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A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Created by Dr. John Brown Prepared by Thomas Kuehl & Laura Groskie Texas Instruments – Tucson, AZ A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Presentation Outline • Biopotentials • Electrocardiogram, ECG • ECG characteristics • ECG electrodes and connections • The DAS/ECG board electrical functions and capabilities • AC and DC applications for the DAS/ECG board Biopotentials – Muscle Cell Muscle Reaction Resting State Biopotentials from Cells Electrical Signals From the Body EVERY CELL IS LIKE A LITTLE BATTERY Action Potential Voltage Reversed Potential +20mV HUMAN CELL Volts -70mV Na K Ca Cl + + ++ - Na K Ca Cl + + ++ - IONS 0V Depolarization -70mV Time Repolarization Resting Potential Biopotentials from Cells Electrical Signals From the Heart Cardiac Conduction System of the Heart ECG Waveforms English E C G, German E K G P, Q, R, S, T, U Left Heart Contracts Biggest Heart Muscle, R Wave Biopotentials from Cells - Electrodes IONS to ELECTRONS CONVERTER Electrodes Convert DIAGNOSTIC Ionic Signals From The Body MONITOR Into Electrical Signals in Wires ECG BP TEMP RESP Na+ K+ Cl - eee- Basic ECG electrode connections ECG is Measure of Heart as a Ionic or Electrical Generator Vin- INA Electrocardiogram Records Electrical Changes From Beating Heart (Left Arm) Vin = Vin+ - Vin- +2.5V dc ECG +2.5V dc Heart +2.5V +2.5V Vin+ INA (Right Arm) Electrodes Transduce Ions Into Electrons Elec +2.5V dc Common-mode Volt = (Vin+ + Vin-)/2 (Used for RL Drive) ECG Einthoven Triangle, 1907 3 Derived Leads I, II, III I = VLA-RL – VRA-RL 3 Body Electrodes II = VLL-RL – VRA-RL RL Ref Einthoven’s Law In electrocardiogram at any given instant the potential of any wave in Lead 2 is equal to the sum of the potentials in Lead I and III. III = VLL-RL – VLA-RL ECG Electrode – Electrical Model 0.5 to 10F 0.5 to 100k Electrode 0 to 500mV Skin 1k 1F Amplifier Body 55 10k 10kΩ 10^10 1k Ions to Electrons 1F Frequency Response BSEA Fo = 1 / 2 π RC Fo = 0.159 / (1k) (1F) = 159Hz ECG and Blood Pressure Waves 120 mm Hg Vessel Maximum Pressure Head Pressure signal has slower rise 30Hz BW, 25 harmonics 60 mm Hg Vessel Relaxation R 1 mV p-p TU P QS ECG signal has faster rise 100Hz BW, 70 harmonics Left Heart Relaxes Left Heart Contracts Actual ECG - Normal Chart Speed: 25mm / sec 24 mm, 0.96 sec 10 mm = 1 mV 1mV Cal R P Q T U S 10 mm, 1 mVp-p = BW 10mm = 0.4sec BASELINE or dc DRIFT Charging Time Constant of High Pass Filter and Changing Electrode Half-Cell Potential 24 mm x 1 sec / 25mm = 0.96 sec / beat => 1 / 0.96 sec = 1.04 bps 62 bpm at rest ECG Irregular Tracings Due to Artifacts 60Hz Pick-Up Muscle Shaking Baseline dc Instability Baseline or dc Drift A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Can Also Be Used As Precision Low-Level Data Acquisition System Front-End “Mr. E. C. Gee” ECG