Emitter-coupled logics(ECL) are logic circuits with bipolar, emitter-coupled transistors and resistors. ECL logics are based on the technology of differential amplifiers with multiple inputs, with which digital signals can be amplified and logically combined.
In ECL technology, the transistors operate in their active operating region and never reach the saturation region. This means that the transistors have no charge times and can change their state extremely briefly. This results in the advantage of short switching times and signal propagation times of less than a nanosecond.
Due to the high clock frequencies and extremely short switching times, high- frequency characteristics such as impedances, line lengths, capacitive interference, etc. must be taken into account when developing ECL circuits. In ECL logics, the signal decoupling takes place at the emitters.