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Patented July 4, 1950 2,514,023 UNITED STATES PATENT OFFICE 2,51<4',023 VOLTAGE GENERATORv Carl A. Bergfors, Yonkers, N. Y., assignor to‘In ternational Business Machines Corporation, New York, N. Y., a corporation of New York Application October 10, 19517,,Serial?No. 779,031 1 Claim. (Cl. 178-44) 1 2 This invention relates to asquare wavegenera tor. and has particular relation to a generator em ploying ,an oscillator and an ampli?er. In prior arrangements, a. vwell shaped square wave is customarily generated by apparatus com 5 prising a multivibrator oscillator and electronic limiter. or clipper ampli?er circuits coupled there tween “a change in the output voltage of the oscillator and the corresponding change in grid voltage of the ampli?er tube which delay pre cludes a, substantially vertical wave front out put for the ampli?er. Accordingly, it is also an object of the inven tion to provide an improved square wave genera tor having a wide frequency band coupling be tween an oscillator and an ampli?er and between are substantially vertical while the tops and bot 10 successive stages of an ampli?er which coupling toms ,of the wave Varesubstantially horizontal. incorporates the advantages of, a direct resistive While such prior apparatus may be satisfac coupling at low frequencies and of a capacitive to. Eye wellshapedsquare .wave is meant one in which ,theleading and trailing wave fronts coupling at high frequencies. torily operated over arange of frequencies, the frequency band within which a well shaped Other objects of the invention will be pointed square wave may be obtained is not as wide 15 out inthe following description‘ and claims and illustrated in, the accompanying drawing, which discloses, by way of example, the principle .91.’ as is, many times desirable. , Theprincipalobjectlof the invention is to pro vide a new and improved square wave generator the invention and the best mode, which has been contemplated; of applying that .principle. operable over an extremely wide band of fre quencies. 20 In the drawing: Another object is to provide a novel square wave generator which is operable over a fre The single ?gure is a schematic wiring diagram of,a square wave generator embodying my inven quency band of'the order of 1 to 800,000. cycles per tion. second. . .As shownin the drawing, theisquare wave gem 7A further object is to provide. an improved 25 erator‘ is made up of a power supply unit lllha. square wave generator comprising a multivibrator oscillator with. clip-per ampli?er circuits coupled ~ thereto which is operable over an extremely wide multivibrator oscillator. ll. and a three stage clipper ampli?er I2. Conventional cathode heater. circuits for, tubes in. the. various units al‘e frequency. band and providesa well shaped square omittedfromv the drawing forv clarity. _ The power supplyunit is energized from an alternating current sourcethrough, a transformer I3. A recti?er tube .Vl ,has its two anodescon nectedv to,_.opposite ends of .a secondary winding waveat any frequency in the band. My invention arises from therealization that inv prior apparatus, as described above,.the width of they frequency band is. limited largely by the nature of the coupling between the multivibrator Mnofwthe transformerl3. The cathode oftrectie and ampli?er and between successive stages of the 35 ?er NT! is connected to .arcent?r tap [5 on. the ampli?er. Usually, a coupling capacitor is em secondary winding l4 througha choke coil~I6 ployed. However, for, low frequencies the capaci in serieslwith .a. capacitor 01 whereby a D. C. tor must have a verylarge capacity and, con voltage of therpolarityindicated in the drawing sequently must eithervbe extremely large or be is providedtacrosscapacitor Cl. Another capaci of the electrolytic type, the leakage resistance 40 tor~C2.y-and~a semievariable resistor R! - are con andv instability of whichmakes, itundesiliable as nected in series across thecapacitor CI’ to provide a coupling capacitor at such points in the gen all C. voltage on the capaictOr'CZ which,‘in erator. Thus, the use of a coupling capacitor for the particular circuit shown, maybe of the'order very low frequencies