"In presenting the dissertation as a partial fulfillment of the requirements for an advanced degree from the Georgia Institute of Technology, I agree

Transcription

1 "In presenting the dissertation as a partial fulfillment of the requirements for an advanced degree from the Georgia Institute of Technology, I agree that the Library of the Institution shall make it available for inspection and circulation in accordance with its regulations governing materials of this type, I agree that permission to copy from, or to publish from, this dissertation may be granted by the professor under whose direction it was written, or, in his absence, by the dean of the Graduate Division when such copying or publication is solely for BCholarly purposes and does not involve potential financial gain. It is understood that any copying from, or publication of, this dissertation which involves potential financial gain will not be allowed without written permission.

2 A PUNCHED TAPE COMPARATOR A THESIS Presented to the Faculty of the Graduate Division by Arno V. A. Mueller In Partial Fulfillment of the Requirements for the Degree Master of Science in Electrical Engineering Georgia Institute of Technology June 1958

3 A PUNCHED TAPE COMPARATOR 12*7 APPROVED T f ^~ f y Date Approved by Chairman: /%j?) V~

4 ACKNOWLEDGMENT The author wishes to express his appreciation to Dr. W. J. McKune, of the School of Electrical Engineering, who suggested the topic for this study, and to Mr. S. P. Lenoir, of the Rich Electronic Computer Center, who gave much helpful advice during the work. Gratitude is also expressed to the World Student Fund, for making possible the stay at Georgia Tech during which this work was performed.

5 iii TABLE OP CONTENTS Page LIST OF ILLUSTRATIONS SUMMARY iv vi Chapter 1. INTRODUCTION... II. DESIGN CONSIDERATIONS OF THE COMPARATOR 2 III. THE READER, 8 IV. THE AMPLIFIERS 13 V. LOGIC OPERATIONS 17 Logic Operations Examples for Circuits Performing Logic Operations The Logic Circuitry in the Comparator VI. THE DRIVE CIRCUIT VII. THE POWER SUPPLY. 28 VIII. PERFORMANCE AND OPERATION OF THE COMPARATOR APPENDIX 32 Calculation of a Set of Characteristic Curves for a Transistor Amplifier in Common-Emitter Configuration with Current and Voltage Feedback BIBLIOGRAPHY 40

6 LIST OF ILLUSTRATIONS Fig. 1. Idealized Comparator with Photoelectric Reader 2. Inputs and Output of Logical Circuit under Ideal Conditions Page 3. Actual Form of the Signals Block Diagram of the Comparator 7 5. Comparison of Different Types of Photodetectors The Reader.. «12 7. Amplifier for One Level of One Tape Layout of an Amplifier-Board Photograph of an Amplifier-Board The pnp Transistor as Logic Element The Logic Circuitry of the Comparator Basic Drive Circuit Comparator Drive Circuit, Power Supply * Basic Regulator Circuits with pnp Transistors Comparator Regulator Circuit Transistor Amplifier Stage Amplifier Stage as Two Terminal-Pair Network Characteristics of a Common-Emitter Amplifier: Voltage-Gain vs. R (R, R as Parameters) 37 Y L Z 20. Characteristics of a Common-Emitter Amplifier: Input Impedance vs. R (R } R as Parameters) Y L Z

7 V Fig. Page 20. Characteristics of a Common-Emitter Amplifier: Output Impedance vs, R (R, R as Parameters).. 39 Y G Z

8 vi SUMMARY The Rich Electronic Computer Center at Georgia Tech had use for a device to test the equality of two seven-level punched paper tapes. The comparator developed in this work has been designed to meet this need. The comparator consists of the reader, the amplifiers, the logic circuitry and the tape drive. It is fully transistorised to make possible its small size, simple circuitry and long life. The reader: A photoelectric reader is used since the high tape speed (400 frames per second) excludes the use of a mechanical sensing system. The reader consists of a single light source and 16 photodiodes, one for each level of each tape including the feedholes. The germanium junction photodiode 1N77B has been chosen as photodetector because of its small size. The amplifiers: There is one amplifier for each photodiode. The amplifiers consist of two ac-coupled common-emitter amplification stages followed by a monostable multivibrator serving as a pulse-shaper and as an inverter. The amplification stages use fixed bias and a large amount of dc-feedback to insure stable operation.

