claim: 1. A resonant transfer circuit for a time division r@iultiplex system comprising at le@ast a pair of multiplex highways, first el,-ctrical energy storagq means coupled to one end of a first of said highways, secbnd cl@ectrical energy st(,rage means counled to oie end of a second of said highways, third electrical energy storage meatis for cou@ pling togelher the other ends of said pair of highways, means for providing a plurality of tin-ic slot signals, r-qeans responsive to a first time slot signal for resonantly transferring ner-ey in digital form from said first storage means oever said first highway to said third storage means, said energy being siored in said digital form in said twrd storage means, means responsive to another time slot signal for resonantly transferring said energy in said digital form from said third storage means over said second hi.-hway to said secorld storage means, and nieans effective during the interval betareen said first and other time slots and comprising a negative inipedance device for increasing the energy stored in said digital folin ori said third storage means@ 2. The circuit of claim I and gate means, said ne,@ative impedance device.havin, at least two terminals, one of said terminals bein., connec',Cd to ground and the other of said te@rminals b--ing connected to said third storage means via said gate means. 3. The circuit of claim I -and a plurality of -said first and secon d storage means, a plurality of first and second gate means individually assoc;aied with each of said first and second stora.-e means respectively, and means for seque-titially and indi @idually @coupling each of !said storage means to said highways selectively responsive to said time slot signals 4. The circi@.it of claim 3 and a plurality of said third @tora.-c means, a plurality of other gate means individually associated. with each of said third storage means, @and means for selectively connecting said ne.-ative impedance means to said third storage means via the other gate means individually associated with said third storage means. S. The circuit of claim 4 wherein said negative impedonc e device comprises two output terminals, said other

9 .-ate mcans being connected to one of said output terminals, and ground connected to the other of said output terminals. 6. The c-ircuit of claim 4 wherein said other gate ineans is normauy blocked, and means for unblockin- said other gate means dtiring each time slot separating said first and other time slots. 7. The circiiit of claim 6 atid means whereby other gate means is unblocked durin- guard time inlervals separatin- said time slols. S. The circuit of claim 7 wherein said means for providin.- said -time slot si-,nals operates at a system frequency, said means for unblockin.- said third gate operates at twice said system frequency, and means whereby the first tiine slot si-,nals for controlling the transfer of ener.-Y over said first hi.-hway is 180' @out of phase with respect to the other time slot signals for controuing the transfer of energy over said second highway. 9. The circuit of claim 3 and means for selectin@,Dne of said first gate means and 4one of said second gate means to complete a single voice channelfrom one of said first storage means over said first and second hi.-hways to one of said second storage means. 10. The circuit of claim 9 wherein said voice channel seler,ting means comprises an array of twO input coinci3,187,100 10 dence gates, means for activating one of said inputs when a time slot is available on said first highnvay, means for aetivatir@g the other of said inputs when a time slot is ' available on said second highwzy, there being a number of said coincidence gates s-ach that all of said coine-idence gates are associated with pairs of time slots separated by minirr@um time intervals. 10 References Cited by the Exanilner UNITED STATES PATENTS 2,927,967 3/60 Edson ---------------- 179-15 2 936 337 5/60 Lewis ---------------- 179-15 2:936:338 5/60 Jam,, et al - ------------ 179-15 15 2,962,551 11/60 Johannesen ------------ 179-15 2,962,552 11/60 Crowley ---------- ---- 179-15 3,061,681 10/62 Richards -------------- 179-15 FOREIGN PATENTS 20 215,909 11/57 Australia. 221,992 6/58 Australia. DAVID G. REDINBAUGH, Primary Exaniiner. 25 ROBERT H. ROSE, Examiner.

