US2188970A

US2188970A - Electric timing system

Info

Publication number: US2188970A
Application number: US226875A
Authority: US
Inventors: John C Wilson
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1938-08-26
Filing date: 1938-08-26
Publication date: 1940-02-06
Anticipated expiration: 1957-02-06
Also published as: GB531712A; FR859499A

Description

Feb. 6, 1940. J, c, wlL N 2,188,970

ELECTRIC TIMING SYSTEM Filed Aug. 26, 1938 2 Sheets-Sheet 1 j FlG.la.

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INVENTOR ATTORNEY L 0 c, 0 T- F162.

Feb. 6, 1940. J w|| 50N 2,188,970

ELECTRIC TIMING SYSTEM wuuuuumnnnannn INVENTOR JEN 0. WILSON 2 B ATTORNEY Patented Feb. 6, 1940 2,188,970

UNITED STATESPATENT OFFICE ELECTRIC TIMING SYSTEM John C. Wilson, Baydde, N. Y., asslgnor to Hazeltinc Corporation, a corporation of Delaware Application sum as. 193s. Serial No. 220.815

10 Claims. (01. 11,-)

This invention relates generally to electrical The way of accomplishing this is to provide a timing systems and more particularly to timing relaxation oscillator including a vacuum tube systems of special utility in television signalcomprising an electrode to which is applied the translating apparatus. control wave and which is unafiected by unde- It is frequently desirable to time an event in sired pulses. The frequency of relaxation oscllan electrical circuit by means of an electrical lators utilized in such prior art timing arrangepulse and to time a second event a predeterments is, in general, controlled by the time conmined interval after the first pulse. Such timstant of a resistance-reactance circuit. Resisting systems are particularly useful in modulatedance is an unstable electrical parameter because carrier television-signal transmitters, certain of it depends mainly upon materials and operating 10 the timing pulses forming component parts oi conditions. The previous difllculties with relaxa the transmitted signal. In such transmitters, it tion oscillators have resided in an inability to is customary to generate high-frequency waves secure an accurately predetermined period and which are stabilized with respect to the source at the same time maintain the oscillator suscepti- 1 of alternating current at the transmitter and to bio of stable synchronization by control pulses. 1o derive therefrom submultiple-frequency waves to It is an object of the present invention. therebe used for various timing operations necessary to fore, to provide an electrical timing system not generate and transmit the composite television subject to the above-mentioned disadvantages. signal. For example, in developing and trans- It is a further object of the invention to provide so mitting a television signal involving double-ina timing arrangement for deriving from a pre- 0 terlaced scanning and 441 lines per second, it determined control pulse a second pulse having is customary to develop a high-frequency wave, an accurately predetermined time delay with refor example, 26,460 cycles, which is stabilized spect to the first pulse. with respect to a source of 60 cycle power sup- It is still another object of the invention to plying the transmitter. From this high-freprovide an electrical timing arrangement lot quency wave a submultiple-frequency wave 01' deriving from a predetermined timing pulse a 13,230 cycles is developed and utilized to prosecond timing pulse of either polarity with reduce line-frequency synchronizing pulses for the spect to the first timing pulse and which has transmitted signal. By a further series of suban accurately predetermined time delay with reso divisions, a 60 cycle wave is developed and utilized spect to the first pulse. to provide field-frequency synchronizing pulses It is a still further object of the invention to for the transmitted signal. provide an electrical timing circuit, the timing A high degree of accuracy is essential in esof which depends only on the reactive constants tablishing the frequencies oi the dlilerent wave of the circuit. generators which go to make up the timing chain In accordance with the invention, an electrical of the system just described. For this reason it timing system for deriving from a predetermined has been customary to develop the waves in the timing pulse a second timing pulse having a premanner described above rather than to generate determined time delay with respect to the first waves of increasingly higher frequencies from timing pulse comprises a confluent wave filter the low-frequency source supplying the transhaving a band-pass which includes the principal 40 mitter. frequencies of the first timing pulse, the filter However, in subdividing a generated high-frehaving a mismatched termination at its remote quency wave to derive the waves of lower ireend so that there is procured a reflection oi the quency, it is difilcult to secure generators or freinmzt pulse from the remote end of the filter. quency dividers for each of the steps which are The filter is designed to have an approximately 45 not subject to some inaccuracy. If a particular uniform time delay over the pass band equal to wave generator of lower frequency is to produce one-half of the required time delay of the second pulses of a frequency of impulse. The input end of the filter is terminated 1 in its image impedance so that there is no rea flection therefrom. A reflected pulse may, there- 5 fore, be derived from the input terminals of the times that of a higher frequency control wave, filter a predetermined time after the timing or it is customary to provide a control circuit for the first pulse has been applied to the input tergenerator which is responsive to pulses in the minals.

control wave which are separated by 11-1 pulses. In accordance with a preferred embodiment of the invention, the filter is coupled at the mismatched termination to an impedance much greater than its proper matching value, for example, it may be open-clrcuited. in which case the reflected pulse appears at the input terminals with the same polarity as that of the first timing pulse. In accordance with another embodiment of the invention, the filter is terminated in an impedance much less than its normal matching value, for example, it may be short-circulted, in which case the second pulse appears at the input terminals of the filter with opposite polarity to the first timing pulse applied to the terminals.

