LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 510.84 I£6r no. 188-199 cop.3L Digitized by the Internet Archive in 2013 http://archive.org/details/applicationofint193afus Kfc-bTJKT 1NU . ±y j AN APPLICATION OF INTERCOUPLED-TRANSMISSION -LINE-AMPLIFIER by Chushin Afuso November 1, 19^5 'MtiiSliYiinUWOis AUG ly ltjoo LIBRARY REPORT NO. 193 AN APPLICATION OF INTERCOUPLED- TRANSMISSION -LINE -AMPLIFIER by Chushin Afuso November 1, 19&5 Department of Computer Science University of Illinois Urbana, Illinois ACKNOWLEDGMENT The author is grateful to Professor W. J. Poppelbaum for his direction. SUMMARY An attempt has "been made to use an intercoupled transmission line with tunnel diodes as a pulse amplifier for driving, in particular, high-speed diode logic circuits. For this purpose hot-electron diodes were used. The voltage swing of the amplifier is limited "by the characteristics of tunnel diodes. It is not large enough to drive hot-electron diodes without bias. Hence it is necessary to bias the diodes properly. A satisfactory result was obtained for the case where overall voltage gain, including voltage attenuation due to internal resistance of hot-electron diodes, was less then unity. Further trials to obtain a higher voltage gain have been done. The results were not satisfactory, however. 1. INTERCOUPLED TRANSMISSION LINE AS A PULSE AMPLIFIER (see Fig. l) Figure 1. Intercoupled Transmission Line In order for an intercoupled transmission line to serve as a re- flectionless pulse amplifier,, the following conditions must be satisfied according to H„ Guckel* Gp = ~G„ G Q G 2 - (G Q - G m ) 1 G 2 - G Q wner* * Guckel, H„, "Properties of Intercoupled Transmission Lines Terminated by Negative Resistance Elements with Applications to Tunnel Diode Pulse Circuits." partment of Computer Science, University of Illinois, Urbana, Illinois. Report #iU: 3 (June, 1963)0 -1- Z : the characteristic impedance of each line without coupling, symmetry of the configuration being assumed. Z : the mutual impedance. Under these conditions the voltage transfer K, the m current transfer K. , G p , and G have the characteristics as functions of G n as shown in Fig. 2. Region I: |k|, |k.| < 1. Region II: K, K. > 1 is possible. Region III: Although |k|, |k. | > 1 is possible, it is not realizable because of instability. Region IV: |k|, |k. | > 1 is possible. G < and G < 0, i.e., two negative resistance terminations are required. Therefore only Regions II and IV have useful gain. As Ragion IV requires two negative resistors, only Region II has been considered. ■2- tf ■3- 2. CHARACTERISTICS OF HOT-ELECTRON DIODES Figure 3 shows the characteristics of hot-electron diodes. From the figures, the incremental resistances are about: 35 ohms at I = 2 ma for hpa 2006 30 ohms at I = 2 ma for hpa 2103 40 ohms at I = 2 ma for hpa 2105 To drive these diodes with the output of the amplifier which has as its output at most 200 mv, it is necessary to bias the diodes. The necessary bias voltages are about: k60 mv for hpa 2006 260 mv for hpa 2103 260 mv for hpa 2105 -ii +++ -+-H-H -H+ +++ II I/ I I I I ++++ -H-H- 3a 1 1 1 1 1 1 1 1 1 1 1 1 Mil 1 1 1 1 1 1 l/l 1 1 1 1 1 1 1 1 1 1 1 1 i i i i II 1 1 1 1 1 I 1 II 1 1 1 1 1 MIL J 1 l/l 1 1 1 1 1 1 1 1 Mil MM 3b -H- -H- -H- 4+ +4+ -M- 3c Figure 3 .c;_ 3. BIAS CIRCUIT FOR HOT-ELECTRON DIODES The circuit shown in Figure h has been found useful, T.D. NEGATIVE RESISTOR * SECONDARY LINE OF TRANSMISSION LIME b a ■o © I is the bias current source Figure h. Bias Circuit for Hot-Electron Diodes When two diodes are the same and the the two resistors are also the same, the bridge so formed is always balanced, i.e., regardless of the value of I there is no potential difference due to I between a and a' . Hence the connection of these terminals to the secondary of the transmission line ) and b 1 does not affect the bias of the tunnel diode circuit that is connected at the other end of the line. Only one diode and one resistor are used for the logic circuit. • pair is connected: (l) to realize a linear resistance as seen from a end a', and (2) to balance the bridge. Since the internal resistance of a hot-electron diode is not 1 comparison with the load resistance R , there is voltage Li on. -6- One might think that the load resistance can be increased so that the voltage drop due to the internal resistance of diode may be neglected. However this is not so. As the voltage swing is limited by the characteristic of the tunnel diode, increasing the load resistance automatically makes the current