What is ECL
ECL, or Emitter-Coupled Logic, is a high-speed logic family known for its fast switching speeds and low power consumption. ECL circuits are implemented using integrated circuits based on bipolar transistors.
The key characteristic of ECL is its design that avoids driving transistors into saturation. This is achieved through a differential amplifier configuration, where the combined emitter current flowing through a resistor remains constant. When the input voltage exceeds a certain threshold, one transistor conducts while the other turns off, resulting in a change in the output voltage.
ECL gates can be constructed by placing transistors in parallel, such as in an ECL OR gate. However, additional buffering may be required to ensure proper voltage swings for subsequent gate inputs. ECL gates offer advantages such as common mode rejection, low output impedance, and the ability to drive capacitive loads effectively.
Although ECL has historically been the fastest logic family among silicon-based technologies, its high power dissipation and the need for high levels of integration have led to its supersession by CMOS (Complementary Metal-Oxide-Semiconductor) technology.