US2457522A - Electronic saw-tooth wave generator - Google Patents

Description

Dec. 28', 1948.- F. BIAS Ef-AL 2,457,522

ELECTRONIC SAW TOOTHIYWAVE GENERATOR Original Filed. Nov. 17, 1944 SOU RC5 0F OBSERVED I 'OSClLLATIONS' I 2 IL I Ill Q M gm; J a Inventors Frafik J. Bias, v I Harald W. L eu Pd,

Their- Attorney.

Patented Dec. 28, 1948 U N I T E D 'S Q'FFI CE 2,457,522 amnio i fsAw groom WAVE 'GENERATOR' Frankll. Bias, Scotia,'-and Harem WztLoml; :Sehenectad-y, YJ, assignorsiftb General :Electric Company, a corporation of :New York 2 Claims. 1 Our invention relates to saw tooth wave generators and isparticularly-applicable to cathoderay apparatus of the type used for analyzing electric oscillations.

This application is a division-of our co'pending application Serial No. 5613;920, filed November till, 1944, now United States Patent 2,449301, :issued Sept. 21, 1948 and assigned to the same-.ass'ignee as the instant application.

It is a general'object of our invention toprovide a new and improved-generator of saw :tooth electric oscillations.

It is a more particular object ofthe invention to provide new and improved means for sweeping'an electron beam along'a time axis at a substantially constant rate.

Our invention itself, togetherwith ;further objects and advantages thereof, will be :more fully understood by referring now to the following detailed specification taken inconjunction-Withthe accompanying drawing; the single figure of'which is a schematic circuit diagram of 1a cathode ray oscillograp'h apparatus embodying our invention;

Referring now to the drawing, we have-shown our invention applied to a cathode ray oscillograph apparatus comprising :a cathode raydischarge device l, a source '2 of "electric oscillations to be observed, and a source 3 ofrsubstantially constant frequency oscillations controlling the sweep and intensity of the electron beam-and synchronizing the operation of thesourcezZ with the beam sweep.

The source-of sine Wave voltage 3 may be an oscillator of any well-known type, such as acrys tal or resonant circuit oscillator, and preferably includes suitable means, such as a variable-condenser, inductance, or the like controlled by -a dial 4 for varying the frequency of thegenerated oscillations. The sine wave oscillations of, selectable constant frequency from thesourcel3 are amplified and distorted by an amplifier '5 and supplied to a diiierentiating circuit comprisinga capacitorB and a resistor I connected across the output of the amplifier 5.

A transformer 8 havin itsprim'ary winding 9 connected across the resistor I supplies .from its secondary winding Ill a series of recurrent voltage pulses to the input of an amplifying -.elec tron discharge device I I having an anode-Ha connectedto a source of positive unidirectional potential B+. The input circuit of the discharge-device H includes a source of negative bias potential such as a battery .12 connected in-series circuit relation with the transformer winding land a grid bias resistor IS. The high frequency os- (01. est-a.)

Z cillations tromrthe transformer winding lllare supplied to. the :control electrode of the discharge device 1M througha capacitor l4 connected in paralrel circuit relation with the resistor l3, It will 'LbGL'UIIQGIStOOd' that, because of-diff.erenti ation of the distorted amplifier output ,wave in the circuit 16, the output :of the transformer 8 hompriseszanzalternate series of positive and-negative mulses; The negative voltage. pulses suppliedtd-the-control electrode of the dischargede: vice 2M have no efiech-since the controlelectrode isqnormally ibiased negative and any negative voltage :pulse serves only to adri fi, thedischarge device I-zl farther into the cut-on region, The positive ,rpulses ifrom the'transformer winding I 0 howevery-overcomethe negative bias from the source Ir-2 thereby :to render the-discharge device ll recurrently conductive ;for short interval-s *ata frequency-determined by the frequency ofthe-source 3. H V

