Vlsi design pass transistor logicpass transistor logic adapted from rabaeys digital integrated circuits, 2002, j. For example, a single cd4007 can be used to make three inverters, an inverter plus two transmission gates, or other complex logic functions such as nand and nor gates. The objective of this lab activity is to reinforce the basic principles of cmos logic from the previous lab activity titled build cmos logic functions using cd4007 array1 and gain additional experience with complex cmos gates. What is the logic switching circuit of xor and xnor gates. The circuit implements the xor function and it is cmos cmos stands for complemantary metal oxide semiconductor. In order to reduce the number of transistors, the output of the xor gate a. Oct 09, 2012 pass transistor logic october 9, 2012 7 8.
Section 2 gives an overview of three conventional pass transistor logic families complementary pass transistor logic cpl, double pass transistor logic dpl, and dual value logic dvl. Pass transistors require lower switching energy to charge up a node, due to the reduces. Combinational logic gates in cmos purdue engineering. Npn transistor xor gate circuit sully station technologies. These four inputs construct an xor logic operation at the transistor level, which is designed using two transistors. Section 3 describes a general method to synthesize basic twoinput and threeinput logic gates andnand, ornor, and xor xnor in each of. Xor and gates of the pass transistor logic style are shown in fig2a, b, c,d. A hybrid cmos logic style adder with 22 transistors is reported 10. Transmission gate xor b a a b 1 off off an inverter b. Transmission gates pass transistors produce degraded outputs transmission gates pass both 0 and 1 well 4 7. The cd4007 is a very versatile ic with many uses as we saw in the previous lab activity1. Studying the internal connection of and, or, nand, and nor.
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. There are several ways in which one can design a xor gate using mosfet. A single bit full adder design with xor pass transistor logic ptl logic is represented in 5. 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. Using dtl diode transistor logic we can implement xor and xnor logic functions with a minimum number of discrete components. And, or, not, nandnot and, nornot or, xor xnornot xor 9 did you know. 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. Nmos devices passes a strong 0 but a weak 1 while pmos transistors pass a strong 1 but a weak 0. The working of the circuit may be explained as follows. The method consists of the implementation of the gates. Pass transistor logic adapted from rabaeys digital integrated circuits, second edition, 2003 j.
Complementary pass transistor logic a general method of karnaugh map coverage and mapping into circuit realizations is applied to design logic andnand, ornor, and xor xnor gates in cpl. In contrast to static cmos primary inputs drive gate terminals. He was born in lincoln, england and he was the son of a shoemaker. Cmpen 411 vlsi digital circuits spring 2012 lecture 07. To make the xor gate operate with full voltage swing at all nodes, a transmission gate tg is added in the xor gate 8. Logic gates in cmos indepth discussion of logic families in cmosstatic and dynamic, passtransistor, nonran tioed and ratioed logic n optimizing a logic gate for area, speed, energy, or robustness lowpower and highperformance circuitdesign techniques 6.
This technique uses the complementary properties of nmos and pmos transistors. Cmos adder circuit design based on transmission gate using 20 transistors is presented in ref 6. Two transistor xor gate based single bitfull adder design. This paper compares the use of complementary passtransistor logic cpl as more powerefficient than conventional cmos design.
Pdf a new 5transistor xorxnor circuit based on the. Amitava dasgupta, department of electrical engineering,iit madras. B is fed through an not gate from the differential node to the pass transistors as a control input. I am using pmos and nmos to implement complement a, means that i am not using complement directly into the circuit. Implementing xor and xnor logic functions using diode.
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 shifters. Pass transistor logic switch network a b b reduced number of transistors. This paper compares the use of complementary pass transistor logic cpl as more powerefficient than conventional cmos design. As shown, the inputs to the pass transistor gates ptgs 1 and 2 are a and a, respectively, and the control gate voltages are b and b, respectively. The design has been compared with earlier proposed 4t and 6t xor gates and a. Cmos adder based on transmission gate using 20 transistors is reported in 5. Here is a diagram of a pass transistor logic implementation of an xor gate.
