Transcript Slide 1

National Conference on Virtual and Intelligent Instrumentation (NCVII -09),
BITS Pilani, 13-14 Nov. 2009
______________________________________________________________
A High Sensitivity
Bioimpedance Detector
B. B. Patil
P. C. Pandey
V. K. Pandey
S. M. M. Naidu
IIT Bombay
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Presentation Outline
•
•
•
•
Introduction
Bioimpedance Detector Circuit
Test Results
Conclusion
<pcpandey [at] ee.iitb.ac.in>
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
• Introduction
• Bioimpedance Detector Circuit
• Test Results
• Conclusion
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Introduction (1/4)
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Sensing of the Variation in the Bioimpedance
Noninvasive 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 Impedance
A 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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Introduction (2/4)
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
ICG Instrumentation
Impedance
Detector
Current
Source
ECG
Extraction
Differentiator
Z(t)
dZ/dt
ECG
Signal
Acquisition
& Processing
Fig. 1 Block diagram of instrumentation for impedance
cardiograph
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[at] ee.iitb.ac.in>
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Introduction (3/4)
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
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Introduction (4/4)
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
<pcpandey [at] ee.iitb.ac.in>
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
• Introduction
• Bioimpedance Detector Circuit
• Test Results
• Conclusion
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Bioimpedance Detector Ckt (1/6)
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
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Bioimpedance Detector Ckt (2/6)
Demodulator using Slicing Amplifier & S/H
S/H
VDD
VCC+
C1 0.1µ
R3
4.7k
VI
8 5
VSS 4
VCC+
GND
VCC
C3
A
1
CS
2 7 0.1µ
3
W6
–
SDI
6
IC2
3
2
SCKL
+ C2 VX
B
4
IC1
0.1µ
7
MCP4150
VCC-
R4
22
2
8
VCC+
C5 C6
0.1µ 10µ
5
VCC+
C6
8 6
– VH 7
VO1 – 0.1µ
IC3
3 VL 6
IC4
+ 4
4
1
+
5
C7
C4 C8
R6 R5
3
22 100 VY
0.1µ 10µ
7
0.1µ
VCCR7
VCC4.7k
VO2
IC3 : AD8037 voltage clamp amp., IC4: HA5351 S/H
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Bioimpedance Detector Ckt (3/6)
Slicing
Amplifier
Waveforms
Vo1: slicing amp o/p
Vo2: S/H o/p
VIN
VY
VO1
VO2
S/H
Time
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Bioimpedance Detector Ckt (4/6)
Bioimpedance
Detector
AM demod. of
the sensed
voltage using
two channels
of slicing
amplifier with
sync. S/H
Inverting
Amp.
Slicing
Amp.
V2
Ref.
Control
S/H Ckt
V6 +
V4
CH2
+
VO
VSH2
VR
Atten.
Vref
V3
E1
Diff. Amp.
V1
Slicing
Amp.
S/H Ckt
V5
E2
CH1
VΦ
Current source
Monostable
I1
V-to-I
Conv.
Monostable
VS
Amp.
Control
<pcpandey [at] ee.iitb.ac.in>
Program.
Source
Atten.
I2
VSH1
Φ Freq.
