US2421025A - Demodulator system - Google Patents

Demodulator system Download PDF

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Publication number
US2421025A
US2421025A US547124A US54712444A US2421025A US 2421025 A US2421025 A US 2421025A US 547124 A US547124 A US 547124A US 54712444 A US54712444 A US 54712444A US 2421025 A US2421025 A US 2421025A
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US
United States
Prior art keywords
pulse
pulses
width
undulations
amplitude
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
US547124A
Other languages
English (en)
Inventor
Donald D Grieg
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.)
STC PLC
Federal Telephone and Radio Corp
Original Assignee
Standard Telephone and Cables PLC
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
Priority to BE474952D priority Critical patent/BE474952A/xx
Application filed by Standard Telephone and Cables PLC filed Critical Standard Telephone and Cables PLC
Priority to US547122A priority patent/US2444437A/en
Priority to US547124A priority patent/US2421025A/en
Priority to GB13867/45A priority patent/GB601128A/en
Priority to GB19333/45A priority patent/GB601135A/en
Application granted granted Critical
Publication of US2421025A publication Critical patent/US2421025A/en
Priority to FR951329D priority patent/FR951329A/fr
Priority to FR57636D priority patent/FR57636E/fr
Priority to FR57637D priority patent/FR57637E/fr
Priority to ES0179746A priority patent/ES179746A1/es
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B14/00—Transmission systems not characterised by the medium used for transmission
    • H04B14/02—Transmission systems not characterised by the medium used for transmission characterised by the use of pulse modulation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K7/00—Modulating pulses with a continuously-variable modulating signal
    • H03K7/08—Duration or width modulation ; Duty cycle modulation
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K9/00—Demodulating pulses which have been modulated with a continuously-variable signal
    • H03K9/08—Demodulating pulses which have been modulated with a continuously-variable signal of duration- or width-mudulated pulses or of duty-cycle modulated pulses

