US2452213A - Wave generating system - Google Patents

Description

1948- c. G. SONTHEIMER 2,452,213

WAVE GENERATING SYSTEM Filed May 30, 1945 IN! 'IJNTOR. 0121 6. Saw/mama BY w g/20pm Patented Oct. 26, 1948 WAVE GENERATING SYSTEM Carl G. Sonthelmer, Riverside, Conn, asslgnor to Radio Corporation of America, a corporation of Delaware Application May 30, 1945, Serial No. 596,685

5 Claims.

The present invention relates to wave generating systems, and more particularly to a system for generating sawtooth waves having substantially linear leading edges.

The invention is concerned primarily with the generation of cyclically varying potentials wherein each cycle comprises a relatively slow potential variation in one direction followed by a relatively rapid potential variation in the opposite direction.

Voltages of the above nature may be employed, for instance, for the time-base deflection of the electron beam developed in cathode ray tubes used for television and oscillographic purposes. In television receivers, for example, reconstitution of a line of the transmitted image occurs during the slow motion of the cathode ray beam, while the rapid motion comprises the return stroke (during which the cathode ray beam is usually suppressed) which is necessary before the next following line of the image can be reconstituted. One of the requirements of such arrangements is that the slow motion of the beam shall be a uniform one, as otherwise distortion of the reproduced image results.

The complexity of conventional circuits for generating sawtooth waves increases in approximate proportion to the linearity of their output. The simplest system in general use is that in which a condenser is charged through a resistance from a source of potential and then discharged through a second lower resistance, (usually a tube) the process being repeated for each cycle of the wave. This latter system, however, yields an output voltage which rises exponentially with time.

According to a feature of the present invention, the linearity of output from a single condenser .network such as above described is materially improved by the addition of a second condenser having a separate charging path connected to the same potential source. The two condensers are then charged simultaneously, the output of the added condenser being applied during the charging interval to the original condenser to act in efiect as an increase in source potential during :the initial portion of the charging interval. As a result, the circuit output voltage has a substantially more linear characteristic than the output of the single condenser network alone.

One object of the present invention, therefore, is to provide a simple and eflectlve system for generating sawtooth waves theleading edges of which are substantially linear.

A further object of the present invention is to provide two energy-storage networks adapted to be simultaneously charged, the output or one of said networks being applied to the other of said networks during the charging interval to cause the charge on the latter to increase substantially proportionally with respect to time during a greater. portion of the charging interval than would normally be the case as a result of the charging of the latter network alone.

Other obiectsand advantages will be apparent from the following description of a preferred form of the invention and from the drawings, in which:

Fig. 1 is a circuit diagram of'a preferred form of the present invention;

Fig. 2 is a graph useful in explaining the operation of the circuit of Fig. 1; and

Fig. 3 is a circuit diagram illustrating an alternative arrangement in accordance with the invention.

Referring first to Fig. 1, there is shown a sawtooth wave generating circuit including three switches S1, S2, and $3, each of which will be assumed to be open for the purposes of the following description setting forth mainly the principles of operation. A'triode V1, normally biased to cut-ofi by any suitable means such as a source of negative potential, (not shown), is rendered conductive when periodically recurring substantially rectangular pulses P of positive polarity are received on the control electrode thereof. During the time that triode V1 is non-conductive, a condenser C1 in parallel with triode V1 is charged through a resistor R1 from a source of positive potential B. As is well known, the charge E01 on condenser C1 will rise exponentially with time t, as shown in Fig. 2, and will depart from a condition of linearity, which has been represented by the broken line L. When triode V1 is rendered conductive by the reception of a positive pulse P of duration ii on the control electrode thereof, condenser C1 discharges throughthe tube, the plate resistance of which has a value chosen to be much smaller than the value of resistor R1.

The sawtooth wave thus produced by that portion of the circuit of Fig. 1 including elements V1, R1, and 01 has an exponential voltage rise given by the equation where Ec1=charge on condenser 01 Es=voltage of battery B e=base of the natural system of logarithms=2.718

3 aboveeduationcanalsobeexpressedas fclear from the above equations that It 'the voltage rise on condenser or will be substantially linear only ii the expression is maintained small, or in other words is c. is

charged only to a small fraction, the batteery voltage En. For example, it E01 is allowed to rise to 10% ct Es, then from the above equations it can be shown that the non-linearity due to the -'quadratic term will be in the order of The non-linearity inherent inthe operation of a circuit of the above nature is materially reduced by means of the present invention. In the leftv on the single condenser network alone. The relhand portion of Fig. l is shown a second wave generating network substantially identical to the network shown in the right-hand portion of Fig. 1. This second network includes a triode Vs, a parallel condenser C2, and a charti'ns resistor R2. The grid of triode Va is biased to cut-oi! in the same manner.as is the. grid of triode Vi. When switch 8: is closed, the plate of triode V: is connected to the plate of triode V1 through an additional resistor Rs, while the battery end of resistor Re is connected to the battery end ct resistor R1 through switch 81, as shown. The

positive pulses P applied to triode V1 are also applied upon closing of switch S0 to triode if: so that both tubes are triggered simultaneously.