U-nited States Patent Office 3,@187,100 3,187,100 REi SONANT TRANSFER TIME, D'.v!7@-,9!ON MULTIPT-EX SYSTEI@ll UTILIZE'IG NEC-ATIVE M@IFEDANCE Ail@LPLIFICATION MEANS Hans Hehnut Adelaar, Antwerp, BelgiNam, assignor tG International Standard Eiect'ric Corr@orition, New York, N.Y., a coypoa-aiion of Delaware Filed Apr. 24,1961, Ser. No. 104,967 Claims prior.-t-.v, 4iplicntio-a NTeth-,rlands, July 21, 1960, 254,030 10 Cla@ms. (Cl. 179-15) The invent;on relates to an arinli'ler system for t;me divis;on multiplex resonant transfer circuits co@-iprising first, szcond and third electrical ener.-Y reo.,ctive storage davices able @o be selectively and repeatedly interconnect,-cl, the first with the th@ird via a fust gate during a first time slot corresDo-Tiding to a first time channel on a mL,Itiplex - hi.-hway, the second with the third via a second gate durin- a second time slot correspond;n,- to a second time cha-inel on a secopd multiplex hi.-hway or on said multiplex highway, amplify-ing means being provided to increase or restore the ener,-y stored on said third device durin- repeated tii-n-- intervals separating a pulse of said f,rst time slot from the next pulse in said second time SIGT. S,,ich an am,@lifier system is disclosed in a 1959 Belgian Patent 579,759. The subjeCL matter of this pat4@nt is also show@i in a co-pe,,ldin-. U.S. patent appl,'.catiG-@i entitled "Transient Rerealer," S.N. 812,640, filed by Hans 14. Adelaar ori May 12, 1959, now Pa'Lent No. 3,117,185. Reson,tnt tra-.isfer circuits are d,-scribed in a 1956 Belgian 'T'ateit 543,262. The slibiect ma.'ter o4 this pdtent is also found in a co-pending U.S. patent appl@ication entitled "Electric. Pvlse 1,,Ioden Circui,," S.N. 550,163 fil@-d by K. W. Cattermole on November 30, 1955, now @atent No. 3,020,34,9, and in a 1959 Bel@,- ian Patent 558,179, which is also co,,,ered in a co-p.-nding U.S. adplication entitled "Pulse i@iloden," S.N. 663,704, fi'@ed by K. W. Catt.-rmole in June, 1957, no@v Patent No. 3,.073,903. Briefiy, resor@ant transfer circuits usi,@ig electrical energy reactive storag@- devices permit a substantidily lossless traiismission of eneray between a source and a load, and this transfer may in fact be bidirectional. The principle of the operation of such resonant transfer circuits may b,-st be described as follows. The signal energy is temp,arari'ly stor,-d in reactive s@Lorage do-vices and by temporarily interconp-.ctin.@ two such storage devices during a well defined time interval corresponding to an interconnectiiig gate bein- rande@-ed corductive, the signal energies stored at the time the t@vo devices are inter,-onnected, may swing from one reactive storage device to t'L-le other and vice versa, whereby at th.- t@me the connection between the tivo devices is inter-rupted, the energies accumulated in the two devices have now been interehanged. This traisfer of ene--.-Y may b-- performed slibstal'ially without losses, and moreover it is bidirectional. This exchange of energy samples can be illust-reted by an irit--rc,han,-e (>f char.-es ivhen the stora.-e devices are each constituted by shunt conder@sers of equal capacity C which are each associated mith a series inducta-nce of value -f_, ,the ends of the condensers not conne-,ted to these inductances being -grounded. When the ends of the two inductances w-hich - are not directly connected to the condensers are momentarily interconnected through a gate, the arTang,-ment effectively constitutes a series tuned circuit. Assumin--- that there are no resistive losses, and that the voltages across the condensers arerespectively equal to V, and V2 at the time of the interconnertion, the instanI-'atented Jtire 1, 1965 2 -tancous voltages across the two:condensers will be respectively equal to the sum and to the difference of Vi-li- V2 5 @and VI - Cos wt 2 10 where w is the ratural resona:nce @frequency defined by lv2LC=I. -With,the initial volta-es respectively eqil-al -to V, and V2, after exactly a hali period of oscillation af,,ter whicl@i the connect:lon is interrupted, these voltages Nvill -.qow be respectively equal to V2 and VI. 15 The resonant @transfer principle has recently @found favor for tim-- division rr@ult@iplex electro-.iie switching systems principally in view of the limited losses vihoreas the sai--,pling process of prior pulse systems involved substanlial etier.