In an npn transistor, the three terminals are named the emitter first nblock, the base pblock, and the collector second nblock. Rtl is the earliest class of transistorized digital logic circuit used. It is called transistortransistor logic because both the logic gating function and the amplifying function are performed by transistors. Two input ttlnand gate the first, let us replace transistor q1 by its equivalent circuits.
Jun 26, 2012 logic of this type is most frequently encountered with the collector resistor of the output transistor omitted, making an open collector output. Logic gates digital circuit that either allows a signal to pass through it or not. Transistor uses, transistor rules, common emitter circuit, small signal amplification, fieldeffect transistors, jfet operating regions. Apr 25, 2012 in this electronics 201 lecture, we look at how to construct any logic gate imaginable from simple npn transistors using not logic. It is called transistortransistor logic because both the logic. Diodes and transistors pdf 28p this note covers the following topics. Transistor transistor logic transistor computer engineering. Transistor has three terminals emitter, base, and collector. Single transistor switches are useful as a way to a interface. Aug 16, 2014 transistortransistor logic ttl is a class of digital circuits built from bipolar junction transistors bjt and resistors. Logic of this type is most frequently encountered with the collector resistor of the output transistor omitted, making an open collector output.
You can always remember that the arrow points at the n material. Transistortransistor logic 4 the maximum collector current that q3 can carry and still be in saturation is. Ttl transistortransistor logic families history and. The current coming out the output terminal is io is the sum of the currents coming down through the base and the collector. Because of the complexity of transistor theory and the newness of the subject matter, two transistor theory manuals have been prepared. The transistor is a three terminal device which offers current gain. If you are using transistors to interface to the outside world you may find fets simpler, easier and better. In electronics, emittercoupled logic ecl is a highspeed integrated circuit bipolar transistor logic family. It is called so because the logic gating function e. Basic semiconductor physics, diodes, the nonlinear diode model, load line analysis, large signal diode models, offset diode model, transistors, large signal bjt model, load line analysis, small signal model and transistor amplification. Transistor theory illustrated, form 22 36794 this manual although both. Resistortransistor logic rtl resistortransistor logic, or rtl, refers to the obsolete technology for designing and fabricating digital circuits that employ logic gates consisting of nothing but transistors and resistors. The traditional interfacing standard component has always been the transistor.
This allows the designer to fabricate logic by connecting the open collector outputs of several logic gates together and providing a single external pullup resistor. Ttl family the logic family refers to the general physical realization of a logical element, such as the ttl, emittercoupled logic ecl, or complementary metal. The circuit on figure 10 shows the fundamental inverter circuit. Due to inevitable factors such as circuit capacitances and a characteristic of bipolar transistors called charge storage, it will take a certain amount of time for the transistor to turn completely off and the output.
Transistor transistor logic 1 chapter 6 transistor transistor logic the evolution from dtl to ttl can be seen by observing the placement of pn junctions. Dtl was initially made with discrete transistors and resistors before being integrated onto silicon. The logic transistors can go into reverse active mode and such charge out of the following transistor, speeding up the logic. For example, the diode d2 from figure 2 in the chapter on dtl can be replaced by a transistor whose collector is pulled up to the power supply. Low level state when lower transistor is on and upper transistor is off.
The configuration shown above is called an npn transistor. Sep 14, 2016 two input ttlnand gate the first, let us replace transistor q1 by its equivalent circuits. Free transistor circuits books download ebooks online. We shall begin this section with a study of the evolution of ttl from dtl. Jun 15, 2018 transistor transistor logic or ttl is a family of logic circuits used in electronics invented in the 1960s. Transistor transistor logic ttl is a class of integrated circuits which maintain logic states and achieve switching with the help of bipolar transistors. Mos transistor theory duke electrical and computer.
Hence the operation of this circuit is also similar. In essence, it describes the amplifying power of the transistor. Thus, the analog resistive network and the analog transistor stage perform the logic function nor. In the transistor, every three regions emitter, base, and emitter has a different width in the transistor. The pulldown resistor r 1 biases the transistor to the appropriate onoff threshold.