small, so that the incremental internal resistance of diode at the lower value of the current should be taken, As seen in Figure 3, the incremental resistance starts to increase at about I = 1 ma „ Thus increasing the load resistance does not improve the situation. ♦I Yr(i) T f 'OUT t r(i)+Ri Figure 5 o Attenuation Due to the Internal Resistance of the Diode Another way to reduce the voltage attenuation is to use several diodes in parallel However, this does not improve the situation either, unless the tunnel diodes, which realize negative resistance, have a high enough current capacity for the currents through each hot-electron diode to remain the same. When tunnel diodes with high current capacity are used a difficulty arises in obtaining stability „ This will be discussed later. Therefore, as long as commercially available hot-electron diodes are used with this amplifier, voltage attenuation is not negligible. -7- k. DESIGN PROCEDURE OF THE INTERRUPTED TRANSMISSION LINE AMPLIFIER According to Figure 2, in order to obtain specific values of K and K the values of G /G are restricted. There are two ways to attain proper values of G^/G Q : (a) given G (i.e., given negative resistance), adjust G Q , i.e., adjust the structure of the transmission line; (b) given G Q (i.e., given a transmission line), adjust G^, i.e., the negative resistance. In case (a), the geometrical size of the transmission line must be well controlled. This is impossible without special precision tools. Therefore a fixed transmission line is taken, i.e., case (b). The geometrical size is shown in Fig. 6. GROUND PLATE S3 t u" iz GROUND PLATE W = y|| inch, B = jl inch Material: Rexolite 2200, E =2.72 Figure 6. Geometrical Size of the Intercoupled Transmission Line For these values, G n = m 27.8 ohms 0.578 -8- Values of G , K, K. are shown in Fig, 2. As nonuniformity of the line width AW is determined Toy the construct- ing process, small values of W increase AW/W and hence are not desirable. To adjust the effective negative resistance R , a shunt passive re- sistance R Is connected as snown in Fig. 7- R-R M " " 3 Figure 7„ Adjusting Negative Resistance -9- 5. RESULTS OF THE EXPERIMENTS Tunnel Diodes: MX-108l (Micro State Electronics Corporation), GaAs diode I = 1 ma P -R = -130 ohms n C = 3 to 5 pf -R (negative resistance of the pair) = -110 ohms Hot-electron diodes: hpa-2105 R = oo (no shunt resistance), instead 2^+0 ft is connected to the load in shunt for matching. Figure 8 shows the circuits which are connected to the secondary line. / 1 * 1 1 1 ( 1 1 1 1 1 1 1 1 1 1 1 WiT 1 1 I l til 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 II I lilt ■ A- Mil tilt 111! till 1 1 1 1 1 1 1 1 1 1 II tilt \ \ r \h r^y~ / Figure 8. Secondary Line -10- The observed waveforms are shown in Fig. 9< Sv4 lion 240iii +*■ Upper traces Input (primary line) negative pulse, 100 rav/div Lower trace;. Output, negative pulse 50 mv/div Time.. 5 nsec/div Figure 9. Waveforms of Input and Output T h f total output voltage across the secondary line was about 150 mv„ rherefore the voltage transfer K is approximately 0,6, while the theoretical ae is about 75 by Fig,, 2. The operation is stable. The voltage transfer as tor- small for practical use. ■11- Tunnel diodes: RCA IN3128, Ge diode I = 5 ma P -R ~ -20 ohms n C ~ 13 pf -R' = -17 ohms n R = 68 ohms, single resistor without hot-electron diodes R = 22 ohms The result was satisfactory. The voltage transfer K ~ 1.0 was ob- served and this agrees with the theoretical value. To obtain useful voltage gain, R = 51 ohms, -h"J ohms, -i+3 ohms with appropriate values of R were tried. The results were unsatisfactory. These values are all supposed to be in Region II. •12- 6. SOME CONSIDERATIONS When the results are unsatisfactory there are two types of phenomenon on the secondary line of the amplifier: (a) oscillation, and (b) bistable mode, Although these have not been analyzed in detail, it would seem that they are caused by the failure to satisfy the stability conditions of the system. In the original thesis by H. Guckel there is no general examination of the stability, Instead he treats the stability only for the case where the source impedance Z = 0. Therefore it is not assured that one can obtain a satisfactory result in genera], even if the matching conditions for reflection- less transmission are satisfied. When the amplifier is used in a practically useful system, it is rather unusual to have Z^ = 0. Therefore the stability conditions must be examined for the general case, and design criteria