Vin- INA (Left Arm) Demo Board About 1mVp-p Heart Vin+ INA (Right Arm) Meter 0 6 0 BPM Single +5V Supply VCM = (Vin+ + Vin-)/2 Common-mode volt Used for RL drive Flashing LED (Right Leg) John Brown, 12/5/2006 Beeping Speaker A Precision Low-Level DAS/ECG Cardiotachometer Demo Board ECG BP Vin- INA (Left Arm) Meter Finger 0.15 – 2.5mVp-p Heart INA & OPAs Vout Cardiotach Circuit 0 BPM Vin+ INA (Right Arm) Vout, Overall Non-Inv Gain With Respect to Vin- INA (Right Leg) Common-mode Volt = (Vin+ + Vin-)/2 (Used for RL Drive) 6 LED Speaker 0 A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Uses 7 TI IC Types, 11 U’s Total Resistor Divider for Creating Differential Voltages on Demo Board Vin +5.2V to +24V dc TPS71550 LDO SubReg Ckt ECG BP RA 499k U7 +5V TLV3491 Auto Power Down Ckt 0.1uF Cb7,8 U8 +4.8V dc, <1mA to 15mA Vin- INA (Left Arm) RB 499k Vdiff Finger 0.15 – 2.5mVp-p Heart RC 499k DIP-8 Socket OPT101 U11 INA326 Vout OPA335s Vin+ INA 0.1uF Cb1,2,3,4,5,6 (Right Arm) Common-mode Volt = (Vin+ + Vin-)/2 (Used for RL Drive) 0 U4, U5, U6 0.1uF Cb9 OPA335 +2.5V out REF3025 U9 Uncommitted Op Amp LED Speaker U10 6 BPM OPA335s TLC556 U1, U2, U3 Vout, Overall Non-Inv Gain With Respect to Vin- INA Meter Cardiotach Circuit 0 A Precision Low-Level DAS/ECG Cardiotachometer Demo Board AC-coupled input stage LPF Normal-Mode dc Removed Normal-Mode dc R 480R 0.48V dc + 2mV p-p G = -480 - G=5 VinTiny Signal 1mVp in - +5V +2.5V Offset INA326 HPF Vin+ + +5 V OPA336, 335 + 4.9V max 4.8Vp-p max +2.5V ±2.4Vp IA Ref Pin 0.1V min 0.48V dc + 1mV p-p +2.5V Input Vcm GT = 2,400 + Integrator in Feedback Common = 0V, Vref = +2.5V +2.5V Offset A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Right leg drive circuit R1 390k Vin- 480mV max dc differential (Left Arm) R6 C1 40.2k100pF Vin = Vin+ - Vin- electrode potential +2.5V dc R4 1k 0.15 - 2.4mVp-p Heart 40.2k R7 R2 390k R51k +2.5V dc Vin+ (Right Arm) +5V 0.1uF 2 U2 +2.5V dc Common-mode Volt = (Vin+ + Vin-)/2 (Used for RL Drive) 8Cb2 1 A1 + 3 4 OPA2335 Self-Zero 2 1 8 3 - U1 INA326 + C3 22pF RG =R6+R7 Vcm + 47pF C4 390k 390k 7 R3 Vcm - 22pF C2 A2 R8 20k R9 + (high inverting gain) Right Leg Drive Amplifier 6 5 +2.5 A Precision Low-Level DAS/ECG Cardiotachometer Demo Board CMOS +5V SINGLE SUPPLY, INA326/7 & OPA2335 GT=1k,2k,4k,6k Stage2, Gain = 200 – 1,200 CLPFext xxxxuF xxxxHz Total Gain = 1,000 – 6,000 Low Pass Filters C7 0.0015uF 100Hz Stage1, Gain = 5 (noise roll off) C8 0.0047uF 35Hz V IA Out 0.1uF C9 0.01uF 17Hz Total Gain, V/V RGext Cb1 4.99k x1k R14 Centered +2.5V +5V 1M x2k R15 2.49k U1 +5V R18 2 7 x4k R16 1.24k 81 INA326, A3 x6k R17 0.825k = Vin x Rgain total 4 0.1uF 327 (shtdn) 6 Vout INA 3 + Cb3 R/R I/O High Pass Filters ac (dc restoration) Self-Zero Hold 5 4C5 R12 R13 R11 R10 316k 80.6k 3.01M 470pF 200k Vout 0.15V to 4.8Vp-p out 0.05Hz dc ac 7 C6 + A4 - 6 2Hz (quick restore) +2.5V Vdc OPA2335 pedestal Self-Zero ½ Vsup U3 C