US2500536A - Pulse-time demodulator - Google Patents

Description

March 14, 1950 HQ GOLDBERG 2,500,536

PULSE-TIME DEMODULATOR Filed Feb. 27, 1947 D HAROLD GOLDBERG Patented Mar. l4, 1950 PULSE-TIME DEMO DULATOR Harold Goldberg, Towson, Md, assignor to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application February 27, 1947, Serial No. 731,197

' modulators.

6 Claims.

' 1 This invention is directed to pulse-time de- More specifically it is directed to an arrangement for detecting the intelligence transmitted on a pulse-time modulated carrier.

In the reception of pulse-time modulated signals of the type having a pulse of width and a spacing representin successive solutions of the equation f(t)+V-Ee- =-K,' difficulty has arisen in attempting to produce a distortionlcss scheme.

It is an object of this invention to provide a pulse-time demodulator for Waves of the character described without the introduction of distortion products in the output signal.

In the drawing:

Fig. 1 is a schematic diagram of a circuit embodying the invention; and,

Fig. 2 is a graph comprising a family of related curves illustrating voltage conditions existing at various points in the circuit of Fig. 1 during the operation thereof.

Referring now to the drawing, there is illustrated a source 10 of positive pulse signals coupled to the control electrode II of a vacuum tube I2 through a condenser 13. The electrode 1! is connected to the grounded cathode 14 through a resistor l5 and a bias battery 16. The battery is so poled as to maintain the tube l2 in a non conducting state between pulses of the source Ill. The anode ll of the tube 12 is connected through a resistor I8 to a source of positive voltage indicated +B, to the control electrode 19 of a tube 29, and through a condenser 2| to ground. The anode 22 of the tube is directly connected to a source of positive voltage +3. The cathode 23 of the tube 20 is connected to ground through a parallel circuit comprising a condenser 24 and a resistor 25. Circuit connections are provided from the cathode 23 to the cathode 26 of a tube 21 and to the anode 28 of a tube 29. The anode 30 of the tube 21 and the cathode 3| of the tube 29 are connected together, and thence to the control electrode 32 of a tube 33. The cathode 34 of the tube 33 is connected to ground through a resistor 35 and the control electrode 32 thereof is connected to ground through a condenser 36. A pair of terminals 31 are operatively associated with the ends of the resistor 35.

The control electrodes 38 and 39 of the tubes 21 and 29, respectively, are tied together, and, thence, through a resistor 40 to the source 10 of pulse signals.

In considering the operation of the above-dcscribed arrangement the state of afiairs immedicombination of 24 and 25 and D shows the voltage at the terminals 3?. By way of example, consider the conditions existing at the end of pulse 50. The condenser 25, which discharged through the anode-cathode circuit of the tube l2 during ately after the end of a pulse, of length a, from the pulse, is being charged exponentially from the source +B, through the resistor E8, to a relatively high positive potential as indicated at 63. Due

to the positive voltage on its control electrode, the.

cathode follower tube 2!] is conductive, and the voltage across the parallel circuit 24, 25 is rising, as shown at 1B, and following, by cathode-follower action, the voltage across the condenser 2!.

The tubes 21 and 29, which comprise a bidirectional switch are non-conductive, and the voltage across the condenser 36, and consequently the voltage across the output terminals 31, is held at a relatively constant value, as illustrated at 80. This constant value is approximately equal to the voltage which was present across the condenser 24 at the instant of the start of the pre vious input pulse, as will be explained hereinbelow.

At the instant of a pulse from the source it the tube l2 becomes conductive and the condenser 2! discharges through the anode-cathode path thereof as indicated at El. Due to the comparatively large time constant of the parallel circuit comprising the condenser 24 and the resistor 25 the voltage across the condenser 24 decreases comparatively slowly as shown at 11, and, as it starts to decrease, the bi-directional switch comprising the tubes 21 and 29 becomes conductive due to the positive pulse applied to the control electrodes 38 and 39. The point at which this occurs is indicated at 12 on curve C. At this juncture the condenser 36 is effectively connected in parallel with the condenser 24 and assumes a voltage across its terminals equal to the voltage across condenser 24. The large time constant of the combination 24, 25 and the resulting decreased slope of the line 1| permits more accurate regulation of the voltage level applied to the condenser 36. By cathode follower action'this voltage appears at the-output terminals and constitutes the output signal. At the conclusion of the pulse from the source I 0 the bi-directional switch opens and the voltage at the output terminals 3 remains substantially constant until the next pulse.