is believed to be impractical. of- LEG-volts. On the other hand, a direct resistive coupling A half ‘wave recti?er V2; shown as a double is satisfactory for lowfrequencies but is not sat diode, is-connected in series with two "resistors isfactory for either the high frequencies within R2~and¢R3~from thev center tap l5 to one end the band of oscillations of the square wave gen erator or the high frequencies represented by the of'the secondary winding ‘ M. A capacitor C3eis in parallel with the resistor R2 so that a DC. steep wave front of each individual pulse of the 60 voltageofiapproximately lOilvolts appears there square wave. At high frequencies the input across. capacitance of‘the ampli?er tube becomes of con A voltage regulator tube V3 is connected in siderable importance with a direct resistive cou series with a resistor R4 across the capacitor 02 pling. This input capacitance in such an ar so that-a regulated voltage of ‘approximately 150 rangement causes an exponential time delay be volts appears across the recti?er tube V3. Four 2,614,028 3 D. C. voltage supply lines, I‘I, I8, I9 and 20 are then provided from the power unit I II, as illus trated in the drawing. The ?rst line I‘! is con nected to the positive terminal of capacitor C2‘ and is grounded. The second line I8 is connected to the anode of the rectifier tube V3 and is approx imately 10 volts negative relative to line ll. The third line I9 is connected to the cathode of the recti?er V3 and therefore to the positive termi nal of capacitor C3 and is approximately 150 "10 volts negative relative to line I8. The fourth line 20 is connected to the negative terminal of the capacitor C3 and is approximately 100 volts nega- > tive relative to line I9. Of course, any suitable‘ D. C. voltage supply source may be employed al 15 though a regulated voltage supply for the oscil- > lator is desirable and I have found the speci?c 4 of the tubes V4 or V5, because of transients or the absence of exact uniformity in the two tubes or their circuits, will conduct more current than the other. As a result a negative signal is passed from the anode of that one tube, because of the increased voltage drop across the corresponding load resistor R5 or R6, through the associated capacitor C5 or Clia to the grid of the other tube. The current through that other tube is thus re duced, which results in the grid of the aforesaid one tube becoming more positive to increase the current therethrough still further. It is appar ent the effect is a cumulative one and the cur rent through the one tube rapidly reaches a max imum while the current through the other tube is out off. This circuit condition remains until the charge on the capacitor C6 or 05a connected to the grid of the other tube leaks o? to permit supply unit described to be highly satisfactory. current to again ?ow through the other tube. The multivibrator oscillator II is of the well known positive bias type. It is supplied with the 20 When this occurs the cumulative eifect again takes place but in the reverse direction. Thus, regulated voltage appearing between supply lines the current flow shifts between tubes V4 and V5. I8 and I9. The multivibrator comprises a twin The output of the multivibrator is taken from triode, the halves of which are designated as V4 the anode of tube V5. This output approaches and V5. The anodes of tubes V4 and V5 are con nected to line I8 through load resistors R5 and 25 a square wave but in itself is a very poorly shaped wave. The frequency of the output of the multi R6, respectively. These load resistors R5 and R6 vibrator is, of course, determined by the various are of a relatively low resistance to minimize the capacitors and resistors in the circuit. The re effects of tube and circuit capacitance in the sistor R9 may be varied to provide a rather coarse the widefrequency band desired. The common 30 frequency adjustment while adjustment of the tap on resistor RI3 effects a ?ner control of fre cathode of tubes V4 and V5 is connected to supply quency. The major frequency control is, of line I9. The control grid of tube V4 is connected course, in the setting of the capacitor banks to through a resistor R1 and a selected capacitor in -m_ultivibrator at the higher frequencies within ‘the capacitor bank comprising capacitors C4, C5, permit operation of the multivibrator at a select C6, C1, C8 and C9 to the anode of tube V5. The control grid of tube V5 is connected to the anode ed frequency over a wide frequency band. Vari able resistors RII and RI Ia may also be adjust of tube V4 through the resistor R8 and a selected ed to control the width of the pulse provided by the multivibrator. The ampli?er I2 comprises three stages rep capacitor of the capacitor bank comprising ca pacitors 04a, 05a, 06a, 01a, 08a, and 09a. The , resented by tubes V6, V1 and V8 respectively. selectors 2|, of the capacitor banks may be oper Tube V6 isconnected as a pentode with its anode ated ‘simultaneously to determine Which of the connected through resistor RN to supply‘line I1 capacitors are connected in their respective cir and its cathode connected to line I9. The screen cuits at any selected setting and that correspond grid 22 of tube V6 is connected to line I‘! through ing capacitors in the two banks are simultaneous a resistor RIB whereby a desired voltage is ob ly so connected. 45 tained on the screen grid. This screen grid volt The grids of tubes V4 and V5 are also connect ed together in a circuit which can be traced from age is stabilized by a capacitor CI3 connected be the grid of tube V4 through the resistor R1, the tween the screen grid and the cathode. . parallel circuit comprising a variable resistor R9 The ampli?er I2 is coupled to the multivibrator on one side and a resistor RIO, a pair of variable 50 oscillator II by a novel coupling arrangement. resistors RI I and RI Ia and a resistor RI 2 on the, Three resistors RI9, R20 and R2I are connected other, side._ The connection between the grids. in series between the anode of tube V5 of the continues through resistor R8 to the grid of tube‘ oscillator and line 20 to form a voltage divider. V5. A voltage divider comprising a pair of series An adjustable tap on the resistor R20 is connected ‘connected resistors R I 3 and Rl3a is connected be- '5 to the control grid of tube V6 through a grid re tween supply lines I8 and I9. The junction be 55 sistor R22. A capacitor CI4 is connected di-. tween variable resistors RII and Rlla is con rectly between the anode of tube V5 and the ad nected through another resistor RI4 to an ad justable tap on resistor R29. justable tap on resistor RI3. A capacitor CID is The tap on resistor R29 is adjusted so that also connected from the junction between resis- ' " the voltage across the divider formed by resistors tors RI I and RI Ia to the supply line I9. To en 60 RI9, R20 and R2I, which voltage is derived from able stabilization of the multivibrator by a syn chronizing pulse, a terminal SI is provided over the anode of tube V5 of the multivibrator II, tends to cause the voltage of the grid of tube V6 which a synchronous input pulse may be sup-‘ 7 .\ to alternate between a ?rst voltage more nega plied. A capacitor C II and a resistor RI5 are thanthe cuto? voltage of the tube and a connected in series from the terminal SI to the 65 tive second voltage more positive than the voltage to supply line I9. An adjustable tap on the resis which the grid is limited by the grid current. tor RI 5 is connected through a capacitor CI 2 and Thus, when tube V5 is conductive, the voltage of another resistor RIS to the grid of tube V4. ‘ The operation of a positive bias multivibrator iii; the grid tube V5 goes below cutoff and negative of this type is well known an consequently only 70 clipping of the wave produced by the multivi brator results. When tube V5 is non-conductive, a brief description thereof is needed here. If it the grid voltage of tube V6 tends to become is assumed that the capacitor banks are set as il highly positive but is limited to a value slightly lustrated in the drawing and the tubes have al ready been warmed, then when voltage is applied - above the cathode voltage and positive clipping to the multivibrator through lines I8 and I9, one 1351111715.. tortion inthe wave’ at ‘high frequencies. ‘ At low the resistor R21 to provide a polarizing .potene. tial to the capacitorto maintain it in goodJcon---~ frequencies, dition. 