US2448070A

US2448070A - Saw-tooth generator with automatic amplitude control

Info

Publication number: US2448070A
Application number: US551949A
Authority: US
Inventors: David E Sunstein
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1944-08-30
Filing date: 1944-08-30
Publication date: 1948-08-31
Anticipated expiration: 1965-08-31
Also published as: GB604939A

Description

D. E. SUNSTEIN SAW TOOTH GENERATOR WITH AUTOMATIC AMPLITUDE CONTROL Filed Aug. 30, 1944 Aug; 31, 1948.

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INVENTOR.

FME

. Q Maw v Patented Aug. 31, 1948 SAW-TOOTH GENERATOR WITH AUTO- MATIC AMPLITUDE CONTROL David E. Sunstein, Elkins Park, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application August 30, 1944, Serial No. 551,949

12 Claims. '(Cl. 250-36) The present invention relates to an automatically synchronized saw tooth generator, and more particuarly to such generator for use as a time axis generator or sweep control for an oscilloscope.

Heretofore cathode ray tubes .or oscilloscopes have been provided for operation in accordance with a synchronization signal. Where the synchronization signal is variable in frequency, it has been necessary to provide a number of manual controls to adjust the operation of the saw tooth generator. Since considerable skill is required in the adjustment of such manual controls, it has been found desirable to provide a saw tooth generator which automatically is synchronized to respond to the variations in frequency of the synchronizing or control voltage. Accordingly in a co-pending application for an automatically synchronized saw tooth generator filed by David E. Sunstein and Millard E. Ames, Jr., Serial No. 551,948, filed August 30, 1944, there is provided a saw tooth generator which has an automatic amplitude control to maintain the amplitude of the saw tooth output wave constant independent of the frequency of operation. In that co-pending application there is disclosed a circuit arrangement wherein a source of potential, a capacitor, a charging device and a discharging device for. the capacitor are provided;

one of which has a rapid operating characteristic and the other has a variable operating characteristic. An automatic amplitude control applies a control voltage to the device having a variable operating characteristic to maintain constant the amplitude of the output voltage. Such an arrangement is characterized by perfect synchronization over a wide range of frequencies from seven cycles per second to seventy kilocycles. Substantially constant amplitude is obtained from the range of seven cycles per second to fifteen thousand cycles per second. A change of frequency within that range from the lowest value to the highest value requires about two seconds to reestablish stability of operation. While that arrangement is highly satisfactory for the use for which the circuit was intended, certain other applications have shown it desirable to provide a circuit wherein a lesser amount of time is required for the automatic adjustment of the system to a sudden change in the synchronizing frequency. In accordance with the present invention an improved automatic amplitude control circuit is provided to obtain a shorter response time to sudden changes in the input frequency.

It, therefore, isan object of the present invention to provide an improved automatically synchronized saw tooth generator for a cathode ray tube or an oscilloscope.

It is another object of the present invention to provide an improved saw tooth generator which is automatically synchronized to a control voltage and which is relatively rapid in response to changes in frequency of the control voltage.

Other and further objects of the present invention subsequently will become apparent from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a diagrammatic representation or block diagram illustrating the present invention;

Figure 2 is a circuit diagram illustrating one manner in which the present invention may be constructed; and

Figures 3, 4 and 5 are graphical representations explanatory of the operation of the circuit in Figure 2.

