Biopotential Amplifiers. Hsiao-Lung Chan, Ph.D. Dept Electrical Engineering Chang Gung University, Taiwan

Transcription

1 Biopotential Ampliiers Hsiao-Lung Chan, Ph.D. Dept Electrical Engineering Chang Gung University, Taiwan

2 Operational ampliier Practical Ideal Biopotential ampliiers

3 Ideal vs. practical OP amp Biopotential ampliiers 3

4 Dierential- and common-mode inputs V o = A d V d + A cm V cm where A d = A ol open-loop gain Ideally, A d =, A cm = CM = log A d A cm = or, = A d A cm Biopotential ampliiers 4

5 Inverting ampliier V o V i = - F I Ideally, in = I and out = Biopotential ampliiers 5

6 Inverting ampliier Biopotential ampliiers 6

7 Noninverting ampliier V o V i = + Ideally, Z i = and Z o = Biopotential ampliiers 7

8 Dierential Ampliier id V V Vo id = V o 4 V V 3 4 V V i 4 3 Biopotential ampliiers 8

9 Dierential Ampliier: Imbalance Eect Vcm Vdm Vdm -ε - + Vo V o V o V V dm cm V V dm cm A dm V dm A cm V cm A dm, A cm CM log A A dm cm log Biopotential ampliiers 9

10 Instrumental Ampliier IA Three OP-AMP IA ealization V + id id = V g ' ' - + V o Vo ' V V g Biopotential ampliiers

11 Analog ilters S. Franco, Design with Operational Ampliiers and Analog Integrated Circuits, Second Edition, 998. Biopotential ampliiers

12 Biopotential ampliiers First-order lowpass active ilter j H j H sc V V s H in O H and C where

13 Biopotential ampliiers 3 First-order lowpass ilter Vi + - Vo C j H j H sc V V s H i O H and C where

14 Biopotential ampliiers 4 First-order highpass ilter H and C where sc sc V V s H in O j j H j H

15 Biopotential ampliiers 5 First-order highpass ilter j j H j H sc sc V V s H i O H and C where Vo - Vi + C

16 First-order bandpass active ilter C Vi C - + Vo log H db - dbdecade H s V V O i sc sc sc H j [ j j ][ j ] where C and C Biopotential ampliiers 6

17 Instrumental ampliier with irst-order highpass ilter V + - ' - Vo V g - + ' + Vre Integrator eedback C - + V o s G V V s C Biopotential ampliiers 7

18 Biopotential ampliiers 8 Second-order ilters s Q s n s n s n s H Low-pass response n = n =, n = ω s Q s s H Q j j H High-pass response n =, n = n = s Q s s s H Q j j H

19 Second-order ilters Low-pass response High-pass response S. Franco, Design with Operational Ampliiers and Analog Integrated Circuits, Second Edition, 998. Biopotential ampliiers 9

20 Second-order Sallen-Key lowpass ilter nc - Vi m + Vo C H j j Q where mnc and Q mn m Biopotential ampliiers

21 Second-order Sallen-Key highpass ilter Vi C nc - m + Vo H j j Q where mnc and Q mn n Biopotential ampliiers

22 Biopotential ampliiers Second-order ilters 3 Band-pass response n =, n =ω Q, n = s Q s s Q s H Q j Q j j H 4 Band-reject response n =, n =, n =ω s Q s s s H Q j j H

23 Second-order band-reject ilters S. Franco, Design with Operational Ampliiers and Analog Integrated Circuits, Second Edition, 998. Biopotential ampliiers 3

24 Biopotential ampliiers 4 Twin-T notch ilter Vo Vi C C C Q j j H 4, Q and C where

25 Twin-T notch ilter Biopotential ampliiers 5

26 Twin-T notch ilter Cont. From WJ. Tompkins, JG. Webster. Design o Microcomputer-Based Medical Instrumentation, Prentice-Hall, 98. Biopotential ampliiers 6

27 Dipole ield o heart when is maximum Biopotential ampliiers 7

28 Electrocardiogram ECG measurements I II + III = Biopotential ampliiers 8

29 Augmented Leads Biopotential ampliiers 9

30 Augmented Leads Biopotential ampliiers 3

31 elation o dierent-lead ECG Einthoven triangle From WJ Tompkins, Biomedical Digital Signal Processing, Prentice-Hall, 993. Biopotential ampliiers 3

32 elation o dierent-lead ECG Cont. From WJ Tompkins, Biomedical Digital Signal Processing, Prentice-Hall, 993. Biopotential ampliiers 3

33 Wilson s central terminal Biopotential ampliiers 33

34 Chest leads Biopotential ampliiers 34

35 ECG measurement using chest leads From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998. Biopotential ampliiers 35

36 ECG at chest leads Biopotential ampliiers 36

37 -Lead ECG Precordial leads: V -V 6 Einthoven leads: I, II & III Goldberger augmented leads: V, V L & V F Biopotential ampliiers 37

