Ttl, ecl, mos and cmos logic circuits, comparison of digital ic families. The low power schottky versions of ttl chips draw only 20% of the power, but are more expensive. The cmos model number will have a c in the middle of it, e. Due to longer rise and fall times, the transmission of digital signals becomes.
In transistor transistor logic or just ttl, logic gates are built only around transistors. When interfacing 5 v cmos logic to ttl, a simple direct connection can be used. Of these families, only ecl, ttl, nmos, cmos, and bicmos are currently still in widespread use. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or ls ttl. This is an nor gate implemented using transistortransistor logic. Ttl transistortransistor logic families history and. Integration levels gatetransistor ratio is roughly 110 ssi emitter coupled logic ecl, cmos a. Transistor transistor logic ttl emitter coupled logic ecl cmos logic family. Emittercoupled logic is based on the use of the currentsteering switch introduced in. Ac, lvc, rivals everything short of advanced schottky ttl and to be fair, a few lowvoltage cmos families are actually faster than as. To overcome the shortcomings of ttl gates more technologically advanced methodologies were designed for gates construction, such as pmos, nmos and the most recent and popular complementary metal oxide semiconductor type, or cmos. What are the basic differences between cmos and ttl signals.
Transistortransistorlogic topics the most commonly used bipolar logic family is transistortransistor logic. To give concreteness to our study of ecl, in the following we shall consider the popular ecl 10k in some detail. As the current is steered between two legs of an emittercoupled pair, ecl is sometimes called. Which one of the following logic family ics is fastest. Each family has its own advantages and limitations. Many logic families were produced as individual components, each. Zion fanout the fanout of a logic gate is the number of inputs that the gate can drive without exceeding its worstcase loading specifications. Which logic family has the highest power dissipation per gate a.
For example mixing 4000 and 74hc requires the power supply to be in the range 3 to 6v. Transistortransistor logic topics the most commonly used bipolar logic family is transistortransistor logic. For example, the diode in the dtl can be replaced by a transistor whose collector is pulled up to the power supply. Unlike the other logic families in this chapter, ecl does not produce a large voltage swing between the low and high levels. Gate 1989 ece comparision of ecl, ttl and cmos logic families. Fanout must be examined for both possible output states. Ttl, cmos characteristics and cmos logic gates purpose logic gates are classified not only by their logical functions, but also by their logical families. When 5v supply is given to ttl and cmos ics, logic levels of ttl and cmos are different. Ttl logic family the evolution from diode transistor logic to transistor transistor logic can be seen by observing the placement of pn junctions. Logic families and their characteristics website staff ui.
Evaluation of logic families using nor and nand logic gates. The advantage of the cmos over the ttl chips is that the cmos has a higher density of logic gates within the same material. Ttl chips consume more power as compared to the power consumed by the cmos chips even at rest. Ttl nor and or gates logic gates electronics textbook. Emitter coupled logic ecl or current mode logic cml 6. Although ics belonging to the same logic family have no special interface requirements, that is, the output of one can directly feed the input of the other, the same is not true if we have to interconnect digital ics belonging to different logic families. The same techniques, however, can be applied to other types of ecl. Is the fastest logic family and has the lowest propagation delay. The logic family refers to the general physical realization of a logical element, such as the ttl, emittercoupled logic ecl, or complementary metaloxide semiconductor cmos logic families. Cmosttl power requirements ttl power essentially constant no frequency dependence cmos power scales as f c v2 at high frequencies mhz cmos dissipates more power than ttl overall advantage is still for cmos even for very fast chips only a relatively small portion of complicated circuitry operates at highest frequencies frequency. A circuit which includes 74ls or 74hct ics must have a 5v supply. With respect to noise margins, hc devices feature significantly better performance than bipolar logic circuits. Logic families that are still in widespread use include ttl, cmos, ecl.
Figure1 depicts ttl to cmos interfacing and cmos to ttl interfacing circuits. Transistortransistor logic first introduced by in 1964 texas instruments ttl has shaped digital technology in many ways one of the most widely used families for small and mediumscale devices rarely used for vlsi standard ttl family e. This notation of ttl or cmos refers to the logic technology used to manufacture. It was soon superseded by the later ttl logic technology. Transistors q 1 and q 2 are both arranged in the same manner that weve seen for transistor q 1 in all the other ttl circuits. Difference between cmos and ttl difference between. Cmos circuits do not draw as much power as ttl circuits while at rest. A basic ttl device draws a power of almost 10mw, which reduces with the use of schottky devices. All of these technologies were developed in the 1950s1960s and evolved over. Ttl differences from cmos asymmetric input and output characteristics. Previous gate questions on ic logic families with solutions.
