RL78/G13 Pulse Oximeter Reference Design
Contents
1. REN ESAS APPLICATION NOTE RL78 G13 R01AN0716EU0100 Rev 1 00 Pulse Oximeter Reference Design November 15 2011 Introduction The primary function of red blood cells is to transport oxygen from lungs to tissues A substance called Hemoglobin carries out this function When blood is circulated in to lungs oxygen is attached to hemoglobin forming oxygenated hemoglobin When the blood is in capillaries oxygen is released from oxyhemoglobin and delivered to the cells The deoxyhemoglobin returns back to lungs to get saturated with oxygen once again The percentage of oxygen saturation of hemoglobin in arterial blood SaO2 is determined by the Pulse oximeter It is a medical instrument which optically measures oxygen saturation SaO2 in patient s blood In modern medical practice the blood oxygen level is considered one of the important vital signs of the body along with the more traditional ones such as blood pressure heart rate body temperature and breathing rate Pulse oximeters provide early information on problems in the respiratory and circulatory systems They are widely used in intensive care operating rooms emergency care birth and delivery neonatal and pediatric care sleep studies and in veterinary care 6 Pulse oximetry combines the principles of photoplethysmography and spectrophotometry to measure noninvasively the oxygen saturation of arterial blood This is an important tool to assess the status of patient oxygenation2. List of Figures Figure 1 Example of a Handheld Pulse OXxiMeter cccscccsssscssstecsssnecsssuecsssuecsesuecsessecsnssecseseecseesecseesesssesesssnees 3 Figure 2 Pulse Oximeter INDUut SIGMA ce ccecccccssscceessseecessseeceessseccessseccessseeceesseccessseccessseeceesseccessseeceetseeeeeaeees 4 Figure 3 Signal Flow Diagram of Pulse Oximeter eee cccceseeeseeeesecesceceeeeeseeeeseeceseeeeseeeeseeceseeeeseeeeseeenseeenseeenaees 5 Figure 4 Block Diagram of Pulse OXIMETED cc ccscccessccsssecsseecsscecsseecescecescecssseceseecessecessecessecessecessecessesessecenseseaees 7 Figure 5 RL78 G13 Simplified Device Architecture Diagram ccc ccccccsccccsssceessecceseccesseecesseecesseecesseeeetseeeeses 11 Figure 6 Hardware implementation Diagram ccccccccccsscccesssecceesseeceesssececesseeceeeseeceesseeecesseeceeesseeeseseeeeesseesesaes 15 Figure 7 Software Architecture sennesneesseessseossressseessrossseessrosseresseosseessseosseesssressrossoeeseeossoessseessressseesseessseesseesseeess 16 Figure 8 Flowchart for Main Program 1 0f 2 s ressrecrsscciiersresorrersors oisean reren saena E EE E NENEA EEan 18 Figure 9 Flow Chart for Main 2 0f 2esispesisrasscesssisseinicae aa ani ai naan aaa aii aani Bai 19 Figure 10 Flow chart for Signal Capture ec cccsccesssecesseeesseeeesseeeesneeeeeeeeeseeeseseeeseseeeseseeeseseeeneseeeseseeessaeeenags 20 Figure 11 Flowchart for Signal NOMMAlZAUGINs siccccossse
3. and Support Renesas Electronics Website http www renesas com Inquiries http www renesas com inquiry All trademarks and registered trademarks are the property of their respective owners RO1AN0716EU0100 Rev 1 00 Page 23 of 23 November 15 2011 tENESAS Revision Record Description Rev Date Page Summary 1 00 November 15 2011 First edition issued A 1 General Precautions in the Handling of MPU MCU Products The following usage notes are applicable to all MPU MCU products from Renesas For detailed usage notes on the products covered by this manual refer to the relevant sections of the manual If the descriptions under General Precautions in the Handling of MPU MCU Products and in the body of the manual differ from each other the description in the body of the manual takes precedence Handling of Unused Pins Handle unused pins in accord with the directions given under Handling of Unused Pins in the manual The input pins of CMOS products are generally in the high impedance state In operation with an unused pin in the open circuit state extra electromagnetic noise is induced in the vicinity of LSI an associated shoot through current flows internally and malfunctions occur due to the false recognition of the pin state as an input signal become possible Unused pins should be handled as described under Handling of Unused Pins in the manual Processing at Power on The state of the product is undefined at the
4. moment when power is supplied The states of internal circuits in the LSI are indeterminate and the states of register settings and pins are undefined at the moment when power is supplied In a finished product where the reset signal is applied to the external reset pin the states of pins are not guaranteed from the moment when power is supplied until the reset process is completed In a similar way the states of pins in a product that is reset by an on chip power on reset function are not guaranteed from the moment when power is supplied until the power reaches the level at which resetting has been specified Prohibition of Access to Reserved Addresses Access to reserved addresses is prohibited The reserved addresses are provided for the possible future expansion of functions Do not access these addresses the correct operation of LSI is not guaranteed if they are accessed Clock Signals After applying a reset only release the reset line after the operating clock signal has become stable When switching the clock signal during program execution wait until the target clock signal has stabilized When the clock signal is generated with an external resonator or from an external oscillator during a reset ensure that the reset line is only released after full stabilization of the clock signal Moreover when switching to a clock signal produced with an external resonator or by an external oscillator while program execution
