Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. In electronics, pass transistor logic ptl describes several logic families used in the design of integrated circuits. It reduces the count of transistors used to make different logic gates, by eliminating redundant transistors. A basic circuit using any generalpurpose bipolar transistor such as the bc549, bc548, or bc547, can be used to construct the and gate.
It is a cmos based switch, in which pmos passes a strong 1 but poor 0, and nmos passes strong 0 but poor 1. The pass transistor based cell library and synthesis tool are constructed, for the first time, to clarify the potential of topdown pass transistor logic. Nmos devices passes a strong 0 but a weak 1 while pmos transistors pass a. 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. Static cmos circuit at every point in time except during the switching transients each gate output is connected to either v dd or v ss via a lowresistive path the outputs of the gates assume at all times the. Pdf a differential double pass transistor logic unit. For some types of functions, this can lead to much more efficient implementations than using gates. In this configuration there are two transistors connected in series. One of the first papers examining passtransistor logic and formalizing passtransistor design style was published by whitaker, in 1983 whitaker, electronics. Nov 08, 2017 problem on nmos pass transistor logic gate 2014 ece paper solution duration. Transistor transistor logic topics the most commonly used bipolar logic family is transistor transistor logic.
In cmos, a gate is defined only when trace a connection all the way. 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. Static cmos circuit at every point in time except during the switching transients each gate output is connected to either v dd or v ss via a lowresistive path the outputs of the gates assume. The presence of the switch driven by b is essential to ensure that the gate is static a lowimpedance path.
Remember nmos transistors pass a strong 0 but a weak 1. A general method in synthesis of passtransistor circuits people. Virtual lab indian institute of technology guwahati. Pass transistor logic adapted from rabaeys digital integrated circuits, second edition, 2003 j. 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. The truth table of xor gate is as shown in table below. Generic static cmos gate v dd v pullup network, connects output to dd, contains only pmos in1 v in out 2 inn pulldown network, connects output to gnd, contains only nmos for every set of input logic values, either pullup or pulldown network makes connection to vdd or gnd if both connected, power rails would be shorted together. Logic network employs input signals at both gate and drain terminals. It is common to use this logic family for multiplexers and latches. Opencollector outputs of some gates have a higher maximum voltage, such as 15v for the 7426, 16 useful when driving other than ttl loads. Logic gates digital circuit that either allows signal to pass through it or not used to build logic functions seven basic logic gates. Transistors are used as switches to pass logic levels between nodes of a circuit, instead of as switches connected directly to supply voltages.
Every cpl gate has two output wires, both the positive signal and the complementary signal, eliminating the need for inverters. As with the nchannel example, a logic signal from the system power management control circuitry turns the load switch on and off via a smallsignal nmos transistor, q1. Cmosbased carbon nanotube passtransistor logic integrated. This technique uses the complementary properties of nmos and pmos transistors.
A logic gate can be defined as digital circuit which either allows a signal to pass through or stops it. Cmpen 411 vlsi digital circuits spring 2012 lecture 07. 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. V s will initially charge up quickly, but the tail end of the transient is slow. When b is low, bottom device turns on and passes a 0.
Hello and welcome original pdf to todays lecture on passtransistor logic circuits this is the page replacement policies pdf second. This paper examines same key issues in the implementation of spl. A general method in synthesis of passtransistor circuits. He was born in lincoln, england and he was the son of a shoemaker. Introduction to passtransistor logic technical articles. When en is low, q1 is off and the gate is pulled up to vin. The result is in some cases conceptual simplification, but the cmos inverters strict logichighlogiclow output characteristic is lost. Nmos devices passes a strong 0 but a weak 1 while pmos transistors pass a strong 1 but a weak 0. The method is general and can be extended to synthesize any passtransistor network. Digital integrated circuits combinational logic prentice hall 1995 overview static cmos conventional static cmos logic ratioed logic pass transistor transmission. Transmission gate logic circuits adapted from cmos logic circuit design by john p. Logic gates digital circuit that either allows a signal to pass through it or not. Nmos passtransistor logic using the nmos transistor as a pass element has. It should be noted that although transmissiongate based and passtransistor 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.
One of the first papers examining pass transistor logic and formalizing pass transistor design style was published by whitaker, in 1983 whitaker, electronics. Hybrid pass transistor logic with dualgate ambipolar cntfets. The transmission gate logic is used to solve the voltage drop problem of the pass transistor logic. Pdf a new 5transistor xorxnor circuit based on the pass.
In this lecture, we will talk about another way to implement logic functions using transistors. 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 the process technology level. Mod01 lec14 pass transistor logic circuits i youtube. The pass transistor logic attempts to reduce the number of transistors to implement a logic by allowing the primary inputs to drive gate terminals as well as sourcedrain terminals. Pchannel passtransistor circuit electrical model for the experiment with the pchannel passtransistor is shown in fig. Differential and passtransistor cmos digital circuits. Mos transistor switches pswitch a b s p a b s s 1 s 0 good 1, poor 0 1 0 1 0 degraded a b s s cmos switch a b s c s 0 s 1 a good 0 good 1 transmission gate b s s 4 signal strength strength of signal how close it approximates ideal voltage source v dd and gnd rails are strongest 1 and 0 nmos pass strong 0. The current drive of the transistor gatetosource voltage is reduce significantly as v.
