Complementary pass transistor logic complementary pass transistor logic 7 consists of. Nmos devices passes a strong 0 but a weak 1 while pmos transistors pass a strong 1 but a weak 0. The source and drain switch whenever the transistor is either charging or discharging the load capacitance. This set of notes cover in greater detail static logic families. Microelectronic systems c the pass transistor implementation needs 6 transistors 4 pass transistors and 2 for the inverter. Once the operation and characterization of an inverter circuits are thoroughly understood, the results can be extended to the design of the logic gates and other more complex circuits. Metaloxidesemiconductor field effect transistor nchannel mosfet nfet nmos pchannel mosfet pfet pmos. It realizes a logic function using nmos pass transistors with cmos restoring buffers. Pass transistor logic the major differences of the pass transistor logic ptl compared with cmos logic is that the source side or drain is connected to some input signals instead of the power lines.
The 3t nand and nor gates design is based on cmos inverter and ptl. Why is pmos good to pass logic 1 and nmos is good to pass. It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. Making the nmos pass transistor and pmos restorer the same size is reasonable. A methodology for synthesis of pass transistor functions was established presenting a modified karnaugh map which employs the pass variables, not only logic zeroes and ones. These circuits act as switches use either nmos transistors or parallel pair of nmos and pmos transistor called transmission gate. Passtransistor adiabatic logic using single powerclock. While pmos logic is easy to design and manufacture a mosfet can be made to operate as a resistor, so the whole circuit can be made with pmos fets, it has several shortcomings as well. Double pass transistor 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. 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. From transistorsto logic gates and logic circuits prof. Used to build logic functions there are seven basic logic gates. Transistor sizing for symmetrical response dc, ac for performance.
It shows some fundamental pass transistor building blocks which became very popular in vlsi design practices. A general method in synthesis of passtransistor circuits people. The term pass transistor logic refers to a different form of mosfet circuitry that doesnt generate logic high and logic low. Sizing the transistors in a cmos transmission gate. Pass transistor logic adapted from rabaeys digital integrated circuits, second edition, 2003 j.
Pass transistortransmission gate logic dynamic cmos logic domino. Anne bracy cs 3410 computer science cornell university the slides are the product of many rounds of teaching cs 3410 by professors weatherspoon, bala, bracy, and sirer. This structure is double pass transistor logic dpl. Lowpower 1bit fulladder cell using modified pass transistor logic n. 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. Recently reported logic style comparisons based on fulladder circuits claimed complementary passtransistor logic cpl to be much more powerefficient than complementary cmos. A selfchecking cmos full adder in double pass transistor. Implementation of low power cmos full adders using pass. Cmos logic is what is used in nearly all electronics these days. Logic gates in conventional or complementary cmos also simply referred to as cmos in the sequel are built from an nmos pulldown and a dual pmos pullup logic network. Nmos and pmos logic electrical study app by saru tech.
Ee 261 james morizio 40 pass transistor ckts v dd v dd v ss v dd v dd v dd v dd v dd v dd. Transistors are used as switches to pass logic levels between nodes of a circuit, instead of as switches connected. Mos transistors silicon substrate doped with impurities adding or cutting away insulating glass sio 2. In this paper, we present a selfchecking full adder based on the double pass transistor technology. Mos transistor theory study conducting channel between source and drain modulated by voltage applied to the gate voltage. Typically pmoss and nmoss are used together, sharing the power supplies.
Pass transistor logic ptl are generally superior to cmos circuits interms of delay and power consumption. The first two are briefly discussed in this section. Mos transistors silicon substrate doped with impurities. But before you can understand pass transistor logic you must first understand normal cmos logic, so go read the wikipedia article. The advantage of ptl is that only one ptl network either nmos or pmos is sufficient to perform the logic operation, which results in. What is the difference between cmos and passtransistor logic. Goals for today from switches to logic gates to logic circuits transistors, logic gates, truth tables. Single transistor pass gate with v t 0 out v dd v dd 5v v dd. The 3t or and and gates design is based on pmos and nmos pass transistor logic ptl.
