Diode transistor logic, or dtl, refers to the technology for designing and fabricating digital. This system facilitates the design of electronic circuits that convey information, including logic gates. Transistors can be combined to create all our fundamental logic gates. Such a switch can be most conveniently realized using the differential pair shown in fig. Jun 19, 2019 in this tutorial, we will have a brief introduction to logic gates. V s will initially charge up quickly, but the tail end of the transient is slow. For simplicity we will show here only two inputs nand gate circuit by using diodes and transistors. Some ttl structures have fanouts of at least 20 for both logic levels. Logic gates are the basic building blocks of any digital system. Introduction to digital logic with laboratory exercises. Transistor sizing for a complex gate brown university. Transistor transistor logic topics the most commonly used bipolar logic family is transistor transistor logic.
A bipolar junction transistor is made up of three pieces of silicon. Transistor q1 thus acts as a backtoback diode rather than as a transistor. The humble transistor q1 emitter e collector c base b transistor basics emitter to base junction is forward biased normally collector to base junction is reverse biased normally transistors are current operated devices, so. Both transistors must be saturated on for an output at q. Design a 3input cmos nand gate punpdn with fanout of 3. Transistortransistor logic ttl is a logic family built from bipolar junction transistors. These days mosfets are more likely to be used to create logic gates than bjts. The pair is biased with a constantcurrent source i, and one side is connected to a reference voltage v r. These are basic circuits, so they can be improved with diodes for reverse voltage protection, for example, or can be simplified xor, xnor gates.
In this tutorial, we will have a brief introduction to logic gates. These are basic circuits, so they can be improved with diodes for reverse voltage protection, for example, or can be simplified. For a junction field effect transistor jfet, its gate must be biased in such a way as to reversebias the pnjunction. There exists a reversible gate which could play a role of a universal gate for reversible circuits. Diode and transistor nand gate or dtl nand gate and nand gate. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20 computer science cornell university see. Even more serious is the voltage degradation for the cascaded andor function.
Thus, the circuit of figure may be rearranged placing not gate immediately after the and gate to yield the nand gate of figure 2. Pass transistor logic xor gate using pass transistor logic. Digital logic and transistor ol ict tutorial part 02 december 3, 2017 ol tutorials, tutorials comments off on digital logic and transistor ol ict tutorial part 02 2,646 views ict is the short form of the information and communication technology and this is vary impotent subjects in present and it will be more useful for future times. Introduction to logic gates not, and, nand, or, nor. Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. Experiment 6 transistors as amplifiers and switches. Resistor is used to keep the output current to a safe value. A gate is an electronic device which is used to compute a function on a two valued signal.
The pn junction of d2 is replaced by the be junction of q2 and with the current gain of the transistor, the current going into the base of q3 is greatly increased, increasing the fanout. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or lsttl. In small, discrete quantities, transistors can be used to create simple electronic switches, digital logic, and signal amplifying circuits. When the baseemitter diode is turned on enough to be driven into saturation, the collector voltage with respect to the emitter may be near zero and can be used to construct gates for the ttl logic family.
A truth table lists all possible combination of inputs and the corresponding outputs. An npn transistor has a piece of ptype silicon the base sandwiched between two pieces of ntype the collector and emitter. Even more important is the fact that nand and nor are complete. Npn transistor tutorial the bipolar npn transistor. Reversible logic fundamentals reversible gates basic. Transistortransistorlogic topics the most commonly used bipolar logic family is transistor transistor logic. 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. Any other gate, and in particular the noninverting gates and and or require more transistors. Only a limited number of series cascaded circuits can be used before the logic levels must be restored to the rails. This will produce an output v ddv tn1v tn2 v dd in out. Depending on what is added to the silicon, it will be either ntype or ptype. In the previous tutorial we saw that the standard bipolar transistor or bjt, comes in two basic forms. In this configuration there are two transistors connected in series. A voltage transfer curve is a graph of the input voltage to a gate versus its output voltage.
