A precision current sensing circuit with chopper amplifier of symmetric topology

Abstract

Precision current detection is essential in smart power switches. In this paper, a current-sensing amplifier with symmetric topology is presented, which adopts the chopping technique to improve sensing accuracy. This design offers four advantages at the same time. Firstly, the rail-to-rail complementary differential pairs are achieved to obtain a full input voltage swing, and the Class AB output stage is incorporated to increase the slew rate. Secondly, symmetric topology with the current shunt source provides moderate gain enhancement without extra power consumption and further increases the gain bandwidth product. Thirdly, the chopping technique is applied to achieve a significant reduction in the amplifier's input offset without an extra low pass filter. Fourthly, the constant GM-C biasing circuit is introduced to improve the robustness of system response and current sensing accuracy under process variations. The four advantages can be substantiated through the application of a 0.5-μm BCD technology process, with multiple simulation results, including frequency responses and current sensing accuracy in process corners and temperature variations. The mismatch Monte-Carlo and noise analyses are also conducted with the chopper on or off. Chip experimental results show that the current sensing error is within ±1.6 % from 0.01 A to 3 A load current. Furthermore, multiple tests have been conducted to determine the absolute values of the input offset voltages, ranging between 20 μV and 50 μV, which is a relatively small amount to vastly improve the sensing accuracy.