Control
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Bioimpedance Detector Ckt (5/6)
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
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Bioimpedance Detector Ckt (6/6)
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Vs
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
V3
V5
V4
V6
VSH1
VSH2
VΦ
Time
<pcpandey [at] ee.iitb.ac.in>
14/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
• Introduction
• Bioimpedance Detector Circuit
• Test Results
• Conclusion
<pcpandey [at] ee.iitb.ac.in>
15/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Test results (1/5)
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
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C11
0.1µ
8
VCC
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
VSS 4
1 GND
E
CS
C
3
A
2
VDD
VCC+
–
A
10
W 6
SDI
B
C12
7
VCCVDD
0.1µ
Ex
5
8
VSS 4
VCC
GND
A
D
1
CS
W 6
C
3
SDI
A
2
VDD
C10
SCKL
–
7
+
7 VSS
EN
B
2
13
P3.3
IC8
CD4066
R10
3.3K
R3
100
C13
0.1µ
VSS 4
GND
1
B
CS
3
C
SDI
A 2
8
VCC
SCKL
7
IC5
MCP4150
R5
2.2K
<pcpandey [at] ee.iitb.ac.in>
Ex2
IC4B
VDD
R2
100
Thorax
Simulator
Ckt
1
A
VSS
R4
2.2K
5
14 VCC
0.1µ
B
7
IC3
MCP4150
IC4C
R21
33K
6
R20
15K
R23
15K
8
+
Rpot
5K
R24
33K
SCKL
IC2
MCP4150
Test results (2/5)
Ex1
9
5
R14
33
5
R15
150
R6
220
I1
R7
220
E1
A
W 6
B
JP5
R13
3.3K
JP6
R8
220
E2
R9
220
I2
R16
2.2K
Ep
I1 & I2: current
injection
E1 & E2: voltage
sensing
♦ Variation in the
thorax impedance
♦ DM & CM
voltages (ECG)
♦ Sync. output
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
VSS
LCD1 VSS
XTL1
18
Microcontroller and Power Supply CktC2
VSS 33p
of the Thorax Simulator
R1
Vss
8.2k
28
DB7 14
27
DB6 13
26
DB5 12
11
25
DB4
6
14
E
4
15
RS
5 VDD
R/W
VCC 2
VEE 3
VSS
1
C1
R
10k
P0.1 38
P0.0 39
VDD
C14
0.1µ VSS
S1
In
1µ
R22
4.7 k
SW2
33p VSS VSS
Out
Com
2
C4
9V
Sync. Test
Outputs
A
B Digi. Pot.
C Control
D signals
E
R19
4.7 k
IC6
7805 3
1
C9
XTL2
SW1
19
C3
12MHz
SW2
33p VSS VSS
12MHz
31
RST EA
40
P2.7
VCC
P2.6
IC1
P2.5
AT89S52
P2.4
1
P3.6
P3.4
2
P3.7
P3.5
1
P1.0
2
P1.1
3
P1.2
4
P1.3
P1.4 5
33p
R22
Test results
4.7 k (3/5)
XTL2
SW1
19
C3
VDD
10µ
9
20 GND
VSS
LCD1 VSS
XTL1
18
C2
VSS
P0.1
P0.0 39
20 GND
C5
0.1µ
0.1µ
VSS
VCC+
VDD
C16
0.1µ
IC7
1 7805 3
In Out
R11
4.7M
Com
2
R12
C6
0.1µ
2
IC4
3
4.7M
4
–
+
C7
0.1µ
1
11
IC4A
LM324
AGnd
C8
0.1µ
VCC-
VDD
<pcpandey [at] ee.iitb.ac.in> IC6
C9
1
7805 3
18/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Test results (4/5)
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%
<pcpandey [at] ee.iitb.ac.in>
19/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Test results (5/5)
Sync. & Det.
Output
Waveforms
(a)
Synch
Vo
Synch
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
(b)
(c)
Vo
Synch
Vo
Synch
(d)
Vo
Time scale: 40 ms/div, Ch1: 5 V/div, Ch2: 500 mV/div.
<pcpandey [at] ee.iitb.ac.in>
20/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
• Introduction
• Bioimpedance Detector Circuit
• Test Results
• Conclusion
<pcpandey [at] ee.iitb.ac.in>
21/23
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
Conclusion (1/1)
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.
<pcpandey [at] ee.iitb.ac.in>
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
THANK YOU
<pcpandey [at] ee.iitb.ac.in>
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Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
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, 1314 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
<pcpandey [at] ee.iitb.ac.in>
24/23
References
Patil et al.,’ A high sensitivity bioimpedance detector’, NCVII-09, Bitis Pilani, 13-14,Nov. 2009
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<pcpandey [at] ee.iitb.ac.in>
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