US2209955A - Wave translation system - Google Patents

Wave translation system Download PDF

Info

Publication number
US2209955A
US2209955A US114390A US11439036A US2209955A US 2209955 A US2209955 A US 2209955A US 114390 A US114390 A US 114390A US 11439036 A US11439036 A US 11439036A US 2209955 A US2209955 A US 2209955A
Authority
US
United States
Prior art keywords
feedback
impedance
amplifier
resistance
input
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US114390A
Other languages
English (en)
Inventor
Harold S Black
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Bell Telephone Laboratories Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US114390A priority Critical patent/US2209955A/en
Priority to GB32727/37A priority patent/GB506791A/en
Priority to FR833669D priority patent/FR833669A/fr
Priority to NL85374A priority patent/NL52895C/xx
Priority to FR49495D priority patent/FR49495E/fr
Application granted granted Critical
Publication of US2209955A publication Critical patent/US2209955A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising
    • H04B3/10—Control of transmission; Equalising by pilot signal
    • H04B3/12—Control of transmission; Equalising by pilot signal in negative-feedback path of line amplifier
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B3/00—Line transmission systems
    • H04B3/02—Details
    • H04B3/04—Control of transmission; Equalising
    • H04B3/06—Control of transmission; Equalising by the transmitted signal
    • H04B3/08—Control of transmission; Equalising by the transmitted signal in negative-feedback path of line amplifier

