1. AD8421ARZ-R7 Substitution Conclusion The AD8421ARZ-R7 cannot serve as a direct replacement for the OP07CDRG4. Although the two share similarities in package type, supply voltage range, and DC parameters such as input offset voltage, their core amplifier architectures and key performance specifications make them suited to entirely different circuits and application scenarios. The fundamental distinction is that the OP07CDRG4 is a general-purpose operational amplifier whose circuit function (e.g., amplification, filtering, comparison) is determined by the external feedback network, offering design flexibility. In contrast, the AD8421ARZ-R7 is an instrumentation amplifier, featuring a fixed internal topology specifically optimized for high-precision differential signal amplification, with very high input impedance and common-mode rejection ratio. Specifically, the AD8421 holds a significant advantage in bandwidth (10 MHz vs. 0.6 MHz GBW) and slew rate (35 V/µs vs. 0.3 V/µs), making it suitable for high-frequency or fast-transient signals. However, its architecture inherently prevents it from implementing common op-amp circuits such as inverting amplifiers or integrators. If the AD8421 is directly used in a standard op-amp circuit designed for the OP07—such as an inverting/non-inverting amplifier or voltage follower—the circuit will not function correctly. The peripheral circuitry and application approach must be completely redesigned according to the characteristics of an instrumentation amplifier.