Advantages of using pmos type lowdropout linear regulators in battery applications introduction. Switches and switch logic can be formed from simple n or p transistors and from the complementary switch i. The output remains in high impedance state when gate voltage is zero. Pass transistor logic digitalcmosdesign cmosprocessingtechnology planarprocesstechnology,siliconcrystalgrowth, twintubprocess, waferformationanalog electronic circuits is exciting subject area of electronics. Nmos is effective at passing a 0, but poor at pulling a node to vdd. In electronics, pass transistor logic ptl describes several logic families used in the design of integrated circuits. V ddv ddv tn while lower switching power is consumed, it may consume static power when output is high the reduced voltage level may be insufficient to turn off the pmos transistor of the subsequent cmos inverter. In the previous lectures, we learned about standard cmos. Some logical circuits using ptl pass transistor logic october 9, 2012 8 9. Oct 09, 2012 pass transistor logic october 9, 2012 7 8. Cmos logic gates1 inverter input output a a v dd gnd pull. Ratioed logic pass transistor transmission gate logic dynamic cmos logic domino.
How to determine which is drainsource in pass transistor. Ee 230 pmos 18 pmos example however, we rarely use pmos transistors with negative supplies as was done in the previous two examples. An nmos switch is on when the controlling signal is high and is off when the controlling signal is low. Pass transistor logic families there are two main pass transistor circuit styles. Vlsi design pass transistor logicpass transistor logic adapted from rabaeys digital integrated circuits, 2002, j. Pass transistor logic adapted from rabaeys digital integrated circuits, second edition, 2003. The specific conditions of the load switch application must be considered to make the final decision to use a pmos or nmos pass transistor. This simple yet extremely effective circuit uses the combination of an nmos transistor and a pmos transistor to generate output signals that are, under normal operating conditions, always either logic high or logic low. Pass transistor logic switch network a b b reduced number of transistors. In complementary cmos logic primary inputs are allowed to drive only gate terminals. Ptl uses a nmos or pmos transistor to transfer charge from input node to the output node, under the control of gate voltage. Problem on complex cmos logic gates gate ece 2012 solved paper electron devices duration. Cmos technology and logic gates mit opencourseware. Basic cmos concepts we will now see the use of transistor for designing logic gates.
Logic circuits adapted from cmos logic circuit design by john p. Figure below shows implementation of and function using only nmos. Since static cmos and pseudonmos were previously discussed, we focus the static logic section on various pass transistor logic families. Ee 261 james morizio 41 pass transistor ckts v dd v dd v s. N3, forms a twoinput pass transistor logic ptlbased and gate to control the discharge of transistor n1.
Oct 06, 2017 choosing a backup generator plus 3 legal house connection options transfer switch and more duration. Sep 17, 2016 realizing constructing a cmos pass gate cmos transmission gate from transistors. Double passtransistor logic is shown to improve circuit performance at reduced supply voltage. Cmpen 411 vlsi digital circuits spring 2012 lecture 07. Here the width of pmos is taken equal to nmos so that both transistors can pass the signal simultaneously in parallel. Complementary pass transistor logic complementary pass transistor logic 7 consists of complementary inputsoutputs, a nmos pass transistor network, and cmos output inverters.
Design of pulse triggered flipflop using pass transistor. A method to reduce circuit power by selectively replacing cmos gates with the. Implementation of cout using pass transistor logic. Output voltage degradation occurs across the pmos and nmos pass transistors due to threshold voltage drop while passing the logic zero or logic one respectively in relation to the input. It passes logic value from input to output when device is on and goes to high impedance state i. Further down in the course we will use the same transistors to design other blocks such as flipflops or memories ideally, a transistor behaves like a switch. A selfchecking cmos full adder in double pass transistor logic. However, new comparisons performed on more efficient cmos circuit realizations and a wider range of different logic cells, as well as the use of realistic. The ttl, the cmos and the ecl logic families are not suitable for implementing digital ics that have a largescale integration lsi level of inner circuit complexity and above. Pdf this paper introduces passtransistor logic design with dualthreshold. How to determine which is drainsource in pass transistor logic i ii hopefully by now, you would recognize the above nmos pmos configurations as pass transistor logic.