Definitions

  • This invention relates to wave translation and aims to control transmission of waves with regard to amplitude or phase relations or both.
  • a feature of the invention relates to effecting such control by-feedback.
  • Objects of the invention are also to control feedback and facilitate application of feedback.
  • the feedback may be, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level withcut feedback. Such feedback is disclosed, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level withcut feedback. Such feedback is disclosed, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level withcut feedback. Such feedback is disclosed, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level withcut feedback. Such feedback is disclosed, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level withcut feedback. Such feedback is disclosed, for example, feedback of a portion of the output wave of a system in gain-reducing phase and in amount sumcient to reduce distortion below the distortion level
  • the invention is an am- 35 pl bomb having a path which produces such feedback, the input (or output) end of the amplifying path being joined to the feedback path and the incoming (or outgoing) circuit of the amplifier by an interconnecting network that has branches 40 w th. mutual impedance and causes the input (or cutout) impedance of the amplifier to stabilize around a fixed value which, with considerable amounts of feedback, is independent of variations within the amplifier, its gain, or the amount 45 of feedback.
  • the interconnecting circuit at the amplifier inut, or the interconnecting circuit at the amplifier output, or each interconnecting circuit may be for instance a hybrid coil or bridge transformer with four pairs of terminals-one pair connecting to the incoming (or outgoing) lines, a second pair to the feedback path, a. third pair to the input (or output) circuit of the amplifying element, and the remaining pair to a two- 55 terminal impedance, thehybrid coil net.
  • the hybrid coil is .a three-winding transformer with a line winding connected between the line and the hybrid coil net, and a feedback winding connected between the feedback path and the hybrid coil net (the net thusbeing across the bridge points of the hybrid coil)
  • the hybrid coil is the input hybrid coil or the output hybrid coil
  • the desired amplifier input or output impedance can be realized by choice of the impedance of 2 the hybrid coil net.
  • This same turns ratio controls the transmission loss from the incoming line to the amplifying path, in the case of the input hybrid coil, or I from the amplifying path to the outgoing line, in the case of the output hybrid coil; and if the turns ratio exceeds .unity say by several times,
  • the input and output impedances of the amplifier are independent of one another and may have the same value or different values.
  • the ratio of signal to resistance-noise in the amplifier output energy can be made as much as three decibels greater than for the, matched impedance condition; and with proper choice of the value of impedance for the net of the input hybrid coil, feedback can make the amplifier input impedance match the impedance of the incoming circuit while the improvement in the ratio of signal to resistance-noise is retained.
  • the improvement that feedback can produce in the ratio of signal to resistancenoise is by no means limited to three decibels, and, as will now be explained, by the aid of feedback action an impedance from which to work the amplifier can be created which does not produce resistance-noise.
  • the relation of the amplifier input or output impedance to the impedance of the input or output hybrid coil net can be used for transforming impedances, i. e., for obtaining from the net impedance an impedance equal to the net impedance multiplied by a constant (unity plus the turns ratio), provided the amount of negative feedback is sufiicient.
  • the impedance obtained is an enlarged copy of whatever impedance is 'used as the hybrid coil net (the impedance across the bridge points of the hybrid coil) and the latter impedance may be of any suitable type.
  • it may be an ordinary impedance such as a resistance, an inductance, a capacity or any complex form of (two-terminal) impedance constructed of resistances, inductances and capacities.
  • feedback action can produce resistances or generalized impedances free from resistance-noise-that feedback action can transform ordinary resistances (or generalized impedances) to resistances (or generalized impedances) that are free of all noise, including thermal agitation.
  • the feedback can transform this resistance by producing an enlarged copy of it as the amplifier input impedance, this copy having the remarkable property of freedom from resistance-noise.
  • any physically realizable impedance can thus be reproduced free of resistance-noise; and of such impedances free from resistance-noice can be constructed all manner of impedance networks or active or passive transducers free from resistance-noise, for example, filters, equalizers, phase shifters, delay distortion correctors, impedance correctors, artificial cables or lines, amplifiers and systems in general.
  • a transmission equalizing network constructed of such impedances can be connected between the incoming line and the input hybrid coil;
  • the incoming line may be, for example, a coaxial system or other cable delivering signals whose lower limit of transmission level is fixed by the cable resistance noise;
  • the equalizer may be, for example, a constant resistance equalizer;
  • the hybrid coil may be such that the amplifier input impedance without feedback would be high compared to the equalizer impedance from which the amplifier works; and the hybrid coil net may be a resistance or impedance of such value that the feedback matches the amplifier input impedance to the equalizer impedance from which the amplifier works.
  • the equalizer and amplifier need not materially increase the ratio of resistance-noise to signal; and thus the desired equalization and amplification of the signal can be accomplished without decreasing the ratio of signal to resistance-noise.
  • resistances and impedances free from resistance-noise render possible large improvements in signal-to-noise ratio (by no means limited to improvements of three decibels) and the penetration of substantial amounts, theoretically as great as desired, below the noise level heretofore considered as an inevitable, natural, impenetrable limit established by thermal agitation.
  • feedback action can abstract heat from a body.
  • a resistance When a resistance is connected to an amplifier, feedback action can be made to abstract heat from the resistance or cool it.
  • the effect of making the connection is to abstract heat from the ordinary resistance or cool it, the ordinary resistance receiving no energy from the other resistance but giving up energy of thermal agitation to the other resistance in the form of an electric current.
  • the resistance to be cooled can be heatinsulated. If it is not insulated, the small losses due to thermal agitation are readily replaced from the relatively vast reservoir of heat surrounding the unit.