Definitions

  • This invention relates to radio impulse systems and more particularly to a system for demodulating pulses, which vary in width in accordance with signal modulation, by translating them into amplitude modulated pulses.
  • an object of the present invention to provide a novel and improved method and means for demodulating pulses which vary in their width in accordance with the instantaneous amplitude of a modulating signal.
  • the pulses are then applied to a pulse width demodulator consisting of a tuned L-C circuit, a damper and a clipper stage, so arranged that only the second undulation is passed when the tuned circuit is shock-excited to produce an oscillatory wave by an externally applied pulse.
  • a maximum amplitude in the wave output is obtained when the incoming pulse width corresponds to the tuned frequency of the damped L-C circuit.
  • a variation of the pulses from this value will produce an output wave of constant period but with a variation in amplitude which is proportional to the change in pulse width.
  • the series of Width modulated pulses of constant amplitude will be transformed into a corresponding series of pulses of constant width but modulated in amplitude.
  • the frequency components corresponding to the pulse sub-carrier may be removed and the audio modulating signal obtained.
  • the absolute audio output is independent of the magnitude of the pulse width change, and is dependent only on the tuning adjustment of the pulse width demodulator, making it possible to utilize more efiiciently the transmitted power by using narrow pulses without reducing the level of the received signal.
  • the width demodulator of this invention will respond only to changes in pulse width and will not be aifected by any changes in pulse frequencies, frequency instability therefore being tolerated without the introduction of noise. This feature may be taken advantage of by a simultaneous pulse frequency modulation or pulse time modulation as a form of an additional communicating channel.
  • the present demodulator may be adjusted so that 0 sponse is obtained for pulses differing appreciably in width (either smaller or larger) from the wanted pulses, and thus, noise produced by such unwanted pulses may likewise be reduced.
  • Fig. 1 is a schematic wiring diagram of the pulse width demodulator system in accordance with my invention.
  • Pig. 2 is a set of curves useful in explaining the operation of the demodulator.
  • a width modulated pulse train as received over a wire or radio frequency transmission link is applied to a control grid I of a limiter tube 2.
  • the pulse are shaped to substantially the same amplitude. This is desirable not only for improving the signal-to-noise ratio by removing the amplitude variations due to the noise, but also for accurate demodulation.
  • the anode output of tube 2 is made to pass pulse energy of constant amplitude.
  • the output pulse energy from the tube 2 is applied through a resistor 3 to a shock-excitable L-C circuit 4.
  • the condenser C of the circuit is preferably adjustable so that it may be tuned to a wave length or a harmonic thereof, which corresponds to the maximum pulse width to which it is anticipated that the pulse will be modulated.
  • the inductance coil shown may also be made adjustable either in place of an adjustment for the condenser C or together with an adjustable condenser, whichever may be desired.
  • a vacuum tube 5 Connected across the tunable circuit 4 is a vacuum tube 5, the cathode 6 of which is connected to the input side 1 of the circuit 4, while the anode 8 is connected to the opposite side 9 of the circuit.
  • the side 9 is also connected to a source of potential 3+ to provide a suitable positive bias for an anode connection It) for the clipper tube 2.
  • the energy output from the anode connection I is applied to a grid ll of the tube so as to block the conduction between the cathode 6 and the anode 8, while pulse energy is applied to the circuit 4.
  • the pulse output of the tube 2, combined with the undulations generated in circuit 4, is taken off through a connection l2 for application to a threshold clipping amplifier stage 13 of known characteristics.
  • the negative bias on grid M of the clipper I3 is obtained over a bias resistor l5.
  • the output from the clipper stage I3, as obtainable across a load resistor I6, is then applied to a low-pass filter i! from which the audio modulation may be had for use in a reproducing type of apparatus, as represented by the phones 18.
  • Fig. 1 The operation of the system of Fig. 1 will be better understood by reference to Fig. 2, where curve it represents pulse input energy 2i as applied to the grid I of the limiter tube 2.
  • the pulseenergy is represented by a train of pulses varying in width in accordance with the instantaneous amplitude variations of a sinusoidal modulating signal. These width modulated pulses may be obtained coming from a transmitting source, as hereinbefore indicated, to the detector of a radio frequency receiver or directly over a wire line or other known type of transmission line.
  • is limit clipped-to a level 19 and applied to the tuned circuit 4 with negative polarity as indicated at 22, for shockexciting a. damped sinuosoidal type of wave train.
  • the grid H of tube 5 is arranged to receive a negative voltage for the duration of each pulse, and the anode and cathode of the tube are so connected across the circuit that when the polarity of the oscillating current is in one direction it blocks conduction by the tube and when in the opposite direction it unblocks the tube.
  • the system operates to suppress oscillations by becoming conductive when the voltage across the circuit has the right polarity and when the voltage of the applied pulse becomes zero.
  • the circuit 4 instead of tuning the circuit 4 to the frequency, the period of which is twice the duration of the modulated pulse at its maximum whole, but rather to a harmonic thereof which corresponds to the period of themaximum change in pulse width, the eifect illustrated in curves 9, h and i will be achieved.
  • the maximum change in pulse width substantially indicates the period of the harmonic frequency to which the circuit 4 is tuned.
  • the leading edge 27 of the negative pulse of curve 9 shock-excites an oscillatory undulation 2-8 which, in the case illustrated, achieves a negative maximum three times within the period of the pulse.
  • the trailing edge of the pulse occurs at 29 or 36, the negative voltage due to the pulse at this point ceases to act on the grid 4 l of the damper tube 5, and at the same time an oscillation in the positive direction is set up, as represented by the undulations 3
  • These undulations 3! and 32 are proportional in their amplitude to the degree of modulation between zero and maximum modulation from a given normal pulse width. They are more or less in phase with the last undulation due to the leading edge 21 and therefore cause relatively smaller or larger resultant undulations following the trailing edges.
  • Curves f and 2' show the type ofundulations obtained after those have been eliminated by clipper tube l3 at the level 33 01135 (curves ,f and h), which occur during the pulse, and which, because of their combination withthgfhegatWe pulse voltage are negatively biased by" the amount of this pulse voltage.
  • the amplitude -of'these remaining undulations is indicative of the fwidth of the modulated pulses, as desired.
  • the clipping level is chosen at such a value as to just eliminate any positive value undulations due to pulse values having zero or minimum modulation as indicated by trailing edges and 29, respectively.
  • the undulation 2% set up by the leading edge 23, tends to revert to zero. Since, however, this return to zero begins at some point on the curved portion of the undulation, that is, starts from a relatively considerable value, the parameters of the circuit are able to intervene to introduce an element of time, causing a somewhat gradual return to zero, as indicated at 36 and 3'! (curve e).
  • curve b is shown the type of pulse train output obtainable from th clipper 13, while curve 0 illustrates the audio output of the low pass filter I! which is effective in eliminating the high frequency pulse carrier components.
  • the amplitude modulated audio signal of curve 0 thus'represents a translation of the width modulated pulse train of curve a.
  • a demodulator system having a resonant circuit the method of demodulating a pulse train the pulses of which are modulated in width in accordance with a given signal, comprising shock exciting said resonant circuit to produce periodic undulations by means of the leading and trailing edges of the pulses of said pulse train, damping out all undulations but those occurring during the duration of each of said pulses and one undulation following the trailing edge thereof so that undulations produced by one pulse will not affect the undulations produced by the next pulse, and threshold clipping said undulations at a level corresponding to the amplitude of said one undulation for-at least one limit of pulse width modulation.
  • a resonant circuit for demodulating a pulse train the pulses of which are modulated in width in accordance with a given signal
  • the steps including shock exciting periodic undulations by means of the leading and trailing edges of the pulses of said pulse train in said resonant circuit tuned to a harmonic of a frequency having a period which is at least twice the maximum Width modulation of any of the said pulses of said train and the half cycle period of Which is of the order of the maximum change in pulse width due to modulation, damping out all undulations but those occurring during the duration of each of said pulses and one undulation following the trailing edge thereof so that undulations produced by one pulse will not affect the undulations produced by the next pulse, and threshold clipping said undulations at a level corresponding to the amplitude of said one undulation for the minimum modulated width of the pulses to eliminate all except those undulations following each pulse which are greater in amplitude than said threshold clipping level.
  • a resonant circuit for demodulating a positive type pulse train the pulses of which are modulated in width in accordance with a given audio signal, tuning said resonant circuit to a frequency having a period proportional to the maximum modulate-d pulse width, inverting in phase the pulses of said train, using said phase inverted pulses to shock excite by means of the leading and trailing edges thereof oscillatory undulations for each pulse in said tuned circuit, each undulation having a constant width and an amplitude varying as the variation in the width of the modulated pulse 7 ca-using the undulation', damping out all undulations but those occurring during each pulse and onefollowing the pulse, using said phase inverted pulses to bias said oscillatory undulations for the duration of the pulses, whereby said undulations following the pulses are rendered distinctive, and segregating said following undulations for demodulation thereof.
  • a resonant circuit for demodulating a pulse train the pulses of which are modulated in width in accordance with a given signal, the steps including shock exciting periodic undulations by means of the leading and trailing edges of the pulses of said pulse train in said resonant circuit tuned to a frequency proportionate in its period to the maximum modulated Width of the pulses of said train, damping out all undulations but those occurring during the duration of each of said pulses and one undulation following the trailing edge thereof so that undulations produced by one pulse will not affect the undulations produced by the next pulse, threshold clipping said undulations at a level corresponding to the amplitude of said one undulation for the minimum modulated width of the pulses to eliminate all except those undulations following each pulse which are greater in amplitude than said threshold clipping level, and eliminating by filtering out the high frequency components of the resultant of said clipping, whereby an amplitude modulated wave corresponding to the original signal is obtained.
  • a system for demodulating a train of pulse energy the pulses of which are modulated in Width in accordance with a given audio type signal comprising a resonant circuit tuned to a frequency proportionate in its period to the maximum modulated pulse width, means to app y said train of pulses to said circuit for shock excitation therein by the leading and trailing edges of said pulses of oscillatory undulations, means for damping out all undulations but those occurring during the duration of any of said pulses and one following the trailing edge of each of said pulses, means for controlling the operation of said last named means by means of energy of said pulses, means for combining the energy of said pulses with the energy of said undulations whereby any undulations occurring during a pulse are biased with respect to their zero axis for the duration of each pulse, and said undulation following each pulse is rendered distinctive, and means for clipping said following undulations at a level which will eliminate all said biased undulations and all said following undulations except those having an amplitude corresponding to