-y losses. Nevertheless, some small losses 20 -inay yat be experienced in some tirie division multiplex sw,,'tching systems using the resor,.ant transfer prineiple, for insta-lice d,.i-- to the resistance inevitably associated with the in-ductances used in such resonant transfer circuits, dLe to the non-zero resistances of the electronic 25 gates, etc. Hence, the above sys@tem hvs the advan-tage of permitti.,lg amplifica@tion of tlie -energy samples on the multiplex highways. T-hus, @it is not necessary to use an audio amplifier per voice frequency torm@inal of 4an electronic swtching 30 exclang.--. The amplifiers cai b-@ associated with the rnultidlex hi.-hways in such a manner that they are concentrated a@nd the total number of amplifier-s is reduced Niell belolv the nuin'oer of @@ubscribers connected to the exchange. NeiTerth--Iess, the amplifiers envisaged in r-,IGS. 35 9 aild 10 of the above mention,-d Belgian Patent No. 579,759 suffer from the chief disadvantage of being unid.@rectional. T@.us, the number of time ehannels seized I ior a comniiinication is necessarily dotibled and one may rot benefit fro@n the b;directional properties of the reso40 nant transfer principle. A general objer,.t of the invention is to realize an improved amplifier syst,-@m for time divis;on multipl--x resonant transfer circuits which is bidirectional and yet does iiot suffer from severe limita-tions im-posed by stability re45 quirements. In accordance with a first characteristic of the invention, in a system as defined a@t the beginning of the descrir)tion, a third gate is provided iiiterconnecting said f-hird device with a negative resistarice at least during part of t-he time 50 intervals separating said first and second time slots. It is to be noted that in the same Belgian Patent No. 579,759 already ment@ioned above, other eribodiments envisaged already the use ol a negative resistance amplifier b,,it Nvithth.- latter perman,-ntly associa-ted to the multiplex 55 bighv7ay and involving the use of at least two negative resistances i'L an actual overall ampliiication was to be secured wi't-hout undesirable reflections. In this earlier syster@i however, the Pe.-ative resistances are effective @at all times in a eircuit including the multiplex hi,-hway, which 60 is generally embodied by a coaxial cable, as well as the term-'@natir-i.- source and load respectively connected to the, -niullipl,-x highway througi, @ates. In fact, there will usually be in a large exchange a plurality of highways co-@inected in cascade. The source a-.id load w!H also in65 volve low Dass fil-ters leading to the callin@g and called subscriber's l@@ne circuits respectively. The highways unavoidably i-ii,troduce additional cirr-uit elen-ents such as parasit@ic capacitances to ground. It is clear there@fore

3,187,100 that such 'circuits will in practice be prone to singing unless caref-ully designed@ On the other hand, as envisaged ,by the present inven@tion, the negative resistance is involved in a purely local circuit which does no,t include highways and the actual characteristics of which may be closely 5 controlled, this circuit being isolated ftom the highways by electronic.gates. . In accorda,nce with another characteristic of tne invention, an ami)lifier svstem as previously characterized is further characterized in that said ne-ative - resistance is 1( grounded. This is obviously an advantage in desi.