US2052183A - Television apparatus - Google Patents

Television apparatus Download PDF

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US2052183A
US2052183A US747068A US74706834A US2052183A US 2052183 A US2052183 A US 2052183A US 747068 A US747068 A US 747068A US 74706834 A US74706834 A US 74706834A US 2052183 A US2052183 A US 2052183A
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voltage
current
saw
tooth
frequency
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Harold M Lewis
Cawein Madison
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BAE Systems Aerospace Inc
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Hazeltine Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K4/00—Generating pulses having essentially a finite slope or stepped portions
    • H03K4/06—Generating pulses having essentially a finite slope or stepped portions having triangular shape
    • H03K4/08—Generating pulses having essentially a finite slope or stepped portions having triangular shape having sawtooth shape
    • H03K4/10—Generating pulses having essentially a finite slope or stepped portions having triangular shape having sawtooth shape using as active elements vacuum tubes only

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  • Douglaston, asset. N. Y., assignors to Hazel and Madison object of this invention is to produce current or I saw-tooth wave form through inductance to provide the field for magnetic control of scanning in a cathode ray television receiver.
  • Another object of this invention is to provide circuits and apparatus for generating the saw-tooth and related wave forms in a precisely controllable and economical manner for use in television.
  • Another object of the invention is to generate voltage and current wave forms related to the sawtooth wave forms which will serve to govern or control the generation of voltage or current of saw-tooth form.
  • Figs. la-ld inclusive illustrate as applied to a cathode-ray tube, the manner in which voltages and currents of saw-tooth and related wave forms are employed to effect scanning in a television receiver.
  • Fig. 2 is a schematic diagram of a cathode-ray television receiver to illustrate the essential units required for receiving, scanning and controlling a television image.
  • Figs. Zia-3e inclusive graphically depict a socalled derivative series of wave forms of which the saw-tooth form is one, to illustrate the voltage and current relationships relative to pure reactances, such as inductance and capacity shown diagrammatically in Figs. 3) and 30 respectively.
  • Figs. 4a, b and c are graphs employed to explain the correct use oi the saw-tooth wave forms when used for scanning the lines in a television picture.
  • Figs. 50-5) inclusive are graphs similar to those of Fig. 4, illustrative of the use of the sawtooth wave form for scanning at picture frequency.
  • Figs. fie-6g inclusive are a series of fundamental circuits pertaining to the generation of voltages and currents of saw-tooth and related wave forms.
  • Figs. "la and b and Figs. 8a and b, are diagrams of the wave forms of current and voltage 5 resulting from operation of certain of the Figs. 6a to 69 circuits.
  • Figs. 9a, b and c, and Figs. 100, b and c are graphs illustrating the use of combined sawtooth and impulse wave form for scanning in tele- 10 Vision.
  • Figs. 11a, b and c are graphs illustrating wave forms suitable for causing current of saw-tooth wave form to flow in an impedance.
  • Figs. 12-20 inclusive show various types of 15 oscillator circuits employing series resistance and capacity for generating saw-tooth and related wave forms.
  • Figs. 21a, b and c illustrate circuits for causing current of saw-tooth wave form. to flow in go inductance.
  • Figs. 22 and 23 are circuit diagrams illustrating the association of television frequency amplifiers and synchronizing circuits with saw-tooth form generators. 25
  • the present application is one of a series of related copendi'ng applications to the same inventors, which in aggregate, describe a complete television transmitting and receiving system employing saw-tooth and related wave forms for line and picture scanning.
  • a complete television transmitting and receiving system employing saw-tooth and related wave forms for line and picture scanning.
  • the transmitting portion of the system utilizing substantially sawtooth scanning for generating the image or vision as frequencies and also synchronizing impulses for controlling the scanning action or the receiving apparatus.
  • the present application is directed more specifically to the generation and synchronized control in the receiving apparatus of the 40 saw-tooth line and picture scanning impulses.
  • a television modulated carrier wave having such essential components as those described in the above mentioned copending application, or its equivalent, is to be received to provide the vision frequency signals and control impulses referred to in this application for reproducing the image at the receiver.
  • the present application therefore, is restricted to just so much of the descriptions of the 00- pending application as is requisite to an understanding pf the novel aspects of this app ication.
  • A represents the luminescent-screen end of a cathode-ray tube K, upon which the scanning traces are indicated as they would appear in their ideal form when no signal is being received and applied to modulate the grid of tube K to control the intensity of the electron beam striking the screen.
  • This ideal trace is of saw-tooth wave form in that each line is a linear trace from left to right (indicated by heavy line m to represent a constant value of illumination of the screen) and a rapid (practically zero time) retrace from right to left (indicated by a light line n) since practically no electrons strike the screen in this brief retrace interval and the illumination is therefore weak.
  • the succession or rate at which the lines are traced is shown to be linear with time from top to bottom of the screen since the lines m and n are evenly spaced for the 20 lines shown and the retrace p, q from bottom to top of the picture is shown to be rapid in that it occurs in the time required for two lines to be traced; and hence these two lines appear oppositely sloped in the picture retrace.
  • the linefrequency m, n saw-tooth wave form has an almost infinite ratio between time of traceand retrace, and the picture frequency p, q,
  • saw-tooth wave form has a ratio of trace to re-' trace shown as 10 to 1. This manner of scanning the picture from left to right and from top to bottom is termed rectilinear scanning.