  • the feedback cannot only transform the net impedance to the desired value of amplifier output impedance, but can do so without materially affecting the impedance into which the output tube works; and this ability of the feedback to change the difference between two impedances (such as the tube impedance and the impedance of the outgoing line) by a different amount for one direction of transmission between them than for the other direction, makes it possible to work the tube into its optimum load impedance and at the same time match the amplifier output impedance and the line impedance, without entailing the transmission loss entailed in doing this without feedback, (as for instance in shunting across the tube impedance aresistance which in combination with this parallel tube impedance is equal to twice the optimum load impedance of the tube and connecting the resistance and the tube to the line with a transformer that changes the difference between the impedances which it connects the same amount for both directions of transmission).
  • the amplifier gain can readily be varied without varying the amplifier input and output impedances, byvarying the attenuation of the feedback path, as for example by an adjustable series or shunt resistance in the feedback path.
  • the resistance may be, for instance, a thermoresponsive resistance, as for example a silver sulphide resistance adjustable by control of its tem-, perature. If desired, the attenuation change made in the feedback path for gain control can be made automatically, as for example in response to transmission level.
  • a silver sulphide resistance unit may be connected in series in the feedback path, to render the amplifier a volume limiter by virtue of decrease in resistance of the silver sulphide due to heating of the silver sulphide resulting from increase of current through it in response to increase in output Voltage of the amplifying path. 4
  • Specific aspects of the invention also embrace feedback systems, including multiple feedback systems and systems involving repetition of the feedback process, with various forms of hybrid coil feedback connections.
  • Fig. 1 shows an amplifier of a specific form referred to above
  • Fig. 2 is a diagram for facilitating explanation of operation of such amplifiers
  • Fig. 3 shows a specific form of network which may be used in such an amplifier to match the amplifier input or output impedance to the impedance of a specific type of attached cable circuit;
  • Fig. 4 shows a cable terminated in an equalizer working into such an amplifier, the equalizer and amplifier being constructed, in accordance with the invention, to avoid increasing the ratio of resistance-noise to signal;
  • Fig. 5 illustrates cooling a resistanceby feedback action produced for example by such an amplifier
  • Fig. 6 shows a gain control for bomb
  • Fig. 7 shows a volume limiting circuit embodying a specific aspect of the invention
  • Figs. 8 to 10 show feedback amplifier systems with a single hybrid coil or bridge transformer network interconnecting the input and the output such an ampliof an amplifying element with an incoming circuit and an outgoing circuit;
  • Fig. 11 shows a multiple feedback amplifier with, a hybrid coil feedback connection
  • Fig. 11A shows an amplifier which is a modification of that of Fig. 11;
  • Fig. 12 shows a two-way transmitting, single loop feedback system with hybrid coil feedback connections through two feedback paths having a common portion
  • Fig. 13 shows a triple loop feedback system with a hybrid coil feedback connection
  • Figs. 14, 15 and 16 show feedback amplifiers with hybrid coil feedback connections and with repetition of the feedback process
  • Fig. 15A shows gain-frequency characteristics of the amplifier of Fig. 15;
  • Fig. 153 shows a type of feedback connectionused in Fig. 15, for facilitating explanation of operation of such connections;
  • Figs. 16A and 163 show curves facilitating explanation of tie operation of the amplifier of Fig. 16;
  • Figs. 17 and 17A show curves for facilitating design of feedback systems
  • Fig. 18 shows a specific form of amplifier of the general type of the amplifier of Fig. 1;
  • Fig. 19 shows an amplifier or system with feedback through hybrid coil connections that are modifications of those of Fig. 1.
  • the amplifier of Fig. 1 may be a stabilized feedback amplifier of the general type disclosed, for example, in the copending applications and published article mentioned above. It comprises an amplifying path or element shown as including tandem connected vacuum tubes I and 2, and comprises a feedback path I shown as including a transmissioncontrol network 3 of generalized impedances.
  • the amplifying path or element may be referred to as the circuit, and the f'edback path may be referred to as the p-circuit, the significance of a and 5 being as indicated in the applications and article just mentioned.
  • the network 3 may be referred to as the p-circuit network.
  • An input hybrid coil 5 couples the incoming circuit 6 and the feedback path I to the input end of the amplifying path; and an output hybrid coil 1 couples the output end of the amplifying path' to the outgoing circuit 8 and the feedback path.
  • One of the important advantages of this type of feedback circuit, with considerable amounts of feedback, is that the input and output imped'ances of the amplifier stabilize around fixed values. that are independent of variations within the amplifier, its gain, or the amount of feedback, regardless of whether, in the passive condition of the amplifier, the hybrid coils are balanced, or in other words, regardless of whether the impedance Zn of the hybrid coil net (i. e., the impedance 9 or 60 across the bridge points of the hybrid coil) .is such as to give passive conjugacy (i.
  • the hybrid coil is shown in the unsymmetrical form (i. e.,as unbalanced to ground).
  • the source of electromotive force E and impedance C represent or replace line 6 of Fig. 1.
  • the capacity Go represents the effective grid-cathode capacity of tube l.
  • the voltage across the input terminals of the amplifier is designated e.
  • the input impedanceof the amplifier is designated Zn.
  • the impedance of the hybrid coil net is designated ZN.
  • the numbers of turns in the line and feedback. windings of the hybrid coil are designated m and m, respectively.
  • the impedance of the amplifier is equal to the impedance of the net connected across the hybrid coil bridge-points multiplied by one plus the turns ratio of the' equality ratio or usually inequality ratio hybrid coil.
  • #5 the impedance of the amplifier can be made to approach what is wanted as closely as can the net.
  • amplifiers have been built and used having remarkably-good impedances. It has been observed that the input or output impedance of the amplifier can easily be varied, for example, in the ratio of 100:1 by merely changing the impedance of the net.
  • the hybrid coil is an inequality ratio hybrid coil with the turns ratio t sufficiently large, so that n1 n2 say by several times, then varying the impedance in this manner will hardly vary the input or output loss at all, and further, each of these losses can readily be kept below a few tenths of a decibel (instead of the usual three decibels for an equality ratio hybrid coil).
