J. Chan-Wai, B. Lawrence, V. Proulx 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 [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.

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 Secondary Goals 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

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 [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

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