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A High Sensitivity Bioimpedance Detector B. B. Patil P. C. Pandey V. K. Pandey S. M. M. Naidu. National Conference on Virtual and Intelligent Instrumentation (NCVII -09), BITS Pilani, 13-14 Nov. 2009 ______________________________________________________________. IIT Bombay. - PowerPoint PPT Presentation
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A High Sensitivity Bioimpedance Detector
B. B. PatilP. C. PandeyV. K. PandeyS. M. M. Naidu
IIT Bombay
National Conference on Virtual and Intelligent Instrumentation (NCVII -09), BITS Pilani, 13-14 Nov. 2009______________________________________________________________
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Presentation Outline• Introduction• Bioimpedance Detector Circuit• Test Results• Conclusion
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• Introduction• Bioimpedance Detector Circuit• Test Results• Conclusion
Patil
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4/23<pcpandey [at] ee.iitb.ac.in>
Introduction (1/4)
Sensing of the Variation in the BioimpedanceNoninvasive technique for monitoring
♦ changes in the fluid volume
♦ underlying physiological events
Impedance Cardiography A noninvasive technique for monitoring stroke volume and obtaining diagnostic information on cardiovascular functioning by sensing the variation in the thoracic impedance during the cardiac cycle.
Sensing of the Thoracic ImpedanceA current ( 20 kHz – 1MHz, <5mA) passed through a pair of surface electrodes and the resulting amplitude modulated voltage sensed using the same or another pair of electrodes.
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ICG Instrumentation
Introduction (2/4)
Z(t) dZ/dt
Impedance Detector
ECG Extraction
Signal Acquisition & Processing
Current Source
Differenti-ator
ECG
Fig. 1 Block diagram of instrumentation for impedance cardiograph
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Bioimpedance Detection
♦ Detection of extremely low modulation index ( 0.2 – 2 %)♦ External noise suppression♦ Carrier ripple rejection
AM Detector Ckts ♦ Peak detector ♦ Precision rectifier det.♦ Synchronous det.♦ Slicing amplifier det. (Fourcin, 1979): high sensit., increased ripple♦ Synchronous S/H at carrier peak: very low ripple
Introduction (3/4)
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Proposed Technique
Features ♦ High sensitivity♦ Carrier ripple suppression without filtering♦ Noise reduction
Realization ♦ Slicing amplifier with sampling at the peaks of the sinusoidal excitation : high sensitivity, low ripple ♦ Summation of the signals obtained by sampling the +ve & -ve peaks : external noise reduction
Introduction (4/4)
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• Introduction
• Bioimpedance Detector Circuit• Test Results• Conclusion
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Demodulation ♦ Two channels of slicing amplifier with synch. S/H at the +ve and –ve peaks of the excitation ♦ Addition of the two outputs: suppression of noise & low freq. drift
Slicing Amplifier ♦ Realized using voltage clamp amplifier IC AD8037 (Greater of the V+ & VL inputs connected as the non-inverting input)
♦ Ckt config. and resistors selection: ♦ V+ > VL : Output diff. i/p ♦ V+ < VL : Zero output
Sample-and-hold (IC HA5351) Sampled near the excitation peak & held for ripple suppression
Bioimpedance Detector Ckt (1/6)
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10/23<pcpandey [at] ee.iitb.ac.in>
72
3
–
+
R3
2
3 6
0.1µ
+
–
4.7k
R422
R5100
10µ
0.1µ 10µ
VCC+
VCC-
4
78
5R622
R74.7k
VCC+
VCC-
4
6
VO1
VI
IC2
IC3
VX VY
CS
SDI
SCKL
IC1 MCP4150
1
3
2
A
W
B
5
6
7
GND84
0.1µVDD
VCC+
C7
0.1µ
IC4
8–
+
VCC+
VCC-
3
4
6
0.1µ
C6
1
5
7
S/H
VO2
C2
0.1µ
0.1µ
C3
Demodulator using Slicing Amplifier & S/H
IC3 : AD8037 voltage clamp amp., IC4: HA5351 S/H
Bioimpedance Detector Ckt (2/6)
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Slicing
Amplifier
Waveforms
Vo1: slicing amp o/p
Vo2: S/H o/p
VY
VO1
VIN
VO2
Time
S/H
Bioimpedance Detector Ckt (3/6)
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AM demod. of the sensed voltage using
two channels of slicing amplifier with sync. S/H
Bioimpedance Detector
Bioimpedance Detector Ckt (4/6)
V-to-I Conv.
VO
Program. Source
VΦ
E1
E2
I1
I2
+
+
Current source
CH1
CH2
Vref
VS
ΦAmp. Control
Diff. Amp. S/H Ckt
Slicing Amp.
Inverting Amp.
Slicing Amp.
S/H Ckt
Mono-stable
Freq.
Atten.
Mono-stable
Control
Atten.
