The Transistor - Successor

THE TRANSISTOR - SUCCESSOR TO THE VACUUM TUBE? By John A. Doremus, Chief Engineer, Carrier and Control Engineering Dept. Motorola, Inc. Reprinted by Motorola Inc. Communications and Electronics Division Technical Information Center 4545 Augusta Boulevard • Chicago 51, Illinois presented to Chicago Section, I.R.E. January 18, 1952 ATIC-251-UM ERRATA Page 5, column 1, paragraph 10 should re a d : "The alternating current equivalent circuit of a Transistor (as shown in Fig. 24) for most - Page 5, column 2, paragraph 4 should re a d : "The output impedance is equivalent to rc plus rb. This may be from 20, 000 ohms to over a megohm. Figure 26 shows typical - -. " Page 5, column 2, paragraph 7 should re a d : "- _ _ _ are not permanently darpaged by elevated temperature as long as the criti cal point is not exceeded. " THE TRANSISTOR - SUCCESSOR TO THE VACUUM TUBE ? We, who work in the communication phase of a transistor is equivalent to a triode. Its phy si- this industry, when we get to the heart of many of can embodiment is extremely small, since its our problems, have the feeling that "There's no ability to amplify does not depend upon its size. thing wrong with electronics that the elimination Three different types of transistors are shown in of a few vacuum tubes would not fix. " This is a F ig s . 1, 2 and 3. sordid thought to have concerning the element around which our industry revolves. Yet many of It is interesting to note that the name is de our basic short comings can be traced back to the rived from the fact that it was called a transit vacuum tube. resistor by early workers in the field who were really searching for new ways of making non Most serious, a tube has a limited and un linear resistors. predictable life. A piece of communication equip ment is often called on to operate continuously The TRANSISTOR is essentially a sm all piece for years. It is desirable that this equipment be of one of the semi-conductor m aterials wherein completely unattended yet tube failures require various portions of it have been constructed to constant and costly maintenance. have different conducting properties. Next, a tube consumes power inefficiently. Its ability to amplify depends upon the un No one knows this better than those of you in the usual property of semi-conductors to support two television industry. Very large power transform kinds of conduction simultaneously: One, the ers are required for our television sets, a good travel through the material of excess electrons share of whose burden is filament power for 15 to which we know of as negatively charged particles, 20 tubes in the set. and Two, the travel through the material of "holes", which are really the lack of electrons Mechanically too, tubes are bulky and fragile. and, therefore, constitute an equal positive charge. In a semi-conductor, electrons travel much slower Now, for the first time, we have an alternate than they do in a conductor and "holes" travel device which can be considered a legitimate con even slower than the electrons. tender to the throne that has been occupied by the vacuum tube for over 35 years. It can do many of TRANSISTORS are constructed in two dis the jobs now done by vacuum tubes and do them tinctly different types. One type is called the more efficiently and more dependably. point contact type whose construction is shown in Fig. 4. The other, called the junction type, is This device is called a TRANSISTOR. shown in Fig. 5. Their construction results in different performance characteristics as will be In this paper, we are going to attempt to give come apparent as this story unfolds. you answers to the following questions: 2. What can the TRANSISTOR do for us? 1. What is a TRANSISTOR? 2. What can it do for us? The TRANSISTOR is extremely important to 3. Why get all excited about TRANSISTORS our industry for two basic reasons: at this time ? 4. How does the TRANSISTOR work? 1. It is a very efficient amplifier. 5. What are its characteristics? 