US2447248A - Stabilized oscillator - Google Patents

Description

Aug. 17, 1948.

L. M. HARRIS STABILIZED OSCILLATOR Filed Dec. 25, 1944 INVENTOR. LESLIE M. HARRIS TTOR Patented Aug. 17, 1948 UNIT D j STATE-S PATENT OFFICE Leslie M. Harris, Williamsville, N. Y.,. assignor tot Gurtiss-Wright Corporation, a. corporation of.

Delaware Application December 23-, 1944, Serial No. 569,612

6 Claims. (Cl. 250-36) This invention relatesto oscillators. More particularly, itrelatesto oscillators which maintain their outputs at constant frequencies and constant levels over wide ranges of temperature.

Modern developments in electronics, and its many and varied applications, make it highly deinductance-capacitancetuned type, the frequency being determined by means of the impedance values in a tuned circuit indicated generally at 2, this circuit including'an inductor 4 and a capaci'tor 5.- Stability of frequency is obtained by means of negative feedback through a'capacitor 6 and aresistor I from the'plate of'a type 6V6 beam-power tube 9- to the cathode of a type 6S J'7 pentode 8-.' The capacity valueof the capacitor 6 and the resistance-value oi resistor T are so adjustedas to attain a constant phase shift in the-amplifier stages when the oscillator output is amplified. This is necessary in order to securelarge. Any' tendency to increase the current.

through the. ballast lamps as aresult of'increa'sed' amplitude of output oscillation will thus tend: to-

increase theresistance of lamps l0, increase the negative feedback, andthereby counteract the tendency of the output oscillation to increase in amplitude. Anytendency of the output oscilla tionto decrease in amplitude will have the opposite result.

When the oscillator is subjected to temperature changes, the impedance of tuned circuit 2: is apt to vary; principally due to change in Q value. of the inductor 4 This inturn- Will cause the output level of the oscillator to vary. In order to avoid this undesirable variation in output level, there is incorporated, in a positive feedback circuit; f-rom the plate of. tube 9 to the grid of tube- 8, a resistor 3' having a conducting element of a material having a negative temperature coefii client of resistance, that is, its electrical resistance decreases with increase of temperature. Such materials are available commercially, and? may include carbon as an ingredient, or other recently? developed materials: such as certain. in-

organic oxides." The temperature coefficient of this resistor is accurately predetermined so that the; gain infeedback from the plate of tube 9- through the capacitor 6 and the'resistor 3 tothe control grid of tube 8, as the temperature increases,. compensates for'theloss due to the decreased impedance of circuit 2 with: rise in temperature.

Theituned circuit 2, in combination with the positive: and negative feedback circuits described above, is also an important feature in bringing. about the desirable results of this invention; By this means the output frequency of the oscillator will.- be accurately controlled over considerable supply; voltage ranges, as long asxthe levelor amplitudeiskept constant by means of ballast lampslll."

1 The oscillator is supplied with a source of 250 volt direct current, which may be a battery; dire'ct'current generator, or other controlled source of direct current, through positive terminal I: and negative terminal H, the latter being grounded to theicasing for-the apparatus; ierence from outside sources is reduced by means of a capacitor i12' connected across. the terminals I and H Thef-p'ositi've terminal I is connected through: the plate'feed' resistor I I to the: plate of: tube 8 and through aresistor l 5' to the screen grid. oft'tubet 8. The cathode. and screen grid of tube B are coupled: to each other through acapac and the cathode of tube 9 through the self-biasing resistor l8 and by-pass capacitor l9. The plate of tube 8 is coupled to the control grid of tube 9 through a capacitor 20.

The heaters of the tubes 8 and 9 are supplied with a source of low voltage (e. g. 22 volts) current through negative terminal H and a positive terminal l3, with a series resistor 24- to reduce the voltag drop across each heater to the proper amount. A shunt resistor 25 around the terminals of the heater for tube 8 serves to equalize the voltage drop across the heaters of the two tubes.

The output of the oscillator is passed through a primary winding 22 of a balanced iron core output transformer 2| The primary of this transformer is connected at one end to the plate of tube 9 and at the other end to the positive terminal l. The output of the oscillator is then taken 01f at the two terminals of the secondary 23. of transformer 2|.

In the oscillator as described above, with properly chosen values of resistance and capacitance, the frequency is highly independent of changes in both plate and heater voltages and of changes in temperature. Thus, a variation in plate voltage from 240 volts;to 260 volts causes a frequency shift'of less than 2 cycles in 40,000 per second. A'similarly small shift results from a change in heater voltage from 5.8 volts to 6.5 volts.

