I sm Dr.P.Thiyagarajan working as Associate Professor in TNOU
|Other roles:||Instructional/Graphic Designer|
|Languages:||Tamil, English, Malayalam, Hindi, Telugu|
- 1 My Profile
- 2 My Aim
- 3 MY PROJECT
- 4 INTRODUCTION
- 5 LEARNING ACTIVITIES
- 6 The Tran sister and Inverter
- 7 The Tramsietr
- 8 The inverter
- 9 History of logic chips
- 10 Sum Up
- 11 Learning Activity
- 12 Answer to Learner Activity
Hai I am Dr.P.Thiyagarajan, working as Associate Professor in Tamil Nadu Open University. Previously I was working as Deputy Director in Indira Gandhi National Open University.
- I have submitted technical Regination in IGNOU in order to take a job in Tamil Nadu Open University. Presently I am involved in promoting in Community College#.
- The International Publishing House in New Delhi has awarded Best Citizen of India Award for promoting Community College#.
I joined as Statistician in Khadi and Village Industries Commission,Trivandram, Kerala in 1988 and become Investigator in National Sample Survey Organization, Sastri Bhavan, Chennai in 1990. I have been given seven transfer in NSSO and again cleared UPSC and appointed as Statistical Investigator in Southern Command Headquarters,Pune in 1991. Again I become Assistant Regional Director/Lecturer in Economics in IGNOU in 1992 and promoted as Deputy Director in IGNOU in 2001.
- DDE-Distance Education*
- MA-Distance Education*
- MCA-Registered in IGNOU*
Promoting Open and Distance Education in Remote and Rural of Tamil Nadu is my intersret.
To serve for the poor and the marginalized
internal This is the page of TNOU external [http//:www.tnou.ac.in/please visit the site]
In this unit you are going to learn about the Transister and Inverster, The Transister in detail and the Inverter in detail with dugrammes and charts with computer icons
After completion of this unit you will be able explain
- The Tran sister and Inverter
- The Tran sister
- The Inverter
The Tran sister and Inverter
A transistor is a three-terminal device that can be used as an amplifier or as a switch. When the transistor is used as an amplifier, it is working in analog mode. When it is being used as an electronic switch, it is functioning in digital mode. The transistor will only be used in digital mode in these labs, which means the transistor will either be on or off. The terms ground, low, zero, zero volts, open switch, and dark lamp are all equivalent to the Boolean value false. Likewise five volts, high, one, closed switch, and lit lamp (LED), are equivalent to the Boolean value true. We will use false (F or 0) and true (T or 1) when speaking of the logical states in this manual. Modern computers contain millions of transistors combined together in digital mode to create advanced circuits.
Transistors are three pin devices that are similar to valves for controlling electricity. The amount of current that can flow between the collector and emitter is a function of the current flowing through the base of the transistor. If no current is flowing through the base of t h e transistor, no current will flow through the collector and emitter. With the transistor operating in digital mode, it will be configured to carry the maximum (if on) or minimum (if off) amount of current from the collector to the emitter that the circuit will allow. The transistor used in this lab, the pn2222 or 2n2222, is an NPN, bipolar junction transistor which is sometimes referred to as a BJT. Other types of transistors exist, and while they differ in how they function, they are used in a similar manner in digital circuits. In this lab, a single transistor will be used to create an inverter. The principles used to build this inverter could be applied to other circuits with other types of transistors. Pinouts of the two types of transistors most likely to be used in these labs are shown in Figure 1.1. Common NPN transistors The transistor used in this lab, the pn2222 or 2n2222, is an NPN, bipolar junction transistor which is sometimes referred to as a BJT. Other types of transistors exist, and while they differ in how they function, they are used in a similar manner in digital circuits. In this lab, a single transistor will be used to create an inverter. The principles used to build this inverter could be applied to other circuits with other types of transistors. Pinouts of the two types of transistors most likely to be used in these labs are shown in Exhibit 1.1.
