When a cmos logic block takes inputs from a passtransistor logic block, the addition of this pchannel transistor eliminates the voltage drop because of the pass transistor. Final design of reversible gates using pass transistor logic. Figure below shows the implementation of xor function using pass transistors. The passtransistor based cell library and synthesis tool are constructed, for the first time, to clarify the potential of topdown passtransistor logic. In complementary cmos logic primary inputs are allowed to drive only gate terminals. This technique uses the complementary properties of nmos and pmos transistors. Nmos devices passes a strong 0 but a weak 1 while pmos transistors pass a. Sum equation contains xor gates whose design using cpl logic is desired for low power system, whereas the carry is designed as per the equation. Knowing the maximum current required by the load, it is possible to calculate the maximum emitter current. Mos transistors silicon substrate doped with impurities adding or cutting away insulating glass sio 2 adding wires made of polycrystalline silicon polysilicon, poly or metal, insulated from the substrate by sio 2 drain source gate n n drain source gate sio 2 insulator ptype doped substrate drain source gate nmos transistor. Realizing constructing a cmos pass gate cmos transmission gate from transistors. A transmission gate tg is an analog gate similar to a relay that can conduct in both directions or block by a control signal with almost any voltage potential.
If these outputs are fed into a cmos circuit to the gate terminal, there are a few issues that arise with reference to voltage and current. The vast array of mosfetbased digital circuitry is built around the cmos inverter. Realize the following gates using pass transistor logic. A new design technique of reversible gates using pass transistor logic md. All exploit passtransistors to implement general logic functions 22feb02 e4. The transmission gate logic is used to solve the voltage drop problem of the pass transistor logic.
Among these, nmosbased passtransistor circuits have a. In ptl, use of either nmos or pmos is enough to send the data. One of the key steps in the use of transmission gates and pass transistors for logic implementation is the identification of pass variables to replace the 1. Pdf topdown passtransistor logic design researchgate. Nc state university with significant material from rabaey. The bipolar transistor has been available for over seventy years its technology is very well established, and although field effect transistor technology is probably more widely used in integrated circuits, bipolar transistors are still used in huge quantities in various analogue and digital circuits, both within integrated circuits and as discrete electronic components. Solution the logic function is the transistor sizes are given in the figure above. Spl singlerail passtransistor logic is one of the most promising logic. It is a cmos based switch, in which pmos passes a strong 1 but poor 0, and nmos passes strong 0 but poor 1.
Digital design with passtransistor logic technical articles. Passtransistorlogic xor gate using pass transistor logic. Problem on nmos pass transistor logic gate 2014 ece paper solution duration. Topdown passtransistor logic design solidstate circuits, ieee. The control signal c logichigh ensuring that both transistors are turned on. Output transist or q4 is again switched off, causing the output voltage to rise to the value of vcc. Transmissiongate digitalcmosdesign electronics tutorial. Passtransistor logic families there are two main passtransistor circuit styles. Digital logic design study guide with questions and answers about algorithmic state machine, asynchronous sequential logic, binary systems, boolean algebra and logic gates, combinational logic, digital integrated circuits, msi and pid components, registers counters and memory units, boolean functions, standard graphic symbols, synchronous. It proposes two new techniques for mapping circuits. Transmission gate an overview sciencedirect topics.
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. 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. Design a passtransistor circuit for a threeinput majority gate. The new logic gate represents an improvement over dpl family achieved by the elimination of the redundant branches and rearrangement of. Over the last 40 years, principles of transistor circuits has provided students and practitioners with a text they can rely on to keep them at the forefront of transistor circuit design. Pdf on pass transistor logic design yashwant malaiya. Pass transistor logic ptl, also known as transmissiongate logic, is based on the use of mosfets as switches rather than as inverters. Expert discussions cover topics ranging from the basics of logic expressions and switching theory to sophisticated programmable logic devices and the design of gaas mesfet and hemt logic circuits. What is the logic function implemented by the cmos transistor network. Among these, nmosbased passtransistor circuits have a great potential to.
Double passtransistor logic dpl the basic difference of pass transistor logic compared to the cmos logic style is that the source side of the logic transistor networks is connected to some input signals instead of the power lines. Journal of chemical and pharmaceutical sciences issn. The output node b connected to a capacitor capacitive loading of the subsequent logic stages driven by the transmission gate. Pass transistor chain can be used in design of regular array based structures such as roms, plas, multiplexers etc strength of output signal the. Behavior of basic and complex logic gates using complementary passtransistor logic cpl under various singlestuck faults are investigated. A multiplexer of 2 n inputs has n selected lines, are used to select. Free download cmos logic circuit design ebook circuitmix.