38 Vectorcardiogram VCG Biopotential ampliiers 38

39 ECG ampliier + C 4, MΩ, kω 3, 4.5kΩ, 4.5kΩ g, 8.5kΩ AD6 G=7.3 Hz Highpass Filter G = Analog Device Application eerence Instrumentation ampliier Drievn-right-leg circuit 49.4k Gain educe common-mode voltage g limits the current to patient. C maintains stability o the circuit. Biopotential ampliiers 39

40 Intererences in ECG Power-line intererence Electromyographic intererence Biopotential ampliiers 4

41 Power intererence in ECG measurement Power line, V, 56 Hz C b i b C C C 3 i d3 Zs i d - SShielding Zs i d g Instrumental Ampliier Zcm Driven-right leg circuit + Biopotential ampliiers 4

42 Common-mode voltage by power-line intererence v i cm db Z G Typical value v cm =. μa 5 kω = mv Biopotential ampliiers 4

43 Impedance mismatch in ECG measurement Degradation o CM due to nonzero source resistance and parasitic capacitance s C V g - I A Vo Vcm - + s C V + V V due to s C s C Biopotential ampliiers 43

44 Driven-right-leg circuit V cm V cm s s + - ' cm V cm g a ' a Biopotential ampliiers 44

45 Driven-right-leg circuit cont. Vcm id cm Vcm + - a Vo + - Vcm V a V a o V V o cm cm a V cm V cm i d id cm cm a Biopotential ampliiers 45

46 Driven-right-leg circuit cont. <EX> i d =. μa. A worst-case electrode resistance cm = kω, a and are selected as 5 kω and 5 MΩ respectively. Find V cm. V cm k.a 5M 5k 5V I no right-leg-driven circuit Vcm id cm k.a mv Biopotential ampliiers 46

47 ECG Ampliier: One-Lead ECG Front-End From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998. Biopotential ampliiers 47

48 Six-Leads ECG Front-End Five Patient Electrodes Voltage at WCT is equal to dc and 6 Hz common-mode voltage L Drive: Inversion o common-mode intererence From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998.

49 Magnetic-ield pickup in ECG measurement Biopotential ampliiers 49

50 Isolation ampliier Basic architecture Equivalent 8 ~ Ω Input Ampliier Modulator Demodulator Output Ampliier Isolation barrier, can be magnetic transormer, optical, capacitive Biopotential ampliiers 5

51 Isolation ampliier cont. Isolation mode rejection ratio IM V IN Input Common - + V OUT Output Common V IM V OUT V IN where IM VIM Gain IM log IM V IN Gain VIM IM Gain Biopotential ampliiers 5

52 Isolation ampliier cont. IM v.s. Frequency IM o ISO, Burr-Brown Corporation Biopotential ampliiers 5

53 Isolation ampliier vs. instrument ampliier Biopotential ampliiers 53

54 IM vs. CM V OUT V IN VCM CM VIM Gain IM IM ISO >> CM IA > CM ISO ISO: Isolation ampliier IA: Instrumental ampliier Biopotential ampliiers 54

55 Transormer-coupled isolation ampliier Biopotential ampliiers 55

56 Transormer-coupled isolation ampliier ISO, Burr-Brown Corporation Biopotential ampliiers 56

57 Optical-coupled isolation ampliier Biopotential ampliiers 57

58 Optical-coupled isolation ampliier ISO, Burr-Brown Corporation Biopotential ampliiers 58

59 Capacitive isolation ampliier ISO, Burr-Brown Corporation Biopotential ampliiers 59

60 Analog channel-to-channel isolation From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998. Biopotential ampliiers 6

61 Analog isolation From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998. Biopotential ampliiers 6

62 Digital isolation From JJ Carr, Introduction to Biomedical Equipment Technology, Prentice-Hall, 998. Biopotential ampliiers 6

63 Digitization trend in physiological monitoring Biopotential ampliiers 63

64 Multichannel EEG recodeings: Neuroscan TM Biopotential ampliiers 64

65 Monopolar measurements Biopotential ampliiers 65

66 Bipolar measuremesnts Biopotential ampliiers 66

67 Pasteless biopotential electrodes Monitoring o pilots alertness Detection o gravitationally induced loss o consciousness caused by extreme g-orces during sharp high-speed light Brain state by EEG Muscle atigue and eye blinks and eyeball movement by EMG Skin preparation to decrease skin-electrode impedance is unacceptable or routine prelight procedures Biopotential ampliiers 67

68 Capacitive active electrode array to record rontal EEG signals Dry electrode Biopotential ampliiers 68

69 eerence JG. Webster, Medical Instrumentation, application and design, 3rd, Houghton Milin,. JJ.Carr, JM.Brown, Introduction to Biomedical Equipment Technology, 4nd Edition, Prentice-Hall,. S. Franco, Design with Operational Ampliiers and Analog Integrated Circuits, Second Edition, 998. D. Prutchi and M. Norris, Design and Development o Medical Electronic Instrumentation: A Practical Perspective o the Design, Construction, and Test o Medical Devices, John Wiley & Sons, 4. 生物醫學工程導論, 滄海書局,8. Biopotential ampliiers 69