Design engineering teams face considerable challenges handling conflicting requirements for portable types of medical devices. Most of these devices are always-on types and must be capable of managing battery life with maximum efficiency and effectiveness. They also must have suitable dimensions tailored to the patient’s comfort, especially as most of these are meant to be worn 24 hours a day. Therefore, not only must their construction be robust, but they must also deliver the highest levels of performance. Designers use PMICs or power management integrated circuits for optimizing the power utilized by the ultra-low architecture, improving the sensitivity of measurements, and keeping the SNR or signal-to-noise figures on the high side.
Wearable technology is benefitting from the growing popularity of mobile networks from the perspective of both, the healthcare and the consumers. Although their design was initially meant for sports and wellness, the medical market is now finding increasing use for wearables. As a consequence, newer generations of medical wearable devices are available using MEMS or micro-electromechanical system sensors, including heart-rate monitors, gyroscopes, and accelerometers. Other sensors are also in use, such as for determining skin conduction and pulse variability. However, the more sensitive the sensor, the more it faces SNR issues so designers need to use better noise reduction techniques along with more efficient energy-saving solutions.
For instance, the accuracy of optical instruments depends on many biological factors. Therefore, design engineers maximize the sensitivity of optical instruments by improving their SNR over a wide range. They use voltage regulator ICs with low quiescent currents along with elements that improve the SNR by reducing ripple and settling times.
Maxim offers a complete SCODAS or single-channel optical data acquisition system, the MAXM86161. They have designed its sensor module for use in in-ear and mobile applications. They have optimized it for SPO2 or oxygen saturation in the blood, HR or reflective heart rate, and continuous monitoring of HRV or heart rate variability. There are three high-current programmable LED drivers on the transmitter part of the MAXM86161. While the receiver part has a highly efficient PIN photo-diode along with an optical readout channel. It features a low-noise signal conditioning ALE or analog front end. It includes a 19-bit ADC or analog to digital converter, a high-performance ALC or ambient light cancellation circuit, and a picket fence type detect-and-replace algorithm.
Optimizing the energy efficiency of an optical measuring instrument is a constraint on its design. Rather than use regular LDO or low-drop-out regulators, designers now use novel switching configurations to improve the efficiency further. The requirement is that the voltage regulation element provides a low level of ripples at high frequencies so that there is no interference when measuring heart rates. To operate LEDs at voltages different from what the Li-ion batteries can supply, designers use new buck-boost converter technologies, thereby curbing energy consumption and saving board space. For instance, they use the SIMO or single-inductor multiple-output buck-boost architecture for reducing the number of inductors and ICs the circuit requires.
The MAXM86161 from Maxim Integrated is a PMIC or power-management integrated circuit and is meant for applications that are space-constrained and battery-powered, where the efficiency must be high within a small space.
