We’re delighted to congratulate Feifei Zhang whose paper entitled “An Active-Under-Coil RFDAC With Analog Linear Interpolation in 28-nm CMOS” has been selected as the Highlight paper of the May 2021 issue of IEEE Transactions on Circuits and Systems I (TCAS-I) journal.

This is a huge achievement given the quality and scope of publications in this journal.  TCAS-I publishes papers in areas of relevance to the IEEE Circuits and Systems Society, namely the theory, analysis, design, and practical implementation of circuits, and the application of circuit techniques to systems and signal processing. The topics of interest covered include: 1. Analog, Digital and Mixed Signal Circuits and Systems, 2. Nonlinear Circuits and Systems, 3. Circuits and Systems for Communications, 4. Power Electronics and Systems, 5. Software for Analog and Digital Circuits and Systems, 6. Control aspects of Circuits and Systems.

Describing the paper as “an intriguing topic with high quality”, Prof Weisheng Zhao, editor–in–chief of IEEE Transactions on Circuits and Systems I, intends to promote the work across all TCAS-I digital platforms – LinkedIn, Twitter, WeChat and Facebook.  We would like to thank Feifei for all her hard work that led to this level of achievement and wish her continued success.


Feifei Zhang (Student Member, IEEE) received the B.Sc. degree in navigation guidance and control from the Beijing University of Aeronautics and Astronautics and the M.Sc. degree in microelectronics from the Beijing Embedded System Key Laboratory, Beijing University of Technology, in 2014. She is currently pursuing a Ph.D. degree from University College Dublin, Dublin, Ireland. Her current research interest includes radio frequency digital-to-analog converters.


This paper demonstrates a wideband 2.4 GHz 2×9 -bit Cartesian radio-frequency digital-to-analog converter (RFDAC). Active-under-coil integration is introduced in the physical implementation, where all key active circuitry is located underneath the matching-network transformer, achieving a core area of merely 0.35 mm 2 . An 8× analog linear interpolation at the RF rate is proposed to suppress replicas close to the carrier while avoiding any high-order and high-speed digital filters in digital processing back-end. The multi-port transformer is adopted in the matching network to improve the back-off efficiency. The measured peak output power and drain efficiency at the center frequency of 2.4 GHz are 17.47 dBm and 17.6% respectively, while the peak efficiency is 19.03%. Moreover, the 6-dB back-off efficiency is at 66% of that at the peak output power. The active-under-coil integration helps this RFDAC to achieve the smallest area among comparable prior arts.

Authors: Feifei Zhang; Peng Chen; Jeffrey S. Walling; Anding Zhu; Robert Bogdan Staszewski

To view the full paper click here

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