US2492018A - Synchronizing system for sawtooth wave generators - Google Patents

Description

Dec. 20, 1949 D. E. sUNsTElN 24929918 SYNCHRONIZING SYSTEM FOR SAW TOOTH WAVE GENERTORS Filed Nov. 11, 1944 2 Sheets-Sheet 2 Z/ l GAS FILLED Kap/d 1 2 Patented Dec. 20, 1949 SYNCHRONEZING SYSTEM FOR SAW- TOOTH J'VAVE GENERATRS David E. Sunstein, Elkins Park, Pa., assigner to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application November 11, 1944, Serial No. 563,027

(Cl. Z50-36) 5 Claims.

The present invention relates to an automatically synchronized saw tooth generator and more particularly to such generator for use as a time axis generator or sweep control for an oscilloscope. For certain applications of the oscilloscope the saw tooth generator is of the type which is synchronized with another operation as in the case of television systems, vibration, acoustic, and speech investigations and studies. Where synchronization is to occur in response to a variable frequency input, generally it has been necessary to provide a number of manual controls to adjust the operation of the saw tooth generator. Considerable skill is required in adjusting such manual controls, which may be rather large in number, in order to provide the desired operation. It, therefore, would be desirable to provide a saw tooth generator which would be synchronized automatically to the variations in frequency of the initiating voltage, and which has a wide range of operation over the desired band of frequencies and which provides a saw tooth wave having an amplitude substantially independent of the frequency.

In accordance with the present invention a saw tooth generator is provided with a frequency to-voltage translator responding` to the control of input frequency which is used to control the rate of operation of an either variable discharging device or a variable charging device for an energy storage circuit. The frequency-to-voltage translator responds to the change in frequency to modify the operation of the charging or discharging device so that the saw tooth wave is maintained at substantially constant amplitude throughout the range of operation over a band of frequencies.

The frequency-to-voltage translator controls the rate of charging or discharging of the capacitor or energy storage circuit on the basis of sev-v eral precedingl cycles of the input control frequency. If it is desired to have an extremely rapid rate of response to the change of the rate of the input frequency, the frequency-to-voltage translator may be modified to measure the period of one previous cycle and to control the charging or discharging on that basis. Such an arrangement may also be combined with an automatic amplitude control responsive to the amplitude of the output of the `saw tooth wave which in conjunction with the frequency-to-voltage translator operates to control the charging or discharging circuit for the capacitor.

It, therefore, is an object of the present in. vention to provide an improved timing axis generator for an oscilloscope which will provide an output wave or signal of substantially constant amplitude independently of the frequency of operation.

Another object of the present invention is to provide an improved saw tooth generator Which is automatically synchronized with a varying frequency control signal, such as speech, music, or the like.

Still another object of the present invention is to provide an improved circuit which may be used as a frequency divider.

Other and further objects of the present in venton subsequently will become apparent from the following description taken in connection with the accompanying drawings in which Figure l is a block diagram of one embodiment of the present invention;

Figure 2 is a block diagram of another embodiment of the present invention;

Figure 3 is the embodiment shown in Figure 1 illustrating certain circuit details;

Figure 4 is a block diagram of still another embodiment simiiar to that shown in Figure 1;

Figure 5 shows certain details of the embodiment of Figure 4;

Figure 6 is a diagram of an embodiment having a more rapid rate of response to frequency change;

Figure 7 is a block diagram of still another embodiment; and

Figure 8 is a diagram showing certain circuit details of the embodiment of Figure 7.

The block diagram in Figure 1 shows a source of signal energy i I arranged to control the operation of a rapid charging device I2 having a suitable source of energy such as the battery I3. The rapid charging device supplies energy to an energy storage circuit in the form of a capacitor I4 which is connected to a pair of output terminals I5.

