1. DC Performance Grade: The most critical distinction lies in the specified input offset voltage (Vos). The KNZ is rated at 300µV, while the JNZ is rated at 750µV. This is not a lot-to-lot variation but reflects ADI's standard letter-grade classification, with the K-grade offering superior performance to the J-grade. In open-loop or high-gain configurations amplifying DC/low-frequency signals, using the JNZ may introduce an inherent output DC error approximately 2.5 times greater, potentially necessitating more costly external nulling or software calibration. 2. Input Bias Current (Ib): The KNZ specifies 3pA, and the JNZ specifies 5pA. While the absolute difference is minimal and both are exceptionally low, this parameter, combined with the Vos discrepancy, indicates that the JNZ is a tested version from the same wafer with slightly inferior DC performance. The impact of this difference is generally negligible in current-to-voltage conversion applications involving high-impedance sources, such as photodiodes or ion sensors. 3. Cost-Performance & Application-Driven Selection: A significant price difference exists, with the JNZ typically costing about half that of the KNZ. This drives the selection strategy: For circuits that are AC-coupled, filtered, buffered, or otherwise not reliant on ultimate DC performance, the JNZ offers excellent cost-effectiveness. For applications such as high-precision instrumentation amplifier front-ends, integrators, or precision DC sensor conditioning, the KNZ is preferable. Its superior initial offset voltage simplifies calibration and enhances long-term system stability.