high pass = 1uF +2.5V dc 0.5Hz 5 Integrator (high pass filter): Time Constant = RC. Fo= 0.05Hz diagnostic mode, 0.5Hz monitor mode, and 2Hz quick restore ac-Coupled 20k +5V supply R19 20k R20 Electrically Isolated from Earth Gnd Power Supply Removes dc electrode offset +Vs -Vs Analog Circuit Common (isolated from earth ground) A Precision Low-Level DAS/ECG Cardiotachometer Demo Board DC restorer - removes electrode offset Vout frequency response U1 INA326 R1 Av Vout INA RG 80.4k R1 + + f-3dB = 1/(2πR2C2) Ref R2 C2 1uF R2 3M C1 470pF R1 200k +5 f 0.05Hz + 2.5v R4 20k +5 + U2 OPA365 +5 R3 20k A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Light Flash <30 to >240 Beats per Minute Sound Burst 6 0 BPM 0 BPM Meter Differentiator Pulse Peak Front-End ECG (Electro) Or BP (Optical) See Detailed Circuits Pulse Stretcher Burst Output Meter Differentiator Peak-to-Peak Detector One Shot Multivibrator Flasher Beep oscillator A Precision Low-Level DAS/ECG Cardiotachometer Demo Board +5V Single Supply Front-End <30 to >240 Beats per Minute Differentiator & Pos-Neg Burst Output Peak-to-Peak Detector One Shot fosc = 1.44 / C15 (R26 + 2R27) 1kHz +5V Pulse Stretcher 0V ECG +2.5V +2.5V Person TON = 1.1R25C13 = 0.1s Common Elec Vout C10 +5V 8 0.1F 2 0.1uF Cb4 3 R19 R20 20k +5V 20k 2 3 D2 6 IN4148 7 5 1 D1 R25 1M R22 5 4 IN4148 OPA2335 2M C11 3.01M 0.1F 4 2 0.1F C13 ½ TLC556 Dual Timer 6 Trig 7 Vdcpedestal = +2.5V = ½ Vsup 28k R27 61.9k 0.01F C15 5 U6 7 Clean Triggering 6 5 R26 100msec 100k OPA2335 U5 14 One-Shot R24 0.1uF Cb5 R23 10k 4 R21 U4 +5V 8 1 1 3 50% osc duty cycle thi = 0.693 C15 (R26+R27), tlo = 0.693 C15 R26 0.1uF Cb6 0.01F C12 +5V +5V +5V 0V 0V 0.01F C14 11 13 12 8 ½ TLC556 Dual Timer 9 R28 R29 4.99k 249 C16 Oscillator 1F 10 Reset 1kHz LED Speaker A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Battery, Power Sub-Regulator and Auto Power Down Circuit <1mA to 15mA On 6A Off Battery +6.5V to +9.25V +5.9V to +8.65V D3 0.6V Drop Ext. External Supply +5.1V to +24V + Reverse bat protect Cb7 C17 0.1F 9V Battery - 4 Reg Output Power Down When C3 is Charged >90% of Vreg 4A Iq TPS 71550 5V Vreg LDO Reg SOT323-5 SC70 U7 2 5 Cb8 C18 0.47F i +5V 10M +5V +4.5V R30 e 0A +4.8V 1A U8 1M R31 4 - R33 1k C19 +4.5V dc Common, Isolated or Ground TLV 3491 Comp sot23-5 100F + 3 4.75M C3 R32 Mom. close SW to Start Timer 40 minutes to Auto Turn-Off 1.2A +1mA to Iq 5 +15mA 2 1 Load 1M R34 90% of 5V Threshold A Precision Low-Level DAS/ECG Cardiotachometer Demo Board “Pin-Plug and Play” features • Wires to pin-sockets, no soldering, plus plug selectable gain & BW • Self contained ICs, resistors, capacitors, LED, speaker, switches • Battery operated (+9V included) or external supply up to 24V max with auto-sleep • Adjustable gain & BW (Separate LPF & HPF), differential or singleended inputs, ac or dc coupled • Breadboard area for additional circuits A Precision Low-Level DAS/ECG Cardiotachometer