Referring to Figure 1, there is shown a source of direct current ll connected between ground and a rapid charging device l2 to charge a capacitor l3 which is connected in series with a grounded resistor M. A discharging circuit is provided for the capacitor i3 which includes a variable discharge device I5 which may have in series therewith a direct current meter IS. The voltage appearing across the capacitor I3 as a result of the operation of the charging and discharging circuits is of very nearly constant amplitude over the normal frequency range of operation, and hence the direct current meter IE will be deflected substantially directly proportional to the frequency of operation. This is brought about by the fact that the charging time of the capacitor I 3 is substantially negligible as compared to the discharge time so that the direct current meter It will respond to current which is substantially directly proportional to the frequency of operation, and hence this meter may be used as a frequency meter. An automatic amplitude control I! indicated by a dotted line rectangle controls the operation of the variable discharge device 15. A pair of output terminals [8 is connected between ground and one side of the capacitor 13. The function of the automatic amplitude control is to adjust the rate of discharge of the variable discharge device IS in accordance with the tendency for changes in the amplitude of the charge to take place with changes in frequency of discharge. The automatic amplitude control includes a number of components indicated by various rectangles and circuit elements. One of these devices is a slow acting automatic sensitivity control H? which is arranged to control the conductance of a vacuum tube forming a portion of the variable discharge device it. The rate of discharge provided by the variable discharge device I5 further is also controlledfor each cycle of operation. of the capacitor |3 by a circuit including a capacitor 2| which has one terminal grounded. A very rapid discharging circuit or device 22 is connected in parallel with the capacitor 2| to discharge the capacitor at the beginning of each charging cycle of the capacitor l3. The capacitor 2| is provided with a rapid charging circuit or device 23 which may be controlled from a circuit including a capacitor 24 and a resistor 25 connected between ground and one side of the capacitor l3. The rapid charging device 23 functions to charge capacitor 2| to a degree proportional to the charge added to the capacitor |3 by the rapid charging device I 2. The charge placed on the capacitor 2| by the charging device 23 is therefore a measure of the amplitude of the previous saw tooth generated across the capacitor" l3, and hence may be used to control the rate of discharge of the discharge device l5 for the ensuing discharge cycle of capacitor |3.

When the rapid charging device is operating at constant frequency then the amplitude of the potential across the capacitor |3 during the ensuing discharge cycle can be controlled on the basis of the amplitude of the potential during the preceding discharge cycle of the capacitor l3. Thus if during the previous discharge cycle of the capacitor l3 the potential charge was of small amplitude, the charge on the capacitor 2| during the ensuing cycle is small, thereby causing the rate of discharge, of the capacitor I3, controlled by the discharge device IE, to be increased through the ensuing cycle. During the ensuing discharge cycle of the capacitor I3, the potential change will be of larger amplitude than the previous cycle. Conversely if during the previous discharge of the capacitor |3 the potential change was of large amplitude, then a large charge is placed on the capacitor 2| which is maintained through-out the ensuing cycle so as to decrease the discharge rate of the discharge device l5, thereby causing a reduction in the amplitude of the potential change during ensuing cycle of the discharge of the capacitor l3. The automatic amplitude control I"! thus permits the rate of operation of the device I5 to be changed with great rapidity so that if the frequency of operation of the rapid charging device I2 is suddenly shifted, the voltage sweep across the capacitor |3 will not exceed or be less than a predetermined value for more than one cycle of operation.

One manner in which the various devices indicated by rectangles in the block diagram of Figure 1 may be constructed is shown by the circuit diagram in Figure 2. In this figure the reference characters applied to the various devices indicated by rectangles are directed to the vacuum tubes included in such devices and to the associated circuits. The positive terminal of the direct cur-rent source of voltage U of Figure 1 has been indicated by the plus sign at various terminals in the circuit of Figure 2.

The rapid charging device for the capacitor |3includes a controlled electric valve 26 which may be of any suitable type containing a gas or other ionizable medium. A convenient type of tube is a t'hyratron tube 884. The grid of the gas substantially tube or controlled electric valve 26 is provided with a grounded grid resistor 21 and the grid is coupled by a capacitor 28 to a square wave generator 29. The square wave generator is provided with a pair of terminals 3| which may be supplied with a suitable synchronizing or signal voltageto initiat'e operation of the generator. The square wave generatcrmay comprise any one of a number of suitable generators, preferably of the peak clipping variety. Alternatively, in stead of a square wave generator, any pulse generator could'be employed, but preferably the magnitude of the pulse so formed should be invariant with changes of signal strength at terminals 3|.

The vacuum tube 26 has a characteristic that whenthe voltage appearing at the grid bears a certain relation to the anode voltage, ionization takes place so that current is conducted between the anode and the cathode until a certain voltage condition exists whereby the effective potential between the anode and cathode is insufiicient to maintainionization. When the capacitor |3has become charged, the potential between the anode and' cathode" of the gas tube 26 is so reduced that ionization cannot be maintained, and the tube becomesnon-conductive. Conductivity of the tube is initiated by the voltage supplied by the square-wave generator" 29. After the capacitor |3 has been charged; the variable discharge device |5 dissipate-s the charge on the capacitor |3'at a controlled rate.