The not gate consists of a single npn transistor, a. This means that any other digital logic gate can be constructed using only nand gates or only nor gates. Logic minimization logic gates in the standard circuits with transistorminimum gate equivalents by taking advantage of nandnor logic results in the minimized pos and sop circuits shown in the green boxes. Experiment 6 transistors as amplifiers and switches our final topic of the term is an introduction to the transistor as a discrete circuit element. Diodetransistor logic, or dtl, refers to the technology for designing and fabricating digital. Low level state when lower transistor is on and upper transistor is off. Mosfets are more powerefficient, which makes them the better choice. The reader will first see how logic gates can be constructed from transistors and then how digital logic functions are constructed using those gates. Digital logic gate tutorial basic logic gates electronicstutorials. Ttl transistortransistor logic families history and. Transistor and logic gates laboratory instruction today you will learn how to use a transistor to amplify a small ac signal as well as using it as a switch to construct digital logic circuits. The truth table of xor gate is as shown in table below.
The gate electrode is placed on top of a very thin insulating layer and there are a pair of small ntype regions just under the drain and source electrodes. We also learnt that the junctions of the bipolar transistor can be biased in one of three different ways. Its name signifies that transistors perform both the logic function the first transistor and the amplifying function the second transistor. Hi guys, in this tutorial i will show you some npn transistor based logic gates. Since an integrated circuit is constructed primarily from dozens to even millions of transistors formed from a single, thin silicon crystal, it might be interesting and instructive to. The pdn is constructed using nmos devices, while pmos transistors are used in the pun. Transistortransistorlogic topics the most commonly used bipolar logic family is transistortransistor logic. Transistors and logic gates uwmadison computer sciences. These gates are the not gate, nand gate, and the nor gate.
Digital logic gate functions include and, or and not. Piv is the peakinversevoltage of the diode forward bias occurs when the ptype block is connected to the positive terminal of the battery and the ntype is connected to the negative terminal of the battery, as shown below. This is the basis for the operation for your computer and any. The current drive of the transistor gatetosource voltage is reduce significantly as v.
Pchannel, through the semiconductive drainsource channel. We will see the different logic levels in ttl circuits, cmos circuits, some simple logic gates like or, not, nand, and, etc. An and gate may be created by adding an inverter stage to the output of the nand gate circuit. 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. It is an electronic circuit having one or more than one input and only one output. This is a transistor transistor logic ttl and gate circuit using bipolar junction transistors. The relationship between the input and the output is based on a certain logic. Drl, diodetransistor logic dtl and transistortransistor logic ttl as. Digital logic gates nand and nor are called universal logic gate because we can construct all other logic gates using nand gate or nor gate alone. Not, or, and and gates are the basic types of gates. Diodetransistor logic 2 and gate and logic 1 drops for the or gate. This nand gate is called dtl nand gate or diode transistor logical nand gate. In electronics, emittercoupled logic ecl is a highspeed integrated circuit bipolar transistor logic family.
What you need a breadboard a bunch of 5k and 10k resistors, and transistors a led you can use any npn type transistor for example 2n3904, bc547, bc548, bc549 etc. Compare the above design with that of a 3input nor punpdn gate. Fundamentals of mosfet and igbt gate driver circuits. Xorgateusingpasstransistorlogic electronics tutorial. Ttl and cmos characteristics purpose logic gates are classified not only by their logical functions, but also by their logical families. Diode transistor logic 2 and gate and logic 1 drops for the or gate.
When both input a and b are given with 0 v, both of the diodes are in forward biased condition that is in on condition. Passtransistorlogic xor gate using pass transistor logic. A basic circuit using any generalpurpose bipolar transistor such as the bc549, bc548, or bc547, can be used to construct the and gate. The highimpedance state plays no role in the logic, which is strictly binary. Diode logic dl resistor transistor logic rtl diode transistor logic dtl emitter coupled logic ecl logic families can be classified broadly according to the technologies they are built with transistor transistor logic ttl cmos logic ttl and cmos logic family is most widely used ic technologies. One way to simplify the circuit for manual analysis is to open the feedback loop.
