Oct.’ 8, 1940. s. HUNT £2,217,277 ' ‘ DEGENERATIVE PLATE cmcun: DETECTOR Filed Sept. '28, 19:8

DEGENERAT/VE PLATE __———_C/RCU/T DETECTOR | /2 6\ M?l/ k7 gmwy 4 i ' + /‘4 i- E 7 4-‘1 :"I'Yl’‘‘‘‘ ‘n I ‘ 7'0 LP 2: J- = ' '

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INVENTOR. Ilse MOUR HUNT BY

ATTORNEY. Patented Oct. 8, 1940 2,2l7,277

UNITED STATES F ICE 2,217,277 DEGENERAT'IVE PLATE CIRCUIT DETECTOR Seymour Hunt, Jackson Heights, Long llsland, N. Y., assignor to Radio Corporation of Amer ica, a corporation of Delaware Application September 28, 1938, Serial No. 232,075 6 Claims. (Cl. 256-4237) My present invention relates to detector cir art are fully acquainted with the construction of cuits, and more particularly to degenerative plate superheterodyne receivers, it is not believed nec circuit detectors capable of substantially ampli essary to explain the construction thereof at any fying the audio voltage output thereof. greater length. The output for the 5 One of the main objects of this invention is to detector circuit includes electrode 4. Preferably, provide a detector of the in?nite impedance type this electrode is a wound grid. The latter is con which includes an electronic section having a nected through load 52 to the plus B negative mutual conductance characteristic terminal of any desired direct current source, which functions to amplify the audio output of such as the usual direct current energizing source 10 the detector. of a . The coupling condenser l3 Another important object is to provide in a transmits the audio voltage, in ampli?ed form, biased plate circuit detector of the degenerative to the following audio ampli?er for ?nal repro type a negative mutual conductance section duction. which acts to increase the current flow through The l—3—t, With associated cir ' the detector plate circuit when the input signal cuits, provide a degenerative plate circuit detect amplitude increases. or, or “in?nite impedance detector” as it Still other objects of my present invention are is sometimes termed. There has been disclosed. to improve generally the e?iciency of degener and claimed by P. A. Farnham in application ative plate circuit detectors, and more especially Serial No. 8,664, ?led March 1, 1935, such a de 2.0 to provide a detector of the latter type which is tector. It is though suf?cient for the purposes of 20 not only reliable in operation but is economically this disclosure to make reference to the latter, manufactured and assembled. and brie?y state that substantially linear detec The novel features which I believe to‘ be char tion is secured in this type of detector by pro acteristic of my invention are set forth in par viding a direct current voltage across resistor 8 25 ticularity in the appended claims; the invention sufficient to bias grid 3 almost to cut-01f in the 25 itself, however, as to both its organization and absence of signals. Further, the audio voltage method of operation will best be understood by across resistor i5 is in degenerative phase, reference to the following description taken in and tends to compensate for the non-linearity connection with the drawing in which I have in of the detection characteristic for weak signals. dicated diagrammatically a circuit organization However, by virtue of this degenerative action the 30 whereby my invention may be carried into ef gain of the detector is less than unity. The pres fect. ent invention provides gain for the detector of Referring now to the accompanying drawing, the degenerative type. there is shown used as the detector an electron This is accomplished by connecting electrode 6 discharge tube of the GA’? or 6A8 type. This type to ground. The screen electrodes 5 and‘ l are 35 of tube comprises a cathode I and a plate 2; be both connected to a source of positive potential, twee-n these electrodes are positioned electrodes and I. F. by-pass condenser it connects the en- ' 3, ll, 5, t, l in succession in the electron stream. ergizing lead to ground. As grid 3 becomes less Plate 2 is left free, whereas cathode i is con negative due to the applied signals, more elec nected to ground through a resistor 8. The high 40 trons ilow to the screens 5—l‘. The flow of cur 40 potential side of the signal input circuit 9 is con rent causes a virtual cathode to build up between nected to the signal input electrode 3. The low the detector plate electrode 4 and the screen potential side of circuit 9 is grounded; condenser electrodes. As the virtual cathode becomes more connects the ground end of input circuit 9 to intense, the potential of grid 6 becomes more neg the cathode end of resistor 8. Condenser iii has a ative due to the increased voltage across resistor low impedance for carrier frequency currents, but 8. The negative potential of grid 8 drives the 45 has a high impedance to audio frequency com electronstowards detector plate i, and, therefore, ponents. Hence, there is developed across re causes the plate current ?ow through output re sister 3 both direct current voltage and audio sistor it“ to increase. Hence, the audio voltage 50 frequency voltage components. These compo developed across the output