5. or EVppiz In addition to the function as digital I O ports these ports have several alternate functions Serial Interfaces Serial array unit O has four serial channels and serial array unit has two Each channel can achieve 3 wire serial CSI UART and simplified I2C communication Simplified I2C does not support slave mode arbitration loss detection and wait detection Clock Output Buzzer Output Controller Buzzer output is a function to output a square wave of buzzer frequency One pin can be used to output a clock or buzzer sound This can be used for adding audio alarm facility for the product BCD correction circuit The result of addition subtraction of the BCD binary coded decimal code and BCD code can be obtained as BCD code with this circuit Multiplier and Divider Multiply Accumulator The multiplier and divider multiply accumulator has the following functions 16 bits x 16 bits 32 bits Unsigned 16 bits x 16 bits 32 bits Signed 16 bits x 16 bits 32 bits 32 bits Unsigned 16 bits x 16 bits 32 bits 32 bits Signed 32 bits 32 bits 32 bits 32 bits remainder Unsigned Analog to Digital Converter The A D converter is a 10 bit resolution converter that converts analog input signals into digital values and is configured to control up to twelve channels analog inputs The analog signals input to ANIO to ANI10 and ANI16 to ANII9 are converted to digital signals based on the voltage applied between
6. photo detector Analog front end electronics to amplify and process the signal before digitization An ADC to digitize the signal A processor to compute the received red and infrared light intensity ratio and hence to derive SpO2 value from the lookup table A LCD display and push buttons to display the values and provide user interface An audio buzzer to sound an alarm on low oxygen level A connectivity block to transfer information to external computer Power supply to power all the electronics using battery RO1AN0716EU0100 Rev 1 00 Page 6 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design KEYPAD Photo Detector Amplifier and Filter Signal receiver Audio Amplifier Electrical Path AUDIO DAC And Speaker DISPLAY User Interface Signal transmitter LED and IR LED LED and IR LED Communication driver Module Figure 4 Block Diagram of Pulse Oximeter R01AN0716EU0100 Rev 1 00 Page 7 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design 2 Pulse Oximeter Device Requirements 2 1 Sensor Requirements Many different types of sensor probes are used in pulse oximetry A typical probe consists of two LEDs one emitting red light and the other emitting infrared These LEDs need to be pulsed alternatively to send a beam of light through underlying tissues A photo detector in the probe which is placed on the other side of the tissue picks up the transmitted light signal and send it to
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8. AVREFP and the side reference voltage AVREFM VSS In addition to AVREFP it is possible to select VDD or the internal reference voltage 1 44 V as the side reference voltage of the A D converter The relationship between the analog input voltage input to the analog input pins ANIO to ANI7 ANI16 to ANI19 and the theoretical A D conversion result stored in the 10 bit A D conversion result register ADCR is shown by the following expression SAR INT VAIN AVREF 1024 0 5 ADCR SAR x 64 where INT Function which returns integer part of value in parentheses VAIN Analog input voltage AVREF AVREF pin voltage ADCR A D conversion result register ADCR value SAR Successive approximation register RO1AN0716EU0100 Rev 1 00 Page 13 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design 4 Reference Design Architecture Table 1 Requirements Table Pulse Oximeter Relevance Renesas Device Required Requirements RL78 G13 External Hardware DACs to control LEDs 2X 8 bit DAC At least 10 bit ADC High 10 bit ADC External 12 bit for High End model Digital signal processing Multiplier Accumulator Keypad Medium Keypad support Alarm Annunciation High Buzzer output RL78 G13 device has a built hardware MAC function which enables the design to implement advanced signal processing algorithms to reduce artifacts in the SpO2 measurement In addition it has on chip
9. Lambert s law for spectral analysis This law states that the concentration of absorbent in solution can be determined as a mathematical function of the amount of light transmitted through the solution providing that the intensity of the incident light the path length and the extinction coefficient of a substance at particular wavelength are known The percentage of oxygen in blood measured by the pulse oximeter is the ratio of oxygenated hemoglobin to the total amount of hemoglobin capable of binding with or transporting oxygen This ratio is commonly expressed as a percentage This parameter is an indicator of the arterial oxygen saturation commonly referred to as SaO2 However when measured by a pulse oximeter this is specifically referred to as SpO2 SpO2 Hb02 RHb HbO2 x 100 where HbO2 refers to oxygenated hemoglobin and RHb refers to hemoglobin with reduced oxygen RO1AN0716EU0100 Rev 1 00 Page 4 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design Pulse oximeters generally use a transmission mode where the light source and photo detector are on the opposite sides of the tissue The photo detector measures the intensity of light transmitted through the tissue The nullify the effect of ambient light the LEDs in the probe are made to follow a cycle The photo detector measures the amount of light received to current signal The amount of current produced when both LEDs are OFF gives an estimate of the
