ECL stands for Emitter Coupled Logic.

ECL avoids saturation effects by operating in differential mode with a limited emitter current.

Unsaturated transistors have a faster switching time because of the absence of minority charge storage.

ECL gates operate at high switching speeds.

ECL, also as called current mode logic or current steering logic, is the fastest of all logic families because of he follwoing reasons:

1. It is a non-saturated logic, i.e. the transistors are not allowed to go into saturation. So, storage time delays are eliminated and therefore, the speed of operation is increased.
2. The limited voltage swing.
3. Currents are kept high, and the output impedance is so low that the circuit and stray capacitances can be quickly charged and discharged.

ECL is used in superfast computers and high speed special purpose applications.