resistor 52 is aug 50 nents are impressed on the input electrode 3. mented by the action of the grid 6 and screen, or The primary circuit H maybe ?xedly tuned plate, 5—'l. Actually as. the signal gets stronger, to the I. F. (intermediate frequency) value of a the electron flow to plate 65 is increased by the superheterodyne receiver; the same being true joint action of grids 3 and 6. g of secondary circuit 9. Since those skilled in the It may be pointed out that electrodes l—5 and 55 2,217,277 6 cooperate with the virtual cathode to provide a jacent the virtual cathode, and responsive to an device having negative mutual conductance. In increase in space current ?ow through the tube, other words, the flow of electrons towards the for causing electrons to ?ow from the virtual ~ plate electrode 4 increases as the bias on grid 6 cathode to said output electrode, an impedance increases. This is the reverse of grid 3 which in the space current path of the tube for deriv causes the current to plate electrode 4 to in ing an audio voltage from impressed signals, said crease with decrease of negative bias thereof. audio voltage being impressed on said signal input There is provided, by means of the present in electrode in degenerative phase. vention, a detector whose detection characteristic 4. In a tube of the type having a cathode and 10 is linear over a wide signal amplitude range, and a positive output electrode, a signal input elec; whose audio voltage output is substantially ampli trode therebetween, means for biasing the input ?ed with respect to the same detector circuit electrode negative with respect to the cathode, a when not employing the invention. second positive electrode spaced from the output While I have indicated and described a sys-v electrode and providing a virtual cathode there 115 tem for carrying my invention into effect, it between, and a control electrode disposed ad will be apparent to one skilled in the art. that myv jacent the virtual cathode, and responsive to an invention is by no means limited to the partic increase in space current flow through the tube, ular organization shown and described, but that for causing electrons to ?ow from the virtual many modi?cations may be made without de cathode to said output electrode, an audio output ‘20 parting from the scope of my invention, as set circuit coupled to said output electrode, said con 20 forth in theappended claims. ' trol electrode being connected .to a point as-J What I claim is: suming an increasing negative potential with vl. In :combination, in a detector tube, an elec respect to said cathode. tronic section having a positive mutual conduct 5. In a detection network, a tube having at 125 ance and having a signal input circuit and an least a cathode, input electrode and output elec- 25 output electrode, a second electronic section hav trode, a signal input circuit connected to the ing a negative mutual conductance and provided cathode and input electrode, means coupled to with a control electrode responsive to the space the output electrode for deriving an audio volt current flow of the ?rst section, said control elec age from detected signals, means for impressing 39 trode being an electrode of said tube other than a portion of derived audio voltage between the 30 said output electrode and being spaced from said input electrode and cathode in degenerative output electrode, the said output electrode being phase, means in said tube for attracting elec common to both sections. > ' trons beyond said output electrode, and addi 2. In a tube of the type having a cathode and tional means in said tube, responsive to space a positive output electrode, a signal input elec current increase, for causing said attracted elec ' trode therebetween, means for biasing the input trons to ?ow back to said output electrode there electrode negative with respect to the cathode, by to increase the magnitude of the audio voltage, a second positive electrode spaced from the out 6. In a detector network, a tube having a cath put electrode and providing a virtual cathode ode, signal grid, output grid, and therebetween, and a control electrode disposed positive electrode arranged in the order named, 920 adjacent the virtual cathode, and responsive to a signal input circuit, an impedance connected an increase in space current ?ow through the between cathode and ground and being traversed tube, for causing electrons to flow from the vir by the space current of the tube, said' input cir tual cathode to said output electrode. cuit being connected between the signal grid and 3. In a tube of the type having a cathode and ground, an audio voltage load connected to the a positive output electrode, a signal input elec output grid, and a connection from the control trode therebetween, means for biasing the input grid to ground whereby an increase in space cur electrode negative with respect to the cathode, a rent of the tube results in an augmentation of second positive electrode spaced from the output audio voltage developed across said load. electrode and providing a virtual cathode thereg' SEYMOUR HUNT. jso. between, and a control electrode disposed ad-'