In electronics, emitter-coupled logic (ECL) is a high-speed integrated circuit bipolar transistor logic family. ECL uses an overdriven BJT differential amplifier with single-ended input and limited emitter current to avoid the saturated (fully on) region of operation and its slow turn-off behavior.[2] As the current is steered between two legs of an emitter-coupled pair, ECL is sometimes called current-steering logic (CSL),[3] current-mode logic (CML)[4] or current-switch emitter-follower (CSEF) logic.[5]