Logic family
Encyclopedia
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 gate
s constructed using one of several different designs, usually with compatible logic level
s 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 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
microprocessor
s 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.
logic circuits similar to RTL. Several early transistor
ized 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.
goes back as far as ENIAC
and was used in many early vacuum tube
computers. Several early transistor
ized computers (e.g., IBM 1401
) used DTL, where it was implemented using discrete components.
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 diode
s 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.
ized IBM 7030 Stretch computer, where it was implemented using discrete components.
The first ECL logic family to be available in integrated circuits was introduced by Motorola
as MECL in 1962.
as Sylvania Universal High–Level Logic (SUHL) in 1963. Texas Instruments introduced 5400 Series
TTL family in 1964.
Transistor–transistor logic uses bipolar transistor
s to form its integrated circuits. TTL has changed significantly over the years, with newer versions replacing the older types.
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. Schottky transistors have a much higher switching speed than conventional transistors because the Schottky junction does not promote charge storage, leading to faster switching gates. Gates built with Schottky transistors use more power than normal TTL and switch faster. With Low-power Schottky (LS), internal resistance values were increased to reduce power consumption and increase switching speed over the original version. The introduction of Advanced Low-power Schottky (ALS) further increased speed and reduced power consumption. A faster logic family called Fast (Schottky) (F) was also introduced that was faster than normal Schottky TTL.
s in a kind of current-steering arrangement to form its integrated circuits.
IIL is slightly easier to construct on an integrated circuit, and so was popular for early VLSI circuits.
. Since the initial devices used oxide-isolated metal gates, they were called CMOS
(complementary metal–oxide–semiconductor logic).
In contrast to TTL, CMOS uses almost no power in the static state (that is, when inputs are not changing). 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).
The first CMOS family of logic integrated circuits was introduced by RCA
as CD4000 COS/MOS, the 4000 series
, in 1968. Initially CMOS logic was slower than LS-TTL. 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. VLSI technology incorporating millions of basic logic operations onto one chip, almost exclusively uses CMOS. The extremely small capacitance of the on-chip wiring, caused an increase in performance by several orders of magnitude. On-chip clock rates as high as 4 GHz have become common, approximately 1000 times faster than the technology by 1970.
voltage
of 5V, CMOS works with a wider range of power supply voltage – usually anywhere from 3 to 15V. Lowering the supply voltage reduces the current required to charge stray capacitance, and so reduces the current drawn by complex microprocessors. This in turn reduces the heat dissipation of the processor. By lowering the power supply from 5V to 3.3V, switching power was reduced by almost 60 percent (power dissipation is proportional to the square of the supply voltage). Newer CPUs have lowered their power supply voltages further.
of the 74LS family with an improved version of CMOS technology inside the chip. It could be used both with logic devices which used 3.3V power supplies (and thus 3.3V logic levels), and with devices that used 5V power supplies and TTL logic level
s.
s, 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.
TTL logic levels are different from those of CMOS – generally a TTL output does not rise high enough to be reliably recognized as a logic 1 by a CMOS input. This problem was solved by the invention of the 74HCT family of devices that uses CMOS technology but TTL input logic levels. These devices only work with a 5V power supply. They form a replacement for TTL, although HCT is slower than original TTL (HC logic has about the same speed as original TTL).
s include cascode voltage switch logic
(CVSL) and pass transistor logic
(PTL) of various sorts. These are generally used "on-chip" and are not delivered as building-block medium-scale or small-scale integrated circuits.
, of which the LVT and ALVT logic families are the most important. The BiCMOS family has many members, including ABT logic, ALB logic, ALVT logic, BCT logic and LVT logic.
There are many others including AC/ACT logic, AHC/AHCT logic, ALVC logic, AUC logic, AVC logic, CBT logic, CBTLV logic, FCT logic and LVC logic.
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. Power per gate is for an individual 2-input NAND gate; usually there would be more than one gate per IC package. 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.
Computer engineering
Computer engineering, also called computer systems engineering, is a discipline that integrates several fields of electrical engineering and computer science required to develop computer systems. Computer engineers usually have training in electronic engineering, software design, and...
, a logic family may refer to one of two related concepts. A logic family of monolithic digital integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
devices is a group of electronic logic gate
Logic gate
A logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
s constructed using one of several different designs, usually with compatible logic level
Logic level
In digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground , although other standards exist...
s 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
Domino logic
Domino logic is a CMOS-based evolution of the dynamic logic techniques which were based on either PMOS or NMOS transistors. It allows a rail-to-rail logic swing. It was developed to speed up circuits....
