US2485925A - Circuit arrangement for electronic tubes operating on dynamic grid current principles - Google Patents

Circuit arrangement for electronic tubes operating on dynamic grid current principles Download PDF

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US2485925A
US2485925A US731105A US73110547A US2485925A US 2485925 A US2485925 A US 2485925A US 731105 A US731105 A US 731105A US 73110547 A US73110547 A US 73110547A US 2485925 A US2485925 A US 2485925A
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grid
anode
current
circuit
cathode
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US731105A
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Sargrove John Adolph
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C3/00—Angle modulation
    • H03C3/30—Angle modulation by means of transit-time tube
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D3/00—Demodulation of angle-, frequency- or phase- modulated oscillations
    • H03D3/02—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal
    • H03D3/22—Demodulation of angle-, frequency- or phase- modulated oscillations by detecting phase difference between two signals obtained from input signal by means of active elements with more than two electrodes to which two signals are applied derived from the signal to be demodulated and having a phase difference related to the frequency deviation, e.g. phase detector

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  • Ihis invention relates to the operation of electronic vacuum tubes or valves.
  • Figs. 1 to 4 are schematic diagrams which show, for tubes with different grid arrangements, the changing direction of travel of a pulse or bunch of electrons during a time period of a few microseconds after the electrons leave the cathode;
  • Fig. 5 is a diagram of a multigrid tube and associated circuit embodying the invention.
  • Fig. 6 is a curve sheet showing the variation of anode current with frequency shift when the Fig. 5 apparatus is operated as a frequency-shift discriminator or detector;
  • Fig. '7 is a fragmentary circuit diagram of a multiple grid tube operated as a trigger relay.
  • F'ig. 8 is a curve sheet showing the sharp variation in anode current with small change in the oscillator voltage input to the dynamic grid current tube.
  • triode valve As described above, and illustrated in Figure 1.
  • a simple representation is shown of a triode having a cathode which is emissive either by thermionic or other physical phenomena, a grid and an anode each having normal operating potentials. Cur rent meters are inserted into these two electrode leads.
  • cathode-space-charge which is a cloud of electrons in a state of instantaneous zero velocity in a forward direction but which may have a sideways velocity without affecting matters at all.
  • This instantaneous condition is due to the fact that the electrons have emerged at varying velocities from the cathode surface, have reached this point in space together with a large number of other electrons all having a negative charge and hence a decelerating influence on each other, and unless attracted by some other influence will reverse their direction and move back to the cathode.
  • FIG. 1 shows a transit-time versus distance diagram, the time axis representing an arbitrary time interval of the order of M 10- to l.0 seconds but naturaly this depends on the operating conditions, distances etc. of the actual valve structure.
  • the cathode is only emissive for an infinitely small instant and this pulse of emission is examined.
  • the electron will be reaccelerated in the opposite direction until it reaches the anode again at wi If by chance it falls towards a gap in the anode from this opposite direction and provided its path is not barred by an overwhelming mass of electrons coming direct from the cathode (which in this case of the examination of an electron emission pulse is not the case), it will again pass through the gap at maximum speed, will then again lose velocity to zero and reverse, repeating the above sequence, passing through the anode at tm going above the anode, reversing again, returning to the anode at tm and so on.
  • the cut-oil grid potential If the first negative control electrode is more negative then the total number of electrons in the two subsidiary space charges will be reduced and the space charges can disappear entirely if the first control electrode has a negative potential large enough to out off the anode current. This is called the cut-oil" grid potential.
  • the oscillatory voltage on the second control electrode has a relatively low frequency no effect will be introduced on grid i in spite of the capacity coupling between control grid 2 and control grid l.
  • the oscillator frequency is a very high frequency whose period is comparable to the transit time, a grid current will flow in grid I circuit in spite of the insertion of a complete de-coupling filter circuit which maintains the grid l at a fixed potential with reference to the cathode and eliminates the capacity coupling.
  • Electrons have finite though exceedingly small mass and hence their emission is not entirely free from inertia when dealing with time intervals smaller than a microsecond (lih second). Hence it takes certain exceedingly small time for an electron to traverse the space between the electrodes as indicated in the time distance diagrams discussed above. This is called the transit time.