must be established accordingly „ However, this is not intended here. It is reasonable to think that when ac stability is not satisfied there is an oscillation, and when dc stability '^stability at zero frequency) is not satisfied there is a bistable mode of operation. Difficulty with High Current^ Tunn el D iodes When high current is required, the tunnel diode must have a high current capacity, i.e v . a high peak current. Since uhe voltage swing of the negative resistance region is characterized by the material of the tunnel diode, as I increases R p n decreases „ The stability condition, for the tunnel diode circuit is L + L R > r + R > ~^-~ n s R C n 13- M-AV-iH Figure 10. Characteristics of Tunnel Diode Ls, Rs, C, and -Rn are equivalent circuit parameters and r and L form the external impedance connected to the tunnel diode as shown in Fig. 11. -Ik- L L, •>r EXTERNAL TUNNEL CIRCUIT DIODE Figure 11, Equivalent Circuit for the Tunnel Liode in the Negative Resistance Region If R n is sufficiently low that .j + 1 R < n tiler; th< stability condition is never satisfied, This situation is not unusual, -■. r example, for RCA .1113128 r = -17 ~ =23 ohms n ' J 1 ~ 0,6 nh C = k„5 pf ~ 13 pf tne manual . = 15 pf is specified. Six out of ten diodes have C ~ 5 pf.) max s r r ■15- L = 1 ~ 2 nh is easily obtained. Suppose L = 1 nh, R = -17 ohms, C = 5 pf, then L+ L s 1.6 IP -9 160 ~ _ . . ._ D B r = To = i 7 v s = !9 ohms > 17 = R R n C 17 X 5 X 10 12 1,T X 5 n The large junction capacitance C may be desirable from this point of view. However, the existence of capacitance violates the matching conditions of the amplifier. Therefore there is a practical limitation on it. -16- REFERENCE Guckel, H., "Properties of Inter coupled Transmission Lines Terminated by Negative Resistance Elements with Applications to Tunnel Diode Pulse Circuits." Department of Computer Science) University of Illinois, Urbana, Illinois. Report #1^3 (June, 1963) . =17- UllLXaOOll _L*~*-l Security Classification DOCUMENT CONTROL DATA • R&D (Security classification ol title, body of abstract and indexing annotation must be entered when the overall report i« classified} I 0<*IGINATIN G ACTIVITY (Corporate author) Department of Computer Science University of Illinois Urbana, Illinois 6l803 2a REPORT SECURITY C L ASSI F I C A T I ON Unclassified 2b CROUP 3 REPORT TITLE An Application of Intercoupled-Transmission-Line-Amplif ier 4 DESCRIPTIVE NOTES (Type ol report and inclusive dates) Technical Report 5 AUTHORfS; (Last name, first name, initial) Afuso, Chushin 6 REPO RT DATE November 1965 7a TOTAL NO OF PACES 22 7 b NO OF REFS 8a. CONTRACT OR GRANT NO. Nonr 1834(15) b PROJEC T NO. 9a. ORIGINATOR'S REPORT NUMBERfSj Report No. 193 9 6. OTHER REPORT HO(S) (A ny other numbers that may be assigned this report) 10 AVAILABILITY/LIMITATION NOTICES Send requests to Department of Computer Science, University of Illinois, Urbana, Illinois, 61803. Report No. 193 II SUPPLEMENTARY NOTES none 12 SPONSORING MILITARY ACTIVITY Office of Naval Research 219 South Dearborn Street Chicago, Illinois 6060^ 13 ABSTRACT An attempt has been made to use an intercoupled transmission line with ,unnel diodes as a pulse amplifier for driving, in particular, high-speed diode logic circuits. For this purpose hot-electron diodes were used. The voltage swing of the amplifier is limited by the characteristics of tunnel diodes. It is not large enough to drive hot-electron diodes without bias. Hence it is necessary to bias the diodes properly. A satisfactory result was obtained for the case where overall voltage gain, including voltage attenuation due to internal resistance of hot-electron diodes, was less than unity. Further trials to obtain a higher voltage gain have been done. The results were not satisfactory, however DD FORM . 1473 ■18- Unclassified Security Classification Security Classification KEY WORDS LINK A LINK 6 LINK C ROLE WT HOLE WT ROLE WT Intercoupled transmission lines INSTRUCTIONS ORIGINATING ACTIVITY: Enter the name and address the contractor, subcontractor, grantee, Department of De- nse activity or other organization (corporate author) issuing e report. i. REPORT SECURITY CLASSIFICATION: Enter the over- 1 security classification of the report. Indicate whether Restricted Data" is included. Marking is to be in accord- ice with appropriate security regulations. ). GROUP: Automatic downgrading is specified in DoD Di- ctive 5200. 10 and Armed Forces Industrial Manual. Enter e group number. 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