In order to build the circuit, a digital design kit that contains a power supply, switches for input, light emitting diodes (LEDs), and a breadboard will be used. Make sure to follow your instructor's safety instructions when assembling, debugging, and observing your circuit. You may also need other items for your lab such as: logic chips, wire, wire cutters, a transistor, etc. Exhibit 1.2 shows a common breadboard, while Exhibit 1.3 shows how each set of pins are tied together electronically. Exhibit 1.4 shows a fairly complex circuit built on a breadboard. For these labs, the highest voltage used in your designs will be five volts or +5V and the lowest will be 0V or ground.
Always make sure to have a clearly documented circuit diagram before you start wiring the circuit.
The inverter, sometimes referred to as a NOT gate, is a simple digital circuit requiring one transistor and two resistors. The circuit should be connected as in Exhibit 1.5. Make sure to start with a neat diagram in your lab notebook before you start constructing your circuit! The input is connected to a switch and the output connected to an LED. The two resistors are current limiting resistors and are sized to insure that the circuit operates in digital mode. If the inverter circuit is altered slightly with the addition of another transistor placed in series with the current one, it results in one more input and the creation of a NAND gate. Likewise, if another transistor is added in parallel with the transistor in the inverter circuit a NOR gate can be built. These two gates are discussed at greater length in the next chapter.
Building the Circuit Throughout these experiments we will use TTL chips to build circuits. The steps for wiring a circuit should be completed in the order described below:
Turn the power (Minilab) off before you build anything! Make sure the power is off before you build anything! Connect the +5V and ground (GND) leads of the power supply to the power and ground bus strips on your breadboard. The +5V supply may be found on the bottom centre of the Minilab with the black switch at the +5V fixed position. Before connecting up, use a voltmeter to check that the voltage does not exceed 5V. Plug the chips you will be using into the breadboard. Point all the chips in the same direction with pin 1 at the upper-left corner. (Pin 1 is often identified by a dot or a notch next to it on the chip package) Connect +5V and GND pins of each chip to the power and ground bus strips on the breadboard. Select a connection on your schematic and place a piece of hook-up wire between corresponding pins of the chips on your breadboard. It is better to make the short connections before the longer ones. Mark each connection on your schematic as you go, so as not to try to make the same connection again at a later stage. Get one of your group members to check the connections, before you turn the power on. If an error is made and is not spotted before you turn the power on. Turn the power off immediately before you begin to rewire the circuit. At the end of the laboratory session, collect you hook-up wires, chips and all equipment and return them to the demonstrator. Tidy the area that you were working in and leave it in the same condition as it was before you started.
Common Causes of Problems
Not connecting the ground and/or power pins for all chips. Not turning on the power supply before checking the operation of the circuit. Leaving out wires. Plugging wires into the wrong holes. Driving a single gate input with the outputs of two or more gates Modifying the circuit with the power on.
History of logic chips
Logic gates could be constructed from transistors and resistors just as the inverter was constructed in the last lab. However, using discrete transistors to build logic gates can be time consuming and prone to problems as increasing the number of connections also increases the possible points of failure. Before the advent of the transistor, and today in certain industrial applications, logic gates are created using mechanical relays. Mechanical devices suffer from similar problems along with the added complication that such devices generally cannot be switched from one state to another quickly enough for modern computer applications. The introduction of the integrated circuit in the late 1950s aimed at placing many individual circuit components in a single package that had all of the connections self-contained in silicon. This revolutionized the computing industry and has led to CPUs today that contain millions of components in a single chip. You will use 7400 series logic chips in this manual. This series of chips has been manufactured since the 1960s. These chips were used to design and build computers during that time; however, they are rarely used in computers built today. Despite this, they still have many uses (in addition to just teaching student’s digital logic). They are still produced, easy to obtain and are fairly inexpensive. The chips come in various packages, but the package used in these labs is a dual in-line package, otherwise know as a DIP as shown in Exhibit 2.1. In order to determine the polarity of the chip, a notch is put on one side of the chip. From a top view, pin one is on the left of the notch with other pins numbered sequentially in a counter clockwise manner. Chips may also have a dot placed near pin one. Chips in the 7400 family are constructed using a variety of different circuit configurations that all have different properties. Some utilize BJT and others, field effect transistors (FETs). The different series (C, HC, L, S, LS, etc. within the 7400 family) are designed with such considerations as the need for low power consumption, switching speed, or reliability under stressful environments that might be incurred in military applications.