  • the number of pictures transmitted per second may be taken as 24, and the line frequency taken as 2880 per second. At least this is a suflicient definition of quality to serve in this application for purposes of describing the inventions.
  • the ratio of picture trace to retrace time is in practice about 40 to 1 (much better than shown in the illustration). Hence, with the line frequency of 2880 per second, there are 117 lines in each picture and three lost in the picture retrace. This ratio has a correspondence dimensionally to the ratio between the height of picture in a standard 35 mm. motion picture film and the Opaque space separatingadjacent picture frames (the film to space ratio being, in fact, about 30 to 1). Hence to scan motion picture film as described in the mentioned copending application Serial No. 747,070, only the time required for three or four lines can be lost in the retrace without losing a. part of the picture height. As for the line frequency, a reasonable trace-to-retrace ratio in practice is about 10 to 1 which is far from the ideal of zero time shown in Fig. 1.
  • the cathode ray may be deflected by magnetic or electro-static fields. Magnetic'deflection is illustrated in Fig. l.
  • the coils Ll, L1 serve to provide the field for the picture frequency scanning while L2, L2 similarly serve to provide the field for line frequency scanning. Since the magnetic field changes proportionally to the current flowing in these coils, the current through L1, L1 must have a saw-tooth wave form recurrent at the picture frequency 1), qv rate, for example 24 per second; and the coils L2, L2 must carry current of saw-tooth wave form at the line frequency m, n rate, such as 2880 per second.
  • a series of wave forms related to the saw-tooth wave form has been plotted and is shown in Figs. 3a to 3e inclusive.
  • This may be termed a derivative series, since any of the wave forms shown is the mathematical derivative of the wave form immediately below it in the series.
  • the utility of this series as it stands relates to pure reactances, since fundamentally the voltage e1, across an inductance, Fig. 3 is the derivative of the current 11. through the inductance, and the current ic through a condenser, Fig. 3g, is the derivative of the voltage ec across the condenser.
  • Fig. 3c is the desired wave form for scanning and is shown as providing a ratio of 10 to 1 in the time of trace to retrace.
  • Fig. 3a. will be referred to as a doubleimpulse; Fig. 3b as an impulse; Fig. 3c as a sawtooth, and Fig. 3d as a parabolic impulse wave form.
  • the form Fig. 3e requires cubic equations to represent it mathematically.
  • the cathode ray tube K employs deflecting plates for electrostatic scanning, wherein P1, P1 are the deflecting plates for the picture frequency and P2, P2 the deflecting plates for the line frequency scanning. Since the deflection of the electron stream is proportional to the voltage between the deflecting plates, the voltage across P1, P1 should be saw-tooth as indicated by the notation 83c and that across plates P2, P2 similarly should be saw-tooth in form as labeled 630.
  • Fig. lc illustrates magnetic deflection, coils L1, for the picture frequency and electrostatic deflection, plates P2, for the line frequency, and hence the voltage required to cause saw-tooth current in L1, L1 is of impulse wave form 63b as indicated, and the voltage across plates P2, P2 is of saw-tooth form 630'
  • the saw-tooth wave is also important in mechanical systems of scanning, which do not use rotating elements but which, nevertheless, must accomplish rectilinear scanning. For example, if a light valve is to be employed to vary the light intensity in accordance with the picture detail and the light is then to be scanned to spread a pattern on a screen similar to the pattern in Fig. 10., then the arrangement of Fig.
  • the cathode ray tube is the source of light as well as the light valve, having in its simplest form a cathode l, a control grid 2, an accelerating apertured anode or plate 3 and fluorescent screen A.
  • the vision frequencies which represent the picture detail are, of course, applied as voltage variations between I and 2 to control the number of electrons which pass through 3 and hence produce light in proportion to their number on striking the fluorescent screen A. No special elements have been indicated here static of magnetic fields as best serves the construction of the particular tube employed.
  • Lens serves to focus the spot of light from A on screen 8 via the mirror surfaces of oscillograph-type vibrator mirrors 6 and 1 which determine the path of the light.
  • Fig. 2 a diagram of the receiver is shown wherein unit blocks serve to indicate broadly the functions of the various receiver parts.
  • the receiver illustrated is of the superheterodyne type in that theincoming carrier wave and sidebands are collected by antenna structure 9, amplified bythe radio frequency amplifier l0, and applied to modulator ll, to gether with heterodyne energy from oscillator l2, to produce an intermediate frequency carrier and sidebands which are amplified by the intermediate frequency amplifier I 3 and applied to detector H.
  • the detector l4 develops the vision frequencies, which represent detail in the picture, and also line and picture frequency impulses, which are to serve for synchronizing the scanning at the receiver with that at the transmitter andto block out illumination of the screen during each line retrace and each picture retrace interval.
  • the proper poling of the output from M as applied to vision frequency amplifier l5 and the proper poling of the output of i5 as applied to the cathode ray tube grid 23 must be observed, so that as the cathode ray traces its pattern on the screen 25, the trace lines will be light or dark in accord with the corresponding line being traced at the transmitter, and the retrace lines will be black.
  • the cathode ray tube is shown as having magnetic control coils L1, L 'for thepicture frequency and electrostatic control plates P2, Pa, for the line frequency as was the case in Fig 1c.
