US2647208A - Electric circuit-arrangement - Google Patents

Description

July 28, 1953 F. DE JAGER 2,647,208

' ELECTRIC CIRCUIT-ARRANGEMENT Filed March 20, 1951 2 Sheets-Sheet 1 w Y .221- ".11. r!

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INVENTOR FRANK DE JAGER AGENT u y 8, 1953 F. DE JAGER I 2,647, 8

ELECTRIC CIRCUIT-ARRANGEMENT Filed March 20, 1951 2 Sheets-Sheet 2 v INVENTQR FRANK DE JAGER AGENT of the tubes.

hereinafter.

Patented July 28, 1953 ELECTRIC CIRCUIT-ARRANGEMENT Frank de J ager, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Comm, as trustee Application March 20, 1951, Serial No. 216,487 In the Netherlands April 28, 1950 11 Claims. 1

This invention relates to trigger circuit-arrangements comprising at least two grid-controlled amplifying tubes cutting ofi each other by mutual feedback, the trigger circuit selecting one of two states of equilibrium in accordance with a control-voltage supplied thereto. In one state of equilibrium, one of the tubes passes cur.- rent and the other is cut off, and in the other state of equilibrium the anode current conditions of the trigger are reversed.

Such trigger circuits are widely used in prac "tice. They may, for example, be used for bilateral limitation or as a non-linear amplifier of a control-voltage supplied to a control-grid of one Across the output circuit of the trigger circuit is produced a rectangular voltage which, for example, is positive depending on whether the control-voltage exceeds or does not exceed a particular critical value, so that the trigger circuit gets into one or the otherstate In reliable forms of known trigger circuits of the aforesaid type the difierence between control- ,voltages required to trip the trigger in different directions, in other words the response sensitiveness when using conventional amplifying tubes, for example triodes or pentodes, is approximately 1 to 2 volts. 7

The object of the present invention is toprovide improved trigger circuits of the type referred to.

I According to the invention a common part of the grid circuits of the two amplifying tubes comprises a grid bias supply, driving the tubes into equal anode-current conditions irrespective- 1y of the control-voltage, and a switch-pulse generator connected in series with the said supply.

In making use of the invention a third state of equilibrium of the trigger circuit is brought about in which either the two tubes of the trigger-circuit are non-conductive or the two tubes pass the full anode current.

Similarly to know trigger circuits, trigger circuits according to the invention may be used for or adapted to various purposes, as will be set out In order that the invention may be readily. carried into effect, three examples will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows a trigger circuit according to the invention, comprising two cross-wise coupled pentodes;

. Fig. 2 shows static characteristic curves asso ciated with the circuit depicted in Fig. 1, which indicate the relationship existing between, the switch-voltage and the output voltage. of the trigger circuit at various valuesof the controlvoltage;

Fig. 3 shows the circuit according to the invention used as a pulse code modulator, and, v

Fig. 4 shows. how the circuit according to the invention may be used as a pulse selector, a pulse generator and a pulse code demodulator.

In the circuit-arrangement shown in Fig. l, the trigger comprises two pentodes l and 2 cutting off one another by crosswise direct-current feedback and having anode resistors 3, 4 respectively and a common earthed cathode resistor 5. The control-grid of the pentode I is connected to a tapping point of an ohmic voltage divider comprising resistors 6, I which is connected on the one hand to the anode of the pentode 2 and on the other hand through a resistor 8, to a point of negative potential with respect to the cathodes of the tubes I. and 2. The latter point is constituted by the negative terminal of a grid bias battery 9, the other terminal of which is earthed. In a similar manner, the control-grid of the p l tode 2 is connected to a tapping point of a voltage divider havin resistors l0 and H, one end of which is connected to the anode of pentode I, while the other end is also connected to sistor 8. 1

In order to prevent the control-grids of the pentodes I and 2 from assuming a positive potential relative to the associated cathodes, the anodes of grid-current limiting diodes I2 and it, the cathodes of which are earthed, are connected to the respective control grids.