-ning suitable negative resistance amplifiers which do not involve D.C. block-ing circuits such as transformers which introduce bandwidth problems. Ea the Belgian Patent No. 579,759 15 previously mentioned, some embodiments do in fact use nega resistances which may be grotln&d, but these are all of the type which necessitates predetermined inductive couplings and though these need not be tight couplings such as necessitated by transformers, it will also 20 be clear that the avoidance,of mutual inductance circuits is a course for simplffication of the circuit desi-n. The negative resistances of the invention may each be associated with their intermediate storage condenser through a corresponding gate, said condensers constitut25 ing said third reactive storage devices. But, in electronic switching systems of the type envisaged, the actual duration of the time slot provided for the repeated intercon. nections of the subscribers is chosen somewhat less than 30 the time channel, i.e. the duration of the sampling period which is usually of the order of 100 nicroseconds, di1 vided by tne nuinber of channels used on the highway. For instance, mith 25 @hannels and a channel time of 100 35 4 microseconds the actual irte@connecting time for each channel may be taken as 6nly 2 niicroseconds, leaving some 2 microsec40 onds guard time between the effective - interconnection times. This guard time will be beneficial with regard to diminishing er6ss talk between channels and it may be us--d to perforpi what are known as clamping operations which essentially r-onsist in discharging common hi@hway capacitances @between the effective channel interconnec- 45 tion time& The- system of the present invention of'ters the advantage that these guard time intervals between effeetiiie interconnection times may also be used to unblock the third gate establishiiig an operaltive circuit between the intermediate storage condenser and the negative resist50 ance. Thus, the @latter may well be provided in common for a number of intermediate storage condensers. With a suitable time constant, each @uard interval may be sufficient to permit a suitable amplification o'L the 55 @ignal- sa.mple temporaiily stored on the intermediate storage condenser, whereby already during the effective time channel immediately following that durin.- which a sample Nvas established on the intermediate storage condenser, ;i sample with amplified energy can already be sent out 60 from, that conden@er, which inay receive a new one in exchange to be amplified during the following guard time, &tc. Negat,lve resistances used in this mtiltiplex manner nevertheless suffer from possible crosstalk difficulties and 65 as they are used at frequencies corresponding to the chann(@l timo, duration, severe high frequency bandwidth requirements will usually be imposed. According to yet another characteristic of the invention, an amplifier system for time division multiplex reso70 nant transfer circuits includes a first and a second time division multiplex highways each respectively associated via gating means with a plurality of said first and second electrical energy reactive storage devices and via a plurality of said first and second gates to a plurality oj' said 75 4 third devices each associated via said third gates to acorrespor@ding negative resistance during repeatcd time intervals Avh-Leh cover several time chaniiels used on said highv,,ays. Thus, dlie to the negative resistances being, in accordance with the invention, used in conju-iietion with the intermediate storage principle, one may choose the two time channels used for passina an energy sample to and from the intermediate sorage condenser, in such a way that an amplifying ti-@ne is available which may be substantially larger than the channel timc or: the guard interval between adjacent eifective interconnectin.- times. In this irlanner, one r@lay considerably ease the frequency bandwidth requirements for the negative resistance amplifiers. The above and other obj'ects and characteristics of the invention and the best manner of attaining them as well as the inveption itself will be best understood from the following description of detailed embodiments to be read in conju-@iction with the accompanying dkamngs vihetl-in: FIG. I represents a general 6mbodiment of the negative resist ance amplifier system of the invention using interinediate storage of energy san-iples; FIG. 2 represents pulse wai7e forms useful to explain the operation of the system of FIG. 1 and FIG. 3 represe@its sel@.er@iatically a time channel selection system which iray be used in accordance with the invention. V Refe@ring to FIG. 1, the latter shows a highway H, @lich is interconnected to a highway H2 through a plurality of interniediate storage devices such as those represented. Esse-@itiafly, these intermediate storage devices each comprise a grounded condenser C. The free end of condenser C is connected to highway HI through a fi rst gale CT,, to hig@way H2 through a second gate G2 and finally to the ungrounded etid of the negative resistance -R through a third -,at-- G3. The other ends of the highways HI aiid 1-12 are connected to a plurality of voice frequency circuits (not shown) each tiriie through a gate such as Go in series with an inductance Lo and a low pass filter LP including the shunt condenser Co facing the indlctance Lo@ The multiplying arrow next to the gate Go indicates tllat the hi.