f The source of energy I3 and the capacitor I4 are each connected to ground. The capacitor I4 is discharged by a variable discharging device I6 the rate of operation of which is controlled by a 40 frequency-to-voltage translator Il, receiving energy from the signal source II. In this circuit arrangement the capacitor It is rapidly charged to a certain voltage value by the rapid charging device I2. Upon reaching this predetermined value the variable discharging device It reduces the charge across the capacitor I4 to a predetermined value in a certain time interval. The time interval is determined by the rate of operation of the variable discharging device It Which is controlled by the frequency-to-voltage translator I'I. The variable discharging device I6 preferably is of a type which discharges the capacitor at a constant rate for any given value of the rate of discharge as determined by the action of the frequency-to-voltage translator il. When the capacitor I4 has been discharged or partially discharged the cycle is repeated. This operation produces a saw tooth output voltage across the terminals I5 having a steep or substantially perpendicular wave front followed by a substantially The capacitor is is connectedto a rapid dis- ,v

charging' device I8 which rapidly dissipatesthe charge across the capacitor I,4 so that the discharging portion of the saw toth wave appearing across the terminals I5 is substantially perpendicular. The capacitor I4 is charged to a predetermined*voltage value by a variable charging device lil connected in series with the 4voltage source i3rso thatrth'e wavefront of the saw tooth generated by the capacitor has a sub*` stantially constant slope for any constant irequency Iof the signalgenerator II. vThewoutput wave obtained by blockudiagram in Figure@ therefore is a reversal of the saw tooth wave obtained by the block diagram of Figure 1. l 4

i To illustrate the manner in which the block diagram of lFigure 1 may be constructed there is shown in Figure 3 a signal generator Il which is connected to a square wavegenerator 2i coupled through a blocking capacitorr22 to the grid of an electric valve 23. The electric valve I2.3 coniprises a tube lof the type` having within its envelope a gas or an io-ninable medium as yis the case in Thyratron tubes. The gas tube 23 constitutes thetube used in the rapid charging device i2 and its anode is connected to the posin tive terminal of a suitable source of voltage such as a source of voltage I3 as shown in Figure 1. The grid of the gas tube 23 has a grid resistor 24 connected to an adjustable contact on a resistor 25 vwhich is connected between ground and a suitable source of positive biasing voltage The Tliyratron 23 has its vcathode connected to the capacitor i t whichin turn is provided with a current limiting resistor n26 having one terminal connected to ground. The circuit thus far described therefore constitutes a 'rapid charging circuit for the capacitor I4. The capacitor I4 is connected between 'the/ anode and cathode of a vacuum tube `2l which preferably is of the pentode type which has the characteristic of maintaining substantially constant anode current even though the voltage between the anode and cathode varies over a substantial range. The pentode 21 is used todischarge the capacitor iii, and the rate of operation ofthe pentode 2l is controlled in accordance with the voltage determined by the frequency-to-voltage translator I? of Figure 1. The `suppressor grid of the vacuum tube 21 is connected to ground. The screen grid of the vacuum tube 21 is connected to a suitable source of potential, preferably through an 1in-bypassed resistor 2G. The vcontrol grid of the vacuum tube 2T is connected to a switch arm 28 adapted to contact a plurality of contact points veachhconnected to different portions of a resistor 29. comprising a resistor 3I and a capacitor 32 connested between ground and the square wave generator 2i integrates the output of the square wave generator t`o supply an integrated output to a diode rectifier 33 having its cathode grounded. The anode of the diode rectifier 33 therefore is connected between the common juncture of the resistor SI and the capacitor 32. The diode rectiyri'er 33 operates t'o form fa 'unidirectional voltage bias "across the capacitor 32, which is inversely An integrating network proportional to the frequency supplied by the signal generator'A Ii at the synchronous input terminals of the square wave generator E I. The unidirectional voltage thus generated is filtered by a resistor 34 and a capacitor 35 to supply voltage to the voltage divider resistor 2Q. *3y rnv/"ement of the switch arm 28, a certain portion of the direct current voltage is supplied to the control grid of the variable discharge tube 2. When the voltage supplied to the control grid oi the vacuum tube 2'! `is a large portion of the voltage appearing across the resistor 2t', a certain step-down ratio is obtained between the irequency of the signal generator Ii and the frequency of the saw tooth voltage appearing across the outputterminals Thus the arrangement Figure 3 by operation of the switch 28 may beused as a frequency divider. The circuit elements associated with the diode comprise the frequency-tolvoltagetranslator Il in the diagram of kiigure 1t `As the frequency of the signal voltage il changes, the direct current cias appearing across tlie capacitor 32 is changed so that the voltage supplied to the discharging vacuum tube 2 is changed therefore modifying the rate of discharge of the capacitor i4 so that the irequency of the output saw tooth wave appearing across the terminals yI5 is rapidly brought into synchronism with the stabilized changed irethrough the variablev discharge device I6.