9 vii The logic circuitry: The output signals of the amplifiers are fed into the logic circuitry where they are compared. An output signal appears if the input signals do not correspond to identical hole-patterns in the two tapes, Only transistors and resistors are used in the logic circuits, The tape drive: The tape is driven by a synchronous motor which is coupled through a magnetic clutch-brake combination to the tape drive sprockets. The drive circuit controls the motion of the tape by energizing either the clutch or the brake coil, An output signal of the logic circuitry (indicating inequality of the two tapes) causes the drive circuit to energize the brake. The tape is stopped and an error signal is produced, If the two tapes to be tested are identical, they will run through the comparator at a speed of 400 frames per second, If they are not identical, the tape will be stopped about five frames after the error has passed the reader.

10 CHAPTER I INTRODUCTION The UNIVAC 1101 computer uses as Input and as optional output seven-level punched paper tape. This tape has seven channels in which holes can be punched. The information on the tape is carried by the presence or absence of these holes. A series of smaller holes, called feedholes, are engaged by the tape drive sprocket to advance and prevent slippage of the tape. These small holes will always be present. For some special applications it Is convenient or even necessary to have a device to test the equality of two punched tapes. These tapes may contain programs, data or results and may be of considerable length. The comparator has been designed to meet this requirement. It tests the equality of two punched tapes by reading simultaneously the corresponding frames of the two tapes and comparing the signals of the corresponding levels. If an error is detected, the tape drive is stopped and an error signal is produced. (In this study, any Inequality in the hole patterns of the two corresponding frames Is designated as error.)

11 2 CHAPTER II DESIGN CONSIDERATIONS OF THE COMPARATOR It was desired to obtain a comparator that would be capable of satisfactory operation over a speed range of 200 to 400 frames a second and also that would be simple to operate. The high tape speed excludes the use of a mechanical reading system such as is used in the comparators which are available commercially, A photoelectric reader was used instead, The signals coming from the readers are amplified and fed to a logic circuit which gives an output if an error occurs. This signal stops the drive and gives an error indication. The block diagram is shown in Fig, 1. A comparator constructed according to the block diagram shown in Fig. 1 would operate under ideal conditions, that is, If the signals from both tapes arrive at the logic circuit at exactly the same time and are of equal time duration (see Fig. 2). This cannot be expected in practice. Since the two tapes will not necessarily be produced by the same punch, there may be a small difference in the distance between consecutive frames. This results in a shift in time of the signals from one tape compared to the signals from the other tape as shown in Fig. 3«

12 3 DRIVE CIRCUIT R A = READER A R B = READER B Fig. 1. Idealized Comparator with Photoelectric Reader,

13 4 EHJ run i rn ri LEVEL IA LEVEL-IB m i~i nirn m EZL LEVEL 7A LEVEL 7B E OUTPUT Firjo 2 Q Inputs and Output of Logical Circuit under Ideal Conditions.

14 ' * - 5 y # * ^ i i - LEVEL IA LEVEL 1B? L L LEVEL 7A LEVEL 7B n j n r j n 1_ n OUTPUT OF p LOGIC CKT 1 L FEEDHOLES A n - FEEDHOLES B n n ERROR - f" SIGNAL kfigo 3 Actual Form of the Signals. ' -

15 6 Fig. 3 shows that an output of the logic circuit is possible although no error has occurred. To overcome this difficulty, the output of the logic circuit is examined only at times when both feedhole pulses are present. To accomplish this, a coincidence circuit which gives an output only when all three input signals (error signal and both feedhole pulses) are present is added to the output of the logic circuit. Fig. 4 shows the block diagram of the comparator modified to incorporate this feedhole coincidence circuit. The design of the different components is discussed in the following chapters.

16 FEEDHOLE - PULSES FROM I SIGNALS FROM THE 7 LEVELS OF "A" V DRIVE CIRCUIT I SIGNALS FROM THE 7 LEVELS OF "B' IFEEDHOLE.-PULSES FROM "B" ERROR - SIGNAL * 1 COINCID. CIRCUIT T 4 I I I J Pig. 4. Block Diagram of the Comparator,

17 8 CHAPTER III THE READER The first step In designing the reader was the selection of a suitable photodetector. Immediately available was the vacuum photodiode 1P42, which is the type used in the photoelectric reader of the UNIVAC It was considered for use in the comparator; however, it has the following disadvantages for this application: a) Its normal operating voltage Is volts and thus would require special dc voltages which would not otherwise be available in the comparator. b) Its Internal impedance is too high to allow coupling to a normal transistor amplifier except through a transformer. The use of transformers is undesirable because of their size. c) Its physical dimensions exceed the desired limits. Two other types of photodetectors were tested: The phototransistor 800 (by Texas Instrument Co.) and the germanium photodiode 1N77B (by Sylvania). Both gave excellent results with the same amplifier circuit. The decision to use the 1N77B rather than the 800 transistor was based on the smaller size of the former, rather than because of any difference in performance.

