US2464607A - Pulse code modulation communication system - Google Patents

Pulse code modulation communication system Download PDF

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Publication number
US2464607A
US2464607A US603990A US60399045A US2464607A US 2464607 A US2464607 A US 2464607A US 603990 A US603990 A US 603990A US 60399045 A US60399045 A US 60399045A US 2464607 A US2464607 A US 2464607A
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Prior art keywords
pulse
conductance
voltage
pulses
signal
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US603990A
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John R Pierce
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AT&T Corp
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Bell Telephone Laboratories Inc
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Priority to NL77660D priority Critical patent/NL77660C/xx
Priority to BE473323D priority patent/BE473323A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US603990A priority patent/US2464607A/en
Priority to GB11874/47A priority patent/GB630095A/en
Priority to CH287037D priority patent/CH287037A/fr
Priority to FR946925D priority patent/FR946925A/fr
Priority to DEP28894A priority patent/DE892605C/de
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/66—Digital/analogue converters
    • H03M1/82—Digital/analogue converters with intermediate conversion to time interval
    • H03M1/822—Digital/analogue converters with intermediate conversion to time interval using pulse width modulation
    • H03M1/827—Digital/analogue converters with intermediate conversion to time interval using pulse width modulation in which the total pulse width is distributed over multiple shorter pulse widths

