512,109

PATENT SPECIFICATION

Application Date: Dec. 24, 1937. No. 36150/38

April 25, 1937. No. 12342/38

(Application No. 36150/38 divided out of Application No. 35791/37 (508,377)

One Complete Specification Left: Dec. 14, 1938.

(Under Section 16 of the Patents and Designs Acts 1907 to 1938)

Specification Accepted: Aug. 29, 1939.

-------------------------

PROVISIONAL SPECIFICATION

No. 36150 A.D. 1938

Improvements in or relating to Television or other Signal Transmission Systems

We, ALAN DOWER BLUMLEIN, a British subject, of 37, The Ridings, Ealing, London, W.5, and ERIC LAWRENCE CASLING WHITE, of 7, Vine Lane, Hillingdon, Middlesex, a British Subject, do hereby declare the nature of this invention to be as follows:

The present Application is a divided Application from No. 35791/37 (Serial No. 508,377) and is concerned with the provision of an improved switch adapted to be controlled by pulses.

The improved switch according to the invention will be described with reference to the accompanying diagrams in which : Figure 1 illustrates a circuit for D.C. reinsertion with which the switch according to the invention may be employed, and Figure 2 shows the switching circuit according to the invention.

The invention will be described with reference to the drawings as applied by way of example for the reinsertion of the D.C. component in television signals on the assumption that spurious signals are generated in the intervals between successive lines and frames.

The arrangement shown in Figure 1 comprises a D.C. coupled amplifier 10 having a substantially flat frequency characteristic from zero to the highest modulation frequencies required by the television picture (say 2.5 m.c. for 100 lines, 25 pictures per second). The amplifier is assumed to have three similar input terminals as may be obtained by a first stage consisting of three valves with their anodes connected in parallel and their three control or input grids providing the three input terminals. The amplifier is arranged to reverse the sense of the signals so that a direct feed-back from output to input is in the negative sense. To the input terminal 11 are applied vision signals in the positive sense which as shown in Figure 1 are fed through a condenser 11a so that they require an added D.C. component to make black in the signal input correspond to zero volts. Another input terminal 14 of the amplifier 10 is supplied with suppression pulses for suppressing the spurious signals. These pulses are large negative pulses occurring between lines and frames. Associated with the amplifier is a further amplifier 21 in this case considered as having no gain, which cuts off sharply at or just positive of zero or the voltage corresponding to black. The third input terminal 15 is supplied with a bias potential obtained from a condenser 22 and resistance 23 constituting the load of a diode rectifier 24. Diagrammatically the anode of the rectifier 24 is shown connected through a switch 25 to the output terminal 20 of the first amplifier 10. This switch is controlled by pulses which are of the same form as the suppression pulses, but preferably of slightly longer duration, beginning before the suppression pulses and ending after them, both for lines and frames. The effect of these pulses is to open the switch 25, so that the switch is always open when suppression pulses are applied to the amplifier.

Figure 2 shows the arrangement according to the invention for replacing the diagrammatic switch 26. In this Figure it is assumed that the output of the first amplifier 10 of Figure 1 has a low impedance, such as is obtained for example, by taking the output from the cathode of a valve. The terminal 20 is connected through a rectifier 27 to the anode of rectifier 24, as shown. The rectifier 27 is maintained normally conductive by a resistance 28 of say 50,000 ohms. Connecting the anodes of the rectifiers 24 and 27 to be slightly more positive than its cathode which can be allowed for, as regards amplifier input bias by means of a suitable bias source as shown at 29 in Figure 2. A third rectifier 30 has its anode connected to the anodes of rectifiers 24 and 27 and its cathode fed with the modified negative suppression signals at terminal 31. These signals are assumed to be negative pulses with respect of earth potential. A bias battery 32 is employed so as to maintain the cathode of rectifier 30 normally positive, so that it will not conduct when the rectifier anodes are made positive by slight positive signals at the terminal 20. The negative signals at terminal 31 will cause the cathode of rectifier 30 and its anode to become very negative. Consequently the whole current (2 m.amps.) passing through the resistance 28 will be absorbed and thus cause the anodes of rectifiers 24 and 27 to become negative. This will prevent positive pulses at terminal 20 passing through rectifier 27 and also the negative excursion of the anode of rectifier 24 will not produce any rectification. Thus during the negative suppression pulses the rectifier is in effect disconnected from the terminal 20. In the absence of suppression pulses rectifier 30 is non-conducting owing to the action of rectifiers 27 and 24. The arrangement therefore performs the function of the switch 25 in Figure 1.

In Figure 2 are also shown three valves 33, 34 and 35 and a delay network 36 for producing the required switch operating and the suppression pulses for application to the terminal 14 from master positive suppression pulses, applied at terminal 37. This part of the circuit does not however form part of the present invention.