, use clocked dynamic techniques
Dynamic logic (digital logic)
In integrated circuit design, dynamic logic is a design methodology in combinatorial logic circuits, particularly those implemented in MOS technology. It is distinguished from the so-called static logic by exploiting temporary storage of information in stray and gate capacitances...
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.
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 logicDirect-coupled transistor logicA special type of resistor–transistor logic , a direct-coupled transistor logic or DCTL gate is one wherein the bases of the transistors are connected directly to inputs without any base resistors. Without the base resistors, DCTL gates are more economical and simpler to fabricate onto integrated...
(DCTL) - Resistor–capacitor–transistor logic (RCTL)
- Direct-coupled transistor logic
- Diode–transistor logic (DTL)
- Complemented transistor diode logic (CTDL)
- High-threshold logicHigh Threshold LogicHigh Threshold Logic is a variant of DTL which is used in such environments where noise is very high.- Operation :The threshold values at the input to a logic gate determine whether a particular input is interpreted as a logic 0 or a logic 1....
(HTL)
- Emitter-coupled logicEmitter-coupled logicIn electronics, emitter-coupled logic , is a logic family that achieves high speed by using an overdriven BJT differential amplifier with single-ended input, whose emitter current is limited to avoid the slow saturation region of transistor operation....
(ECL)- Positive emitter-coupled logic (PECL)
- Low-voltage positive emitter-coupled logic (LVPECL)
- Gunning transceiver logicGunning Transceiver LogicGunning transceiver logic or GTL is a type of logic signaling used to drive electronic backplane buses. It has a voltage swing between 0.4 volts and 1.2 volts—much lower than that used in TTL and CMOS logic—and symmetrical parallel resistive termination. The maximum signaling frequency is specified...
(GTL) - Transistor–transistor logic (TTL)
- P-type metal–oxide–semiconductor logicPMOS logicP-type metal-oxide-semiconductor logic uses p-type metal-oxide-semiconductor field effect transistors to implement logic gates and other digital circuits...
(PMOS) - N-type metal–oxide–semiconductor logicNMOS logicN-type metal-oxide-semiconductor logic uses n-type metal-oxide-semiconductor field effect transistors to implement logic gates and other digital circuits...
(NMOS)- Depletion-load NMOS logic
- Complementary metal–oxide–semiconductor logicCMOSComplementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
(CMOS) - Bipolar complementary metal–oxide–semiconductor logicBiCMOSBiCMOS is an evolved semiconductor technology that integrates two formerly separate semiconductor technologies - those of the analog bipolar junction transistor and the digital CMOS transistor - in a single integrated circuit device....
(BiCMOS) - Integrated injection logicIntegrated injection logicIntegrated injection logic is a class of digital circuits built with multiple collector bipolar junction transistors . When introduced it had speed comparable to TTL yet was almost as low power as CMOS, making it ideal for use in VLSI integrated circuits...
(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
Philips NORbits
The 60-series NORbit is a very early form of digital logic developed by Philips that uses modules containing discrete components to build logic building blocks. There are three basic types contained in a large 17 pins Dual in-line package, with nine pins on one side and eight pins on the other side...
family of logic building blocks.
The PMOS and I2L logic families were used for relatively short periods, mostly in special purpose custom LSI
LSI
LSI may mean* Lord Steel Industry, a manufacturer of stainless steel tubing and piping* Labour and Socialist International, a former socialist international* Lake Superior and Ishpeming Railroad, a railroad service in Michigan, U.S....
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 4004
The Intel 4004 was a 4-bit central processing unit released by Intel Corporation in 1971. It was the first complete CPU on one chip, and also the first commercially available microprocessor...
, Intel 4040
Intel 4040
The Intel 4040 microprocessor was the successor to the Intel 4004. It was introduced in 1974. The 4040 employed a 10 μm silicon gate enhancement load PMOS technology, was made up of 3,000 transistors and could execute approximately 60,000 instructions per second.- Extensions :*Instruction Set...
, and Intel 8008
Intel 8008
The Intel 8008 was an early byte-oriented microprocessor designed and manufactured by Intel and introduced in April 1972. It was an 8-bit CPU with an external 14-bit address bus that could address 16KB of memory...
microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
s 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
NMOS logic
N-type metal-oxide-semiconductor logic uses n-type metal-oxide-semiconductor field effect transistors to implement logic gates and other digital circuits...
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.