The -positive voltage pulses suppliedto the zinput of'the .discharge'gdevi ce ;l; l are amplified and supplied'a-s negative pulses from the anoderof the device all to ,the anodeof a .regenerati ve pulse generating electron discharge device I 5 having an anode ll 6 ,-.a cathode l1 and a control electrodes-t8. Inresponseto-the triggering impulses supplied to the discharge device ,{5 from the discharge device :II a pulse generating circuit as; sociated with [the device l5 zproducesa seriesof recurrent voltage pulses havii ga frequencyeciual to ,the \trequency of the triggering ,pulses. lhe pulse generating circuit associated with the discharge .device. .lfi ncludes apulsegtransformer l9 and a pulseforming and pulse-determining capacitive storage element- 20. The capacitive ele mentrZO is preferably constituted by an op en-fiendedgartificial; transmission .linesection made up of The anode capacitors @l f. and inductances 22. V l5 .i-sconnected throughtaprimary winding 23 of the trga rlsforrner,l9 tothe source .of unidirectional current :supplyeindicated onth'e drawing winiIfhe -open-ended ltransmissi'online section 20 is connected between the control electrode 1.8 and the grounded cathode ill in series circuit relation with a resistor arena a s'eco n'dary winding -25 of the pulse transformer J9. The resistor 25 preferably has a resistance substantially equal to trie ur ge impedance of the transmission line sect ionlll. The control. .electrode i8 is also'cone necte'dto the cathode I? through a suitablegrid bias resistor 7.6 and a source of negative bias; po-v f jal such as a bait ry 1.1. 'The pulse output fromthe discharge device-r515 supplied from ,a tertiary winding '18 onthe pulse transformer l9;

comprises an evacuated discharge envelope 43 having at one end a grounded cathode 44 and at the other end an anode 45. A suitable source of unidirectional current supply, such as a battery 46,-is connected between the cathode 44 and anode 45, and the cathode ray discharge is controlled by the grid or control electrode 42. The

-'.grid 42 is provided with a negative bias from a trol electrode |8 of the discharge device l posi tive and impressing across the input end of the transmission line 20 a short voltage pulse. The

discharge device |5 thereupon begins to conduct.

The additional current through the transformer winding 23 resulting from conduction of thedefvice l5 induces an additional positive potential in the winding 25, so that the control electrode |8 is driven more positive and the discharge device I5 driven rapidly to saturation. Conduction continues until the voltage pulse impressed across the input end of the transmission line 20 travels to the remote open end and reflects back to the input end. This reflected pulse is of such polarity and intensity that it drives the control electrode l8 of the discharge device abruptly negative and beyond cut-off, thereby suddenly terminating conduction in the device I5. Thus, the period of the pulses derived from the output of the discharge device IE is determined by the reflection characteristics of the transmission line section 20, and the frequency of the pulses is determined by the frequency of the triggering impulses received from the discharge device II. It will, of course, be understood that the maximum permissible triggering frequency'is limited by the time necessary for the transmission line 20 to discharge through the resistor 26.

A regenerative pulse generating circuit of the type described immediately above is described and claimed in the copending application Harold W. Lord, Serial No. 464,033, filed October 31, 1942', now United States Patent 2,444,782, issued Jul 6, i948, and assigned to the same assignee as the instant application.

The voltage pulses derived from the output winding 28 of the pulse transformer l9 are sup plied to the input circuit of an amplifying electron discharge device 30 having an anode 3|, a grounded cathode 32, and a control electrode 33. The pulse transformer winding 28 is connected between the cathode 32 and control electrode 33 in series circuit relation with a suitable source of negative bias potential, such as a battery 34 and a grid bias resistor 35 shunted by a capacitor 36. The anode 3| of the amplifying discharge device 30 is connected to the positive potential source B+" through a primary winding 31 of a three-winding pulse transformer 38. Positive pulses appearing at the upper terminal of the pulse transformer winding 28 in response to recurrent pulsed conduction of the discharge device l5 recurrently render positive the control electrode 33 of the discharge device 30 thereby to produce amplified negative voltage pulses upon the anode 3| of the device 30. These amplified pulses appear across the primary winding 31 of the pulse transformer 38 and induce pulses of opposite polarity in a pair of oppositively wound secondary windings 39 and 40 on transformer 38.

The pulse transformer winding 39 is grounded at one end and connected at its other end to sup- 3 ply positive pulses through a coupling capacitor 4| to a control electrode or grid 42 of the cathode ray discharge device I. The discharge device I material.

source 42a through a resistor 4222. When the electrode 42 is sufliciently positive to permit the projection of an electron beam from the cathode 44 toward the anode 45, the beam passes between two pairsof deflecting plates 41 and 48 and falls upon a sensitive screen 49 of a suitable fluorescent The deflecting plates 41 and 48 are preferably arranged to deflect the, beam laterally along mutually perpendicular axes.

