Патент USA US2122851код для вставки
My 5, 1938. B. J. THOMPSON 2,122,851 AMPLIFYING CIRCUITS Filed Dec.‘ 29, 1957 Inventor‘: BrowderJ-Tho p'son, by 1/0/1476 ‘ His Attorney.’ I Patented July 5, 1938 2,122,851 UNITED STATES PATENT oFFicE 2,122,851 AMPLIFYING' CIRCUITS Browder J. Thompson, Basking Ridge, N. J., as signor to General Electric Company, ration of New York Application December 29, 1937, Serial No. 182,267 4 Claims. (Cl. 179—171) The present invention relates to an improved meral 4. This ampli?er includes a cathode 5, an amplifying circuit especially useful in connec anode 6, a control grid 1, a screen grid 8 and a tion with control apparatus such as photosensitive space charge grid 9 whose nature and function devices which are adapted to produce very small will be more fully explained hereinafter. The 5 potentials varying in accordance with a physical output voltage of the ampli?er, which is de-‘ 5 condition. veloped across a resistor It], may be impressed It is one object of the invention to provide a on the control grid of a suitable triggering or con circuit of the type in question which can be oper trol device, exempli?ed in the present case by a ated satisfactorily from an alternating current thermionic discharge tube l2. For impressing a Y 10 power source. difference of potential between the various elec Known types of photosensitive devices are trodes of the ampli?er and associated devices characteristically of very high impedance and re there is provided a source of alternating current quire to be used. with an amplifying circuit which potential, illustrated as including a transformer has an input impedance of commensurately high having a secondary l3 and a primary M. value. However, it has been observed that as the The photosensitive device is connected in the input impedance of an amplifying circuit is in cathode-control-grid circuit of the ampli?er 4 creased, the relative importance of interelectrode capacitance also increases. With a circuit adapt~ ed to be energized by alternating current and hav ing a su?iciently high input impedance to assure proper cooperation with a conventional ‘photo sensitive device, the effect of interelectrode capac itance may be such as to prevent the normal func tioning of the ampli?er. It is a more particular object of this invention as applied in connection with an amplifying cir cuit adapted for use with an alternating current source to provide means for effectively neutralizing the capacitance between the control grid and the remaining electrodes of the ampli?er. In accordance with a preferred embodiment of the invention this object is accomplished by suit ably connecting a condenser between the control grid of the ampli?er and a point of the alternat ing current source of supply whose voltage phase relation with respect to the connection point of . the input impedance element cathode is opposite to that of the remaining electrodes. In this way the tendency of the control grid to accumulate charges as a result of its capacitive relation to the other electrodes is offset by the equal and opposite e?ect of the neutralizing condenser. The features of my invention which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, to gether with further objects and advantages there of will best be understood by reference to the fol lowing description taken in connection with the accompanying drawing in which the single ?gure ' shows schematically a control circuit suitably em bodying the invention. Referring to the drawing, there is shown a photo-sensitive device (comprising a cathode I and an anode 2) connected to a vacuum tube am pli?er which is designated as a whole by the nu and is associated with an input resistance I 6. As previously noted, for purposes of cooperation with the high impedance photosensitive device this resistance should have an extremely high value, for example, on the order of 1,000 megohms. As a result of the high impedance of the in put circuit thus formed, the capacitance between the control grid and the anode and various other grids of the ampli?er 4 may have a relatively im portant effect on the operation of the ampli?er. These capacitances (indicated in dotted outline as condensers ll, l8 and I9) permit a substantial flow of alternating current through the resistor it. With a low value of the resistor Hi the re sultant drop across it and the attendant swing of the control grid voltage may be negligible. However, with a resistance of the value required in the present connection the potential developed across the resistor from this cause may be suffi cient to cause the control grid to swing positive at the same time as the grids 8 and 9 and the anode B and thus substantially to nullify the effect of variations in the current ?owing through the photo tube and to prevent the normal func tioning of the ampli?er. In order to overcome this difficulty, I provide a neutralizing condenser 22 connected between the control grid I and a point 23 of the alternat ing current source whose voltage phase relation with respect to the connection point 24 of the resistance !6 is opposite to that of the points to which the remaining electrodes are connected. By proper adjustment of this condenser it is pos sible to eliminate the blocking effect referred to and obtain. good performance of the ampli?er. The requirement for neutralization is that the voltage between the points 23 and 24 multiplied by the capacitance of condenser 22 must equal the sum of ( 1) the voltage between the point 24 2,122,851 2 and the screen grid connection point multiplied by the capacitance between the control grid and screen grid plus (2) the voltage between the point 24 and the space charge grid connection point multiplied by the capacitance between the if used will increase the effective ampli?cation of the device and shield the control grid 1 from the effects of the anode ?eld. Although I have described my invention espe cially in connection with a photosensitive device it space-charge grid and control grid plus (3) simi lar products of voltage and capacitance for such other electrodes as may be involved. The simplest method of arriving at the proper value of the 10 condenser 22 is to put in a small ?xed condenser and to slide the tap along or to put in a small variable condenser with a ?xed tap and to ad. just the condenser until in either case satisfac tory operation is achieved. A further dii?culty resulting from the use of 15 the high resistance element 16 is the fact that any current however minute, which may flow from the cathode 5 to the control grid 1 during the half-cycle in which the latter is positive will pro is by no means limited to such use and may be alternatively employed in connection with any electrical device, the electrical characteristics of which are variable automatically in. accordance with variations in a physical condition to which 10 the device is subjected. Furthermore, while