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Electrotherapy Devices (AREA)
  • Particle Accelerators (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Channel Selection Circuits, Automatic Tuning Circuits (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)
  • Manipulation Of Pulses (AREA)
  • Transmission Systems Not Characterized By The Medium Used For Transmission (AREA)
  • Amplifiers (AREA)
US547124A 1944-07-29 1944-07-29 Demodulator system Expired - Lifetime US2421025A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
BE474952D BE474952A (enrdf_load_stackoverflow) 1944-07-29
US547122A US2444437A (en) 1944-07-29 1944-07-29 Modulating system
US547124A US2421025A (en) 1944-07-29 1944-07-29 Demodulator system
GB13867/45A GB601128A (en) 1944-07-29 1945-06-01 Improvements in or relating to arrangements for demodulating duration modulated pulses
GB19333/45A GB601135A (en) 1944-07-29 1945-07-27 Electric pulse modulating systems
FR951329D FR951329A (fr) 1944-07-29 1947-08-06 Systèmes de communication pour impulsions électriques
FR57636D FR57636E (fr) 1944-07-29 1947-08-06 Systèmes de communication par impulsions électriques
FR57637D FR57637E (fr) 1944-07-29 1947-08-06 Systèmes de communication par impulsions électriques
ES0179746A ES179746A1 (es) 1944-07-29 1947-09-16 Mejoras introducidas en sistemas de moduladores