  • the generator unit It! serves to generate and supply saw-tooth voltage (labeled 83c) of line frequency to the deflecting plates P2, P2 and the generator unit 2
  • Unit 19 is, for example, a lowpass filter suitable for passing the picture frequency impulse undistorted in wave form to unit 20 which is the picture impulse amplifier to pass the line impulse to amplifier II which in turn serves to apply the line impulses properly poled and adjusted in amplitude as a control or synchronizing voltage to l8.
  • the transmitter's line trace starts at w which is prior to the cathode ray beam having reached the left edge of the picture so that in effect the left side of the picture is folded under".
  • Other relations giving improper synchronism will be seen to be possible depending upon the relative phase of the synchronizing impulses and the relative ratios of trace to retrace time between the transmitter's scanning and the receivers scanning processes.
  • Fig. 5d indicates that the saw-tooth current from generator 2
  • generator units I8 and 28 of Fig. 2 In that they must supply saw-tooth voltage orcurrent as the case requires having good linearity in the trace, adequate ratio of trace to retrace time, and proper response to synchronizing, control voltages.
  • the units l6 and H for the line control and I9 and 20 for the picture control must fulfill two functions: (a) apply the synchronizing impulse undistorted and in proper amplitude and phase to units I8 and 2!, to effect synchronism; and (b) prevent reactions between these units and the rest of the system.
  • Figs. 6a to 69 a number of fundamental circuits are shown for producing current and voltage wave forms related to the saw-tooth derivative series.
  • the circuits of Figs. 6a, b and c will be termed the R, C, type in that the desired wave form results from the charge and discharge of a condenser through resistance.
  • the circuits of Figs. 6d, e, f, and y, are termed the L/R type in that the wave form results from the flow of current through an inductance as affected by resistance.
  • a pendulum S periodically short circuits 2.
  • S is assumed to be actuated bysome mechanism, as for example the usual clock escapement, so that the frequency of recurring short circuits is here determined by S.
  • the voltage across C relative to ground and the current through C are to a close approximation as shown in Figs. 7a and 7b, respectively.
  • the current through L increases slowly and exponentially during the trace part of the cycle according to the time constant L/r. During the retracethe current falls rapidly and exponentially according to the time constant L/R. It will be noted that during the retrace the part of the circuit which includes E and r can be neglected (i. e., considered as of zero resistance) since R is large compared with r. The error in making this assumption is very small.
  • the voltage across the coil is in this case the mathematical derivative of the current through the inductance and is as shown in Fig. 7b.
  • the exponentiality of retrace in both cases is unimportant but the time of the retrace interval is quite important.
  • the frequency in each case is determined by the periodicity of the pendulum, and the ratio of trace to retrace isobvirously'determined by the ratio of the time that the contact to the pendulum is closed to the time it is open.
  • Fig. 6b the same elements of the R, C type switch W are open, the condenser C is exponencircuit are present with the exception that S in this case is a shorting device which acts to short circuit C through 1' when the voltage across C has reached a predetermined maximum value.
  • S in this case is a shorting device which acts to short circuit C through 1' when the voltage across C has reached a predetermined maximum value.
  • a typical relaxation oscillater is this circuit in which S is a gaseous discharge tube such as a Thyratron.
  • the device 0 is substituted for the pendulum of O of Fig. 6d and is assumed to be a device normally closed or conductive and of zero resistance when closed, until the current through it reaches a predetermined maximum value at which instant it opens to become non-conductive.
  • Fig. 7 representing the current through L
  • Fig. 7b the voltage across L.
  • the frequency can be controlled primarily by changing r or L, or both. The equation for frequency is as given below, and again for a fixed condition of 0, the frequency can be varied without changing the amplitude of output current through L.
  • synchronization is generally eflected in connection withv the controlling of S or 0 as the case may be, as will appear later.
  • the device H replaces R. of the preceding R,C circuits, and in the simple form illustrated is a two-element vacuum tube having the cathode temperature adjusted (adjustment not shown) to give limited electron emission, so that current through the tube is the same throughout a wide range of voltage across it.
  • The; tube is therefore a constant current device and the charging of C through H, during the trace of the saw-tooth voltage cycle is therefore linear with time as desired.
  • Fig. 8a the voltagoacross (whicl'ris also that across C alone plus a direct current component) is as shown in Fig. 8a and the current through C is as shown in Fig. 8b which is the mathematical derivative of Fig. 8a:
  • the condenser C passes no direct current it is immaterial as to whether its lower terminal is connected at point 1 as shown or whether this terminal is connected to ground G or to some intermediate point on the battery E.
  • the action is entirely the same as to the current through C and the alternating voltage across it; a change in only the direct current voltage component across C results.
  • the curve, Fig. 8a is the voltage between X and G and is obviously the voltage across C plus E or simply the voltage across H.
  • a constant-current device serves to linearize the voltage trace.
  • a constant voltage device will serve to linearlze the current trace in the L/R type generator.
  • the trace is exponential due to the fact that as the current increases through L, it likewise increases through r and the voltage drop across 1' prevents the voltage across L remaining constant during the trace.
  • Fig. 3c is the current through L then the voltage across L as shown by Fig. 3b must be constant during the linear trace.