The novel features which are believed to be characteristic of this invention are set forth with particularity in the appended claims, the invention itself, however, both as to its organization and method of operation, together with other and further objects thereoL-will best be understood by reference to the iollowing description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Reference is made to the drawings in which Fig. 1 isacircultdiagramoia timingfilter oftheinvention; Figs. 1a and 1b are graphs illustrating certain of the operating characteristics oi the circuit oi Fig. 1; Fig. 2 is a circuit diagram 01' the filter of another embodiment oi the invention; Figs. 2c and 2b illustrate certain operating characteristics oi the circultotFig. 2; Fig. 3lsacircuit diagram of a timing filter oi the invention utilized for deriving a broad timing impulse; Fig. 3a illustrates certain of the operating characteristics of the circuit of Fig. 3: Fig. 4 illustrates the method by which the timirm signals of a standardised television signal may be synthesized, utilizing timing circuits in accordance with the invention; while Fig. 5 illustrates the manner in which the circuit of the invention may be utilised in a television receiving system as a synchronislug-signal separator.

Referring now more specifically to Fig. 1, there is shown a low-pass filter comprising input terminals II to which is coupled an impedance-match ing m-derived half section including a series arm comprising an inductance L1 and a shunt arm comprising a series-connected inductance La and condenser C2, a series of constant-k whole sections individually comprising series inductance arms'ls and shunt condenser arms Cs, and a midshunt element The filter of Fig. 1 is terminated at the input terminals ill by an impedance shown as a resistance R which approximately matches the input image impedance of the filter over the pass band, while the filter is open-circuited at the remote end; that is which is that 01' .the impedance-matching m-derived section including series arm Li. and shunt arm Ls. Cs, at the terminals H remote from input terminals it, the filter has a mismatched the principal frequencies of the timing impulse of Fig. la and that the timing impulse is applied to the terminals ll. Due to the fact that there is an improper termination or mismatching at the end of the filter remote from terminals i0, an electrical impulse which is the image of the applied impulse is reflected from the terminals II and appears, after a predetermined delay, across the input terminals It. The time delay of the filter is made one-hall oi the desired time delay and the filter is terminated at the input terminals III in its image impedance It so that there is no further reflection of the echo or reflected impulse. These characteristics are illustrated by the graph oi! Fig. lb in which a represents the first timing pulse initiating at time in and 1) represents the second timing pulse which appears across terminals it at time n, that is, with a predetermined time delay At with respect to the initial impulse a.

I! it is desired to derive from a first impulse a second impulse of opposite polarity to that of the first impulse, the circuit of Fig. 2 is utilized. The filter of Fig. 2 is generally similar to that of Fig. 1

and similar circuit elements have been given identical reference numerals. The circuit of Fig. 2 diil'ers from that of Fig. 1 only in that the filter is short-circulted at the terminals ll instead or being open-circulted, as in the case of the filter oi the circuit of Fig. 1.

The operation of the circuit of Fig. 2 is generally simflar to the operation oi the filter oi the circuit of Fig. 1 except that the second derived timing pulse, present at the input terminals It at time t1, is of opposite polarity to that of the first timing pulse applied at to as indicated in Figs. 2a and 2b.

A broad pulse may be derived from the pulse a shown in Figs. 1a or 2a having a duration At, by utilizing the characteristic of the circuit of Fig. 2 together with a suitable integrating arrangement. One circuit for deriving such a broad pulse is shown in Fig. 3, wherein the filter coupled to the input terminals III is in all respects similar to that 01' Fig. 2. Coupled to the terminals in through a transformer I2 is a wave generator comprising a condenser II and circuits for charging and discharging condenser it from a suitable source such as battery ll, the charging and discharging circuits being responsive to the timing pulses derived from the filter. The charging circuit for condenser it comprises a vacuum tube I! having its input electrodes connected across a portion of the secondary winding of transformer l2 and its output electrodes connected in series with condenser l3 and battery H. The discharging circuit oi condenser It comprises a second vacuum tube It having its input electrodes coupled across a portion of the secondary winding of transformer I2 and its output electrodes connected to short circuit condenser II. The control circuit of Fig. 3 comprising transformer II is designed so that the filter Ii is terminated substantially in its image impedance at terminals Ill.