The pulse transformer winding on the pulse transformer 38 is connected at one end to the positive potential source 3+ and at the other end through a unilateral conducting device, such as a diode rectifier 50, to the anode 5la of an electron discharge device 5|, and is so disposed that voltage pulses induced in the Winding 40 in response to voltage pulses in the winding 3! cppose the voltage of the source B+. The intensity of the voltage pulses in the Winding 40 is substantially equal to or greater than the intensity of the voltage of the source B+. The electron discharge device 5| is preferably of the pentode type and includes, in addition to the anode 5la, a cathode 52, a control electrode or grid 53, a screen grid 54, and a suppressor grid 55. The cathode 52 is grounded and the control electrode 53 and suppressor grid 55 are connected together and to the cathode. The screen grid 54 is connected'through a bias resistor 56 to the source of unidirectional potential B+ and through a condenser 51 to ground. The positive bias impressed upon the screen grid 54 through the resistor 55 is sufficient to render the discharge de-v vice 52 normally conductive. Furthermore, it is well known that the arrangement of the remaining grids in a pentode discharge device of this character is such that the magnitude of anode current remains substantially constant over a wide rang'eof anode potentials.

A plurality of capacitors 58, 59, and 60 are arranged to be selectively connected'between the anode 5|a and cathode 52 ofthe discharge device 5| by means of a selector switch 6|. As shown on the drawing, the low capacitance point 62 of the selector switch BI is an open circuit. In=this connection, the only capacitance between the-anode and cathode is that introduced in the circuit by the interelectrode capacity itself and the capacitance of the various leads and selector switch parts. V

The circuit including the discharge device 5|, the diode rectifier 50, and the capacitors 58, 59, and 60 generates a saw-tooth voltage Wave unilized to effect a recurrent timing sweep of the cathode ray beam along one axis of the fluorescent screen 49. For this purpose, the anode 5|a of the discharge device 5| is connected to one of the horizontal deflection plates 48 in the cathode ray tube 43. The other plate 48 is grounded, so that the voltage between the plates 48 is that between the anode 5|a and cathode 52 of the discharge device 5|, as determined by the selected condenser 58, 59, or 60.

The sweep circuit described above operates in the following manner to produce saw-tooth oscillations. When no pulse voltage is present in the primary'winding 31 of thepulsetransformer 38,110 voltage isinduced in the tertiary winding 48. Thus, normally the diode rectifier 50?-is con'-. ductive and current flows from B+- through the tertiary winding ll], the diode rectifier 50, and the positively biased pentode discharge device to ground. During conduction of the discharge device 51 from the source 13+, denser 68, 59 or 66 remains charged to a constant voltage equal to the voltage drop between the anode 5la and cathode 52' of the discharge device 5i.

Whenever a voltage pulse appears'in-the trans-- former'winding 31, a pulse ofvoltage is-inducedinthetransformer winding 40 in such a direction'as to oppose the voltage of the unidirectional-voltage source B+. Since the pulse voltage is equal toor greater than the unidirectional" voltage, the net voltage around the circuit including the-di-= ode rectifier 56 and pentode discharge-device 51 is reduced to Zero or reversed, so that the diode rectifier 50 becomes non-conductiveand remains non-conductive for the period of the pulse. er ing this pulse period, the selected charged capac itor 53, 59, or 68 serves as a parallel voltage-source and continues the discharge through the'di'scharge device 5|. Discharge of the" capacitor through the source B+ is prevented by the diode 56. As the energy stored in the sweep capacitor 58, 59; or 50 diminishes; the voltage of the ca-'- pacitor decreases. However as'previously pointed out, the current through the discharge device 5I'remains constant over a wide range of anode voltages, so that the sweep capacitoris discharged at substantially constant current; As is well known to those skilled in the art, a constant current discharge of a capacitor efiectsa substantially linear decreasein capacitor voltage. It is the linearly decreasing sweep capacitor voltage which is applied between the horizontal deflectionplates 48 of the cathode ray discharge device 43.

