Transistor–Transistor Logic (TTL) is a class of digital circuits built from transistors and resistors. It is called transistor–transistor logic because the logic function (e.g., AND) and amplification is performed by transistors. Many integrated circuits have TTL technology. They are used in applications such as computers, industrial controls, test equipment and instrumentation, synthesizers, etc.
TTL gates define a voltage below 0.5V as 0, and a voltage of 4–5V as 1.
- 74 - the "standard TTL" logic family (long obsolete) had no letters between the "74" and the specific part number.
- 74L - Low power (compared to the original TTL logic family), very slow (rendered obsolete by the LS-series)
- H - High speed (rendered obsolete by the S-series, used in 1970s era computers)
- S - Schottky (obsolete)
- LS - Low Power Schottky
- AS - Advanced Schottky
- ALS - Advanced Low Power Schottky
- F - Fast (faster than normal Schottky, similar to AS)
- C - CMOS 4-15V operation similar to 4000 series
- HC - High speed CMOS, similar performance to LS, 12nS
- HCT - High speed, compatible logic levels to bipolar parts
- AC - Advanced CMOS, performance generally between S and F
- AHC - Advanced High-Speed CMOS, three times as fast as HC
- ALVC - Low voltage - 1.65 to 3.3V, tpd 2nS
- AUC - Low voltage - 0.8 to 2.7V, tpd<1.9nS@1.8V
- FC - Fast CMOS, performance similar to F
- LCX - CMOS with 3V supply and 5V tolerant inputs
- LVC - Low voltage - 1.65 to 3.3V and 5V tolerant inputs, tpd<5.5nS@3.3V, tpd<9nS@2.5V
- LVQ - Low voltage - 3.3V
- LVX - Low voltage - 3.3V with 5V tolerant inputs
- VHC - Very High Speed CMOS - 'S' performance in CMOS technology and power
- G - Super high speeds at more than 1 GHz, 1.65V to 3.3V and 5V tolerant inputs, tpd 1nS (Produced by Potato Semiconductor)
- BCT - BiCMOS, TTL compatible input thresholds, used for buffers
- ABT - Advanced BiCMOS, TTL compatible input thresholds, faster than ACT and BCT
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