ZHCSNI6A March 2023 – April 2024 OPA928
PRODUCTION DATA
The input offset voltage (VOS) of the op amp is another significant source of error. The input offset voltage forces a voltage across the effective shunt resistance of the diode (RPD) and creates an error current (IRPD) equal to VOS / RPD as illustrated in Figure 7-12. The shunt resistance of the photodiode is commonly specified in the manufacturer's data sheet. In some cases, VOS can be the dominant source of error. For example, a VOS of 50μV and an RPD of 1GΩ creates an IRPD of 50fA, which is more than double the maximum leakage current of the OPA928. Consider offset voltage variation with temperature and common-mode voltage.