  • Fig. 8a represents the current through L
  • Fig. 8b the voltage across L for the constants which follow:
  • a negative resistance --1' may be introduced as is illustrated in Fig. (if.
  • a generator 83c of saw-tooth voltage properly poled and adjusted in amplitude is introduced in series with r and L. If the resultant current through L is of saw-tooth wave form then the voltage drop across 1' will be of saw-tooth wave form, and hence the insertion of generator e30 will compensate for the voltage drop across r to maintain the voltage across L constant during the trace.
  • Fig. 8a represents the current through L and Fig. 8b the voltage across L for this figure. Also the voltage across 0 is of impulse form since the sum of the voltage drops across 1', L, R and 83c must add up to the constant direct current voltage E.
  • the L/R circuit may be developed as an amplifier of an R, C generators output to produce saw-tooth current through scanning inductances. Or it may be developed as a self-sustaining generator as will appear later. For various economic reasons in construction and operation of cathode ray tubes as television projectors, it appears that magnetic control of scanning may be favored. Hence the precise production and control of sawtooth current through an inductance is required.
  • the R, C generator may be employed to provide saw-tooth, impulse, or a combined saw-tooth impulse voltage.
  • Fig. 9a the ,two wave forms of Fig.0, both now understood to be voltages, are shown first separately and then combined to give a resultant saw-tooth plus impulse voltage wave form.
  • Such a resultant voltage is, for example obtainable between points Y and Z of Fig. 60. If, for example, this voltage is applied across deflecting plates of the cathode ray tube for picture frequency scanning, (with a saw-tooth form of control simultaneously operating for the line scanning) the pattern on the screen will be as shown in Fig. 9b.
  • the picture retrace block-out will appear as shown in Fig. 90. This blocks out that part of the picture retrace which lies across the field to be viewed and throws that part of the retrace which was not blocked out above the field of view.
  • These lines showing above the field of view constitute, of course, the top lines of the picture which now must be sacrificed and may be obscured by an opaque mat (frame) which will present only the field of view to the observer. In effect, however, the retrace time has been shortened.
  • a perfect saw-tooth wave form having zero retrace time involves frequencies extending to infinity in the harmonic composition of the wave and it would be impossible to provide circuits for their use. It can, however, be shown that the plot of the summation of the first ten harmonics of the infinite Fourier series required to represent a saw-tooth wave having a 10:1 ratio of trace to retrace, Fig. 3c, is a curve very closely approximating the ideal. Similarly, it can be shown that the plot of the summation of the first ten harmonics of the infinite Fourier series required to represent a saw-tooth wave having zero retrace time does not, in comparison give a close approximation of its ideal.
  • the current through the scanning coils can, of course, be made very large in the type of load circuit of Fig. 110 by having L and C resonant at, or near, the fundamental frequency of the wave form.
  • Such a design materially attenuates the harmonic components and generally results in requiring that R be made large
  • Fig. lie the first cycle shown is of form Fig. 30, indicated as the wave form of voltage e applied.
  • the current, and hence the voltage ea, Fig. 11c, is shown as having approximately exponential trace and retrace.
  • the difference in voltage between e and ex is Co which is of the form Fig. 3d (parabolic impulse) as shown of 5 small amplitude in Fig. 11c.
  • this wave form is composed primarily of the low frequency fundamental and the lower harmonics; that is the amplitude of the harmonics decreases rapidly with frequency and hence the observation that discrimination against the low frequency components tends to make the saw-tooth wave form appear exponential is confirmed.
  • Fig. 6c the essential elements of Fig. 6c are embodied in a form involving no movable elements.
  • Condenser C is charged by current through the constant current device H which is shown to be a vacuum tube of the pentode type.
  • the well known typical load curves of such a tube show that for a given control grid potential and screen grid potential, the plate current is constant over a wide range of variation in plate voltage. The same, is true. (over a smaller voltage range of a tube of thetetrode, or screen grid, class and hence the tetrode would similarly serve as the constant current device.
  • the potential from biasing source 26 applied to the control grid of H from variable tap f controls the value of current to C and hence the frequency as shown by Formula (3).
  • the shorting tube S is here assumed to be of the grid controlled gaseous discharge type. S is normally non-conducting until the voltage across C, which is between cathode and plate of S, has increased to a maximum value determined by the characteristics of the tube S and the bias on its grid supplied from battery E through resistance 28. In this circuit there is a fixed voltage spread" between grid and plate of S, and as the voltage across C increases, the voltage between cathode and grid of S decreases until the critical value is reached when current can flow through S to discharge C,.
  • the contact 21 is therefore a setting for amplitude of voltage developed across 0 as well as a control of frequency.
  • the discharge of C through S is rapid since such a gaseous discharge tube may have a very low, or even negative, resistance when conductive.
  • a limiting factor in the use of gaseous tubes for S is the de-ionization time.
  • the saw-tooth output voltage developed across C may be taken off for use as shown between point x and ground, the capacity 3
  • a resistor can be included in the discharge circuit as shown at r, and the voltage between Z and ground will then be the out put voltage. If the contact 2Iislocated nearer to the positive end of E, a lower voltage across C will suflice to cause S to operate. Hence a voltage applied across resistor 28 will, if it be poled to makethe grid end of 28 positive, cause the discharge to C to occur earlier in time.
