Answer: ECL
Explanation:
ECL is basically stand for the emitter coupled logic and it is the high speed integrated logic circuit. In this ECL logic circuit, the transistor does not enter in the saturation mode.
In the emitter coupled logic, the output resistance are low and the input emitter impedance are high so, the state of the transistor are get changes quickly. Hence, it is fastest device as compared to all other options.
Therefore, ECL is the correct option.