-hway HI is co-linected to a plurality of such ireqliency voice circuits rientioned in-miediately above.. Tho mul'Liplying arrow marked by 2n on the other side of the highway HI indicates that the latter is mul'Liplied to a 'olurality of 2n intermediate storage circuits. detailed above, 2n being the number @of available time channels on th-@ highway HI; the connections are similar for the seco-.id highway H2- Normally, assu-r@iing the two highways HI and H2 would be sel--ctive-'Ly interconnect-Id at their inner ends, or permanently. associated with one another, upon the simultaneous unblocking of the gates Go and G'O, bidirectional exchange, of signal ener@ could take place between the con@y d--,nsers Co and C'O, and this on a resonant transfer basis due to the series inductances Lo and L' Witb the intermediate storage scheme shonvn in FIG. 1, it is honvever possible to perform the transfer of energy in two steps, between which the signals iray be amplified t-b any desirable extent, particularly as necessitated by the losses incukred in the nor-inal transfer due for instance to the resistive losses of the gates such as Go and of the inductances s-ach,as Lo. In FIG. 2 are shwnn various pulse wave forms and the first four wave forms indicated COTrespond to some of the time channel interconner-tin,@ pulses tll2ll- These are 2n in iiumber although only fotir wave forins are shown, and it will be seen from the fi,,ure tha@t the dtiration of the pulse is shown as only half the time channel whic-h is evidently determined by the samp] I ing period, corresponding to the repetition period of these pulses, divided by 2n, the nuinber of channels. T@hus thtre is a guard time, useful

8,187ilOO 5- froin the crosstalk viewpoint, betwe-.n adiacent Pulses such as t, and t2 which guard time is taken eoual to the aelual interconnectin.- time. During a first time cha:nnel, say tl, the @-ates Go and GI m,ill be simultaneously unblo--I?-ed w-it-h th@- result that ex- 5 chan,-e of si,-nal ener.-Y will tale place between the condensers Co and C ivhich may be of equal value while the inductance Lo is given a su-itab'le vilue to obtain an adeq,uate resonant transfer. Th;s inductance La is shown as an individual element pertaining to each voice frequency 10 @circuit, but of coiirse it ma3, be an element used in eGmmon for several voice frequenay circuits, since in principle it may b-- associated with the hi.-hv/ay. Actually, for symmetry reasons, the cor=oned ends of gales G, and G,_ might be connected to the junction of 15 condenser C with gat-, G3 throti,-h furtlier inductances xvhich nu,-ht have ,he same -value as the inductances L., L'o. The eitective series indtietanc,- for the resona5-@i tr,@nsfer would tlaus be twice the common value o@i' all tbefe inductances. 20 Dur-ing th-- i.,iterval of ti,,ne separating th-, end of the t, p,alse from the be.-i- inin.- of the t@, pulse, i.e. pulse t'l, gate G,3 will -Tiow be unbloGk-,d, witli the result that th-, cor@d-,nser C will nc,,,v be associaLe,,! -,vith the ne.-ative resis@,ance -R. During this time interval set)aratin,@ the 25 end of -the positive 1)ulse ti fton.-i the start of ,he positi-,ic pulse t2, the potential across cor@denser C will th,-refore be exponentially increased and by a proper choice of the -Tieg.-,Live ti@iie constant CR a suitable amo-Lnt of .-ain may be see,ared. Of course, this gain o-ay merely comDensa'Le 0 lasses, eien those incurred by intermediate stora,@e on condenser C dac to the latter b@-in.- shunted by paras-itic resistances le"@din.@ no.,-Mally 'lo some decay of the stored volta.