  • the ability to vary the amplifier input or output impedance (or both) in such an easy manner without much affecting the transmission is a highly desirable feature.
  • Zn is a surprisingly accurate copy of ZN, either enlarged or attenuated according as m is greater than or less than 112.
  • ZN is for example a capacity
  • the (input or output) impedance of the amplifier is a capacity, etc.
  • the transmission between the (incoming or outgoing) line and the and the feedback path is affected by the impedance of the (incoming or outgoing) connecting line; and as a corollary the amount of feedback obtained for any setting of the [El-circuit network such as network 3 is somewhat dependent upon the impedance of the connecting line.
  • the hybrid coils inequality ratio hybrid coils with one of the quantities m or m sufliciently exceeding the other, as for example, with one of these quantities several times as large as the other, the effect of the line impedances upon the amount of feedback can be made negligibly small and likewise the effect that the value of the impedances of the feedback path as seen from the hybrid coils has upon the transmission between the incoming or outgoing line and the amplifying path can be made negligibly small.
  • an indication of the degree of conjugacy may be obtained by noting the change in if as the p-circuit impedance is changed. Changing the B-circuit impedance (generator impedance producing in) will change the value of p. But it can be seen from equation (2) above, that Zr is dependent on due to changes in all are nil, or Zr is independent of /.I.,B. Therefore, regardless of the turns ratio,
  • the input impedance presented to the connecting circuit is rendered independent of the feedback path. But the converse is not true, i. e., the value of ,ufi is not independent of the connectin circuit, unless the hybrid coil possess a passive impedance balance.
  • the incoming and outgoing lines are in conjugacy with the feedback path when the proper hybrid coil balancing nets 9 and ID are used.
  • the amplifier output impedance is not a function of the impedance of the feedback path by direct transmission, but is controlled by the apparent plate impedance resulting from the feedback that the impedance of the feedback path provides. That is, feedback causes the apparent plate impedance to approach such a value that the output hybrid coil will be in dynamic balance. It is this property of hybrid coils, in conjunction .with sufficient negative feedback, that causes the nets 9 and Ill of the input and output hybrid coils to determine the amplifier input and output impedances.
  • an input hybrid coil or an output hybrid coil can render the amplifier input and output impedances independent of one another (regardless of whether the hybrid coil is in passive balance), it results that if an input hybrid coil is used, or an output hybrid coil is used, or both are used, the amplifier input and'foutput impedances can be given equal values or altogether different values, at will.
  • any, across its winding attached to the grid and cathode of the first tube) can be, chosen so that the amplifier input impedance without feedback is high, and at the same time the value ZN of the impedance of the net of the input hybrid coil can be chosen so that the negative feedback will cause the amplifier input impedance to be improved and stabilized around a proper value that will match the input connecting circuit.
  • the amplified resistance-noise at the output of the two amplifiers will be the same (because in either amplifier the noise in question depends upon the resistance component of the passive impedance without feedback between the grid and cathode of the first tube), and yet the feedback amplifier will have a matched impedance instead of a very high impedance.
  • the general noise level is of the order of magnitude of resistancenoise, it can be shown, other things being equal, that under certain circumstances this may amount to a 2:1 saving in the amount of output power on the basis of comparable signal-to-noise ratios.
  • the improvement that feedback can produce in the ratio of signal to resistance-noise is by no means limited to three decibels, and feedback action in circuits such for example as those of Figs. 1 and 2 can produce stable impedances which do not create resistance-noise and from which the amplifier can be worked.
  • the relation of the amplifier input or output impedance to the impedance Zn of the input or outputhybrid coil net 9 or it! can be used for transforming impedances, or in other words for producing from the net impedance an impedance equal to the net impedance multiplied by the con stant provided the amount of negative feedback is sufficient.
  • the impedance produced as the amplifier input or output impedance is an enlarged copy of-whatever impedance ZN is used as the net 9 or ill of the input or output hybrid coil
  • the impedances 9 and I may be of any suitable types.
  • either may be an ordinary impedance such as a resistance, an inductance, a capacity or any complex form of (twoterminal) impedance constructed of resistances, inductances and capacities.
  • the feedback action can transform ordinary resistances or generalized impedances that produce resistance-noise to corresponding resistances or generalized impedances that are free of all noise, including thermal agitation.
  • the feedback can, as just noted, transform this resistance by producing an enlarged copy of it as dance is a generalized impedance produced from a corresponding generalized impedance across the hybrid coil bridge-points by the feedback action.
  • the impedance Zn of the net 9 of hybrid coil 5 in Figs. 1 and 2 may be the impedance Zn shown in Fig. 3, which, with and s 1 causes the stabilized input impedance of the amplifier to be an extremely close match, over the 12 kilocycle to 60 kilocycle frequency range, for the impedance of a 19 gauge, non-loaded, .062 capacity standard toll cable; and then this input impedance (the input to the amplifier) 'is free from noise due to thermal agitation.
  • ZN any combination of coils, resistances or condensers, or a generalized impedance.
  • impedances free from resistance-poise canbe constructed all manner of impedance networks or active or passive transducers free from resistance-noise.
  • Fig. 4 shows an equalizer M and an amplifier 52 which are substantially free from resistance-noise notwithstanding the fact that the equalizer may, if desired, include resistance.
  • the equalizer may be, for instance, a constantresistance equalizer for equalizing the cable attenuation.
  • the amplifier' may be of the type shown in Fig. 1, and may have any desired number of stages, G and P designating the grid of the first tube and the plate of the last tube (in this figure and also in other figures of the drawings).
  • the incoming line 6 may be, for example, a coaxial system or other cable delivering to the equalizer signals .whose lower limit of transmission level is fixed by the cable resistance-noise.
  • the input hybrid coil 5 may be such that the amplifier input impedance without feedback would be high compared to the equalizer impedance from which the amplifier works; and the net 9 may be a resistance or impedance of such value that the feedback matches the amplifier input impedance to the equalizer impedance from which of the hybrid coil 51s large, giving low loss for transmission from the equalizer to the grid G, (and correspondingly a high loss results for transmission from the feedback path f to the grid G).
