## 3 System Overview
### Current Measurement Topologies  
Current measurement instruments use either a shunt ammeter or a feedback ammeter configuration. The Shunt ammeter topology uses a specific known resistor and takes into consideration the voltage difference between two sides of the resistor. The voltage dropsacross the resistor; this is called the burden voltage and is directly proportional to the load current profile in the device under testing. The shunt resistor value needs to create a large enough voltage drop to be read from the instrument. On the other hand, if it is too big, the burden voltage will be added to the circuit. The Shunt ammeter topology has an unlimited bandwidth measurement. The feedback ammeter topology uses a voltage-to-current converter. The burden voltage is an extremely small value. There is a feedback resistor to control the gain. It creates high current sensitivity which is ideal to measure the low current profile. The bandwidth is the only limitation of this method. It is good for using low frequency current measuring devices. Apart from those two topologies, an oscilloscope with the current probe can be used to measure the device's current profile. Hall effect-based current probes eliminate the need to break the circuit. There is a challenge is in detecting the sleep mode current because of inadequate sensitivity; probes can only detect down to the mA level. These current probes will cost hundreds of dollars as well, depending on the sensitivity. The combination of an oscilloscope with a shunt resistor is a cheaper current measurement method for low power IoT systems. Figure 10 shows such an experiment set up. Almost all laboratories are equipped with basic function oscilloscopes. The shunt resistor value needs to be selected within the proper range. This eliminates the high value of burden voltage from the system. On the other hand, to measure the low current states, the basic oscilloscope cannot be used. Since deep sleep current is a constant value, a microammeter or other method can be used to detect the sleep mode's current value. There is another frustrating element of oscilloscope probing. The probe's ground is connected to the power ground in the electrical system. If the voltage source is not a ground isolated power supply or a battery, there will be a ground loop. In this situation another current path is created due to the potential ground difference. To address this particular challenge, differential measurement can be used. It is best to use differential probing, yet it is an expensive solution. This solution eliminates the ground looping and other challenges associated with ground potential difference. The other alternative solutions are to design a differential op-amp circuit or an instrumental op-amp circuit that is sensitive enough to detect the difference of a few microvolts (\(\upmu\)V). Again, there are a lot of design challenges associated with such a design with offset calibration and the bandwidth. There are sensitive current digital multimeters that can measure at microamp levels. These multimeters typically use a shunt ammeter configuration that can cause a low voltage burden in the microamp region. There is an advantage in measuring the deep sleep current with such a meter, since it is a constant value. However, those meters cannot measure short current bursts due to their slow measurement rate and limited triggering options. Additionally, the displays are numerical or small graphical displays. If micro- or nano-measurements are not available in the ammeter, there is another alternative method to measure the static deep sleep current [34]. [PERSON] et al. [34] mention the multimeter as basic instrumentation. In our experiment setup, we used a basic oscilloscope as the measuring instrument. Figure 11a shows the basic hardware connection related to  
Figure 10: Current measurement using shunt resistor with oscilloscope. our measurement setup. We proposed a simpler hardware setup based on the concept of capacitor charging and discharging.