Heart beat "Pulse Oximeter
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Transcript of Heart beat "Pulse Oximeter
PULSE OXIMETER
EVANDER LEMOSORCIDIO SANTOS
EE3113PROFESSOR AUGUST ALLO
WHAT IS PULSE OXIMETER?
• Measure the Pulse rate • Monitoring oxygenation • Fitness monitoring• Several Medical applications
Circuit Overview
Simplification:Neutral Reference
Stage Breakdown
Principles of Operation LC Oscillator generates 5kHz signal Filters trim frequencies above and below desired signal High-pass filters double as amplifier stages to boost gain Constant Amplifier boosts gain significantly Comparator generates a square wave when signal
exceeds reference value
Frequency Sweep
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 340
10
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Gain vs Frequency
Filter A (band pass)Net Gain (dB)Filter B (high pass)
kHz
Gai
n
Band-Pass Detail
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100
0
0.1
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0.5
0.6
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0.9
1
Bandpass Filter Gain vs Frequency1 2 3 45 6 7 89 10 11 1213 14 15 1617 18 19 2021 22 23 2425 26 27 2829 30 31 3233 34 35 3637 38 39 4041 42 43 4445 46 47 4849 50 51 5253 54 55 5657 58 59 6061 62 63 6465 66 67 6869 70 71 7273 74 75 7677 78 79 8081 82 83 8485 86 87 8889 90 91 9293 94 95 9697 98 99 100
100 Hz Increments
Gai
n
Gain at 5kHz
Circuit Sensitivity Huge gain in target band Comparator Reference only 0.5V above Neutral
Reference Result: Comparator can trip with an input of just 36
microvolts above Neutral Reference Original Designer compensated with stronger filtering on
power supply Reducing the final gain stage or raising the Comparator
Reference would have also worked.
BLOCK DIAGRAM
INFRARED TX AND RXPULSE SENSOR
SIGNAL CONDITIONING STAGE OUTPUT SIGNAL
COMPONENTS• Photosensor APDS9008• Op Amp MCP6001• IR Diode• Capacitors• Resistors
PROPOSED CIRCUIT
EQUIVALENT CIRCUIT
CIRCUIT ANALYSIS• Infrared TX and RX• Photodiode operating in Photoconductivity mode
fbw= 1/(2*pi*Rload*Cj)
Max Reverse Voltage = …
CIRCUIT ANALYSIS• Signal conditioning
Av = -Rf/Rin = (3.3x10^6)/(10x10^3) = 330 = 50 dB
CIRCUIT ANALYSIS
• Simulation
CHALLENGES
• Simulating the circuit • Hardware implementation• Limitation
Interesting Notes Voltage dividers cannot be separated from the amplifiers
Circuit more sensitive to noise than anticipated
Band-pass filter does not contribute gain
CONCLUSION
• The implementation of a heart monitor involves low cost amplifier and filter components which can be find everywhere.
THANK YOU
Circuit Source
Maxim Integrated https://www.maximintegrated.com/en/app-notes/index.mvp/id/3845