As soon as the voltage pulse in the pulse-trans former winding 40 is terminated, the diode rectifier' 50 again becomes conductive and the source- B+ supplies current to the discharge-device 51'. When the rectifier 50" becomes conductive at the termination of a pulse, the voltage of the anode cm of the discharge device 5! is raised suddenly,

thereby abruptly to increase the charge and the voltage of the sweep capacitor 58, 59, or 60. Thus, the cathode ray beam is moved along the horizontal axis of the fluorescent screen"49at' a substantially' constant rate determined" by the rate of voltage diminution of the sweep capacitor'during discharge to establish a time base for wave analysis and is suddenly returned to its starting point, when the sweep capacitor voltage is abruptly increased upon termination of the pulse voltage in the winding 40.

V The positive pulses appearing onthe: pulse transformer secondary windingx39i are suppliedv not only through the couplin condenser M to the control grid'42, but also through a lead 63 to a time delay or phase shifting circuit 64 tocontrol a trigger pulse generator 65; Pulses in the transformer winding 39 are coincident int-time with those in the transformer winding 40 which control the discharge of the sweep capacitors 58, 58, and 60. Pulses from the pulse generator 65 delayed in time with respect to pulses in the windings 39 and 40 are amplified in a discharge device 66 and supplied through a transformer 61 to trigger or render operative the source 2 of oscillations to be observed or analyzed. The oscillations to be analyzed from the source 2 are supplied to the vertical deflection plate 41 of the the selected concathode rayidischarge :device 43.2.. Thus, thesin-i glepulse transformer 38- serves to initiatethe; sweep, tosimultaneously establish a cathode ray beam through control of the grid or intensifier; 42, and to -render operative the source 2 of ob-' served oscillations through the time delay circuit Bland trigger pulse generator 6.5. Thus, the trigger'pulsesare synchronized with and delayed in; time withrespectto the initiation of the beam sweep.-

The time delayacircuit lidcomprisesa source of. substantially constant unidirectional potential, such as a battery 68, connected in opposing-sh ries circuit relation with the pulse transformer secondary winding 39 across an integrating circuit consisting of a variable resistor Stand ca pacitor 16. A primary winding 1 I of a pulse transformer l2 is connected across the condenser: 10: through-a unilateral conducting device such as-a diode rectifier 13. This circuit functions to: es tablish in the transformer winding 'i! a recurrent series of voltage pulses delayed in time or phaserela'tion with respect to the series of- Te current voltage pulses appearing in the transformer-winding 39. I

The operation of the time delay circuit 64' depend s 'upon-the characteristics of the integratingcircuit 69310: When no voltage pulse is present in the transformer winding 39 thebattery 68 maintains the condenser I'll charged to the bat teryvoltage Whenever a pulse appears upon the transformenwinding 39, the pulse voltage op poses 'thevoltage' of the battery 68; Since the puLlseis 'ofsubstantially rectangular wave shape and-its intensity is greater than the voltage of the battery 68, the sudden reversal of voltage applied to=the condenser 'lil causes the condenser charge todecay exponentially to zero and their tore-- verse: As soonasthe voltage of the condenser 16 reverses, the'voltage appliedto the unilaterally conducting circuit through the pulse transformer winding 'I-"lis reversed, so that the diode recti fier T-3'- becomes conductive to apply a triggering" pulse to the transformer winding it. It v'villtl"1usbe evident that the time delay between the im tiationof a pulse in the transformer winding 39 an'd 'the" initiation of a pulse in the transformer winding 7 I is determined by the time taken for the charge of the condenser ill todecay exponentially tozero andto reverse sufficiently? to render the discharge device ls'con'oluctive. This time is determined by the resistance of the resistor 69;"

and the capacitance of the capacitor 16', and may; suitably be controlled by utilizing a variable resistor' 69, as indicated on the drawing; Upon termination of each pulse in the transformer winding. 39', the battery 68' again reverses the charge upon the condenser TB and brings it back to its, normalvaluet The triggering pulse in the transformer winding. .H is not necessarily oflthe same duration asthe initiating pulse in the transformer windin 39, but its duration is determined by the length of time for which the voltage'of thecapacitor 10 remains reversed by the voltage pulse inthe transformer Winding; 3 91 The time delay circuit 64 is particularly claimed in copending application Serial No. 663,320, filed April 19, 1946, which is also a division of our aforesaid copending application Serial No. 563,920.

