IIT Bombay

25
A High Sensitivity Bioimpedance Detector B. B. Patil P. C. Pandey V. K. Pandey S. M. M. Naidu IIT Bombay National Conference on Virtual and Intelligent Instrumentation (NCVII -09), BITS Pilani, 13-14 Nov. 2009 ______________________________________________________________

description

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

Transcript of IIT Bombay

Page 1: IIT Bombay

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

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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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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

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5

6

7

GND84

0.1µVDD

VCC+

C7

0.1µ

IC4

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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

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

Time

V6

V5

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• 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

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CS

SDI

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A

C

E

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IC2 MCP4150

IC3 MCP4150

1

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B

5

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B

VCC+

VCC-

Ex1

Ex2

9

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GND84

0.1µ VSS

14

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EN

VDD

+

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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

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R19

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1

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VCC+

In Out

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In Out

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33p

VSS

VSSVSS

VSS

VSS

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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

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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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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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THANK YOU

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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.

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