  • impulse voltages for synchronization may be effectively applied to the grid of S to trip the shorting tube and control the generated frequency'in synchronism with the corresponding line or picture frequency of the transmitter.
  • the poling of such a control impulse should be such that the impulse peaks are positive 'as applied to the grid of S, and
  • the controlling impulse voltage applied to 29 readily causes the frequency generated to pull in step" at the correct synchronous frequency.
  • the circuit of Fig. 13 is the inverse of Fig. 12 in that the voltage generated between points 3 and G is oppositely poled. Since it is generally desirable to obtain output voltages relative to ground as shown the arrangement of the component units (which perform the same functions as in Fig. 12 and hence are similarly labeled) is somewhat different.
  • the constant current device H is again shown to be a pentode through which C is charged, and the shorting tube S is of the grid controlled gaseous discharge type. Since the cathode of H is above ground potential and varies relative to ground G by the sawtooth voltage developed across C, the battery connection necessary to fix the potential of the screen grid relative to the cathode of H is made via resistor 32.
  • This resistor 32 with capacity 33 which connects from screen grid to cathode, has a time constant R, C preferably lower than the lowest fundamental frequency at which the circuit is to oscillate whereby the screen remains fixed in its potential relative to its own cathode, regardless of the fact that the potential between cathode and the point on E, at which the tap is made, is varying.
  • the voltage drop across resistor 34 serves as the bias for the control grid of H the position of contact 1 serving as a control of frequency.
  • the shorting tube S again has the voltage de veloped across C applied between its cathode and plate, the maximum value tg which this voltage will rise being determined bythe characteristics of S and the bias on its grid as determined by the position of contact 2? on battery 2E.
  • the saw-tooth output voltage is developed across 3
  • An impulse voltage could be added by having this connection made to point Z, for example, thus Resistor 28 and condenser-29 permit the application of synchronizing control voltages between cathode and grid of S and again the poling of impulses for synchronous control should be, as indicated in the diagram, such that the peaks are positive as applied to this grid.
  • Fig. 14 is similar in form to the R, C type generator of Fig. 12, the elements being identical except that an important modification provides that S is here a thermionic vacuum tube and an additional vacuum tube Rv has "been added.
  • the time constant of resistance-capacity combination 36, 31 should be lower than the fundamental of the lowest frequency to be generated. In practice, however, it is found that a high time constant may be employed here, without harming this operation.
  • the combination of S with Rv as a feedback (reversing) tube is the equivalent of a gaseous discharge tube but with improved results. Furthermore, it offers a point where synchronizing impulses of opposite polarity may be employed. Thus the illustration shows that synchronizing impulses poled with peaks positive may be employed at the grid of S or the impulses oppositely poled may be appiled to the grid of Rv- Saw-tooth voltage of the form as in Fig.
  • the circuit of Fig. 15 is one possible inverse arrangement of Fig. 14.
  • H may be a pentode arranged as the unit H of Fig. 13 or some other arrangement such as a diode as in Fig. 66 to serve as a constantcurrent device, or the unit may be merely a variable resistor as inFig. 6b.
  • the device is is here, as in Fig. 14, a thermionic tube made to serve effectively as a shorting device by virtue of the action of the feedback or reversing tube Rv.
  • the voltage drop across 35 is applied directly to the grid of Rv.
  • the capacity and resistor 31 of Fig. 14 could, of course, be employed instead of the direct connection but it is more economical to use the arrangement shown which omits these elements.
  • the oppositely poled impulse developed by By in resistor 38 is applied to the grid of S through capacity 39.
  • Resistor 40 connects the grid of S to battery 26.
  • the points 1! on the circuit and ground G provide a source of combined saw-tooth and impulse voltage.
  • a sawtooth voltage alone, or impulse voltage alone, can be obtained from the circuit and the circuit can be modified by one skilled in the art to supply such voltages as desired relative to ground without changing the described functioning of the circuit.
  • the synchronizing points in the circuit are as labeled.
  • the circuit of Fig. 16 should be directly compared with those of Figs. 12 and 14.
  • battery E charges C through the constant current device or resistor H, which is the control for the frequency generated.
  • the shorting device S is, asin Fig. 14, a thermionic tube which is made tofunction' satisfactorily for this purpose by virtue of a feedback (reversing) transformer T, instead of by means of the reversing tube of Fig. 14.
  • a feedback (reversing) transformer T instead of by means of the reversing tube of Fig. 14.
  • this circuit is a vacuum tube arrangement having inductance in both plate and grid circuits with the coupling poled so as ordinarily to produce oscillations
  • the circuit to oscillate as an ordinary vacuum tube oscillator at a frequency determined by the inductance and distributed capacities of the feedback circuit unless precaution is taken to prevent such action.
  • Fig. 1'7 is the inverse form of Fi 16 wherein S serves as a shorting device to discharge C when a predetermined v ltage maximum has been developed across C. e potential at wh ch S will act to short C depends upon the characteristics of tube S and the bias as determined by the setting of 21 on battery 26.
  • the transformer T damped by resistors 4
  • Unit S might for example be similar to a telephone receiver whereby the vibrating element (the diaphragm) will move according to the frequency generated in response to the setting of condenser 43.
  • the contact adjustment of S is assumed to be such that the contact is made 15 only for a brief interval during each cycle of vibration of the diaphragm.