10. Page 21 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design Appendix A References 1 2 3 4 9 6 7 8 9 10 11 12 13 14 Yitzhak Mendelson Pulse Oximetry in Encyclopedia of Biomedical Engineering Vol 5 Wiley Interscience 2006 pp 2923 2940 Ahmad Elsharydah Randall C Cork Blood Gas measurements in Encyclopedia of Medical Devices and Instrumentation Second edition Vol 1 Wiley Interscience 2006 pp 471 474 Yitzhak Mendelson Optical sensors in Encyclopedia of Medical Devices and Instrumentation Second edition Vol 5 Wiley Interscience 2006 pp 166 Richard k Bogan Shawn D Youngstedt Sleep laboratory in Encyclopedia of Medical Devices and Instrumentation Second edition Vol 6 Wiley Interscience 2006 pp 212 Renesas Electronics RL G13 User Manual Rev 0 01 Renesas Electronics Nov 2010 J G Webster Design of Pulse Oximeters Bristol U K Inst Phys 1997 P Jalan B R Bracio P J Rider H Toniolo Rapid Prototyping of Pulse Oximeter Proceedings of the 28th IEEE EMBS Annual International Conference New York City USA Aug 30 Sept 3 2006 W S Johnston and Y Mendelson Investigation of Signal Processing Algorithms for an Embedded Microcontroller Based Wearable Pulse Oximeter Proceedings of the 28th IEEE EMBS Annual International Conference New York City USA Aug 30 Sept 3 2006 Maziar Tavakoli L
11. This is the one of the most advanced patient monitoring technology It provides safe continuous and cost effective monitoring of blood oxygenation noninvasively at the patient bedside Pulse oximeters are widely used in clinical practice They are used extensively in the intensive care units to monitor oxygen saturation and to detect and prevent hypoxemia They are used to monitor patients during procedures like bronchoscopy endoscopy cardiac catheterization exercise testing and sleep studies They are also commonly used during labor and delivery for both mother and infant A pulse oximeter is connected to the patient using a finger probe to detect the actual level of oxygen in the patient s blood stream Contents Dee PUSS OS Dy nerpa e aun yecs cuteness ccseadsucebad e E E 3 2 Pulse Oximeter Device Requirements cccccccseesecceceeeeeeeeeceeeeceeeeaeeueeeeesseeeeeeeessaeeeeeessaaeeeeessaaess 8 3 Renesas RL78 G13 Device Architecture OVErVieW ccccccccseeeeeeeeeeeeeeeaeeseeeeeeeeeeaeaaeeeeeeeeessaaaaees 10 4 Reference Design Architecture cccccccssscecccesececceeseecceeececeaseecseuscesseaueeessageeeesageeesteaseessseeeeeens 14 Os Inlgh Level Sorwale FIQWCNAUS secs cenceaseriersccsciaressacdecaesmenutaderiassencoiameces casewadenctadentaressaalaerecestucacoie 18 TaN 851 4 0 De AV sea a 21 5 2 eee ee ee Oe a ee ee ee ee eee ee 22 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design
12. a flash Data can be written to flash memory using any of the following methods e Writing to flash memory by using flash memory programmer e Writing to flash memory by using external device that Incorporates UART e Self programming The RL78 G13 supports a security function that prohibits rewriting the user program written to the internal flash memory so that the program cannot be changed by an unauthorized person RO1AN0716EU0100 Rev 1 00 Page 11 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design 2 Data Flash The following are the main features of data flash supported in RL78 G13 architecture The data flash memory can be written to by using the flash memory programmer an external device or through self programming Programming is performed in 8 bit units half word writing and blocks can be deleted in 1 KB units Because the data flash memory is an area exclusively used for data it cannot be used to execute instructions code fetching and CPU can only access data flash in byte unit needs four clock cycles Instructions can be executed from the code flash memory while rewriting the data flash memory That is dual operation is supported Accessing the data flash memory is not possible while rewriting the code flash memory such as during self programming Because the data flash memory is stopped after a reset ends the data flash control register DFLCTL must be set up in order to use the data flash me
13. copy or otherwise misappropriate any Renesas Electronics product whether in whole or in part Descriptions of circuits software and other related information in this document are provided only to illustrate the operation of semiconductor products and application examples You are fully responsible for the incorporation of these circuits software and information in the design of your equipment Renesas Electronics assumes no responsibility for any losses incurred by you or third parties arising from the use of these circuits software or information When exporting the products or technology described in this document you should comply with the applicable export control laws and regulations and follow the procedures required by such laws and regulations You should not use Renesas Electronics products or the technology described in this document for any purpose relating to military applications or use by the military including but not limited to the development of weapons of mass destruction Renesas Electronics products and technology may not be used for or incorporated into any products or systems whose manufacture use or sale is prohibited under any applicable domestic or foreign laws or regulations Renesas Electronics has used reasonable care in preparing the information included in this document but Renesas Electronics does not warrant that such information is error free Renesas Electronics assumes no liability whatsoever for any damages incurred by
