Transistors and digital circuits instructional physics lab. Xor gate xor o,r exclusive or, gate an xor gate produces 0 if its two inputs are the same, and a 1 otherwise note the difference between the xor gate and the or gate. In the simulator i used a 200 ohms resistor, but you should use one around 1k. The xorxnor gate is the major consumer of power in the fa cell. The xor gate has a much wider range of implementations in mos and cmos. A high speed full adder circuit using 3 transistor xor. Exclusiveor xor digital logic gate electrical technology.
An xor gate circuit can be made from four nand gates. 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. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20. The twoinput version implements logical equality, behaving according to the truth table to the right, and hence the gate is sometimes called an equivalence gate. A basic cmos structure of any 2input logic gate can be drawn as follows. The current drive of the transistor gatetosource voltage is reduce significantly as v. Npn transistor xor gate circuit sully station technologies. Logic gates objective to get acquainted with the analogdigital training system. Reducing the number of transistors in digital circuits using gate. Topology of 2 input subnanowatt xor gate in 65nm cmos technology. Xor schematic using nmosfets and diodes is given below.
Building logic gates with transistors digilent inc. If we connect transistors in parallel as shown in figure 5, applying a signal to the base of either transistor is sufficient to allow current to flow through the resistor and pull the output. In this schematic 4 diodes are used in a bridge configuration for sorting out input logic. Here the output of first xor gate is applied as a input to the next xor gate, second xor gate has c as second input and produce the sum as output. From transistors to functions for the purpose of this class, we will consider transistors to be the basic building blocks of computer hardware. How many transistors do i need to design a cmos xor gate. Discrete xor gate can be made with mosfets and diodes. Diode logic uses the fact that diodes conduct only in one direction. Basic digital logic gates perform logical operations of and, or and not on binary numbers.
Now lets understand how this circuit will behave like a nand gate. Simple digital logic gates can be made by combining transistors, diodes 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 proposed gate has been implanted in an already existing 52 compressor cell to test its driving capability. The nandgate based implementation incurs 2 gate delays between the data inputs and the output, whereas the transmissiongate based and the passtransistor based. 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. Heres how all of the xor gate combinations will look in a truth table with a and b being inputs, and q being the output. A resistor can commonly be used as a pullup or pulldown resistor. Jul 14, 2015 the exor gate is defined as, the hybrid logic gate with 2 or more inputs to perform the exclusive disjunction operation. The digital logic gate is the basic building block from which all digital electronic circuits and microprocessor based systems are constructed from. I am using pmos and nmos to implement complement a, means that i am not using complement directly into the circuit. One layout option with horizontal transistors l runs horizontally ignore the size w for now 2input nand pmos 2 parallel. Hybrid fas are made of two modules, including 2inputxorxnor or simultaneous xorxnor gate and 2to1 multiplexer 21mux gate.
Xor gate is a digital logic gate that gives a true 1 or high output when the number of true. That means that if both of its inputs are the same, the output will be 0 false. If both the inputs are same, then the output is low. Therefore the electrical output is logic 0 for the xor gate.
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. The operation of a transistor could be explained by making an analogy to faucets. Right to make changes nexperia reserves the right to make changes. Passtransistorlogic xor gate using pass transistor logic. There are two kinds of transistors used, pmos and nmos, here are their symbols. The xor gate realization of the circuit using six transistors can be found in 4 after modifying their four by transistors xor gate design cascading a standard inverter as a driving output. Schematic of xor using cmos logic by using transmission gates logic, the number of transistors is reduced from the conventional cmos xor gate. The configuration for an ionic xor gate is shown in fig. The circuit output should follow the same pattern as in the truth table for different input combinations. Jan 25, 2015 this feature is not available right now. How to derive xor from only nor gates physics forums.
The schematic of xor gate using cmos logic is shown in figure 4. The xor circuit with 2 inputs is designed by using and, or and not gates is shown above. V out is low only when both transistors are turned on. In digital logic design only two voltage levels or states are allowed and these states are generally. This design has improved the poor signal output for a certain input signal by using this topology. Most modern devices made of billions of transistors you will build a processor in this course. Digital logic basics 21 implementation using nand gates.
There are xorxnor gate, one 21mux gate, and not gates on. I will deal with cmos since 99% of all logic that has ever existed in number count exists as cmos. Voltage controlled ring oscillator design with novel 3. Logic and gate tutorial with logic and gate truth table. Schematic of xor using cmos logic by using transmission gates logic, the number of transistors is reduced from the conventional cmosxor gate. The merits and limitations of such a cntxor gate with respect to conventional xor. Just like a transistor, a faucet is connected to a source the water company, the faucet drains in a sink, and the flow of water through the faucet is controlled by a gate the knob. The only difference is that instead of connecting the output to the emitter of the second transistor, the output is obtained before. This construction entails a propagation delay three times that of a single nor gate and uses five gates. The use of transistors for the construction of logic gates depends upon their utility as fast switches. The transistors are electrically controlled current sourcessinks. One input terminal of xor gate is connected to control voltage vc and signal is applied to other terminal so that circuit works as an inverter. When we need to design logic circuits operating for higher than standard supply voltages, such as 30 and 24v, we can implement it by using regulators with standard logic family and interfacing it through level s. Blue and green lines represent the electrical and strain inputs applied on sgt 1 and sgt 2.