  • the purpose of the invention is to make use of this kinetic grid current which hitherto has been considered a parasitic phenomenon and a nuisance, as follows: Viewing Figure 5, if a resonance circuit is connected to grid i of a multi-grid valve, grid 2 acting as a positive accelerator, grid 3 having a high frequency oscillation of say 19 megacycles or more impressed upon it, the kinetic electrons reaching the first grid after grid 23 approached its own cut-oii potential, will cause a uni-directional high impedance coupling be tween the cscillation on grid 3 and resonant circuit connected to grid l which will excite the resonant circuit and cause it to oscillate, this causing grid l to follow an approximately sinusoidal voltage sequence.
  • the second anode current of the valve will have a magnitude proportional to the multiple of the two oscillatory voltages, hence it can be shown that the anode current will have a component twice the frequency of the oscillator frequency and also a D. C. component proportional to the cosine of the phase angle between the two control voltages.
  • Ia c(E; sin wot) (E sin w0t+a) If we filter out the higher frequencies from the second anode circuit we are left with an anode current only varying due to the variation in phase angle mentioned above.
  • the tuned circuit on grid 5 has a constant tuning (which can if desired be maintained by a resonant piezo-electric crystal, or the whole circuit can be substituted by a crystal in any known manner) and the frequency on the second control grid is varied or modulated the D.
  • C. anode current of the second anode will vary very rapidly from a maximum value when the phase angle is approximately zero to a minimum value when the phase angle is approximately as shown by the thick line in Figure 6.
  • the present invention is based on the realisation of the fact that in this F. M. demodulator circuit, if the negative amplitude of the grid voltage greatly exceeds the cut-off value and by a simple grid-leak-grid-condenser limiter is not allowed to exceed zero voltage in a positive direction to any appreciable degree, 1. e. if the second control grid is overloaded, the demodulation slope of the device is very great due to the very high kinetic energy imparted to the electrons moving to grid l and thus exciting this too to a very large amplitude oscillation. But due to the control on the second anode current being in the form of what amounts to square waves of fixed amplitude, the demodulation slope is constant and independent of the carrier amplitude.
  • this device is the demodulator in an F. M. receiver, the device acts as its own amplitude limiter.
  • this function plus the demodulator function is usually accomplished by three or more valves, the new device consisting of only one valve is clearly of considerable advantage (the valve can be a simple pentode or a hexode etc., the incorporated triode shown in Figure not being required for this demodulating purpose).
  • FIG. 5 shows an example of a device in accordance with the invention for converting frequency shift or frequency modulation input into input circuit power variations with the oscillation generator incorporated in the form of a selfcontained triode and associated circuits.
  • valve is a triode-hexode of the type in which the triode grid is internally connected to the third grid of the hexode whose function is that of second control grid.
  • a filter network is included consisting of inductance i and two capacitances k and 7' followed by an output power dissipating device; this can be a simple current meter or a loading resistance or impedance across which a voltage drop will appear, or the like, in which the power variations of the device can be developed.
  • the accelerator anodes of the hexode valve are supplied with positive potential (with reference to the cathode) by known means of keeping this potential constant, for instance by a series resistance Z connecting them to the source of positive potential and a shunt means of stabilisation which can be a condenser 12?. (or a gas discharge stabiliser or any other device having a large capacitance e. g. a floating battery or the like).
  • the oscillator anode is fed through a feed impedance n and the grid through a grid leak 0, both having known functions, and tend to make the oscillator less dependent on supply voltage fluctuations than if they were absent.
  • condensers p and q The function of condensers p and q is to make the oscillator tuned circuit consisting of condensers 'r and s, and inductance t (either of which may be variable) independent of the D. C. potentials of the triode anode w and grid.
  • the tuned circuit connected to the hexode control grid nearest to the cathode and which is excited by the kinetic grid current effect consisting of inductance v and capacitance u (either of which may be variable) and which can be tuned to the mean frequency of the oscillator or to any desired part of the frequency sweep of the frequency modulated oscillator.
  • the grid bias of the first control gridof the hexode is shown connected for convenience to the negative end of the heater circuit battery (but can clearly be fed from any suitable source of negative potential).
  • the frequency-shift discrimination sensitivity of this device is also exceedingly high, and thus it can be used as a capacity change detector having a sensitivity of the order of lmA/10 farads which increases with frequency.
  • the device can also act as an inductance variation detector capable of use in many ways.