  • the equalizer can produce the desired equalization without adding resistance-noise.
  • the amplifier restores the signal level, amplifying the signal without introducing resistance-noise.
  • the desired equalization and amplification of the signal can be accomplished without decreasing the ratio of signal to resistance-noise.
  • the impedances Zn and ZF2 are input impedances of suitable feedback amplifiers.
  • they may be input impedances of amplifiers such as the amplifier of Fig. 1 or Fig. 2, and may be obtained by giving the nets of the input hybrid coils of the amplifiers the impedance values l+t respectively,
  • Fig. shows how a suitable feedback amplifier such, for example, as amplifier l2 cancool a resistance l5 by the feedback action.
  • the resistance is of the ordinary type producing thermal agitation electromotive force. It is shown in a heat-insulated chamber l6, and a switch [1 is shown by which the resistance can be connected to the input impedance of the amplifier. Since, as indicated above, the input impedance of the amplifier can be made a resistance free from thermal agitation by having the net 9 of the input hybrid coil 5 a resistance, it results that with switch I'I closed power is abstracted from resistance 15 without power being returned, and hence resistance l5 loses heat.
  • the impedance of net ID will not materially affect theimpedance into which tube 2 works, the tube, though its n t and "impedance may differ from its optimum load tration of the advantageous nature of such operation is when the output tube 2 is a pentode.
  • the output impedance R0 of the pentode is 1,000,000 ohms, and it delivers maximum power when the output impedance it works into is 25,000 ohms. Then if it were to connect through a transformer, say a two-winding transformer, to an output cable or line having a resistance of 100 ohms, a 25,000z100 impedance ratio output transformer would be required.
  • the output impedance of the transformer on its low side match the impedance. of the connected line or amplifier load.
  • this requirement could not be met because the output impedance of the amplifier would be the low side impedance of the coil when its high side was terminated by 1,000,000 ohms or practically open, whereas the high side winding of the coil would have to be terminated by 25,000 ohms for the low side impedance to be 100 ohms.
  • the pentode can be worked into its optimum load impedance and at the same time the output impedance as presented by the amplifier can be kept on a matched impedance basis and hence, since practically no power is wasted, the available output is doubled as compared to the case without feedback.
  • gain characteristics are parallel and fiat, they are preferably made as parallel as required or possible, and, in addition, as flat as possible. This distinction is made because for applications requiring great refinement, if the curves are parallel and almost fiat, then the slight lack of flatness can be corrected by the addition of a fixed equalizer.
  • Fig. 6 shows an amplifier similar to that of Fig. 1,' but shows the B-circuit network by way of example as a thermo-sensitive shunt element, preferably a resistance -23 of silver sulphide for controlling the gain of'the amplifier.
  • G and P in this figure, and wherever appearing in other figures of the drawings, designate the first grid of the first stage and the plate of the last stage of the amplifier, and indicate that the amplifier may have any suitable number of stages.
  • This temperature variation is accomplished by adjusting a resistance 24 which controls heating current supplied from an alternating currentor direct current power source 25 to a heating element 26 for the silver sulphide resistance 23.
  • the amount of power required to heat the silver sulphide resistance so as to produce a gain change of a few to as much as to 100 decibels would not exceed a small fraction of a watt and in many instances could be as little as one milliwatt or even a fraction 'of a milliwatt. Used in this manner it would often be required that the silver sulphide be stable with time and humidity. Where efiects of room temperature variations tend to be objectionable, the silver sulphide resistance may be enclosed in a heat insulated chamber 21.
  • the heat insulated container possessing sufficient heat capacity with respect to the size and heat capacity of the silver sulphide resistance, is very helpful in reducing efiects of variations in ambient or room temperatures upon the silver sulphide resistance. If desired, to compensate for effect of room temperature on operation of the silver sulphide unit, the heat insulated container can be maintained at a constant temperature, above the highest room temperature.
  • a thermostatic control This could be done by a thermostatic control, but in Fig. 6 is accomplished by a chamber-heating element 28 supplied with heating current from alternating current or direct current power .source 29 through a regulating network such for example as network 30.
  • the network 30 is shown as having a series resistance arm 3! and a shunt arm comprising a resistance 32 in series with two parallel resistances 33 and 3d, resistance 33 being a silver sulphide resistance.
  • the constants of the network depend upon the thermal and other properties of the particular silver sulphide'unit 33.
  • the chamber-heating unit 28 With the temperature of the chamber 2'8 elevated above the highest room temperature by the chamber-heating unit 28, if the room temperature rises the resistance of the silver sulphide element 33 falls sufiiciently to reduce the heating current in the element 28 so that the temperature of the chamber 21 is held constant.
  • the voltages or currents from the power supply sources 25 and 29 should be relatively stable.
  • the gain control 3 in Fig. 1, or the adjustable gain-control contact of resistance 24 in Fig. 6, may be operated manually; or if desired it may be operated automatically, for example asthe gain-varying element is operated by the pilot apparatus in the transmission control system disclosed in H. S. Black Patent 1,956,547,, May 1,
  • Silver sulphide is preferred as the temperature responsive transmission control element because of its large (negative) temperature coefiicient of resistance, constancy and uniformity of performance as disclosed more fully in the Fisher and Mallinckrodt application just mentioned.
  • the specific form of the silver sulphide element may be, for instance, the form disclosed therein; and the preparation of the element may be, for example, as disclosed in J. R. Fisher Patent 2,082,102, June 1, 1937.
  • the silver sulphide element can be placed in series'in the feedback path in the manner indicated in Fig. '7, about to be described; and if it is. then desired that the circuit be symmetrical (balanced to ground), two such ele ments can be used, as indicated in Fig. 7. Both can be in the same heat chamber, both heated by the same heater 26 oreach heated by an individual heater such as 26.
  • the resistance of silver sulphide has such a large negative temperature coefiicient that passage of even a small current will heat it up sufficiently to reduce its resistance as compared to the value of its resistance at ambient temperatures.