Sep 03, 2016 ttl logic in transistortransistor logic ttl, logic gates and other digital circuits are made using bipolar junction transistors and resistors. For example, the ttl logic gates use transistors with multiple emitters in a commonbase configuration as the input stage. Cmos and ttl are the two most widely used logic families. Click on the inputs on the bottom to toggle their state. However, it is also possible to prevent saturation by using a radically different circuit structure, called currentmode logic cml or emittercoupled logic ecl. For example, a certain amount of current is needed in order to operate correctly. It is best to build a circuit using just one logic family, but if necessary the different families may be mixed providing the power supply is suitable for all of them. Inputs source significant current in the low state, leakage current in the high state. Ttl logic in transistortransistor logic ttl, logic gates and other digital circuits are made using bipolar junction transistors and resistors. If allowed to float then ic will quickly break down. In electronics, emittercoupled logic ecl is a highspeed integrated circuit bipolar transistor logic family.
Difference between cmos and ttl compare the difference. Anyway, if you use 74hc cmos you can probably find pincompatible parts in cmos, ls ttl and more modern logic families such as vhc cmos. There have been many improvements in logical families such as ttl and cmos. 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. Standard commercially available digital logic gates are available in two basic families or forms, ttl which stands for transistortransistor logic such as the 7400 series, and cmos which stands for complementary metaloxidesilicon which is the 4000 series of chips. Technology of digital components, ttl logic families, ttl. On semiconductor ecl logic gates are available at mouser electronics. Cmos chips are much lower in power requirements drawing about 1 ma and operate with a wide range of supply voltages typically 3 to 18 volts. Difference between ttl and cmos ics and how to choose. There are different families of logic gates in digital logic design.
A bipolar families b mos families c hybrid devices. Translation to and from ecl technology is discussed in three section divisions. Ecl is used only in systems requiring highspeed operation. Translation between differently supplied ecl drivers and receivers section 2. Greenred productions relaxing music recommended for you. Lower current draw requires less power supply distribution, therefore causing a simpler and cheaper design. Fill in the banks of the statements below concerning the following logic families. The basic classification of the logic families are as follows. Combinational logic gates in cmos purdue university. An ecltottl converter comprising an ecl current switch having an input terminal and an output terminal, said ecl current switch comprising a pair of transistors with the emitters of said pair of transistors connected together and the base of one of said pair of transistors being said input terminal, said ecl current switch further comprising a resistor electrically connected to the. Cmos logic families many families of logic exist beyond static cmos comparison of logic families for a 2input multiplexer briefly overview pseudonmos differential cvsl dynamicdomino complementary passgate. Logic families are sets of chips that may implement different.
Within each logic family are one or more logic series that have distinctive characteristics, relative to other series within the same logic family. Cmos technology and logic gates mit opencourseware. Digital electronics lesson10 gates logic families cmos and ecl duration. This document describes the main logic families and their characteristics. Rather than functioning as amplifiers, q 1 and q 2 are both being used as twodiode steering networks. In any implementation of a digital system, an understanding of a logic elements physical capabilities and limitations.
Ecl devices and ttl 5 v, cmos 5 v, or lvttllvcmos 3. Evolution of ttl family ecl cmos family and its evolution overview 2. Difference between ttl cmos ecl ttl vs cmos vs ecl. Table 1 shows the minimum highlevel output voltage voh and the maximum lowlevel output voltage vol of cmos, ttl, btl, and gtl signals. The differing voltage level requirements of ttl and cmos technology present problems when the two types of gates are used in the same system.
Cmos logic has also been evaluated for different scaling in nor and nand gate. In simple words, logic families are specific configurations of logic gates that are designed for specific purposes. The term transistortransistor is because both logic function and amplification is done by transis. To make the and gate of ttl type can be used ic 7408. For example, a part that might be used is a 573 latch. Integration levels gate transistor ratio is roughly 110 ssi gates chip msi gates chip. A single logic gate in a cmos chip can consist of as little as two fets while a logic gate in a ttl chip can consist of a substantial number of. Ttl logic family digital logic families electronics.
Bipolar transistor transistor logic ttl first introduced by in 1964 texas instruments ttl has shaped digital technology in many ways standard ttl family e. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or lsttl. The propagation delay of cd4k gates is greater than that of ttl. The cmosttl logic level problem interconnecting any two logic families often required special techniques such as additional pullup resistors, or purposebuilt 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 and cmos have several subfamilies some consuming more power. Difference between ttl, cmos, ecl and bicmos logic families. For the ttl circuit shown in the figure, find the current flowing through the collector of transistor q 4, when v o 0. The input of a ttl logic gate is characterized by a multi. Gate 2003 ece comparision of logic families dtl, cmos, ecl. Lets examine the following ttl circuit and analyze its operation.
