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Edward Jezisek
Brandon Autrey
Edward Nowlin
Renato Ortega
Group 2
Motivation
• To improve the quality of ECG signals acquired from patients in an
MRI environment
• ECG quality in MRI machines is lacking
• Current filter selection is confusing
• Current filters are imperfect
• New MRI scans create problems
Objectives
• To further the use of adaptive algorithms in medical practice
• Make patient monitors easier to use
• Improve the quality of ECG Signals
Specifications and Requirements
Component
Requirement/Specification
DAC
1 kHz (Diagnostic Quality)
3 Parallel Pins
ADC
50 kHz (Diagnostic Quality)
6 Parallel Pins
Processor
Obtain Data, Perform the LMS and
Output data at 150 kHz
Noise Contributions
• Electrical interference from power lines add 50 or 60 Hz power-line
frequency.
• Muscle contraction and muscle activity can generate high frequency
electromyography (EMG) noise.
• Motion artifacts such as movement of the electrode over the skin
surface.
Overall System Diagram
Hardware
PCB Layout
• 417 components
• 6 layers
• Digital and Analog ground plane
• ESD/Defibrillation protection
• Front end amplification and filtering
• 4 ECG inputs and outputs
• 3 gradient antenna inputs
• ARM Cortex M4 Processor
Digital to Analog Converter (AD5640)
• 14 Bit conversion resolution
• Single channel
• 3 wire serial interface
• Clock rate up to 30 MHz
ARM Cortex M4F
• RISC based microprocessor
• 80 MHz clock speed
• Two 12-bit ADC modules with maximum sample rate of 1 MSPS
• 256 KB Flash memory
• Four SSI Modules
• 105 GPIOs including 24 shared analog input channels
• Single-precision Floating Point Unit (FPU)
PCB Schematic
Input from each ECG lead
• Removed because of NDA
Input from each gradient antenna
• Removed because of NDA
ESD/Defibrillation Protection
• In a situation when a patient goes into heart failure, a defibrillator may
need to be utilized
• A SG75 gas discharge tube is used to short the current going into the
filter when voltage exceeds 75V
• Clamping diodes are also used after the discharge tube to short the
circuit then the voltage exceeds +/-3.3V
ESD/Defibrillation Protection
• Removed because of NDA
Sallen Key Filter
• Front end filtering is used to eliminate as much interference as possible
before the analog signal is converted into a digital signal
• The Sallen key filter has a cut off of about 5500 rad/s or 9kHz
rd
3
order Sallen key filter
• Removed because of NDA
Op amp biasing and gain
• Op amp is biased to 1.2V to allow for proper operation of the analog to
digital converter.
• Biasing is achieved through the use of applying a voltage to the circuit
and using a voltage divider
• The Op amp circuit is configured to have a gain of 1.5
Op amp biasing and gain
Removed because of NDA
Op amp biasing
R2
Vin  Vout *
R1  R 2
10k
Vin  5V *
 1.2V
31.6k  10k
Gain
R1
gain  1 
R2
5k
gain  1 
 1.5
10k
PCB Power
• Analog and Digital ground planes are separated by a CLC filter
• Input voltage is 5V
• Voltage reference is used to step voltage down to 3V for applicable
components
• Linear regulators are used to maintain a steady voltage
• Digital and Analog grounds are separated by a CLC filter
PCB Power
• Removed because of NDA
Printed Circuit Board
Software
Linear Filters
• Pros:
•
•
•
•
Easier to make, and is already implemented in many machines
Is possible to implement with an analog system(few or no extra parts)
Quick and usable for diagnostic quality devices
Cheaper
• Cons:
• Requires a professional to select the correct linear filter
• Easy to make mistakes; if a mistake is made that can be costly in terms of receiving
useless data. And in the medical profession; time is of the essence.
• Training is confusing
• Quality is lacking
Adaptive Filters
• Pros:
• Much better quality
• Less input data from user
• Cons:
• Difficulties filtering the incoming amount of data
• More research is required for a full implementation of it
• Costs more (R&D)
Least Mean Square Filter Example
Noise Prior to FIR Processing
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Reference Signal
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Signal
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-5
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Real-Time Matlab Plot
• Video removed due to file size limitations
Important Data Points
Analog to Digital Converter
• Two ADC modules that use Successive Approximation Register (SAR)
architecture to deliver low-power 12-bit conversion resolution
• Supports 24 input channels
• Maximum sampling speed of 1 million samples per second
• Four programmable sample conversion sequencers
• ADC logic runs at 16 MHz
• 3.3 V reference voltage
Programmable Sequencers
• We used sequencer SS0 is used
to sample 6 signals at once
• 3 ECG signals
• 3 Gradient signals
• Sample sequencer is triggered
by processor interrupt
Sequencer
# of samples
Depth of FIFO
SS3
1
1
SS2
4
4
SS1
4
4
SS0
8
8
Synchronous Serial Interface (SSI)
• Programmable data frame size from 4 and 16 bits
• Transmit FIFO 16 bits wide and 8 locations deep
• Master or slave operation
• Three types of frame formats
• MICROWIRE and Freescale SPI
• FSS pin is active low for duration of frame transfer
• Texas Instruments Synchronous Serial Interface
• FSS pin is pulsed for one serial clock period prior to frame transmission
• Three SSI modules used for the three DACs.
Continuous TI Synchronous Serial Frame
Format
SPI Digital Data
Digital to Analog Converter
• Single channel 3-wire serial interface compatible with SPI
• SYNC, SCLK, and DIN
• Clock rate up to 30 MHz
• Reference voltage of 2.7 V
AD5660
AD5640
Conversion resolution
16-bit
14-bit
Input Shift Register
24-bit
16-bit
Write Sequence for DAC
DAC output of 1 KHz sine wave
Class Diagram
Testing Procedures
Functional Testing
• MATLAB
• Used to confirm the device sends the correct signal
• Oscilloscope
• Used to read the data from the PCB, ensures correct signals sent and received
• Function Generator
• Supplies various signals that were filtered with the LMS
ECG Generator
Connections
ECG Signal with No Filtering
ECG Signal with Adaptive Filtering
• Video removed due to file size limitations
Issues
• Noise of about +-30 mV on the board
• UART is not working on PCB
• Difficulty selecting step size and filter order
Budget
Parts
Price
Quantity
Total
Tiva C Series Dev. Board
$200.00
2
$400.00
Analog to Digital Converter
(ADS8556EVM)
$101.00
1
$101.00
Components
$1000
Varies
$1,000.00
Circuit Board
$750.00
2
$1,500.00
PCB Assembly
$2500.00
1
$2,500.00
JTAG Programmer
$79.00
1
$79.00
Total Costs
$5,580.00
Total Budget
$10,000.00
Extra Budget
$4420.00
Progress
120
100
80
60
40
20
0
Project Development
Research
PCB Completion
Parts Acquisition
Software Development
Testing
Total
Work Distribution
Tasks
Group Member
Front End Design
Edward Nowlin
PCB Design and Layout
Edward Nowlin and Renato Ortega
Integration of PCB
Brandon Autrey and Edward Jezisek
Least Mean Squares Filter
Edward Jezisek
MATLAB Display
Edward Jezisek and Brandon Autrey
ADC
Brandon Autrey
DAC and SPI
Edward Jezisek and Brandon Autrey
Questions?