Xor has the worstcase karnaugh mapif implemented from simple gates, it requires more transistors than any other function. Realizing constructing a cmos pass gate cmos transmission gate from transistors. Transmission gate gives good non degraded logic levels. O c t o b e r 9 t h, 2 0 1 7 pass transistor logic 2. Apr 05, 20 i have come across several pass transistor interview questions on the internet, many of them asking to figure our the final output voltage level. Remember pmos transistors pass a strong 1 but a weak 0. Its symmetrical arrangement and doubletransmission characteristics. Pdf dualthreshold passtransistor logic design researchgate. We can see here, this inverters i can expand one of the two inverters.
The complex transmission gate came into picture because of the undesirable threshold effects of the simple pass transistors. Pmos latches and inverters which are used by means of complementary pass transistor logic. The term passtransistor logic refers to a different form of mosfet circuitry that doesnt generate logichigh and logiclow. How to determine which is drainsource in pass transistor logic i ii hopefully by now, you would recognize the above nmospmos configurations as pass transistor logic. Cmos pass gate, transmission gate, wl ratio, on resistance. This comes because in pass transistor logic the source and drain nodes are not fixed. Differential and passtransistor cmos digital circuits.
Only when that 100% is clear to you should you read about pass transistor logic. Dpl uses both pmos and nmos devices in the passtransistor network to avoid non full swing problems 9. Gatetosource voltage considerations the applied gatetosource voltage of the pass transistor directly affects the efficiency of. Introduction to passtransistor logic technical articles. It should be noted that although transmissiongate 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.
In the past, i have gotten confused with the terminals of a pass transistor because in general, transistors are symmetric and the source and drain terminals are interchangeable. Double pass transistor logic dpl uses both pmos and nmos devices in the pass transistor network to avoid non full swing problems, but it has higharea and highpower drawbacks 5. Mos transistor theory duke electrical and computer. The input current to the ldo is equal to the sum of the ground current. Nmos inverter for any ic technology used in digital circuit design, the basic circuit element is the logic inverter. How to determine which is drainsource in pass transistor logic. 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 gives rise to a pseudo nmos logic style design, and the charge. A weak pullup pmos transistor mp1 with gate connected to the ground is used in the first stage of the tspc latch. For an nmos to pass vdd logic 1 from input node to output node gate should be logic 1. Transmission gate an overview sciencedirect topics. The transmission gate logic is used to solve the voltage drop problem of the pass transistor logic. Like other mosfets, pmos transistors have four modes of operation.
Minimum size pmos transistors with shorted drainsubstrate contacts are used as gatecontrolled, very. Xor has the worstcase karnaugh mapif implemented from simple gates, it requires more transistors. Hides underlying nmosand pmos transistors and atomic interactions in out vdd vss in out out a d b a b d out. Latch latch vs flip flop linear logic gate master slave d flip flop mealy message message from the blogger miss penalty moore mux nand nmos nmos pass transistor nonblocking nor not operating regions or pass transistor physical design issues pipeline pmos positive edge triggered puzzles rtl saturation setup time. The competitors for lsiclass digital ics are the pmos, the nmos and the integrated injection logic i2l. A pmos transistor acts as an inverse switch that is on when the controlling signal is low and off when the controlling signal is high. Vlsi design pass transistor logicpass transistor logic. This technique uses the complementary properties of nmos and pmos transistors. In the circuit at right, v ds v gs, and so v ds pdf. Passtransistor adiabatic logic using single powerclock supply vojin g. Mosfet is a symmetrical device that means source and drain can be interchangedif body is not short circuited to any of the drain or source. A general method in synthesis of passtransistor circuits.