Definitions

  • FIG/.3 xfij E 12221 7 LOW PAS! V OUTPUT F ILTE R PROPORT/OAML E TO M INVENTOR By J R PIERCE A TTORNE Y March 15, 1949. J. R. PIERCE 2,464,607
  • J sou/P1 MICROPHONE g m //v l/EN TOR J R. PIERCE WLLIZM.
  • This invention relates to communication systems for the transmission of complex wave forms of the type encountered in speech, music, sound, mechanical vibrations and picture transmission by means of code groups of a uniform number of impulses of a plurality of difierent types or signaling conditions transmitted at high speed.
  • An object of the present invention is to provide a communication system capable of transmitting and reproducing with high fidelity a complex wave form over an electrical transmission path in such a manner that the signal-to-noise ratio of the received signal is materially improved over the signal-to-noise ratio through the transmission path.
  • Another object of this invention is to provide improved and simplified methods and apparatus capable of transmitting and receiving signal impulses over a channel having a low signal-to-noise ratio and deriving therefrom signals having a high signal-to-noise ratio. In one sense this is obtained by using a wider band width, that is, trading band width for signal-to-noise ratio.
  • the present invention to provide methods of and circuits and apparatus for transmitting in succession a group of pulses in sequence over a given channel representative of the amplitude of a complex Wave at successive instants of time.
  • the pulses to be transmitted are, in general, of short duration so that the duty cycle of the various elements of the system is low, thus permitting large momen tary power without overloading various elements, such large power tending to override such noise as may be inherently present, giving thereby a l more favorable signal-to-noise ratio.
  • the amount of noise picked up at the receiver may be correspondingly reduced.
  • a feature of the present invention relates to methods and apparatus for determining the magnitude of an electrical quantity and transmitting a series of pulses representative of said amplitude.
  • Another feature of the invention relates to methods and apparatus for building up an electrical quantity which is proportional to and'a measure of the amplitude of a sample of a complexadmittance.
  • This quantity may take on the nature of a conductance or an admittance.
  • Still another feature of this invention relates to methods and means to perform building up of this electrical quantity step by step by an additive or a subtractive process to a total which is proportional to the amplitude of a sample of a complex Wave.
  • Another feature of the invention relates to the use of conductances to be so built up by an additive or subtractive process to the total required.
  • Another feature relates to the transmission of information in the form of a code regarding each conductance added or subtracted.
  • equipment for generating a control pulse or a group of pulses of predetermined time relation one with another.
  • control pulses are employed to control a code element timing circuit, which circuit in turn generates a series of very short pulses some of which are posgenerates a series of code element timing pulses and these in combination with the sampling means derive an electrical quantity having a magnitude related to the magnitude of the complex wave at the time of the control pulse.
  • This electrical quantity takes on the character of an admittance which may be varied step by step, cooperating with the complex wave sample to determine the next step of variation in the More specifically, the electrical quantity is in the nature of a conductance made up of a plurality of conductances of different magnitudes which may be added to each other or omitted in such combinations as to yield a conductance related to the magnitude of the complex a smaller and smaller change is made. in the:
  • plan is followed that" if" the ma nit-udeof the conductance due to the last addition is in excess of that required; then it is removed and an on signal is transmitted. If 'theaddition is below that required, then it" remains-in and information to thisefiect-ispassed' tothe remote point bytheabsence of the transmitted signal, the identification of the information being specified by theti'meatwhich-the informational pulse istransmitted or not trans-- mitted.
  • Thisform of comparing the sample with the potential difference-set upby the conductance; is then carried on.step: by. step. to asfarza point.v as may bev desired. and in any case; to; an: extent so thatthegranularity ofthe signal finally reproduced ata; receiving point will be;within1 the. limltsyof fidelity contemplated: for: the y tem.
  • FIGs. 1 and 2 show-in functional block'formthe various elements and the mannerin which they cooperate to form an exemplary communication system embodying the present-invention
  • Figs; 3"and 4 illustrate the timing and nature of" the pulses andwaves characteristic of my system
  • Fig. 5 1s explanatory: of the method and" ap- J off, or 00010101.
  • FIGs. 8 to 13 when positioned as shown in Figs. 6 and 7, give in detail the various circuits, equipment and operation of an exemplary system embodying the present invention.
  • Fig. 14 is a circuit diagram of acontrol portion of a conductance.
  • Fig. 1 Let M be a: modulating; function representative of any complex: wave such as a speech Wave, a small portion of which is indicated by curve 35 of Fig: 3.
  • a modulatons ends out a series of signals forth. Each series consists of 1+n signals of the onl*-off"" variety; (The signals need not be on croif but each signal distinguishes between two positions called on and off. These might be positions of time, frequency or amplitude.
  • OI-1 might be transmitted as a current being of! and"oflf as that oi?- current being on.)
  • The-*fi'rst signal oftheseries or group is used to tell the polarity ofthe function M at the time tm.
  • the next 12' signals of the group specify themagnitude of M at imwithrespect to some- These 11.
  • the first zero carries, the information that, M. is. of. negative polarity and the. remaining. signals that, M is. of amplitude 21,times,the arbitrary unitvalueemployed, this value. being, obtained. by. binary counting. group. of pulses. of this type may be regarded as a permutated. series of. impulses in which the on" conditions. represent. marking selections and. the, oil conditions represent. spacing selectionsor-viceversa.
  • Whilethdfunctions describedcould be carried out without frequency conversion, grounding problems" are; simplified by first impressing the modulatingjunction Mon a balanced modulator I of-Fig. ,1, togetherwith the output of a local oscillator II or'frequency fa, high compared with the; frequencies occurring in M. At the time tm shown; on Fig; 3., a pulse which will be referred tOyflS fitll Mipulse, from a pulse generator VI is impressed on I. During the interval T between in.
  • outputcurrent Im has a fre-- quency fe andanzamplitudeproportional to M atria.bcingz plusrwhen Miisplus at tm and minus when M is minusat I'm.