  • the functioning of" the circuit to generate a saw-tooth voltage across C and an impulse current in the loop circuit containing C and S will be understood from the de 20 scription of Fig. 6a. Synchronization is best effected at the grid of V.
  • the adjustment of H determines amplitude of the generated saw-tooth voltage.
  • Fig. 19 the control of frequency is likewise 25 consigned to a typical vacuum tube oscillator V identical to that of Fig. 18.
  • the battery E again charges C through unit H which controls the amplitude of generated voltage.
  • Vacuum tube S acts as the short circuit device to discharge C. During the. trace part of the cycle, S is nonconducting. Once, however, during each cycle of the frequency generated by V, the voltage applied to the grid of S, via the capacity 46 and resistor 28, is suiflciently positive to cause S to short circuit C for the retrace part of the cycle. With this arrangement, it will be difficult to obtain a rapid retrace unless the voltage generated by V is of large amplitude, since V generates a voltage which is essentially sinusoidal. The positive voltage peak of this sine wave form will be less efllcient in actuating the grid of S than if tube V were arranged to generate an impulse wave form.
  • Fig. 20 is essentially that of Fig. 16 but the frequency determination has been transferred to tube S in that the grid circuit of S is tuned by the grid winding of T and condenser 43 and the circuit is undamped.
  • This circuit is subject to the limitations of a slow retrace as was the case with preceding circuit Fig. 19 when V acted as a sine wave control generator.
  • Fig; 21a shows an amplifier arrangement in which the current through the scanning inductance List: will be of the same wave-form as that of the applied grid voltage 630.
  • V is an amplifier, of the pentode type, having an energizing battery source 49 and bias" source 48 and a plate or load circuit which comprises resistive, capacitive, and inductive elements 50, Si, 52, 53. Leo and 54.
  • the circuit having the elements enumerated comprises a band-pass filter in which the input arrangement is mid-shunt" and the output to resistor 54 is mid-series".
  • the voltage applied between input elements of V is assumed .to be of saw-tooth wave form (as shown by the notation eat) and the design of the filter structure is such as to pass the fundamental and a sumcient number of the harmonics comprising the saw tooth form so that it is, in effect, a pure resistance load for'the band of frequencies under consideration.
  • the voltage across the filter input resistor 50 will be an amplified replica of the grid voltage and hence the voltage across the filter output terminating resistor 54 is also of the original sawtooth'wave form. Since 54 is a pure resistance the current through it must also be of saw-tooth wave form and hence the current through filter element Lac in series with 54 is of the required saw-tooth wave form.
  • Lac is assumed to function also as the scanning inductance to control the cathode ray beam so that current in the scanning coil is of the same wave form as that applied to the control grid of V.
  • the saw-tooth voltage for the input of V can be had from any of the R, C type generators thus far described.
  • the amplifier tube V is of the pentode type, in which, because of its high platecathode'resistance, the output current will normally follow closely the wave form of grid voltage.
  • the arrangement here shown, has been found particularly well suited for the line frequency 2880 cycles.
  • the energizing potentials for the control grid, screen and plate of 'V are derived from a voltage divided GI, 55 and shunting the voltage source 49 which is closer to actual practice than the showing of simply a battery E.
  • Elements 51, 58, 59, and Lao resemble closely in appearance the filter of 2la.
  • the form of an amplifier V for'use with an R,C type saw-tooth voltage generator
  • V for'use with an R,C type saw-tooth voltage generator
  • the triode arrangement is generally preferable for V as shown, and the reactance 51 of Fig. 21 is omitted since it can seldom be made sufliciently large to be effective at very low frequencies.
  • the capacity 59 present primarily to eliminate the direct current component through Lsc, is made very large to 20 avoid a distortion of the saw-tooth wave form to an exponential form.
  • Fig. 22 is intended to give a completed picture of that'part of the television receiver which includes (a) the final detector and vision frequency amplifier of the receiver proper: (b) the cathode ray tube; (0) the power supply, and (d) the scanning and synchronizing control wherein R,C type saw-tooth voltage generators are employed to eifct scanning by magnetic control of the cathode ray. Exclusive of power supply there are three circuit sections leading to the cathode ray tube.
  • the top section L is primarily the amplifier'for applying vision frequencies and block-out impulses to the control grid of the cathode ray tube, as well as to supply the synchronizing impulses to the other two lower sec tions M and N which are alike'in that they comprise units' for generating and synchronously controlling the scanning currents through th deflecting coils of the cathode'ray tube.
  • Vacuum tube 64 and interstagecoupling unit 65 are represented as the final intermediate frequency stage of the intermediate frequency amplifier of a superheterodyne-type of-receiver.
  • Vacuum tube 66 is the detector which is illustrated to be of the diode form havingras its load circuit the low-pass filter unit 61 across which the vision frequencies and synchronizing 70 aosaras tures being transmitted.
  • the cathode ray tube 15 has been illustrated as of a type employing magnetic focus of the ray for which purpose coil 16 is employed to establish a non-varying magnetic field longitudinally along the axis of the tube.
  • the intensity of this focus field is controllable by rheostat H which determines the amount of direct current which will flow in coil 16 from the power supply P in the lower left part of the diagram, since the terminals 16 there shown connect with corresponding terminals 19 of coil 16.