Provided the bias from the grid bias battery '9 has a suitable value, the circuit-arrangement so.

the other. If, for example, the pentode I is cut off and the pentode Z'passes current, the latter will pass current upon va suitable increase'in potential "of the control-grid of pentod el ljand .3 will cut off the pentode 2, a subsequent decrease in potential of the control-grid of pentode l causing the trigger to resume its initial state of equilibrium.

The trigger circuit comprises a grid bias source 0 having a value such that, in the absence of a control-voltage, the two trigger tubes 1, 2 are operated under equal anode-current conditions. In the circuit-arrangement shown in Fig. 1, the two pentodes l and 2 are cut oil in this third state of equlibrium. A pulse-shaped switch-voltage us, shown diagrammatically in the drawing and applied through a capacitor l5 at the resistor 8 connected in series with the grid bias battery 53 is supplied, in series with the said cut-off grid bias, to terminals l4. During the positive peaks of this switch-voltage the influence of the source of negative grid bias cutting on the two tubes is reduced to such a degree that the trigger circuit becomes normally operative and selects one or the other of the normal states of equilibrium in accordance with a control-voltage supplied to it.

The control-voltage for the trigger circuit might be supplied. to the control-grid of one of the trigger pentodes, but this produces a sometimes undesirable reaction of the voltage pulses occurring in the trigger circuit on the source of controlvoltage. Therefore, as shown in Fig. 1, the control-voltage w is supplied, as is known per se, to the control-grid of a pentode 'l 0 which is connected in parallel with the pentode l and the resistor 5 included in the cathode lead thereof. The output voltage of the trigger shown in Fig. 1 is taken from a tapping point ll of a voltage divider comprising resistors l8 and 19 which are connected between the anode of pentode and the negative terminal of the grid bias battery 9. The output voltage set up between the tapping of this voltage divider and earth is designated Us.

and is positive (for example +10 volts) or negative (for example -30 volts) accordingly as the trigger circuit is in one or in the other of the normal states of equilibrium.

The principal elements usedjin an experimental trigger circuit-arrangement as shown, in Fig. 1 are the following.

R10 27,000 ohms.

R11 27,000 ohms.

R13 27,000 ohms.

R19 39,000 ohms.

Grid bias source: 9:150.volts. Anode voltage: 250 volts. Switch-voltage: about 50 volts.

Fig. 2 shows a number of static characteristic C'Lll'VBS holding for the circuit shown in Fig. 1. These characteristic curves show the relationship existing between the output voltage He. and the negative grid bias as set up at the junction of the grid resistors l and H at various values of the control-voltage a1 supplied to the tube 'l, as stated with the characteristic curves in question.

With a control-voltage u1=1.3 volts'a characteristic curve A was recorded, which is formed upon a variation of the voltage as between, say, 10 volts and 150 volts through a branch A1 and upon a, variation of the voltage Ho between volts and l0 volts through a branch A2. The characteristic curve A thus forms a loop with branches A1 and m which are shown in part in broken lines, since the points corresponding to these parts do not constitute stable Working points for the circuit.

In a similar manner loop characteristic curves B and 'C are found at control-voltages or" 1.1 volts and l.l8 volts respectively.

If the voltage 160 is approximately 20 volts the two trigger tubes pass current. At a voltage as between approximately volts and volts the trigger tube l is cut oil and the trigger tube 2 passes current and this state of equilibrium occurs at the last-mentioned value of U0 with a control-voltage of at least -1.18 volts, for example l.3 volts, while at a control-voltage 1n of l..1'7 volts or less, for example 0.8 volt, the characteristic curve B or a characteristic curve designated E or F is found, in which case, at a voltage uo of approximately l00 volts the tube l passes current and the tube 2 is out off. The series of characteristic curves appeared to be satisfactorily reproducible with the circuitarrangement shown and the trigger takes up one or the other of the normal states of equilibrium according as the control voltage is l.1'75 volts or 10.005 volt. Consequently, the response sensitiveness is approximately 0.01 volt.

Of this high response sensitiveness full advantage is taken if, owing to the switch-voltage us, the voltage varies periodically between, for example, 20 volts and l00 volts or, volts and -100 volts. As appears, in effect, from the series of characteristic curves they embrace a cross-hatched area in which no stable states of equilibrium of the trigger circuit occur.

