Biomedical Devices Design and Troubleshooting (BME520) Chapter 4 PDF

Biomedical Devices Design and Troubleshooting (BME520 ) Chapter 4: Applied Electronics Claudio Becchetti, 1th Edition Dr. Qasem...

Biomedical Devices Design and Troubleshooting (BME520 ) Chapter 4: Applied Electronics Claudio Becchetti, 1th Edition Dr. Qasem Qananwah 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 1  Chapter 4: Applied Electronics Part I: Theory Introduction Figure : Medical device architecture 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 2  Chapter 4: Applied Electronics Part I: Theory Introduction In this chapter, we will focus on the electronic functions that are to be implemented by the dedicated electronics (circuit protection, analog front-end, amplifiers, analog processing, filtering, power etc.) In real electronic design, the solution is often a tradeoff between the various performance to be achieved. For example, improving the protection immunity may increase noise and possibly decrease the input impedance. Unfortunately, all these three parameters (impedance, immunity and noise) have to be over a specific threshold as for example in the ECG (AAMI, 1991). 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 3  Chapter 4: Applied Electronics Part I: Theory Introduction Real circuits often fail because real component behavior is not taken into account – that is, ‘the devil is in the details’. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 4  Chapter 4: Applied Electronics Part I: Theory Introduction Table 1 The main steps in electronic design 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 5  Chapter 4: Applied Electronics Part I: Theory Sensors biomedical quantities to be measured: Mechanical Magnetic Thermal (temperature) Electrical Chemical Radiation 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 6  Chapter 4: Applied Electronics Part I: Theory Sensors Sensors can be considered as the interface between the biological environment and the medical device. This suggests that the overall device performance is limited by the characteristic of the sensor itself. Sensors are therefore critical to the medical instrument performance. They may also impact on patient safety 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 7  Chapter 4: Applied Electronics Part I: Theory Sensors Figure : Sensor conceptual scheme. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 8  Chapter 4: Applied Electronics Part I: Theory Sensors Example: Temperature sensor- Resistance Temperature detector Resistance changes with temperature. TCR is the temperature coefficient of resistance 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 9  Chapter 4: Applied Electronics Part I: Theory Sensors Table: Examples of conversion principles Input quantity to Conversion principle be measured Temperature Thermistors: Resistance variations in metals Resistance variations in semiconductors Thermocouples: Seebeck effect Capacitance variations Infrared radiations Displacement Resistance variations Inductance variation Capacitance variations Hall effect Ultrasonic time of arrival Optical properties Velocity and Doppler effect acceleration Piezoelectric effect 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 10  Chapter 4: Applied Electronics Part I: Theory Sensors Table: Examples of conversion principles Input quantity Conversion principle to be measured Force Displacement on elastic materials Pressure Hydraulic pressure converted into displacement that is converted into a measurable electrical quantity Fiber optic deflection induced by pressure that induces a variation on the intensity of the light Flow Voltage variation proportional to the flow obtained in a uniform magnetic field Doppler effect Chemical Resistance (conductance) dependent on the concentration and the nature of properties the given solute (composition, Voltage/current (conductance) dependent on concentration and the cell PH, potential of the given solute concentration Optical variations etc.) 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 11  Chapter 4: Applied Electronics Part I: Theory Sensors Sensors introduce errors according to the specific conversion principle. In general, errors in medical instruments are roughly due to the measurement method, artifacts in the specific measurement process, and errors generated within the sensor and the associated measurement circuit/instrument. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 12  Chapter 4: Applied Electronics Part I: Theory Sensors Since sensors are the interface of the medical instruments, the sensors performances is directly related to the performance of the medical instrument itself. Performance is degraded by the errors 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 13  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function The I/O and power pins that connect an electronic device to the external world are a major source of failure. This is due to: electrical fast transient/burst ElectroStatic Discharge (ESD) Interference conducted with cabling or emitted/absorbed through radiation. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 14  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function In the worse case, electronic magnetic interference EMI may threaten the patient or the operator’s life, for example through electric shock. This suggests that all the circuit board connections must somehow be protected from the external world and must guarantee: immunity to the EMI in the working environment that emissions of the device will not interfere with other electronic devices. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 15  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Standard IEC/EN 60601-1-2 defines the type of interference that medical devices have to withstand When interference is applied within the limits of the standard, the device must continue to work without degradation, 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 16  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function The interference must not provoke: 1. failure in diagnosis or treatment, 2. errors (artifacts, distortion) inducing wrong actions on diagnosis or treatment (such as misleading interpretation), 3. false alarms, 4. termination of the intended operations or activation of unintended operations, 5. changes in parameters or in the internal memory followed by false alarms, 6. changes in operating modes, and 7. failures on components or in the PCB, such as short-circuit or opening of PCB tracks. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 17  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Table : IEC/EN 60601-1-2 immunity requirements for conducted/radiated EMI: 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 18  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Table : IEC/EN 60601-1-2 immunity requirements for conducted/radiated EMI: 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 19  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Over-voltage may create input voltage or current that exceeds the maximum allowed value of the components that are connected to the I/O lines. Figure : Measurement of heart potential. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 20  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Regarding the packaging of the components there are two technologies: surface mount technology/device (SMT/ SMD) and through-hole technology (THT) 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 21  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Electronic circuits often fail because the performance of real components is not as ideal one (resistance tolerance is an example, power rating…etc). Resistors must withstand transients ( there are many manufacture who produces this types of resistors). Resistors may have a limited long-term power dissipation. They can dissipate short term higher power peaks Example: 1.5 W for surface mount resistors of size 2512 but it can withstand 250 W for 1 ms 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 22  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Voltage has the similar consideration like power for any component, therefore components have voltage limits. Two constraints apply for these components: 1. they have to withstand the maximum current when in conduction 2. they have to be fast enough to switch to the conducting state when thresholds is passed to avoid failure in the device they are protecting. