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 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)

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

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 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!

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

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

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

متشک رم

谢谢！ありがとう！