Medical Applications User Guide (pdf) - Freescale Semiconductor

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Home Portable Medical 5.3 Filters and Amplification Noise and interference signals acquired in this type of system can be caused by electricity, such as radiation from electricpowered fluorescent lamps. These generate a lot of common-mode voltage and noise. Other aspects that generate noise are muscle contractions, respiration, electromagnetic interference and noise from electronic components. Because the electrical signals from the heart are not strong enough, it is necessary to amplify the signals and reduce the common-mode voltage in the system. Cardiac motion generates electrical currents with different potentials in the body. These can be sensed with electrodes, usually connected to the right and left hands. The electrical potential is an AC signal in a bandwidth from 0.1 Hz to 150 Hz with a magnitude of approximately 1 mV peak to peak, and with presence of common-mode voltage noise in a frequency range from approximately 40 Hz to 60 Hz. Knowing this information, a circuit can be designed for amplification and filtration (see figures 5-3, 5-4, 5-5 and 5-6 for details). 5.4 Amplifier and Filtering Requirements The amplification is fixed at 1000 with a band-pass filter and cut frequencies of 0.1 Hz and 150 Hz. The reject-band filter has cut frequencies of 40 Hz and 60 Hz. Frequency Response • Diagnostic grade monitoring -3 dB frequency, bandwidth of 0.1 Hz–150 Hz • Band-pass filter Rl = 1 kΩ R = 1.5 MΩ C = C = 1 uF p hp lp hp • AC line noise -3 dB frequency bandwidth of 40 Hz–60 Hz • Reject–band filter R = 1 kΩ R = 1.5 MΩ C = 4 uF C = 1.7 nF lp hp lp hp This application requires two types of amplifiers: an instrumentation amplifier and an operational amplifier. Figure Figure 5-1: 5-1: Typical Typical Heart Heart Signal Signal P T Figure 5-2: Heart Rate Monitor (HRM) General Block Diagram Heart Rate Monitor (HRM) Special Conductive Glove or Finger Touch to Conductive Area Amplifier Power LED Coin Cell Battery Coin Cell Battery Amplifier Freescale Technology Optional 32 Medical Applications User Guide ADC ADC Conductive Rubber Chest Strap or Special Clothing Display MCU USB To PC MCU Q R S Keypad Receiver/ Amplifier Antenna Figure 5-3: Signal Conditioning Block Diagram Figure 5-3: Signal Conditioning Block Diagram Instrumentation Amplifier Amp and Modulator Antenna PWM Wireless Comm Speaker Drive Circuitry To Remote Sensor System Main Receiver System To Main Receiver System Remote Sensor System ADC
Instrumentation amplifier requirements include: • Low gain 10 • High common-mode rejection ratio (CMRR) • Low offset R1 = 500 Ω R2 = 4.5 kΩ Requirements for the operational amplifier, the second part of the instrumentation amplifier, include: • High gain 100 • Output voltage around 1V • Low offset R3 = 1 kΩ R2 = 100 kΩ 5.5 Obtaining QRS Complexes The QRS complex has to be detected in every heartbeat. This complex is the highest peak generated from the heart waveform. Although the signal has been filtered and amplified, it is necessary to include a digital band-pass filter with a bandwidth of 10 Hz to 25 Hz to remove high-frequency noise and low-frequency drift. Afterwards, filtering a derivation is implemented and a threshold is taken to determine whether the data is part of the QRS signal. 5.6 Heart Rate Monitor Design For more information on how to design a heart rate monitor, refer to AN4323: Freescale solutions for Electrocardiograph and Heart Rate Monitor Applications. This application note describes how to use the MED-EKG development board, a highly efficient board that can be connected to the Freescale Tower System to obtain an electrocardiogram signal and measure heart rate. The application is implemented using either the MK53N512, MC9S08MM128 or MCF51MM256 MCUs. Home Portable Medical Figure 5-4: 5-4: Instrument Instrument Amplifier Amplifier to Acquire to Acquire Heart Heart Signal Signal Vi 1 Vid= (Vi 1 -Vi 2 ) Vi 2 2R 1 Figure 5-5: Passive Band-Pass Filter Circuit Operating Frequencies 0.1 Hz-150 Hz Figure 5-5: Band-Pass Filter Circuit Operating Frequencies 0.1 Hz–150 Hz Figure 5-6: Active Band-Pass Filter Circuit Operating Frequencies 0.1 Hz-150 Hz Figure 5-6: Band-Pass Filter Circuit Operating Frequencies 0.1 Hz–150 Hz Figure 5-7: Digital Signal Processing to Obtain the QRS Complex Figure 5-7: Digital Signal Processing to Obtain the QRS Complex X(n) Raw ECG LPF HPF Differentiate Integrate freescale .com/medical 33 R 2 Vid/2R1 R2 Y(n) R 3 R 3 Q Vid(1+2R 2 /2R 1 ) R S R 4 R 4 Square Vo=R 4 /R 3 ( 1+R 2 /R 1 )Vid A=Vo/Vid
