And, or, not, nand not and, nor not or, xor, and xnor not xor later building functions. Oct 22, 2017 this feature is not available right now. Introduction the ta will show you the emitter, base and collector for the transistor. This is a diodetransistor logic dtl nor gate circuit using a generalpurpose bipolar junction transistor bc547, and generalpurpose diodes 1n4148. Jul 19, 2019 im trying to build some bjt logic gates and have opted to use the 2n2222 transistor and a 12v power source. Transistors and logic circuits transistor control voltage in voltage out control high allows current to flow. 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. 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. Bipolar junction transistor as a switch, iosr journal of electrical and electronics engineering iosrjeee, volume, pp 5457. In a batterypowered device where you have limited power and the load is variable and often low, using bjt is a bad idea. A functionally complete logic system may be composed of relays, valves vacuum tubes, or transistors. Jul 25, 2018 realizing nand gate using diode and transistor.
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. Using transistors as logic gates electrical engineering. A combinational circuit has no memory characteristic, so its output depends only on the current value of its inputs. This page shows how to make this circuit, and the implementation is on a breadboard using discrete components. Digital logic or gate digital gates electrical technology. Logic gates have been made out of dna see dna nanotechnology and used to create a computer called maya see mayaii. Basic digital logic gates perform logical operations of and, or and not on binary numbers. The basic operations are described below with the aid of truth tables. Nand gate can be built using 4 mosfets 2nmos and 2pmos. 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. 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. 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.
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. Transistortransistorlogic topics the most commonly used bipolar logic family is transistortransistor logic. 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. It produces the exact reverse output to that of given input. 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. 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. This creates trees of gates that depend on each other. These families vary by speed, power consumption, cost, voltage. Resistortransistor logic rtl gates objectives be familiar with logic gates using resistors and bipolar transistor connected with rlt techniques.
Transistortransistor logic topics the most commonly used bipolar logic family is transistortransistor logic. We set up a circuit that has some constant source voltage connected to it. Introduction to computer engineering csece 252, fall 2012 prof. 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. The and gate is an electronic circuit that gives a high output 1 only if all its inputs are high. 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. Apply a 1 khz sine wave at the input with a peaktopeak amplitude of 0. 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. Bcause you can simply set the baseemitter current to be a small fraction of the led current to achive better efficiency. Electronic circuits with matlab, pspice, and smith chart. The or gate is a logic boolean gate that represents addition in basic algebra. 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. 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.
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 are the basics of a many digital electronic circuit. Most questions regarding the behavior of the device that arise when developing a system can be answered with the information given. The digital logic gate is the basic building block from which all digital electronic circuits and microprocessor based systems are constructed from.
Used to build logic functions there are seven basic logic gates. This means that any other digital logic gate can be constructed using only nand gates or only nor gates. Basically, all logic gates have one output and two inputs. Logic gates can also be constructed from truth tables using parallel branches of nfets or pfets. Operation of logic gates and, nand, or, nor with single.
Fill in the truth table, given the following logic circuit made from logic and, or, and not gates. Only use nfets to pull the output down and pfets to pull the output up. Building functions from logic gates weve already seen how to implement truth tables using and, or, and not an example of combinational logic. An output of one logic gate can be an input to another logic gate. 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. These gates are the and, or, not, nand, nor, exor and exnor gates.
Diodetransistor logic 1 chapter 5 diode transistor logic resistortransistor logic was an early form of logic used in the 1950s and early 1960s. If a bjt is used to power something with a predictable current draw like leds, using bjt isnt as bad. 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. 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. Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. The relationship between the input and the output is based on a certain logic. Combining a number of basic logic gates in a larger circuit to produce more complex logical operations is called.
Diode and transistor nand gate or dtl nand gate and nand gate. Also note that you can in theory, ymmv mix up pass transistor logic with pushpull logic. 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. Studying the internal connection of and, or, nand, and nor. 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. 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. Logic gates can be made using pneumatic devices, such as the sorteberg relay or mechanical logic gates, including on a molecular scale. To do this, we design branches to block the pull up or pull down action.
The output bjt switches between its cutoff and saturation regions to create logic 1 and 0, respectively. 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. Like diode, transistor also acts as electronic switch. Operation of logic gates and, nand, or, nor with single circuit using bjt bipolar junction transistor. Basic logic gates pdf created with pdffactory trial version. What are the logic low and high levels of ttl ics and cmos ics. The circuit driving voltage v is applied to the parallely connected diodes and the output is collected as the voltage drop at the diodes. Introduction to logic gates not, and, nand, or, nor. A gate is an electronic device which is used to compute a function on a two valued signal.
Any logic function can be implemented as sum of products. If we put a small current into one of the terminals, called the base, then the switch is oncurrent may flow. 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. Combinational logic circuit output depends only on the current inputs stateless sequential logic circuit output depends on the sequence of inputs past and present. Adjust the potentiometer so that it is in the center of its travel.
Logic gates actually look like weird bugs in real life. Logic gates digital circuit that either allows a signal to pass through it or not. Im looking for how to size the current limiting resistors to achieve both cutoff and saturation cleanly. Hi guys, in this tutorial i will show you some npn transistor based logic gates. Therefore it should be used wisely, and may eventually not be convenient. 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. It gives students, researchers, and practicing engineers the necessary design and modelling tools for validating electronic design concepts involving bipolar junction transistors. Digital systems are said to be constructed by using logic gates.
Any other gate, and in particular the noninverting gates and and or require more transistors. Logic gates use switch behavior of mos transistors to implement logical functions. 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. For simplicity we will show here only two inputs nand gate circuit by using diodes and 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. 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. Rtl was made from discrete transistors and resistors and manufactured on printed circuit boards with several gates per board. 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.
In this alternative way to achieve nor logic, only one transistor is used with the two inputs tied to its base through resistors. Pdf operation of logic gates and, nand, or, nor with. Realize the ex or gates using minimum number of nand gates. Some logic gates like not gate or inverter has only one. I used bipolar junction transistors bjt to design this. The simplest family of logic gates uses bipolar transistors, and is called resistortransistor logic rtl. Ttl and cmos characteristics purpose logic gates are classified not only by their logical functions, but also by their logical families. If a gate drives several similar gates in parallel problems may occur. This nand gate is called dtl nand gate or diode transistor logical nand gate. 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. Saturation in ecl is avoided by using the bjt differential pair as a current switch. Even more important is the fact that nand and nor are complete. Jun 20, 2015 and gate can be designed by using two simple diodes. 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.
From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20. 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. 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. Make the circuit below using a bjt, 2n2222 transistor. The use of transistors for the construction of logic gates depends upon their utility as fast switches. However, the diagrams we use are easier to understand. Lets have a look about the transistor made logic gates. A combinational circuit has no memory characteristic, so its output depends only on. And gate can be designed by using two simple diodes. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20 computer science cornell university.