Demo Board – top side Can Hold Right Side of Board Against Table to Steady Skin-Electrode Contact Speaker On Left Thumb G = 1kV/V OPT Not Used In This Example Right Thumb Right Finger Underneath 0.05Hz to 35Hz BW Plugged Into ac-Coupled Position Forward, Out put Swing Up From Mid +2.5Vdc Towards +5V ac-coupled ECG Waveform Appear at Vout A Precision Low-Level DAS/ECG Cardiotachometer Demo Board – top side Gain Control, Selected By Changing Shorting Bar Position Input Pins LA Input LED 40 minute Gain x1k,2k,4k,6k Timer Start Ext Vsup Ext Off/On Switch Speaker ac dc RA Input RL back LPF 17,35,100Hz HPF Ext dc,0.05,0.5,2Hz Vout +5V Com Vin+, Vin-, and Vin common-mode (RL on back) Digital Burst Out Independent Op Amp Burst Test Point U9 with Pin Socketsac Peak-to-Peak Start Timer Comparator Oscillator Detector U4, U5 Push LED U8 TLV3491 Left Arm Pad, +2.5V REF3025 U6 4 Op Amps Button U10 with Test Vin- of IA TLC556 Point 8-pin DIP Socket U11 with Pin Sockets ½ Vsup test pt IA Out test pt External Pwr Supply Input A Precision Low-Level DAS/ECG Cardiotachometer Demo Board – top side Off/On Switch Vout OPA U2 CM ac dc Sel LPF Gain x1k,2k,4k, 17,35,100Hz, Ext 6k,Ext HPF 0.05,0.5, Breadboard 2Hz Area Right Arm Pad, Vcm, +, -, or 3 R Div Can Convert Instrumentation U1 OPA U3 2nd +5V LDO U7 Vin+ of IA Com Select Single-ended to Diff Amplifier 1st Stage Gain Stage Gain TPS71550 Speaker A Precision Low-Level DAS/ECG Cardiotachometer Demo Board – back side This Demo Board Supports Many Applications Brief Instructions Easy-to-Use Pin Sockets (No Soldering) Speaker +9V Battery Breadboard Area Left Arm Pad, Vcm from IA, Vcm, +Vcm, Com Low-Level DAS / ECG Cardiotachometer Demo Board - Standing Gently Hold Electrode Pad Areas (relax fingers), Standing can be ok. Sit Down if Possible A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Additional Applications • Industrial pressure, temperature flow and humidity and general sensor signal conditioning • Medical diagnostic and biophysical monitoring • Analytical and scientific instrumentation • Communications sensor and signal amplification • Automotive sensors A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Vref Puffing Pressure Tube Pressure Bridge Application Quickly Puffing on Tube ac-Coupled Low-Level DAS / ECG Cardiotachometer Demo Board – Puffing Pressure Bridge Silicon Microstructurers Inc. Milpitas, CA, Press Bridge SSM5410-005-G-P 408-577-0100 Stage2, Stage1, Gain = 5 Vref = +5V Vbrg offset = 43mVdc 2 (-) R1 390k Vin+2.5VCM 1 R6 C1 100pF 40.2k 5 (+) 3.3k ΔVin 1.5mVP-P 0.15 – 2.4mVP-P 40.2k R7 R2 390k R51k Vin+ 3,4 +2.5VCM Spec is 100mV diff out for 5psi input: 0.75mVp out for 0.0375 psi input R4 1k +5V 2 A1 + U2 3 C3 22pF +5V 7 INA326, 327 (shtdn) 6 R/R I/O ac Hold + Self-Zero 5 4C5 U1 R10 200k dc ac 7 470pF + A4 - C6 47pF C4 390k 390k 7 R3 Vcm - A2 R8 20k R9 + Common-mode Volt = (Vin+ + Vin-)/2 (NOT USED) 2 1 8 3 Gain = 600 GT = 2000V/V 0.1uF Cb1 Vcm + 8 1 4 OPA2335 Self-Zero +2.5V 22pF C2 6 +5V 1M R18 81 A3 4 0.1uF 3 + 2 Vout INA High Pass Filters (dc restoration) Cb3 R11 3..01M 0.05Hz 5 +2.5V Vdc OPA2335 pedestal Self-Zero ½ Vsup U3 6 Vout = Vin x Rgain total 2.5VDC ± 1.5Vp 1.0 to 4.0V 20k +5V supply R19 20k R20 ac-Coupled Removes 43mVdc brg offset +2.5V dc 5 Power Supply (high inverting gain) It’s possible to omit A1, depending on resistances. +Vs -Vs Analog Circuit Common (isolated from earth ground) Low-Level DAS / ECG Cardiotachometer Demo Board – Puffing Pressure Bridge +5V Excitation Directly From Sub Regulated Supply Pressure Bridge NOTE – Same Phase - Bridge (2) Out => Vin+ INA + Bridge (5) Out => Vin- INA Makes Vout Have Same Phase as Vin diff That is Vout 2nd Stage Increases When Vin- INA Increases With Respect to Vin+ INA VinINA +5V Gtotal = 2kV/V 2Hz to Vin+ INA 17Hz BW Plugged Into ac-Coupled Position 5mmHg, 0.0375psi Change When Puffing ac-Coupled Puffing Pressure Input Mechanical Pressure Gage Same Phase Low-Level DAS / ECG Cardiotachometer Demo Board – Puffing Pressure Bridge 0.2 second per puff 300 puffs per minute SIGNAL 1.5Vp-p ac +2.5V Offset Scope Trace Puffs 0.2 second 0V +4V 2nd Timer 100ms, 1kHz Burst Osc Out 0V A Precision Low-Level DAS/ECG Cardiotachometer Demo Board Squeezing Vref Tube Circuit Uses OPA336s Instead of OPA335s Pressure Bridge Application Slowly Squeezing on Tube dc-Coupled A Precision Low-Level DAS/ECG Cardiotachometer Demo Board dc-coupled dc bridge offset (Normal-Mode voltage) is not removed Vout ac + dc +4.9V max swing Bridge offset will shift output voltage up or down Output Signal +2.5V mid scale 0.1V min swing time In single supply circuits, a mid-scale offset is used with the amplifiers to assure linear operation. Low-Level DAS / ECG Cardiotachometer Demo Board – Squeezing Pressure Bridge Silicon Microstructurers Inc. Milpitas, CA, Press Bridge SSM5410-005-G-P 408-577-0100 Vref = +5V Vbrg offset = 43mVdc 2 (-) R1 390k Vin- R4 1k +2.5VCM 1 R6 C1 100pF 40.2k 5 (+) 3.3k RG = 4.21k [RA ║(R6+R7)] 3,4 R7 R2 390k Vin+ +2.5VCM Spec is 100mV diff out for 5psi input: 0.75mVp out for 0.0375 psi input 40.2k RA R51k +5V 2 A1 + U2 3 22pF C2 2 1 8 3 C3 22pF INA326 R3 Vcm - + dc 6 +2.5V dc 5 Vout INA High Pass Filters (dc restoration) ac + A4 - 7 Vout = Vin x Rgain total Cb3 ac Hold 4 R11 C5 3..01M 470pF 0.05Hz R8 20k R9 A2 5 R10 200k 47pF C4 390k 7 6 C6 390k +5V 1M R18 81 A3 4 0.1uF 3 + 2 - + GT= 100V/V G2= -1V/V +5V 7 U1 Vcm + 8 1 4 OPA2336 not used +2.5V G1= 100V/V G= 2(R10/RG) 5 +2.5V U3 6 20k +5V supply R19 20k R20 OPA2336 not used dc-coupled amplifies 43mVdc bridge offset Power Supply +Vs -Vs Analog Circuit Common (isolated from earth ground) Low-Level DAS / ECG Cardiotachometer Demo Board – Squeezing Pressure Bridge #2, +2.5V Excitation Buffered Through Op amp Or #1, +5V Excitation Directly From Sub Regulated Supply NOTE – Opposite Phase + Bridge (5) Out => Vin+ INA - Bridge (2) Out => Vin- INA Makes Vout Have Opposite Phase as Vin diff That is Vout 2nd Stage Decreases When Vin+ INA Increases With Respect to Vin- INA VinINA Gtotal = 100V/V dc +2.5V +5V 17Hz BW Vin+ INA INA326 RG = 4.02k OPA336 RF = 1M Circuit Uses OPA336s Instead of OPA335s for Op Amps Plugged Into dc-Coupled Position dc-Coupled Pressure Bridge Pressure Tubing T-Connection Slowly Squeezing Tube Opposite Phase Low-Level DAS / ECG Cardiotachometer Demo Board – Squeezing Pressure Bridge Scope Trace #1 +5V on Bridge 0.99V SIGNAL, with +5V Bridge Excitation 0.99V out G=100 = 9.9mV in => 0.255psi bridge #2 +2.5V on Bridge 0.51V Half signal amplitude, due to half excitation 0V voltage SIGNAL, with +2.5V Bridge Excitation 0.51V out G=100 = 5.1mV in => 0.495psi bridge 5 seconds Vdc offset + Vac sig 43mV + 0.99V 2nd Timer 100ms, 1kHz Burst Osc Out Slow Squeeze Pulse Triggered P-P Detector +4V 0V A Precision Low-Level DAS/ECG Cardiotachometer Demo Board - Optical Relative Blood Pressure Monitor Optical Finger Plethysmograph Records Volume Changes Due to Blood Flow BP is Measure of Heart as a Mechanical Pump +5V Single Supply Stage1, Gain = 5 +2.5V dc 22pF 499k VinBP +2.5V +2.5V Mech Finger 390k Vsig 40k +Vcc 1k 100pF Photodiode 499k Light Heart Source Lamp or LED 40k +2.5V dc 390k Vin+ 499k +Vcc 3 2 1 8 3 +2.5V dc Vishay/Telefunken BPW34, 7.5mm2 Area Hamamatsu S1227-BR, S2387-16R, 6.49mm2 Area TI OPT101, Just PD, 5.2mm2 Area INA326, R/R I/O Self-Zero + 22pF 7 +5V 8 1 A1 + 4 6 4 5 200k 470pF + A4 - 6 5 47pF 20k 390k Photodiode Examples - 1k -Vcc 2 +5V 7 -Vcc 390k 7 A2 + 6 5 +2.5V dc (high inverting gain) Right Leg Drive Amplifier It’s possible to omit A1, depending on resistances. A Precision Low-Level DAS/ECG Cardiotachometer Demo Board - Optical Relative Blood Pressure Monitor ac-Coupled Photodiode Inside OPT101 (Can Use Separate Photodiode) Gt=6kV/V 2Hz 17Hz acCoupled Differential Input Voltage OPT101 Photodiode Connected to 3-R Divider to Create Differential Input Voltage A Precision Low-Level DAS/ECG Cardiotachometer Demo Board - Optical Relative Blood Pressure Monitor 0.94 second per beat 64 beats per minute SIGNAL 0.7Vp-p ac Optical 1st Timer Trigger Input Scope +2.5V Offset 0.94 second 0V Trace 1st Timer Output 2nd Timer 100ms, 1kHz Burst Osc Out 0V 0V Missing Sound Burst Did Not Trigger P-P Detector or Maybe DIGITAL O-SCOPE Abnormality A Precision Low-Level DAS/ECG Cardiotachometer Demo Board The low-level DAS/ECG demo board: • Provides a useful platform for low signal level circuit development. • Is useful as a portable, self-contained cardiotachometer. • Demonstrates the ability of very small amplitude signals to be amplified in the presence of large common-mode signals. • Provides either AC or DC coupling, but very large gain may be difficult to use for DC due to offset. • Accommodates a variety of medical and non-medical sensors and applications.