14. d or signed On chip key interrupt function On chip clock output buzzer output controller On chip BCD adjustment I O ports 16 to 120 N Channel open drain 0 to 4 Timer o 16 bit timer 8 to 16 channels o Watchdog timer 1 channel o Real time clock 1 channel o Interval timer 1 channel Serial interface o CSI o UART UART LIN bus supported o 2C Simplified I2C communication 8 10 bit resolution A D converter VDD EVDD 1 6 to 5 5 V 6 to 26 channels Power supply voltage VDD 1 6 to 5 5 V A simplified Renesas RL78 G13 device architecture is shown in the Figure 5 RO1AN0716EU0100 Rev 1 00 Page 10 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design Figure 5 RL78 G13 Simplified Device Architecture Diagram Processor The processor core is 16 bit and supports 78KOR microcontroller instruction set Memory RL78 G13 architecture can access a 1 MB memory space It supports up to 32 KB of internal RAM The internal RAM can be used as a data area and a program area where instructions are written and executed The internal RAM is also used as a stack memory 1 Flash Memory The RL78 G13 incorporates the flash memory to which a program can be written erased and overwritten while mounted on the board The flash memory includes the code flash memory in which programs can be executed and the data flash memory an area for storing data RL78 G13 supports 16 64 KB of program flash and up to 8 KB of dat
15. data flash which can be used to implement LUT functionality required for pulse oximeter A pulse oximeter built using RL78 G13 and an external high performance analog front end including 12 bit ADC is a good choice for high performance and lucrative ambulatory and hospital environment markets 4 1 Hardware Architecture The reference hardware uses Renesas RL78 G13 16 bit microcontroller to implement Pulse oximeter Since all the functionality required by pulse oximeter specifications are not available in the device external hardware is required to make it suitable for the application The microcontroller does not have a built in display controller which required the addition of an external LCD display controller The DAC required to drive the LED driver is also implemented externally A Zigbee or Bluetooth module can be interfaced to microcontroller using the high speed CSI port The reference design block diagram is shown in Figure 6 RO1AN0716EU0100 Rev 1 00 Page 14 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design LCD Display LCD Controller Amplifier Program And Flash Filter Finger Sensor Assembly MAC LED And IRLED Driver S iff 78KOR LX3 a RL78 G13 Power Batter Management Fig
16. ed memory allocation could allow the use of a smaller and more power efficient processor but also highlighted the importance of evaluating software timing characteristics Despite steady progress in the miniaturization of pulse oximeters significant challenges remain because advanced signal processing must be implemented efficiently in real time by a relatively small size microcontroller 8 The algorithm to calculate SpO2 consists of two parts One is for the DC measurements and the other corresponding to AC measurements The DC part utilizes a 5th order f 0 1 Hz IIR Butterworth LPF The AC part utilized signal derivatives to identify individual PPG pulses and subsequently the amplitude difference between the peak and nadir of each pulse was determined In the derivative approach to measure HR a two point derivative of the PPG is used to identify individual pulse peaks These derivatives were assessed one data point at a time Each point was compared to a predetermined threshold value When the data point exceeded this threshold it was used to indicate the occurrence of the systolic slope in the PPG Subsequently the following zero crossing in the derivative was marked as a peak To account for variations in slopes due to changes in HR and pulse shape the threshold was adjusted every time a new peak was located This procedure minimized noise and minor signal RO1AN0716EU0100 Rev 1 00 Page 5 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oxi
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18. er with other monitoring signals e New Pulse oximeters are being developed for ambulatory service medical transport and homes These devices incorporate novel techniques to reduce the errors due to patient motion during observation These methods need processing resources to implement real time corrections e Wearable pulse oximeters with motion artifact compensation are being developed for both civilian and military personnel use RO1AN0716EU0100 Rev 1 00 Page 9 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design 3 Renesas RL78 G13 Device Architecture Overview The following are some of the highlights of Renesas RL78 G13 device architecture Minimum instruction execution time can be changed from high speed 0 03125 us 32 MHz operation with internal high speed oscillation clock to ultralow speed 61 us 32 768 kHz operation with subsystem clock General purpose register 8 bits X 32 registers 8 bits X 8 registers X 4 banks ROM 16 to 512 KB RAM 1 to 32 KB Data flash memory 4 8 KB On chip internal high speed oscillation clocks On chip single power supply flash memory with prohibition of chip erase block erase writing function Self programming with boot swap function flash shield window function On chip multiplier and divider multiply accumulator o 16 bits x 16 bits 32 bits Unsigned or signed o 32 bits 32 bits 32 bits Unsigned o 16 bits x 16 bits 32 bits 32 bits Unsigne
