Medical Applications User Guide (pdf) - Freescale Semiconductor

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Appendix Digital Filter Examples Digital FIR vs. IIR Filters A digital finite impulse response (FIR) filter can implement non-realizable analog functions, with many more multiplies, adds and data moves. y(n) = N-1 a(i)x(n-i) i=0 A digital infinite impulse response (IIR) filter provides a digital imitation of analog filters. It generally has the fewest operations, but is often 10x more efficient. y(n) = N-1 M a(i)x(n-i) + b(j)y(n-j), M>N i=0 j=1 Signal Reconstruction To reconstruct the signal to the original, we use the digital signal reconstructed by the DAC and then use passive filters to shape it in a smooth manner. See Figure A-5. Figure A-3: Anti-Aliasing Filter and Sampling Figure A-3: Anti-Aliasing Filter and Sampling Signal + Noise LPF (Signal + Noise) Numbers that we can use in DSP techniques Volts Volts Time Analog Low-Pass Filter Figure A-4: Low- and High-Pass Filters Figure A-4: Low- and High-Pass Filters Sample and Hold ADC Sample Rate Numbers that we can use in DSP techniques 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 y(n)+0.0732x(n)=0.1464x(n-1)+0.0732x(n-2) +1.099y(n-1)-0.3984y(n-2) Figure A-5: Signal Reconstruction Figure A-5: Signal Reconstruction 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 Sample Rate Sample and Hold ADC Sample Rate 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 106 Medical Applications User Guide DAC Volts Volts Time Low Pass Digital Filters High Pass Time 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 1.6060e+000 2.4394e+000 2.2457e+000 1.4378e+000 7.7448e-001 7.9937e-001 1.4447e+000 2.0849e+000 2.0000e+000 9.1704e-001 -7.6317e-001 -2.2173e+000 Analog Low-Pass Filter Reconstruction Filters Time Analog Low-Pass Filter Sample Rate Volts Volts DAC Time Time
Freescale Technologies • ColdFire MAC architecture enables DSP algorithms • IIR and FIR filters gain performance with MAC instructions • Single instruction: Multiply-accumulate with load • Multiply two 16-bit word or 32-bit longword operands • Add 32-bit product to 32-bit accumulator (ACC) register • Load 32-bit longword for next instruction and increment address register (ptr) • Sample analog accelerometer data with ADC (3 kHz) • Execute two parallel digital filters • Send via USB: raw and filtered data, timestamp, filter execution cycles For more information, download the PDF ColdFire Technology and DSP from freescale.com/files/dsp/doc/ref_manual/ CFDSPTechnology_DSP.pdf. Instrumentation Amplifier In medical instrumentation it is common to process signals with a lot of noise and small amplitude. For these reasons an instrumentation amplifier, which has high entrance impedance and high CMRR, is often used. This device can be built with discrete elements or can be obtained pre-built. The amplifier gets the differential between the signal and amplifier depending on the gain, which determines the signal amplitude. The gain recommended for medical applications is 1000 because the signal oscillates around 1 mV, and with this gain the signal can be amplified up to 1V. It is also recommended that for the first part you generate a gain of only 10 to avoid amplifier common-mode signals. Only filter the noise signals with this part, and amplify the rest of the signal with the differential amplifier. A =1+ 1 R2 R1 R +R 1 2 A = 1 R1 R 2 =(A 1 R 1 )-R 1 A 2 = R 4 R 3 R 4 = A 2 R 3 Appendix Figure A-6: ColdFire Demo Board (M52221 DEMO) Figure A-6: ColdFire Demo Board (M52221DEMO) Accelerometer Mechanical Oscillator A 1 = A 1 A 2 Values to obtain a signal around 1V: Low gain: 10, High gain: 100, Total gain: 1000 freescale .com/medical 107 ADC Timers Filter 1 Filter 2 USB Debug Lab View ColdFire V2 MCU Laptop Host Figure A-7: Instrumentation Amplifier Design Diagram Figure A-7: Instrumentation Amplifier Design Diagram Vi 1 Vid= (Vi 1 -Vi 2 ) Vi 2 2R 1 R 2 Vid/2R1 R2 R 3 R 3 Vid(1+2R 2 /2R 1 ) R 4 R 4 Vo=R 4 /R 3 ( 1+R 2 /R 1 )Vid A=Vo/Vid
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Medical Applications User Guide TM
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freescale.com/medical 3 Introductio
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Introduction 1.1 Freescale Offers T
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Monebo Kenetic ECG Algorithms Free
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Home Portable Medical 2.1 Introduct
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3.2 Home Health Hub (HHH) Reference
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3.3 Power Management Every design n
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MC34704 The MC34704 is a multi-chan
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3.7 How it Works The external capac
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eliably monitor and manage non-crit
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3.19 Standard Medical USB Communica
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Freescale has developed sample code
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4.2 Heartbeat Detection The heartbe
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4.6 Blood Pressure Monitor Referenc
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MCF51MM: Flexis 32-bit ColdFire V1
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Heart Rate Monitor 5.1 Introduction
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Instrumentation amplifier requireme
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6.2 Test Strip A test strip consist
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fully featured products at lower co
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Freescale’s Xtrinsic acceleromete
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7.2 Signal Acquisition This applica
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AN4327 Pulse Oximeter Fundamentals
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8.2 Electrocardiography (ECG) Acqui
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Xtrinsic Touch-Sensing Software Xtr
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• Internal voltage reference •
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9.2 Microphone Amplifier The microp
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9.5 Digital Signal Processor The di
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