4 quencynoi the signal generator I I.

V1n order to increase the range of operation of the system shown inyigures 1 and 3 certain modications may be introduced as illustrated by the block diagram of Figure 4. In this arrangement the various parts yhavebe'en given reference characters corresponding to the same parts in Figures 1 and 3 fromlwhich it will be seen that the output terminals I5 appear across the series circuit comprising the capacitor I4 andthe current limiting resistor 2li. The variable discharging device Iiiuis directly connected across the caps citorl I4. The operation'oi 4the discharging device I6 is controlled. by the Vdifference between two signalsq One of these signals is derived from the frequencyfto-voltag'e translator I'I, and the other signal is derived 4from the current limiting resistor 25. The second signal is proportional to the direct current component of current owing The voltage component appearing across the resistor 26 is supplied to a low pass lter 3l the output of whichis connected to a direct current amplifier 38. The variable v discharge I6 also receives a voltage component vfrom the frequency-to-voltage translatorl'l from which is subtracted the direct current component supplied by amplifier 38. This produces a Icurrent degeneration which insures a greater rangev of'loperation than is obtainable by the circuit arrangement of Figure 3 by overcoming any inherent lnonlinearity between the rate of discharge of the vacuum tube 27 and the signal supplied` from the frequency-to-voltage translator Il. Thus there is insured that the currevnttdraw'n by the'discharge tube 2l will bear a nearly linear relationship to the voltage sup plied to its control gri'd over a very wide range of voltages supplied thereto, as contrasted to a relatively narrower 'range capable of being handled by the circuit 'arrangement in Figure 3. i One manner in which the modification of Jigure '4 may b'eapplied to the circuit arrangement shownin Figure3 is illustratedin Figure 5. The adjustable contact 28 for 'the resistor 2e is connectedvto the control grid of the Variable discharge tub'e 2,1. v'The 4screen grdis supplied from a suitable source of potential through a resistor l 39 which is by-passed to ground by a capacitor 4I. The voltage supplied to the screen grid of the vacuum tube 21 is modified by the direct current component obtained across the current limiting resistor 26 which is connected to -a lowpass filter comprising a resistor 42 and a capacitor 43. The common juncture between the resistor 42 and the capacitor 43 is connected to a grid of a vacuum tube 44 having its anode connected to the screen grid of the vacuum tube 21. The cathode of the vacuum tube 44 is connected through a biasing resistor 45 to ground. The vacuum tube 44 operates as a direct current amplier with the resistor 39 operating as a plate or load resistor for the vacuum tube 44. The alternating current components are by-passed by the capacitor 4I. The voltage appearing at the anode of the vacuum tube 44 therefore is the voltage which is supplied to the screen grid of the vacuum tube 21. If it is assumed that the signal source II is increased in frequency, the integrator circuit including the resistor 3| and the capacitor 32 will cause the diode rectifier 33 to operate to reduce the negative bias applied to the grid of the variable discharge vacuum tube 21. This produces an increase in the rate of discharge of the capacitor and in the current flow through the tube 21 so that an increased voltage drop is produced across the current limiting resistor 26. This voltage drop across the resistor 26 is amplified by the direct current amplifying tube 44 to lower the screen grid voltage of the discharge tube A21 thereby tending to reduce the current drawn by that discharge tube. This tendency therefore tends to maintain more nearly linear the modified rate of discharge of the capacitor I4 for the changed signal frequency. The circuit therefore obviates the frequency range limitation obtained by the circuit arrangement in Figure 3 which has -an inherent nonlinearlty above a certain frequency range.