19. ignal based on adaptive filter which can be implemented on the microcontroller is presented The motion artifact which is a main problem in pulse oximetry is restricted effectively by this method and can be implemented on a microcontroller 11 A simple signal processing for pulse oximetry 1s presented which can use 10 bit ADC popular with microcontroller implementations This can be used to implement very low cost pulse oximeter 12 Mathematical calculations SpO2 and heart rate can be calculated from detection of two kinds of light infrared and red light The signal from two kinds of light has both AC and DC component From the AC and DC component from each of the wavelength need to be measured and the equation using for calculation is as followed log Ers log Rae R is ratio between both lights In the same way the SpO2 can be calculated from calibrated equation as followed SpO2 10 0002R3 52 887R 26 871R 98 283 The heart rate is determined by measuring the elapsed time between peaks of the IR signal The heart rate is calculated using the equation as followed 60 BPM Period Seconds The infrared light because it has low noise and can be used in various environments 13 1 3 System Description Pulse oximeter has following functional blocks A probe consisting of a red LED an infrared LED and a sensitive photo detector A timing control circuit to sequence the LEDs and to synchronize with the
20. intensity of ambient light The current produced by the photodiode is converted to equivalent voltage and filtered using low pass filter The filtered signal is digitized and demodulated before subtracting the ambient light effect The ratio R which is the ratio of voltage level at red 660 nm to that of infrared 940 nm is calculated The SpO2 value corresponding to ratio R is computed from empirical data using lookup table To reduce the effect of absorption of light by the surrounding tissue measurements are only made on detection of arterial pulse Blood has a light absorption coefficient greater than that of the surrounding tissue An arterial blood pulse increases the volume of the artery due to an increase in the blood This results in greater absorption of light by blood as compared to that by surrounding tissue 7 Figure 3 Signal Flow Diagram of Pulse Oximeter 1 2 Signal Processing There is lot of challenge in implementing the advanced signal processing algorithms on microcontroller in real time for portable and wearable pulse oximeters There are several digital signal processing algorithms for computing SpO2 and heart rate which were implemented on microcontroller Studies found that differential measurement approach combined with a low pass filter LPF yielded the most suitable signal processing technique for estimating SpO2 while a signal derivative approach produced the most accurate HR measurements In addition a reduc
21. is in progress wait until the target clock signal is stable Differences between Products Before changing from one product to another i e to one with a different type number confirm that the change will not lead to problems The characteristics of MPU MCU in the same group but having different tyoe numbers may differ because of the differences in internal memory capacity and layout pattern When changing to products of different type numbers implement a system evaluation test for each of the products Notice All information included in this document is current as of the date this document is issued Such information however is subject to change without any prior notice Before purchasing or using any Renesas Electronics products listed herein please confirm the latest product information with a Renesas Electronics sales office Also please pay regular and careful attention to additional and different information to be disclosed by Renesas Electronics such as that disclosed through our website Renesas Electronics does not assume any liability for infringement of patents copyrights or other intellectual property rights of third parties by or arising from the use of Renesas Electronics products or technical information described in this document No license express implied or otherwise is granted hereby under any patents copyrights or other intellectual property rights of Renesas Electronics or others You should not alter modify
22. itialize storage pointer to begining ood Initialize storage pointer nitialize timer Interrupt Figure 8 Flow chart for Main Program 1 of 2 RO1AN0716EU0100 Rev 1 00 Page 18 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design If user Input Start Capture display and store SpO2 If user Input History Display History Data Stop all capture History and wait for user Input If user Input Stop Figure 9 Flow Chart for Main 2 of 2 RO1AN0716EU0100 Rev 1 00 Page 19 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design Begin Capture Switch ON Red LED Capture Red Sensor value Switch OFF Red LED Switch on IR LED Capture IR sensor value Switch OFF IR LED End Capture Figure 10 Flow chart for Signal Capture RO1AN0716EU0100 Rev 1 00 Page 20 of 23 November 15 2011 stENESAS RL78 G13 Pulse Oximeter Reference Design Begin Normalization Read Both Red and IR values Apply Gain and Offset correction Using LUT Calculate the ratio Use the ratio to get the SpO2 value from Selected LUT Display and store the value End Normalization Figure 11 Flow chart for Signal Normalization Get the ADC reading Apply required normalization Read the value from the LUT Convert the value to engineering units RETURN Figure 12 Flowchart for Engineering unit conversion RO1AN0716EU0100 Rev 1 00