Ref. Control
VR
V4
V3
VSH2
VSH1
V1
V2
V6
V5
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Sinusoidal Excitation & S/H Pulse Generation Two direct digital synthesizer (DDS) chips (AD 9834)
♦ DDS-1: Sinusoidal o/p for current excitation
♦ DDS-2: Square o/p with settable phase shift for S/H pulses
Circuit Features Microcontroller based digital control of
♦ Excitation current level using a digital pot.
♦ Excitation frequency
♦ Slicing amplifier ref. level, using a digital pot.
♦ Phase shift between the two DDS outputs for precise alignment of hold edge of S/H pulses to the +ve and –ve peaks of the excitation
Bioimpedance Detector Ckt (5/6)
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Detector Ckt Waveforms
Vs: DDS-1 o/p (exc.)
VΦ: DDS-2 o/p (phase shifted w.r.t. Vs)
V3 & V4: slicing amp. Outputs
V5 & V6: S/H outputs
VSH1 & VSH2: sampling pulses
Bioimpedance Detector Ckt (6/6)
V3
Vs
V4
VSH1
VSH2
VΦ
Time
V6
V5
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15/23<pcpandey [at] ee.iitb.ac.in>
• Introduction• Bioimpedance Detector Circuit
• Test Results• Conclusion
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Impedance Detector Performance Parameters♦ Range of basal resistance
♦ Sensitivity (ΔVo / ΔR)
♦ Frequency response
Thorax Simulator for Testing
the Bioimpedance Detector♦ Basal resistance (settable: 20 200 )
♦ Periodic resistance variation (settable: 0.1 1.2 %)♦ µC & digital pot.: settable ΔR, F, waveshape
Test results (1/5)
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IC4B
IC4C
R24 R21
R23 R20
IC8 CD4066
1
2
13
7
P3.3
Rpot
CS
SDI
SCKL
CS
SDI
SCKL
A
C
E
C
A
D
IC2 MCP4150
IC3 MCP4150
1
3
2
2
3
1
A
W
B
5
6
7
5
6
7
A
W
B
VCC+
VCC-
Ex1
Ex2
9
10
8
6
5
GND84
0.1µ VSS
14
7
A
B
EN
VDD
+
–
–
+
33K
15K15K
33K 5K
0.1µVDD
0.1µVDD
4 8GND
Ex
R3
R2
R4 R6
R8
R9
R7
R5
I1
I2
E2
R14 R15
JP5 JP6
R13
EpR16
E1
2.2K
2.2K
2.2K
100
100220
220
220
220
15033
3.3K
CS
SDI
SCKL
B
A
C
IC5 MCP4150
1
3
26
7
5
A
W
B
R103.3K
GND84
0.1µVDD
Thorax
Simulator
Ckt
I1 & I2: current injection
E1 & E2: voltage sensing
♦ Variation in the thorax impedance
♦ DM & CM voltages (ECG)
♦ Sync. output
Test results (2/5)
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P2.6
P2.5P2.4P3.4P3.5
XTL1
VCC27
28
26
25
40
18 19
31
VSS
VCC
RSR/W
E
DB4
DB5
DB6
DB7 14
32
1
12MHz
C2 C3
33p
C14
10kR
SW1 SW2
C1
38
EA
P1.0
P2.7
GND P0.0P0.1
3920
8.2kRST
9
1415
VEE
4.7 k
13
1211
64
XTL2
4.7 k
P1.1P1.2P1.3P1.4
Vss
IC1AT89S52
5
R1
R19
R22
1
2345
ABCDE
VCC+
In Out
Com
1
2
3
C60.1µ
R114.7M
R12
4.7MC70.1µ
C80.1µ
AGnd
2
3
1
IC77805
VCC-
In Out
ComS1
C9
0.1µ
1
C5
0.1µ2
3IC6
7805
C41µ
9V
C16
0.1µ
33p
VSS
VSSVSS
VSS
VSS
P3.6P3.7
1
2Sync. Test Outputs
Digi. Pot. Control signals
IC4
+
–
IC4ALM324
VDD
VDD
VDD
4
11
10µ
0.1µ
VSS
VSS
C3
LCD1
VDD
P2.6
P2.5P2.4
P3.4P3.5
XTL1
VCC27
28
26
25
40
18 19
31
VSS
VCC
RSR/W
E
DB4
DB5
DB6
DB7 14
3
2
1
12MHz
C2 C3
33p
C14
10kR
SW1 SW2
C1
38
EA
P1.0
P2.7
GND P0.0P0.1
3920
8.2k
RST9
14
15
VEE
4.7 k
13
1211
64
XTL2
4.7 k
P1.1P1.2P1.3P1.4
Vss
IC1AT89S52
5
R1
R19
R22
1
2345
ABCDE
VCC+
In Out
Com
1
2
3
C60.1µ
R114.7M
R12
4.7MC70.1µ
C80.1µ
AGnd
2
3
1
IC77805
VCC-
In Out
ComS1
C9
0.1µ
1
C5
0.1µ2
3IC6
7805
C41µ
9V
C16
0.1µ
33p
VSS
VSSVSS
VSS
VSS
P3.6P3.7
1
2Sync. Test Outputs
Digi. Pot. Control signals
IC4
+
–
IC4ALM324
VDD
VDD
VDD
4
11
10µ
0.1µ
VSS
VSS
C3
LCD1
VDD
Microcontroller and Power Supply Ckt of the Thorax Simulator
Test results (3/5)
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Testing Using the Thorax Simulator
♦ Excitation: 1 mA rms, 100 kHz
♦ Thorax Simulator
F: 1 - 250 Hz
Ro = 196 ΔR / Ro = 0.1 to 1.2%
Test results (4/5)
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Sync. & Det.
