Analog Electronics
The typical input stage of an opamp has a

  single - ended input and differential output.
  single - ended input and single-ended output.
  differential input and single - ended output.
  differential input and differential output.

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Analog Electronics
Optocouplers combine

 IGBTs and MOSFETs.
  Infrared light emitting diode and a silicon photo transistor.
 Power transistor and silicon transistor.
 SITs and BJTs.

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