23. meter Reference Design irregularities from being falsely identified while simultaneously also reducing the chances of missing a systolic phase due to a shallow slope In a more recent literature an alternate approach is proposed to implement a very low power pulse oximeter In one approach signal processing is achieved by using an energy efficient transimpedance amplifier Most of the signal processing is done using analog hardware A low power microcontroller combined with this design will yield a versatile pulse generator with low power consumption The majority of this power reduction is due to the use of a novel logarithmic transimpedance amplifier with inherent contrast sensitivity distributed amplification unilateralization and automatic loop gain control The transimpedance amplifier together with a photodiode current source form a high performance photoreceptor with characteristics similar to those found in nature which allows LED power to be reduced Therefore our oximeter is well suited for portable medical applications such as continuous home care monitoring for elderly or chronic patients emergency patient transport remote soldier monitoring and wireless medical sensing 9 In another approach the feasibility of a ratiometric approach to compensating for ambient light and motion artifacts in a reflective photoplethysmography PPG sensor suitable for wearable applications was investigated 10 A method of preprocessing the PPG s
24. mory Manipulating the DFLCTL register is not possible while rewriting the data flash memory Timers The timer array unit has eight 16 bit timers Each 16 bit timer is called a channel and can be used as an independent timer In addition two or more channels can be used to create a high accuracy timer Timer array unit has the following functions By operating a channel independently it can be used for the following purposes without being affected by the operation mode of other channels l Interval timer Each timer of a unit can be used as a reference timer that generates an interrupt INTTMOn at fixed intervals Square wave output A toggle operation is performed each time INTTMOn interrupt is generated and a square wave with a duty factor of 50 is output from a timer output pin TOOn External event counter Each timer of a unit can be used as an event counter that generates an interrupt when the number of the valid edges of a signal input to the timer input pin TIOn has reached a specific value Divider function channel 0 only A clock input from a timer input pin TIOO is divided and output from an output pin TOOO Input pulse interval measurement Counting is started by the valid edge of a pulse signal input to a timer input pin TIOn The count value of the timer is captured at the valid edge of the next pulse In this way the interval of the input pulse can be measured Measurement of high low level width of inp
25. nsist of a pair of small and inexpensive R and IR LEDs and highly sensitive silicon photo diode These components are mounted inside a reusable rigid spring loaded clip a flexible probe and disposable adhesive wrap Pulse oximetry uses a light emitter with red and infrared LEDs that shine through a reasonably translucent site with good blood flow The light that passes through the measuring site is received by a photo detector and used to calculate the oxygenation of hemoglobin The ratio of Red R and infrared IR light received is calculated and a look up table can be used to convert to this to pulse oxygen saturation SpO2 value The look up table is made using empirical formulae Pulse oximetry uses the measurement technique which includes arterial pulsation to differentiate the light absorption in the measuring site due to skin tissue and venous blood from that of arterial blood At the measurement site there are several high absorbers such as skin tissue venous blood and the arterial blood Figure 2 However with each heart beat the heart contracts and there is a surge of arterial blood which momentarily increases the arterial blood volume across the measuring site This results in more signal absorption during the surge The light signals received look as a wave form peaks at every heart beat and troughs between heart beats If the light absorption at the trough which includes all the constant absorbers is RO1AN0716EU0100 Rev 1 00 Page 3
26. ny different types of probes and store the measured data locally for further display A microcontroller with in built data flash will be a good choice for implementing pulse oximeter design 2 5 Display Requirements Portable pulse oximeter needs a LCD Display with large digits Since software can calculate other parameters from the signal apart from the oxygen saturation the display should be custom made to show other parameters apart from Oxyhemoglobin saturation SO2 readings High end designs may support a graphical display 2 6 Power Requirements Portable Pulse oximeter should be powered using battery The battery can be of non charging type or a rechargeable lithium battery solution can be used In case of wireless connectivity support care should be taken to calculate the power budget for all use cases before battery capacity is specified The battery operation should be long enough to reduce ownership cost The processor and electronics should have capability to switch in to deep sleep to conserve power Similarly the display backlit should be switched to reduce the power consumption Ze Connectivity Requirements A connectivity port is a must in order to connect to computer The connectivity can be Bluetooth or USB The same port can be used to field upgrade the software for the device as well as retrieval of data by a computer Low cost low speed connectivity like Zigbee can be supported When selecting connectivity solution overall