RTL
The Atanasoff–Berry Computer used vacuum tubeVacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
logic circuits similar to RTL. Several early transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
ized computers (e.g., IBM 1620
IBM 1620
The IBM 1620 was announced by IBM on October 21, 1959, and marketed as an inexpensive "scientific computer". After a total production of about two thousand machines, it was withdrawn on November 19, 1970...
, 1959) used RTL, where it was implemented using discrete components.
A family of simple resistor–transistor logic integrated circuits was developed at Fairchild Semiconductor
Fairchild Semiconductor
Fairchild Semiconductor International, Inc. is an American semiconductor company based in San Jose, California. Founded in 1957, it was a pioneer in transistor and integrated circuit manufacturing...
for the Apollo Guidance Computer
Apollo Guidance Computer
The Apollo Guidance Computer provided onboard computation and control for guidance, navigation, and control of the Command Module and Lunar Module spacecraft of the Apollo program...
in 1962.
Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
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.
DTL
Diode logicDiode logic
Diode logic or diode-resistor logic constructs Boolean logic gates from diodes acting as electrically operated switches. While diode logic has the advantage of simplicity, the lack of an amplifying stage in each gate limits its application...
goes back as far as ENIAC
ENIAC
ENIAC was the first general-purpose electronic computer. It was a Turing-complete digital computer capable of being reprogrammed to solve a full range of computing problems....
and was used in many early vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
computers. Several early transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
ized computers (e.g., IBM 1401
IBM 1401
The IBM 1401 was a variable wordlength decimal computer that was announced by IBM on October 5, 1959. The first member of the highly successful IBM 1400 series, it was aimed at replacing electromechanical unit record equipment for processing data stored on punched cards...
) used DTL, where it was implemented using discrete components.
The first diode–transistor logic family of integrated circuits was introduced by Signetics
Signetics
Signetics, once a major player in semiconductor manufacturing, made a variety of devices which included integrated circuits, bipolar and MOS, the Dolby circuit, logic, memory and analog circuits. They developed microprocessors like the 2650, the bipolar 8X300 and had licensed Motorola 68000...
in 1962. DTL was also made by Fairchild and Westinghouse
Westinghouse Electric (1886)
Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...
.
A family of diode logic and diode-transistor logic integrated circuits was developed by Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
for the D-37C
D-37C
The D-37C is the computer component of the all-inertial NS-17 Missile Guidance Set for accurately navigating to its target thousands of miles away. The NS-17 MGS was used in the Minuteman II ICBM...
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 diode
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
s 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.
ECL
The ECL family, ECL is also known as current-mode logic (CML), was invented by IBM as current steering logic for use in the transistorTransistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
ized IBM 7030 Stretch computer, where it was implemented using discrete components.
The first ECL logic family to be available in integrated circuits was introduced by Motorola
Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...
as MECL in 1962.
TTL
The first transistor-transistor logic family of integrated circuits was introduced by SylvaniaOsram Sylvania
Osram Sylvania Inc. is the North American operation of lighting manufacturer Osram GmbH, which is owned by Siemens AG. It was established in January 1993, with the acquisition of GTE’s Sylvania lighting division by Osram GmbH....
as Sylvania Universal High–Level Logic (SUHL) in 1963. Texas Instruments introduced 5400 Series
7400 series
The 7400 series of transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic. It was used to build the mini and mainframe computers of the 1960s and 1970s...
TTL family in 1964.
Transistor–transistor logic uses bipolar transistor
Bipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
s to form its integrated circuits. TTL has changed significantly over the years, with newer versions replacing the older types.
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
Walter H. Schottky
Walter Hermann Schottky was a German physicist who played a major early role in developing the theory of electron and ion emission phenomena, invented the screen-grid vacuum tube in 1915 and the pentode in 1919 while working at Siemens, and later made many significant contributions in the areas of...
formulated a theory predicting the Schottky effect, which led to the Schottky diode
Schottky diode
The Schottky diode is a semiconductor diode with a low forward voltage drop and a very fast switching action...
and later Schottky transistors. Schottky transistors have a much higher switching speed than conventional transistors because the Schottky junction does not promote charge storage, leading to faster switching gates. Gates built with Schottky transistors use more power than normal TTL and switch faster. With Low-power Schottky (LS), internal resistance values were increased to reduce power consumption and increase switching speed over the original version. The introduction of Advanced Low-power Schottky (ALS) further increased speed and reduced power consumption. A faster logic family called Fast (Schottky) (F) was also introduced that was faster than normal Schottky TTL.
