Agilent 5991-4268EN Evaluating Oscilloscopes for Low-Power Measurements - Application Note c20140416 [9] free download

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Evaluating Oscilloscopes for Low-Power Measurements Application Note Increasing market demand for products that are portable, mobile, green, gies for addressing the challenges of low-power measurements can be and that can stay powered for long periods of time is driving a change a huge boost in an engineer's ability to gain insight, understand, debug, in new-product innovation. It's low power, not performance, that is king. and characterize those designs. The ever-increasing need for power reduction drives engineering teams to devise innovative methods and architectures. The low-power mega This application note articulates key low-power measurement attri- trend has resulted in a changing landscape for devices, sub-systems, butes for oscilloscopes including software features and probes. It will and system-level products. A key requirement to fuel low-power innova- use the Agilent Infiniium S-Series oscilloscopes and N2820A current tion is the ability to measure and characterize device and sub-system probe in examples. The principles in this application note can be power consumption. Oscilloscopes designed with innovative technolo- applied to all oscilloscopes used for low-power measurements. Limitation on Getting Good Low Power Measurements There are many factors that go into making a good low power mea- surement. Some are inherent in the scope and some in the probe. The basis for low-power consumption measurements are current probes. Since power = V*I and voltage for many low-power applications is steady, current measurements are a good proxy for power. Historically, current probes have been designed to clamp around a power line, and either measure the Hall Effect, use transformer technology, or a hybrid between the two methods to continuously report an associated current value for display on an oscilloscope's display. Low-power measurements challenge testing in several ways. The two biggest challenges are dynamic range (impacted by noise) and sensitivity as shown in Figure 1. Figure 1. Vertical sensitivity is a key challenge for low-power measurements. Traditional current probes have limited dynamic range, and the total Scaling to see peak power and noise buries important signal details of low dynamic range is a function of both the probe itself as well as the power states. scope to which it is connected. We are going to take a closer look at each of these components and offer some best practices to help give you the most accurate current measurement on a low power device possible. Noise Let's look first at some low-power challenges related to the oscillo- scope. Noise inherent to the oscilloscope diminishes the ability to see small signal detail. At higher vertical scaling, oscilloscop