2. It shows promise of extreme dependa 6. How do we use it in circuits? bility and unbelievable long life. 7. What new problems does it pose? In most circuits, the transistor will do the 1. What is a TRANSISTOR? same job as a vacuum tube while consuming l/l 000 as much power. Let us look at a radio or televi Transistor is the name given to a crystal- sion set. In all stages up to the second detector, type amplifying element made of a semi-conduc the signal level is less than a milliwatt and in tor such as silicon or germanium. At present, most of them, less than a microwatt. Yet we -1- burn upon the average of a watt or more filament of these predictions point toward a figure of power and a watt of plate and screen power to ob 70, 000 to 90, 000 hours. This is approximately tain the amplification we desire. 10 years. Since a TRANSISTOR does not stop suddenly, as there is nothing to burn out, the life Transistors can give us 20 to 50 db of gain, figures above have beenbased on the time at which depending upon the type, while consuming less its gain will drop 3 db. For most applications, than two milliwatts of power. The junction type this is not necessarily the end of its useful life. TRANSISTORS are about 10 times more efficient The change in lan d the output impedance of a than the point contact type for small - signal sample lot of TRANSISTORS is shown in Fig. 6. amplification. The TRANSISTOR is extremely small and ru g g ed . The TRANSISTOR has no filament so there are no problems of filament burn-out. TRANSIS Let's look ata tabulation of the properties of TOR life has been predicted in several ways. All both types. Point Contact Type Junction Type T u b es G ain 20 - 30 db 30 - 50 db 20 - 50 db Efficiency (Class A) 30% 45 - 49 % 1 to 25 % ( C la s s C) 90% 95% 70% L ife 70,000 hrs. 90,000 hrs. 5 ,0 0 0 h r s . V ib ratio n 100 g 100 g Shock 2 0 ,0 0 0 g 2 0 ,0 0 0 g U n iform ity ±3 db ±2 db ±3 db Minimum Powers 1 m w: 1 microwatt 1 /1 0 w att Temperature 7 0 ° C 7 0 ° C 5 0 0 ° C F re q u e n c y 30 - 70 m e 3 - 5 m e 60, 000 m e Gain X Bandwidth 1000 m e 120 m e 1000 m e Noise Figure 45 db 15 db 10 - 30 db Maximum Power 100 mw 1 w att 1 m egaw att Summarizing - up to 30 me, transistors can do a better job than tubes within the lim its of power and temperature. Photo Transistors strong in the red and infra-red region as shown in F ig . 8. It is important to mention one other charac teristic at this time. The boundary in a junction The second is its efficiency. A PN junction type transistor is extremely photo sensitive and, unit (diode) has a sensitivity of 30 ma/lumen, 10 therefore, can be made into an attractive photo to 15 milliwatts of AC can be obtained from the cell. The first types made were simply diodes as simple circuit using this type of unit shown in shown in Fig. 7. F ig . 9. One important characteristic of a transistor An NPN photo transistor can give a light con photocell is its spectral sensitivity which is most version efficiency about 30 times greater than -2- this or about 1 ma/millilumen. The construction properties where, under certain conditions, they of this unit is shown in Fig. 10. seem like insulators, while under other conditions they seem like conductors. These elements have Using the same circuit, about the same out been called semi-conductors. put level can be obtained from this unit. Fig. 11 shows a photograph of several photo-transistors In the molecular structure of a m aterial like compared to a normal pencil. diamond, shown in Fig. 13, all valence bonds are satisfied and the m aterial behaves like an insulator. 3. Why get all excited about TRANSISTORS at th is tim e ? If the crystal is heated, the thermal excita tion can cause a valence electron to be knocked 1. Production of practical quantities of the out of its usual place, and this electron (negative point contact units has begun. charge) is free to move about in the crystal. The 2. Large advances in circuit design have place from where the electron came is called a been accomplished in the past year. "hole" and this area exhibits a local positive 3. The bringing out of the laboratory of the charge. Under this condition, the diamond behaves junction transistor and readying it for somewhat like a conductor. production opens even newer field of application. Eventually, the electron-and the hole may re 4. Stability of design has been established. combine. At all times, however, the entire crys 5. Dependability of units has been assured tal is electrically neutral. by uniform production. 6. Designability has been established. Units Certain other elements in the fourth column can now be designed to a certain set of of the Periodic Table, like siliconand germanium, parameters.

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