IIL
The integrated injection logic (IIL) uses bipolar transistorBipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
s in a kind of current-steering arrangement to form its integrated circuits.
IIL is slightly easier to construct on an integrated circuit, and so was popular for early VLSI circuits.
CMOS
CMOS logic gates use complementary arrangements of N-channel and P-channel Field effect transistorMOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
. Since the initial devices used oxide-isolated metal gates, they were called CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
(complementary metal–oxide–semiconductor logic).
In contrast to TTL, CMOS uses almost no power in the static state (that is, when inputs are not changing). 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).
The first CMOS family of logic integrated circuits was introduced by RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
as CD4000 COS/MOS, the 4000 series
4000 series
The 4000 series is a family of industry standard integrated circuits which implement a variety of logic functions using Complementary Metal–Oxide–Semiconductor technology, and are still in use today. They were introduced by RCA as CD4000 COS/MOS series in 1968, as a lower power and more versatile...
, in 1968. Initially CMOS logic was slower than LS-TTL. 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. VLSI technology incorporating millions of basic logic operations onto one chip, almost exclusively uses CMOS. The extremely small capacitance of the on-chip wiring, caused an increase in performance by several orders of magnitude. On-chip clock rates as high as 4 GHz have become common, approximately 1000 times faster than the technology by 1970.
Lowering the power supply voltage
One very important feature of CMOS chips is that they work with a broader range of power supply voltages. While TTL ICs all require a power supplyPower supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
of 5V, CMOS works with a wider range of power supply voltage – usually anywhere from 3 to 15V. Lowering the supply voltage reduces the current required to charge stray capacitance, and so reduces the current drawn by complex microprocessors. This in turn reduces the heat dissipation of the processor. By lowering the power supply from 5V to 3.3V, switching power was reduced by almost 60 percent (power dissipation is proportional to the square of the supply voltage). Newer CPUs have lowered their power supply voltages further.
HC logic
Because of the incompatibility of the CD4000 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 CD4000 family. It was known as the 74HC (High-performance silicon gate) family of devices and used the pinoutPinout
In electronics, a pinout is a cross-reference between the contacts, or pins, of an electrical connector or electronic component, and their functions.- Purpose :...
of the 74LS family with an improved version of CMOS technology inside the chip. It could be used both with logic devices which used 3.3V power supplies (and thus 3.3V logic levels), and with devices that used 5V power supplies and TTL logic level
Logic level
In digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground , although other standards exist...
s.
The CMOS–TTL logic level problem
Interconnecting any two logic families often required special techniques such as additional pull-up resistorPull-up resistor
Pull-up resistors are used in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or high-impedance...
s, or purpose-built interface circuits, since the logic families may use different voltage levels
Logic level
In digital circuits, a logic level is one of a finite number of states that a signal can have. Logic levels are usually represented by the voltage difference between the signal and ground , although other standards exist...
to represent 1 and 0 states, and may have other interface requirements only met within the logic family.
TTL logic levels are different from those of CMOS – generally a TTL output does not rise high enough to be reliably recognized as a logic 1 by a CMOS input. This problem was solved by the invention of the 74HCT family of devices that uses CMOS technology but TTL input logic levels. These devices only work with a 5V power supply. They form a replacement for TTL, although HCT is slower than original TTL (HC logic has about the same speed as original TTL).
Other CMOS families
Other CMOS circuit families within integrated circuitIntegrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s include cascode voltage switch logic
Cascode Voltage Switch Logic
Cascode Voltage Switch Logic refers to a CMOS-type logic family which is designed for certain advantages. It requires mainly N-channel MOSFET transistors to implement the logic using true and complementary input signals, and also needs two P-channel transistors at the top to pull one of the...
(CVSL) and pass transistor logic
Pass transistor logic
In electronics, pass transistor logic describes several logic families used in the design of integrated circuits. It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. Transistors are used as switches to pass logic levels between nodes of a...
(PTL) of various sorts. These are generally used "on-chip" and are not delivered as building-block medium-scale or small-scale integrated circuits.
BiCMOS
One major improvement was to combine CMOS inputs and TTL drivers to form of a new type of logic devices called BiCMOS logicBiCMOS
BiCMOS is an evolved semiconductor technology that integrates two formerly separate semiconductor technologies - those of the analog bipolar junction transistor and the digital CMOS transistor - in a single integrated circuit device....
