Contains reports on six research projects

Boisvert, M.

Craig, J. W., Jr.

Hurtig, C. R.

Kosowsky, D. I.

Miller, C. R.

Morrow, W. E., Jr.

Pinson, J. C.

Schwartz, S.

Strieby, M.

Vorndran, J. W.

Contains reports on seven research projects.Lincoln Laboratory (Contract AF19(122)-458

Blom, S. R.

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X. TRANSISTORSProf. R. B. Adler J. W. Craig, Jr. J. C. PinsonS. R. Blom C. R. Hurtig S. SchwartzM. Boisvert W. E. Morrow, Jr. J. W. VorndranA. I-F AMPLIFIER DESIGN STUDIESA Butterworth characteristic of order three was realized in a three-stage amplifier,with an over-all Q of 20 and a center frequency of 200 kc/sec, using the design methodoutlined in the Quarterly Progress Report, October 15, 1952. A power gain of 36 dbwas obtained from point-contact transistors. Variations of the collector bias on allthree transistor stages did not affect the frequency response to a noticeable degree,although the power gain decreased to 17 db.In connection with the receiver study previously reported (see also sec. D of thisreport), the same design procedure was next applied to a more elaborate i-f ampli-fier, with the following prescribed characteristics:a. Center frequency: 455 kc/secb. Three bandwidths as follows:2 kc/sec between 6-db points; 10 kc/sec between 70-db points4 kc/sec between 6-db points; 14 kc/sec between 70-db points8 kc/sec between 6-db points; 26 kc/sec between 70-db pointsc. Power gain: 60 db (using point-contact transistors)d. Maximum Q of the coils: 150.As is evident from Fig. X-1, the design uses multiple-order poles, staggered in sucha way as to give a flat-top frequency response. The amount of staggering is varied bythe capacitors to give the three required bands. Seven stages are used, and the valuesgiven for one stage in the figure are typical. The interstage transformers are all physi-cally realizable and all alike. The amplifier has not been built; the design was carriedout for comparison with that employed in connection with electromechanical filters(see sec. D).As a convenient means of studying the interaction present (in the grounded-baseconnection) when complementary impedances are not used to isolate tuned stages,the iterative method of analysis has been applied to the i-f amplifier problem. Usinga derivation and notation similar to that of E. A. Guillemin (Communication Net-works, Vol. 2, John Wiley, New York, 1935, pp. 163-65), we obtain for the kth unitin a cascade of identical stages of active devices (each with parameters zll, z12'z 2 1 , z 2 2 ):An asterisk denotes work that has been undertaken in cooperation with members ofLincoln Laboratory under Contract AF19(122)-458. This report is therefore dupli-cated in the Lincoln Laboratory Quarterly Progress Report.-75-42 \6 CASCADED STAGES IN 2 GROUPS OF3 IDENTICAL STAGESC: IN 1gfL: IN mhFig. X-lRepresentative stages for three-band i-f amplifier (power supply not shown).CNdaI(X. TRANSISTORS)Ek = (Al e-yk + A 2 ek) erkIk  (B 1 eYK + B 2 eYk)erkScosh-1 Z Zll + zZ2 Z y e -r -z I z2 1/2 Z 0 1 = 1 - z22r 1 log e z22 Z 0 2 = z 2 2 -z 2 1 eAs an example, we may consider a shunt-tuned circuit in the collector of a resistivetransistor with an ideal transformer of turns ratio (r 2 /r 1 1 )l/.Letting1 r221 jxck + Lxandz12 z21T -z 11 z22we findSoh- 1 2 + jx(1-T)y = cosh 1/2r11 1/2 -y01 1 + jxrl 1  1/2 y02 1 + jxSome work is now under way for wide-band i-f amplifiers using series-tuned circuitsas interstage networks. It seems, from an iterative analysis similar to that exempli-fied above, that they may be especially suitable for wide-band applications.M. BoisvertB. BROAD-BAND I-F AMPLIFIERSTwo additional studies pertinent to i-f amplifier design have been expanded sincethe Quarterly Progress Report, October 15, 1952: (a) experimental verification of theamount of attenuation necessary to isolate cascaded tuned stages; (b) theoretical studyof the over-all power-gain bandwidth product for different methods of cascading in amultistage i-f amplifier.In connection with the first study (a), four separate pairs of transistors were coupled-77-Table IGain-Bandwidth ComparisonMatched Flat-Staggered Doubles Compared to SynchronousStages Mismatched to Give Same Over-all Bandwidth.Doubles Mismatched Synchronous11B) BBm KGB )1.41 0.351.14 0.0711.01 0.0160.93 0.0036G 1/nBm m (_ B ~ GBm kGMB m0.707 2.2 0.810.57 2.610.505 2.880.465 3. 110. 2390.0640. 0154(m BM1.070. 770.640.56Comparison[ GB(n/2 doubles)GB(n mismatched synch.0. 66 (1.56)*0. 74 (1.84)*0. 79 (2. 04)*0. 835 (2. 19)Matched Flat-Staggered Triples Compared to SynchronousStages Mismatched to Give Same Over-all Bandwidth.TriplesB( (2.0 0.101.73 0.0043Mismatched Synchronous( GmBm)0.740.636B M3.9 0.254.9 0.0086( G mBm0.711ComparisonGB(n/3 triples)GB(n mismatched synch.0. 