  • the feedback currents do not heat the silver sulphide appreciably; and; as a result, the silver sulphide resistance introduces nearly a constant insertion loss and, therefore, will not appreciably vary the amplifier gain.
  • the amplifier increases the useful range of the volume limiting circuit. Further, the useful range of operation, and also the precision of the control, can be considerably extended by refinements in the design of the silver sulphide resistance and in the design of the feedback circuit associated with it. 1
  • the output voltage at which regulation takes place in Fig. '7 can be reduced by decreasing the volume of the silver sulphide unit.
  • Another way to increase the sensitivity is to elevate the temperature of the unit, for example to a temperature just below that at which it begins to regulate, by an auxiliary or indirect heater such for instance as the heater 26 shown in Fig. 6.
  • the useful range of the volume limiting system of Fig, '7 can be increased by connecting volume limiting devices, such as the device shown, in tandem with each other in the feedback path I, and adjusting one to operate when the limit of the useful range of the preceding device has been reached; or the resistances 46 and 41 may each be made a silver sulphide resistance and a constant resistance in series, these additional silver sulphide resistances then being adjusted to begin their regulating or limiting action when the volume limiting device shown has reached the limit of its useful range.
  • the answer depends upon the speed with which the silver sulphide heats up and which includes a frequency as low as 1000 cycles per second.
  • Silver sulphide changes its resistance with temperature apparently faster than any other known material which simultaneously would satisfy the additional practical requirements that such a resistance be stable, that its temperature effects and behavior be accurately reproducible and that it be capable of being manufactured cheaply tofall within closely specified limits.
  • Silver sulphide meets these latter specifications and in addition, for all temperatures below 179 0., its resistance. is halved every time its temperature is increased approximately 13.9 C. At 179 C. its resistance is abruptly divided by more than 40, and for still higher temperatures its resistance increases.
  • the volume limiting circuit of Fig. '7 is of general application. For example, it is suitable for use as a receiving amplifier in a carrier transmission system, automatically keeping the voice frequency equivalent constant independent of high frequency variations; as a substitute for the volume control circuits now used in radio receiving circuits; as a volume limiter in front of a loud speaker, to prevent overloading; as a volume limiter to prevent overloading a detector, a group modulator or a broad band amplifier carrying a number of channels (the effect in this case resulting in an important increase in theuseful operating level of the amplifier or repeater); as a control to keep the pilot current fixed at the sending end of a pilot channel system; as a control to maintain theroutput of multi-frequency carrier supply systems at a constant voltage; as acontrol to limit the volume of voice frequency telegraph signals superimposed on carrier telephone systems; or as acontrol for an alternating current supply voltage to render the voltage constant for operation of alternating current apparatus or for testing or measuring purposes.
  • the hybrid coils render the equalization independent of the flexibility of the amplifier input and output impedances, the impedances of the amplifier being adjustable through very wide ranges by means of the hybrid coil nets 9 and it] without affecting the equalization or distortion correction.
  • the equalizing or transmission controlling network in the feedback path or c-circuit has important advantages.
  • the equalizer is located in the B-circuit, in most instances this loss can be considerable without affecting the overall transmission performance. Generally speaking, increasing head-end loss will permit appreciable economies in size and cost of the parts.
  • pre-equalization there is an advantage with respect to load rating. If the equalizer is located in the c-circuit and, in addition, the cable or transmitting medium is free from practically all noise but resistance noise, pre-equalization will result in a substantial number of decibels of improvement in the level rating of the amplifier depending upon the band width, number of channels, and attenuation-frequency characteristic of the medium. As compared to locating the equalizer in front of the amplifier, the input levels can be reduced by the total amount of loss of the equalizer for either high or low frequencies.
  • Another advantage is reduced modulation requirements. If the pre-equalization is one-half of the cable slope, attenuation vs. frequency, in stead of the full amount as just discussed, a worthwhile portion of the improvement in level rating of the amplifier is still retained. However, with re-equalization, if and only if the equalizer is in the fi-circuit, the modulation requirements are uniformly reduced at all frequencies in the transmitted band by an amount approximately equal to one-half the difference in the cable attenuation at the highest and lowest used frequencies. For the same performance as before, this leads to a worthwhile reduction in the gain without feedback which is more important the wider the frequency band transmitted and the higher the top frequency.
  • the customary way where the network for correcting attenuation and phase over the frequency band of interest is not in a feedback path, delays the time of transmission by a period that exceeds the time required for a particular frequency to travel down the cable, this particular frequency generally being that one in the band of interest which is most slowly transmitted.
  • the time is the time for a particular frequency, which is the one most rapidly transmitted, or in other words, it is the time required for current no matter how trivial to make its appearance at the receiving end. All other velocities for all other frequencies for which the circuit is properly operative are made equal to this most rapid speed.
  • this speed apparently corresponds to a speed less than the velocity of light in a vacuum, depending upon the dielectric constant and permeability of the cable. It should be noted that this time is independent of the wave form impressed at the sending end. It is also independent of lumped series inductance, either positive or negative, and likewise is independent of lumped shunt resistance, either positive or negative.
  • apparatus the feedback amplifier
  • the fl-circuit instead of being a like section of cable may have a difierent indicial admittance, as now to be explained.
  • two such systems are on the one hand a cable of length l-where Z is many wavelengths and on the other hand a lattice network of one section whose four elements are two impedances each equal to the cable impedance of length with far end shortcircuited and two other impedances each equal to the cable impedance of length where v is the velocity of propagation referred to above, 1. e., 1- is the time for the first current to appear at. the distant end.