  • thesecond line shows'the potential across a condenser (later to be described) and the graph BScihrjhQ lastgroupr shown in line. I, this is reso described in this specification for illustrative At tin-H another sample ofthe complex wave is taken and for the next aseaeor corded by a reversal of phase of the modulated current of frequency In.
  • Im is fed to a balanced transformer III.
  • This and the local oscillator II are very low impedance sources.
  • Two homodyne detectors are fed with signals in opposite phase from the balanced transformer.
  • the drop across a resistance R caused by current flowing from terminals 0, d of the local oscillator II through conductances G1 Gn. This drop will be proportional to G1+ G11.
  • an output from terminals d, e of local oscillator II This is adju'sted to be equal and opposite to the drop across R' caused by the current flowing through G1 G11 in their minimum conductance condition.
  • the voltage across d, e taken in series with the drop across R is proportional to the changein G1+ G11.
  • a polarity and amplitude detector is shown at V.
  • the two inputs A and B from the homodyne detectors IVA and IVB are shunted with biased diodes so that the voltage across their outputs can never become negative or positive by more than a certain fixed amount regardless of the input to the homodyne detectors.
  • the conductances G1 G11 are controlled electrically by (a) pulses from the pulse generator VI, and (b) the amplitude output of the polarity and amplitude detector V.
  • the character and timing of these pulses are shown in Fig. 4 which is an expansion of the time interval between two sampling pulses or the time required for one cycle of operation.
  • the second time interval T is shown expanded.
  • the negative portion of the M pulse resets the modulator I and the positive portion immediately thereafter takes the sample of the complex wave.
  • the initial negative pulse shown on lines I to n of Fig. 4 places all Gs in the minimum conductance condition.
  • the sample of the complex wave causes operation of the homedyne detectors IVA and IVB.
  • a polarity pulse at a time indicated by the P line of Fig. 4 is applied to V and information on the polarity of M is transmitted.
  • a plus pulse is applied to G1 at a time indicated by line I of Fig. 4. This puts in 64Go of conductance.
  • a negative pulse is applied to G1.
  • VI sends a resetting pulse to the conductances. This puts all G's at minimum conductance condition. This pulse may also send a marker signal from the transmitter denoting the end of one interva1 or cycle of operation and the beginning of the next. This pulse may be simultaneous with the M pulse applied to I.
  • Figs. 3 and 4 showing the character and time spacing of the pulses required from the pulse generator VI.
  • a series of pulses coming over the channel M to the modulator I and a sample of the complex signal wave at the instant of each modulator pulse is taken.
  • the sample causes the modulator to emit, until pulsed again, a current Im of frequency f0 and amplitude proportional to M at tm. All this is indicated in the second and third lines of Fig. 3.
  • a polarity pulse to the polarity and amplitude detector V arrives an interval later and this is succeeded by pulses over the channels l, 2 n which operate on the conductances G1, G2 G11.
  • There is also a pulse channel T to the transmitter necessary if the ofi signals are transmissions and not merely omissions. All this is shown in Fig. 4 which is an expansion on a time basis of one of the sampling periods of the system.
  • channels i and n are pulsed with strong negative pulses setting G1 Gn in the minimum conductance conditions.
  • the polarity and amplitude detector V is pulsed. This results in a pulse to the transmitter VII if the polarity is negative and an on signal, or no pulse to VII if the polarity is positive and an off signal.
  • the n amplitude channels are pulses in sequence, first positively and then negatively.
  • the positive pulse inserts conductance, the negative pulse removes conductance if it is too large and in doing so sends an on signal, otherwise the conductance stays in and there is an off" signal.
  • the channel T may apply pulses to the transmitter VII at all times whether an on,
  • Thecomplex .wave transmitted is impressed on the1balanced .modulator system I, this complex wave having come-from any suitable source such as.a microphone 805 through appropriate terminal equipment 800. It is then sampled periodically and goes through the process to be described in further detail.
  • Pulse generator VI It will be advantageous to now describe the pulse generating system VI, one form of which is shown in detail in Fig. 10.
  • the first controlling element in this portion of the system is a relaxation oscillator comprising agas-tube mm.
  • This relaxation oscillator is of a form well known in the art and includes a resistance IIJEI for charging a condenser IOI2. Assuming that to start with the condenser IOI2 is discharged then on closure of the circuit it is charged at a rate determined by the resistance 50. potential of the condenser and consequently the plate of tube I0! 0 rises to a firing value, the condenser suddenly discharges through the tube and resistor IBM.
  • the duration of the discharge is short and gives rise to a sharp positive pulse across the resistor IBM.
  • the duration of this pulse and'the rate at which it is followed by'identical pulses can be completely controlled bythe parameters of the circuit; in particular, by the values of the elements Hill to IOMtaken with the potential of the grid of tube IOI0 as determined by the potentiometer IOI5. While any of'several forms of relaxation circuits may be used at this point the one shown is simple and satisfactory. Its operation is more fully described in many places, suchas on page 184 of Ultra-High Frequency Technique by Brainerd et-.al., published by Van Nostrand Company, 1942.
  • a positive pulse travels through this network, the time of arrival at each section being uniformly spaced and giving rise to corresponding positive pulses going out over channels I, 2 n forpurposes to be described.
  • the delay network is terminated by a load I040 of proper value to suppress any reflected Wave.
  • the parameters of therelaxation oscillator maybe adjusted so that pulses are derivedacross resistance; IOI4r attanygfrequency desired; For. the purposes of my invention.it;is-.preferred...to;. have a samplingfreqllency; higherthan that of the highestfrequencycomponent in the complex.
  • the delay circuit'or timestiok? I0l6 By meansof the delay circuit'or timestiok? I0l6, one has available at the ends oftherespec-e tive sections, positive! pulses similar to that initiated in IBM andspaced in time, one after the; otherbyan intervaldetermined by the elements in a-section of the timestiok. At time in wheni. the pulse is formed at H4 (or point M) it'is; transferred immediately :to tube I02 0- and iszthen transferred to I asthe M pulseof Fig. 3.. The function of, this pulse will be described herein after.-
  • the positive pulse.- from I 0I4- will have reached the point P on the timestiok and this will be identified as the P. pulse.
  • This P pulse operates on the grid of tube I02I -to give a positive. pulse over the resistor.
  • I 022 which pulse is transmitted to the polarity," and amplitude detector: V, appearing there asa. positive pulse ofa vform and at a-time indicated.- by line P of Fig. 4.