74 (1. 96)*0.89 (2.47)*Gain-bandwidth figures for pentodes are shown in parentheses.NumberofStagesi" nitMatchedSynchronousStages orPentodesm~~d1.000.640.510.440. 390. 350.320. 30NumberofStages"n"1MatchedSynchronousStages or*Pentodes1.000.640.510.440.390.350.320.30r I ~----~C---(X. TRANSISTORS)through variable attenuators, and the frequency response measured in each case as afunction of the amount of isolating attenuation. Apparently, 3 db of isolation is sufficientto prevent coupling between synchronously tuned stages, while 5 db is necessary toisolate stagger-tuned stages. Smaller amounts of attenuation sometimes produceundesired peaks in the response.The second study (b) has been made subject to the following assumptions: (a) Band-width is limited by the capacitance of the coupling transformers. (b) Transistor para-meters are real and independent of frequency. (c) Stages are isolated, but the lossdifferences associated with such isolation in various cases are neglected (see sec. A).(d) All transistors employed have been made short-circuit stable (by padding, if neces-sary). (e) The power gain is computed at band center.The results are shown in Table I, where G m and Bm refer respectively to powergain and bandwidth of a single stage under matched conditions, while G and B referto the over-all power gain and bandwidth for the number of stages considered. Becausepower gain and bandwidth in these circumstances cannot be traded (maintaining a fixedproduct), the following points must be noted in connection with Table I: (a) In columnscomparing doubles and triples to mismatched synchronous stages, the over-all band-width of each type of connection has been made the same. (b) Comparisons of doublesand triples to matched synchronous stages have not been listed explicitly because ofthe bandwidth differences, but comparisons may be made by inspection if desired.Table I indicates that (when the number of stages is less than nine) synchronous cas-cading is always preferable. Thus, whenever the bandwidth of n matched synchronousstages is at least as large as that desired, the highest over-all power-gain bandwidthproduct is obtained by matched synchronous tuning. In the case of six synchronousstages, for example, the over-all power-gain bandwidth product is 22 times larger thanthat for three doubles, and 81 times larger than that for two triples. Similarly, ifbandwidths wider than those obtainable from matched synchronous cascades are needed,mismatched synchronous tuning is better than stagger tuning.J. W. VorndranC. PHASE MODULATORThe 164 kc/sec crystal-controlled oscillator has been redesigned to operate froma 22. 5-volt supply. As before, transistors having a current gain greater than 2. 3 and acollector resistance higher than 15, 000 ohms function satisfactorily in the circuit. Theefficiency of operation is approximately 23 percent. The amplifiers in the phase mod-ulator have been redesigned to ensure stable operation for all Western Electric 1698transistors that satisfy their tentative specifications. A padding resistor is placed inseries with the emitter lead to accomplish this result. Of course, the gain of the-79-(X. TRANSISTORS)amplifier varies with different transistors, but it is maintained above an acceptableminimum if the transistors remain within the specifications.The dynamic range of this phase modulator, as well as that of other diode modulatorswhich have been studied, is still limited by the temperature stability of the diodes em-ployed. A large variety of point-contact germanium diodes, p-n diodes, and seleniumdiodes has been tested, but in no case is the dynamic range satisfactory unless the tem-perature is held within + 10 C or less.J. C. Pinson, C. R. HurtigD. RECEIVER STUDYThe design of transistor circuits for the developmental Signal Corps receiver hasbeen continued. A Collins Radio Company electromechanical filter having a 3-kc/secbandwidth between 6-db points has proved quite satisfactory for the i-f selectivity. Ifthese filters become available in 2-kc/sec and 4-kc/sec bandwidths, it is probable thatthe remaining 8-kc/sec bandwidth can be obtained from the interstage networks of therest of the i-f amplifier. This conclusion is supported in part by the design studyoutlined in section A, although that study was made for point-contact transistors whichcreate some power-supply problems in this particular mobile receiver application.Principally because of the aforementioned power-supply problems, junction tran-sistors have been investigated for the i-f stages of the receiver. At 455 kc/sec, a p-n-pjunction stage in the grounded-base connection has a power