7 The vcapacitor'C I 4 i provided-‘- to prevent disa an —-eflicient ‘ direct ~ * coupling-yv - rela-~~ > ~ To obtain another square wave output ,'l80° out;-_ of phase with that appearing between terminals“ A and G, the third stage is provided in the am.--' pli?er l2. Tube V8 is illustrated-as a pentode' ti'vely/ ¥free~ vof distortion, ‘is afforded ~ by‘ the’ are». rangement' of~resistorsRl 9;‘ R2 0~and~1R211 How~ ever,~,when the multivibrator-operates at aihigh frequency; the input capacitance-ofthe tube V15v becomes appreciable and ‘with’ the impedance‘ connected as a triode with its anode connected through resistor R3itc line I‘! and its cathode. connected to line l9. Tube V8'is coupledlto the output of tube V‘! by coupling similar to that be-" tween tubes V1 and V6. This coupling comprises» offered by resistors R19 "and ‘Rue-‘between the anOdeof-tube V5" and the grid~of ‘tube V6; this ‘ input capacitance would~,in the absence'of capaci tor C I‘4,‘-prevent the grid oftube- V6‘ fromfollow ing-instantaneousvoltage changes at t‘heanodev resistors R28 and R29 connected between. the 1 anodeof tube .V‘l and. line 20 and capacitor C18 of ‘tube V5? The capacitor Cl4= is of 'a'size-o?‘er ing a relatively "low impedance at high ~frequen= cies- and so provides a';low impedance path “from the anode‘of-tube-VE to-the grid of tube V6‘. The: capacitor C14 thus servessto- balanceout the ef-fect of the input capacitance-of the tube "and . connectedin shuntacross resistor R28 with the. fér's' ell-relatively’ high impedance. However, the a terminal B and the ground terminal G. Thev terminal B is connected to the junction point be, junctionbetween resistors R28 and R. 25 con-v nected to the control grid of tube V8 through re sistor R30. The. action of. tube. V8 is the same asthat; thereby eliminates the'distortion in the wave 20 described fortube Vl, but of course, the output. which otherwise would appear at: high frequen willbe ‘18.0;o out of phase with the output ofv tube _ V1. The output fortube V3 is obtained between... cies. ‘At low frequencies, thecapacitor CH of input capacitance of the tube V6 is not suffi ciently great tocauseappreciable‘.‘distortion at these lowv frequencies. 25 tween a resistor R32 connected .in series with a pairof parallelcapacitors C19 and C20; between Thus,: this coupling: are. . rangement. provides efficient coupling at both the an adjustable tap. on resistor R3l and the line highzand .low frequencies over a very wide fre quency: band. I ‘l. "Capacitors C19 and C20 are similar in struc: ture and function to vc'apacitorsCHi and 0H,. The second stage of they ampli?er I2,,1corn~ 30 prising :tube V1, is connected to, the ?rststage- by respectively. . A synchronizing. outputimpulse of ?xedv ampli-.,, a coupling arrangement similar to that between the oscillator and the ?rst stage of the ampli?er. tude may be obtained from a terminal S2 con nected through a capacitor C2l to the junction between a pair of resistors R33 and R34 con triode with its anode connected to line I‘! through 35 nected between the anode of tube V8 and line a resistor R26 and its cathode connected to line IT. This synchronous output may be used for Tube V1 is shown as a pentode connected as a l9. Resistors R23 and R24 are connected be many purposes which are well known to those tween the anode of tube V6 and the supply line familiar with the use of square Wave generators. 20. The junction between resistors R23 and R24 In a typical square wave generator constructed is connected to the control grid of tube V'I 40 and operated satisfactorily and connected as through a resistor R25 and a capacitor Cl5 is shown in the drawings, the components have the connected in shunt across the resistor R23. following values or types: As previously explained, the tube V6 of the ?rst ampli?er stage has a clipping action. Tube V6 also provides sui?cient amplitude in its output voltage to permit further positive and negative 4.5 clipping by the tube V‘! of the second stage. A pair of parallel connected capacitors Cl 6 and CI‘! are connected in series with a resistor R2‘! between the adjustable tap on the resistor R26 50 and the line H. An output terminal A is con nected so that between terminal A and a grounded