Design of a low offset operational amplifier for current detection

Aiming at the requirement of current detection for operational amplifier performance, a new low offset operational amplifier circuit is proposed. The closed-loop current sampling circuit is composed of low-loss op-amp, PMOS tube and resistor. The whole op-discharge route is composed of main op-amp and auxiliary op-amp. The high frequency path composed of main op-amp controls the circuit bandwidth, the auxiliary amplifier low-frequency path uses chopper technology and self-zeroing technology to reduce the circuit offset. The circuit was simulated based on the 180BCD process. The simulation results show that the temperature is 27 ℃, the input offset voltage is stable at 9 μV, the operation amplifier gain is 95.50 dB, the gain bandwidth product is 28.2 MHz, the phase margin is more than 76.6°, the CMRR value is 148 dB, and the PSRR value is more than 116 dB. The circuit can be used for high measurement current detection.