18 9 The 1N77B has the advantage that its diameter is less than 0.1 inch, the distance between the levels of a punched paper tape. It is thus possible to mount 8 diodes side by side directly underneath the tape without the use of bent plexiglass rods to guide the light as would be required with larger photodetectors. This simplifies the mechanical design and reduces the space requirements for the reader. Although the amplifier was designed for the 800 transistor j satisfactory operation resulted when the 1N77B was substituted. This was not anticipated since the sensitivity of a grown junction phototransistor is normally much higher than that of a junction photodiode (see Fig. 5)* Th e reduction in sensitivity was apparently compensated by the high efficiency of the lens which was possible with smaller units. The following considerations had a decisive influence on the design of the reader: a) The operator should be able to check and mark the tape in any of the ten frames following the reader. b) The light source should be on top to avoid the necessity of a cooling fan inside the housing. c) It should be virtually impossible for dust particles to obstruct the light path between source and diodes. d) The light system should illuminate the diodes equally. A parabolic reflector is used to obtain parallel light. The reflector consists of an aluminum layer deposited in vacuum on a piece of plexiglass which is cut and polished

19 Photodetector Darkcurrent Sensitive area of typical unit Sensitivity Net response to flux of 0.1 lumen/in 2 JIB. m 2 a/lumen ;ua 929 vacuum photodiode , iua/ lumen A photomultiplier ,000 1P22 photomultiplier ,600 Photodiode (point contact) 1~3 ma (0.0009) Photodiode (junction) 1-10 (0.0009) Phototransistor (npn grown jet.) (0.0009) Phototransistor (pnp fused jet. ) Fig. 5. Comparison of Sensitivity and Response of Various Photodetectors to Incandescent Light. (From: Hunter, L., Handbook of Semiconductor Electronics, New York, McGraw-Hill, 1956, p. lb-19.j"

20 to form a parabola. At the focal point there is a hole for the light source. Commercially available incandescent lamps with a diameter of less than one inch can be used. The reader is shown in Fig. 6.

21 PLEXIGLASS PARABOLIC REFLECTOR osb.glass TAPE J DIODES NOT ALL DIODES ARE SHOWN Fig. 6. The Reader. ro

22 13 CHAPTER IV THE AMPLIFIERS Fig. 7 shows the circuit of one of the sixteen identical amplifiers. It consists of a two-stage common-emitter amplifier followed by a monostable multivibrator serving as a pulse-shaping network and as an inverter. Outputs are taken from the collectors of both multivibrator transistors, making both positive- and negative-going pulses available. Both types of pulses are needed in the logic circuit. Only the positive-going pulses are needed from the amplifier which produces the feedhole pulses. The two amplifier stages use fixed bias and a large amount of dc-feedback. This makes possible the use of any of a wide variety of low-power transistors without seriously affecting the performance of the circuit. Care was taken to obtain a high input impedance and low current drain. In the design of the amplifier, the curves given in the appendix have been used. The amplifiers were constructed breadboard-style, each board holding the two amplifiers for the corresponding levels of the two tapes and the first part of the logic circuit. Fig. 8 shows the layout of the circuit on the board and Fig. 9 a photograph of one of the eight Identical boards.

23 e -10 V A "-$v lo/uf IN77B ALL TRANSISTORS 2NI07 Fig. 7 0 Amplifier for One Level of One Tape.

24 15 ] INPUT I + IO>uF - IOO Kn is Kn ] -10 V 8.2 KH. 8.2 KQ 47 Kn -IOyuF + 47 Kn -I0/UF + io Kn 47 Kn 47 Kn 6.8 Kn OUTPUT LEVEL OUTPUT FEED 6.8 Kn 47 Kn 47 Kn io Kn -IO/JF + 47 Kn - IO^JF + 47 Kn 8.2 Kn 8.2 Kn GROUND GROUND -10 V ] INPUT 2 Figo 8. Layout of an Amplifier-3oard.