Page 1 and 2: Medical Applications User Guide TM
Page 3 and 4: freescale.com/medical 3 Introductio
Page 5 and 6: Introduction 1.1 Freescale Offers T
Page 7 and 8: Monebo Kenetic ECG Algorithms Free
Page 9 and 10: Home Portable Medical 2.1 Introduct
Page 11 and 12: 3.2 Home Health Hub (HHH) Reference
Page 13 and 14: 3.3 Power Management Every design n
Page 15 and 16: MC34704 The MC34704 is a multi-chan
Page 17 and 18: 3.7 How it Works The external capac
Page 19 and 20: eliably monitor and manage non-crit
Page 21 and 22: 3.19 Standard Medical USB Communica
Page 23 and 24: Freescale has developed sample code
Page 25 and 26: 4.2 Heartbeat Detection The heartbe
Page 27 and 28: 4.6 Blood Pressure Monitor Referenc
Page 29 and 30: MCF51MM: Flexis 32-bit ColdFire V1
Page 31: Heart Rate Monitor 5.1 Introduction
Page 35 and 36: 6.2 Test Strip A test strip consist
Page 37 and 38: fully featured products at lower co
Page 39 and 40: Freescale’s Xtrinsic acceleromete
Page 41 and 42: 7.2 Signal Acquisition This applica
Page 43 and 44: AN4327 Pulse Oximeter Fundamentals
Page 45 and 46: 8.2 Electrocardiography (ECG) Acqui
Page 47 and 48: Xtrinsic Touch-Sensing Software Xtr
Page 49 and 50: • Internal voltage reference •
Page 51 and 52: 9.2 Microphone Amplifier The microp
Page 53 and 54: 9.5 Digital Signal Processor The di
Page 55 and 56: Diagnostic and Therapy Devices 10.1
Page 57 and 58: 10.4 Filtering ECG The ECG has thre
Page 59 and 60: Features: • ColdFire V1 core deli
Page 61 and 62: The eMAC improvements target three
Page 63 and 64: 11.2 Circuit for Capacitive Dischar
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Page 67 and 68: • i.MX Processors The most versat
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Page 71 and 72: S08MM: Flexis 8-bit MCUs The 9S08MM
Page 73 and 74: 13.2 Brief Theory As mentioned in C
Page 75 and 76: Vital Signs 14.1 Introduction A vit
Page 77 and 78: 14.6 Motor Control with Freescale D
Page 79 and 80: State-of-the-art technology—inclu
Page 81 and 82: 15.5 Communication Interfaces USB P
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15.7 Multimedia Applications with i
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16.2 Ultrasonic Probe The ultrasoni
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segments. Devices start from 128 KB
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Powered Patient Bed 17.1 Introducti
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accelerometer is required. The Free
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Table 17-1. Freescale Technologies
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18.2 Ultrasound Ultrasound is a non
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The depth in color used in the fina
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significant amount of precision ana
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All the devices featured are pin co
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Summary Summary Applications Freesc
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Appendix Digital Signal Processing
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Freescale Technologies • ColdFire
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ADC Analog-to-digital converters (A
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freescale .com/medical
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Medical Applications User Guide (pdf) - Freescale Semiconductor

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