In considering the operation of the circuit of Fig. 3, it will be assumed that a timing impulse oi the form a of Fig. 2a is applied to the input terminals it. It will thus be seen that a reflected wave having the characteristics of impulse b of Fig. 2b may be derived from input terminals Ill after the predetermined interval At. Tube II is so biased that it becomes conductive only when impulse a is applied to its grid and charges condenser II which remains charged until such time as tube It becomes conductive to discharge the condenser. Tube II is rendered conductive by the negative pulsebofllsdbwhich is appliedto its grid with reversed or positive polarity by transformer II.

An output voltage pulse may, therefore, be derived from condenser II which has the wave form shown in Fig. 3a.

It will be understood that each of the filters is terminated at terminals III in its image impedence R which may be comprised in whole or in part in the circuit constants of the external circuits coupled to the terminals Ill.

The circuits oi the invention are particularly useful in deriving a wave of the form or the proposed standardized synchronizing wave for television-signal transmitters. This wave form is completely described in an article entitled R. M. A. Completes Television Standards" in the July, 1938 issue of "Electronics at pages 28 and 29. A portion of the proposed standardized wave form is shown in curve A of Fig. 4. This wave comprises line-scanning synchronizing pulses s, equalizing pulses e of half the width of synchronizing pulses a, and broad field-scanning synchronizing pulses 12 combined in a manner described in the above-mentioned article. A wave oi the type shown in curve A of Fig. 4 may be derived by means or synthetic pulses developed in accordance with the principles described in the preceding portion of the specification. In order to produce such a wave, there are developed pulses of a constant period and duration, as shown in curve B, which are of the width of the equalizing pulses e of composite wave A and which are spaced by the interval between line-synchronizing pulses in the desired wave A. Certain of the pulses of wave B are selected for reflection, as shown by curve C, in the manner described above for obtaining a positive reflected impulse (see Fig. 1), the period of delay being exactly equal to the pulse width. Certain oi the other pulses are selected for reflection as shown in curve D, the period of delay being one-half the horizontal scanning period; that is, one-half the spacing of the pulses of curve B. Certain of the pulses of curve B are selected and combined with certain of the pulses of curve D as shown by curve E and are then inversely reflected (see Fig. 2) with a delay of about four-tenths of the horizontal synchronizing period, thereby producing the wave shown by curve F. By integrating the waves of curves E and F in the manner described with reference to Fig. 3 above, the group of broad field-synchronizing impulses shown by curve G is obtained. By combining the wave forms 01 curves B, C, D and G, and limiting in a suitable and known manner, the proposed standardized wave form A may be built up.

The timing circuits of the invention may be utilized for separation of synchronizing signals in a similar manner. Thus, the line-synchronizing signals may be separated from the field-synchronizing signals by the following procedure: In apparatus for performing this function it is desirable to obtain a precisely timed impulse suitable for field synchronizing and at the same time to utilize all of the regular pulses to maintain line synchronization. This may be accomplished by reflecting the whole complex synchronizing wave to delay the wave by a predetermined amount to the undelayed complex wave, so determining the delay period that the line-synchronizing and equalizing pulses fall between each other but the field-synchronizing pulses, or parts thereof, fall on top of their counterparts. The double amplitude of the resultant field-synchronizing pulses provides a precisely timed impulse for field synchronization. The characteristics obtained by such procedure are illustrated by the curves oi Fig. 5 wherein curve H represents the undelayed complex wave, curve I illustrates the delay complex wave, and curve J illustrates the resultant of the two waves H and I. It is thus seen that the complex timing wave H may be used in the normal manner to maintain horizontal synchronization and that a timing impulse of increased amplitude of curve J may be utilized to eflect field synchronization.

While there has been described what is at present considered to be the preferred embodimnt of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An electrical timing system for deriving from a given timing pulse a second timing pulsehaving a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a mismatched termination remote from said terminals and having an approximately uniform time delay between said terminals and said termination over said pass band equal to a predetermined fraction of said predetermined time delay, an output circuit coupled to said filter for deriving said second pulse, and an impedance-matching filter section terminating said filter at the end opposite said mismatched termination and approximately matching the image impedance of said filter with said output circuit over said pass band.

2. An electrical timing system for deriving from i a given timing pulse a second timing pulse of the same polarity having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a termination remote from said terminals oi an impedance appreciably greater than its image impedance at such termination and having an approximately uniform time delay between said terminals and said termination over said pass band equal to a predetermined fraction of said uniform time delay, an output circuit coupled to said filter for deriving said second pulse, and an impedancematching filter section terminating said filter at the end opposite said termination and approximately matching the image impedance 01' said filter with said output circuit over the pass band 01' said filter.