The pulse generating circuit 65 is similar to that previously described comprising the artificial transmission line 20 and the electron discharge device !5. The pulse generating circuit 65 comprises an electron discharge device 14, an

artificial transmission line 15, a source of negative'bias potential such as a battery '16, a grid bias resistor 71, a resistor 18 between the transmission line 15 and the control electrode of the electron discharge device 74, and the pulse transformer '12. The operation of the pulse generating circuit 65 is entirely similar to that of the pulse generating circuit previously described, the only difference being that in the circuit 65 the triggering pulses are supplied through the transformer winding ll rather than directly to the anode of the discharge device 14. An, output winding 19 of the pulse transformer 12 supplies to the input circuit of the amplifying discharge device 66 a series of recurrent voltage pulses having a length or period determined by thev characteristics of the transmission line 15 and a frequency determined by the frequency of the delayed triggering pulses derived from the pulse transformer 38. the amplifier 39 and its input circuit comprises a source of negative bias potential, such as} a battery 80, a grid bias resistor 8|, and a shunting capacitor 82. The amplified trigger pulses from the transformer 67 are supplied to the oscillation source 2 to render the source 2 operative in synchronism with the beam sweep. The oscillation source or generator 2 is connected to the vertical deflection plates 41 of the cathode ray discharge device 43. e

By way of illustration of one application of our invention we have illustrated upon the nuorescent screen 49 a typical picture which may appear in the event that the oscillation source 2 is a radio direction and range finding apparatus of the type comprising a pulse transmitter and a receiver of echo or reflected pulses. In accordance with our invention, the cathode ray beam is turned on and horizontal sweep of the beam initiated at the beginning of each pulse appearing upon the transformer winding 37.

The horizontal sweep of the beam traces a line- 82 upon the fluorescent screen 49. Synchronously with the initiation of the beam sweep and in fixed time delay relation with respect thereto, triggering pulses are supplied to the source through the circuit 6G to render the transmitter operative. Upon triggering of the transmitter, a

transmitted pulse 83 appears upon the fluorescent screen 49 by operation of the source 2 and the vertical deflection plate 47. In the event that the pulse 83 encounters a detected object and is refiected back to the receiver of the source 2, a reflected pulse 84 will appear upon the fluorescent screen 59 a predetermined time after the pulse 83, as determined by the distance between the source 2 and the reflecting object. In this man; ner, the range of a reflecting object may be de-' termined.

While we have shown and described'only a preferred embodiment of our invention, many modifications will occur to those skilled in the art and we therefore wish to have it understood that we intend in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

The amplifier 66 is similarto,

What, Weclaim as new and'desire to secure 1 said anode and said cathode, said rectifying device and unidirectional potential source being poled to provide a normal anode current flow through said discharge device in the absence of said pulses, and a capacitive energy storing element connected between said anode and said cathode in parallel circuit relation with said voltage sources, saidpulses rendering said rectifying device non-conductive and permitting said element to discharge through said discharge I device during saidpulses.

2. A saw-tooth wave generator comprising a source of substantially constant unidirectional potential, a source of recurrent voltage pulses of substantially rectangular wave shape having an intensity at least equal to the intensity of saidunidirectional potential, aunilateral conducting device, -a pentodeelectron discharge device having an. anode, a cathode and a plurality of control electrodes, means connecting said control electrodes to maintain. said discharge device; normally;conductive and to render the anode current of said discharge device substantially independent of anode Voltage over a wide range of anode voltage, means including said unilateral conducting device for connecting said constant potential source and said pulse voltage source in opposing series circuit relation between saidanode and saidcathode, said rectifying device and unidirectional potential source being I poled to provide a normal anode current flow through said discharge device in the absence of said pulses, and a capacitor connected between said anode and "said cathode in parallel circuit relation withsaid voltage sources, whereby said voltage pulses recurrently render said unilateral conducting device non-conductive and permit discharge of said capacitor through said discharge device at a substantially constant rate.

FRANK J. BIAS. I HAROLD W. LORD.

REFERENCES CITED Number Name Date 2,161,948 *Bull et a1 June 13, 1939 2,241,256 Gould May 6, 1941

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