An RF Cochlea

The biological inner ear or cochlea is an amazing custom analog computer capable of the equivalent of 1GFLOPS of spectral-analysis and gain-control computations with 14uW of power on a 150mV battery and a minimum detectable signal of 0.05 angstroms. It achieves such efficiency because of the clever use of an active nonlinear transmission line implemented with fluids, membranes, active piezoelectret cells, micromechanics, and electrochemistry.The cochlea has an amazingly large input dynamic range of 120dB, analyzes frequencies over a 100-fold range in carrier frequency (100Hz-10kHz), and amplifies signals at 100kHz even though its cells have time constants of 1ms. We use inspiration from the cochlea to construct an RF cochlea a fast, ultra-broadband, low-power spectrum analyzer. Instead of working with sound waves from 100Hz to 10kHz as in the audio cochlea, we work with radio waves from 100MHz to 10GHz but the principles of wave processing are similar and inspired by the biological cochlea. The actions of fluid mass in the ear are mimicked with inductors, the actions of membranes in the ear with capacitors, and the actions of outer hair cells in the ear with active RF amplifiers. Electrically, the cochlea can be modeled as an active, nonlinear, adaptive transmission line with characteristic frequencies that scale exponentially with position. Nonlinear behavior is important in the biological cochlea, particularly for signal detection in noise and gain control. We are researching how the RF cochlea may be used as a front end for universal radios, software radios, and cognitive radios and improve the detection of radio signals in noise.

Selected Publications

1. FIRST RF COCHLEA PAPER: S. M. Zhak, S. Mandal, and R. Sarpeshkar, "A Proposal for an RF Cochlea", invited paper, Proceedings of the Asia Pacific Microwave Conference, New Delhi, India, 4 pages, December 15-18, 2004.

2.RF COCHLEA CIRCUITS: S. Mandal, S. Zhak, and R. Sarpeshkar, "Circuits for an RF Cochlea", Proceedings of the International Symposium on Circuits and Systems (ISCAS 2006), Kos, Greece, pp 3610--3613, May 21--24, 2006.

Bio-inspired Projects in Sensing and Computing

Other bio-inspired projects in the lab have led to interesting innovations and applications: A bio-inspired analog-to-digital converter built with two spiking neurons is currently at or near the state-of-the-art in energy efficiency (0.12 pJ per quantization level) for A-to-D converters. It was inspired by how spiking neurons perform pattern recognition with time rather than with voltage or current, and was the first time-based converter whose conversion time scaled linearly with bit precision instead of exponentially. A bio-inspired companding algorithm, inspired by the operation of the silicon and biological cochlea, led to an architecture for doing spectral analysis that has shown improvements in subjects for hearing in noise and for speech recognition in noise. A bio-inspired asynchronous interleaved sampling algorithm (AIS), inspired by the operation of winner-take-all spiking neurons, led to an algorithm for efficient low-power neural stimulation that preserves phase information well and is thus useful for encoding music or tonal languages (e.g. Chinese) in cochlear implants. A cochlear-implant chip processor that exploits this algorithm has just been built. Research in the lab on low-power wide-dynamic-range spike-based imagers and on a silicon cochlea promise improvements in imagers and audio processing in the near future. Some of Professor Sarpeshkar's early work on motion processing in Analog VLSI was inspired by motion processing in flies.

Selected Publications

1. BIO-INSPIRED A-TO-D: Yang, H. and R. Sarpeshkar, “A Bio-inspired Ultra-Energy-Efficient Analog-to-Digital Converter for Biomedical Applications”, IEEE Transactions on Circuits and Systems I, special issue on Life Sciences and System Applications, Vol. 53, No. 11, pp. 2349-2356, November 2006.

2. BIO-INSPIRED AIS ALGORITHM: J. Sit, A. M. Simonson, A. J. Oxenham, M. A. Faltys, and R. Sarpeshkar, “A low-power asynchronous interleaved sampling algorithm for cochlear implants that encodes envelope and phase information”, IEEE Transactions on Biomedical Engineering, Vol. 54, pp. 138-149, 2007.

3. BIO-INSPIRED AIS PROCESSOR: J. Sit and R. Sarpeshkar, “A Cochlear-Implant Processor for Encoding Music and Lowering Stimulation Power,” IEEE Pervasive Computing, Vol. 1, No. 7, pp. 40-48, 2008.

4. BIO-INSPIRED COMPANDING ALGORITHM:L. Turicchia and R. Sarpeshkar, “A Bio-Inspired Companding Strategy for Spectral Enhancement,” IEEE Transactions on Speech and Audio Processing, Vol. 13, No. 2, pp. 243-253, March 2005

5. BIO-INSPIRED SILICON COCHLEA: R. Sarpeshkar, R.F. Lyon, and C.A. Mead, “A Low-Power Wide-Dynamic-Range Analog VLSI Cochlea,” Analog Integrated Circuits and Signal Processing, Vol. 13, pp. 123-151, 1997.

6. BIO-INSPIRED VISUAL MOTION PROCESSING:R. Sarpeshkar, J. Kramer, G. Indiveri, and C. Koch, “Analog VLSI Architectures for Motion Processing: From Fundamental Limits to System Applications,” Invited Paper, Proceedings of the IEEE, Vol. 84, No. 7, pp. 969-987, 1996.

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