  • the direct radio-frequency conversion of mechanical displacement into voltage or current change such as the displacement of the diaphragm of a condenser microphone, a condenser pick-up for gramophones or the like detection of irregularities in a surface, or variation of minute dimensions (ultra micrometer) etc., the displacement of the core of the inductance by minute amounts, the detection of frequency or phase shift and the like.
  • the output meter shown can be substituted in both valve anode circuits by a difference indicating instrument of known type or a balanced bridge type output load circuit.
  • the preliminary set up can provide for the synchronisation of the two oscillators either by operating them in parallel or in push-pull the two circuits 1; and it connected to the first control grid being independent.
  • the difierence indicator in the anode circuits will show a signal with the same high order of sensitivity as that mentioned above for one valve but with considerably reduced dependence on fluctuating operating conditions.
  • the other valve can also be set to have an internal phaserelationship in quadrature.
  • triode hexode valves Two different types exist. A type in which the triode grid is internally linked to the hexode control grid farthest from the cathode (as shown in Figure and a type in which the triode grid is internally linked to the hexode control grid nearest to the cathode.
  • the quadrature relation in one can be obtained in a leading sense and in the other in a lagging sense i. e. for instance the grids connected to the oscillator triodes can be in phase opposition whilst the two other grids are in phase hence any change applied from an external signal which alters the reactance of the circuit connected to the two phase grids, causes, an exceedingly sudden chan e from the initial quadrature relation with balanced anode currents corresponding to the horizontal line in Figure 6 in both valves, to an entirely out of balance condition when in one valve the maximum current flows whilst in the other the minimum.
  • valves can of course be made use of also with other initial phase relationships providing different features. For instance if both valves are set to pass minimum current (per Figure 5) without outside signal one valve can be made to ignore the input signal if it has an incremental sense, whilst the other responds to it and vice versa if the input signal is in a decremental sense.
  • This type of sense discrimination having special advantages for instance in navigational instruments, such as automatic pilots, blind landing apparatus and goniometric applications and the like.
  • the sensitivity and stability of operation in all these circuits increases as the oscillation amplitude increases beyond the linear limits of the valves i. e. when the oscillations become amplitude limited.
  • the instrument. in which the device, according to the invention, is used has for its purpose the detection of radiant energy or the reception of a message or communication transmitted by modulation of such radiant energy it is possible to connect the radiation detector such as a photo-cell and the like in a manner so that it upsets the phase relationship of the quiescent condition in many ways and the detection takes place on the sloped part S of curve Figure 6.
  • a radiation detector of a non linear type (such as one relying on a barrier-layer phenomenon for its operation) connected into the reactive circuit u, 22', above described in a manner that irradiation causes shift in the phase response of this circuit to the frequency produced by the oscillator circuit.
  • a preferred manner of operation is to set the device to 0D- erate at one of its extreme points of operation (say at the maximum anode current or the minimum anode current part of the curve in Figure 6) and to arrange the radiation detector shunted across the reactive circuit 1), it ( Figure 5).
  • any device where any physical phenomena can be changed into a variation of capacitance or a variation of inductance or, for that matter, a variation of both or a variation of either combined with a variation of resistance etc. such change can be resolved into a current or voltage change with this exceedingly sensitive device.
  • Figure 6 shows that outside the boundaries of A the anode current varies in a complex manner depending on circumstances not yet investigated as they have no bearing on the present invention. These parts of the curve are shown dotted in Figure 6.
  • Figure 7 shows a high vacuum pentode device used as a trigger relay, th individual parts of the circuit are designated with references similar to those in Figure 5 except the generator of high frequency oscillations in this case is assumed to be a separate device shown symbolically 7' which silo-5n to be tiredness sterilised by having connected thereto a piezo-electric crystal X2 through a condenser 90.
  • the resonator circuit consisting of o and u both of which can be variable is shown to be frequency controlled b the piezoelectric crystal .13 This can be compressed by the application of a polarizing potential applied as an input at terminals marked in vie. H. F. choice 1 and isolated from the resonator circuit from the D. C. point of View by condenser q
  • grid bias is applied to the first control grid by its own action as an amplitude limiter causing a voltage to be built up across the series grid resistor ⁇ J1 by the grid current that flours during the periods corresponding to the clipped off peaks of the amplitude limited waves.
  • a condenser d shunts the resistor 9
  • the resonant frequency of crystal m1 is shifted and hence the phase angle of the oscillating voltage (built up on the resonant circuit 22 and u with reference to the exciting oscillator voltage.
