiers for high bandwidth, high PAR signals, European Microwave Week, Utrecht, the Netherlands (Online), 2020
O. Bengtsson, S. Paul, S. Preis, N. Wolff
- "Wideband Vector Corrected Measurements on a Modified Vector Network Analyzer (VNA) System", 99th Automatic Radio Frequency Techniques Group, ARFTG, 2022
C. Schulze, W. Heinrich, J. Dunsmore, and O. Bengtsson
(See online at https://doi.org/10.1109/ARFTG54656.2022.9896558)