The operating of the D.C. reinserting circuit is more fully described in the Specification of co-pending Application No. 35791/37 (Serial No. 508,377)

Dated this 12th day of December, 1938

F.W. Cackett

Chartered Patent Agent

PROVISIONAL SPECIFICATION

No. 12342 A.D. 1938

Improvements in Electrical circuits controlled by Pulses, suitable for use in Television

We, ALAN DOWER BLUMLEIN, a British subject, of 37, The Ridings, Ealing, London, W.5, and ERIC LAWRENCE CASLING WHITE, of 7, Vine Lane, Hillingdon, Middlesex, a British Subject, do hereby declare the nature of this invention to be as follows:

This invention relates to electric signal pulse controlling circuits and is concerned with improvements in or modifications of the invention described in co-pending Application No. 7941/37 (Serial No. 497,637).

In the said application there is disclosed a switch which may be employed for a variety of purposes. The arrangement comprises a pair of uni-directional conducting devices which under the operation of controlling impulses act as an uni-directional switch. One of the electrodes of one of said uni-directional devices is connected to a like electrode of the second uni-directional conducting device, the common electrodes being connected to a conductive impedance. Switching pulses are applied to one or more of the electrodes of said arrangement so that the switch is rendered conductive or insulating.

The object of the present invention is to provide an improved switch of this type which requires controlling pulses of smaller amplitude than those of the co-pending arrangement and which operates in a quicker and improved fashion.

The switch described in the co-pending application is a uni-directional conducting device and a further object of the present invention is to provide an improved bi-directional conducting switch.

According to the present invention an electrical switching circuit adapted to be controlled by switching pulses comprises three uni-directional conducting devices having three similar electrodes joined together and connected to a conductive impedance, a controlling pulse being applied to one of said devices whereby the switching circuit is altered from the operative (conducting) into the inoperative (non-conducting) condition or vice-versa.

In one form of the invention the three cathodes of three diode valves may be connected together and the controlling pulse may be applied to an anode of one of the diodes, if desired, from a further valve. Alternatively three diode valves with their anodes connected together may be used, the pulses being applied to the cathode of one of the diodes. In another form of the invention triode or other multi-electrode valves may be used with the cathodes connected together. This last arrangement has the advantage that as the controlling potentials are applied to the control electrode, or electrodes, of the valve, or valves, the device places substantially no load on the controlling circuits.

The invention may be employed to provide a uni-directional conducting switch or a switch which is bi-directionally conductive. In the latter case two sets of three valves may be employed, the cathodes of one of said sets being connected together, whilst the anodes of the other set are similarly connected together, the two sets being connected back-to-back. Controlling pulses are applied to the cathode of one valve of one set and similar controlling pulses reversed in phase are applied to the anode of one valve of the other set.

In a modification of this bi-directional conducting switch instead of applying the controlling pulses through the two diodes, these diodes are omitted and the controlling pulses are applied through suitable impedances.

For the purpose of describing the invention more in detail reference will now be made to the accompanying drawings in which Figures 1, 2 and 3 illustrate particular embodiments according to the invention.

Fig. 1 shows an arrangement using three thermionic diode rectifiers 23, 24 and 25 (which may be a triple-diode valve) the cathodes of which are joined to a resistance 27 connected to a source of negative potential (not shown). Any other form of rectifier may be used, but if high speeds of switching are required rectifiers of low capacity are desirable. The three diodes form a switch adapted to connect the line 21 with the line 22 under the control of controlling pulses applied to terminal 32 and thus effectively at point 26. The anode of diode 23 is connected to the line 21 and the anode of valve 25 is connected to line 22. The terminal 32 is associated with the control grid of valve 28 to which it is coupled by a suitable condenser and grid leak. The cathode of valve 28 is taken to a suitable negative potential and the anode of the valve is connected to a positive source of potential via resistance 29. The resistance of 29 is preferably lower in valve than the impedance 27, which latter may be inductive, its function being to take a constant current from the diode cathodes to a negative potential. If the potential of point 26 is made more positive than the potentials of 21 and 22 then all the current in impedance 27 flows through diode 24. Should point 26 now be made negative the current in the impedance 27 tends to make diodes 23 and 25 conduct, thus providing a conducting path between lines 21 and 22. If 21 and 22 are greatly different in potential the current in the impedance 27 will only flow through one or the other of diodes 23 or 25, but this current will tend to draw the lines 21 and 22 together in potential.