-e. Duriiig pulse t2, it ;S .-ate G2 to.-e-ther with gite Go 35 wtiich will simultaiieously be uiiblocked -@vith ,he result th,Lt Pn exchange of sigral e-,ier,-ies will tal,-e Diace between cond,-nsers C and C'O. An aindlified sigti@l sample has thus b-,en transmitted fro-Tn condeilser Co to condenser C'o -vviiile a-Ti am,,)Iified signal satnple from condenser C'(, 40 is novi stored on conderser C. Provided gate G3 is a.-ain unblock-ed by the pulse t'2, during the guard time foll-,@iving t2, exactly th@- same amplification will be secured for ,the samole from C'o as that obtained bythe u--lblockin.- of G,, durin.- t'l, for the sample coming from cond,n@er 45 Co. At the end of t'2, cond--nser C is left N@iith an arrpliiied s,@imple from condenser C'o and dur@ing the next t, @r,u!2,c, the .-ates Gc, ard GI viill again be unbloe,@ed p-,rm,ittin- tl,-- a-mDlifi--d sariiple from condenser C'o to be issued from intermediate storage coiidenser C to co-Tidenser Co. It will be noted that if this amplifier system is applied to a coi-=unication network already usin.- the pr-ir@oiT)le of intermed,ate stora- - disciosedinth.- 1957 B@algian Pater-t I-,Io. 55@,096 (E. 'Pp G. Wri,@ht et al.) and ij' the orig- f@5 inal losses are for instance mainly due to this intermediate storage, the voill-age across the condenser C decaying b,-'Lwe.-n the time intervals s-,paratin,,- the two channel interconnec,tin.- times respectively used on the two hi.-hways HI and P.2. the gat.- GB may be repeatedly unblocked dur- 60 each such time i-@itervals as those correspondin.- to the 'tive pulses t'l, t'2 etCpos@ Tlius, there woiild in sLOli a case be no need for a selective unblocl-,ing of the gate G3 wh.ich would be p,-riodically unblocked at 2n times the samplin- frequency. In this manner, the arr@-plificatic-n C,5 times w@ui@ also -be proportional to th@, decay titnes and a p@-rfect comp,-nsation af sucli losses could b.- secured. When ttic traimc on hi.@hivay H2 does not merely corresDGpd to the traffic on hi.-hnvay 1-11, or in other words N,@,@'en these two highv/ays ar-- not exclusively associate@d 70 v,Tith one another bu-t may work with other high@,vays, some restrigtions in thA, choice of the time channels on the t@vo hi.-hways are bound to app,-ar. But if this is the case o-tie may still use the negative resi&tance during only one guard time such as t', immedi- 75 6 ately following the iiiterconnecting ehannel time stich as tl. In this event, the negative re.@,istance may even be used in m@ultiplex manner since after it has perform. ed its function during one guard t;me to amplifythe si.-nal on a partictilar storage cond-@nser, it can again be used durip.- the next g,,iard time viilh re.-ard to another intermediate stora.-e con-lenscr, etc. Thus, a negative resistan-,e such as -R wruld be connected in rr@iilti-Dle to a plurality <)f @ates such as G3. However. if there is an exelusiv-- asso@iation between the t-%vo hi,-.Iiways 1-11 atid H2, individtial ne.@at@ive resistinces per intermedible stora,-e condenser may be retained with the advanta.-e of bein@,- able to work at a substant;ally lower frequency than if they are used in m,@lilti-olex .-ashior@. For each commu-.iication over the tnvo high.,@ays in ca,,eade, o-iie -tnp-y choose a time c-i@annel tn+i)m,d 2, ()n the high@liay 1-12 v-,,hen tirre channel ti is cho,@en on h-ig hway I-11. In this r@nanner, the two time channels will be exactly in -,ntiphase and there is iriaximum separatio@i bet,@veen these 'Lv@o time channels, ivhich maximum s--paration may be ext)loiled for cou.t)lin.- the ne,,-atiie resistance -R te, its associaled interinediate storage coiidenser C by unblocking -ale G3 daring the ccrresponding time interval. T'-,ius, a p@ulse ww,,e forn-i sucli as tll in FIG. 2 -tnay be used, ti@ie latter - ,)@rovidin@,- a rositive pulse @vhir-h exteiids from the end of the positive t, pulse to the start of the pos;tive t,,+, pdlse, t'tiis rtiLP- beiri.- repea'Led a.-ain froir'che end of the i3 asiti,@e t,,@-I pul@se up to the start of the next ti pLIsc, etc. The repetit,on freoiiency of st,.en a pi-ilse wave form as tll is o-@ily t,,vic@, the sampliri.- fr@- qtiency and nearly a half period is therefore ,ivailible for unbloc@-,itig the -ate G3 for securin.