Transistor transistor logic ttl family one basic function of ttl ic is as a complimenting switch or inverter. Basic bjt inverter circuit if the voltage is zero low the transistor is in the cutoff region, the current and the voltage high. No portion of this material may be reproduced, in any form or by any means, without permission in writing by the publisher. Thus, we can use transistors in place of diodes to obtain logic gates that can be implemented with transistors and resistors only. The transistor is a three semiconductor current controlled device. Transistor theory and application, form 223 6783 2. You may wonder why the nand gate is so popular in the ttl logic families.
Ttl input or output lead is defined to be positive if the. This is a logic family which is mainly build up of npn transistors, pn junction diodes and diffused resistors. Transistors and logic circuits transistor control voltage in voltage out control high allows current to flow switch is closed on control low stops current flow switch is open off 2 not gate one transistor in out in high, switch is closed so current flows to ground out is low. The bipolar junction transistor is the realworld component of this sandwich. Mar 15, 2020 the full form of ttl is transistor transistor logic. Cmos transistor theory cmos vlsi design slide 3 introduction q so far, we have treated transistors as ideal switches q an on transistor passes a finite amount of current depends on terminal voltages derive currentvoltage iv relationships q transistor gate, source, drain all have capacitance. Actually, there are many different ttl families, with a range of speed, power consumption, and other characteristics. Ttl transistortransistor logic families history and applications. Transistortransistor logic or ttl is a family of logic circuits used in electronics invented in the 1960s. Transistortransistor logic ttl a common semiconductor technology for building discrete digital logic integrated circuits. Its name signifies that transistors perform both the logic function the first. Under the control of one of the terminals, called the base, current can flow selectively from the collector terminal to the emitter terminal. Transistor logic and then transistor transistor logic, dtl and ttl respectively. The output is inverted since the collectoremitter voltage of transistor q 1 is taken as output, and is high when the inputs are low.
Operation of a bipolar transistor as a current amplifier requires that the collectorbase junction be reverse biased and the emitterbase junction be forward biased. If the transistor is a pnp, then the arrow points to the base of the transistor, otherwise it points to the output. The circuit of figure 1 is similar to that of figure 3. The input to a ttl circuit is always through the emitters of the input transistor, which exhibits a. The most commonly used bipolar logic family is transistortransistor logic. Its name signifies that transistors perform both the logic function the first transistor and the amplifying function the second transistor. Zion problem with standard ttl transistor storage time significant propagation delay r l i l t computer engineering technology g. Mos transistor theory study conducting channel between source and drain modulated by voltage applied to the gate voltagecontrolled device nmos transistor. One early form of dtl, used by ibm corp in the 360 family of computers, was really a hybrid technology. The following is an internal schematic of a ttl logic gate. We will try to keep the article as brief and easy as possible. Transistortransistor logic article about transistor. Transistor transistor logic ttl is a logic family built from bipolar junction transistors. Bipolar junction transistors solidstate device theory.
Rtl gates are now seldom used, if at all, in modern digital electronics design because it has several drawbacks, such as. If a and b both are connected to ground, then both the be junction of the transistor t1 are forward biased. Resistor is used to keep the output current to a safe value. Rtl gates are now seldom used, if at all, in modern digital electronics design because it has several drawbacks, such as bulkiness, low speed, limited fanout, and poor. There are two varieties, the pnp and the npn, but we will focus on the more common npn configuration. It is a semiconductor device and it comes in two general types. Transistortransistorlogic topics the most commonly used bipolar logic family is transistortransistor logic. Not that hc and hct should be ignored, but they arent subtypes of ttl. Diodetransistor logic dtl is a class of digital circuits that is the direct ancestor of transistortransistor logic. It overcomes the main problem associated with dtl, i. Transistortransistor logic ttl is a logic family built from bipolar junction transistors. From switches to transistors, logic gates and logic circuits hakim weatherspoon cs 3410, spring 20. As the current is steered between two legs of an emittercoupled pair, ecl is sometimes called. Use of transistors q4 and diode is to provide quick charging and discharging of parasitic capacitance across q3.
Following our study of amplifiers, we turn to the use of the as a. Ttltransistortransistor logic, a logic family to realize logic gates, can be open collector, totem pole or tri state. Resistortransistor logic rtl sometimes also transistorresistor logic trl is a class of digital circuits built using resistors as the input network and bipolar junction transistors bjts as switching devices. Transistor logic and then transistortransistor logic, dtl and ttl respectively. This is the basis for the operation for your computer and any.