Heres a transistor circuit that implements an inverter, or not gate. Fundamentals of mosfet and igbt gate driver circuits laszlobalogh abstract the main purpose of this application report is to demonstrate a systematic approach to design high performance gate drive circuits for high speed switching applications. In a pnp transistor, the type of the layers are reversed. What you needa breadboarda bunch of 5k and 10k resistors, and transistorsa led you can use any npn type transistor for example 2n3904, bc547, bc548, bc549 etc. In this tutorial well introduce you to the basics of the most common transistor around. Use switch behavior of mos transistors to implement logical functions. Based on this, logic gates are named as and gate, or gate, not gate etc. How to make resistortransistor logic gates custom maker pro.
Digital logic and transistor ol ict tutorial part 04. Apr 25, 2012 in this electronics 201 lecture, we look at how to construct any logic gate imaginable from simple npn transistors using not logic. Ttl nand and and gates logic gates electronics textbook. Jul 25, 2018 realizing nand gate using diode and transistor. Question 3 the simplest type of digital logic circuit is an inverter, also called an inverting bu. The interconnection of gates to perform a variety of logical operation is called logic design. Logic and gate tutorial with logic and gate truth table. These devices are used on buses of the cpu to allow multiple chips to send data. Logic and gates are available using digital circuits to produce. The use of transistors for the construction of logic gates depends upon their utility as fast switches.
As well as ttl and cmos technology, simple digital logic gates can also be made by connecting together diodes, transistors and resistors to produce rtl, resistor transistor logic. A diodes iv characteristic is shown in figure 6 below. As engineers, one of our primary goals is to implement circuits efficiently. For the and logic, the transistors are in series and both transistors must be in the. A threestate logic gate is a type of logic gate that can have three different outputs. Metaloxidesemiconductor field effect transistor mosfet. An npn n egative p ositive n egative type and a pnp the most commonly used transistor configuration is the npn transistor. However, during turn off, q1 functions as a transistor thereby reducing the storage charge as will be obvious below. What you needa breadboarda bunch of 5k and 10k resistors, and transistors a led you can use any npn type transistor for example 2n3904, bc547, bc548, bc549 etc. Digital logic is the basis of electronic systems, such as computers and cell phones. The reader will first see how logic gates can be constructed from transistors and. This manual concentrates on the basic building blocks of digital electronics. Here is a schematic diagram for an inverter gate constructed from bipolar transistors transistortotransistorlogic.
Logic operation is same as the open collector output. A ttl nand gate can be made by taking a ttl inverter circuit and adding another input. This forms the threeinput positive nand gate using dtl logic. Logic gates not, or, and, nor, nand, xor, xnor gate, pdf. Published under the terms and conditions of the design science license. In this electronics 201 lecture, we look at how to construct any logic gate imaginable from simple npn transistors using not logic. Simple digital logic gates can be made by combining transistors, diodes and. Use of transistors q4 and diode is to provide quick charging and discharging of parasitic capacitance across q3. The nand gate may be easily implemented by putting a transistor logic not gate immediately at the output of a diode and gate. Thus, the base voltage of q2, which is the same as the collector voltage of q3, is at 0. In this gate if the b input is low then left nmos transistor is on and the logic value of a is copied to the output f. Power dissipation of reversible circuit, under ideal physical circumstances, is zero. Transistor transistor logic ttl family one basic function of ttl ic is as a complimenting switch or inverter.
Digital logic and transistor ol ict tutorial part 02. Figure below shows the implementation of xor function using pass transistors. Digital logic and transistor ol ict tutorial part 04 december 31, 2017 ol tutorials, tutorials comments off on digital logic and transistor ol ict tutorial part 04 1,836 views ict is the short form of the information and communication technology and this is vary impotent subjects in present and it will be more useful for future times. Digital logic is rooted in binary code, a series of zeroes and ones each having an opposite value.
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