  • a negative biasing voltage developed between ground and point 85 of source P is applied over connection 86 to the grid 13 of the cathode ray tube whereby the background" or average value of illumination on the screen can'be controlled by adjustment of potentiometer 91.
  • the circuit section M immediately below the amplifier section is the picture frequency generator and its control unit comprising tube 89 which is a synchronizing amplifier, 99 which is the constant current tube for the RC type generator, 99 the shorting tube, 9
  • the saw-tooth voltage thus synchronously generated is applied via resistor 98, capacity '99 and potentiometer I99 to the grid of amplifier 92 which is illustrated as a modern type of multi-grid tube connected to operate as a triode.
  • the output circuit comprising elements I 9
  • Resistor I94 in the cathode branch likewise serves the function described for corresponding resistor 63 of Fig. 210.
  • Current through the picture scanning coils is of saw-tooth form so that the magnetic control of the cathode ray at picture frequency is saw-tooth.
  • Potentiometer I95 of the power supply P is adjustable to set the bias on constant current tube, 99 to con; trol the picture frequency generated. Adjustment of potentiometer I99 determines the output current amplitude and hence the height of the picture projected on the screen. The setting of potentiometer 94 controls synchronization.
  • the third section N from the top of the diagram is the line frequency generator section consisting of the synchronizing amplifier I96, constant current tube I91, shorting tube I96, reversing tube I99 and amplifier tube II9.
  • Theprincipal part of the circuit is entirely similar to the picture frequency section M already described.
  • Potentiometer III in the power supply P controls frequency
  • potentiometer II2 controls synchronization
  • potentiometer H3 controls the amplitude of saw-tooth current output and hence controls the width of the picture.
  • the settings of potentiometers I99 and H3 set the ratio of width to height of the picture (the aspect ratio) to correspond to that of the picture being transmitted so that the subject depicted will be properly proportioned in heighth and width.
  • Resistor Ill included in the discharge circuit has voltage of impulse wave form developed thereacross.
  • the wave form of voltage applied to tube II9 through potentiometer H3 is, therefore, of combined saw-tooth plus impulse wave form.
  • the amplifier arrangement here shown is a pentode circuit the arrangement being similar to that of Fig. 21b.
  • Bias for the grid of tube H9 is taken from a tap on the power supply over conductor H5.
  • the plate or output circuit of tube II9 contains a filter circuit I I6 supplying the scanning coils La. Saw-tooth current will flow through coils L2. The retrace will be rapid due to the inclusion of the impulse component as explained in connection with Figs. 9 and 11.
  • the power supply circuit P needs no description. It will be noted, however, that capacity 'I I6 and inductance III serve effectively to prevent reactions at line frequency through the power supply. Similar by-passing for the picture frequency amplifier 92 is not illustrated since for the very low frequency fundamental of 24 cycles such an arrangement is not generally serviceable.
  • the circuit comprising elements 98, 99, I99 and H9, II 9, H3 must be of high impedance and of good fidelity to effectively pass the generated voltages to the grids of amplifiers 92 and I I9 respectively without aflfecting the operational characteristics of the saw-tooth voltage generators.
  • Fig. 23 is an abbreviated showing of an amplifier section and the line and picture frequency generator sections of a receiver. Only one stage, tube I26, of vision frequency amplification is shown. Since the carrier wave is of the type having negative" modulation, the poling of the detector I2! is made as shown, the cathode being above ground potential to properly pole th the vision frequencies applied to the control grid of cathode ray tube 15 and the impulses as applied for synchronization.
  • the point labeled +Synch.” in the detector output is, therefore, a source of voltage relative to ground of synchronizing impulses with peaks poled positive.
  • the point labeled Synch. in the output of amplifier I26 is a source of impulse voltage with peaks poled negative relative to ground and hence of opposite poling.
  • the elements of the generator circuits for both line and picture frequency are labeled according to the notation employed in the several preceding diagrams, both circuits illustrated being of the R, C type similar to Fig. 14.
  • the amplifiers indicated by V may be arranged for either saw-tooth current or saw-tooth voltage output according to whether the tube 15 is adapted to magnetic or electrostatic scanning.
  • the vacuum tubes used for S and Ry are each illustrated as having synchronizing grids. A positive voltage applied to' an extra control grid in the shorting tubes S will cause these tubes to become conductive earlier in the cycle.
  • filter circuits may be employed between the amplifier section and the synchronizing grids to prevent particularly the line frequency from tripping the picture frequency as was illustrated in Fig. 2. If the picture impulse peaks are of greater amplitude than the line impulse peaks such precautions may be omitted, since the relative adjustment of 96 and 2 (Fig. 22) may be made such that the line impulse as applied to the grid of tube 88 will be insumcient to trip the picture frequency generator.
  • the condenser may be considered as charged linearly with time for the trace and discharged rapidly during the retrace; or alternatively as being charged rapidly during the retrace and discharged linearly with time for the trace.
  • charge has been used to designate voltage changes across the condenser during the trace part of the cycle
  • discharge designates voltage changes across the condenser during the retrace.