25 Fig. 9. Photograph of an Amplifier-Board.

26 17 CHAPTER V THE LOGIC CIRCUIT Logic operations.--boolean algebra deals with a set of variables which can assume only two different values. These are designated by 1 and 0, true and false, on and off, positive and negative, etc. In this set three operations are defined: a) ("") = not. This changes the value of a variable to the other state, e.g. from 1 to 0 or vice versa. b), = and. This operation is defined by the following truth-table: A. B = C (1) i l l c) V = or. This operation is defined by the following truth-table: A V B = C (2) : i For the description of the logic circuit used in the comparator, it is convenient to define an additional operation + by the truth-table: A + B - C (3)

27 18 This additional operation, called exclusive or, can be expressed as a combination of the three basic operations as is shown below: A + B = A.BvI.B = (AvB).(AvB) (4) The + operation is exemplified by a circuit giving an output signal when one of the two inputs is present and no output signal when both or none of them is present. This is the type of circuit needed for comparing the corresponding levels of the two tapes, where an output signal is desired only if the two tapes are not identical, Examples for circuits performing logic operations.--in logic circuits, the two different states of the variables are usually represented by two voltage levels. For the comparator, the following choice has been made: 0 corresponds to ground 1 corresponds to -10 volts Circuits for the realization of the three basic operations may be constructed using relays, diodes, vacuum tubes, magnetic cores or other devices. Size and speed-of-operation considerations eliminated the use of relays. Size and power requirements eliminated the use of vacuum tubes. The need for a clock generator made the use of magnetic cores unfeasible. Diodes have the disadvantage that when the diodes are conducting their input impedance is low and when the diodes

28 19 are cut off, their output Impedance is high. This creates difficulties if several logic stages are placed in cascade. Therefore, logic stages with transistors have been used in the comparator. Transistors very closely resemble ideal switches. The residual collector voltage of a low-power pnp transistor which is driven into saturation is approximately volts. This is sufficiently low to cut off a following stage completely. It is thus possible to put any number of transistor logic stages in cascade without deterioration of signal levels. Fig. 10 shows a transistor logic stage. By a proper choice of the input signals A and B it can be made to perform various logical operations. It basically performs the operation and simultaneously with not: A.B = C (5) However, if B has the value of one, it performs the not operation A.l = C = A (6) Further, by taking the dual of (5) AvB- C (7) Equation (7) shows that the circuit can also perform the operation or simultaneously with not. The process of dualizatlon requires the change of the polarity of the input

29 20 o C B wwwv J A.B = C Pig. 10: The pnp Transistor aa Logic Element

30 21 signals, hence the input polarities must be reversed in order for the circuit to accomplish this operation. Thus the circuit of Fig. 10 can perform any of the three operations. And since any logical expression can be put into a form which utilizes only these three operations, any logical function can be realized using exclusively this circuit. The logic circuitry in the comparator.--the logic circuitry compares the signals from the corresponding levels of the two tapes. It must produce an output signal if, and only if, the signals from the two tapes are not identical at the time when both feedhole pulses are present. This operation can be put into the following mathematical form: where E = [(A +B )v(a +B )v... v(a +B )].A.B (8) L l l 2 2 / % 7 7 J f f = (ABvABvABvABv... vab ). A.B f f E = error signal A = signal from i-th level of tape A i B = signal from J-th level of tape B J A = feedhole pulse from tape A f B = feedhole pulse from tape B f Letting S = A.B and S = A.B i 1 i i j 2 J J T = (S V S v S v... vs )

31 22 we can rewrite (8) as E = (S vs VS vs V...VS ).A.B = T m A,B f f The operations to be performed yield S 9 T, and E. ij They are easily performed by transistor stages. Fig. 11 shows the diagram of the logic circuitry of the comparator. In order to avoid an excessive number of terminals on the amplifier boards, the first logic stages are mounted on the boards of the amplifiers to which they are connected. This reduces the number of necessary output terminals from four to one. The remaining two stages (the or and the feedhole coincidence and circuit) are mounted on the same board as the drive circuit.

