The Web This site. The logic gates introduced in Module 2. As well as the basic logic functions, compatible ICs are available, which contain particular useful combinations of gates providing a convenient way of constructing more complex circuits. Hundreds of different, but directly inter-connectable logic ICs are available.
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In computer engineering , a logic family may refer to 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 refer to 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.
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:. The PMOS and I 2 L 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.
Several early transistorized computers e. A family of simple resistor—transistor logic integrated circuits was developed at Fairchild Semiconductor for the Apollo Guidance Computer in Texas Instruments soon introduced its own family of RTL. This was made by Texas Instruments as their "51XX" series.
Diode logic was used with vacuum tubes in the earliest electronic computers in the s including ENIAC. 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 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 DC Minuteman II Guidance Computer in , 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. Mohamed M. Texas Instruments introduced the series TTL family in Transistor—transistor logic uses bipolar transistors to form its integrated circuits. Since the transistors of a standard TTL gate are saturated switches, minority carrier storage time in each junction limits the switching speed of the device.
Variations on the basic TTL design are intended to reduce these effects and improve speed, power consumption, or both. The German physicist Walter H. Schottky formulated a theory predicting the Schottky effect , which led to the Schottky diode and later Schottky transistors.
For the same power dissipation, Schottky transistors have a faster switching speed than conventional transistors because the Schottky diode prevents the transistor from saturating and storing charge; see Baker clamp. Gates built with Schottky transistors use more power than normal TTL and switch faster. CMOS logic gates use complementary arrangements of enhancement-mode N-channel and P-channel field effect transistor.
Since the initial devices used oxide-isolated metal gates, they were called CMOS complementary metal—oxide—semiconductor logic. A CMOS gate draws no current other than leakage when in a steady 1 or 0 state. When the gate switches states, current is drawn from the power supply to charge the capacitance at the output of the gate. This means that the current draw of CMOS devices increases with switching rate controlled by clock speed, typically.
However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies.
CMOS gates can also tolerate much wider voltage ranges than TTL gates because the logic thresholds are approximately proportional to power supply voltage, and not the fixed levels required by bipolar circuits. The required silicon area for implementing such digital CMOS functions has rapidly shrunk. The extremely small capacitance of the on-chip wiring caused an increase in performance by several orders of magnitude.
CMOS chips often work with a broader range of power supply voltages than other logic families. Reduced energy implies less heat dissipation. By lowering the power supply from 5V to 3. Many motherboards have a voltage regulator module to provide the even lower power supply voltages required by many CPUs.
Because of the incompatibility of the CD series of chips with the previous TTL family, a new standard emerged which combined the best of the TTL family with the advantages of the CD family. It was known as the 74HC which used anywhere from 3. Interconnecting any two logic families often required special techniques such as additional pull-up resistors , or purpose-built interface circuits, since the logic families may use different voltage levels to represent 1 and 0 states, and may have other interface requirements only met within the logic family.
These devices only work with a 5V power supply. These are generally used "on-chip" and are not delivered as building-block medium-scale or small-scale integrated circuits.
With HC and HCT logic and LS-TTL logic competing in the market it became clear that further improvements were needed to create the ideal logic device that combined high speed, with low power dissipation and compatibility with older logic families.
A whole range of newer families has emerged that use CMOS technology. A short list of the most important family designators of these newer devices includes:. The integrated injection logic IIL or I 2 L uses bipolar transistors in a current-steering arrangement to implement logic functions. The following logic families would either have been used to build up systems from functional blocks such as flip-flops, counters, and gates, or else would be used as "glue" logic to interconnect very-large scale integration devices such as memory and processors.
Not shown are some early obscure logic families from the early s such as DCTL direct-coupled transistor logic , which did not become widely available. Propagation delay is the time taken for a two-input NAND gate to produce a result after a change of state at its inputs. Toggle speed represents the fastest speed at which a J-K flip flop could operate. Values are very typical and would vary slightly depending on application conditions, manufacturer, temperature, and particular type of logic circuit.
Introduction year is when at least some of the devices of the family were available in volume for civilian uses. Some military applications pre-dated civilian use. Several techniques and design styles are primarily used in designing large single-chip application-specific integrated circuits ASIC and CPUs, rather than generic logic families intended for use in multi-chip applications. These design styles can typically be divided into two main categories, static techniques and clocked dynamic techniques.
See static versus dynamic logic for some discussion on the advantages and disadvantages of each category. From Wikipedia, the free encyclopedia. Main article: Resistor—transistor logic. Main article: Diode—transistor logic. Main article: Emitter-coupled logic. Main article: Transistor—transistor logic.
Main article: CMOS. Main article: Integrated injection logic. Archived from the original on Retrieved History of Semiconductor Engineering. Semiconductor History Museum of Japan. Retrieved 5 July Blood Jr. Sams and Co. Logic families. Static Dynamic Domino logic Four-phase logic. Categories : Logic families. Hidden categories: Wikipedia articles needing clarification from July Namespaces Article Talk. Views Read Edit View history.
Electronic Logic Circuits