The full form of ttl is transistor transistor logic. There are three configurations that cna be used for a transistor. A transistor differs from a pair of back to back diodes in that the base, the center layer. Indeed, the bulk of digital systems applications employing ssi and msi packages were designed using ttl. The transistor actively pulls the output down to logic 0, but the resistor is not active in pulling the output up to logic 1. This allows the designer to fabricate logic by connecting the open collector outputs of several logic gates together and. The humble transistor q1 emitter e collector c base b transistor basics emitter to base junction is forward biased normally collector to base junction is reverse biased normally transistors are current operated devices, so. One of the prominent features of transistor transistor logic signals is the ability of the inputs of the gate rise to the logical 1 if left unconnected. In this electronics 201 lecture, we look at how to construct any logic gate imaginable from simple npn transistors using not logic.
This nand gate is called dtl nand gate or diode transistor logical nand gate. The maximum current the gate can sink when the output is low iolmax icsatmax i4 81. The circuit examples in this section are based on a representative ttl family, lowpower schottky ls or lsttl. Building block of computers microprocessors contain millions of transistors intel pentium ii. Using transistors as electronically controlled switches is critical for building modern digital logic. Cmos transistor theory cmos vlsi design slide 3 introduction qso far, we have treated transistors as ideal switches qan on transistor passes a finite amount of current depends on terminal voltages derive currentvoltage iv relationships qtransistor gate, source, drain all have capacitance i c. Transistors and logic circuits transistor control voltage in voltage out control high allows current to flow switch is closed on control low stops current flow. The terminal on the left is called the emitter, the terminal on the right is.
Ttl is a digital logic design where transistors act on dc pulses. Transistor transistor logic gate electronics tutorials. Transistortransistor logic ttl transistortransistor logic, or ttl, refers to the technology for designing and fabricating digital integrated circuits that employ logic gates consisting primarily of bipolar transistors. This is a logic family which is mainly build up of npn transistors, pn junction diodes and. Bipolar transistors conduct current using both electrons and holes in the same device. Now, many s and ls circuits use schottky diodes for logic functions, so arent strictly ttl, but otherwise are similar enough. The symbol of the transistor has an arrow on the emitter. The basic building block of this logic family is nand gate and there are various subfamilies of this logic gate those are standard ttl, advanced schottky ttl, schottky ttl, low power ttl, high power ttl, fast ttl etc.
Transistor transistor logic watch more videos at videotutorialsindex. Each has differnet characteristics, and by designing the circuit around one of these configurations it is possible to achieve the characteristics required. Generally speaking, ttl logic ics use npn and pnp type bipolar junction transistors while cmos logic ics use complementary mosfet or jfet type field. This module is devoted to the design of a transistor amplifier and this involves choosing the values of five resistors and three capacitors. Transistor basics emitter to base junction is forward biased normally collector to base junction is reverse biased normally transistors are current operated devices, so kcl should be applied first. Zion fanout the fanout of a logic gate is the number of inputs that the gate can drive without exceeding its worstcase loading specifications.
Ttl family the logic family refers to the general physical realization of a logical element, such as the ttl, emittercoupled logic ecl, or complementary metaloxide semiconductor cmos logic families. When both input a and b are given with 0 v, both of the diodes are in forward biased condition that is in on condition. Logic operation is same as the open collector output. In an npn transistor, the three terminals are named the emitter first nblock, the. Transistor transistor logic topics the most commonly used bipolar logic family is transistor transistor logic. The three elements of the twojunction transistor are. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. Transistor and diode chips were glued to a ceramic substrate. Some ttl logic gates are fabricated onto an integrated circuit ic. Ecl uses an overdriven bjt differential amplifier with singleended input and limited emitter current to avoid the saturated fully on region of operation and its slow turnoff behavior. A ttl inverter is designed as a 1input nand gate, omitting diodes d1y and d2y in figure ttl1. Transistortransistor logic ttl is a class of digital circuits built from bipolar junction transistors bjt and resistors. For simplicity we will show here only two inputs nand gate circuit by using diodes and transistors. Nmos transistor g g connect source to drain when v g v supply g n.