The complementary cmos circuit style falls under a broad class of logic circuits called static circuits in which at every point in time except during the switching transients, each gate output is connected to either v dd or. In a batterypowered device where you have limited power and the load is variable and often low, using bjt is a bad idea. Give the truth table for exnor and realize using nand gates. At first i tried the circuit without the r1 and r2 resistors but the output was 1 when b was 1 second input and 0 otherwise, regardless of a. This creates trees of gates that depend on each other. Help with design of bjt logic gates all about circuits. Apply a 1 khz sine wave at the input with a peaktopeak amplitude of 0. A combinational circuit has no memory characteristic, so its output depends only on. Basically, all logic gates have one output and two inputs. Jul 01, 2017 based on this, logic gates are named as and gate, or gate, not gate etc and gate a high output 1 results only if both the inputs to the and gate are high 1. Pdf operation of logic gates and, nand, or, nor with.
These gates are the and, or, not, nand, nor, exor and exnor gates. Logic families discussed so far are the ones that are commonly used for implementing discrete logic functions such as logic gates, flip flops, counters, multiplexers, demultiplexers etc. Digital systems are said to be constructed by using logic gates. In this alternative way to achieve nor logic, only one transistor is used with the two inputs tied to its base through resistors. Logic gates are the basics of a many digital electronic circuit. Used to build logic functions there are seven basic logic gates. Only use nfets to pull the output down and pfets to pull the output up. In this paper, we have developed a circuit which gives the output for 4logic gates of and, nand, or, nor simultaneously by taking only two inputs a and b. Building functions from logic gates weve already seen how to implement truth tables using and, or, and not an example of combinational logic. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20 computer science cornell university.
Realize the ex or gates using minimum number of nand gates. Resistortransistor logic rtl gates objectives be familiar with logic gates using resistors and bipolar transistor connected with rlt techniques. Hi guys, in this tutorial i will show you some npn transistor based logic gates. Basic digital logic gates perform logical operations of and, or and not on binary numbers.
Combining a number of basic logic gates in a larger circuit to produce more complex logical operations is called. Rtl was made from discrete transistors and resistors and manufactured on printed circuit boards with several gates per board. A bipolar junction transistor is a threeterminal device which acts as a currentcontrolled switch. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or lsttl.
Electronic circuits with matlab, pspice, and smith chart. A gate is an electronic device which is used to compute a function on a two valued signal. Instead of using four ics for four logic gates if we use this single ic for all the four logic gates then the space used for the remaining three ics can be used for other purposes. Even more important is the fact that nand and nor are complete. If a bjt is used to power something with a predictable current draw like leds, using bjt isnt as bad. Diodetransistor logic 1 chapter 5 diode transistor logic resistortransistor logic was an early form of logic used in the 1950s and early 1960s. Based on this, logic gates are named as and gate, or gate, not gate etc and gate a high output 1 results only if both the inputs to the and.
Any other gate, and in particular the noninverting gates and and or require more transistors. Bcause you can simply set the baseemitter current to be a small fraction of the led current to achive better efficiency. From the above examples and discussion, we conclude that we can construct the main logic functions and, or, and not using transistors. 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. We set up a circuit that has some constant source voltage connected to it. However, the diagrams we use are easier to understand. And, or, not, nand not and, nor not or, xor, and xnor not xor later building functions. Jul 25, 2018 realizing nand gate using diode and transistor. Operation of logic gates and, nand, or, nor with single circuit using bjt bipolar junction transistor. Transistortransistor logic topics the most commonly used bipolar logic family is transistortransistor logic. The or gate is a logic boolean gate that represents addition in basic algebra.
A functionally complete logic system may be composed of relays, valves vacuum tubes, or transistors. It gives students, researchers, and practicing engineers the necessary design and modelling tools for validating electronic design concepts involving bipolar junction transistors. Combinational logic circuit output depends only on the current inputs stateless sequential logic circuit output depends on the sequence of inputs past and present. Saturation in ecl is avoided by using the bjt differential pair as a current switch.
Logic gates actually look like weird bugs in real life. Make the circuit below using a bjt, 2n2222 transistor. The relationship between the input and the output is based on a certain logic. Im not clear on how to achieve the base current and drive the collector current. The basic operations are described below with the aid of truth tables. Logic families logic families are sets of chips that may implement different logical functions, but use the same type of transistors and voltage levels for logical levels and for the power supplies. 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. These circuits can be classified as combinational logic circuits because, at any time, the logic level at the output depends on the combination of logic levels present at the inputs. Most questions regarding the behavior of the device that arise when developing a system can be answered with the information given.
If we put a small current into one of the terminals, called the base, then the switch is oncurrent may flow between the other two terminals, called the emitter and the collector. The circuit driving voltage v is applied to the parallely connected diodes and the output is collected as the voltage drop at the diodes. Logic gates have been made out of dna see dna nanotechnology and used to create a computer called maya see mayaii. Instead of using four ics for four logic gates if we use this single. Transistortransistorlogic topics the most commonly used bipolar logic family is transistortransistor logic. The use of transistors for the construction of logic gates depends upon their utility as fast switches. Jun 20, 2015 and gate can be designed by using two simple diodes. Logic gates use switch behavior of mos transistors to implement logical functions.