Pass transistortransmission gate logic dynamic cmos logic. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or lsttl. If the faucet knob gate is turned on water flows from the source to the sink, otherwise if the faucet. The ntype pass transistor can pass an input signal when a logic 1 is biased on the gate, and it is turned off when a logic 0 is biased on the gate.
These circuits act as switches use either nmos transistors or parallel pair of nmos and pmos transistor called transmission gate. This is a transistortransistor logic ttl and gate circuit using bipolar junction transistors. Us6084437a logic circuit utilizing pass transistors and. The operation of a transistor could be explained by making an analogy to faucets. The dpl gate consists of complementary adder using passtransistor logic. In conventional logic families input is applied to gate terminal of transistor but in ptl it is also applied to source drain terminal.
Even a logical operation that cannot be expressed efficiently. The paper describes how the logic functions can be efficiently and optimally built using pass transistor logic. Cell circuits for the 4 bit adder is realized with the cmos pass transistors using the 123 decision diagram and 4 bit adder is completed by combining the cells. Used to build logic functions there are seven basic logic gates.
Digital gates fundamental parameters purdue engineering. Here the width of pmos is taken equal to nmos so that both transistors can pass. In contrast to static cmos primary inputs drive gate terminals. The transistor count can be reduced by modifying the or gate at the last stage of the carry. Figure below shows the implementation of xor function using pass transistors. It shows some fundamental pass transistor building blocks which became. Pass transistor logic circuits nmos pass transistor transmission properties transmission gates transmission gate applications mux xor d latch d flip flop clock skew management pass transistor logic families 17.
Apply to the circuit in figure 2 the voltages listed in table 2, and observe and record the voltage v o at the output of the pass transistor. Pass transistor pt logic a b f b 0 a 0 b a b b f a b. The current drive of the transistor gate tosource voltage is reduce significantly as v. A carry propagation tech inputsoutputs and is thus a dual rail logic like cpl. Complementary pass transistor logic or differential pass transistor logic refers to a logic family which is designed for certain advantage. Passtransistor logic switch network a b b reduced number of transistors no static power consumption.
Slide set 3 pass transistor logic transmission gates. 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. A logic circuit combines a plurality of pass transistor logic trees and a multipleinput logic gate for receiving intermediate logic signals from the respective pass transistor logic trees, and can express a complex logical operation while decreasing the number of stages in pass transistor logic trees and improving operation speed. Dualgate ambipolar carbon nanotube transistors dgacntfets have two independent gates that enable polarity switching between electron and hole conduction see fig.
A semiconductor diode pn junction acts as a closed switch when it is forward biased, i. Digital integrated circuits combinational logic prentice hall 1995 overview static cmos conventional static cmos logic ratioed logic pass transistortransmission. Oct 09, 2012 in conventional logic families input is applied to gate terminal of transistor but in ptl it is also applied to source drain terminal. 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. 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 the process technology level 1. Complementary passtransistor logic a general method of karnaugh map coverage and mapping into circuit realizations is applied to design logic andnand, ornor, and xorxnor gates in cpl. And, or, not, nandnot and, nornot or, xor xnornot xor 9 did you know. Dual gate ambipolar carbon nanotube transistors dgacntfets have two independent gates that enable polarity switching between electron and hole conduction see fig.
Complementary pass transistor logic a general method of karnaugh map coverage and mapping into circuit realizations is applied to design logic andnand, ornor, and xorxnor gates in cpl. Pdf a new 5transistor xorxnor circuit based on the. Passtransistor logic ptl, also known as transmissiongate logic, is based on the use of mosfets as switches rather than as inverters. Jun 21, 2012 mod01 lec14 pass transistor logic circuits i. Transmission gate an overview sciencedirect topics. Broadening the ptl concept, we can make some more interesting gates. Vlsi design pass transistor logicpass transistor logic. The method consists of the implementation of the gates. Complementary pass transistor logic a general method of karnaugh map coverage and mapping into circuit realizations is applied to design logic and nand, ornor, and xorxnor gates in cpl. B c and ab are used as multiplexing inputs in order to sum both terms with the or gate operation. Problem on nmos pass transistor logic gate 2014 ece paper solution duration. Single transistor pass gate with v t 0 out v dd v dd 5v v dd 0v 5v 0v watch out for leakage currents. Pass transistor logic has been considered a low power logic 14,15. Vlsi design pass transistor logicpass transistor logic adapted from rabaeys digital integrated circuits, 2002, j.
Problems design 4 to 1 multiplexor using transmissiongates. The passtransistor based cell library and synthesis tool are constructed, for the first time, to clarify the potential of topdown passtransistor logic. Digital integrated circuits combinational logic prentice hall 1995 combinational logic. 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. Cmos technology and logic gates mit opencourseware.
Transistor transistor logic ttl family one basic function of ttl ic is as a complimenting switch or inverter. Passtransistorlogic xor gate using pass transistor logic. Implement an xor gate using minimum number of transistors. Examples of this type of gate are the 7401 15 and 7403 series. A new 5transistor xorxnor circuit based on the pass transistor logic conference paper pdf available december 2011 with 3,665 reads how we measure reads. If any of the logic gates becomes logic low transistor conducting, the combined output will be low. 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. It is possible to use a single nmos transistor as a ptl switch. Complex logic gates in cmos design methodology 2 when.
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