  • the p-circuit should have an indicial admittance equal to the imiicial admittance of the cable when, referring to the admittance characteristic of the latter,,t is replaced by (i''r). If this is done and pfl 1, the output of the amplifier will be a replica of the input at the sending end except it will appear 7' seconds later.
  • the p-circuit be a like section of cable (assuming Nyquists rule is satisfied by appropriby making additions) the time of transmission is still 1' but for an interval 1' at the beginning and a corresponding interval at the end, the wave form apparently will be incorrect. This effect would be something more than multiplying the time of transmission by two as compared to the method of the preceding paragraph. It would make the received wave distorted in a manner analogous to that of a loaded cable.
  • the response without feedback to the excitation canbe viewed as the forced or steady state response plus the free flow or transient response.
  • the amplifier does not amplify the transient response for the conditions above described.
  • the first currents to arrive of necessity carry information as to the signal impressed so that the amplifier sends out a copy of the signal wave form applied at the sending end, and, when the main body of the transmitted signal arrives later and appears at the input to the-amplifier, it just is not amplified.
  • an attenuation equalizer or other corrective network - is located in the feedback path between the hybrid cells as in the case of the ,B- circuit network 3 of Fig. 1, since the corrective network does not afiect the amplifier input or output impedance the equalization or correction can be accomplished by merely inserting a simple series or shunt arm between two arbitrary fixed impedances. Usually this requires less than half as many elements as the corrective network requires when it is so located that it affects the amplifier impedance seen from theline.
  • a system such for example, as that shown in Fig. -8 (which is dominated by R. S. Caruthers application Serial-No. 114,409, Patent 2 .166,929,-issued July 25, 1939, entitled Electric wave amplifying systems, filed of even datehere- -with) can be built, comprising an amplifier (with pfl 1) that works on a matched impedance basis from a -resistance R1 into a greater, resistance C2 and has its gain
  • the amplifying element is designated 50. It may be of any suitable type, as for example, a
  • the vacuum tube device such as the amplifying deand ately modifying a, or the cable itself is modified
  • the loss is precisely the same as the previous gain (i. e., from R1 to R2).
  • the gain or loss is independent of frequency by virtue of the method of operation of the circuit.
  • the circuit of Fig. 8 can be rearranged as in Fig. 9, wherein to work from a resistance R1 into a resistance R2 that is greater than R1, giving a gain and giving a loss from R2 to R1 equal to this gain Gp.
  • the amplifier 59' and the hybrid coil 5! correspond to the amplifier 50 and hybrid coil 5
  • Figs. 8 and 9 can transform impedances, in the manner indicated in the discussion above of Figs. 1 and 2, the circuit of Fig. 9 dividing an impedance by a number greater than unity.
  • Fig. 10 shows an amplifier circuit obtained by combining two circuits such as those of Figs. 8 and 9.
  • the input impedance Z02 and output impedance Z01 of the amplifying system equal respectively the impedance Zc2 of the output connecting circuit and the impedance Z01 of the input connecting circuit.
  • the amplifying system has a gain (from west toeast) equal to and has a loss (from east to west) equal to If desired, to reduce the gain without afiecting the impedance relationships, the pad 52 of impedance level Zn can be inserted as shown.
  • Figs. 8 to 10 show that power is dissipated in stabilizing an impedance by feedback as in Fig. 2. In the case of Figs. 8 to 10 (with network 52 omitted) all such power is dissipated in the output load.
  • Afeedback loop with more than one path from the same output to the same input is'a multiple loop, but as noted in that copending application, if the multiple loop can be theoretically replaced by a single loop, the feedback is regarded as parallel feedback, except that a special case of parallel feedback is termed repetition of the feedback process (referred to below).
  • a repetition-of the feedback process is considered to occur whenever a complete feedback system (single loop or multiple feedback) may be viewed and treated as a unit and, in addition, is used to form a new ,ufl-path which path in every way is independent of the first feedback system except in so far as it utilizes the original over-all properties of the first feedback system.
  • This requires conjugacies or their equivalent and the use of transformers, assuming no new unilateral devices or their equivalent be added.
  • repetitions of the feedback process are but a special case of parallel feedback, namely, with an added restriction regarding conjugacy. Accordingly, unless active elements are used to separate the feedback paths the various paths or loops theoretically can be replaced by a single path or loop. However, repetition of the feedback process can have practical advantages, for example, as pointed out hereinafter.
  • -if negative may be desired, for example, to
  • Fig. 11A shows an amplifier which is a modification of the circuit of Fig. 11, the potential, with respect to ground, that is fed back from the hybrid coil. to the grid of the first tube being applied across resistance 64.
  • the voltage across resistance 65 is transmitted also to the grid of the second tube through the plate-cathode path in the first tube and the interstage coupling circuit, before phase reversalin the first tube, but the voltage thus applied to the grid of the second tube is small in view of the high impedance of that plate-cathode path.
  • the amplifier is suitable, for example, as a high quality voice frequency amplifier for program transmission circuits.
  • the tubes are shown as a screen grid tube 55 and a coplanar grid tube 56' which may be Western Electric Company 259A and 281A tubes, for example.
  • one portion goes through the hybrid coil to line LE, and another portion goes through the hybrid coil and the p-circuit-network TI to the hybrid coil 13, there dividing be-
  • waves from the output of amplifier RE are fed back through hybrid coil 16, fi-circuit network 11 and hybrid coil 13 to the input of amplifier
  • transmission from line LE is amplified by amplifier RW and transmitted to line LW, and the amplifier RW feeds back through hybrid coil 13, fi-circuit network Ti and hybrid coil 16 to amplifier RW.
  • the grid-cathode impedance of the first tube of the amplifier forms one arm of a second input bridge 88, the other arms being resistances 89, 9d and SI.
  • the winding 83 is in one diagonal of this bridge, and the other diagonal includes a feedback path, which will be called the ,81 path, this feedback path comprising a two-winding transformer 92 and also comprising a p-circuit network 93 for controlling transmission through this feedback path in the same general manner as explained above for the case of network 3 in the feedback path in Fig. l.
  • Bridges 88 and 94 need not be balanced. .As