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US547124A US2421025A (en) 1944-07-29 1944-07-29 Demodulator system

Publications (1)

Publication Number Publication Date
US2421025A true US2421025A (en) 1947-05-27

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Application Number Title Priority Date Filing Date
US547124A Expired - Lifetime US2421025A (en) 1944-07-29 1944-07-29 Demodulator system

Country Status (5)

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US (1) US2421025A (enrdf_load_stackoverflow)
BE (1) BE474952A (enrdf_load_stackoverflow)
ES (1) ES179746A1 (enrdf_load_stackoverflow)
FR (3) FR951329A (enrdf_load_stackoverflow)
GB (2) GB601128A (enrdf_load_stackoverflow)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2462100A (en) * 1946-04-18 1949-02-22 Fed Telecomm Lab Inc Demodulator system for time modulated pulses
US2507176A (en) * 1945-03-15 1950-05-09 Hartford Nat Bank & Trust Co Receiver for pulse modulated waves
US2529172A (en) * 1948-12-30 1950-11-07 Gen Electric Pulse discriminating circuits
US2532338A (en) * 1945-11-15 1950-12-05 Columbia Broadcasting Syst Inc Pulse communication system
US2570236A (en) * 1945-04-28 1951-10-09 Conrad H Hoeppner Discriminator circuit
US2605409A (en) * 1946-03-27 1952-07-29 Forbes Gordon Donald Pulse narrowing circuit
US2702853A (en) * 1950-02-08 1955-02-22 Gen Electric Wave shaping circuits
US2822470A (en) * 1953-11-04 1958-02-04 Gen Electric Co Ltd Circuits for controlling the peak amplitude of electric current pulses
US3067291A (en) * 1956-11-30 1962-12-04 Itt Pulse communication system
US4521736A (en) * 1979-05-09 1985-06-04 Ampex Corporation Demodulator for pulse width modulated signals

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2113214A (en) * 1936-10-29 1938-04-05 Rca Corp Method of frequency or phase modulation
US2181309A (en) * 1935-04-09 1939-11-28 Telefunken Gmbh Electrical impulse segregation circuit
US2266401A (en) * 1937-06-18 1941-12-16 Int Standard Electric Corp Signaling system
US2359447A (en) * 1942-06-20 1944-10-03 Rca Corp Electrical circuit
US2391776A (en) * 1943-05-29 1945-12-25 Rca Corp Intelligence transmission system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2181309A (en) * 1935-04-09 1939-11-28 Telefunken Gmbh Electrical impulse segregation circuit
US2113214A (en) * 1936-10-29 1938-04-05 Rca Corp Method of frequency or phase modulation
US2266401A (en) * 1937-06-18 1941-12-16 Int Standard Electric Corp Signaling system
US2359447A (en) * 1942-06-20 1944-10-03 Rca Corp Electrical circuit
US2391776A (en) * 1943-05-29 1945-12-25 Rca Corp Intelligence transmission system

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2507176A (en) * 1945-03-15 1950-05-09 Hartford Nat Bank & Trust Co Receiver for pulse modulated waves
US2570236A (en) * 1945-04-28 1951-10-09 Conrad H Hoeppner Discriminator circuit
US2532338A (en) * 1945-11-15 1950-12-05 Columbia Broadcasting Syst Inc Pulse communication system
US2605409A (en) * 1946-03-27 1952-07-29 Forbes Gordon Donald Pulse narrowing circuit
US2462100A (en) * 1946-04-18 1949-02-22 Fed Telecomm Lab Inc Demodulator system for time modulated pulses
US2529172A (en) * 1948-12-30 1950-11-07 Gen Electric Pulse discriminating circuits
US2702853A (en) * 1950-02-08 1955-02-22 Gen Electric Wave shaping circuits
US2822470A (en) * 1953-11-04 1958-02-04 Gen Electric Co Ltd Circuits for controlling the peak amplitude of electric current pulses
US3067291A (en) * 1956-11-30 1962-12-04 Itt Pulse communication system
US4521736A (en) * 1979-05-09 1985-06-04 Ampex Corporation Demodulator for pulse width modulated signals

Also Published As

Publication number Publication date
GB601128A (en) 1948-04-28
ES179746A1 (es) 1947-11-01
FR57637E (fr) 1953-03-17
GB601135A (en) 1948-04-28
FR951329A (fr) 1949-10-29
FR57636E (fr) 1953-03-17
BE474952A (enrdf_load_stackoverflow)

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