US2443922A

US2443922A - Control circuit for relaxation oscillators

Info

Publication number: US2443922A
Application number: US547719A
Authority: US
Inventors: Robert C Moore
Original assignee: Philco Ford Corp
Current assignee: Space Systems Loral LLC
Priority date: 1944-08-02
Filing date: 1944-08-02
Publication date: 1948-06-22
Anticipated expiration: 1965-06-22
Also published as: GB611731A

Description

June 22, 1948. R. c. MOORE 2,443,922,

' CONF'ROL CIRCUIT FOR RELAXATION OSCILLATORS v Filed Aug. 2, 1944 Cat Patented June 22, 1948 2,443,922 CONTROL cmcorr FOR RELAXATION OSCILLATORS Robert C. Moore, Philadelphia, Pa., assignor, by mesne assignments, to Philco Corporation, Philadelphia, Pa., a corporation 0! Pennsylvania Application August 2, 1944, Serial No. 547,719 3 Claims. (or 250-36) This invention relates to the control of relaxation oscillators, and more particularly to the control of an oscillator whose operation is initiated and maintained in response to a control signal.

It is sometimes desirable to utilize a relaxation oscillator arrangement in which the operation of the oscillator takes place only during the occurrence of a control signal, i. e., the oscillator is started in response to commencement of the control signal and is stopped when the signal terminates. Prior devices of this character have exhibited an undesirable tendency to produce a transient or disturbance during the starting of the oscillator,

The principal object of the present invention is to effect improved control of such an oscillator, and more particularly to effect starting of the oscillator without the production of any undesirable transient or distur ance.

Another object of the invention is to provide a novel control circuit by which the oscillator is started after a predetermined time interval following the commencement of the control signal, to the end that at the instant of starting the oscillator shall be conditioned for normal operation and there shall be no tendency toward the production of any transient or disturbance.

A further object of the invention is to provide a novel control circuit of the stated character in conjunction with a relaxation oscillator of the multivibrator type.

Other objects and advantages of the invention will become apparent during the course of the following description with reference to the accompanying drawings, in which:

Fig. 1 illustrates schematically one embodiment of the invention; and

Fig. 2 is an explanatory diagram illustrating the voltage wave forms at various parts of the circuit of Fig. 1.

Referring to Fig. 1, there is shown a relaxation oscillator of the multivibrator type comprising vacuum tubes T2 and T3 and their associated circuit elements. A control tube T1 and its associated circuit elements serve to control the operation of the multivibrator. While the tubes are shown as triodes, it is to be understood that multi-grid tubes maybe employed together with the necessary circuit modifications to accommodate the particular tubes employed in any instance. Furthermore, tubes T2 and T3 may be combined in one envelope, as in the well known twin type vacuum tube.

The control tube T1 is arranged to receive a negative timing pulse through a grid coupling condenser ll). Preferably the grid of tube T1 is operated at zero bias, being connected to the cathode by means of grid resistor H. The cathode of tube T1 is connected to ground through a variable cathode resistor or potentiometer l2, shunted by a condenser iii. The anode of tube T1 is directly connected to the grid of the first multivibrator tube T2 and may receive its potential from the cathode circuit of the multivibrator by way of grid resistor l4. Alternatively, the return for grid resistor I4 (and also resistor l9) may be made to a separate supply. The two tubes T2 and T3 are arranged generally in conventional multivibrator fashion, with the cathodes tied together and connected to ground through a common cathode biasing resistor 15 having a by-pass condenser It. The grid coupling condenser and plate load resistor :t'or tube T2 are shown at I! and 18, respectively, while the grid resistor. grid condenser and plate resistor for tube T2 are represented at 19, 20 and 2|. A suitable source IB+ serves as the anode potential supply for the multivibrator tubes T2 and T3. A resistance network consisting of resistor 22 and potentiometer 23, in series, may be connected between the anode voltage supply B+ and the common cathode connection of tubes T2 and T2. By connecting the grid resistors l4 and IQ of tubes T2 and T2 to the movable arm 24 of potentiometer 23, an arrangement is provided for controlling and adjusting the frequency of the multivibrator.

The input terminal of the device is shown at 25, while the output of the multivibrator may be obtained from the anode of tlibe T3 by way of the output terminal 26.

It will be apparent to those familiar with the art that grid resistor ll of control tube T1 may, alternatively, be connected to ground instead of to the cathode of tube T1, as shown in Fig. l, in which case potentiometer l2 would become a variable cathode biasing resistor.

The operation of the circuit will now be de-' scribed with reference to the embodiment shown in Fig. 1 and the voltage wave forms of Fig. 2.

With no signal applied to the grid of control tube Tl, this tube is conducting since its grid is at zero bias, and the magnitude of its plate current is governed in part by the adjustment of potentiometer I2. The plate current of tube T1. flowing through grid resistor l4, produces 9. voltage drop thereacross which biases the grid of tube T2 well below cut-off, thereby preventing tube T2 from conducting and preventing the multivibrator from oscillating. The other multi- 3 vibrator tube '1': is, of course, conducting since its grid is at cathode potential or .some small positive potentiahdepending upon the positio of potentiometer arm 24. r

fThe voltage wave forms at several parts of the circuit for this no-signal input condition are shown in Fig. 2 for the interval between the time reference lines t1t2. Referring toFig. 2, the grid potential of tube T1 with respect to its cathode islrepresented by curve egTl; the potential of the grid of tube T: with respect to its cathode is represented by curve e Tz, the dotted lines indieating other potentials for diiferent settings of the potentiometer I2; the potential on the plate of tube T2, which is approximately equal to the supply voltage B+ since this tube is not conducting, is represented by curve ,e Ta; the grid potential of tube T3 with respect to its cathode, assuming that the contact arm 24 or potentiometer 23 in Fig. 1 is at the cathode end, is zero as represented at 831 3; and the potential on the plate of tube T: which is conducting, iszrepresented by curve epT3.

