Logic Families - Technologies

Technologies

The list of packaged building-block logic families can be divided into categories, listed here in rough chronological order of introduction along with their usual abbreviations:

• Resistor–transistor logic (RTL)
  • Direct-coupled transistor logic (DCTL)
  • Resistor–capacitor–transistor logic (RCTL)
• Diode–transistor logic (DTL)
  • Complemented transistor diode logic (CTDL)
  • High-threshold logic (HTL)
• Emitter-coupled logic (ECL)
  • Positive emitter-coupled logic (PECL)
  • Low-voltage positive emitter-coupled logic (LVPECL)
• Gunning transceiver logic (GTL)
• Transistor–transistor logic (TTL)
• P-type metal–oxide–semiconductor logic (PMOS)
• N-type metal–oxide–semiconductor logic (NMOS)
  • Depletion-load NMOS logic
• Complementary metal–oxide–semiconductor logic (CMOS)
• Bipolar complementary metal–oxide–semiconductor logic (BiCMOS)
• Integrated injection logic (I2L)

The families (RTL, DTL, and ECL) were derived from the logic circuits used in early computers, originally implemented using discrete components. One example is the Philips NORbits family of logic building blocks.

The PMOS and I2L logic families were used for relatively short periods, mostly in special purpose custom LSI circuits devices and are generally considered obsolete. For example, early digital clocks or electronic calculators may have used one or more PMOS devices to provide most of the logic for the finished product. The F14 CADC, Intel 4004, Intel 4040, and Intel 8008 microprocessors and their support chips were PMOS.

Of these families, only ECL, TTL, NMOS, CMOS, and BiCMOS are currently still in widespread use. ECL is used for very high-speed applications because of its price and power demands, while NMOS logic is mainly used in VLSI circuits applications such as CPUs and memory chips which fall outside of the scope of this article. Present-day "building block" logic gate ICs are based on the ECL, TTL, CMOS, and BiCMOS families.