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Envelope Detector Control Path Enhancements for Low-Power Medical Applications

Envelope Detector Control Path Enhancements for Low-Power Medical Applications. J. Chan-Wai, B. Lawrence, V. Proulx ELG 4135 Electronics III Dr. Riadh Habash November 24 th 2006. Team Members. Jason Chan Wai Brian Lawrence

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Envelope Detector Control Path Enhancements for Low-Power Medical Applications

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  1. Envelope Detector Control Path Enhancements for Low-Power Medical Applications J. Chan-Wai, B. Lawrence, V. Proulx ELG 4135 Electronics III Dr. Riadh Habash November 24th 2006

  2. Team Members Jason Chan Wai Brian Lawrence Valerie Proulx

  3. Conventional Envelope Detector • Envelope detectors are used to obtain the envelope of an AM modulated signal.

  4. Relevant Research • Envelope Detector Proposed in Research Paper [1] Alegre, J.P., Celma, S., Sanz, M.T., and Garcia del Pozo. ‘Low-ripple fast-settling envelope detector’, Electronics Letters, 2006, 42, (18), pp. 1-2.

  5. Application: Hearing Aids and Cochlear Devices • We are interested in engineering for medical applications • Hearing aids are designed for frequencies ranging from 250 to 4,000 Hz

  6. Application: Hearing Aids and Cochlear Devices

  7. Original Control Path • Control path proposed in referenced research paper

  8. Problems • Cannot receive low voltage signals • High-pass filter • No amplification • Hearing aids require low voltage and low frequency signals • Noise amplified due to three stage MOSFET inverters • Two separate control paths (180° out of phase) required to minimize the effect of noise

  9. Simulation • Simulation was performed on researched control path using PSpice

  10. Simulation Results 1 • Output when input signal is 3V (large) • Circuit functions as intended

  11. Simulation Results 2 • At small voltages (300mV) the proposed control path does not function properly!

  12. Simulation Results • Input signal not strong enough to drive MOSFET inverters • Therefore, control path is unable to properly switch the peak hold circuits at a peak in the input signal • Problematic with low frequency signals (due to high-pass filter)

  13. Primary Goal • Enhance the circuit’s response to weak, low frequency signals to ensure that they can switch the CMOS inverters and therefore properly detect signal peaks Secondary Goals • Minimize output noise • Eliminate the need for a second control path

  14. Optimized Control Path • Proposed design utilizes active components in the input network!

  15. Simulation Results 1 • Output of proposed control path with 300mV, 2kHz input signal

  16. Simulation Results 2 • Output of proposed control path with 300mV 500Hz input signal

  17. Simulation Results • Capable of receiving low voltage input signals within the desired frequency band • Number of CMOS stages reduced (lower output noise) • Single control path now capable of driving two control signals, eliminating the need for a second control circuit!

  18. Analysis Comparison: Passive Circuit PROS • Energy efficient • Passive input network requires no power • Speed CONS • Inability to receive low frequency, low voltage signals • Requires two control paths

  19. Analysis Comparison: Active Circuit PROS • Ability to receive low frequency, low voltage signals • Single control path required • Lower output noise CONS • Active stage requires more power usage than passive equivalent

  20. Conclusion • Researched envelope detector employing passive control path proves to be inadequate when utilized in hearing aids and cochlear devices • Control path implementing active stage demonstrates acceptable performance for low voltage, low frequency signal reception as required in Audio Sensory Medical (ASM) devices • Recommended future work – define an alternative implementation to the op-amp that provides equivalent performance at lower power consumption

  21. Followed Schedule

  22. References • [1] Alegre, J.P., Celma, S., Sanz, M.T., and Garcia del Pozo.: ‘Low-ripple fast-settling envelope detector’, Electronics Letters, 2006, 42, (18), pp. 1-2 • [2] Communication Systems Tutorial: Envelope Detection, Utah State University: http://images.google.ca/imgres?imgurl=http://www.engineering.usu.edu/classes/ece/5660/lab2/envdetpic.jpg&imgrefurl=http://www.engineering.usu.edu/classes/ece/5660/lab2/lab2.html&h=144&w=324&sz=7&hl=en&start=11&tbnid=Z7GdbY9TXA0qoM:&tbnh=50&tbnw=114&prev=/images%3Fq%3Denvelope%2Bdetector%2Bcircuit%26svnum%3D10%26hl%3Den%26lr%3D • [3] Advanced frequency division bat detector: http://images.google.ca/imgres?imgurl=http://bertrik.sikken.nl/bat/pix/envlop1.gif&imgrefurl=http://bertrik.sikken.nl/bat/advdiv.htm&h=108&w=269&sz=2&hl=en&start=6&tbnid=tGVJMzfqre9kUM:&tbnh=45&tbnw=113&prev=/images%3Fq%3Denvelope%2Bdetector%2Bcircuit%26svnum%3D10%26hl%3Den%26lr%3D • [4] RAMALINGAM, RAVI RAMALINGAM Choice of hearing aids. The HINDO Newspaper: http://www.hinduonnet.com/2001/08/12/stories/1312048d.htm

  23. Ευχαριστώ DMnvwd Dankie go raibh maith agaibh 谢谢！ ありがとう！ WAD MAHAD SAN TAHAY GADDA GUEY متشکرم Urakoze Asante

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