A-4-4 V Input Common-Mode Range Bidirectional Current Shunt Monitor

This study describes a novel bidirectional current shunt monitor (CSM) circuit operating at both positive and negative common-mode (CM) voltages. The proposed CSM circuit mainly consists of two comparators, three error amplifiers, several current-mirror transistors and a few resistors. One comparator is used to detect current flowing direction, and the other one is utilized to ensure good operation of CSM circuit with both positive and negative CM voltages. The proposed CSM circuit has been implemented in SMIC 0.18 mu m standard CMOS process and its performances have been verified by simulations. The simulated results show that the proposed CSM circuit, at a supply voltage of 5V and with an input CM voltage range from -4 to 4V, can sense a voltage difference of 4-40mV and keep a constant scaled gain of 100V/V. The gain error is less than 0.65% and the common-mode rejection ratio (CMRR) is higher than 130dB at 1kHz. Simulation results show that the output voltage of CSM circuit varies linearly with the CSM input sense voltage.