  • this shift in phase angle can also be produced by the input energy being applied to the crystal X2 instead of X1.
  • the input energy can be made to influence the inductive or capacitive components of the resonator or oscillator directly for instance by causing the input energy to alter the permeability of the core of the inductance v or by causing it to alter the dielectric constant of condenser m or the like.
  • both control grids are overloaded, i. e. the A. C. signal on them exceeds the negative grid bias range of the valve, and hence the main anode current which is the main circuit current (shown thick line) can be switched on and off by input voltage control.
  • This control voltage can be applied either to the pie-zo-eiectric crystal thereby altering the natural frequency thereof and controlling the frequency discrimination of the circuit network 22 and u attached to control grid nearest to the cathode or to a crystal controlling the frequency of the oscillator or by any other voltage, or current operated tuning shift converter system.
  • the anode current of the device follows a law as that shown by the full line in Figure 8 in which the device has either no anode current at all or rapidly reaches a saturation value.
  • the anode current attempts to follow a law similar to that shown in Figure 6 but as this curve is larger than the anode current limits of the valve we get this reversible trigger phenomenon.
  • a device of this type is superior to a gas-discharger grid-controlled trigger relay as it has no inertia up to sreeds two to three orders of magnitude higher than that of the gas-discharge devices.
  • anode current can be switched both on and off by pure grid control.
  • the size of the main circuit current that can be switched on and off is at present only limited by the size of multi-control grid valves available and could in theory be developed to very large sizes given the necessary demand permitting the manufacture of such large high vacuum devices.
  • these devices can and preferably would be so coupled to the circuit that they can cause a shift in first control grid bias from a point where the kinetic grid current.
  • phenomenon occurs with, say, a minimum anode current flowing to a point where the absorbed grid current clamps the resonant system cou led to it, causing the anode current to revert to a mean value.
  • the circuit contained a multigrid mixer valve and an oscillatory circuit connected to one grid of the mixed valve and by the said oscillatory circuit being excited by an unmodulated or frequency modulated control potential applied to another grid of the valve a change of frequency was converted into current variations.
  • An electronic circuit comprising an electronic tube having three electrodes in series arrangement between a cathode electrode and an anode electrode, the inner and outer electrodes as measured from the cathode being control grid electrodes and the intermediate electrode being an accelerator electrode, voltage source means establishing relative static potentials on the control grid electrodes to prevent flow of grid current, means maintaining the static potentials of the anode and accelerating electrode positive with respect to the cathode, whereby space charges between the accelerating electrode and the respective control grid electrodes set up control fields at opposite sides of said accelerator electrode, input circuit connected between the inner control grid electrode and the cathode, and a control circuit connected between the outer control grid electrode and the cathode to impose upon said outer control grid electrode an oscillatory voltage of an amplitude suflicient to block anode current during a part of the oscillatory cycle and to drive electrons in reverse direction through the accelerating electrode to reach the inner control grid, the oscillatory voltage having a period of the order of the electron transit time and said input circuit being resonant at approximately
  • An electronic circuit as recited in claim 2, wherein said means for varying the phase angle comprises means for adjusting the resonant frequency of one of said circuits.
  • control circuit includes means for modulating the oscillatory voltage impressed upon the outer control grid electrode in frequency or phase.
  • control circuit includes an electronic oscillator.
  • control circuit includes an electronic oscillator, said oscillator having the elements thereof enclosed within the envelope of said tube.

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US731105A 1942-03-28 1947-02-26 Circuit arrangement for electronic tubes operating on dynamic grid current principles Expired - Lifetime US2485925A (en)

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GB4136/42A GB558036A (en) 1942-03-28 1942-03-28 Improvements relating to the operation of electronic vacuum tubes or valves

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BE (1) BE465751A (xx)
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2294372A (en) * 1941-10-31 1942-09-01 Rca Corp Phase modulation
US2332540A (en) * 1941-02-27 1943-10-26 Philco Radio & Television Corp Method and apparatus for receiving frequency modulated waves

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2332540A (en) * 1941-02-27 1943-10-26 Philco Radio & Television Corp Method and apparatus for receiving frequency modulated waves
US2294372A (en) * 1941-10-31 1942-09-01 Rca Corp Phase modulation

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FR925494A (fr) 1947-09-04
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