  • the first T pulse may, for instance, be approximately twice the length of the subsequent pulses.
  • a chain of'tubes I024'to I025 is provided for the formation of the T pulses.
  • the grid of tube I024' is operated on directly by the pulse from M.
  • delay circuits may be introduced wherever necessary.
  • One such delay circuit is shown in the T channel at I050.
  • the number of sections in the timestick will usually be made equal to the number of digits required for setting up the amplitude code to be transmitted from VII. If there should be n of these then the number of possible codes by permutation of on and ofi signals would be 2. Thus, if number of digits in the code is seven this will make possible 128 combinations so that in the system it will be possible to discriminate between amplitudes of 128 different values.
  • a circuit Associated with conductor I from the timestick and tube IOBI is a circuit comprising tube I06I and transformer I'II'.
  • the tube I06I is shown as a double triode.
  • the grid of the left-hand section of this tube receives a positive pulse at tm which is then converted at the plate to a negative pulse.
  • This negative pulse is transferred through transformer Hill as a negative pulse to the control of the corresponding conductance, device G1 in Fig. 9 and serves as hereinafter described to set this conductance element to a minimum conductance.
  • a positive pulse arriving over conductor I to tube I08I is inverted and appears as a negative pulse on the grid of the right-hand section of tube I 06L
  • the load circuit of tube I08I includes the inductance I09I which causes the negative pulse generated on the plate of I08I to be immediately followed by a positive pulse 50 that the pulse arriving on the grid of the right-hand section of I06I is a negative-positive pulse.
  • This pulse in turn is inverted by the right-hand section of tube I06I to a positive-negative pulse which is then transmitted through the transformer I'0'II to the control circuit of conductance G1.
  • the character and timing of this positive-negative pulse is that indicated in line I of Fig. 4.
  • a similar circuit is associated with each of the conductors 2, 3 n to give at the time of the M pulse a negative pulse to the corresponding conductance control devices setting each conductance to a minimum conductance and at a later time transmitting a positive-negative pulse sponding transformers and to suppress their differentiating action, thus preventing the setting up of a reverse pulse.
  • Other elements all serve purposes well known to those skilled in the art and need not be described further.
  • the positive pulse When the positive pulse arrives immediately thereafter it causes current to flow through 8 charging the condenser 8H3 to a definite potential, this potential being equal to the positive pulse plus that of the amplitude M at tm minus a constant bias potential determined by battery M0.
  • the grid of triode 820 is held at this potential minus a bias potential due to 82I until another pulse is applied at tm+1.
  • the output of the amplifier tube 820 appears as a voltage across the resistance 825 and controls the operation of a conventional balanced modulator of any suitable form. As here shown it involves two varistors v1 and 02. Associated with this balanced modulator is also a source of local oscillations II of frequency in large compared to the pulse frequencies present in thesystem.
  • the local oscillator II may be of any one of the suitable forms well known in the art yielding a substantially sinusoidal output of reasonably constant frequency.
  • Homodyne detector IV Associated with the output of the pentode 835 is the transformer 90I which connects to two homodyne detectors IVA and IVB in a manner now to be described.
  • the primaries of two transformers 903 and 904 are connected in series and transfer the modulated carrier of frequency in to the input of amplifying tubes 905 and 900, the amplitude of this carrier being determined by the amplitude of the signal sample.
  • a bridge circuit from the mid-point of 90I to the common point of 903 and 904 includes certain elements described below.
  • the output of tubes 905 and 906 through transformers 901 and 908 is supplied to the two similar balanced demodulators IVA and IVB.
  • These demodulators may take on any of the wellknown forms. Here they are shown as each including a pair of varistors and being supplied with a carrier of frequency fo from the local oscillator through transformer 909. As a result, there will appear across the output resistors 9H and 9I2 a potential difference of pulse frequency,
  • ' purpose comprises a circuit connected from the mid-point of the secondary of 9! to the common point of the primaries of transformers 903 and 904. Included in this branch is the secondary of a transformer-9
  • resistor R is connected to an intermediate point of the secondary 9i 8, this point being so selected that when the conductance G (9 i 6) is at'its .mlnimum value'the drop over R will be equal and .oppoSite to the electromotive force across the upper portion of M8. 'Thus the potential difference between fand g is equal to zero when thee conductance-G is at minimum. 'As noted here- "tofore; thetransformersfillll and 9l1an'd associated tubes supplyinr-f'them are designed to act as very low'impedance sources. If, also, the
  • This potential difference-andits direction is indi- 3 -catedat anyone instant by e and by the downward pointing arrow.
  • theconductance is increased so that e takes onadefinite value then, for the'directions indicated, it will be apparent'thatthe current flowingthrough the primary of "903' will be reduced and that through 904 will'be increased. Accordingly, the potential at '70 will become less positive with respect to the point I and the poten- -tial at in will become more negative with respect "to Z. If the polarity of'the signal sample should 'reversewthen the. polaritiesacross 9H and 9
  • control circuits C1 tion of negative polarity The operation of 'the amplitude measuringfeaturewill be described below.
  • Conductance III *In' Fig. 9 there'areshown a plurality of con- Cm, and conductance Cn,-'one for eachdigit in the-amplitude code. These 'conductances-taken in parallel, in whatever combination desired, constitute the conductance G symbolically repre- -sented at 9l6. Three such units are shown but inasmuch as their action is identically-the same except for timing and conductance value, it is necessary to describe 'only one 'of these identified bythe-b1ock III which includes the first conductance G1 of the-series and its controlling unit/C1.
  • the conductance circuit is essentially a' shunt 'feedback amplifier.
  • 'It includes the resistances R1 and R'i connected in" series the intermediate point being connected-t0 the three-stage amplifier-including the tubes*94
  • the control circuit 01 comprises a plurality of diodes -'95l, 952, 953 and-associated elements.
  • polarity and amplitude detector V for testing or measuring the amplitude will be better understood by reference to Fig. 9A. If the potential difference e is equal to zero, corresponding to G at minimum, the potential It would be positive with respect to Z by say Vi;
