Current sensing is a critical function in electronic systems but comes with complexities that are often underestimated. Accurately measuring current flow is not nearly as easy as measuring voltage and is even more difficult when trying to measure the current flowing through a load connected to relatively high-power supply voltages.

 
Current sense resistors, also called shunt resistors, like Microhm Electronics' MPR series, MVR series, MMS series are the technology of choice for measuring current flow due to their high measurement accuracy, low temperature coefficient, and relatively low cost. Because of their low impedance, the small voltage across the shunt resistor usually must be boosted. This task is frequently performed by a current sense amplifier connected in either a low side or high side configuration.
 
However, when the load is being driven by relatively high voltage power sources, such as in industrial control applications, the sense resistor can be significantly larger without depriving the load of too much drive voltage. These increased resistances produce much larger current sense voltages compared to the voltages generated by sense currents flowing through low impedance shunt resistors with values that are usually measured in milliohms or micro-ohms. These sense voltages can often be as large as several volts in high power industrial applications, which range from motor control to power conversion.

 
Such sense voltages often need attenuation and level shifting before they can be applied to an analog-to-digital converter (ADC), typically operating from a unipolar 3 volt or 5 volt power supply. The attenuating and level shifting signal conditioning chain is sometimes called a funnel signal chain because the sensed voltage signal narrows as it makes its way through the signal conditioning chain to the ADC. A conventional approach to reducing or funneling these sense voltages is to use passive attenuation, but a differential funnel amplifier offers an alternative that improves the measurement’s precision while reducing component count.