32 23 A, o-vwwv -to v COLLECTOR RESISTORS = 4.7 Kfl COUPLING RESISTORS = 47 KA Bi On/wWV 1 -=fc A o-wvwv B o^ww ' J- Bp o-wvw ON AMPLIFIER BOARDS ON DRIVE CIRCUIT BOARD Fig 0 11o The Logic Circuitry of the Comparator

33 24 CHAPTER VI THE DRIVE CIRCUIT The tape drive sprockets are connected to the drive motor through a magnetic clutch-brake combination. The drive motor runs continuously, and the movement of the tape is controlled by energizing either the clutch or the brake. Fig. 12 shows the circuit diagram of the basic drive circuit. It consists of a bistable multivibrator (T and T ) which controls the power transistors T and T. These act as 3 4 switches in the brake and clutch circuit respectively. If no error has occurred, transistor T is cut off; T is therefore 1 3 saturated and the clutch is energized. If an error occurs, the multivibrator changes to its alternate stable state, cutting T off and thereby driving T into saturation. The brake is energized and the tape is stopped. The diodes connected across the clutch and the brake provide overvoltage protection for the power transistors. Pig. 13 shows the drive circuit including all controls necessary for the operation of the comparator. The circuit has three possible states: 1) Run. The START-button has been depressed, the clutch is energized, no error has occurred. T and T are cut off; T and T saturated. The start-stop relay is energized. The error light is extinguished.

34 250 a VWWV CLUTCH n \ RESET -10 V BRAKE - 30 V o Kl 1.2 KH 3.3 KH ^1 WWW 1.2 KO. WWW If o INPUT WWW 22 KQ. (ERROR SIGNAL E) 0_ Eigo 12. Basic Drive. Circuit *

35 IOO a f, 6^F I /WWV if CLUTCH BRAKE ERROR-. SIGNAL 22 KA -y/s/ww "START" "STOP-RESET" I, T T,,T 2 = 2NI07 T 3,T + = 2N235A 115 V AC L.J RELAY 1,2 AND 3 ARE CONTACTS OF THE RELAY, Fig Comparator Drive Circuit

36 27 2) Error. An error has been detected in the tapes. The multivibrator has changed to its alternate stable state: T 1 and T are saturated: T and T cut off. The relay and the brake are energized. The error light is energized. 3) Stop. The STOP-RESET switch has been actuated. The startstop relay is open. This resets the multivibrator to the run state and extinguishes the error light. The brake is energized by a reduced current, which reduces the braking action to a point where it is possible to adjust the tapes by turning the drive shaft manually. This state will also exist when the line switch has been switched from off to on.

37 28 CHAPTER VII POWER SUPPLY The following voltages are needed in the comparator: a) 10 v dc at approximately 150 ma for the eight amplifier boards. b) 10 v dc at approximately 50 ma for the drive circuit and as reference voltage for the 30 v regulator. c) 30 v dc for the clutch and the brake. d) 115 v ac for drive motor } reader lamp and relay. Fig. 1^ shows the diagram of the 115 v ac circuit, Two ERA TR-10 transistor power supplies are used to supply the two 10 v circuits. A regulator was needed in the 30 v circuit since the current varies between '0-150 ma and the voltage must remain within the limits volts. A higher voltage would be dangerous for the power transistors 3 and a lower voltage would increase the response time of the brake. Fig. 15 shows the two possible basic systems of voltage regulation with pnp transistors. The circuit (b) was chosen, since a reference voltage with the positive terminal grounded is available from the 10 v supply. Fig. 16 shows the complete voltage regulator circuit which is constructed on the drive circuit board,

38 29 1/4 A o-lov TO AMPUFIERS o -10 V TO DRIVE CKT. 115 V AC o -30 V TO DRIVE CKT READER LAMP 1 RELAY DRIVE MOTOR Flgo l4 Q Power Supply \

39 o- IN 1 f REFERENCE + <? =o o- OUT IN \ g REFERENCE 4-9 OUT + o 4-0- * + A) SHUNT REGULATOR B) SERIES REGULATOR Fig. 15. Basic Regulator Circuits with pnp Transistors o- 2 N 235 A -o IN +» ra KH "-vww\r u 2NI07 ±JL 2NI07 REFERENCE J II A OUT o + I, Figo I60 Comparator Regulator Circuit.

40 31 CHAPTER VIII PERFORMANCE AND OPERATION OF THE COMPARATOR Preliminary tests of the comparator were successful. Its performance is as follows: When the START-button is pushed, the first frame that Is compared is the frame immediately preceding the reader. If an error is detected, the tape is stopped. The erroneous frame is one of the first five frames following the one in the reader. The five-frame limit is attained if the tape is moving at maximum speed when the error is detected. If an error is detected soon after starting the tape, the tape will stop in less than five frames. The following simple operating procedure makes it possible for untrained personnel to make effective use of the comparator: 1) Insert tape In reader and engage the drive sprocket in the feedholes. The first frames of both tapes must be at equal distance from the reader. 2) Push START-button. 3a) If the tapes have run through without being stopped, they are Identical. Stop comparator. 3b) If the tapes are stopped and the error light is on: Mark the erroneous frame. Depress STOP-RESET-button. Manually turn the drive shaft back until the erroneous frame Is again in the reader. Continue as under 2).