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US114390A 1936-12-05 1936-12-05 Wave translation system Expired - Lifetime US2209955A (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
US114390A US2209955A (en) 1936-12-05 1936-12-05 Wave translation system
GB32727/37A GB506791A (en) 1936-12-05 1937-11-26 Improvements in or relating to amplifying systems using negative feedback
FR833669D FR833669A (fr) 1936-12-05 1937-12-04 Systèmes translateurs d'ondes électriques
NL85374A NL52895C (fr) 1936-12-05 1937-12-06
FR49495D FR49495E (fr) 1936-12-05 1938-03-23 Systèmes translateurs d'ondes électriques

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US114390A US2209955A (en) 1936-12-05 1936-12-05 Wave translation system
GB32727/37A GB506791A (en) 1936-12-05 1937-11-26 Improvements in or relating to amplifying systems using negative feedback

Publications (1)

Publication Number Publication Date
US2209955A true US2209955A (en) 1940-08-06

Family

ID=26261532

Family Applications (1)

Application Number Title Priority Date Filing Date
US114390A Expired - Lifetime US2209955A (en) 1936-12-05 1936-12-05 Wave translation system

Country Status (4)

Country Link
US (1) US2209955A (fr)
FR (2) FR833669A (fr)
GB (1) GB506791A (fr)
NL (1) NL52895C (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2451858A (en) * 1945-01-26 1948-10-19 Gen Electric Controlled frequency oscillator
US2589184A (en) * 1949-09-13 1952-03-11 Bell Telephone Labor Inc Electronic impedance equalizer
US2616987A (en) * 1948-04-02 1952-11-04 Soc Ind Des Procedes Loth Amplifying circuit arrangement with periodically varying load connected in the cathode circuit
US2646218A (en) * 1950-04-25 1953-07-21 Sperry Corp Distortionless electrical resolver
US3108157A (en) * 1959-06-15 1963-10-22 Bell Telephone Labor Inc Multiple station communication circuit
US3177303A (en) * 1960-10-07 1965-04-06 Budelman Electronics Corp Voice frequency hybrid telephone repeater
FR2823618A1 (fr) * 2001-04-13 2002-10-18 Electricite De France Etage d'un generateur de puissance d'un courant haute frequence
US20110038406A1 (en) * 2008-04-14 2011-02-17 Stephan Pfletschinger Method and digital communication device for receiving data using qam symbols

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2451858A (en) * 1945-01-26 1948-10-19 Gen Electric Controlled frequency oscillator
US2616987A (en) * 1948-04-02 1952-11-04 Soc Ind Des Procedes Loth Amplifying circuit arrangement with periodically varying load connected in the cathode circuit
US2589184A (en) * 1949-09-13 1952-03-11 Bell Telephone Labor Inc Electronic impedance equalizer
US2646218A (en) * 1950-04-25 1953-07-21 Sperry Corp Distortionless electrical resolver
US3108157A (en) * 1959-06-15 1963-10-22 Bell Telephone Labor Inc Multiple station communication circuit
US3177303A (en) * 1960-10-07 1965-04-06 Budelman Electronics Corp Voice frequency hybrid telephone repeater
FR2823618A1 (fr) * 2001-04-13 2002-10-18 Electricite De France Etage d'un generateur de puissance d'un courant haute frequence
WO2002084860A1 (fr) * 2001-04-13 2002-10-24 Electricite De France Service National Etage d'un generateur de puissance d'un courant haute frequence
US20040108894A1 (en) * 2001-04-13 2004-06-10 Georges Roussy Stage of a power generator of high frequency current
US6909322B2 (en) 2001-04-13 2005-06-21 Electricite De France Service National Stage of a power generator of high frequency current
US20110038406A1 (en) * 2008-04-14 2011-02-17 Stephan Pfletschinger Method and digital communication device for receiving data using qam symbols
US8503552B2 (en) * 2008-04-14 2013-08-06 Fundacio Centre Tecnologic De Telecomunicacions De Catalunya Method and digital communication device for receiving data using QAM symbols

Also Published As

Publication number Publication date
FR49495E (fr) 1939-05-01
NL52895C (fr) 1942-08-15
GB506791A (en) 1939-05-26
FR833669A (fr) 1938-10-27

Similar Documents

Publication Publication Date Title
US3973089A (en) Adaptive hybrid circuit
US2659773A (en) Inverted grounded emitter transistor amplifier
EP0020044B1 (fr) Dispositifs d'égaliseur
US2209955A (en) Wave translation system
US3444474A (en) Active equalizer circuit
US3204048A (en) Negative impedance repeaters for non-loaded lines
US2758281A (en) Variable attenuation correcting electric impedance network
US3646464A (en) Active delay and amplitude equalizers
US2806200A (en) Ambient temperature compensation of thermistors
US2659774A (en) Bidirectional transistor amplifier
US2777994A (en) Level regulating devices for transmission systems for coaxial cables
US2131366A (en) Electric wave amplifying system
US3867589A (en) Enhancing impedance characteristics of negative impedance repeaters operating at high gain
US4027259A (en) Line equalizer with differentially controlled complementary constant resistance networks
US2087316A (en) Volume control system
US2281312A (en) Wave translation
US2683777A (en) Automatic control of amplification in long distance transmission systems
US2231542A (en) Transmission control circuit
US2267286A (en) Negative feedback amplifier
US2065344A (en) Control means for signal control transmission systems
US2428363A (en) Negative feed-back amplifier
US2131393A (en) Electric wave amplifying system
US2223161A (en) Negative feedback amplifier circuit
US2342822A (en) Amplifying system
US1993758A (en) Wave translation system