US2024489A - Circuit arrangement for generating or amplifying electric oscillations - Google Patents

Description

1935- B. VAN DER PO L ET AL 2,024,489

CIRCUIT ARRAIIGEMEIJ'I' FOR GENERATING OR AMPLIFYING ELECTRIC OSCILLATIONS 1 Filed Jan. 14, 1953 if d: I I 2 z' 5' mmu 1 4 AME/170177014! 12 FRiOUEA/C) wmuss P15 25 J J if,

0 zzffiflnnnztff INVENTORS BALTHASAR VAN DER POL JAN VAN DER K AfidRNEY Patented Dec. 11, 1935 ism-m omen I CIRCUIT ARRANGEMENT FOR GENERATING OR ELECTRIC OSCILLA- TIONS Balthasar wander-Pol and Jan vanderMark,

Eindhoven, Netheriands, assignors to Radio Corporation of America, a corporation of Delaware Application January 14,. 1933,,S erlal a... 651,804

In the Netherlands January 8, 1932 1 Claims. (01. ire-111) The invention has referencetoa circuit ar- 10 the use 01 circuits tuned by means of inductances and capacities. In the circuit arrangement accordingito the invention either inductance coils and resistances or capacities and resistances are used, reaction being provided for in a determined l5 manner so that nevertheless the properties of a circuit comprising inductance and capacity with 4 reaction are obtained.

According to the invention, a circuit arrangement for generating or amplifying electric oscil- 20 iations includes one or more thermionic valves the output circuit or circuits of which includes or include a combination either of resistances and capacities or of resistances and inductances which jointly bring about for the desired. fre- 25 quency range a phase displacement of 180 a reactionbeingprovided for which is sostrongly negative for a frequency for which no phase dis-- placement occurs that a voltage of that frequencyis not amplified. v f 30 In order that the invention may be clearly understood and readily carried into effect two embodiments thereof will now be described more fully, by way of example, with reference to the accompanying drawing, in which 35 Figures 1 and 3 show diagrammatically circuit arrangements according to the invention; and, 4

Figure 2 shows a characteristic curve of amplification for explaining the action of the said circuit arrangements.

denser 5. In addition, grid leaks 6 are provided 45 and capacities I are connected in parallel with the resistances 4. By making the grid connections to resistors 6 adjustable, the alternating voltages applied to the respective grids may be adjusted at will. If desired screen grids Ill may be employed in the valves to reduce the capacity effect between the anodes and control grids, and the grids in may be connected to the B battery or other positive voltage source through a resistor II and leads [2. In certain cases when 55 using triodes, the anode-cathode capacities of the Referring to Figure l, 2 and 3 designatethermionic valves each of whiclris coupled to the next valve by means of a resistance 4 and a convalves may replace condensers I but in this case 'the advantage of their adjustability is lacking.

As is well known, such a resistance amplifier yields for a given range of frequencies a substantially uniform amplification. For lower frequen- 5 cies the amplification decreases as a result of the presence of, the condensers 5 and resistances 6 and for higher frequencies the decrease in amplification is due to the capacities I and the resistances 4 since these impedances bring about 10 for given frequencies a certain phase displacement which results in a decrease in amplification.

The grid filament capacity and the grid anode capacity of the valves affect the characteristic curve of amplification. Usually, screen grid valves are used orsome well known means are resorted to in order to neutralize the influence of the anode grid capacitys In the well known resistance amplifying cir- 2o cuit arrangements, care is always taken that the frequency band for which the phase displacement is so great that the amplification is reduced to half the maximum amplification falls outside the range of frequency to be amplified. In contradistinction to this, according to our invention the occurrence of phase displacements for given I frequencies is used for securing a selectively act ing set. For this purpose the resistances and condensers should be such that, apart from the phase reversion brought about by the valves, forthe. desired frequency occurs at a given point of the circuit arrangement avoltage phase displacement of 180 relatively to the phase of the voltage ,in or appliedto theinput circuit of the first valve. Now, if a reaction is provided foracting from the said point on the input circuit of the first valve and if for the frequencies which originally were amplified to the maximum value this reaction is rendered so highly negative that the said ampli- 0 fication is reduced to practically naught, a sharp maximum value of the amplification will occur .for the frequencies for which the phase displacement is exactly 180.

Referring to Figure 2, III shows the characteristic curve of amplification of a resistance ampli-- Generally, a high amplification is only desired for one given frequency. In. this case care can be taken that the second maximum value falls outside the range to be amplified. or again a higher damping may be used for "the undesired form of the invention if desired.

frequency.