Upon periodical variation of the bias 'LLo between the said values (1. e., 20 v. and -l00 v. or l50 v. and l00 v.), by means of a pulseshaped switch-voltage Us, the trigger circuit appears to select in each instance, starting from the enforced third state of equilibrium, one of the two normal states of equilibrium with a'high response sensitiveness and rapidity at an instant determined by the leading edge of the switchpulse, the state of equilibrium chosen depending on a value of the applied control-voltage m above or below a critical value, the amplitude of the switch-pulses playing only a very minor part in the selection.

It is advantageous for the trigger tubes l and 2 both to pass current in the third state of equilibrium, since in this case the amplification upon response and thus the response sensitiveness of the circuit-arrangement is particularly favourable. The voltage uo is thus preferably chosen to be approximately -20 volts. As an alternative, however, this voltage 1L0 may, for example, be 150 volts for the position of rest of the circuit. In this case the two trigger tubes do not pass current in the third state of equilibrium. Upon a variation of the voltage Mo to about -l00 volts, the circuit again selects one of the two normal states of equilibrium in accordance with the control-voltage applied, but the response sensitiveness of the trigger is slightly lower.

In the embodiment shown by way of example in Fig. 1 and in the following embodiments, the bias voltage bringing about the third state of equilibrium and the switch-voltage are operative across the control-grid circuits of the'trigger tubes. The increased response s'ensitiveness aimed at may, as an alternative, be obtained by causing the said voltages to be operative across circuits other than the control-grid circuits, for

example across the screen grid or suppressor grid circuits of the trigger tubes.

In trigger circuits according to the-invention, provision should be made with respect to the switch-pulses, that the time intervals T1 between the switch-pulses T2 is sufliciently great, so that at the beginning of a switch-pulse, it does not matter whether'one or the other trigger tube was conductive during the preceding switchpulse. Any residua1 voltages introducememory effects which detract from the response-sensitiveness. In view'thereof the value of the coupling resistors 6 and ID, if necessary shunted by small capacitors (for exampleof micromicrofarads) must not be made excessively high at a high switch-voltage frequency (for example 60 kc.) .and parasitic capacities and inductances should be minimized.

Fig. 3 shows one embodiment of a trigger circuit, used for pulsecode modulation. The trigger circuit comprises a hexode 20 and a triode 2|, which are cross coupled conductively in a manner similar to Fig.1 through resistors 22, 23, 24 and 25/ The junction point of the resistors 23 and 25 is connected through a resistor 26 to a point of strongly negative potential with respect to the cathodes of the trigger tubes 20 Similarly to Fig. 1 a rectangular switchvoltage is supplied through a capacitor 21 to the control-grids of the trigger tubes. This switchvoltage is again shown diagrammatically in the drawing and consists of switching pulses having a duration T2 and an interval T1.

The anode voltage of the trigger tube 2| is capable of cutting ofi a pentode 30 by way of a voltage divider comprising resistors 28 and 29. The anode circuit of this pentode comprises an integrating network including a capacitor 3| and a parallel-connected resistor 32. A signal in, for example a speech signal, to be converted in pulse code modulation is supplied to the controlgrid circuit of a pentode 33 used as an amplifying tube and comprising'an anode resistor 34. As will be described more fully hereinafter, a voltage approximating the signal to be transmitted occurring across the resistor 34 is set up across the integrating network 3|, 32 of this circuit-arrangement. the two anode voltages is utilised as a controlvoltage for the trigger circuit and supplied, for

this purpose, to the second control-grid of the hexode 20 through coupling resistors 35- and 36,

to the junction point 31 of which a voltage divider comprising resistors 38 and 39 is connected. The free end of the resistor 39 is connected to a point of negative potential, and the tapping point of the voltage divider 38, 39 is connected directly to the second control-grid of the hexode 20. For the sake of simplicity, Fig. 3 shows only those connections which are required for a clear understanding of the embodiment of invention; it is, for example, not shown how the screengrids and suppressor-grids of the tubes employed are connected to the remainder of the-circuitarrangement.

