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51 Engineering a More Sustainable Future | ADI 10BASE-T1L Ethernet PHY/MAC-PHY. Signal coupling capacitance, power coupling inductors, common-mode choke and other EMC protection components are modelled. The power coupling inductance is nominally 1000 µH, which accounts for two 220 µH inductors with two windings each ( 880 µH plus margin ) . For some components, the recommended component value and tolerance range are added using LTspice Monte Carlo syntax. Figure 4 shows the corresponding Monte Carlo simulation waveform and limit line added using LTspice. The chosen components and tolerances will meet the return loss mask specification. How to Design an Ultralow Noise Power Supply Wired condition monitoring sensors have stringent noise immunity requirements. For CbM of railway, automation, and heavy industry ( for example, pulp and paper processing ) , vibration sensor solutions need to output less than 1 mV of noise to avoid triggering a false vibration level at the data acquisition/controller. This means that the power supply design needs to output very little noise ( low output ripple ) into the measurement circuit ( MEMS signal chain ) . The power supply design for the MEMS sensor must also be immune to noise coupled to the shared power and data cable ( high PSRR ) . Ensuring that a MEMS sensor can detect very small vibrations requires a very low noise supply. The ADXL1002 MEMS accelerometer has an output voltage noise density specification of 25 µg √ Hz. During normal operation, the MEMS power supply needs to meet or exceed this specification to avoid degrading sensor performance. Figure 5. Power supply design for a digital wired MEMS sensor. Wired CbM sensors are typically powered from 24 V DC to 30 V DC , which requires a buck converter with high input range and high efficiency to minimize power dissipation and improve sensor long-term reliability. Due to nonideal capacitive loading, the buck converter voltage ripple can be 10s of millivolts, which is not suitable for supplying 3 V/5 V MEMS sensors. Using a common- mode choke or bulk capacitance can reduce the buck output ripple voltage. However, an ultralow noise LDO regulator is required at the buck output to ensure that a power supply with microvolts of noise is supplied to the MEMS sensor. 3 4 5 Figure 4. Monte Carlo simulation waveform. Figure 3. MDI return loss simulation using the LTspice Monte Carlo function. Adobe Stock / Yingyaipumi – stock.adobe.com