1 Introduction

Unlike the ideal operational amplifier, real operational amplifiers have input and output limitations that dictate a realistic range of values of where they can operate and remain working in a linear state.

In the case of current sensing amplifiers, the typical input restriction of the standard operational amplifier is removed. This is due to an internal topology of input stage transistors that allows for common mode voltages far in excess of the supply voltage(s). This common mode voltage is rejected,the differential voltage is level shifted down, and is then processed by the output stage. The ability of such a front end is useful in various scenarios, from the avoidance of additional components for level shifting data for operation by an analog to digitial converter, avoiding additional supply voltages simply for biasing operational amplifiers, and many more.

However, when discussing the output structure of a current sense amplifier, the output stage typically contains design constraints that must be taken into account for the device to operate linearly. Typically, current sense amplifiers employ CMOS type output stages, which display a small amount of swing loss as the demand for load current increases. These restrictions are made apparent in the datasheet, and reside in a graph commonly referred to as a "claw" curve.