As each combination of resistance 4 and capacity I can only bring about a phase displace ment which is smaller than 90, a combination of ohmic resistance and capacity is required at least three times to secure a phase displacement of 180'. In the case of Figure l-it will therefore be,

' amplifier or as an oscillator in accordance with necessary to provide for a reaction acting from the output circuit of the third or a subsequent valve on the input circuit of the first valve. The reaction is obtained in the given case by means of a conductor I and condenser I. The number of valves used should always be odd if a negative reaction is to be obtained.

The condensers I and/or I may be variable so that the frequency to be amplified is regulable. As this frequency depends on the product R0. the variation in capacity exercises a much greater infiuence with this circuit arrangement than when using tuned circuits in which case the frequency depends on LC. This ensures the advantage that it is possible to regulate throughout a much wider range of frequency with a given size of condenser without the exchange of tuning elements being necessary.

It is also possible to obtain variation in frequency by altering the value of the resistances used.

The value of the reaction will preferably be regulable. In the example shown this is effected by carrying to the input circuit part of the voltage occurring in the resistance 4. As shown, a contact or slider I1 is adjustable along the turns of I resistor l. The resistors used are preferably of the non-inductive type especially when the tuning means employed are condensers, as 1 and 5. It is also possible to obtain a regulation of the reaction by connecting the grids of the valves to a variable point of resistances 8 as shown.

As an alternative, the reaction may be regulated by rendering variable the grid bias of one or more of the valves. When used as an amplifier for a narrow band of frequencies, a source of variable frequency energy such as the antenna of a radio or television receiver may be connected in any preferred manner across the resistor I of the first stage. The receiver is adapted to amplify radio frequencies such as are in use in radio broadcasting and also ldwer radio frequencies.

The reaction may be increased to such extent that the system goes into free oscillation. If in This phase displacement is obtained here by the I condensers l8, l9 and It in conjunction with the plate impedance of the amplifying valve and the resistances 2i and 22. The condenser it has connected in parallel with it a resistance 23 which serves as a direct current path for the anode current from battery B. A partial rotation of the condensers l8, l9 and 20 which may be mounted on a single spindle as indicated by the dotted line or again a partial rotation of one or more of these condensers results in a variation of the natural frequency transmitted to the output circuit of the amplifier. Ascreen grid'llimaybeusedinthis 5 This system will allow particularly the higher frequencies such as radio frequencies to be amplified in a satisfactory manner. If it is desired to amplify low frequencies it will be necessary to use 11 series condensers and parallel resistances.

Again, this system may be constructed as an 'so that the total phase-displacement for the desired frequency is again As an alternative, 25 three or more resistance-inductance combinations may be used, the inductances being preferably variable to produce the desired phase displacement of 180.

Preferably care will be taken that each of the 30 resistance-capacity or resistance-inductance combinations brings about a substantially identical phase-displacement, as in this case the frequency band that can be amplified or generated is as wide as possible.

The condensers and resistances of the circuit arrangements described need not be exactly equal to each other. It is only essential that for any desired frequency a total phase-displacement of 180' can be adjusted. This introduces therefore 40 variable condenser having one side directly connected to said plate and its other side t0 the cathode of said tube and a resistor and con- .denser in series connected in shunt to said variable condenser. Y Y

' 2. In a device of the class described, the combination of three vacuum tubes, each having a cathode, grid and plate, means for impressing radio frequency signal currents across thevgrid and cathode of the first stage, a high resistance connected between the plate and cathode of each of the other stages. a condenser shunted across each of said resistances, said condensers being designed to limit the high frequency currents in the output circuit of the third stage, a reactor. connected between a point on said resistance and the grid of the succeeding stage and a reactor connected between a point on the resistance in the plate circuit of the third stage and the grid of the first stage.

3. In an amplifying device, the combination of a vacuum tube having a cathode, a control grid 7 and a plate, a resistor connecting said grid and cathode, means for applying a positive potential to said plate, a series circuit connecting said plate and grid and comprising two resistors and a reactor. and two condensers connected in series 75 across the ends of each of said last named resistors.

4. The combination defined in the preceding claim in which said condensers are equal and a uni-control operating means for adjusting said condensers.

5. In an amplifying device, the combination of a vacuum tube having a cathode, grid and plate, an input circuit connecting said cathode and grid and including a resistor, a plate circuit connecting said plate and cathode and including a plurality of similar filter networks so designed that a point in one of said networks has voltage variations substantially 180 degrees out of phase with the grid voltage and a condenser having one side directly connected to said point and its other side directly to said grid.

6. The combination defined in the preceding claim in which each filter network comprises two similar variable condensers, a direct connection 5 between one side of each of said condensers and said tube cathode and a uni-control operating means for adjusting said condensers.

'7. The combination defined in claim 2 in which the values of the high resistances and reactors 10 JAN VAN DER MARK. l5

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