Transistor-Transistor Logic(TTL) A common semiconductor technology for building discrete digital logic integrated circuits. It originated from Texas Instruments in 1965. There have been several series of TTL logic:
7400: 10 ns propagation time, 10 mW/gate power consumption, obsolete; 74L00: Low power: higher resistances, less dissipation (1 mW), longer propagation time (30 ns); 74H00: High power: lower resistances, more dissipation: less sensitivity for noise; 74S00: Schottky-clamped: faster switching (3 ns, 19 mW) by using Schottky diodes to prevent the transistors from saturation; 74LS00: Low power, Schottky-clamped (10 ns, 2 mW); 74AS00: Advanced Schottky: faster switching, less dissipation, (1.5 ns, 10 mW); 74ALS00: Advanced Low power Schottky (4 ns, 1.3 mW).For each 74xxx family there is a corresponding 54xxx family. The 74 series are specified for operation at 0 - 70 C whereas the 54 (military) series can operate at -55 - 125 C See also CMOS, ECL.