1. AD621ARZ-RL Substitution Conclusion From a core functionality perspective, the AD621ARZ-RL, as an instrumentation amplifier, can replace the INA118UB/2K5 for signal amplification tasks. However, it is not a direct, pin-compatible drop-in replacement. The feasibility of substitution depends heavily on the requirements of the specific application circuit. The AD621ARZ-RL offers advantages in input bias current (500 pA vs. 1 nA) and output drive capability (18 mA vs. 12 mA), making it better suited for interfacing with high-impedance sensors or driving heavier loads. Its key disadvantages lie in its significantly higher input offset voltage (75 µV vs. 10 µV) and higher minimum supply voltage (4.6 V vs. 2.7 V). These characteristics preclude its use in systems demanding extremely high DC precision or those powered by ultra-low voltage sources, such as a single lithium cell (3V). Furthermore, its quiescent current (900 µA) is approximately 2.6 times that of the INA118, which will have a noticeable impact on power-sensitive devices like portable instruments. Substitution is viable in applications with an adequate supply voltage (>4.6V), where power consumption is not a primary concern, and where its offset error is acceptable or can be calibrated out at the system level. However, it is not feasible in designs prioritizing high precision, low voltage operation, or low power consumption.