580 California St., Suite 400
San Francisco, CA, 94104
Key research themes
1. How can amplitude modulation techniques mitigate intermodulation distortion in parametric loudspeakers?
This research theme focuses on experimentally evaluating the impact of various amplitude modulation (AM) schemes on intermodulation distortion (IMD) in parametric loudspeakers, which leverage nonlinear acoustic effects to generate focused audible sound. Addressing IMD is critical for improving sound quality via predistortion and modulation technique selection.
Experimental Evaluation of Distortion in Amplitude Modulation Techniques for Parametric Loudspeakers
Key finding: This study provides a detailed experimental comparison of frequency response, harmonic distortion, and intermodulation distortion across multiple AM techniques and modulation indices using a carefully controlled measurement... Read more
Key finding: The paper analytically and experimentally demonstrates that properly controlling phase shifters and biasing in Dual-Drive Dual Parallel Mach Zehnder Modulators (DD-DPMZM) can suppress third order intermodulation distortion... Read more
Key finding: This work proposes and validates an adaptive baseband polynomial predistortion algorithm aimed at minimizing mean square error between the actual nonlinear power amplifier output and an ideal linearized output. The polynomial... Read more
2. What physical mechanisms contribute to passive intermodulation distortion (PIM) in wireless systems and how can they be modeled or mitigated?
Passively generated intermodulation distortion, arising from nonlinearities in passive RF components and conductor joints, introduces unwanted interference severely impacting wireless systems' performance. Understanding physical sources, such as nonlinear electrical, thermal, and mechanical effects at metallic contacts, is essential for predicting, measuring, and mitigating PIM in radio network hardware.
Key finding: This article systematically classifies sources of passive intermodulation (PIM) distortion in base station radio systems into internal (passive components like transmission lines, connectors, antennas) and external origins... Read more
Key finding: The work reveals that PIM arises from concurrent electrical (e.g., Metal-Insulator-Metal junctions), thermal (electro-thermal processes), and mechanical nonlinearities at conductor joints with rough surface asperities. It... Read more
Key finding: This paper introduces a novel heuristic model showing that the power of third-order PIM terms decreases when additional non-contributing carriers (not directly involved in generating those terms) are present, contrary to... Read more
3. How can digital demodulation techniques be improved to suppress distortion and intermodulation in interferometric and digital communication systems?
This theme investigates algorithmic and signal processing approaches to reduce errors and intermodulation distortion caused by nonlinearities and signal variations in digital demodulation, including in interferometric optical sensors and multiband power amplifiers. Advances in demodulation algorithms and predistortion methods enable enhanced measurement accuracy and linearization in complex communication systems.
Key finding: The paper derives analytical expressions quantifying phase demodulation errors induced by target signal variations in digital harmonic phase modulation schemes for interferometric sensors. It develops a novel 4+1 point... Read more
Analysis and Digital Predistortion of in-Band Cross Modulation in Concurrent Multi-Band Transmitters
Key finding: This study identifies previously unreported in-band cross-modulation products arising when frequency separations between dual-band transmitters approach sub-harmonics of the bands, generating nonlinear distortion components... Read more
Key finding: This work analyzes chopper-induced intermodulation distortion (IMD) in low-offset amplifiers, showing that IMD originates primarily from amplifier delay causing chopping spikes. It proposes a fill-in technique employing dual... Read more