I have shown a particular embodiment of my in vention, it will be understood that many modi? cations may be made by those skilled in the art without departure from the invention. I aim by the appended claims to cover all such modi?ca ,20 duce a considerable voltage drop across the re sistance I6. This drop will tend to charge the condenser 22, the interelectrode capacities I1, I8, and I9, and such stray capacities as may exist going disclosure. I claim: ' ampli?er having a 20 plurality of electrodes including at least a 1. In combination, an cathode, an anode and a control grid, an alter electrode is negative with respect to the cathode such charged capacities will oppose the action nating current source having various points thereof connected to said electrodes for supplying desired potentials thereto, an input circuit in cluding a high impedance element connected be tween the control grid and a point on said alter nating current source, and a condenser connected of the photosensitive device and render the con between the control grid and a point of said source between the control grid and the associated ele 25 ments of the circuit. During the portion of the alternatingr current cycle in which the control .30 trol circuit unable to respond in the intended V44) tions as fall within the true scope of the fore whose voltage phase relation with respect to the 30 manner to the stimulus of a light beam impinging connection point of the impedance element is op posite to that of the points to which the elec on the photosensitive element. This difficulty is overcome by providing electro- ‘ trodes of the ampli?er other than the control static means associated with the control grid 1 grid are connected, the condenser being effective 35 to neutralize the capacitance existing between the and the cathode 5 for preventing current flow be control grid and the said other electrodes. tween them. This. means may suitably comprise 2. In combination, an ampli?er having a a space charge grid 9 which is adapted to be plurality of electrodes including a cathode, a negatively charged whenever the control grid be comes positive with respect to the cathode, so control grid and an anode, an alternating cur 40 rent source connected to said electrodes ior im~ that its e?ect is to inhibit the movement of elec trons from the cathode. As illustrated, the de sired potential relationship is obtained by con necting the grid 9 to a point of the alternating current source whose voltage phase relation is 45 opposite to that of the control grid when referred to the cathode as a reference point. In order further to block the random electron current which tends to flow from the cathode during the period in which all the electrodes are 50 at substantially zero potential, additional means are provided in the connection between the grid 9 and the transformer secondary 13 for de?nitely biasing the grid negatively with respect to the cathode 5 whenever the control element ceases 55 to be negative with respect thereto. This means as illustrated comprises a condenser 20 in, par allel with a resistance 2!, these elements being so related in magnitude that any charge accumu~ lated on the condenser will not be lost in less than a full cycle of the alternating current. Under these conditions current drawn by grid 9 during the period of normal conduction of the ampli?er charges the condenser 20 and thus maintains a negative bias on the grid when a reversal of the’ .65 alternating potential occurs. The use of a space charge grid in this connec tion and apart from the use of a neutralizing condenser as claimed herein is fully described and claimed in my copending application S. N. -70 101,612, ?led September‘ 19, 1936 and assigned to the same assignee as the present invention. ' The electrode 8 comprises a screen grid which may be interposed between the anode and the control grid if desired. This element does not .78 constitute an essential part of my invention but pressing desired potentials thereon, an electrical device connected in, the cathode-grid circuit of the ampli?er and having its electrical character istics variable automatically in accordance with variations in a physical condition to which the device is subjected, means including a high ini pedance element connected between the control grid of the ampli?er and a point on said alternat ing current source for causing variations in the electrical characteristics of said device to affect 50 the potential of the control grid in a desired man ner, and a condenser connected between said grid and a point of said source whose voltage phase relation with respect to the connection point of the impedance element is opposite to that of the 55 points to which the electrodes of the ampli?er, other than the control grid, are connected, the condenser being effective to neutralize the capaci tance existing between the control grid and the 60 remaining electrodes of the ampli?er. 3. In combination, an ampli?er having a plurality of electrodes including at least a cathode, an anode, a control grid, and a screen grid, an alternating current source for impressing desired potentials on said electrodes, a photo 65 sensitive device connected in the cathode-con trol-grid circuit of the ampli?er, a resistance ele ment of at least about 1,000 megohms connected between the control grid and a point of said alternating current source, and a condenser con~ 70 nected between the control grid and a point of the alternating current source whose voltage phase relation with respect to the connection point of the resistance element is opposite to that of the points to which the remaining electrodes, 2,122,851 other than the control grid are connected, the condenser being of su?icient capacity to neutral ize the capacitance existing between the control grid and the said remaining electrodes. 4. In combination, an ampli?er including at least an anode, a cathode, a control grid between the anode and cathode, and. a space charge grid between the cathode and control grid, an alter nating current source for impressing desired 10 potentials on said electrodes, a photo-sensitive device connected in the cathode-control-grid cir cuit of the ampli?er, a high impedance element connected between the control grid and a point on said alternating current source associated with 3 the cathode-control-grid circuit, means connect ing the space charge grid to a point of said source whose voltage phase relation with respect to the cathode is opposite to that of the connection point of said impedance element, and a condenser con nected between the control grid and a point of said source whose voltage phase relation with respect to the connection point of the impedance element is opposite to that of the space charge grid, the condenser being effective to neutralize 10 the capacity existing between the control grid and the space charge grid. BROWDER J. THOMPSON.