- ar@iplif@;cation in both transnussion dircetions. Of co,-lrse, if the system shown i-Ti FIG. I should be used for unidireotional transinission of si,,@nals, the f,,ill interval bet.,2v@-en the end of a positive t, nuise and the star-t of the next @2,, POSitiVe P'I-llge coiild be iised for u-,iblocking the gate G3. Pr@lso t, wo,.ild thus be us,-d for unblooldng gate G, vvhile pulse t2n is t,,sed to uiiblock, gate G2. Tlien, tllo negative resistance -R mi.-ht be in shii-lit across its assoc,,.ated intermedia,Le stora,@e condenser C darin.- most of the sampling period. . In the bidirectional transmission case, the pulses ti aid tn-, 1 will be Lised for one commlinicatior., the plilses t2 and t,,'+2 (no,, shown) for another and so on, this for the u.,ibloclcin- of the gttes GI and G2 re,@,p-.ctively, while -ate G,3 will be u@iblocked by the pulses t,,, t,2 respectively etc. The system of FIG. I riiay evidently be used if all the voice frequency circui',s si-ich as LP to be interconnect.-d are assoc@.ated with the same Iiigl,@vay s,,ich as I-JI. Th-@i ihe gates such as G2 in FIG. I v,,ould evidently be sil-ppressed since there v;ould b.- no hi.-b@way 1-1,. only the gates GI ?nd 03 vioi-ilrl remain, but inst@-ad of there b,-ing 2it suc@h gates witli their associat,-d i@itermediate stora-e condenser C and negitiv-@ resistaiiec -R, there wo-,ild b'e o-Tily n such int@-rmediate stora,@e ci.-cuits, and the -atcs such as G, would b-- uilblocked t@vice iii a - sari.rilin.- p--riod, first to @ecure commiinication wifti the first voice freqi-ie-iicy circuit LP vi,-, its Iiie gate Go. a@-@d sr.,,-ond to @@ecur-- a similar conne-,tion, -after amplification of thp. signal sample on C, with anothpr voice frequency circuit also connected to the hi,,,' iivay Ill. Such an arrangement COLlld be -Lised either with a pre-assignedrelat-lonship between Ilie two lime c4iainels used or,@,vitho-it such a preassi.-Iled relationship, dependin.a upon the circumstar@ces already detail@ed above. When the system of FIG. I usin.@ amplified in',--rmed,',- ate storage betweeli two Iii.-h,@vays, or for the same Wg@nway, is to b-, u-sed in a way that the rf-,Iation between the t,'.Me channels cannot be pred--termined, it i3 possible to coias,-',d-,r a spec;al chann@l association selection eirci-lit whi@,h will permit to secure connecting tim, es for the negat,ve resistaices ,tsso,-iated witti the intermediate storageconiensers which may be substantially lar,-er

3,1$7,100 7 than a ti-tne chaniiel or sub@stantially lar,-er than the time interval separating two adjacent effeative channel times. In the Belgian Patent No. 515,605 (S. Van MierloH. Adelaar) it has been explained how one may select the same time channels Dn two cascaded highways. In 5 the U.S ' application S.N. 55,647, filed on September 13, 1960, and entitled "System for Determinin-. and Selectin.@ Free Aligned Telecommunication Channels" (J. Masure), , another channel alignment selectioii system has been explained by means of which in the case of - ali.-nment on 10 two cascaded highways for instance, once the identity of these two highways to be in-@,olved in a commtinir-ation is known,.information about the free br busy state on the time channels on these highways can be se@@ured from some channel @availability store. This information 15 pertaining to the busy or free state of all the chann-cls on the two highways considered, can be extracted fror@i that source and staticized durin.- a suitable ambunt time irterval on two sets of bistate circuits such as Rig-flops, there being therefore altonther as niany flip-flops as 20 i@vice the rumber of channels on a hi_ ghway; If the two flip-flops corres-conding to the same ci'xannel indicat@- that the latter is free on bbth highways, by means of a coincidence gate, they produce an activating si,@nal which is sent to a lock@-out circuit having thiis as manv such 25 inputs as there are time channels, and having aiso the saine number of outptits. This lock-out circuit then takes ,care of producing an activating signal at only one of the variot,.s ol@tpiits irrespective oj' whether several activatin.