I made an xor gate with only 2n2222 transistors, not xnor like i said in the video. I got a simulator and created a xor gate and looked for the problem and i found it at two transistors. Si11,12 based multigate single electron transistors fabricated in a different. The proposed xor gate which is consists of six transistors, it can reduce the area overhead of 35% compared to the existing crc, 50% of the gate delay can be reduced. Recall from the electric circuits web lecture that switches can be connected in series or parallel. If both of an xor gate s inputs are false, or if both of its inputs are true, then the.
Logic gates can be made of resistors and transistors, or diodes. We make use of a gate that is reconfigurable from nand to. It would require quite a few transistors to make an xor yourself. Different designs for xor and xnor gates using four transistors have been presented in 9, 1517. Here is a diagram of a pass transistor logic implementation of an xor gate. Digital circuits page 1 of 4 instructional physics lab. To get acquainted with different standard integrated circuits ics. Two transistor xor gate based single bitfull adder design. The above drawn circuit is a 2input cmos nand gate. Exclusiveor gate with a single carbon nanotube maxplanckinstitut. Fets made of individual carbon nanotubes cnts have proven to be a.
I messed around and made an and gate the way i stated above but i feel like its a. A transistor is an electronic device that has three ends. The xor gate exclusive or is a logic gate that outputs 1 true when exactly one of its inputs is 1 true. The 14t full adder contains a 4t ptl xor gate, shown in figure, an inverter and two transmission gates based. He was born in lincoln, england and he was the son of a shoemaker. I would like to know what the process for deriving this would look like. Sep 09, 2012 i made an xor gate with only 2n2222 transistors, not xnor like i said in the video. A simple 2input logic and gate can be constructed using rtl resistortransistor switches connected together as shown below with the inputs connected directly to the transistor bases.
Figure below shows the implementation of xor function using pass transistors. These are basic circuits, so they can be improved with diodes for reverse voltage protection, for example, or can be simplified xor, xnor gates. Introduction the ta will show you the emitter, base and collector for the transistor. And, or, not, nandnot and, nornot or, xor xnornot xor 9 did you know. Xor and xnor functions using discrete electronics components. For the nand gate if input a and b are both high, the. We contribute new gates like exclusiveor xor gates and multiplexer mux gates that make.
Nor not or, xor, and xnor not xor later 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. The output of an xor gate is true only when exactly one of its inputs is true. If the gate voltage is high, then the transistor is on and current will flow from drain to source. Logic gates digital circuit that either allows signal to pass through it or not used to build logic functions seven basic logic gates. To start with you have to understand transistors in a simple way. For the nor logic, the transistors are in parallel with the output above them so that if either or both of the inputs are high, the output is driven low. The truth table of xor gate is as shown in table below. This gate and also practically all gates shown in the table 1 permits low transistor count note that the common nand and nor gates cost 4 transistors, the xor.
This paper proposes a low voltage noise tolerant xorxnor gate with 8 transistors. The xnor gate sometimes xornt, enor, exnor or nxor and pronounced as exclusive nor is a digital logic gate whose function is the logical complement of the exclusive or gate. A nand gate circuit is almost identical to an and gate circuit. And if you have two of the same inputs, like a 0 and a 0, or a 1 and a 1, then youll get a 0 for an output. This paper proposes a low voltage noise tolerant xor xnor gate with 8 transistors. And to put a xor gate on a schematic, be on the lookout for this symbol. If we need a or gate we can use a 4071 or cmos ic or a ttl 7432 or ic. The nand gate is very closely related to the and gate. This paper proposes a new design of xor gate using six transistors for low power. Cntfetbased 5input xor gate based on a novel design method is proposed. Pdf a new 5transistor xorxnor circuit based on the pass. The simple 2input dioderesistor gate can be converted into a nandnor. Hi guys, in this tutorial i will show you some npn transistor based logic gates.