The result is in some cases conceptual simplification, but the cmos inverters strict logic high logic low output characteristic is lost. In other words, this resistor acts as a current source load. The objective of the new logic gates and the synthesis method developed for passtransistor logic is to minimize the number of transistors used in dpl and preserve the speed of the logic. The purpose of resistor r is to limit the current when the nmos transistor is turned on. The next set of lectures is dedicated to lowpower techniques which is becoming a must not only in mobile and portable environment but are equally important issue in highperformance processor design. The output logic level is restored using additional circuitry. It is one of the logic styles which use less number of transistors than the regular cmos logic style. Transistors are used as switches to pass logic levels between nodes of a circuit, instead of as switches connected directly to supply voltages. Pass transistor chain can be used in design of regular array based structures such as roms plas, multiplexers etc strength of output signal the strength of a.
Differential and passtransistor cmos digital circuits. A general method in synthesis of passtransistor circuits. In electronics pass transistor logic ptl describes several logic families used in the design of integrated circuits. The aim of this experiment is to design and plot the characteristics of a 4x1 digital multiplexer using pass transistor and transmission gate logic introduction. Fast global gate collapsing technique for high performance. In a previous article, i introduced the concept and basic characteristics of pass transistor logic ptl. It will be replaced with a pmos transistor in later circuit design. One of the first papers examining passtransistor logic and formalizing passtransistor design style was published by whitaker, in 1983 whitaker, electronics. There are several logic design topologies that supply a output voltage less than vdd level pass transistor topology for example.
The first method, known as the oddlevel transistor replacement otr method, has a goal that is similar to that of technology mapping, but. Digital integrated circuits combinational logic prentice hall 1995 combinational logic. Sizing the transistors in a cmos transmission gate. Disadvantage that output levels are always lower than the input level. Testing complementary passtransistor logic circuits ieee xplore. A selfchecking cmos full adder in double pass transistor. Introduction to passtransistor logic technical articles.
Topdown passtransistor logic design, ieee journal of solidstate circuits vol. This simple yet extremely effective circuit uses the. Introduction the increasing demand for lowpower very large scale integration vlsi can be addressed at different design levels, such as the architectural, circuit, layout, and. A new design methodology for mapping circuits is discussed in this paper. Hence, it is a technique often used to balance circuittiming measurements and optimize circuit. In electronics, pass transistor logic ptl describes several logic families used in the design of integrated circuits. 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 circuit design techniques 6. However still the tranistor pass good 0 and considerable 1 in nmos when used as a pass tranistor that of threshold voltage. Logic circuits dapted from cmos logic circuit design by john p. In this volume drawn from the vlsi handbook, the focus is on logic design and compound semiconductor digital integrated circuit technology. Domino logic characteristics only noninverting logic very fast only 1 0 transitions at input of inverter affects the next domino static inverter increases noise immunity, increase the size of pmos to increase v m proper sizing of inverter to drive the fanout in optimal way add a levelrestoring transistor to overcome.
Although integrated circuits have widespread application, the role of discrete transistors both as important building blocks which students must understand, and as practical solutions to design problems. The truth table of xor gate is as shown in table below. The current drive of the transistor gatetosource voltage is reduce significantly as v. A multiplexer or mux is a combinational circuits that selects several analog or digital input signals and forwards the selected input into a single output line. It shows some fundamental pass transistor building blocks which became. Size the nmos and pmos devices so that the output resistance is the same as that of an inverter with an nmos wl 4 and pmos wl 8. Note that the addition of t p improves the t f measure on v out. The pass transistor logic is required to reduce the transistors for implementing logic by using the primary inputs to drive gate terminals, source and drain terminals. It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. It is a simple matter to design a series pass voltage regulator circuit like this. Pass transistor logic pass transistor logic involves nmos or pmos transistors to transfer the charge from one node of a circuit to another node under the control of mos gate voltage. Practical low power digital vlsi design emphasizes the optimization and tradeoff techniques that involve power dissipation, in the hope that the readers are better prepared the next time they are presented with a low power design problem. Topdown passtransistor logic design article pdf available in ieee journal of solidstate circuits 316.
1437 944 414 96 85 311 936 979 515 144 626 15 555 1119 825 446 883 1223 1192 1248 1154 250 995 1256 499 1161 1139 657 855