In order to explain the operation of the circuit;

shown in Fig. 3 it is'assumed that the controlvoltage supplied to the second control-grid of the hexode 20 exceeds a certain critical value, so that, if the trig er circuit is capable of selecting between-the two normal states of equilibrium-At The difference between takes up that state of equilibrium in which the 'hexode 20 passes current and the triode 2| is cut off. Considering the operation of the switchvoltage us, by which the two tubes of the trigger are urged into the non-conductive condition during the interval T, it will be obvious that at the --instant t,- after which the trigger is capable of selecting one of the two normal states of equilibrium, the. triode 2| remains non-conductive and the hexode 20 tends to pass current. The fpentode 30 then passes an appreciable anode 'current, owing to which an increase in voltage set upat the integration capacitor 3| is produced across the latter and the potential of the second control-grid of the trigger hexode 20 is decreased. Ifzthis decrease is such that the potential of the second control-grid of the hexode 20 drops below the critical value, the triode will then pass ourrentand cut off the integrator pentode 30 at the beginning of a next following switch pulse. In this event, no energy is supplied to the integration capacitor 3| and the available charge slowly decreases through. the discharge resistor v32. Accordingly as the value of the signal approximation voltage across the integration capacitor 3| is higher or lower than the signal voltage, a potential having a value below or above the critical value is set up at the second control grid of the hexode 20. Upon each switch pulse, however, the trigger circuit will select such a state ofequilibrium that any difference between the compared voltages setup at the resistor 34 and the integration capacitor 3| is counteracted and, if necessary, over-compensated, so that irrespectively of tube characteristic curves the circuit-arrangement shown in Fig. 3 strives for a minimum divergence of the potential of the'sec- 0nd control-grid of the hexode 20 from the said critical value and maximum response sensitiveness. The latter is substantiallyensured by the negative feedback circuit provided between the output circuit and input circuit of the trigger circuit arrangement and comprising an integrating network, and is of particular importance for various practical uses.

In'the circuit shown in Fig. 3, the anode circuit of the triode includes a differentiating network connected to the anode resistor 40 and comprising a capacitor 4| and an output resistor 42.

This'difierentiating network supplies a positive pulse whenever the triode 2| is cut off in its conductive condition. This is only possible at the instants designated t" in Fig. 3 at the switchvoltage us, when the integrator tube 30 was cut off during the preceding time interval T2. When these positive pulses are transmitted to a receiver and supplied after reception, if necessary through a pulse generator to correct the shape, theamplitude and the time of occurrence, to an integrating network followed by a low-pass filter to restrict the quantization noise inherent with code modulation, the signal obtained at the output of the low-pass filter substantially corresponds to the signal to supplied to the input of the circuit shown in Fig. 3. It is pointed out that in the circuit-arrangement shown in Fig. 3 variations of the difference voltage controlling the hexode' 20 will not practically affect the height or the width of the pulses supplied to the integrating network 3|, 32, and consequently the voltage across the integration capacitor 3| provided that the switch-voltage us has sufii- .ciently steep flanks.

The itrig er circuit-arrangements described -maybe=used in the'manner illustrated in Fig.4

'9 I to separate the. channels at the receiver end in a time-multiplex signal transmission system by pulse code modulation, in which the signal pulses are alternately present and absent in accordance with the signals to be transmitted. At the transmitter end, the signals to be transmitted may be converted per channel into pulse code modulation with the use of a circuit shown in Fig. 3 and then be assembled in time division.

The circuit-arrangement shown in Fig. .4 comprises a trigger circuit similar to Fig. 3, followed by an integrator tube, in the :anode circuit of which an integrating network is connected. In Fig. 4, 'circuitelements similar to those of Fig. 3

of all the channels received in time multiplex to be supplied to the said control-grid by way of the input terminal 43, only the incoming pulses coinciding with the leadingiedges at the instants it being supplied to the integrator tube 30. "By providing that the switch-voltage 1.1.5 has a recurrence frequency correspondingfwith the cycle frequency of the incoming pulses, only the pulses associated with a particular signal channel will produce corresponding pulses across the controlgrid of the integrator tube in thecase of suitable synchronization of the switch-voltage relative to the incoming pulse trains, since the state of equilibrium of the trigger circuit for the time intervals T2 is only determined by the controlvoltage at each preceding instant t.

