Envelope Detector Control Path Enhancements for Low-Power Medical
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 Team Members Jason Chan Wai
Brian Lawrence Valerie Proulx Conventional Envelope Detector Envelope detectors are used to obtain the envelope of an AM modulated signal.
Relevant Research Envelope Detector Proposed in Research Paper  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. 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
Application: Hearing Aids and Cochlear Devices Original Control Path Control path proposed in referenced research paper 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 Simulation
Simulation was performed on researched control path using PSpice Simulation Results 1 Output when input signal is 3V (large) Circuit functions as intended Simulation Results 2
At small voltages (300mV) the proposed control path does not function properly! 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) Primary Goal Enhance the circuits 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 Optimized Control Path
Proposed design utilizes active components in the input network! Simulation Results 1 Output of proposed control path with 300mV, 2kHz input signal
Simulation Results 2 Output of proposed control path with 300mV 500Hz input signal 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! 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 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
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 Followed Schedule
References  Alegre, J.P., Celma, S., Sanz, M.T., and Garcia del Pozo.: Low-ripple fastsettling envelope detector, Electronics Letters, 2006, 42, (18), pp. 1-2  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:&tb nh=50&tbnw=114&prev=/images%3Fq%3Denvelope%2Bdetector%2Bcircuit %26svnum%3D10%26hl%3Den%26lr%3D  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:&tbn h=45&tbnw=113&prev=/images%3Fq%3Denvelope%2Bdetector%2Bcircuit
%26svnum%3D10%26hl%3Den%26lr%3D  RAMALINGAM, RAVI RAMALINGAM Choice of hearing aids. The HINDO Newspaper: http://www.hinduonnet.com/2001/08/12/stories/1312048d.htm
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