The variable discharge device l5 includes a vacuum tube 32 which preferably is'of the pentode type having a characteristic of maintaining constant: anode current even though" the voltage between the anode and cathodevaries appreciably. The anode of the vacuumtube 32" may be connected through the direct current meter 5 to one side of the capac-- itor 3. The cathode of the vacuum tube 32 is connected to the other side of the capacitor I3, or directly to ground. The screen grid of the vacuum tube'32 is connected to an intermediate point on the source of voltage. A control grid is connected to the negative terminal of a source of potential 33, the positive terminal of which is connected to the anode of avacuum tube 34. The cathode of the vacuum tube 34 is connected to the positive terminal of abiasing source of voltage 35, the negative terminal of which is connected to ground.

The vacuum tube 34 constitutes a polarity reversingstage to'bias the control grid of the vacuum tube 32 negatively during the time that the capacitor I3 is being charged and to make the control grid more negative when a higher potential charge is to be placed on capacitor 2|. The grid of" the vacuum tube 34 is connected to a resistor 36 which in turn'is connected to a capacitor 2| having one terminal grounded. The grid of the vacuum tube 34 is also connected to the positive terminal of a source of biasing potential 38, the-negative terminal of which is connected to the grid of an electric valve 39. The cathode of the valve 39 is connected to the ungrounded terminal of the capacitor 2|. The anode of the valve 391 is connected to one terminal of a resistor 25, the other terminal of which is grounded.

The electric valve 39 is included in a circuit comprising the device 23 for rapidly charging the capacitor 2|. A discharging circuit is provided for the capacitor 2| which includes an electric valve 4| having an anode connected through the resistor 36 tothe capacitor 2|. The

cathode of the electric valve 4| is connected to a positive terminal of a biasing voltage source 42. The grid of the vacuum tube 4| has a grounded grid resistor 43, and the grid is coupled by at capacitor 44 to the juncture of resistor M with capacitor Hi. The electric valve 4| and the associated circuit constitute the rapid discharge de vice 22, for rapidly discharging the capacitor 2|.

The charging circuit for the capacitor 2|, which includes the gas tube 39, receives its potential from the capacitor 24 which is interconnected with capacitor l3 by an isolation stage. This isolation stage includes a vacuum tube 45 which may be of the pentode type having its anode and several of its grids connected through a load resistor 50 to the source of anode potential. The cathode of the vacuum tube 45 is connected to the capacitor 24, The grid of the vacuum tube 45 is coupled by a capacitor 46 to one side of the capacitor l3, so that the conductivity of the vacuum tube 45 is determined by the voltage appearing across the capacitor l3. Hence the voltage supplied through the capacitor 24 to .the electric valve 39 would ordinarily be proportional to the voltage across the capacitor l3. However, the resistor 25, of relatively small value, in conjunction with the capacitor 24 acts as a difierentiating circuit so that anode voltage of the valve 39 is proportional to the rate of change of the potential appearing across capacitor I3. The grid of the vacuum tube 45 is connected to a grid resistor 41 which is connected to another resistor 48. The common juncture between the

resistors

41 and 48 is connected to a by-pass capacitor 49 connected to the cathode of the vacuum tube 45. A voltage divider comprising two resistors 5| and 52 is connected across the output terminals l8, and the common juncture between these resistors is connected to one end of the resistor 48. The isolation stage thus described operates to reduce any load on the capacitor l3, since such load must be made negligible compared to the anode current of the discharge tube 32 if the discharge is to be maintained substantially linear. A further advantage of the isolating stage is to permit the net resistive component of the impedance across the capacitor |3 to be maintained at a relatively high value so that the capacitor l3 may be of a small size even at low operating frequencies. of the capacitor l3 as small 'as possible, the charging time is maintained at a low value even at the highest audio frequencies.

Another grid of the vacuum tube 32 is connected to a filter circuit including

series resistors

53 and 54 and grounded filter capacitors 55 and 56. The filter circuit thus described is con? nee-ted to the anode of a. diode vacuum tube 51.

An anode circuit resistor 58 is connected between ground and the anode of the diode 51, and the anode is coupled by a capacitor 59 to the anode of tube 45. The cathode of the vacuum tube 51 is connected to the positive terminal of a suitable source of biasing voltage 6| so as to provide the desired degree of delay bias in the operation of the diode rectifier. This delay permits the operation of the vacuum tube 51 to be responsive only to a potential of sweep amplitude appearing across capacitor IS in excess of a predetermined value. The diode rectifier 51 and associated filter and control circuit components therefor comprise the slow acting automatic sensitivity control l9 used to adjust the sensitivity of discharge device |5 so as to maintain a constant By maintaining the size amplitude output at the terminals l8, as shown in Figure 3.