In the circuit shown in Fig. 4 there will, in generaL be no need for utilizing the high response sensitiveness, in other words the considerable amplification thus obtainable, but such use 'is made of the property of this circuit that the A sensitiveness for thecontrol-voltage is exclusively present at the time of the leading edges of the switch-pulses. With a sufficient amplitude of the input pulses, the presence or the absence of a signal pulse determines whether or not an'output.

pulse will occur. The amplitude of the input pulses, their shape and the exact instant of the occurrence of the centralpart of an inputpulse do not ailect the shape, the amplitude and the instant of occurrence of the output pulse. Referring to Fig. 4, the trigger circuit consequently operates at the same time as a pulse regeneratcr to correct the shape-the amplitude and the instant of occurrence of the incoming pulses, which may be utilised to eliminate noise in pulse code modulation receivers or in relay apparatus for pulse code modulation.

Finally, it has been found experimentally that trigger circuit-arrangements according to the invention operate in the optimum manner, if the two trigger tubes have substantially the same steepness characteristic with respect to their crosswise coupling. It has furthermore been found that trigger circuit-arrangements of the present kind are sometimes diihcult to handle when using variable mu tubes. 1

What I claim is:

1. A trigger-circuit arrangement comprising first and second electron discharge tubes each .havinga cathode, a grid'andan anode, means,

cross-coupling said tubes whereby said arrangement exhibits two normal states f equilibrium, in one state of which said first tube is conductive and said second tube non-conductive, in the other stateof which the converse relationship exists, means to apply a control voltage to one of said tubes. to flip said arrangement from one normal equilibrium state to another, and a common grid circuit coupled to the grids of said tubes, said common circuit including a bias voltage source having .a value at which saidtubes are both driven into equal anode current conditions representing a; third state of equilibrium, and a pulse generator connected in series with said source and producing rectangular switching pulses having an amplitude and polarity at which said trigger arrangement alternates between said third state and one charge tube connected across said first tube, the

control voltage being applied to the grid of said third tubea 5. A trigger-circuit arrangement, as set forth in claim -l,wherein said control voltage is constituted by periodic pulses having a repetition rate whichis a harmonic of the repetition rate of said switching pulses.

'6. A trigger-circuit arrangement, as set forth in -claim l, wherein said means to cross-couple said tubes includes a pair of voltage dividers each connected between the anode and cathode of a respective tube, a tap on each divider being connected to the grid of the tubeassociated with the other divider.

.7. A trigger-circuit arrangement, as set forth in claim 1, further including a voltage divider connected between the anode of one of said tubes and through said bias voltage source to the oathode thereof, and an output circuit coupled to a tap on said divider.

8. A trigger-circuit arrangement comprising first andsecond electron discharge tubes each having a cathode, a grid and an anode, means cross-coupling said tubes whereby said arrangement exhibits two normal states of equilibrium, in one state of-which said first tube is conductive and said second tube is non-conductive, and in the other state of which the converse relationship exists, an input circuit coupled to the grid of said first tube, an output circuit coupled to the anode of said second tube, means to apply a control voltage to said input circuit to flip said arrangement from one normal equilibrium state to another, a common grid circuit coupled to the grids of said tubes and including a bias voltage source having a 'value at which both tubes are driven into equal anode current conditions representing a third state of equilibrium and a pulse generator connected in series with said source and producing rectangular switching pulses by which said trigger arrangement alternates between said third state and one of said normal states.

9. An arrangement, as set forth in claim 8, further including a negative feedback voltage cir- 9 1G 'cuit coupled between said output circuit and said wherein said output circuit includes a differentiinput circuit and including an integrating netating network to yield code modulation pulses. work. FRANK DE JAGER.

10. An arrangement, as set forth in claim 8, I wherein said control voltage varies in accordance 5 References Cited in the fi e O this P te t with a signal to be converted into pulse code UNITED STATES PATENTS modulation, and wherein pulses are derived from N b N said output circuit. um er ate 11. An arrangement, as set forth in claim 10, 2555999 Ringlee June 1951

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