  • V negative by the same amount Vz so that the point q on resistor 93l would be at the potential of Z.
  • the limiting diodes 932 and 933 will not allow the potential of m to fall lower than a designated value V2, or the potential of k to rise above an equal value V1 and the potential of q will still be the same as the potential of the point Z, say V0.
  • V'2 When G1 is introduced the potential V'2 would tend to become lower but is still limited to V2. also tends to become lower and is still limited to V1.
  • troduced is such that e exceeds signal voltage, then the conductance is first introduced and is then removed by the negative pulse at q. It will be noted that if the polarity of the signal at 9M reverses then the polarity of k and m also reverse. In this case the voltage 6 will reduce the current in 904 instead of 903, thus reducing the potential of m. The potential of It tends to become more negative but is limited. When the cross-over point is passed the potential of 111. goes negative and q drops to the same negative value The potential V1 as in the first instance. Thus, q goes negative for excess value of e for either polarity.
  • pulses modulated on a suitable carrier will have been transmitted from VII bearing the information to the remote station on what conductances are being introduced.
  • the amplitude of each of the pulses so transmitted from VII will be the same and each element of the signal is purely an oil? and on matter. Since only integers are sent such a signal can be repeated indefinitely without adding distortion or noise to the recovered intelligence, even though distortion and noise below a certain threshold level may be present in the repeaters. Thus, even for very high quality transmission the requirements on the repeater units are low. This makes possible transmission over long paths with many repeaters.
  • the presence or introduction of noise in the transmission path from VII to the remote receiving station will be of no influence so long as the noise thus introduced is relatively small compared to the amplitude of the signal being transmitted over the path. Such noise, therefore, would not appear in the signal later reproduced.
  • G1 may be of a value such that the voltage e takes on a value of 64 units of potential difference
  • G2 of such a value as to introduce 32 units and so for the succeeding ones as indicated on column 5 of the specification. If two or more conductors are introduced the value of e will be equal to the sum of the effects of these conductances taken individually and thus the total value of 6 can be made equal to the sample voltage
  • Fig. 5 exclusive of the polarity pulse, a five-unit code is to be used on a binary system. If, for illustration, the sample amplitude is slightly over 22 units on the scale of 32, as shown at the left of Fig. 5, then G1 is such a conductance that its introduction by the pulse over channel I results in a change in voltage e of 16 units. This is less than the sample Voltage and therefore G1 remains in and an off pulse is transmitted to the distance station.
  • the positive pulse over channel 2 now introduces G2 which adds another eight units to the voltage e giving a total of twenty-four conductance units and a total of twenty-four voltage units.
  • Thepulse overchannel ,4 nowintroduces G4 building 6 up .to twenty-two units.
  • :FigHQA can be adjusted to as small :a valueas .desired, this-being controlled mainly by the bias- -.ing.batteries of the diode limiters 932 and 933. In general, it should be adjusted to be appreciably less than that corresponding to the voltage-developedby the smallest change Gain .con- .ductance, as this voltage appears at IE0? or 908 .after amplifications.
  • Transmitter unit VII During this procedure therehas been arriving attransforiner 856 a seriesof pulses over channel T,.one for each pulse'from the pulse generator, .timed as indicated on the bottom'line of Fig. 4. These pulses may be used to. operate ona grid of .the tube 855. In addition,'there arrives at'the transformer 852 certain pulses, one "for each on pulse, relating to polarity or indicating that oneof .the conductances has been introduced and then .removed. No pulse will come to 'the'transformer .852 if a conductance has been introduced'but'inot removed, this corresponding to anoif signal.
  • the secondary of the transformer 852 may operate on a second grid of tube '855 and this tube :in turn controls the transmission or absence of transmission over a suitable medium to a remote station.
  • Fig. 8 it is shown .as controlling a transmitting terminal unit'BBll for a radiochannel on a suitable carrier including carriers having wavelengths in the microwave region wherethe Waves have quasioptical properties of propagation.
  • a suitable carrier including carriers having wavelengths in the microwave region wherethe Waves have quasioptical properties of propagation.
  • it is to be 'understood'that .thepulses coming from the tube 855 may go'directly'to'any suitable transmission path such as apairof wires, "In such cases .it is.not necessary and may not be desirable to use the pulses for modulating a carrier.
  • connection of the transformers 850 and .852 are such that apulse arriving at 850 alone will not cause the transmission of a signal but the simultaneous presence of a pulse on 850 and on 852 would be effective in causing such transmission and would correspond to an on signal.
  • the 'T channel may be omitted, including the chain of tubes H124 to (029 of Fig. '10 and the transformer 850. In this case also the adjustment of the transformer 852 and tube 855 .is such that a pulse on 852 will then be sufficient to cause transmission.
  • Receiver A lo v .of the low-pass filter
  • the pulse generator applies .a P vi-pulseto aphase shifter IX. If thereis an ofi s signal or no signal .pulse the phase shifter isset ...to shift phase 180 degrees; .if an on signal the phase shifter is .set .to .shift phase .zero degrees. The phase shifter remains in this position until zreceiving another -P ,pulse.
  • a pulse from the pulse generator enables the local oscillator X.
  • This .acts as a constant voltage source of desired frequency sending cur- ;rent through G1 Ga .and resistance R and .to lthehom0dynedetector XI.
  • R. is made small compared to (G1+Gz+ Gn) From the voltage .drop across Rthere is produced an output pulse from the homodyne detector XI nearly proportional to .the amplitude of M at tm.
  • a reset pulse mayfollow the pulse to oscillator X.
  • a receiving unit 106 here indicated as a -radio .receiVer associated with a suitable receivzingantenna H05.
  • This code pulse message .is amplified to any necessary extent as illustrated by the tubes H08 and .ljllllland the output of 3
  • I09 is shown as going to a plurality of control devices C1 Cn, one associated with each of a plurality of conductances G1 G11, in a manner hereinafter to described.
  • Receiver pulse generator VIII A derived path from the output of H08 passes through suit-able amplifiers as shown at III2 and III4 and an output pulse therefrom is used to control a relaxation oscillator shown in Fig. 13.
  • This relaxation oscillator centering about the gas tube I3II1, may be simpliar in every respect to the relaxation oscillator at the transmitting station and shown in detail in Fig. 10.
