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

20

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50

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90

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

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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