An Amplifier for High-Precision Current Detection Circuit

In order to improve the detection accuracy of weak current signal, a rail-to-rail operational amplifier with low-offset and low-noise was designed. Two parallel amplifier channels formed an offset-stabilized structure. The gain of the secondary channel was higher, which could effectively suppress the offset of the main channel, and suppressed its own offset by chopping. The main channel compensated for the bandwidth limitation caused by chopper modulation on the secondary channel. After chopper demodulation, a switched capacitor notch filter was used to filter the ripple at the chopper frequency and its multiples effectively. A complementary difference pair biased in the subthreshold region and a Class-AB output stage were used to achieve the rail-to-rail input and output range and reduce power consumption. It was fabricated with 0.18 μm BCD process. The post-simulation results show that the standard deviation of the input offset voltage is 1.1 μV, the equivalent input noise is 16.3 nV/Hz 1/2 and the open-loop gain is 187 dB. The quiescent current is 67 μA when the supply voltage is 3.3 V.