In the preceding arrangements shown in detail in Figures 3 and 5 the rate of discharge of the vacuum tube 21 was controlled in accordance with the average of several preceding cycles of energy obtained from the signal source. It, therefore, will be appreciated that there is -a certain time delay between the change of frequency of the signal source and the time when the variabe discharge device reaches synchronism so as to produce a saw tooth wave of uniform amplitude in synchronism with the signal frequency. If it is desired to have an arrangement whereby the output wave responds very rapidly to any change of the frequency of the input wave, certain modifications may be made as are illustrated in Figure 6. A pulse generator 46 is arranged to be energized from the signal source l I; and the pulse generator, which preferably is of the type having an output wave of the peaked variety, supplies this wave to the grid of a Thyratron 41. The Thyratron 41 is connected, between the suitable source of anode potential and ground, in series with a capacitor 48 and a current limiting resistor 49. The peaked pulses of short duration impressed upon the grid of the Thyratron 41 produce ionization so as to bring about the charging of the capacitor 48 in synchronism with such pulses. The capacitor 48 is discharged at a substantially constant rate, either by a resistor or by a pentode vacuum tube I having its anode connected to the capacitor 48 and its cathode connected to ground. The pentode 5I has its suppressor grid connected to ground, its screen grid connected to a suitable source of potential, and its control grid is connected to the cathode. This produces a saw tooth wave which is fed through a coupling capacitor 52 to a diode vacuum tube 53. A resistor 54 is connected to the capacitor 52 so that the capacitor and resistor combina tion constitute a differentiating circuit which pro duces at the anode of the diode rectifier 53 a.r peaked wave having amplitude inversely propor-rv tional to the incoming frequency. This peaked rwave supplied to the diode rectifier 53 is utilized to charge a capacitor '55. The capacitor 55, however, is so arranged as to have been discharged at the time that the capacitor 48 was being charged. This is obtained by a Thyratron 56 and a biasing source of voltage 51 connected in parallel with the capacitor 55. The control electrode or grid of the Thyratron 56 receives energy from the common juncture between the capacitor 48 and the current limiting resistor 49 so that the "Thyratron 56 operates to discharge the capacitor 55 during each cycle or pulse corresponding to the frequency of the signal voltage I I. Since the capacitor 55 is arranged to be discharged once during each cycle, each succeeding charge is inversely proportional to the incoming frequency. The voltage appearing across the capacitor l55 therefore may be supplied to a phase inverter 58 so as to control the variable discharging device I6. The phase inverter 58, which may comprise a single stage amplifier, is provided in order to make the grid of the discharge tube of the variable discharging device I6 more negativev as the input frequency of the signal generator Il is decreased. Such an arrangement will control the bias of the variable discharging device I6 so as to adjust the rate of discharge to the incoming frequency `within a time interval represented by one cycle of the incoming frequency, thus insuring rapid adjustment of the output frequency and amplitude appearing across the terminals I5 with respect to the change in frequency of the signal voltage Il.

While the systems heretofore described have the inherent characteristic of maintaining a constant amplitude saw tooth output independent of changes in the signal frequency, oversensitivity of frequency-to-voltage translator I1 or of variable discharging device I6 or of variable charging device I9 will cause the amplitude to fall off with an increase of frequency, and undersensitivity will have the opposite effect. Therefore, in some cases it may be desirable to introduce an action which has inherently the characteristic of tending to produce a slightly reduced amplitude of saw tooth wave with an increase in the operating frequency. Such an arrangement is illustrated in Figure '1 which in addition to the previous components illustrated by the block diagrams in Figures 1 and 2 utilizes an automatic amplitude control 59 arranged to be energized directly from the capacitor I4. A component derived from the automatic amplitude control 59 is combined with a component of voltage derived from the frequency-to-voltage translator I1 by a voltage adder 6|. The voltage adder 6I is arranged to control the operation of the variable discharging device I6. The manner in which the automatic amplitude control serves to supply the voltage component is illustrated in Figure 8 where one terminal of the capacitor I4 is connected through a coupling capacitor 62 to the grid of a vacuum tube 63 which serves as an isolation stage. The cathode of the vacuum tube 63 is connected to one of the output terminals I5, the

other output terminal l5 being connected tol ground. A voltage divider comprising resistors 64 and 65 is connected between ground and the cathode oi the vacuum tube 63. The grid of the vacuum tube 63 is connected to series resistors 66 and 61 having their common juncture by'- passed by a capacitor 68 to the cathode of the vacuum tube 63. The other terminal of the re sistor 61 is connected to thecommon juncture of the resistors 64 and 65. The resistor 66 corresponds to a grid resistor, and the resistor 61 and the capacitor 68 constitute a filter circuit. The isolation stage thus described operates to reduce' any load on the capacitor I4 since it is desiredl to make such load negligible so as to maintain the discharge rate of the capacitor linear and' controllable by tube 21. The isolation stage therefore permits the' net resistive component of the impedance across theA capacitor I4 to be keptl at a relatively high value so' that the' size of the capacitor may be relatively small even at low frequencies.