27. of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design subtracted from the that at the peak the absorption characteristic of the added volume of blood arterial blood can be obtained Pulse oximetry technique has some limitations Reduction in pulsation skin pigmentation and dyshemoglobinemias may interfere with signal processing The sampling rate filtering and proprietary algorithms for signal processing will affect the resolution of the signal There are several software algorithms implemented to improve the accuracy of the pulse oximeter The sensors also embed chips which contain the calibration and operating characteristics which makes it more flexible monitor design This technique can be used to develop a microcontroller based pulse oximeter with both local display as well as with connectivity to use a remote monitor which can be a laptop or a tablet Similarly additional parameters can be monitored using intelligent sensors which greatly decrease the limitations of common pulse oximeter The signal processing capability of the microcontroller can be applied to calculate other parameters from the pulse oximeter sensor signal which will add more functionality to the instrument Waveform due to arterial Waveform due to arterial Pulsatile signal G6O0nm Pulsatile signal 940nm Figure 2 Pulse Oximeter input signal Basic Principle of operation The working principle of a pulse oximeter is based on the Beer
28. orenzo Turicchia and Rahul Sarpeshkar An Ultra Low Power Pulse Oximeter Implemented with an Energy Efficient Transimpedance Amplifier IEEE Transctions on Biomedical circuits and systems vol 4 No 1 February 2010 James A C Patterson Guang Zhong Yang Ratiometric Artefact Reduction in Low Power Discrete Time Reflective Photoplethysmography International Conference on Body sensor Networks 2010 Zhang Da Wang Haitao Wang Yugi A Method of Pre processing Photoplethysmographic Signal Based on Adaptive Filter for Pulse Oximeter International Conference on Intelligent Computation Technology and Automation 2010 Dvorak J Havlik J Simple signal processing method for pulse oximetry Dept of Circuit Theor Czech Tech Univ in Prague Prague Czech Republic Applied Electronics AE 2010 International Conference on 8 9 Sept 2010 pp 1 3 N Watthanawisuth T Lomas A Wisitsoraat A Tuantranont W ireless Wearable Pulse Oximeter for Health Monitoring using ZigBee Wireless Sensor Network International conference on Electrical Engineering Electronics and Information Technology ECTI CON 2010 Z Jones E Woods D Nielson S V Mahadevan Design of a Pulse Oximeter for Price Sensitive Emerging Markets 32nd Annual International Conference of the IEEE EMBS Buenos Aires Argentina August 31 September 4 2010 RO1AN0716EU0100 Rev 1 00 Page 22 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design Website
29. ots High Quality Transportation equipment automobiles trains ships etc traffic control systems anti disaster systems anti crime systems safety equipment and medical equipment not specifically designed for life support Specific Aircraft aerospace equipment submersible repeaters nuclear reactor control systems medical equipment or systems for life support e g artificial life support devices or systems surgical implantations or healthcare intervention e g excision etc and any other applications or purposes that pose a direct threat to human life You should use the Renesas Electronics products described in this document within the range specified by Renesas Electronics especially with respect to the maximum rating operating supply voltage range movement power voltage range heat radiation characteristics installation and other product characteristics Renesas Electronics shall have no liability for malfunctions or damages arising out of the use of Renesas Electronics products beyond such specified ranges Although Renesas Electronics endeavors to improve the quality and reliability of its products semiconductor products have specific characteristics such as the occurrence of failure at a certain rate and malfunctions under certain use conditions Further Renesas Electronics products are not subject to radiation resistance design Please be sure to implement safety measures to guard them against the possibility of physical injur
30. power budget and use cases need to be considered RO1AN0716EU0100 Rev 1 00 Page 8 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design 2 8 User interface requirements The user interface should consist of pushbuttons touch buttons to scroll through the menus and do user parameter selection The interface should provide configuration of the device to set up communication with a computer either by wired or wireless connection A graphical symbolic user interface is preferred to cater to non English speaking users The user interface should have an audio alarm generator like a buzzer or a tiny speaker This can be used to generate an audio alarm when the SpO2 is low needing immediate attention 2 9 Other requirements In the market research it was found that reliable data from pulse oximeter is important but sophisticated algorithms are not a priority in the consumer market Instead customers care more about cost reduction and improved usability 14 But in the highly lucrative ambulatory and hospital environment markets a highly accurate device is more important and desirable than the price 2 10 Future Trends To reduce false alarms and provide more reliable readings under conditions of low perfusion new hardware and more advanced software algorithms are being developed e The trends include improvement of signal processing algorithms more flexible and intelligent alarm settings and combination of pulse oximet