Standard ttl 74 xxxll, low power ttl 74lxx low power schottky. Jun 01, 2014 ttl vs cmos technology \\ comparison \\ interview questions electronic devices. Very fast bipolar logic but consumes too much power and hence not used. The applications discussed here include those where these devices are used to provide a specific function in a larger digital circuit. Ttl and cmos characteristics purpose logic gates are classified not only by their logical functions, but also by their logical families. They deliver speed and drive on a par with ttl, quashing worries about highspeed systems built with cmos alone.
The set of logic gates constructed using coupled transistors and resistors are collectively known as ttl gate family. Explain why the allowable power supply voltage range for a true ttl not highspeed cmos logic gate is so narrow. Ttl input or output lead is defined to be positive if the. Each ic family has its own characteristics, limitations and advantages.
A single logic gate in a cmos chip can consist of as little as two fets while a logic gate in a ttl chip can consist of a substantial number of parts as extra components like resistors are needed. But even then, the 74ls series logic used a different input circuit a diode and gate for a different compromise between speed and power. Digital logic gates nand and nor are called universal logic gate because. Overview integration, moores law early families dl, rtl ttl evolution of ttl family ecl cmos family and its evolution overview 2. Memory music, improve memory and concentration, binaural beats focus music duration. It means it can support at most 10 gates at its output. These logical families contain basic logical systems interconnected to form a larger. Logic signal voltage levels logic gates electronics. This page compares ttl vs cmos vs ecl logic families and mentions difference between ttl and cmos and ecl based on various parameters such as fanout,power consumption,noise immunity etc. The cmos driver must have a strong enough pull down to sink iil when the input to the ttl gate is low 0. Among the technologies discussed here are dl, rtl, dtl, ecl, ttl, cmos and bicmos. Supplanted ttl, thanks to its superior speed and low power consumption. This now offers the opportunity of using mixed cmos and ttl families at various. You can constrain your design to allow the use of any of them.
There are various logic families namely diode logic dl resistortransistor logic rtl diodetransistor logic dtl emitter coupled logic ecl logic families can be classified broadly according to the technologies they are built with transistortransistor logic ttl cmos logic ttl and cmos logic family is most widely used ic technologies. The storage time is eliminated as the transistors are used in difference amplifier mode and are never driven into saturation. The other two families are for military and industrial application. Concept of ttl logic family with questions digital. What is the typical range of supply voltages for a true ttl gate, and why cant this type of logic gate operate from a wider range of voltages as cmos gates can. Static cmos circuit at every point in time except during the switching transients each gate output is connected to either v dd or v ss via a lowresistive path the outputs of the gates assume at all times the value of the boolean function, implemented by the circuit in contrast, a dynamic circuit relies on temporary. However, cmos power consumption increases faster with higher clock speeds than ttl does. Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. They are widely used in large scale integrated circuits because of their high component density and relatively low power.
Integrated injection logic i 2 l family comparison of different logic families. Logic signal voltage levels logic gates electronics textbook. Voh and vol levels for various families logic level vohmin v volmax v cmos 3. Logic families digital electronics wiley online library. Alternatively, a logic family is also the connectivity of electrical components to implement logic in vlsi verylargescale integrated circuitry, such as processors and memory systems. In any implementation of a digital system, an understanding of a logic elements physical capabilities and limitations, determined by its logic family, are critical to proper operation. Ecl was the first type of logic ic family to be developed and it appeared around 1962. Ecl uses an overdriven bjt differential amplifier with singleended input and limited emitter current to avoid the saturated fully on region of operation and its slow turnoff behavior. Mos and cmos, are based on field effect transistors.
Cmos can be made compatible with ttl t cmos logic families cmos vs. Ttl is the largest family of digital ics, but the cmos family is growing rapidly. Ttl has a wellestablished popularity among logic families. Ecl is used for very highspeed 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. In this logic, transistor is used in conjunction with resistors to create a logic circuit. Threestate output also called tristate output in addition to the two usual output states high and. In computer engineering, a logic family may refer to one of two related concepts.
Ttl stands for transistor transistor logic, cmos stands for complementary metal oxide semiconductor and ecl stands for emitter coupled logic. The complementary metal oxide semiconductor family cmos has equivalents to most of the ttl chips. The lowlevel noise margin s l is the most critical value for all three logic families, ranging from 18. The primary advantage of cmos chips to ttl chips is in the greater density of logic gates within the same material. Ecl is based on use of current steering switch realised using differential transistor pair. The dtl logic family or series used diodes on the inputs to create functions such as and and or and then had transistors on the output. The power consumption of the cmos depends on various factors and is variable. Ecl emitter coupled logic, pdf file ecl backplane design ecl outputs are perfectly suited to drive transmission lines.
955 1146 826 640 1350 1389 1332 348 797 1582 1302 877 638 50 1577 783 1240 1171 923 988 580 324 1396 674 692 1455 294 681 101 1493 570 109 237 434 1394 1343 1060 697 1038 1040 1339 665 709 251