Im just trying to help a classmate understand the lectures note from a class. Mos transistors silicon substrate doped with impurities adding or cutting away insulating glass sio 2. Logic families comparison for xor and nand of full adder in this section, a description for the different logic families to implement xor and nand gates of the full adder gate level implementation that was agreed upon in the previous section. The main motive of this paper is to determine the comparative study of power, delay, power delay product pdp of different full adder designs using cmos logic styles. Full adder for embedded applications using three inputs xor is also reported in. The output of the first stage i1 xor logic, a b, is connected to the gate of the cmosbased pair of pass transistors labelled 3, 3 to decide whether to pass input b a also works here or. V s will initially charge up quickly, but the tail end of the transient is slow. Comparative performance analysis of xorxnor function based. From switches to transistors, logic gates and logic circuits hakim weatherspoon. The basic function of xor using gdi cell the working of gdi logic of xor gate is shown in table 2. Transmission gate logic circuits adapted from cmos logic circuit design by john p. Used to build logic functions there are seven basic logic gates. Designing complex gates using kmaps a b c pullup network d 00 01 11 10 00 01 11 10 ab cd 0 1 0 0 0 0 0 0 1.
Section 3 describes a general method to synthesize basic twoinput and three input logic gates. The similar approach is shown in the switching diagram that when the bulb will glow and in which. Pdf comparison of different design techniques of xor. Using an nmos transistor as the switch is certainly a good way to reduce transistor count, but a lone nmos isnt impressive in terms of performance. The basic cmos 28t full adder design with good load driving capability and high noise margin 3. That means a cmos circuit will use both nmos and pmos type transistors. Logic gates digital circuit that either allows a signal to pass through it or not. Transistorlevel optimization of three input xorxnor gate. So we need not, and and or gates to form an xor circuit. Schematic of xor using cmos logic by using transmission gates logic, the number of transistors is reduced from the conventional cmos xor gate. Hi, these videos are not a study guide nor am i an expert.
In this circuit and gates and or gates of full adder replaced with a multiplexer, instead of using pass transistor logic to represent multiplexer in the above circuit a. Another design of full adder with 10 transistors using xor xnor gates is also reported in 9. Section 3 describes a general method to synthesize basic twoinput and threeinput logic gates. In this paper, we propose an efficient selfchecking adder. In the last lecture, we talked about how simple cmos gates can be built. Note that the caret does not denote logical conjunction and in these languages, despite the similarity of symbol. Problems design 4 to 1 multiplexor using transmissiongates. How to perform an xor function using a transistor quora.
Transmission gate xor a b f b a b b m1 m2 m3m4 6 devices including inverter for b vs. Implementation of low power cmos full adders using pass. How many transistors do i need to design a cmos xor gate. Vlsi design pass transistor logicpass transistor logic. As demonstrated in the preceding section, ptl is built around mosfet switches that either pass hence the name or block a signal. Logic gates in cmos indepth discussion of logic families in cmosstatic and dynamic, pass transistor, nonran tioed and ratioed logic n optimizing a logic gate for area, speed, energy, or robustness lowpower and highperformance circuitdesign techniques 6. A truth table of xor gate can easily be followed to get a mos based circuit for the gate. A general method in synthesis of passtransistor circuits people. Transmissiongate digitalcmosdesign electronics tutorial. Topology of 2 input subnanowatt xor gate in 65nm cmos. Basic function of xor using gdi n p g output function b. Transistor level optimization of three input xor xnor gate using cmos logic design g. A general method in synthesis of passtransistor circuits.
Single bit full adder design using 8 transistors with. A novel 3input andxor gate circuit for reedmuller logic. Other authors use the term complementary pass transistor logic cpl to indicate a style of implementing logic gates using dualrail encoding. For example, pass transistor logic transmission gates makes it pretty simple. B are fed as inputs to the pass transistors and form an xor logic gate. This function is very useful, for instance in parity calculations. Different schematic designs of xor a 2 input xor gate is designed by using cmos. Cmos fulladder circuit is proposed using lowpower xor and xnor gates, pass transistors, and transmission gates in 6. Transistor q1 and q2 acts as xor gate, q3 and q4 also acts as second xor gate. Layout and stick diagram of xor gate using pass transistor. This structure is proposed using pass transistor logic with finfets. Differential and passtransistor cmos logic for high performance. Cmos logic circuits, transmission gate xor objective. I dont see how it is relevant that there are a number of problems with it wikipedia has thousands of other articles that discuss things that have problems, and yet people use those things every day.
