4 Zero-drift Amplifiers to Minimize V_OS and V_OS Drift

Zero-drift amplifiers use an internal circuitry to continuously correct the V_OS and V_OS drift. Chopper and auto-zero are two different architectures used to achieve the V_OS correction, so the terms zero-drift, chopper, and auto-zero are often used interchangeably. The internal offset correction generally reduces maximum V_OS to less than 10µV and V_OS drift to less than 0.05µV/°C. Other parameters such as A_OL, PSRR, CMRR, and EMIRR are also improved by the reduction in offset. The main limitation of zero-drift amplifiers are input bias current transients from switching charge injection and clock-feedthrough. These transients can translate into an additional V_OS when large feedback resistors are used. Also, this transient can introduce unwanted noise tones at the zero-drift auto-correction frequency. The application note, Optimizing Chopper Amplifier Accuracy covers details on using zero-drift amplifiers and minimizing the errors introduced by the I_B transients.

Figure 4-1 Zero-drift Amplifier V_OS Correction and I_B Transients