terminal G on line I‘! there appears a square wave as produced across the resistor R21. The capacitor-resistor circuit CIG, CH, and R21 pro vides a coupling whereby the output of the gen Capacitors 55 erator may be coupled to various other apparatus without affecting the generation of the square CI, C2—40 mfd. 350 wv. C3—16 mfd. 350 wv. wave itself. The capacitors CIS and C1‘! are C5, C5a--0.2 mfd. thus coupling capacitors. One of these capaci 60 C6, CHIP-0.015 mfd. tors CNS is quite large and is preferably an elec C1, Ola-0.00115 mfd. trolytic capacitor, while the other capacitor C" C8, C8a-—0.000075 mfd. is quite small and is preferably a paper ca C9, C9a-—0.000025 mfd. pacitor. Thus, the capacitor Cl‘! can efficiently [email protected]—-0.25 mfd. pass the high frequency while capacitor CIB ef 65 CH, CH, 020-01 mfd. ?ciently passes the low frequency. An elec Cl2-~0.01 mfd. trolytic capacitor C16 may be satisfactorily em Cl3, C16, CIB, C2 l--50 mfd. ployed in this position in as much as the square wave has now been provided at a sufficiently am CH, CH‘), Cl8-25 mfd. Resistors pli?ed strength that any inaccuracies arising 70 therefrom are negligible. Consequently, a leak age through the electrolytic capacitor will not have any material effect. It is also to be noted that the more positive terminal of the electrolytic capacitor C l 6 is connected to the ground through 75 RI—1500 ohms 25 W. R2-16000 ohms R3, RI 4-15000 ohms R4-—400 ohms 10 W. R5, R6, R1, R8-5000 ohms 2,6 1 4,028 R9-—2 megohms RI 0, RIM, RI5, RIB, R33--5000 ohms RI I, RI Ia, RIB, R21, R32—100,000 ohms RI2—200,000 ohms RI3-25,000 ohms RI'I--2500 ohms RI 9, R2 I—360,000 ohms R20--250,000 ohms R22, R25, R30, R34-—10,000 ohms R23—510,000 ohms R24—390,000 ohms R26, R3 I—3,000 ohms R28, R29—ll70,000 ohms said means being adjustable to provide said oscillating voltage at any selected frequency with in a predetermined Wide frequency band, an electronic ampli?er tube having an anode and a cathode connected in an output circuit with the cathode connected to a source of voltage to be substantially maintained at a second voltage level more positive than said ?rst level, said tube also having a control grid, a grid resistor connecting 10 said grid to an intermediate point on said divider having a voltage below cut-oil voltage of the grid during the more negative portion of the oscillat- > ing voltage and above said second level during the more positive portion of the oscillating volt While there have been shown and described age, and a shunting capacitor connected from the and pointed out the fundamental novel features 15 end of said divider opposite said one end to said of the invention as applied to a preferred embodi— ment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its opera-. tion may be made by those skilled in the art without departing from the spirit of the inven tion. It is the intention, therefore, to be limited only as indicated by the scope of the following claim. What is claimed is: ‘A square wave generator comprising a resistive voltage divider having one end thereof connected to a source of voltage to be maintained at a point and‘ offering relatively high impedance at low frequencies and relatively low impedance at high frequencies with said band. CARL A. BERGFORS. REFERENCES CKTED The following references are of record in the ?le of this patent: UNITED STATES PATENTS Number _ Name Date 2,118,626 2,120,823 Smith ___________ __ May 24, 1938 White ___________ __ June 14, 1938 ?rst voltage level, means connected to said divider for impressing thereacross an oscillating voltage 2,131,566 Lindenblad _____ __'_ Sept. 27, 1938 2,200,073 Bedford __________ __ May 7, 1940 having a Wave form approaching a square wave, 2,324,279 Clark ___________ __ July 13, 1943 Certi?cate of Correction Patent No. 2,514,023 July 4, 1950 CARL A. BERGFORS It is hereby certi?ed that error appears in the printed speci?cation of the above numbered patent requiring correction as follows: Column 8, line 19, for the Word “with” read within; and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent O?ce. Signed and sealed this 3rd day of October, A. D. 1950. [sun] THOMAS F. _MURPHY, Assistant (Jammz'ssz'oner of Patents.