The best replacement for op amp is comparator.

The best alternatives to op amp are rated as following:
★★★★★  comparator
★★★★★  transistor
★★★  audio amp
★★  transistor amplifier
★★  instrumentation amp
★★  amplifier
★  ota

Your alternative for op amp is not listed? Suggest!
Speaking about op amp, one probably shouldn't forget about hysteresis.

Other search terms related to op amp and their ratings are:
★★★★★ hysteresis
★★★★★ negative feedback
★★★★ inductor
★★★ dc offset
★★★ current source
★ gain
agc
You have in mind a companion for op amp and it is not yet here? Propose!



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op amp
comparator
transistor