Output
Waveforms
F = 8 Hz, Ro = 196 .
Resistance variation
ΔR / Ro:
(a) 1.2 % sinusoidal
(b) 0.6 % sinusoidal
(c) 1.2 % square
(d) 0.6 % square
(a)
(b)
(c)
(d)
Synch
Vo
Vo
Vo
Vo
Synch
Synch
Synch
Test results (5/5)
Time scale: 40 ms/div, Ch1: 5 V/div, Ch2: 500 mV/div.
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• Introduction• Bioimpedance Detector Circuit• Test Results
• Conclusion
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22/23<pcpandey [at] ee.iitb.ac.in>
A bioimpedance detector for ICG instrumentation
♦ Slicing amplifier for AM demod. with mod. index < 2%
♦ Sync. sampling for ripple rejection without lowpass filtering
the output
♦ Digital control of
▫ Exc. parameters (Frequency, current level)
▫ Demod. parameters (Slicing amp. ref., Φ-shift for sync. S/H)
Ckt operation verified using a thorax simulator
for detecting ΔR / Ro well below 2%, sinusoidal & square wave variations with freq. of 1 - 250 Hz.
Conclusion (1/1)
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23/23<pcpandey [at] ee.iitb.ac.in>
THANK YOU
Patil
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B. B. Patil, P. C. Pandey, V. K. Pandey, and S. M. M. Naidu, “A high sensitivity bioimpedance detector”, Proc. National Conference on Virtual and Intelligent Instrumentation (NCVII-09), BITS Pilani, 13-14 Nov. 2009.
Abstract: A bioimpedance detector is developed as part of instrumentation for impedance cardiography. It uses slicing amplifier for increasing the sensitivity for the impedance variation and synchronous sampling for a ripple-free output. The circuit provides digital control of excitation current and frequency used for the measurement. Its operation has been verified using a thorax simulator for detecting the impedance variations well below 2%.
Prof. P. C. Pandey Address: EE Dept. / IIT Bombay / Powai Mumbai 400 076 / India / E-mail: pcpandey [at] iitb.ac.in
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References
1. J. Nyboer, Electrical Impedance Plethysmography. 2nd ed., Springfield, Massachusetts: Charles C. Thomas, 1970.
2. L. E. Baker, "Principles of impedance technique", IEEE Eng. Med. Biol. Mag., vol. 8, pp. 11 - 15, 1989.
3. M. Min, T. Parve, A. Ronk, P. Annus, and T. Paavle, "Synchronous sampling and demodulation in an instrument for multifrequency bioimpedance measurement", IEEE Trans. Inst. Measurements, vol. 56, pp. 1365 - 1372, 2007.
4. W. G. Kubicek, F. J. Kottke, and M. U. Ramos, "The Minnesota impedance cardiograph – theory and applications", Biomed. Eng., vol. 9, pp. 410 - 416, 1974.
5. M. Qu, Y. Zhang, J. G. Webster, and W. J. Tompkins, "Motion artifact from spot and band electrodes during impedance cardiography", IEEE Trans. Biomed. Eng., vol. 33, pp. 1029 - 1036, 1986.
6. J. Fortin, W. Habenbacher, and A. Heller, "Non-invasive beat-to-beat cardiac output monitoring by an improved method of transthoracic bioimpedance measurement", Comp. Bio. Med., vol. 36, pp. 1185 - 1203, 2006.
7. J. N. Sarvaiya, P. C. Pandey, and V. K. Pandey, “An impedance detector for glottography”, IETE J. Research, vol 55, no. 3, pp 100-105, 2009.
8. A. J. Fourcin, "Apparatus for speech pattern derivation", U. S. Patent No. 4,139,732, Feb. 13, 1979.
9. B. B. Patil, "Instrumentation for impedance cardiography", M.Tech. Dissertation, Biomedical Engineering, Indian Institute of Technology Bombay, 2009.
10. V. K. Pandey, P. C. Pandey, and J. N. Sarvaiya, "Impedance simulator for testing of instruments for bioimpedance sensing", IETE J. Research, vol. 54, no. 3, pp. 203 - 207, 2008.
11. B. B. Patil, V. K. Pandey, and P. C. Pandey, "A microcontroller based thorax simulator for testing and calibration of impedance cardiographs", in Proc. Int. Symp. Emerging Areas in Biotechnology & Bioengineering (ISEABB), Mumbai, India, 2009, pp. 122-125.