, of which the LVT and ALVT logic families are the most important. The BiCMOS family has many members, including ABT logic, ALB logic, ALVT logic, BCT logic and LVT logic.
Improved versions
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:- LV logic (lower supply voltage)
- LVT logic (lower supply voltage while retaining TTL logic levels)
- ALVT logic (an 'advanced' version of LVT logic)
There are many others including AC/ACT logic, AHC/AHCT logic, ALVC logic, AUC logic, AVC logic, CBT logic, CBTLV logic, FCT logic and LVC logic.
Monolithic integrated circuit logic families table
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 1960s 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. Power per gate is for an individual 2-input NAND gate; usually there would be more than one gate per IC package. 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.
| Family | Description | Propagation delay (ns) | Toggle speed (MHz) | Power per gate @1 MHz (mW) | Typical supply voltage V (range) | Introduction year | Remarks |
|---|---|---|---|---|---|---|---|
| RTL | Resistor–transistor logic | 4 | 10 | 3.3 | 1963 | the first CPU built from integrated circuits (the Apollo Guidance Computer Apollo Guidance Computer The Apollo Guidance Computer provided onboard computation and control for guidance, navigation, and control of the Command Module and Lunar Module spacecraft of the Apollo program... ) used RTL. |
|
| DTL | Diode–transistor logic | 10 | 5 | 1962 | Introduced by Signetics, Fairchild 930 line became industry standard in 1964 | ||
| CMOS | AC/ACT | 3 | 125 | 0.5 | 3.3 or 5 (2-6 or 4.5-5.5) | 1985 | ACT has TTL Compatible levels |
| CMOS | HC/HCT | 9 | 30 | 0.5 | 5 (2-6 or 4.5-5.5) | 1982 | HCT has TTL compatible levels |
| CMOS | 4000B/74C | 30 | 5 | 1.2 | 10V (3-18) | 1970 | Approximately half speed and power at 5 volts |
| TTL | Original series | 10 | 25 | 10 | 5 (4.75-5.25) | 1964 | Several manufacturers |
| TTL | L | 33 | 3 | 1 | 5 (4.75-5.25) | 1964 | Low power |
| TTL | H | 6 | 43 | 22 | 5 (4.75-5.25) | 1964 | High speed |
| TTL | S | 3 | 110 | 19 | 5 (4.75-5.25) | 1969 | Schottky high speed |
| TTL | LS | 10 | 33 | 2 | 5 (4.75-5.25) | 1976 | Low power Schottky high speed |
| TTL | ALS | 4 | 34 | 1.3 | 5 (4.5-5.5) | 1976 | Advanced Low power Schottky |
| TTL | F | 3.5 | 100 | 5.4 | 5 (4.75-5.25) | 1979 | Fast |
| TTL | AS | 2 | 105 | 8 | 5 (4.5-5.5) | 1980 | Advanced Schottky |
| TTL | G | 1.5 | 1125 (1.125 GHz) | 1.65 - 3.6 | 2004 | First GHz 7400 series logic | |
| ECL | ECL III | 1 | 500 | 60 | -5.2(-5.19 - -5.21) | 1968 | Improved ECL |
| ECL | MECL I | 8 | 31 | -5.2 | 1962 | first integrated logic circuit commercially produced | |
| ECL | ECL 10K | 2 | 125 | 25 | -5.2(-5.19 - -5.21) | 1971 | Motorola |
| ECL | ECL 100K | 0.75 | 350 | 40 | -4.5(-4.2 - -5.2) | 1981 | |
| ECL | ECL 100KH | 1 | 250 | 25 | -5.2(-4.9 - -5.5) | 1981 |
See also
- 7400 series7400 seriesThe 7400 series of transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic. It was used to build the mini and mainframe computers of the 1960s and 1970s...
- List of 7400 series integrated circuits
- 4000 series4000 seriesThe 4000 series is a family of industry standard integrated circuits which implement a variety of logic functions using Complementary Metal–Oxide–Semiconductor technology, and are still in use today. They were introduced by RCA as CD4000 COS/MOS series in 1968, as a lower power and more versatile...
- List of 4000 series integrated circuits
- Logic gateLogic gateA logic gate is an idealized or physical device implementing a Boolean function, that is, it performs a logical operation on one or more logic inputs and produces a single logic output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and...
- Pin-compatibilityPin-compatibilityIn electronics, a pin-compatible device, such as a logic integrated circuit , memory module or microprocessor, is one that has the same functions assigned to the same particular pins....
- Open collectorOpen collectorAn open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...