'It may be assumed now that a signal or control voltage is applied to the terminals 3| of the square wave generator 29 thus causing this generator to supply to the grid of the electric valve 26 a positive potential. The positive potential produces ionization so as to render this valve conductive so that the capacitor I3 is new connected in a charging circuit which includes the resistor I4. T-he resistor M has a relatively low value so as not to render the rate of charge of the capacitor l3 excessively great and yet the value of resistor i4 must be sufficient to supply the necessary voltage to initiate operation of the electric valve 4|.

The initiation of the conductivity of the electric valve 26 generates a. voltage drop across the resistor M which is applied through the coupling capacitor 44 to the control grid of the electric valve 4|. The electric valve 4| is arranged to discharge the potential appearing across the capacitor 2| to a predetermined value. The change in voltage produced across the resistor 36 by the discharge of the capacitor 2| applies a potential to the control grid of the electric valve 39 so as to render this valve non-conductive. The increase of potential appearing across the capacitor |3 which is being charged is transmitted through the isolation stage including the vacuum tube 45 to the capacitor 24 so that the charging circuit including the electric valve 39 will charge the capacitor 2| to a voltage directly proportional to the change in voltage produced across the capacitor |3 by electric valve 26.

When the charge being developed across the capacitor l3 increases to a certain value, the potential appearing between the anode and the cathode of the electric valve 26 is insufficient to maintain ionization so that the valve then becomes non-conductive. Similarly, as the capacitor 2| is charged to a certain value, the potential appearing between the cathode and anode of the electric valve 39 becomes insufficient to support ionization so that this valve becomes non-conductive. The capacitor 2| therefore now has a certain potential thereon which potential is utilized to control the rate of discharge of the discharging circuit for the capacitor l3. The potential appearing on the capacitor 2| is applied through the resistor 36 to the grid of the polarity reversing vacuum tube 34 so as to reduce by the desired amount the negative biasing appearing at the control grid of the discharging vacuum tube 32. Upon completion of the discharge of the capacitor |3 at a rate as determined by the operation of the vacuum tube 32, the apparatus is then again in condition to repeat the previously described cycle of operation.

Each time, the capacitor 2| is very rapidly discharged by the electric valve 4| and then charged by the electric valve 39 to a voltage directly proportional to the charge being placed on the capacitor l3. If the frequency of operation of the square wave generator 29 is varied in accordance with the change in the frequency of the control signal applied to the terminals 3|, it will be appreciated that any variation produced in the charge across the capacitor I3 will be corrected in one cycle of operation. Thus there has been provided a circuit which can follow with rapidity any changes in the frequency of the input signal even though such changes are over wide ranges and are made suddenly.

Proper operation will be achieved only when the 1'7 variable discharge device I including the vacuum tube 32 is operated in accordance with a given and proper relationship between the rate of discharge and the amplitude of applied controlling signal supplied by the capacitor 2|. Let it be assumed that a condition of operation exists in which the charging device I2 is operating at constant frequency and in which the tube 32 of variable discharge device I5 is overly sensitive, i. e., in which the rate of discharge varies too much for changes in controlling signal from the capacitor 2|. Then the wave form of the voltage across the capacitor l3 will appear as in Figure 4, instead of as in Figure 3 which represents proper operation resulting when variable discharge device |5 has proper sensitivity. In Figure 4 the capacitor 13 is charged over portion III of the curve by the rapid charging device l2. Then let it be assumed that the capacitor I3 is discharged rapidly over the portion ll of the curve thereby causing a large amplitude of discharge up to the time indicated by point 12. At the time indicated by point 12, the rapid charging device I2 is again operated to charge capacitor I3 over the portion '13 of the curve. discharge H was of large amplitude, the capacitor 2| receives a large charge by the time that curve 13 reaches the point 14. Since it is assumed that the vacuum tube 32 of the variable discharge device [5 is overly sensitive, this large charge on the capacitor 2| causes the ensuing discharge cycle 15 of the capacitor l3 to be made at a very slow rate, resulting in small amplitude of discharge up to the time 16. The capacitor 2| then is discharged and it receives a small charge 'because of the fact that the cycle 15 was of small amplitude. This will cause the ensuing cycle 18 to be of even greater amplitude than cycle thereby causing cycle I9 to be of even less amplitude than cycle 15, etc. Thus a condition of oscillation is established if variable discharge device I5 is overly sensitive.

