2. AD621BRZ‑R7 Substitution Conclusion Direct substitution is not viable. The AD621BRZ‑R7 is an instrumentation amplifier (In‑Amp) featuring an internal multi‑op‑amp integrated structure specifically designed for differential signal amplification and high common‑mode rejection. Its function and interface method—typically requiring external gain‑setting resistors—are entirely different from those of the original part (a single‑channel general‑purpose op‑amp). Notable differences include: superior input offset voltage (50 µV) and similarly low bias current (500 pA), which may offer better DC precision; however, its fixed‑gain architecture cannot implement the various circuit configurations possible with a general‑purpose op‑amp (e.g., filters, comparators, etc.). Moreover, while its bandwidth (800 kHz) and slew rate (1.2 V/µs) exceed those of the original part, they remain in the medium‑to‑low speed range. Direct replacement would result in functional mismatch, preventing the circuit from performing as originally intended.