3. An electrical timing system for deriving from a given timing pulse a second timing pulse of the same polarity having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having an open-circuited termination remote from said terminals and having approximately uniform time delay between said terminals and said termination over said pass band equal to a predetermined fraction of said predetermined time delay, an output circuit coupled to said filter for deriving said second pulse, and an impedance-matching filter section terminating said filter at the end opposite said open-circuited termination and approximately lll iii

matching the image impedance of said filter with said output circuit over said pass band.

4. An electrical timing system for deriving from a given timing pulse a second timing pulse of opposite polarity having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a termination remote from said terminals coupled to an impedance appreciably less than its image impedance at such termination and having an approximately uniform time delay between said terminals'and said termination over said pass band equal to a predetermined fraction of said predetermined time delay, and an output circuit coupled to said filter for deriving said second pulse, said filter being terminated at the end opposite said termination in an impedance approximately matching its image impedance over said pass band.

5. An electrical timing system for deriving from a given timing pulse a second timing pulse of opposite polarity having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a termination remote from said terminals which is shortcircuited and having an approximately uniform time delay between said terminals and said termination over said pass band equal to a predetermined fraction of said predetermined time delay, and an output circuit coupled to said filter for deriving said second pulse, said filter being terminated at the end remote from said shortcircuited termination in an impedance approximately matching its image impedance over said pass band.

6. An electrical timing system for deriving from a given timing pulse a second timing pulse having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, a resistance termination for said filter, a matching filter section for said filter coupled to said filter at one end and having an impedance approximately matching the image impedance of said filter to said resistor over said pass band, said filter having a mismatched termination at the other end and having an approximately uniform time delay between said terminals and said other end over said pass band equal to a predetermined fraction of said predetermined time delay, and an output circuit coupled to said filter for deriving said second pulse.

7. An electrical timing system for deriving from a given timing pulse a second timing pulse having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said pulse, a resistance termination for said filter at one end, said filter comprising an m-derived section coupled to said resistance termination and matching the impedance of said filter with said termination over said pass band, said filter having a mismatched termination at its other end remote from said terminals and having an approximately uniform time delay over said pass hand between said terminals and said other end equal to a predetermined iraction of said predetermined time delay. and an output circuit coupled to said filter for deriving said second pulse.

8. An electrical timing system for deriving from a mven timing pulse a second timing pulse of opposite polarity having a predetermined time delay with respect to said first pulse comprising, a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a termination remote from said terminals coupled to an impedance'appreciably less than its image impedance at such termination and having an approximately uniform time delay between said terminals and said termination over said pass band equal to a predetermined fraction of said predetermined time delay, an output circuit coupled to said filter for deriving said second pulse, and means coupled to said filter for deriving a broad pulse from said two pulses of opposite polarity, said filter being terminated at the end opposite said termination in an impedance approximately matching its image impedance over said pass band.

9. An electrical timing system for deriving from a given timing pulse a second timing pulse of opposite polarity having a predetermined time delay with respect to said first pulse comprising,

a wave filter having input terminals and having a pass band including the principal frequencies of said first pulse, said filter having a termination remote from said terminals coupled to an impedance apreciably less than its image impedance at said termination over said pass band and having an approximately uniform time delay between said terminals and said termination oversaid pass band equal to a predetermined fraction of said predetermined time delay, an output circuit coupled. to said filter for deriving said second pulse, and pulse-generating means coupled to said filter comprising capacitance means, means for charging said capacitance means in response to one of said timing pulses and for discharging said capacitance means in response to the other of said timing pulses, said filter being terminated at the end remote from said termination in an impedance approximately matching its image impedance over said pass band.

10. An electrical timing system for deriving from a given timing pulse a second timing pulse of opposite polarity having a predetermined time delay with respect to said first pulse comprising. a wave filter having input terminals and having a pass band including the principal frequencies of said first timing pulse, said filter having a termination remote from said terminals coupled to an impedance appreciably less than its image impedance at said termination over said pass band and having an approximately imiform time delay between said terminals and said termination over said pass band equal to one-half said predetermined time delay, an output circuit coupled to said filter for deriving said second pulse, pulse generating means coupled to said filter including capacitance means, means comprising a vacuum tube responsive to one of said pulses for charging said capacitance means, and means comprising a vacuum tube responsive to the other of said pulses for discharging said capacitance means, said filter being terminated at the end remote from said termination in an impedance approximately matching its image impedance over said pass band.

JOHN 0. WILSON.

CERTIFICATE OF CORRECTION. Patent No. 2,188,970. February 6, 19b0,

JOHN C. WILSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, second column, line 1, for "The way" read The usual way; page 2, first column, lines 62, 65 and 6h, strike out "which is that of the impedance-matching m-derived section including series arm L and shunt arm L C and insert the same in line 60, after "band" and before the comma; and that the said Letters Patent should be read with this correction therein that the same may conform. to the record of the case in the Patent Office Signed and sealed this 9th day of April A. D. 191.10.

Henry Van Arsdele,

(Seal) Acting Commissioner of Patents