41 32 APPENDIX Calculation of a set of characteristic curves for a transis tor amplifier in common-emitter configuration with current and voltage feedback.--from typical values for the transistor parameters, expressions were calculated relating the voltage gain, input impedance and output impedance and R, G, R and R (Figs. 17 and 18). L Y Z The parameters used to characterize the transistor were the familiar h-parameters defined by V = h I + h V (10) i ill 12 2 I = h I + h V with the positive direction of currents and voltages as shown in Fig. 18. used: The following numerical values of the parameters were h = ohms h " h = 50 h 25.10~ 6 mhos If in a common-emitter transistor stage current feedback is introduced by the insertion of a resistance R in the Z emitter circuit, the h' -parameters of the stage including feedback are given by

42 Flgo" 17. Transistor Amplifier St,age r * v,j z, fc> RQI I i 1 o.i «-z 2 jv 2 R L Fig. l8 0 Amplifier Stage as Two Terminal-Pair Network

43 3* (1 + h )R 21 7 h' = h + - (11) h R 22 Z h + h R <7 h' = ^ (12) h R 22 Z h - h R i rf - (13) 1 + h R 22 Z h h' = (14) h R 22 Z where the h are the parameters of the transistor. ij If in addition voltage feedback is introduced by the insertion of a resistor R between collector and base, the Y parameters h" of the transistor stage are given by ij h' R h ii + R Y h' (1 - h # ) i;l 12, h" = h* + (16) 12 12, h ii + R y

44 35 It h' R - h' 2 1 V 11 h" = -1 (17) 21 h f n + R y (1 + h' )(1 + h' ) h" = h' + (18) h + R 11 Y If it is assumed that h R «1 (i.e. R «40 kxl ), 22 z z» h' (i.e. R» 2 kil ) and 1» h (which is true for a Y 11 Y ^ ^ commom-emitter stage), then (15) through (18) reduce to: h" = h' = h + (1 + h )R (19) h" = h* = h (20) , i h' h + (1 + h )R 1X l h" = h + = h + h R + - (21) v R * R Y Y 1 + h' 1 + h» 21 h' = h + = h + (22) R R The voltage gain, Y input impedance Y and output admittance expressed in terms of these parameters are: 21 IV I h" 2 21 VI h Y + h h - h h 1 11 T (23)

45 36 V h" h" = = h (24) l li ff i h + y 1 22 L 1 I h" h" = = h 22 (25) Z V h" + R 2 11 Q These relations were evaluated for different values of R, R, R and R (Y = 1/R ). The results are plotted Y Z G L L L In Figs, 19, 20 and 21.

46 v 2 u R L a 10 Kfl R L = 5 K0. R L = 2 Kn R L = I KA 2MQ "I I I I 1 1 T I MO 500 KO 200 KG Eig Characteristics of a Common-Emitter Amplifier: Voltage Gain vs. R (R and R as Parameters) 0 x JJ Zi

47 38 2 M A I ' i ' ' I 1 IMA 500 KO 200 KH I i I i i loo Ka so Ka 20 KO T R Y %Pig. 20o Characteristics of a Common-Emittor Amplifier: Input Impedance vs 0 R (R and R ao Parameters). y L z

48 39 KQ Kn KA r> «' r 100 KA 50 K A 20 KQ Big. 21. Characteristics of a Common-Emitter Amplifier: Output Impedance vs. R (R and R as Parameter). X (J* J

49 40 BIBLIOGRAPHY Literature cited: Hunter, L., Handbook of Semiconductor Electronics, New York: McGraw-Hill, 195b, P. lb-19. Other references: 1. Bevitt, W.D., Transistor Handbook, New York: Prentice- Hall, Keister, W., Ritchie, A. and Washburn, S., The Design of Switching Circuits, Princeton: D. Van Nostrand, Lo, Endres et al_., Transistor Electronics, New York: Prentice-HaTT, Millman, J. and Taub, H., Pulse and Digital Circuits, New York: McGraw-Hill, 195^7"