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
  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)

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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

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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 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!

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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

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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

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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?imgurlhttp//www.e
  ngineering.usu.edu/classes/ece/5660/lab2/envdetpic
  .jpgimgrefurlhttp//www.engineering.usu.edu/clas
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  start11tbnidZ7GdbY9TXA0qoMtbnh50tbnw114p
  rev/images3Fq3Denvelope2Bdetector2Bcircuit26
  svnum3D1026hl3Den26lr3D
• 3 Advanced frequency division bat detector
  http//images.google.ca/imgres?imgurlhttp//bertr
  ik.sikken.nl/bat/pix/envlop1.gifimgrefurlhttp//
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• 4 RAMALINGAM, RAVI RAMALINGAM Choice of
  hearing aids. The HINDO Newspaper
  http//www.hinduonnet.com/2001/08/12/stories/13120
  48d.htm

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DMnvwd
Dankie
go raibh maith agaibh
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WAD MAHAD SAN TAHAY
GADDA GUEY
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Urakoze
Asante
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