- signals are present at the various inputs. Thus, in this 30 man-ier, according to a predetermir@ed preference, a signal indicating an available aligned channel is selected out of s--veral whiel- mi.-ht be availabl@. In the. present case, due to the intermediate stidrage principle, alignment is no longer required, but in ord-- r 35 to obtain a suitable minimil-m interval of time between the two time channels used, thp- association between the two time channels must nevertheless be selective. FIG. 3 shows how this may readily be p-.rformed by way of an example w,@@ich assumes that @cascadin@ on two 40 highv,,ays is r-lquired, each of these catering for only ten time channels. The inputs Al/lo and Bi/lo correspond to the outputs Of the two sets of flip-ffop iiidicating that the corresponding channel an the corresponding highway is free, in the 45 manner outlined above.- Thus, when the vertical con,ductor is activated, this means that the first tinle channel t, is available on hi.@hway Hl,,while when hbrizontal con. ductor B6 is activated, this means that tinie cha.,lnel to ce on highnvay 1-12. A plurality of gates such as G is fr 16 50 have been shown to interconnect selected pairs of vertical and horizontal conductors su ch as Al and B6. Each conductor of a set is only iiiterconnected each time via a ,@ate, with three conductors of the other set and these @are chose.,i so that there is maxinium time spacing between 55 the pairs of channels whi.-h may thus be - associated on the hvo highvvays. Hence, for instance, time channel t, can bnly be associated with time channel t5, t6 or t7 on the other highway, as indicated by the three gates, such as Glcl which interconileet Al with B5, B6 or B7 on the 60 bne hand, and B, with A , A6, or A7 on the other hand .5 T'hus, altogether, there are 30 gates such as G,6, aiid various combinations of these gat--s may be simultaneously activated when an attempt is i-nade to determine the selectibn of a suitable pair of time channels. The 65 30 outputs of these gat-@s such as GIG may then be fed to a lock-out circuit (notshown) of the type disclosed in the above me ntioned Dutch patent application. WWr,hever pair of tinie channels is selected ho'ver, TO it is clear from FIG. 3 that t-here would always be a minimum of three full time channels separating the two paired time channels. Thiis, these intervals of tiine may be exploited in the manner indicated to secure a desirable amount of amplification @y connectin@ the,negative re- 75 sistance to its associated in,@ermediate storage condensdr by unblogking the g@ate G3. It will be evident that -whenever intermediate storage is used, the invention can be usefully applied. Thus, for instance, in the Belgian Patent No. 576,802 (H@ Adelaar) where a two--@vire/four-wire converter is disclosed as a substitute for the conventional hybr@id arrangeirent @and using an intermediate storage condenser, durin.- suitable ir@tervals of time s-.parating thf, tl-zoe time channels used in that,converter system, ariiplification of the signal stored on that cordenser co.uld be - secured by an associated negative xesistanc,-@ Also, in the Belgian Patent No. 579,759 (H. Adelaar), it has been pointed out that crrors in timin.- (>f the unblocking of the gates will h-,tve a minimum inflilence o-ti the ami)Iification, if the volta.-e versus time char-acteristic of the signal across the intermediate storage condenser during the time the negative resistance is effective, offers a zero slope at the time the gate connecting the negative resistance in the circuit is blocked. As explained in that patent , a suitable resonant transfer circuit may achieve tWs, and with the present systein, this could also be secured byassociating an inductance with th.- condenser and the negative resistance cirr-uit (C-R) )Ahen the gate G3 is unblocked to interconnect these two elements. By a suitable choice of the inductance value ,vith regard to the other parameters including the time of effective iiaterconnection, this zero slope can readily be secured to stabalize gain if need be. WWle the prineiples of the , invention have been described above in connection with specific app.,,iratus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention. 1