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 23  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Increasing the input resistance Rlim seen in the previous Figure will reduce current in the front-end component at the cost of an increase in the generated noise power (Johnson Noise). This may be unacceptable for some applications 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 24  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Johnson Noise All conductors produce thermal Johnson noise due to Brownian motion of carriers in the conductor. The root mean square (rms) value of the noise voltage is proportional to temperature and the resistance as follows: where K is the Boltzmann’s constant (1.38×10-23), R is the resistance in ohms, Tk is the temperature in kelvin (room temperature  27C 300K) and f is the bandwidth in hertz over which the noise is measured. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 25  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Transient Voltage Suppressors Over-voltage may be handled by various components also cited as transient voltage suppressors (TVS). Their role consists of clamping the transient over-voltage to an acceptable voltage level. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 26  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Transient Voltage Suppressors When voltage (signal) is under the clamping value, an ideal TVS component should be in an open-circuit state. When the voltage (signal) is higher than the clamping value, an ideal component will immediately switch to short-circuit state. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 27  Chapter 4: Applied Electronics Part I: Theory Circuit Protection Function Transient Voltage Suppressors Table : Voltage clamping technology components 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 28  Chapter 4: Applied Electronics Part I: Theory Buffer Stage Figure : Measurement of heart potential. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 29  Chapter 4: Applied Electronics Part I: Theory Buffer Stage The main requirements that have to be defined for the buffer stage are 1. input impedance 2. maximum over-voltage allowed at input 3. input dynamic range 4. contribution to system noise 5. frequency response and linearity. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 30  Chapter 4: Applied Electronics Part I: Theory Buffer Stage The input impedance must be much higher than the source impedance. For an ECG, the source impedance may exceed 220k for 5% of the population and the input impedance must be greater to 2.48M to avoid unacceptable errors according to (AAMI, 1991). 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 31  Chapter 4: Applied Electronics Part I: Theory Buffer Stage Op-amps are widely used in medical devices especially in the analog interface between the device and the external sensors (electrodes, photodiodes, chemical arrays…etc.). The Market offers thousand of different models, with a wide range of specifications suitable for many different applications. For example, in battery-powered applications, there are many low power and small footprint models. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 32  Chapter 4: Applied Electronics Part I: Theory Buffer Stage Here are some op-amp applications in medical devices: ECG, EEG and heart rate monitors: 1. instrumentation op-amp amplifiers with high common-mode rejection ratio (CMRR) to reduce common mode interference 2. operational amplifiers for the buffer stage, amplification and filter stages Photodiode applications including glucose meters (amperometric and photometric): 1. traditional operational amplifiers as buffers: low noise, low input bias current and low offset voltage amplifiers. Blood pressure applications: 1. low power, high precision instrumentation amplifiers for the bridge sensor application. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 33  Chapter 4: Applied Electronics Part I: Theory Buffer Stage for any design, we must consider first the ideal op-amp behavior, and then analyze How real behavior affects the implemented circuit. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 34  Chapter 4: Applied Electronics Part I: Theory Analog Signal Processing Analog signals have continuous amplitude-time values, and their processing requires that signal waveforms be not distorted significantly with respect to their intended use. Noise cannot be eliminated in analog processing, its interference has to be limited by careful design choices. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 35  Chapter 4: Applied Electronics Part I: Theory Interference and Instrumentation Amplifiers Sensor measurements are often affected by significant electromagnetic interference (EMI) contained in the environment. The signals measured by medical sensors may contain interference, whose amplitude may be in the same order of magnitude as the measurand. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 36  Chapter 4: Applied Electronics Part I: Theory Interference and Instrumentation Amplifiers When the interference is located outside the frequency band of the desired signal, a filter can eliminate the interference. When the interference lies in the same frequency band of the measurands, other approaches have to be considered. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 37  Chapter 4: Applied Electronics Part I: Theory Interference and Instrumentation Amplifiers Figure : Medical parameters and interference. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 38  Chapter 4: Applied Electronics Part I: Theory Interference and Instrumentation Amplifiers Figure : Current flows from power line. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 39  Chapter 4: Applied Electronics Part I: Theory Interference and Instrumentation Amplifiers The interference may be reduced by Shielding consists of enclosing the device by a conductive surface, the shield must be sufficiently high and the holes in the shield are smaller than the wavelength of the radiation. The Faraday cage also reduces the RF electromagnetic fields propagation. (blocks the propagation of external electric fields inside the device) 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 40  Chapter 4: Applied Electronics Part I: Theory Analog Filters Filtering is the process that removes undesired components by reducing the amplitude of certain specific frequencies where target signal can be neglected. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 41  Chapter 4: Applied Electronics Part I: Theory Analog Filters Figure : Main filter design parameters. 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 42  Chapter 4: Applied Electronics Part I: Theory Analog Filters Analog filtering involves physical hardware that alters analog signals before they are passed off to other components to be processed. Digital filters introduce additional latency into a system, as the analog data that comes out of the hardware must be processed on a computer before it is filtered as desired. The standard disadvantage of a digital filter is that digital filters are significantly slower than analog filters 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 43  Chapter 4: Applied Electronics Part I: Theory ADC Conversion The analog to digital converters (ADC) are the interface of the analog signal to the digital world. Figure : ADC Conversion 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 44  The Chapter is complete Questions ??? 12/21/2022 BME520: Biomedical Devices Design and Troubleshooting Biomedical Systems and Informatics Engineering Department 45