A. Logic symbols
As mentioned in the previous lab, NAND and NOR gates can be constructed with fewer components than AND and OR gates. For this reason, the inverter, NAND and NOR make up four of the seven chips used in all of the labs. Symbols used to represent the NAND, NOR, AND, OR and inverter or NOT are provided along with the truth tables for the NAND and NOR. The truth tables have “0” representing false and ”1” representing true. A circuit that can be used to create a NAND gate using two transistors is shown in Exhibit 2.7. Circuit configurations for NAND gates provided by the 7400 series chips, while logically equivalent, vary from this design.
Notice that only the small circle is used to indicate the inversion of the AND to produce the NAND instead of using the full inverter symbol in Exhibit 2.2. This shorthand is often used at the input of a gate, shown in Exhibit 2.8 which is equivalent to (A' AND B).
Since the NAND gate is used more often, how do you obtain a simple AND or OR gate? One way would obviously be to simply combine a NAND gate along with an inverter as in Exhibit 2.9. While this works, as each chip contains more than one gate, if an extra NAND is available, it may be more advantageous to use a spare gate rather than to use an entirely new chip as in Exhibit 2.10.
Exhibit 2.11 demonstrates how to implement a simple logical expression using the gates provided. Make sure to use only those gates that are provided in your kit when designing your circuit. This diagram implements the function f(A,B,C) = AB + BC. Since there are three inputs to this function, there are eight possible logical input conditions as shown in the truth table.en building a logical circuit, it is important to document the circuit diagram as shown above. However, even this diagram could be made clearer for those attempting to build and debug the circuit. Exhibit 2.12 yields a much more detailed description of how the circuit should be built.You should include a diagram for every circuit that you build in your lab notebook and you should follow the format in Exhibit 2.12. Let us examine the type of information contained here. First, chips are labeled as IC1, IC2 and IC3. Then a legend is included that specifies the type of chip for each of the IC or integrated circuits. The IC numbers should appear in the order that they will appear in your breadboard from left to right or top to bottom, depending upon how the breadboard is configured in your digital trainer. Second, the pins used for each connection on the chip are also given, which makes connecting the circuit possible without having to continually consult the datasheet for that logic chip. Third, the switches and LEDs are labeled in the order that they are used for the respective inputs and outputs.
All of this makes it much easier to construct and demonstrate the circuit. But above all, the greatest benefit comes if the circuit does not work and needs to be debugged! In this case, with all of the pins clearly labeled on your diagram, it is much easier for someone to examine your circuit, compare it to your diagram, trace the various connections and hopefully find and correct any problems in the circuit.This circuit would require three different 7400 series logic chips and ten different connections, yet if designed with individual transistors using the inverter from the last lab, as well as the NAND circuit shown in Exhibit 2.7, this would take nine different transistors, fifteen resistors, and many more connections than if just the chips were used.
It is no wonder that the decrease in complexity of digital circuits that followed the introduction of the 7400 series chips led to a revolution in the computing industry! Let us examine one more simple circuit. This one is used to implement an exclusive or (XOR), which is represented by the symbol in logical expressions. he truth table for A XOR B follows along with the gate used to represent it in circuit diagrams. As no XOR chip is provided in the kit, in order to implement this circuit, the XOR must be built by examining the truth table to find the resulting logical function, A'B + AB'. The circuit diagram for the XOR is shown in Exhibit 2.14. Remember, a diagram such as this should be included in your lab manual to ease construction and debugging of the circuit.
We will discuss how to build more complicated circuits in the next chapter, as well as how to logically simplify the functions with Boolean algebra. Both circuits designed in this chapter can be simplified significantly with the use of De Morgan's law, also discussed in the next chapter.
In this Unit you have studied about the Transister,Inverter and Logical functions
1. What is transistor?
Answer to Learner Activity
A transistor is a three-terminal device that can be used as an amplifier or as a switch. When the transistor is used as an amplifier, it is working in analog mode. When it is being used as an electronic switch, it is functioning in digital mode. The transistor will only be used in digital mode in these labs, which means the transistor will either be on or off.
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