  • the adjustment of the parameters in the relaxation oscillator of Fig. 13, however, is such that the circuit does not normally oscillate but is triggered off by a pulse arriving from tube III4.
  • this relaxation oscillator is so adjusted that the circuit will be triggered ofi by the first pulse in a group (correspording to the M pulse at the transmitter) after which the cscillator cannot be triggered oil until the arrival of the next M pulse.
  • a timestick I3I6 from which a series of pulses may be derived with a time spacing as nearly identical as may be necessar to the time spacing of the pulses derived from the timestick at the transmitting station.
  • This timestick has an additional section given rise to a pulse indicated by n and delayed only slightly behind the previous pulse.
  • the function of the pulse 12 will be given hereinafter.
  • the timestick is terminated with a suitable impedance I318 to suppress reflection.
  • a series of tubes I325 to I329 from which a series of positive pulses derived from cathode followers is initiated corresponding to the pulses from the timestick.
  • Receiver conductances XIII The utilization of the various pulses to control the setting up of a series of conductances G Go corresponding to those set up at the transmitting station will now be described.
  • Fig. 12 shows a plurality of conductances G1 Gn which may be identical with those at the transmitting station or may be proportional to them.
  • G1 Gn which may be identical with those at the transmitting station or may be proportional to them.
  • three such circuits are shown but inasmuch as their action is identically the same expect for timing, it is necessary to describe only one of these identified by the block XIII including the first conductance G1 of the series and its controlling circuit.
  • the conductance circuit is again essentially a shunt feedback amplifier. It includes the resistances R1 and R'i connected in series, the intermediate point being connected to the threestage amplifier including the tubes I261, I242, I 243 with resistance capacitance coupling. there being a feedback connection from the plate of the last tube I243 through condenser I244 to the grid of I24I. There is either zero or a large gain around the loop depending on whether the 18 control voltage applied to terminals a and b cuts off one or more tubes in the loop or allows them to operate. In this instance, as in Fig. 9, the loop is held open by a sufiiciently high negative bias on the grid of tube I242.
  • G1 is essentially or more diodes or combination of diodes and triodes or multigrid tubes in a variety of ways as will be clear to those skilled in the art. Specifically, in Fig. 12 it is shown as a combination of a diode with a triode.
  • the receiving station is provided with a local oscillator X shown in Fig. 11 as I I20. This may, but need not, be of the same frequency as the local oscillator II at the transmitting station. In other words, no synchronism between the two oscillators is required.
  • Phase shifter IX is shown as comprising two triodes I22I and I222 the grid circuits of which are supplied in parallel from the local oscillator H20 through the transformer I223.
  • the output circuit comprises transformer I224, the midpoint of the primary of which is connected to the positive terminal of the plate battery.
  • the grid circuit of tube I22I contains the condenser I225 and the grid circuit of tube I222 includes the battery I226 which tends to give a positive bias to the grid. Normally, therefore, the transconductance of tube I222 will be higher than that of I22I and there will be an alternating current of local oscillator frequency in the secondary of I224. The phase of the current in the secondary current may, however, be reversed by means of the phase shifter.
  • diodes I23l and I232 biased so that normally they are non-conducting.
  • a pulse from the tube I326 corresponding to P pulse arrives at transformer I232 it is so poled as to render diode I23I conducting, giving a positive charge to condenser I225 of such magnitude as to give tube I22! a higher transconductance than I222, whereupon the current in the secondary of I224 is reversed in phase.
  • This reversal occurs if the pulse code at the transmitter was an off" signal, meaning an absence of a received pulse.
  • the condenser I225 is so connected as to retain its charge for the duration of one complete cycle.
  • the M pulse from tube I325 operates through transformer I236 to make diode I232 conducting, whereupon the condenser I225 is discharged or reset to normal condition.
  • the secondary of transformer I224 is connected in series with a resistance I2I6 corresponding to R of Fig. 2. In series with this also is the combination of conductances G1 Gn. Resistance I2I6 is small compared to the resistance of the conductances taken in parallel. Also the tubes I22I and I222 should appear as a low impedance source by any suitable means, such as using tubes of low impedance, or by use of a cathode follower circuit or by a step-down transformer. In this case the current in and the voltage across I2I6 'will be proportional to the conductances which have been introduced and, therefore, proportional to the sample current or voltage at the transmitter.
  • the homodyne detector XI comprises a. balanced demodulator including varistors I2 and I2 I2 connected in a standard bridge circuit.
  • the demodulator is supplied directly with local oscillator frequency through transformer I2I3 and also with the same frequency through transformer I2I4.
  • the primary of transformer I2I4 is included in the plate circuit of triode I2I5, the grid circuit of which includes the resistance I2I6.
  • the detected current of pulse frequency appearing across resistance I2II will be proportional to the current in I2 I4 and therefore proportional to the amplitude of the complex wave sample.
  • it polarity will be determined through the phase shifter IX to correspond with the polarity of the complexwave sample at the transmitter.
  • Fig. 12 shows a specific arrangement for control of the conductances, which control comprises the diode I25I and the triode I251.
  • control comprises the diode I25I and the triode I251.
  • Fig. 14 shows a modification of this control circuit in which the triode is replaced by a second diode I253.
  • the resetting pulse coming in over the transformer I252 will discharge the condenser I254 as before.
  • a pulse from the pulse generator coming over transformer I256 is so poled as to render diode I253 conducting if that is the only pulse arriving.
  • the local oscillator at the receiving station may be on all the time instead of being triggered on occasionally, for even if left on it is ineffective at the terminal apparatus unless and until the tube I2I8 has been enabled by the pulse coming from n. Still further it will be evident that the modulation and demodulation features of the transmitter station may be omitted, the sample signals out of tube 82B going directly to the input of tube 835 and directly from tube 901 to the resistor 90?, or its equivalent, without the intermediation of the demodulator in the homodyne unit IV. This would mean also the omission of the oscillator II. Corresponding alterations could be made at the receiving station in connection with its local oscillator. In general, however, such omissions or simplifications would lead to sacrifice in operation or quality and it would be a matter of engineering judgment as to how far one may carry out such simplifications.
