In computer engineering, a logic family is one of two related concepts:
A logic family of monolithic digital integrated circuit devices is a group of electronic logic gates constructed using one of several different designs, usually with compatible logic levels and power supply characteristics within a family. Many logic families were produced as individual components, each containing one or a few related basic logical functions, which could be used as "building-blocks" to create systems or as so-called "glue" to interconnect more complex integrated circuits. A logic family may also be a set of techniques used to implement logic within VLSI integrated circuits such as central processors, memories, or other complex functions. Some such logic families use static techniques to minimize design complexity. Other such logic families, such as domino logic, use clocked dynamic techniques to minimize size, power consumption and delay. Before the widespread use of integrated circuits, various solid-state and vacuum-tube logic systems were used but these were never as standardized and interoperable as the integrated-circuit devices. The most common logic family in modern semiconductor devices is metal–oxide–semiconductor (MOS) logic, due to low power consumption, small transistor sizes, and high transistor density.
Technologies The list of packaged building-block logic families can be divided into categories, listed here in roughly chronological order of introduction, along with their usual abbreviations:
Resistor–transistor logic (RTL) Direct-coupled transistor logic (DCTL) Direct-coupled unipolar transistor logic (DCUTL) Resistor–capacitor–transistor logic (RCTL) Emitter-coupled logic (ECL) Positive emitter-coupled logic (PECL) Low-voltage PECL (LVPECL) Complementary transistor micrologic (CTuL) Diode–transistor logic (DTL) Complemented transistor diode logic (CTDL) High-threshold logic (HTL) Transistor–transistor logic (TTL) Metal–oxide–semiconductor (MOS) logic P-type MOS (PMOS) logic N-type MOS (NMOS) logic Depletion-load NMOS logic High-density NMOS (HMOS) Complementary MOS (CMOS) logic Bipolar MOS (BiMOS) logic Bipolar CMOS (BiCMOS) Integrated injection logic (I2L) Gunning transceiver logic (GTL) 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 NORBIT family of logic building blocks. The PMOS and I2L logic families were used for relatively short periods, mostly in special purpose custom large-scale integration 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 F-14 Central Air Data Computer, 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.
Resistor–transistor logic (RTL)
Class of digital circuits built using resistors as the input network and bipolar junction transistors (BJTs) as switching devices. The Atanasoff–Berry Computer used resistor-coupled vacuum tube logic circuits similar to RTL. Several early transistorized computers (e.g., IBM 1620, 1959) used RTL, where it was implemented using discrete components. A family of simple resistor–transistor logic integrated circuits was developed at Fairchild Semiconductor for the Apollo Guidance Computer in 1962. Texas Instruments soon introduced its own family of RTL. A variant with integrated capacitors, RCTL, had increased speed, but lower immunity to noise than RTL. This was made by Texas Instruments as their "51XX" series.
Diode–transistor logic (DTL)
Class of digital circuits in which the logic gating function (e.g., AND) is performed by a diode network and the amplifying function is performed by a transistor. Diode logic was used with vacuum tubes in the earliest electronic computers in the 1940s including ENIAC. Diode–transistor logic (DTL) was used in the IBM 608, which was the first all-transistorized computer. Early transistorized computers were implemented using discrete transistors, resistors, diodes and capacitors. The first diode–transistor logic family of integrated circuits was introduced by Signetics in 1962. DTL was also made by Fairchild and Westinghouse. A family of diode logic and diode–transistor logic integrated circuits was developed by Texas Instruments for the D-37C Minuteman II Guidance Computer in 1962, but these devices were not available to the public. A variant of DTL called "high-threshold logic" incorporated Zener diodes to create a large offset between logic 1 and logic 0 voltage levels. These devices usually ran off a 15 volt power supply and were found in industrial control, where the high differential was intended to minimize the effect of noise.
PMOS and NMOS logic
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