HomeResearch → Digital/ Adaptive Microwave System

Digital/Adaptive microwave systems take advantages of (i) the intelligence and computational accuracy of DSP (ii) the high efficiency and robustness in the generation of digital pulse waveforms to improve the performance of traditional microwave transceivers in terms of their dynamic range, signal to noise ratio, power efficiency and linearity etc.

Adaptive Transceiver Leakage Cancellation

On (i),the group published the first work about adaptive transceiver leakage cancellation with real-time DSP in a continuous wave radar system in 2004. It has demonstrated that the transceiver leakage can be cancelled by more than 30dB over a 2 GHz bandwidth in the center frequency of 26GHz. The concept has later been extended by many and applied to overcome the leakage problems not only in radar systems but also in full duplex wireless communication front-ends.

K. Lin, Y. E. Wang, C-K. Pao and Y-C. Shih, "A Ka Band FMCW Radar Front-End with Adaptive Leakage Cancellation" IEEE Transactions on Microwave Theory & Techniques, Vol. 54, No.12, pp.4041 - 4048, December 2006. 

Bitstream RF Transmitters for High Efficiency and Linearrity

On (ii), the group's focus is on bitstream RF transmitters. Such transmitters are capable to achieve both high efficiency and high linearity in the power amplification of RF signals modulated by non-constant envelopes, through digitizing the RF waveforms with digital bitstreams. In 2003, the group proposed a novel bitstream modulation architecture that requires much lower sampling rate than conventional ones, and coined the term Envelope Delta-Sigma Modulation (EDSM) for this technique. Since then, the group has continued to work on “digital” RF transmitters based on bitstream modulations and become a leader in this area.

In 2007, the group proposed a practical RF power amplifier architecture that works with bitstream modulations such as EDSM and with high-Q output filters acting as power efficient D/A converters. This technique is called Pulsed Load Modulation (PLM), which is a proven solution in providing high efficiency and linearity through a "digital" way of power amplification. In 2010, the group presented a full system demonstration of the bitstream transmitter for WCDMA signal, which was published in IEEE Journal of Solid State Circuits.

Recently, the group has proposed a novel active noise filtering technique called Channelized Active Noise Cancellation (CANE) to overcome the quantization noise issue in the bitstream transmitter caused by the digitization. This work was presented as the invited talk in the San Diego Power Amplifier Symposium in September, 2014. With the combination of EDSM+PLM+CANE, the last road block that prevents the bitstream transmitter concept from being practical may have been cleared.

S. Liao and Y. E. Wang, "High Efficiency WCDMA Power Amplifier With Pulsed Load Modulation (PLM)," IEEE Journal of Solid-State Circuits, vol.45, no.10, pp.2030-2037, Oct. 2010.

J. Jeong and Y. E. Wang,  " Pulsed Load Modulation (PLM) Technique for Efficient Power Amplification" IEEE Transactions on Circuits and Systems, II.,Oct. 2008.