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Background
1
Preliminary Report on the Use of Equalization Filters to Derive High CMRR Hongfang (Linda) Xia Advisor: Professor Edward A Clancy Department of Electrical and Computer Engineering Worcester Polytechnic Institute 1. Background The conventional EMG signal is electrical activity of muscle, and is detected by the electrodes. High CMRR can be achieved via the use of flexible array electrodes, but it is expensive and inflexible. Bipola r +1 -1 Linear Double Difference (LDD ) +1 +1 -2 +1 +1 -4 +1 +1 Normal Double Difference (NDD ) Also, it can be achieved via the use of software channel equalization. Electrode Inputs Equalized Channels e 1 Analog Signal Conditionin g Circuit #1 A/D Linear Equalizatio n Filter #1 EMG 1 e 2 Analog Signal Conditionin g Circuit #2 A/D Linear Equalizatio n Filter #2 EMG 2 Hardware Software 2. Research Goal Comparing using the hardware to achieve high CMRR, the software channel equalization is cheaper and more flexible, so the goal here is to construct software equalization filters to correct channel imperfections due to the tolerance of hardware components. Hardware characteristic • Excite input with chirp form (0-2kHz): 2 0 cos t w t w k t x Initial frequency ½ sweep rate Initial phase • Measure channel output y(t): • Compare vs. an ideal channel: jw jw jw jw i jw jw i jw jw e X e Y e Ideal e E or e Ideal e E e X e Y Equalizer Issues: • Chirp contains all frequencies. • For high CMRR (e.g., 80dB, bipolar): - Need accuracy > 1 part in 10,000! - Noise is a big problem!!!! - Need very accuracy algorithm. • Noise commonly ≈ 0.5% MVC Limits. • Bipolar CMRR to ≈ 45 dB (Very Poor). • Equalization requires low noise!! • Can’t eliminate all hardware noise FILTER • Chirp frequency is time-varying. 3. Solutions: Solution 1: Modulate with another chirp, then LTI filter. Solution 2: Time–varying, linear, bandpass FIR filter (LTV). • FIR bandpass filter: Center frequency tracks input chirp The equalization filter test modulation: e I N Analog Signal Conditionin g Circuit #1 A/D Linear Equalizatio n Filter #1 EMG 1 Analog Signal Conditionin g Circuit #2 A/D Linear Equalizatio n Filter #2 EMG 2 S e OUT + - CMRR = 20log 10 (2|e IN | / |e OUT |) 4. The results: For solution 1: 2. Equalizer filter Zoom view 3. LPF length simulation INPUT = Chirp only (0- 1kHz) No Equalization Equalizati on Equalizatio n; Frequency Smoothing For solution 2: INPUT = Noise only INPUT = Noise only INPUT = Chirp only (0- 1kHz) No Equalization Equalizatio n Equalizatio n; Frequency Smoothing x(t ) Mix : Cosine chirp Low Pass Filter Extract Magnitude , Phase Informati on M(t) Φ(t) Mix : Sine chirp Low Pass Filter 1. 60Hz input, time domain 5. Conclusion and future work Conclusion: Modulating with another chirp and using a low pass LTI filter can achieve high CMRR (above ~80dB). Future work: Can cascade LTV filter and modulator. Use a signal with longer duration.
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Linear Double Difference (LDD ). Normal Double Difference (NDD ). Bipolar. +1. +1. +1. +1. +1. -4. -1. -2. +1. +1. Electrode Inputs. Equalized Channels. Zoom view. Linear Equalization Filter #1. EMG 1. Analog Signal Conditioning Circuit #1. A/D. +. S. e OUT. e IN. -. - PowerPoint PPT Presentation
Transcript of Background
Preliminary Report on the Use of Equalization Filters to Derive High CMRR Hongfang (Linda) Xia Advisor: Professor Edward A Clancy
Department of Electrical and Computer Engineering Worcester Polytechnic Institute
1. Background
The conventional EMG signal is electrical activity of muscle, and is detected by the electrodes.
High CMRR can be achieved via the use of flexible array electrodes, but it is expensive and inflexible.
Bipolar
+1
-1
Linear DoubleDifference (LDD)
+1
+1
-2
+1
+1
-4 +1+1
Normal DoubleDifference (NDD)
Also, it can be achieved via the use of software channel equalization.
Ele
ctro
de
Inp
uts
Eq
ualized
Ch
ann
els
e1
Analog Signal Conditioning
Circuit #1A/D
Linear Equalization
Filter #1EMG
1
e2
Analog Signal Conditioning
Circuit #2A/D
Linear Equalization
Filter #2EMG
2
Hardware Software
2. Research Goal
Comparing using the hardware to achieve high CMRR, the software channel equalization is cheaper and more flexible, so the goal here is to construct software equalization filters to correct channel imperfections due to the tolerance of hardware components.
Hardware characteristic • Excite input with chirp form (0-2kHz):
20cos twtwktx
Initial frequency
½ sweep rate
Initialphase
• Measure channel output y(t):• Compare vs. an ideal channel:
jw
jwjwjw
i
jwjwijw
jw
eXeY
eIdealeE
or
eIdealeEeXeY
Equalizer
Issues:• Chirp contains all frequencies.• For high CMRR (e.g., 80dB, bipolar):
- Need accuracy > 1 part in 10,000! - Noise is a big problem!!!! - Need very accuracy algorithm.
• Noise commonly ≈ 0.5% MVC Limits.• Bipolar CMRR to ≈ 45 dB (Very Poor).• Equalization requires low noise!!• Can’t eliminate all hardware noise FILTER• Chirp frequency is time-varying.
3. Solutions:
Solution 1: Modulate with another chirp, then LTI filter.
Solution 2: Time–varying, linear, bandpass FIR filter (LTV).• FIR bandpass filter: Center frequency tracks input chirp
The equalization filter test modulation:
eIN
Analog Signal Conditioning
Circuit #1A/D
Linear Equalization
Filter #1
EMG
1
Analog Signal Conditioning
Circuit #2A/D
Linear Equalization
Filter #2 EMG
2
S eOUT
+
-
CMRR = 20log10(2|eIN| / |eOUT|)
4. The results:For solution 1:
2. Equalizer filter
Zoom view
3. LPF length simulation
INPUT = Chirp only (0-1kHz)
No Equalization
Equalization
Equalization; Frequency Smoothing
For solution 2:
INPUT = Noise only
INPUT = Noise only
INPUT = Chirp only (0-1kHz)
No Equalization
Equalization
Equalization; Frequency Smoothing
x(t)
Mix:Cosine chirp
Low Pass Filter
ExtractMagnitude,PhaseInformation
M(t)
Φ(t)Mix:
Sine chirpLow Pass
Filter
1. 60Hz input, time domain
5. Conclusion and future workConclusion:
Modulating with another chirp and using a low pass LTI
filter can achieve high CMRR (above ~80dB).Future work:
Can cascade LTV filter and modulator.Use a signal with longer duration.…