The effect of temperature on frequency is controlled by the compensation applied through careful selection of the capacity of capacitor 5. Level or amplitude is controlled by the ballast lamps l and the temperature compensating element of the resistor 3, and the amount of variation may thus be kept as low as 0.04 per cent per degree centigrade. It may also be desired, however, to control the ambient temperature within narrow limits by means of a thermostatically controlledblower. or other suitable means. The wave shapes generated by the oscillators are closely sinusoidal, with not over 0.2% distortion for 'an output signal of 4 volts into 120 ohms.

In the above description, it is obvious that any of the resistance, capacitance or inductance elements may be either simple or compound. It is understood that many other changes may be made without departing from the spirit and scope of the invention as defined in the appended claims. 7

' I claim:

1. In an oscillator having a plurality of vacuum tubes each with a plate, cathode and control grid and with each cathode connected to a ground wire through an impedance, the signal output of a first vacuum tube being fed to the control grid of a second vacuum tube, the combination comprising a negative temperature coefficient resistor included in series in a positive feed-back circuit from the plate of the second vacuum tube to the control grid of the first vacuum tube, and a capacitor and an inductor connected in parallel at one set of terminals thereof to said ground wire and at the other set of terminals thereof to the control grid of said first vacuum tube.

2. In an oscillator having a plurality of vacuum tubes each with a plate, cathode and control grid and with each cathode connected to a ground wire through an impedance, the signal output of a first vacuum tube being fed to the control grid of a second vacuum tube, the combination comprising a negative temperature coefiicient resistor included in series in a positive feed-back circuit from the plate of the second vacuum tube tothe control grid of the first vacuum tube, a capacitor and an inductor connected in parallel at one set of terminals thereof to said ground wire and at the other set of terminals thereof to the control grid of said first vacuum tube, and a resistor whose resistance varies directly and substantially with the current passing therethrough, said lastnamed resistor being included in the impedance circuit between said ground wire and the cathode of said first vacuum tube.

, 3. In an oscillator having a plurality of vacuum tubes each with a plate/cathode and control grid and with each cathode connected to a ground wire through an impedance, the signal output of a first vacuum tube being fed to the control grid of a second vacuum tube, the combination comprising a negative temperature coeificient resistor included in series in a positive feed-back circuit from the plate of the second vacuum tube to the control grid .of the first vacuum tube, a capacitor and an inductor connected in parallel at one set of terminals thereof to said ground wire and at the other set of terminals thereof to the control grid of said first vacuum tube, and a ballast lamp whose resistance varies directly and substantially with the current passing therethrough, said ballast lamp being included in the impedance circuit between said ground wire and the cathode of said first vacuum tube 4. In an oscillator having a plurality of vacuum tubes each with a plate, cathode and control grid and with each cathode connected to a common conductor, the signal output of a first vacuum tube being fed to the control grid of a second vacuum tube, a circuit comprising a capacitor and an inductor connected in parallel between the control grid of the first vacuum tube and said common conductor, a positive feed-back circuit from the plate of the second vacuum tube to the control grid of the first vacuum tube, said positive feed-back circuit having included therein a negative temperature coefficient resistor to compensate for change in impedance in said first mentioned circuit in response to temperature changes, and a negative feed-back circuit between the plate of the second vacuum tube and the cathode of the first vacuum tube. v

5. In an oscillator having a plurality of vacuum tubes each with a plate, cathode and control grid and with each cathode connected to a common conductor through an impedance, the signal output of a first vacuum tube being fed to the control grid of a second vacuum tube, a circuit comprising a capacitor and an inductor connected in parallel between the control grid of the first vacuum tube and the common conductor, a resistor whose resistance varies directly and substantially in accordance with the current passing therethrough, said resistor being included in the impedance circuit between the common conductor and the cathode of the first vacuum tube, a positive feed-back circuit from the plate of the second vacuum tube to the control grid of the first vacuum tube, said positive feed-back circuit having included therein a negative temperature coeflicient resistor to compensate for change in impedance in said first mentioned circuit in response to temperature changes, and a negative feed-back circuit between the plate of the second vacuum tube and the cathode of the first vacuum tube.

6. In an oscillator having a plurality of vacuum tubeseach with a plate, cathode and control grid,

the signal output of a first tube being fed to the ture coeflicient resistor included in series in 2 UNITED STATES PATENTS positive feed-back circuit from the plate of the second tube to the control grid of the first tube, i ggg i K llama g? 1934 and a, capacitor and an inductor connected in 2186'571 J 1940 parallel between the control grid of the first tube F and the cathodes of said tubes 5 2,231,542 Malhnckrodt Feb. 11, 1941 2,258,128 Black Oct. '7, 1941 LESLIE HARRIS- 2,268,872 Hewlett Jan. 6, 1942 2,303,862 Peterson Dec. 1, 1942 REFERENCES CITED 2,394,018 Shank Feb. 5, 1946 The following references are of record in the 10 file of this patent:

Images