The transmission gate logic is used to solve the voltage drop problem of the pass transistor logic. Though it has high speed due to low input capacitance, it has limited capacity to drive a load. For some types of functions, this can lead to much more efficient implementations than using gates. Mar 03, 2014 pass transistor logic families complementary pass transistor logic family dual pass transistor logic family swing restored pass transistor logic family 31. Xor logic gates though requiring 6 total then, obviously, xnor is the inverse of xor. A new 5 transistor xor xnor circuit based on the pass transistor logic. It should be noted that although transmission gate based and pass transistor based designs can reduce silicon area, placing a pass transistor on a normal signal path could lead to difficulty in testing, because a highimpedance state is introduced at the output of the pass transistor when the pass transistor is stuck at the off state.
Resistor transistor logic rtl gates objectives be familiar with logic gates using resistors and bipolar transistor connected with rlt techniques. Individually, this is how we build a not gate using a transistor. For some types of functions, this can lead to much more efficient implementations. Xorand gates of the pass transistor logic style are shown in fig2a, b, c,d. Layout and stick diagram of xor gate using pass transistor logic vlsi talha bin aslam. The xor gate realization of the circuit using six transistors can be found in 4 after modifying their four by transistors. The truth table of xor gate is as shown in table below. Lowpower and fast full adder by exploring new xor and xnor gates. Logic gates digital circuit that either allows signal to pass through it or not used to build logic functions seven basic logic gates. 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. Pass transistor logic xor gate using pass transistor logic.
Pdf a new 5transistor xorxnor circuit based on the pass. Figure below shows the implementation of xor function using pass transistors. Xor has the worstcase karnaugh mapif implemented from simple gates, it requires more transistors than any other function. Single full adder design using 10 transistors with low power and high delay presented in ref 7. Transmission gate an overview sciencedirect topics. 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. Multiple series transistors draw poly gates sidebyside part ii. Inverters and transmission gates are particularly useful for building transmission gate exclusive or xor and xnor logic functions. How many transistors do i need to design a cmos xor gate and.
The xor gates with ptl design are suitable for arithmetic gates and other vlsi. Some logical circuits using ptl pass transistor logic october 9, 2012 8 9. The current drive of the transistor gate tosource voltage is reduce significantly as v. Digital integrated circuits combinational logic prentice hall 1995 overview static cmos conventional static cmos logic ratioed logic pass transistortransmission. The rss resistor prevents shunting current directly from a and b to the output. Slide set 3 pass transistor logic transmission gates. What this circuit is, its a pass transistor logic gate. Lecture series on digital integrated circuits by dr. Complementary pass transistor logic or differential pass transistor. I also agree that this 6transistor circuit is more accurately called a pass transistor logic xor gate. The logic switching circuit for xor gate looks like this. Every cpl gate has two output wires, both the positive signal and the complementary signal, eliminating the need for inverters.
Passtransistor logic i n p u t s switch network out out a b b b n transistors. A novel 3 transistor xor gate based full adder design for. In 4 a full adder design with xor pass transistor logic ptl is reported. You can find circuits using 4, 6, 8, 9, 10 or 12 transistors, again with varied strengths for the inputs and the output. Jan 25, 2015 this feature is not available right now. Andnand, ornor, and xorxnor in each of these families. Cmosbased carbon nanotube passtransistor logic integrated. Digital integrated circuits combinational logic prentice hall 1995 combinational logic. This paper compares two different logic styles based on 45 nm technology for implementing logic gates of upto two inputs in terms of their layout area, delay and. From the truth table it is evident that, when a b, y 0. Implement an xor gate using minimum number of transistors. In 11 a full adder circuit using 22 transistors based on hybrid pass logic hpsc is presented.
Simple xor makes it attractive for structures like adders. In this lecture, we will talk about another way to implement logic functions using transistors. In rtl resistor transistor logic, all the logic are implemented using resistors and. Pass transistor logic often uses fewer transistors, runs faster, and requires less power than the same function implemented with the same transistors in fully complementary cmos logic.1404 699 1206 1575 1000 342 527 843 1622 749 864 852 1529 903 202 846 1310 1216 407 175 881 302 34 352 740 413 572 130 1027 1061 514 1577 97 123 1496 263 857 378 1326 11 1043 156 1241 224 1088