Electrocardiograph (ECG)

Demonstration Board

6/3/2013 Design Team 3 1

Team Members Justin Bohr

Xie He Yuan Mei

Chaoli Ang Nate Kesto Mike Mock

Sponsor Peter Semig

Texas Instruments – Precision Analog

Facilitator Professor Ramakrishna Mukkamala

Project Background

Develop an ECG demonstration board for the Precision Analog group at Texas Instruments.

TI intends to showcase their integrated circuit (IC) performance using the demonstration board. Provides TI with customer interest in specific precision analog components.

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Definition of Success

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Expectations Functionality

Professional Display

Process signals from CardioSim II (simulator)

Display ECG output signal with Stellaris EVB Oscilloscope

Include TI components in design

Project Objective Develop several iterations of analog front-end (AFE)

circuits to interface a cardio simulator with an oscilloscope

Simulate, build, and test to optimize a final design

Development Strategy

Research ECG Systems

Software and Simulations

Breadboard Testing

Develop AFE Printed Circuit Board

Measure System Performance

Optimize Design

Develop Final Solution

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Research

Studied ECG systems to observe functionality

ECG signals

Noise Artifact Mitigation

Battery-Powered Applications

Observations

Bandwidth: 0.7 – 100 Hz

Amplitude: 1.0mVpp – 1.5mVpp

Active and passive filtering

Linear dropout regulator or Buck converter (9V to 5V)

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TI Components

Final Texas Instrument Circuit Components

• Instrumentation Amplifier – INA333

• Operational Amplifier – OPA378

• Linear Drop-Out Regulator (LDO) – TPS7A4201

• Buck Converter – TPS62120

OPA378 INA333 TPS7A4201

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ECG System Structure

Vre

f

VCC

VCC

Vref

VCC

VC

C

RG1 10k

RG2 10k

R3 10k

R5 1M

NS

NS1 2.5

R14 1

M

NS

NS2 2.5R7 1k

C4 47n

R4 1k

C2 47n

R8 63.4k R9 63.4k

C5 3

3p

C6 3

3p

R10 63.4k R11 63.4k

C7 3

3pC8 3

3p

C9 3

30p

+

-

+

U2 OPA333

+

-

+

U4 OPA333

R16 1

M

RG

+

-V-

RefOut

V+RG

U3 INA333

+Vin

C1 1

T

VF

VoA

Vin

L2 1T

R12 1

MC10 1u

+

-

+

U1 OPA333

NS

NS3 2.5

R15 1M

R13 1

M

V3 0

V4 0

R17 100k

R1 100k

R2 100k

ECG Signal

Input LP Filter

Instrumentation Amplifier

Output LP Filter

Stellaris μC Display

Right Leg Drive

Servo HP Filter

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Simulation Results

DC Servo loop attenuates low frequency wandering below 0.7 Hz

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Breadboard Testing

Using adapters for INA333 and OPA333

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Phase 1

Analog Front End Circuit (AFE)

Printed Circuit Board (PCB) Layout

Buck Converter Reference Design (TPS62120)

Test Points & Jumpers

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Phase 1 Results

PCB layout error

Successful operation

Buck converter measurements

Phase 1 AFE output using CardioSim II

40.00

45.00

50.00

55.00

60.00

65.00

0.09 0.9 9 90

Ga

in (

dB

)

Frequency (Hz)

Measured Bode Plot of System Bandwidth

Bandwidth: 0.7 Hz – 23 Hz Passband Gain: 64 dB

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Phase 1 Results

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Phase 2

Fixed PCB trace error

Battery Connector

Thumb Pad Test

LDO vs. Buck Converter Comparison

RLD switch

Increased System Bandwidth to 50 Hz

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Phase 2 Results

Successful implementation of thumb pad sensors

Power circuit comparison

Increase bandwidth to 50 Hz for more ECG spectral content

TPS7A4201 TPS62120

Input Voltage (V) 9.5 9.5

Input Current (mA) 0.74 0.43

Input Power (mW) 7.03 4.08

Output Voltage (V) 4.93 5.12

Output Current (mA) 0.67 0.71

Output Power (W) 3.30 3.63

Efficiency (%) 47.00 88.98

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Phase 2 Results

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Phase 3

LDO for Power solution

Thumb pads orientation

Organized layout

Selectable bandwidth 50 Hz or 100Hz

Created holes for board mounting

Battery on bottom of board

LED power indicator 6/3/2013 16 Design Team 3

Phase 3 Results

Selectable output filters

Labeled sub-circuits for demonstration purposes

Battery life of 211 hrs

Optimized thumb pad position

Improved connections for inputs and outputs

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Phase 3 Results

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Acrylic Display

Mount AFE on standoffs

Display Stellaris at 45 degrees

SolidWorks 3D model

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Code Modifications

Larger timebase options including 100 ms/div and above

Smoother screen updating

Default settings changed for optimized ECG viewing

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Demonstration

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Future Design Improvements

Implement a FFT for digital filtering on the Stellaris

Calculate BPM from FFT and display on LCD screen

Design the analog system using higher-order filters

Integrating Stellaris display board and AFE board into one PCB

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Questions?

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