| | APRIL 20189Long and predictable battery life is critical for medical battery powered devices. Insufficient battery life not only causes inconvenience but in some cases death if a medical device runs out of power before its specified duration of intended use. Patients with implants like pacemaker and neuro-stimulator, which require periodic battery replacement, will benefit greatly if the implants have longer service life as the replacement surgery is costly and presents risk to patients. Optimizing and managing power consumption of medical and healthcare devices becomes ever more critical in this digital age with more devices equipped with wireless technologies. Energy efficient devices can go a long way from having longer battery life (less frequent need to charge or change batteries) to being self-sustainable when adequately powered by energy harvesters. Where, When & How Much? Before you can even begin to op-timize the run time or reduce the energy consumption of your device, you first need to charac-terize the device, its sub-circuits and the battery, independently or in combination. For instance, you need to determine the duration and amount of energy consumed in each activity or operating state. It is also important to characterize the transition between the differ-ent states. Ideally, you would want to characterize the device oper-ating profile(s) continuously in one single acquisition. There are three measurement challenges to address: Challenge 1: High Dynamic Range: As the voltage stays rela-tively constant, the current is the test parameter which varies great-ly. From sleep to transmit, the current may vary as high as 4-5 orders in magnitude. In the case of a wireless device, this depends from how low current the device can achieve in sleep/idle mode to how high the current is drained during wireless transmission. To better understand the energy re-quirement of the device, it is es-sential to be able to measure these dynamic current changes. Challenge 2: Low Current: Low power design and technol-ogies enable more energy effi-cient devices. Modern wearable monitoring devices whether it is a smartwatch, headphones, or a chest patch integrate ultra-low power components which con-sume very little. Low current mea-surement capability with accuracy and resolution down tosub-micro-ampere enables the design and de-velopment of low power devices, as every microampere counts.Challenge 3: High Band-width: To save energy, portable devices are designed to avoid unnecessary energy usage by spending as much time in stand-
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