31. sccsssesverasasceanceaveronessussehsabeenencgousneneansevereanseasacsvacaeneansbevaueweenuats 21 Figure 12 Flowchart for Engineering unit conversion cceccccccccessccccesseeecesseeceeeseeceeeseeecsseeeeeesseecesseeesenseeeeeaes 21 R01AN0716EU0100 Rev 1 00 Page 2 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design 1 Pulse Oximetry 1 1 Theory of Operation Figure 1 Example of a Handheld Pulse Oximeter Pulse Oximetry Theory The main principle of pulse oximetry is based on Lambert Beer s law with differential light absorption of two wavelengths The wave lengths of the most commonly used sources are red 660 nm and infrared 940 nm Beer Lambert Law follows the equation lout lin e Where Jout is the light intensity transmitted through fingertip tissue Tin is the intensity of the light going into the fingertip tissue and A is the absorption factor Pulse oximetry exploits the time variant photoplethysmograpic PPG signal that is generated by changes in arterial blood volume and changes in the orientation of red blood cell associated with cardiac contraction and relaxation It differs from other types of oximetry in that it does not depend on the absolute measurements but rather on pulsations of arterial blood Oxygen saturation is determined by monitoring pulsations at two wave lengths and then comparing the absorption spectra of oxyhemoglobin and deoxygenated hemoglobin Pulse oximetry sensors co
32. the processing circuits The electronics need to generate proper timing to control the LEDs and to measure the light from the photo detector The measurement should be synchronized to the LED activation 2 2 Signal Processing Requirements The input signal is of very low amplitude and the approximately 2 of the signal is of interest The signal processing is required to separate the desired signal from the steady state signal to give accurate readings The processing can be analog or digital Low power microcontroller with some support for digital signal processing will be an ideal solution to achieve the required accuracy In addition motion artifacts removal requires digital signal processing capabilities 2 3 Computational Requirements The processing requirements include some support for digital signal processing The processor can be a low power 8 16 32 bit device with support for 10 to 12 bit ADC The computation involves ratio calculation and look up table implementation to calculate final SpO2 for display For heart beat calculations a precise time interval between peaks and averaging are required So a microcontroller with hardware MAC will be a suitable choice for implementing high end pulse oximeter designs 2 4 Storage Requirements A non volatile storage is required to store the lookup tables and calibration curve values The device software should be field upgradable If the non volatile memory is available data can be stored for ma
33. ure 6 Hardware implementation Diagram 4 2 Software Architecture Pulse oximeter firmware consists of drivers for controlling LED and IR LED driving with pr cis timing signal acquisition from the probe signal processing and computation and to display the result on the LCD A high level architecture is shown in Figure 7 There is also firmware to store the computed SpO2 values in data flash for later retrieval Since low power consumption is mandatory feature power management software is essential and optional communication driver can be added for connected device USB or wireless The computation is done using look up table technique the empirical data is put in to data flash using different LUTs The firmware provides an user interface to select the required one for a particular type of sensor R01AN0716EU0100 Rev 1 00 Page 15 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design Computation Data p Archiving Power Manage ment LED and o LCD ADC Flash Communication IR LED Driver Driver Driver driver driver Figure 7 Software Architecture RO1AN0716EU0100 Rev 1 00 Page 16 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design RO1AN0716EU0100 Rev 1 00 Page 17 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design 5 High Level Software Flowcharts The following sections describe the required firmware flow charts Initialize Hardware n
34. ut signal Counting is started by a single edge of the signal input to the timer input pin TIOn and the count value is captured at the other edge In this way the high level or low level width of the input signal can be measured Delay counter Counting is started at the valid edge of the signal input to the timer input pin TIOn and an interrupt is generated after any delay period By using the combination of a master channel a reference timer mainly controlling the cycle and slave channels timers operating according to the master channel channels can be used for the following purposes l One shot pulse output Two channels are used as a set to generate a one shot pulse with a specified output timing and a specified pulse width PWM Pulse Width Modulation output Two channels are used as a set to generate a pulse with a specified period and a specified duty factor Multiple PWM Pulse Width Modulation output By extending the PWM function and using one master channel and two or more slave channels up to seven types of PWM signals that have a specific period and a specified duty factor can be generated RO1AN0716EU0100 Rev 1 00 Page 12 of 23 November 15 2011 2tENESAS RL78 G13 Pulse Oximeter Reference Design Ports The RL78 G13 microcontrollers are provided with digital I O ports which enable variety of control operations Pin I O buffer power supplies depend on the product The power supply can be Vpp or EVppo or EVpp
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