The common juncture between the' resistors' 64 and 65 is capacitively coupled by a capacitor' 68' to the anode of a diode re'c'tier 69. The' anode' o'f the diode rectifier is provided with a grounded resistor 1l, and the voltage developed thereacr'oss is supplied to a lter circuit comprising resistors' 12 and 13 and by- pass capacitors 14 and 15. The output of the filter isv connected to a resistor 16 which also receives the voltage component frorn the frequency-toevoltage translator l1. The' juncture of resistors' 13r andl 1B is connected to the grid of discharge tube 21 so thatv the discharge tube 21 has its rate of dischargecontrolledby theA i sum of two voltage components so as to' give the desired operational characteristic. Thus resistor 16 working with resistors 1|', 12 and 13`cons'titute the voltage adder 6I.

While for the purpose o'f describing and illusi-y trating the present invention, certain specic embodiments have been shown in the drawings, itis t0 be understood that the invention is not to be limited thereby since such variations' in the circuit arrangements andin the' instrumentalitiesf employed are contemplated as may be commen` surate with the spirit and scope ofthe invention deiined in the following claims;

This invention is hereby claimed as follows:

1 The combination comprising a source ofT unidirectional voltage, a capacitor, means for charging said capacitor from saidsource of volt-r age, i eens for discharging said capacitor, vone of sai means having a rapid `rate of operation;

the other of said means having a variable rate 5.5

of operation, a source of signal volt'ag'e'ior` controlling the operation of theV iirst oneof said? means, means for deriving a rst control voltagel from said signal source, the' amplitude of said5r control voltage depending upon the frequency oi` said signal, means for deriving ase'co'nd'con'trolj voltage from the current through either ofvv saidl first two means, and means for applying bothL of said control voltages tothe meanshaving: a variable rate of operation .so` asto' control-thelatter.

2. The combination comprising asource' ofi unidirectional current', a capacitor; means for'v charging said capacitor fromsaidsourceoff volt-` age, means for discharging said'- capacitor, one' of said means having a rapid' rate of operation;

8i th'e'- other' of said means having a rate of operation`l which may be varied, a sources of signal voltage' for controlling the frequency of operation cf one' of said means, means responsive to the voltage` diference appearing across said capacitor for producing a control voltage, means for deriving a' second control voltage in accordance withthe frequency of said signal voltage, and means for combining said control voltages for varying the rate of operation of said second means.

3. The' combination' comprising a source of unidirectional' current, an energy storage circuit, means for charging said circuit from said source of voltage,y means for discharging said circuit, one of said' means having a rapid rate of operation, the other' of said means having a rate of operation which' may be varied, a source of signal voltage for controlling the frequency of operation' of one of said means, means responsive to' the` voltage difference appearing across said circuit for producing a control voltage, means 'for' driving ai secondcontrol voltage in accordance withI the frequency of said signal voltage, and means for combining said control voltages for varying the' rate' of operation of said second means.

41The' combination! comprising a source of unidirectional voltage, an energy storage device, means' forchaiging said' device from said source o'i voltage, means for' discharging said device, onev of said means having a rapid rate of operation, the other of said means having a rate of operationr which maybe varied, a source of sig nal' voltage' for controlling the frequency of operation of 'the rst one of said means, means for deriving a rst control' voltage from said signal source, the' amplitude off said control voltagev depending upon' the frequency of said signal, means for deriving a"4 second' control' voltage from the current' through` either of said first two means,

and means for applying both of said controlv stantially constant rate, a second capacitor,

means responsiveI to the voltage across said rst capacitor'for charging said second capacitor in inversev proportion' to the' frequency of said pulses, means' for discharging said' second capacitorCduring' the occurrence of each pulse, and

means'for deriving ari output' voltage `from across said'secondlcapacitor.

' DAV ID E. SUNSTEIN.

REFERENCES CITED lThe following references are of record in the le' of this patent:

UNITED STATES PATENTS Number Name Date 2,265,290" Knick-y Dec. 9, 1941 2,266,516 Russen Dec. 16, 1941 2,420,303 De France May 13, 1947 2'j448g069 Ames, Jr. Aug. 31, 1948- 21448Q0'70" Sunstein Aug. 31, 1948

Images