It will be seen, therefore, that the signal at the output terminals comprises a step function which is a close approximation to the original modulation, and depends solely on the spacing between the input pulses. The train of pulses shown in 1 curve A of Fig. 2 are modulated by an abrupt change in their repetition period which follows pulse 52. Thismodulation is accurately recovered in the amplitude excursions of the voltage,

across terminals 3? as indicated in the curve D.

It win be noted that the decrease of repetition period following the pulse 52 is reflected in the curve D by the abrupt voltage drop. at 8| to the new level 82 corresponding to the reduction in period. In order to properly demodulate. pulses having aspacing which represents successive solutions of the equation f(t)+VEe =:+KI

it is necessary that the time constant of the resistor l8 and the condenser 21 be equal to the value of RC which is involved in those solutions.

tion of said pulse period; means operating on said Wave form to decrease the slope of the trailing edges of said excursions; an energy storage circuit; and means clamping said energy storagecircuit to said slope changing means during each of said pulses.

'3. In combination, a source of energy pulses modulated in repetition period; a saw tooth wave 1 generator excited by said pulses; means operat- 1 ing on the output of said generator to decrease the slope of the trailing edges of the saw tooth excursions thereof; an energy storage circuit; and

p means actuated by said pulses to momentarily connect said energy storage means to said Slpe changing means during each of said pulses.

4. In combination, a source of energy pulses modulated in repetition period; means generating a saw tooth wave form, the amplitude of the excursions of which is a function of the modulation of said pulse period; means operating on said wave form to decrease the slope of the trailing edges of said excursions; an energy storage circuit; and means actuated by said pulses to momentarily connect said energy storage circuit to said slope changing means during each of said pulses.

5. In combination, a source of energy pulses modulated in repetition period; means generating a saw tooth wave form, the amplitude of th excursions of which is a function of the modulat tion of said pulse period; means operating on said wave form to decrease the slope of the trailing edges of said excursions; an energy storage circuit; means connecting said energy storage circuit to said slope changing means, said connecting means including an electronic switch, said switch normally interrupting said connecting means; and means applying said pulses to said switch, whereby said connecting means is momentarily completed during each of. said pulses,

- 6. In combination, a condenser; a charging; cirflcuit for said condenser including a source of unidirectional energy and an impedance; a discharge circuit for said condenser including the space discharge path of a normally non-conducting electron tube; a source of energy pulses modulated in repetition period; means impressing said Pulses upon said tube to render it conductive during each of said pulses; a cathode follower circuit including an electron discharge tube having an anode, a

cathode and a control grid; means impressing the voltage across said condenser upon said control grid; a condenser and an impedance connected in parallel in the circuit of said cathode, the time constant of said parallel combination being greater than that of the first. mentioned condenser and its discharge circuit; an energy storage circuit; and means clamping said energy storage circuit to said parallel combination during each of said pulses. I

HAROLD GOLDBERG.

REFERENCES clean The following references are of record in the file of this patent:

warren STATES. PATENTS,

. Number Name. Date,

2,275,930. Torcheux Mar. 10, 1942 2,335,265. Dodington Nov. 30, 1943 2,413,023 Young Dec. 24, 19.46

. 2,416,286 Busignies Feb. 25, 1947 2,436,890 l-Iiginbotham Mar; 2, 1943 Disclaimer 2,500,536.Har0ld Goldberg, Towspn, Md. PULSE-TIME DEMODULATOR. Patent dated Mar. 14, 1950. Dlsclaimer filed June 19, 1950, by the assignee, Bendix Aviation Corporation.

Hereby enters this disclaimer to claim 1 of said patent.

[Ofiicial Gazette July 25, 1950]

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