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
 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 fastsettling 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=Z7GdbY9
TXA0qoM:&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&s
tart=6&tbnid=tGVJMzfqre9kUM:&tbnh=45&tbnw=113&prev=/images%3Fq%3De
nvelope%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
谢谢！
ありがとう！
‫متشکرم‬