  • This invention is related to my inventions dcscrlbed and claimed in my copending applications Ser. No. 592,961, filed May 10, 1945, and Ser. No. 603,989, filed July 9, 1945. It is the .more closely related to the latter application and difiers from it in that whereas in the system of that application conductances are added in parallel across the load circuit of pentode 835 until the residual voltage available across the conductances in parallel becomes less than a certain small reference level, in this application the introduction of conductances in parallel builds up a voltage 6 which is compared with and made equal to the signal voltage. Also in that system, the sum of the conductances G1 G1: in the low conductance position or state should be small compared with the smallest conductance step. In the present disclosure this restriction is not necessary because in that state the voltage e across R is balanced by the voltage in the upper portion of 9 l8 and I find that certain advantages accrue thereby.
  • apparatus for obtaining samples of the instantaneous amplitude of the complex wave comprises means for synthesizing a reference voltage by successively smaller and smaller steps, apparatus for comparing the synthesized voltage and the sample, and means for controlling the signaling condition of each of said pulses by said comparing means.
  • a transmitting station comprising means for sampling a signal Wave periodically and storing on a condenser a potential proportional to the sample amplitude, an amplifier tube the input of which is connected across the storage condenser, a network in the load circuit of said tube including two similar detectors connected to receive the tube output in series, and means for increasing the current in one de-- tector and decreasing the current in the other in proportion to the sample amplitude.
  • a transmitting station comprising means for sampling a signal wave periodically and storing on a condenser a potential proportional to the sample amplitude, means for impressing a voltage proportional to the condenser potential on a network comprising a pair of balanced impedances, and a circuit associated with the network and connected to a local source of current and adapted to unbalance the impedances, the voltage in said associated circuit being made proportional to the sample amplitude and serving to reduce the current in one impedance to zero.
  • a transmitting station comprising means for intermittently sampling a signal wave periodically and developing a potential difierence proportional to each sample amplitude, a source of local oscillations, at modula tor controlled by the local oscillator and the sample voltage to yield a modulated wave of local oscillator frequency, a network comprising a pair of balanced detectors and connected to receive the modulated Wave, and a circuit associated with the network and connected to the source of local oscillations and adapted to unbalance the detectors, the voltage in said associated circuit being made proportional to the sample amplitude and serving to reduce the current in one detector to zero.
  • the means for the step-by-step adjustment comprises a plurality of conductances connected in parallel and each normally possessing a minimum conductance but adapted to be brought to a larger preassigned conductance, and means for compensating the initial minimum conductance whereby the added conductance is proportional to the sample.
  • a system for transmitting information on the shape of a signal wave comprising a transmitting station and a receiving station the transmitting station comprising a circuit for periodically sampling the amplitude of the wave and for deriving a carrier frequency wave proportional to the said sample amplitude, a pulse gen erator giving rise to a plurality of cycles of pulses, one cycle for each sample, one pulse in the cycle detecting the polarity of the sample, a controllable conductance to be introduced in series with a source of voltage and a resistor, the current through the resistor being substantially proportional to the conductance, a plurality of the pulses in the cycle operating in coordination with the sample amplitude to introduce conductances 23 step by step from larger to smaller steps on an additive basis until the voltage drop across the resistor is equal to the sample amplitude.
  • a system for transmitting information on the shape of the signal Wave from a transillitter to a receiver station comprising a circuit for periodically sampling the amplitude of the wave, a current source adapted to deliver a current proportional to the sample amplitude and constant for the duration of the sampling interval, a circuit for transferring the said current to a polarity and amplitude detecting circuit, a plurality of n conductances adapted to be connected in parallel with each other and in series with a resistor and a current source, a control circuit for each conductance, and a pulse generator to generate cycles of pulses, one pulse in the cycle serving as a marker pulse and as timing the sampling of the signal Wave, another serving as a polarity pulse to cooperate in testing the polarity of the sample amplitude, the remaining pulses operating successively through the control circuits of the conductances in cooperation with the voltage drop over the resistor to introduce one or more conductance steps until the resistor drop is equal to the sample amplitude within an arbitrary small value.
  • a combination of claim characterized by means to compensate for the resistor drop due to the conductances when in their minimum conductance state.
  • a network including a pair of balanced detectors in series with the voltage source, a branch circuit supplied with current from an independent source of the same frequency as said unknown alternating current voltage, the voltage due thereto in an impedance tending to unbalance the detectors in a direction depending on the polarity of the source to be measured, means for adjusting the current through said impedance until the voltage across it is equal to the unknown voltage, indicated by the reduction of the currentin one detector to zero.
  • the means for adjusting the current comprises a plurality of conductances adapted to be connected in parallel in such amount as to be itself proportional to the unknown voltage.
  • a pair of balanced homodyne detectors in series with the voltage source, a branch, circuit supplied with current from a source of the same frequency as said unknown voltage and of constant voltage, the voltage'due to said current in a resistor tending to unbalance the detectors in a direction depending on the polarity of the source to be measured and to yield rectified voltage of unequal value in the homodyne detectors; means for ad.- justing the current through said resistor until the voltage across it is equal to the unknown voltage, indicated by the reduction of the output of one homodyne detector to zero.