The output of 2 input xor gate is high only when one of its inputs are high. Exclusiveor gate tutorial with exor gate truth table. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20 computer science cornell university. To understand formulation of boolean function and truth table for logic circuits. Xor gate simple english wikipedia, the free encyclopedia. Request pdf new 4transistor xor and xnor designs exclusiveor and exclusivenor gates are important in digital circuits. Both transistors must be saturated on for an output at q. Permission to make digital or hard copies of all or part of this work for. Oct 08, 2010 hi, through some searching and guessing with logisim i was able to see how to build a xor gate from only nor gates. Or and and logic gates made with diodes electronics area. What is logic gate and, or, xor, not, nand, nor and xnor. The example transistor xor gate circuit is implemented here using pn2222a npn transistors a variant of the 2n2222a but many common npn bipolar junction transistors. The xor gate does what is called an exclusive disjunction in logic symbols. Four transistors ptl based xor gates with limited driving capabilities have been reported in 14.
The nand gate has its transistors connected in series. Notice that the nand gate is an and gate without the not gate at the end. That is the fact that if both of the inputs are ones, then the output is also a one. Combination of q5 and q6 transistors carry out cout as output. Pdf a new 5transistor xorxnor circuit based on the. How logic gates work in digital electronics eagle blog. The or gate is very similar to the and gate, except that the nfets are in parallel rather than the pfets being in parallel. Design of xor gates in vlsi implementation nabihah ahmad, rezaul hasan. This enables the use of current limiting resistors to interface inputs to voltages in excess of vcc. If both of an xor gates inputs are false, or if both of its inputs are true, then the output of the xor gate is false. Xor gate which is actually made out of an integrated circuit, or ic.
The reason behind the usage of transmission gate here is, usage of pass transistor logic creates voltage degradation that can be. For example, the first embedded system, the apollo guidance computer, was built exclusively from nor gates, about 5,600 in total for the later versions. Lowpower and fast full adder by exploring new xor and xnor gates. Single bit full adder design using 8 transistors with. Xor a nand b and a or b and this you already know you can make from composite nand gates a b c xor logic gates though requiring 6 total then, obviously, xnor is the inverse of xor so just stick an inverter on the output of xor exclusive or operator. May 28, 2012 using dtl diode transistor logic we can implement xor and xnor logic functions with a minimum number of discrete components. A twoinput nand gate produces a low output if both of its inputs are high.
Using this xor gate, reduction in size of full adder is achieved and overall leakage is also reduced. You can find circuits using 4, 6, 8, 9, 10 or 12 transistors, again with varied strengths for the inputs and the output. Pullup or pulldown resistors are used when there are any unused logic gate inputs to connect to either a logic level 1 or 0 respectively. Digital circuitsnor logic wikibooks, open books for an. Lowpower and fast adders using new xor and xnor gates. Xor gate based on eight transistors and six transistors have been used in many earlier designs 1. The nandgate based implementation uses a total of 14 transistors, whereas the transmissiongate based and the passgate based implementations use 6 and 4 transistors, respectively. A nor gate is a logic gate which gives a positive output only when both inputs are negative like nand gates, nor gates are socalled universal gates that can be combined to form any other kind of logic gate. The exor gate is defined as, the hybrid logic gate with 2 or more inputs to perform the exclusive disjunction operation. If we need a and gate we can use a 4081 and cmos ic or a ttl 7408 and ic but sometimes it is easier to use diodes. Whereas the or function is equivalent to boolean addition, the and function to boolean multiplication, and the not function inverter to boolean complementation, there is no direct boolean equivalent for exclusiveor. Lowpower and fast full adder by exploring new xor and.
If the faucet knob gate is turned on water flows from the source to the sink, otherwise if the faucet. Xor gate sometimes eor, or exor and pronounced as exclusive or is a digital logic gate that gives a true 1 or high output when the number of true inputs is odd. For the nand logic, the transistors are in series, but the output is above them. The circuit was made of two antiparalleled batteries, each incorporated with a gate electrode. Exclusiveor gate tutorial the exclusiveor logic function is a very useful circuit that can be used in many different types of computational circuits in the previous tutorials, we saw that by using the three principal gates, the and gate, the or gate and the not gate, we can build many other types of logic gate functions, such as a nand gate. Representing numbers using transistors is one thing, but getting the. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20 computer science cornell university see. A a it is clear from this and the last exercise that by controlling one input call it control input, we can turn an xor gate into either an inverter or a buffer. An xor gate sometimes referred to by its extended name, exclusive or gate is a digital logic gate with two or more inputs and one output that performs exclusive disjunction. Or gates are very useful, but they have one odd feature that can work just fine, but in certain applications can cause problems. They both are given 0v yet they still let almost 3v through. For example, pass transistor logic transmission gates makes it pretty simple. One element conspicuously missing from the set of boolean operations is that of exclusiveor, often represented as xor.
Transmission gate an overview sciencedirect topics. As can be seen in the logic diagram below, the xor gate is built by combining three more simple gates, the or gate, the nand gate and the and gate to produce the desired result. The gate length of all three transistors has been taken as 0. If both inputs are false 0low or both are true, a false output results. Its easy enough to create a nand gate by using just two transistors. V s will initially charge up quickly, but the tail end of the transient is slow.
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