Envelope Detector Control Path Enhancements for Low-Power Medical Applications
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Transcript of Envelope Detector Control Path Enhancements for Low-Power Medical Applications
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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
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Team Members
Jason Chan Wai
Brian Lawrence
Valerie Proulx
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Conventional Envelope Detector
• Envelope detectors are used to obtain the envelope of an AM modulated signal.
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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.
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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
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Application: Hearing Aids and Cochlear Devices
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Original Control Path
Control path proposed in referenced research paper
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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
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Simulation
Simulation was performed on researched control path using PSpice
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Simulation Results 1
Output when input signal is 3V (large) Circuit functions as intended
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Simulation Results 2
At small voltages (300mV) the proposed control path does not function properly!
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Simulation Results Input signal not strong enough to drive
MOSFET invertersTherefore, 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)
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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 GoalsMinimize output noiseEliminate the need for a second control
path
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Optimized Control Path
Proposed design utilizes active components in the input network!
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Simulation Results 1
Output of proposed control path with 300mV, 2kHz input signal
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Simulation Results 2
Output of proposed control path with 300mV 500Hz input signal
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Simulation ResultsCapable 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!
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Analysis Comparison: Passive Circuit
Energy efficient Passive input network requires no power
Speed
PROS
CONS
Inability to receive low frequency, low voltage signals
Requires two control paths
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Analysis Comparison: Active Circuit
Ability to receive low frequency, low voltage signals
Single control path required Lower output noise
PROS
CONS
Active stage requires more power usage than passive equivalent
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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
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Followed Schedule
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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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متشک رم
谢谢!ありがとう!
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