From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20. Ttl and cmos characteristics purpose logic gates are classified not only by their logical functions, but also by their logical families. Introduction the ta will show you the emitter, base and collector for the transistor. Logic gates are the basic building block of digital circuits. From the above examples and discussion, we conclude that we can construct the main logic functions and, or, and not using transistors since we will be using these functions or gates in future designs, we will give them symbols so that we dont have to draw all the transistors and all the connections each time we want to use say an or gate. The simplest family of logic gates uses bipolar transistors, and is called resistortransistor logic rtl. Stroud combinational logic design 106 7 functionally complete set of gates if any digital circuit can be built from a set of gates, that set is said to be functionally complete functionally complete sets of gates. 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.
Any logic function can be implemented as sum of products. Since we will be using these functions or gates in future designs, we will give them symbols so that we dont have to draw all the transistors and all the connections each time we want to use say an or gate. Adjust the potentiometer so that it is in the center of its travel. Introduction to logic gates using transistor technology, we can create basic eve engels, 2006 slide 1 of 20 logic gates that perform boolean operations on high 5v and low 0v signals. The logic level shift problem of drl gates is not present in dtl and ttl gates so that gates may be connected in series indefinitely. Some logic gates like not gate or inverter has only one. Logic gates a b out 0 0 0 0 1 1 1 0 1 1 1 1 a b out 0 0 0 0 1 0 1 0 0. This page shows how to make this circuit, and the implementation is on a breadboard using discrete components. Logic gates 4 oo software design and construction 2input logic gate hierarchy it is sensible to view each of the 2input logic gates as a specialized subtype of a generic logic gate a base type which has 2 input wires and transmits its output to a single output wire. 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. It produces the exact reverse output to that of given input. Feb 05, 2011 i find the things we are doing in lab quite interesting, but i really lack a good understanding of what we are doing.
Operation of logic gates and, nand, or, nor with single. Logic gates can be made using pneumatic devices, such as the sorteberg relay or mechanical logic gates, including on a molecular scale. Also note that you can in theory, ymmv mix up pass transistor logic with pushpull logic. These families vary by speed, power consumption, cost, voltage. Using transistors as logic gates electrical engineering. I used bipolar junction transistors bjt to design this. This means that any other digital logic gate can be constructed using only nand gates or only nor gates.
The and gate is an electronic circuit that gives a high output 1 only if all its inputs are high. This nand gate is called dtl nand gate or diode transistor logical nand gate. A combinational circuit has no memory characteristic, so its output depends only on the current value of its inputs. Similarly a flipflop can be built by using a combination of logic gates and the logic gates itself can be built by using a few transistors. Unlike simple diode logic gates which do not have a gain element, rtl gates can be cascaded indefinitely to produce more complex logic functions. Logic gates digital circuit that either allows a signal to pass through it or not. Like diode, transistor also acts as electronic switch.
The output bjt switches between its cutoff and saturation regions to create logic 1 and 0, respectively. Introduction to logic gates not, and, nand, or, nor. What are the logic low and high levels of ttl ics and cmos ics. Digital logic or gate digital gates electrical technology. Fill in the truth table, given the following logic circuit made from logic and, or, and not gates. If either of the inputs or both inputs to a basic or gate are forced to logic high 1 the output is forced to logic high 1. If a gate drives several similar gates in parallel problems may occur. Logic gates can also be constructed from truth tables using parallel branches of nfets or pfets. Basic logic gates pdf created with pdffactory trial version. If we put a small current into one of the terminals, called the base, then the switch is oncurrent may flow. An output of one logic gate can be an input to another logic gate. Lets have a look about the transistor made logic gates. Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. Either due to the cost or due to the foot print space taken on the pcb, building a gate using a couple transistors can be interesting.
Provides practical examples of circuit design and analysis using pspice, matlab, and the smith chart this book presents the three technologies used to deal with electronic circuits. 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. In this paper, we have developed a circuit which gives the output for 4 logic gates of and, nand, or, nor simultaneously by taking only two inputs a and b. Nand gate can be built using 4 mosfets 2nmos and 2pmos. Oct 22, 2017 this feature is not available right now. The digital logic gate is the basic building block from which all digital electronic circuits and microprocessor based systems are constructed from. 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. For simplicity we will show here only two inputs nand gate circuit by using diodes and transistors. To do this, we design branches to block the pull up or pull down action.
Jul 19, 2019 im trying to build some bjt logic gates and have opted to use the 2n2222 transistor and a 12v power source. And gate can be designed by using two simple diodes. Introduction to computer engineering csece 252, fall 2012 prof. Bipolar junction transistor as a switch, iosr journal of electrical and electronics engineering iosrjeee, volume, pp 5457. This is a diodetransistor logic dtl nor gate circuit using a generalpurpose bipolar junction transistor bc547, and generalpurpose diodes 1n4148. Sometimes, on a circuit, you need a single nor logic gate, but you dont want to use a 14 pin ic containing 4 gates, and only use one of them. Im looking for how to size the current limiting resistors to achieve both cutoff and saturation cleanly. For instance for the xor used in the previous example, line 0 would convert to two parallel pfets with gates connected to x and y.
618 1528 741 725 1415 818 2 909 30 218 1646 1265 1100 667 406 1401 63 1202 90 880 697 1086 1455 1476 1430 108 270 88 183 519 561