Referring again to Fig. 1, when a negative pulse is applied to the input terminal 25, driving the grid potential of tube Tl below its cut-oil value, the grid potential of tube T2 rises as the charge on grid condenser ll leaks oil through resistor l4 and the conducting tube T3. When the grid potential of tube T2 reaches its cut-ofi value, this tube conducts and the multivibrator begins to oscillate in normal multivibrator fashion. The multivibrator will then continue to function for the duration of the negative pulse on the grid of control tube Ti. At the end of this timing pulse, the grid potential of tube Tl rises to its normal no signal value, whereupon tube Tl conducts, thereby lowering the grid potential of tube T2 below its cut-oii value and interrupting multi vibrator oscillation. The application of another negative timing pulse causes repetition of the above cycle of operation.

The voltage conditions in "the circuit during the .interval between the commencement of the negative timing pulseand the time that the grid potential of tube T2 reaches its cut-oil value are represented in Fig. 2 between the vertical lines 12-42. It will be noted that the only changes in the circuit conditions are the drop in grid po- .tential of tube T1 to so: .e value below'cut-ofl, as shown by curve egTl, and the exponential rise in grid voltage of tube T2, as shown by curve 8gT2. At the instant the grid potential of tube T2 reaches its cut-oil value, i. e., at time is, the multivibrator is ready to function in its normal manner, as indicated by the grid voltage and plate vpltage wave forms for tubes T2 and T3 in Fig. 2, since the voltages on the plate of tube Ta and on the grid and plate of tube T2 are identical to those conditions during that portion of the multivibrator cycle when the grid voltage of tube Ta is below its cut-ofi valu Since themultivibrator goes into oscillation at some time, t3 in Fig. 2, after theapplication of the negative pulse at time t2, it is apparent from wave form egT2 that the time ta, at which multivibrator action begins, depends upon the potential of the grid of tube T2 during the no signal input period. The dotted lines in Fig. 2 for the grid potential of tube T2 (wave form e Tz) show that for less negative potentials the time required for the grid of tube T2 to reach its cut-off value is shorter than for more negative potentials. The delay interval between the time of application of the negative timing pulse to the input ter- Condensers lll-0.005 microfarad Resistor I I220,000 ohms.

Potentiometer |2-l00,000 ohms.

Condensers l3 and I 6-0.005 microfarad each Resistors It and Iii-100,000 ohms each Resistor Iii-4,700 ohms Condensers l1 and 20l00 micrmmicrofarads each Resistors l8 and ii-4,700 ohms each,

Resistor 22--l50,000 ohms Potentiometer 23-25,000 ohms It will be understood, of course, that the invention is not limited to the specific embodiment illustrated and described herein nor to the values of the various elements given as a specific example. The invention is capable of various embodiments or modifications which may be resorted to without departing from its scope.

I claim:

1. In combination, a multivibrator comprising a pair of inter-coupled vacuum tubes having at least triode elements, means normally biasing the grid of one of said tubes below cut-oil value, thereby rendering said multivibrator normally inoperative, means responsive to a control signal for decreasingthe bias of said one grid so as to render said multivibrator operative .for the duration of said signal only, and means for delaying the starting of said multivibrator for a predetermined time interval following the commencement of said signal.

2. In combination, a multivibrator comprising a pair of inter-coupled vacuum tubes having at least triode elements, a normally conductive control tube, means controlled by the anode current of said control tube for normally biasing the id of one of said multivibrator tubes below cut-oii value, thereby rendering said multivibrator normally inoperative, means for applying to said control tube a control signal adapted to reduce the anode current of the control tube and thereby decrease the bias of said grid, so as to render said multivibrator operative for the duration of said signal only, and means for delaying thestarting of said multivibrator for a predetermined time interval following the commencement of said signal.

3. In combination, a multivibrator comprising a pair of inter-coupled vacuum tubes having at least triode elements, a resistor connected between the grid and cathode of one of said tubes. a control, tube having its anode connected to the junction between said resistor and said grid, 8. source of anode potential connected to the opposite end of said resistor, whereby said resistor serves to bias said grid under control of the anode current of said control tube, means for normally operating said control tube so as to bias said grid below cut-off Value thereby rendering said multivibrator normally inoperative, means for applying to said control tube a control signal adapted to reduce the anode current of the control tube REFERENCES CITED The following references are of record in the file of this patent:

7 Number UNITEDSTATES PATENTS Name Date Lubke Apr. 14, 1936 Smith Oct. 11, 1938 Reeves Dec. 16, 1941 Geiger May 5, 1942 Bartelink Dec. 19, 1944 Morrison Aug. 20, 1946