If it is assumed that the vacuum tube 32 of the variable discharge device I5 is under sensitive, the output wave appearing across the capacitor [3 will be similar to that shown in Figure 5, in which stable equilibrium is reached after many cycles, but at very small amplitude.

In order to maintain the sensitivity of the variable discharge device l5 at the particular value for proper operation represented by Figure 3, the slow acting sensitivity controllS is included which adjusts the sensitivity of discharge device in accordance with the average amplitude of several preceding cycles of discharge. Thus if the average peak amplitude of the discharge is large, the sensitivity control [9 acts to reduce the sensitivity of the variable discharge device I5. Conversely, if the average peak amplitude of discharge is small, the sensitivity control IS increases the sensitivity of the variable discharge device 15. Thus operation with the proper sensitivity of the variable discharge device I5 is insured so that the output wave will be as in Figure 3 for the case of constant frequency operation of the charging device l2.

The ability of the circuit shown in Figure 2 to follow rapid or great changes in the frequency of operation as determined by the control signal applied to the terminals 3|, is dependent upon a particular transconductance value for the vacuum tube 32. This transconductance value, which is the ratio of the change in plate current compared to the control grid voltage producing the change, is directly related to the ratio of the Since the discharge current of the vacuum tube 32 com-' pared to the voltage appearing across the capacitor 2|. This relationship must have a particular value since if the transconductance is too small, then each successive saw tooth of the output appearing across the terminals l8 will be decreased in amplitude as in Fig. 5. If the transconductance is too large, the eiiect will be as in Fig. 4. While the transconductance of the vacuum tube 32 may be controlled by a manually adjustable control, thus adjustment is rather critical and is obviated by the provision of a slow acting automatic sensitivity control. Therefore, the operation of the vacuum tube 51 is such as to control the transconductance of the vacuum tube 32 according to the average amplitude of several successive saw tooth voltages appearing across the output terminals IS. The capacitor 59 is connected to the ungrounded terminal of the grounded resistor 53 so that a potential is developed across this resistor porportional to the saw tooth voltages appearing across the output terminals. The cathode of the vacuum tube rectifier 53" has been provided with a small positive bias to provide the desired degree of delay. The voltage appearing across the resistor 58 is developed by voltages obtained from a plurality of successive saw tooth voltages at the output terminals. When the anode end of the resistor 58 exceeds a certain voltage value, the diode rectifier 57 will become conductive to a greater degree thereby modifying the voltage being supplied through the filter network including the

resistors

53 and 54 and the capacitors 55 and 56 'to one of the grids of the vacuum tube 32. A variation of the voltage supplied to this grid of the vacuum tube 32 controls the transcondu-ctance of the tube in accordance with the average of several saw tooth voltages appearing in succession across the output terminals 18.

While for the purpose of explanation and illustration of the present invention, there has been shown in the drawing a certain arrangement embodying the present invention, it is to be understood that the invention is not to be limited thereby since obviously other circuit arrangements may be provided, and such variations in the circuit arrangements and in the instrumentalities employed are contemplated as may be commensurate with the spirit and scope of the invention "as set forth in the appended claims.

This invention is hereby claimed as follows:

1. The combination comprising a source of unidirectional current, an energy storage device, a charging device for charging said storage device from said source, a discharging device for said storage device, and means responsive to the magnitude of the voltage of each charge of said storage device for controlling the rate of discharge of said discharging device.

2. The combination comprising a source of unidirectional current, an energy storage device, means for charging said device from said source, means for discharging said device at a controlled rate, means responsive to a signa1 voltage for controlling the operation of said charging means,

and means responsive to the magnitude of the charge supplied to said device for modifying the rate of discharge of said discharging means, and an output circuit arranged to be energized by said device.

3. The combination comprising a source of unidirectional current, an energy storage device, a circuit for rapidly charging said device from said source, a circuit for discharging said device at a controlled rate, an output circuit arranged to be energized by said device, means operating on each cycle of said charging circuit to determine the rate of operation of said discharging circuit, and means for further modifying the rate of operation of said discharging circuit in accordance with the value of the output potential appearing across said output circuit averaged for a plurality of cycles.

4. The combination comprising a source of di rect current, an energy storage device, a circuit for rapidly charging said device from said source, a discharging circuit for said device, said discharging circuit including a vacuum tube having a control circuit including an energy storage device responsive to the maximum voltage of the charge appearing across said first device to control the rate of discharge of said first device.