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Control Of Amplification And Gain Control (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Arrangements For Transmission Of Measured Signals (AREA)
US603990A 1945-07-09 1945-07-09 Pulse code modulation communication system Expired - Lifetime US2464607A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
NL77660D NL77660C (xx) 1945-07-09
BE473323D BE473323A (xx) 1945-07-09
US603990A US2464607A (en) 1945-07-09 1945-07-09 Pulse code modulation communication system
GB11874/47A GB630095A (en) 1945-07-09 1947-05-02 Improvements in or relating to signalling systems
CH287037D CH287037A (fr) 1945-07-09 1947-05-19 Installation de communication servant à la transmission d'une onde complexe.
FR946925D FR946925A (fr) 1945-07-09 1947-05-19 Système de communication
DEP28894A DE892605C (de) 1945-07-09 1948-12-31 Elektrisches UEbertragungssystem fuer nichtsinusfoermige Schwingungen mittels Impulskodemodulation

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US603990A US2464607A (en) 1945-07-09 1945-07-09 Pulse code modulation communication system

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US2464607A true US2464607A (en) 1949-03-15

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US (1) US2464607A (xx)
BE (1) BE473323A (xx)
CH (1) CH287037A (xx)
DE (1) DE892605C (xx)
FR (1) FR946925A (xx)
GB (1) GB630095A (xx)
NL (1) NL77660C (xx)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2541932A (en) * 1948-05-19 1951-02-13 Bell Telephone Labor Inc Multiplex speech interpolation system
US2586825A (en) * 1948-01-16 1952-02-26 Int Standard Electric Corp Signal compression and expansion arrangements in electric communication systems
US2592308A (en) * 1948-09-01 1952-04-08 Bell Telephone Labor Inc Nonlinear pulse code modulation system
US2592061A (en) * 1948-03-25 1952-04-08 Oxford Alan John Henry Communication system employing pulse code modulation
US2603714A (en) * 1948-09-01 1952-07-15 Bell Telephone Labor Inc Percentage time division multiplex for pulse code modulation
US2610295A (en) * 1947-10-30 1952-09-09 Bell Telephone Labor Inc Pulse code modulation communication system
US2629857A (en) * 1946-08-10 1953-02-24 Int Standard Electric Corp Communication system utilizing constant amplitude pulses of opposite polarities
US2640105A (en) * 1947-10-10 1953-05-26 Bell Telephone Labor Inc Wave transmission system and method for synthesizing a given electrical characteristic
DE892605C (de) * 1945-07-09 1953-10-08 Western Electric Co Elektrisches UEbertragungssystem fuer nichtsinusfoermige Schwingungen mittels Impulskodemodulation
US2662113A (en) * 1948-10-04 1953-12-08 Hartford Nat Bank & Trust Co Pulse-code modulation communication system
US2662118A (en) * 1948-05-22 1953-12-08 Hartford Nat Bank & Trust Co Pulse modulation system for transmitting the change in the applied wave-form
US2710397A (en) * 1950-06-24 1955-06-07 George E Foster Electrical measuring apparatus
US2841649A (en) * 1950-09-22 1958-07-01 Thomson Houston Comp Francaise Pulse code modulation system

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Publication number Priority date Publication date Assignee Title
US1928093A (en) * 1927-04-11 1933-09-26 Harold B Coyle Signaling system
US2262838A (en) * 1937-11-19 1941-11-18 Int Standard Electric Corp Electric signaling system
US2266401A (en) * 1937-06-18 1941-12-16 Int Standard Electric Corp Signaling system
US2272070A (en) * 1938-10-03 1942-02-03 Int Standard Electric Corp Electric signaling system
US2352634A (en) * 1938-07-18 1944-07-04 Maury I Hull Signaling system
US2415329A (en) * 1944-11-06 1947-02-04 Arndt Oscar Center drill

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Publication number Priority date Publication date Assignee Title
BE473323A (xx) * 1945-07-09 1900-01-01
US2508622A (en) * 1945-07-09 1950-05-23 Bell Telephone Labor Inc Pulse code modulation communication system

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1928093A (en) * 1927-04-11 1933-09-26 Harold B Coyle Signaling system
US2266401A (en) * 1937-06-18 1941-12-16 Int Standard Electric Corp Signaling system
US2262838A (en) * 1937-11-19 1941-11-18 Int Standard Electric Corp Electric signaling system
US2352634A (en) * 1938-07-18 1944-07-04 Maury I Hull Signaling system
US2272070A (en) * 1938-10-03 1942-02-03 Int Standard Electric Corp Electric signaling system
US2415329A (en) * 1944-11-06 1947-02-04 Arndt Oscar Center drill

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE892605C (de) * 1945-07-09 1953-10-08 Western Electric Co Elektrisches UEbertragungssystem fuer nichtsinusfoermige Schwingungen mittels Impulskodemodulation
US2629857A (en) * 1946-08-10 1953-02-24 Int Standard Electric Corp Communication system utilizing constant amplitude pulses of opposite polarities
US2640105A (en) * 1947-10-10 1953-05-26 Bell Telephone Labor Inc Wave transmission system and method for synthesizing a given electrical characteristic
US2610295A (en) * 1947-10-30 1952-09-09 Bell Telephone Labor Inc Pulse code modulation communication system
US2586825A (en) * 1948-01-16 1952-02-26 Int Standard Electric Corp Signal compression and expansion arrangements in electric communication systems
US2592061A (en) * 1948-03-25 1952-04-08 Oxford Alan John Henry Communication system employing pulse code modulation
US2541932A (en) * 1948-05-19 1951-02-13 Bell Telephone Labor Inc Multiplex speech interpolation system
US2662118A (en) * 1948-05-22 1953-12-08 Hartford Nat Bank & Trust Co Pulse modulation system for transmitting the change in the applied wave-form
US2603714A (en) * 1948-09-01 1952-07-15 Bell Telephone Labor Inc Percentage time division multiplex for pulse code modulation
US2592308A (en) * 1948-09-01 1952-04-08 Bell Telephone Labor Inc Nonlinear pulse code modulation system
US2662113A (en) * 1948-10-04 1953-12-08 Hartford Nat Bank & Trust Co Pulse-code modulation communication system
US2710397A (en) * 1950-06-24 1955-06-07 George E Foster Electrical measuring apparatus
US2841649A (en) * 1950-09-22 1958-07-01 Thomson Houston Comp Francaise Pulse code modulation system

Also Published As

Publication number Publication date
DE892605C (de) 1953-10-08
BE473323A (xx) 1900-01-01
FR946925A (fr) 1949-06-17
NL77660C (xx) 1900-01-01
GB630095A (en) 1949-10-05
CH287037A (fr) 1952-11-15

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