  • a source of. direct current potential a condenser, a charging path connecting said condenser to said source, and a discharge path for said condenser, said charging path including the space path of a vacuum tube having at least a cathode, an anode, a control grid and ,a screen grid,.and means for supplying direct current operating potentials to said grids relative to the cathode to predetermine a c nstant current rate of charge, at least one of sa (1 means including a condenser directly conn cted between one of said grids and the cathode of said tube and a series resistance cooperating with said condenser to prevent alternating potentials from affecting said grid, said discharge path including the space path of a three-electrode dispath connecting said condenser to said source,
  • said charging path including a constant current device
  • said discharge path including the space path of a shorting vacuum tube
  • a source of direct, current potential a condenser, a charging path connecting said condenser to said source, and a discharge path for said condenser, said charging path including a constant current device and a resistor in series with said condenser, said discharge path including said resistor and the space path of a shorting vacuum tube, means for feeding back energy from the output circuit of said shorting tube to its input circuit, comprising a vacuum tube having a plate, a control grid, and a cathode, a connection from the junction of said condenser and said resistor to the control grid of said feed-back tube, means coupling the plate of said feed-back tube to the grid of said shorting tube, thereby to derive voltage of sawtooth plus impulse wave form across said condenser and said resistor in series.
  • a source of direct current potential a condenser, a charging path connecting said condenser to said source nd a discharge path for said condenser, said c arging path including a resistor variable over a range such that the time constant determined 35 by said resistanceand said condenser is large compared with the period of the generated wave,
  • said discharge path including the space path of a vacuum tube provided with a control grid, said condenser being common to the space path and grid circuit of said tube, means connecting the control grid of said tube to a point on said source for providing a substantia ly constant potentialdifference between grid andplate thereof;
  • vacuum tube oscillator providing a source of aiternating voltage of predetermined frequency
  • a scanning current generator a vacuum tube having input and output circuits, means for applying voltage of saw-tooth wave form to said input circuit, a load circuit included in said output circuit comprising resistance and a scanning inductance in series, said resistance being high relative to the reactance of said scanninginductance at the essential frequencies constituting said saw-tooth wave form thereby to cause the current in said load circuit to follow the wave form of voltage applied to said input circuit.
  • a television scanning current generator a vacuum tube having input and output circuits, means for supplying'voltage of saw-tooth wave form to said input circuit, a scanning inductance of high reactance at the essential frequencies constituting said saw-tooth wave, said scanning inductance being included in said output circuit, and said output circuit having an impedance in addition to that of said scanning inductance of such characteristic and magnitude that the current through said inductance is also of saw-tooth wave form.

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US747068A 1934-10-05 1934-10-05 Television apparatus Expired - Lifetime US2052183A (en)

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BE411610D BE411610A (enMihai) 1934-10-05
US747068A US2052183A (en) 1934-10-05 1934-10-05 Television apparatus
FR799203D FR799203A (fr) 1934-10-05 1935-10-05 Disposition pour la reproduction d'images de télévision

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2455373A (en) * 1943-03-25 1948-12-07 Sperry Corp Time base sweep and intensifier pulse generator
US2456754A (en) * 1945-03-20 1948-12-21 Rca Corp Electronic saw-tooth pulse generator
US2458771A (en) * 1943-03-15 1949-01-11 Univ Michigan Supersonic reflectoscope
US2489312A (en) * 1944-01-04 1949-11-29 Us Sec War Oscilloscope sweep circuit
US2497766A (en) * 1943-03-17 1950-02-14 Automatic Elect Lab Oscillation generator
US2509761A (en) * 1948-03-16 1950-05-30 Motorola Inc Saw-tooth voltage generator
US2521008A (en) * 1944-06-27 1950-09-05 John H Homrighous Television and sound multiplex system
US2522957A (en) * 1942-06-27 1950-09-19 Rca Corp Triangular signal generator
DE756225C (de) * 1936-02-04 1951-12-20 Emi Ltd Selbstsperrender Kippschwingungserzeuger
US2602888A (en) * 1945-09-04 1952-07-08 Cutler Hammer Inc Electronic timer
US2660691A (en) * 1953-11-24 Bertram
US4321597A (en) * 1980-07-22 1982-03-23 Documation Incorporated Expanded character generator

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2660691A (en) * 1953-11-24 Bertram
DE756225C (de) * 1936-02-04 1951-12-20 Emi Ltd Selbstsperrender Kippschwingungserzeuger
US2522957A (en) * 1942-06-27 1950-09-19 Rca Corp Triangular signal generator
US2458771A (en) * 1943-03-15 1949-01-11 Univ Michigan Supersonic reflectoscope
US2497766A (en) * 1943-03-17 1950-02-14 Automatic Elect Lab Oscillation generator
US2455373A (en) * 1943-03-25 1948-12-07 Sperry Corp Time base sweep and intensifier pulse generator
US2489312A (en) * 1944-01-04 1949-11-29 Us Sec War Oscilloscope sweep circuit
US2521008A (en) * 1944-06-27 1950-09-05 John H Homrighous Television and sound multiplex system
US2456754A (en) * 1945-03-20 1948-12-21 Rca Corp Electronic saw-tooth pulse generator
US2602888A (en) * 1945-09-04 1952-07-08 Cutler Hammer Inc Electronic timer
US2509761A (en) * 1948-03-16 1950-05-30 Motorola Inc Saw-tooth voltage generator
US4321597A (en) * 1980-07-22 1982-03-23 Documation Incorporated Expanded character generator

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Publication number Publication date
FR799203A (fr) 1936-06-09
BE411610A (enMihai)

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