5. The combination comprising a source of 'direct current, an energy storage device, a circuit for rapidly charging said device from said source, and a circuitfor discharging said device at a controlled rate, said discharging circuit includ-- ing a vacuum tube, means for varying the transconductance of said vacuum tube in accordance with the average values of a plurality of successive values appearing across said device, and means for modifying the conductivity of said vacuum tube in accordance with the magnitude of each charge of said device.

6. The combination comprising a source of direct current, a capacitor, a circuit for rapidly charging said capacitor in response to a control signal, a discharging circuit for said capacitor including a vacuum tube, an output circuit arranged to be energized by said capacitor, means for varying the transconductance of said vacuum tube in accordance with the average values of a plurality of successive potentials appearing across said output circuit, a control circuit for said vacuum tube for controlling the rate of discharge of said capacitor in accordance with the value of each charge appearing across said capacitor including a second capacitor arranged to receive a charge proportional to the charge supplied to said first capacitor by said circuit for rapidly charging said first capacitor.

7. The combination comprising a source of direct current, a capacitor, a circuit for rapidly charging said capacitor from said source, and a circuit for discharging said capacitor at a controlled rate, said discharging circuit including a vacuum tube having a control circuit including a second capacitor for supplying potential thereto, means for discharging said second capacitor While said first capacitor is being charged, and means for charging said second capacitor to a voltage proportional to the charge across said first capacitor while said first capacitor is being charged.

8. The combination comprising a capacitor. a source of unidirectional current for rapidly charging said capacitor, a discharging circuit for said capacitor including a vacuum tube having a control circuit for modifying the rate of discharge in accordance with the magnitude of the charge appearing across said capacitor, said control circuit including a second capacitor, a discharge circuit for said second capacitor arranged to be responsive to the initiation of the charging cycle of said first capacitor, and a charging circuit for said second capacitor arranged to rapidly charge said second capacitor during the charging period of said first capacitor to a voltage proportional to the charge placed upon said first capacitor by said source of unidirectional current.

9. A sawtooth wave generating system, comprising a capacitor, means responsive to a synchronizing signal for charging said capacitor, means for discharging said capacitor, whereby to generate a sawtooth wave, and means responsive to the magnitude of the charge on said capacitor during each charging cycle for varying the rate of discharge of the capacitor, so as to maintain synchronization over a range of frequencies of said signal and to maintain the amplitude of the generated sawtooth wave substantially constant.

10. A sawtooth wave generating system, comprising a capacitor, means responsive to a synchronizin signal for charging said capacitor, means for discharging said capacitor, whereby to generate a sawtooth wave, a second capacitor, means for charging said second condenser proportionately to the charge on said first capacitor, and means responsive to the charge on said second capacitor for varying the rate of discharge of said first capacitor, so as to maintain synchronization over a range of frequencies of said signal and to maintain the amplitude of the generated sawtooth wave substantially constant.

11. A sawtooth wave generatin system, comprising a capacitor, means responsive to a synchronizing signal for charging said capacitor, means for discharging said capacitor, whereby to generate a sawtooth wave, said discharging means including a controllable device whose sensitivity may be varied, means responsive to the magnitude of the charge on said capacitor during each charging cycle for controlling said device so as to control the rate of discharge of the capacitor, to thus maintain synchronization over a range of frequencies and also to maintain the amplitude of the generated sawtooth wave substantially constant, and means for controlling the sensitivity of said device in accordance with the average voltage across said capacitor during a number of cycles.

12. A sawtooth wave generatin system, coInprising a capacitor, means for alternately chargin and discharging said capacitor to produce a sawtooth voltage wave in response to a synchronizing signal, a second capacitor, means responsive to each cycle of the sawtooth Wave for charging and discharging said second capacitor, and means controlled by said second capacitor for controlling the amplitude of said sawtooth wave so as to maintain synchronization over a range of frequencies of said signal and to maintain the amplitude of said wave substantially constant,

DAVID E. SUNSTEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,102,951 Hackenberg Dec. 21, 1937 2,126,243 Busse Aug. 9, 1938 2,153,217 Mark Apr. 4, 1939 2,167,496 Bauer July 25, 1939 2,180,365 Norton Nov. 21, 1939 2,227,815 Toulon Jan. 7, 1941 2,265,290 Knick Dec. 9, 1941 OTHER REFERENCES A. P. C. Application of De France, Serial No. 464,750, published June 8, 1943.