Receiver Linearity Enhancement Techniques

Receiver Linearity Enhancement Techniques
Dr. William S. Song
Location: MIT Lincoln Laboratory Cafeteria
Signal Processing Society meeting – 5:30PM Social, 6:00 PM Talk, Thursday, 6 November

Linearity is increasingly becoming more important in radio frequency (RF) receiver and sensor systems including communication, radar, Electronic Warfare (EW), and Signal Intelligence (SIGINT) systems. High linearity is essential for these systems to operate properly in presence of large interfering signals such as jammer and clutter. Insufficient linearity would result in high level spurs and intermods that can interfere with the small target signal detection. Currently, the linearity of these sensor systems is largely limited by the linearity of analog-to-digital converters (ADCs).

In order to prevent the spurs and intermods from interfering with small signal detection, the linearity needs to be enhanced to reduce the spur and intermod levels. MIT Lincoln Laboratory has developed the nonlinear equalization (NLEQ) and Time Varying Quantization (TVQ) technologies to enhance linearity of mixed-signal sensor systems. The NLEQ technique can digitally model the ADC nonlinearities and subtract them out from the digitized output to suppress the spur and intermod levels. However, because NLEQ algorithm can only suppress low-order nonlinearities, linearity improvements have often been limited until recently.
The new TVQ technology can achieve significantly higher linearity by suppressing high order nonlinearities that the NLEQ technique cannot address. An especially designed additive signal (TVQ signal) is inserted at the input of the ADC. The TVQ signal is designed to minimize the coherent integration of spurs and intermods, including high-order spurs/intermods that are difficult to equalize. The resulting digitized signal mainly contains low-order nonlinearities that are then be attenuated by the NLEQ technique.

The preliminary experimental results indicate up to four orders of magnitude higher spur-free dynamic range (SFDR) and intermod-free dynamic range (IFDR) may be possible with the linearity enhancement techniques. This means that sensors would be able to operate properly in environments with a ten thousand times higher interference signals. We believe that many commercial and military applications could benefit from the TVQ/NLEQ technology especially for systems that need to operate in challenging environments.

Dr. William S. Song is a senior staff member in the Embedded and Open Systems Group at MIT Lincoln Laboratory. He received his B.S., M.S., and Ph.D. degrees from the Massachusetts Institute of Technology in 1982, 1984, and 1989, respectively.

Since his arrival at Lincoln Laboratory in 1990, Dr. Song has been working on high-performance sensor and VLSI signal processor technologies for various applications. He has developed numerous advanced signal processing algorithms, architectures, real-time embedded processors, and sensor array systems. Recently, he has been working on the graph processor, communications processor, linearity enhancement techniques, mixed-signal system on chip, high-throughput low-power VLSI signal processors, and highly digitized wideband sensor arrays.

Dr. Song has been the technical director for a number of programs, including the cooperative communication processor, graph processor, wideband linearity enhancement processor, X-band element-level digitized sensor array, receiver-on-chip, space-based radar onboard signal processor, high-dynamic-range digital receiver, adaptive digital beamformer processor, and miniaturized mixed-signal receiver/processor programs. He has also designed a series of high-performance special-purpose signal processor ICs for these applications. His accomplishments include 14 U.S. patents with 1 more pending, 24 invention disclosures, and 28 journal and conference publications. He received MIT Lincoln Laboratory Technical Excellence Award in 2006. He is also an IEEE Senior Member.

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All attendees must present a valid driver’s license to MIT Lincoln Laboratory security. To get to the Cafeteria, proceed toward the Main Entrance of Lincoln Laboratory. Before entering the building, proceed down the stairs located to the left of the Main Entrance. Turn right at the bottom of the stairs and enter the building through the Cafeteria entrance. The Cafeteria is located directly ahead.