A consideration oi the circuit of 1 will show that capacity C1 charges exponentially through R1 during the intervalta during which triode V1 is cut oil, if switches 81, S: and S: are open. Assume now, however, that switches 81,

8-.- and S: are closed. If resistor R1 were removed, capacity C1 would charge through resistors R: and Rs. However, since the voltage on capacity C: is zero, at the beginning 01' charging interval is (triodes V1 and v: are triggered together), it is apparent-that the current through capacity C: is zero at the beginning of charging interval t2, and therefore the equation for the charge on capacity C1 can have no linear time term. It will instead be of the form ac, -E;:=a:tI+ t+ i n where a: and a: are constants.

The constants of the circuit of Fig. 1 may be chosen so that the non-linearity introduced by "the charging path through resistors Ra, Ra bucks out in part the non-linear terms in the exponential seriesrepresenting the charge through resistor R1. For example, .the quadratic term in the equation for the charge on capacity C1 may always be made to vanish ii the circuit constants are-so chosen that m= R1 (4) This may be accomplished ior example by settina R1=Ra=Rd (5) and C1=2Cs (6) The i'ollowing table illustrates the improvement in linearity of output voltage from the twocondenser network in the circuit of Fig. 1 as compared with the linearity of charge obtained ative output of the] two networks is likewise shown graphically by the curves in Fig. 2.. These curves have not been drawn to scale, however, and are merely intended to illustrate the relation; ship or the voltage output of the two networks.

s em, (two-condenser denser network network with with switches switches 8|, 5|, 8 8: and 8s and Es ml E. El

.001 (.1 .nooomo, .001000 .010 z. .ooms .0100: .1 (10% .005

From the above table it willbe seen that the departure from linearity of the two-condenser network. with switches 81, S: and 8: closed and allowing O1 to charge up to. 10% of En, is approximately 1.2%; whereas for the single-condenser network with switches 81. B2 ands: open, the

, departure is approximately 5% ior the same values of circuit components. Expressed in other terms, the single-condenser network requires about four times as much battery voltage (Ea) to limit the distortion to 1.2% for the same maximum output voltage as the two-condensernetwork of the present invention.

The condenser C: of Fig. 1 may be charged through resistor Ra from a separate source of that various substitutions, omissions and changes potential 31 as shown in Fig. 3, instead of from the common sources 3 as in the former figure. By varying the relative voltages of sources B and B1, diirerently compensated charging curves may be obtained.

While I have shown and described, and have,

pointed out in the annexedclaims, certain novel features of my invention, it will be understood in the form and details 01 the system illustrated may be made by those skilled in theiart without departing from the spirit of the invention. For

example, while only two charging networks have denser, means for periodically charging and discharging said second condenser respectively concurrently with the operation of the first-memtioned charging and discharging means, and means for applying the charge on said second condenser to said first condenser to thereby lengthen that portion of each charging period during which the charge on said first condenser increases substantially linearly with time as a result of the operation of said first-mentioned charging means alone.

2. A-wave-generating system comprising a first energy-storage means, means for periodically charging and discharging said first energy-storage means, a second energy-storage means, means for periodically charging and discharging said second energy-storage means respectively concurrently with the operation of the first-men-' tioned charging and discharging means, and means for applying the charge on said second energy-storage means to said first energy-storage means to thereby lengthen that portion of each charging period during which the charge on said first energy-storage means increases substantially linearly with time as a result of the operation of said first-mentioned charging means alone.

3. In a device of the class described: a first condenser; a first resistor; a source of potential; means for charging said first condenser through said first resistor from said source 01' potential; a second condenser; a second resistor: means for charging said second condenser through said second resistor from said source 'of potential concurrently with the operation of said first-mentioned charging means; a third resistor; and means for applying the charge on said second condenser to said first condenser through said third resistor.

20 2,235,385 Rava CARL G. 80. ant-cannons c rran The following references are 01' recordin the "file of this patent:

' UNITED s'ra'rns PATENTS Name Man. 18, 1941 Number 2,341,562 Klemperer Feb. 15, 1944 to respectively discharge

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