gain of 18 db. To achievethis gain, some conjugate-matching must be employed. Such a stage consumes about15 mw of supply power, and has a bandwidth between 3-db points of 20 kc/sec. It shouldbe possible to reduce this bandwidth to approximately 10 kc/sec by employing speciali-f coils, ordered from the F. W. Sickles Company. These coils should have a Q of200 at 455 kc/sec. While two electromechanical filters, combined with a junction-transistor i-f strip, offer promise of providing both the gain and the three bandwidthsrequired for this receiver, it should be kept in mind that filters with the correctresponses for the 2-kc/sec and 4-kc/sec bands are not yet available. Moreover, theinsertion loss of the present 3-kc/sec filter is 26 db at band center. Even if this losswere reduced to 10 or 15 db, as suggested by the Collins Radio Company, it implies atleast one extra i-f stage. For these reasons, the possibility of using crystal filters isbeing surveyed. It is almost certain that quartz crystals would be unsatisfactory forthese large bandwidths, but EDT, DKT, and ADP crystals offer greater electrical pos-sibilities (correct bandwidth and insertion loss of about 5 db or less). Unfortunately,the mechanical, thermal, and hygroscopic properties of these crystals will probablymake them unsuitable for this particular application, but in the general matter of tran-sistor circuit applications 'they cannot be overlooked.-80-(X. TRANSISTORS)A conventional detector employing a 1N34 crystal diode has been built to drive asingle p-n-p junction-transistor audio amplifier. The audio amplifier had a power gainof 26 db, delivered 16 mw, and operated at an efficiency of 20 percent (including trans-former loss). Since the audio-power stage of the receiver is required to deliver 200 mwinto a speaker load, it now appears that it will probably be necessary to employ specialp-n-p junction power-transistors. These may be available in the near future.W. E. Morrow, Jr., S. Schwartz, J. W. Craig, Jr.E. FREQUENCY MULTIPLIERSFurther study has been given to the problem of frequency multiplication, using adiode full-wave rectifier to produce the harmonics and a succeeding transistor as am-plifier. To conserve components in the long run, a biased-diode quadrupler (instead ofa doubler) was built and tested. An over-all loss of 12 db was sustained between theinput to the diode circuit and the output of the single-transistor amplifier stage. Thisloss is much greater than was expected. The excess appears to reside principally inthe diodes and the interstage transformer. It may be possible to reduce this loss bytransferring the diodes to the high-level side of the transformer.Since the auxiliary losses due to transformers and diodes are of the same order ofmagnitude as that which would be produced merely by generation of the fourth harmonicwith ideal elements, a high-ratio multiplier chain may operate most efficiently if eachstage multiplies by more than four to one.C. R. HurtigF. STUDY OF P-N-P TRANSISTORSAn investigation has been undertaken of the effects of space-charge widening uponthe small-signal characteristics of p-n-p junction transistors of the alloy type. Thephenomena in question were first reported for grown n-p-n transistors by J. M. Early(Proc. I.R.E. 40, 1401-1406, 1952), but no published work on p-n-p alloy units isavailable.Preliminary data indicate the presence of the effects to a major extent. Furtherwork will cover: (a) quantitative evaluation of the effects in the form of Early's modi-fied equivalent circuit; (b) significance of the modified equivalent circuit in connectionwith the design of lowpass and bandpass amplifiers.S. R. BlomG. LOW-FREQUENCY OSCILLATORThe 2000-cps oscillator has been redesigned using two p-n-p junction transistors.-81-(X. TRANSISTORS)Grounded-collector and grounded-emitter stages are used. One coil has been elimi-nated by combining it with a transformer in the frequency-determining network. Thepower drain is now reduced to 180 mw, the output signal power increased to 27 mw, andthe over-all efficiency is 15 percent. A study is currently being made of the temperaturestability of the oscillator frequency. As far as the tuned circuit alone is concerned, theinductance is the major problem; a toroid inductor varies approximately 200 ppm perdegree centigrade. This cannot be balanced by a capacitor with negative temperaturecoefficient, because the temperature coefficient of the inductance is not sufficientlyconstant. The effect of temperature on the rest of the oscillator components remainsto be determined.C. R. Hurtig-82-

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Transistors

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