In a particular application it may be necessary to charge a condenser 30 (shown connected between line 22 and earth) to a potential which is representative of the potential of the line 21 during certain periods of time when the device is made operative. In this case the anode of diode 24 is normally maintained positive by means of the resistance 29. The current form impedance 27 then flows through diode 24 and the diodes 23 and 25 insulate, since the anode of diode 24 and consequently the cathode of 24 makes the cathodes of diodes 23 and 25 positive with respect to their anodes. The valve 28 is arranged to make the anode point 26 negative when a positive controlling pulse is applied to the grid of valve 28. When point 26 becomes negative the anode of diode 24 and therefore its cathode also become negative. The cathode potential of diode 24 falls negatively until diode 23 or 25 conducts and robs diode 24 of the current flowing in impedance 27. Suppose, for instance, that during the operative period the potential of 21 is less than the potential of 22. The diode 25 will conduct and charge condenser 30 negatively until the anode of diode 25 drops in potential to the same potential as the anode of diode 23. This latter diode will then conduct and if 21 is connected to a low impedance potential source (the potential of which may be varying), the charging of condenser 30 will cease and 21 and 22 will have been effectively joined. If the potential of 22 is negative of 21 however, and if 21 is connected to a low impedance source of potential so that the current through impedance 27 cannot bring the potential of line 21 to that of line 22, the two lines will not be joined. A leak resistance 31 from a source of positive potential is therefore connected to line 22 in order to make the potential of condenser 30 positive, so that each time the device is operative a negative charge is applied to condenser 30, so that the potential of line 22 follows that of line 21 during the operative periods.

The diodes of Fig. 1 may, if desired be connected in a reverse sense so as to charge 30 positively instead of negatively. With all three diodes reversed, i.e., with the cathodes separate and the anodes connected together, the impedance 27 must be taken to a source of positive potential and resistance 31 to a source of negative potential. The valve 28 will then require a negative pulse to be applied to its grid in order to switch the device into the operative condition.

The arrangement of Fig. 1 may be used as an "observing" device the purpose of which is described in British Patent Specification No. 458,585, the potential on condenser 30 being the observed potential of line 21 during periods determined by the switching pulse applied at terminal 32. The arrangement can also be used in place of the pentode valve 24 shown in Fig. 2 of Patent Specification 449,242, by inserting a condenser prior to 21 with a leak resistance from 21 to a source of positive potential, line 22 being connected to a fixed potential source.

The arrangement illustrated in Fig. 2 is a modification of the circuit of Fig. 1. In this figure the diodes 23 and 24 are replaced by triode valves the grid of valve 23 being connected to line 21 and the grid of valve 24 being taken to point 26. The anodes of the two triodes are taken to suitable sources of positive potentials. The end of the common impedance 27 is taken to a suitable negative potential. The impedance of 27 should preferably be larger than the reciprocal of the mutual conductance of the valves 23 and 24 and thus the cathode potentials of the valves 23 and 24 tend to follow the potentials applied to their grids. For this reason the valves 23 and 24 will be termed "cathode follower rectifiers". The action of this circuit is similar to the three diode arrangement of Fig. 1 except that no load need be thrown on line 21 or on point 26. The condenser 30 will not be charged exactly to the potential of line 21 as there will be a difference of potential representing the grid bias on valve 23 necessary to pass the current through impedance 27. An advantage of this arrangement is that the pulses applied at 26 need not be very large in amplitude and they need not be as large as the signals on line 21. For example, if point 26 is made positive in order to keep the device inoperative, and a large signal on line 21 drives the grid of valve 23 very positive, then 23 will conduct and the current flowing through valve 24 will be reduced. This will not affect the condenser 30 since the cathode of valve 25 will be made positive. If line 21 makes a large negative excursion, it will have no effect on the potential of the cathode of valve 23 or of valve 25. If, however, point 26 is made negative so that valve 24 insulates for any working potential of condenser 30, the current in impedance 27 will charge condenser 30 negatively through diode 25 until the cathode of valve 25 and therefore the cathode of valve 23 falls so low in potential that valve 23 passes all the current through impedance 27. Similar remarks apply to the arrangement of Fig. 1 except that large positive potentials on line 21 will make valve 23 conduct thus loading line 21. Of course, if 21 is fed from a low impedance source this is immaterial. If, however, it is required not to load line 21 when the switch is inoperative, a sufficiently positive potential must be applied to the cathode of valve 23 to prevent it from conducting for any positive potential excursion of line 21.

The arrangement of Fig. 2 may be adapted to be used for "observing devices" as required as Specification No. 458,584 and as switched conductors as in Specification No. 449,242. In the latter case, the diode 25 is connected to the condenser in the signal lead and the grids of valves 23 and 24 to a fixed potential and to the pulse source.

Fig. 3 shows two devices such as are shown in Fig 1 connected back to back to form a two-way (bi-directionally conductive) switch. When operative diodes 23, 25, 231 and 251 serve to join lines 21 and 22 for current flow in both directions. Negative and positive potentials are applied to impedances 27 and 271 respectively and to maintain the device inoperative (that is, to open-circuit the switch) positive and negative controlling potentials are applied to terminals 26 and 261 respectively. If terminals 26 and 261 are made respectively negative and positive of the potentials of line 21 and 22, the currents in impedances 27 and 271 are diverted into the diodes 23, 25 and 231 251 in such a direction as to draw the potentials of 21 and 22 together. If the rectifiers differ slightly in the potentials at which they begin conducting there may be a possible potential difference between 21 and 22 where, say 23 and 231 are conducting and 25 and 251 are insulting due to these differences in the rectifiers. This difficulty can be overcome by inserting small resistances directly in series with the rectifiers 23, 25, 231 and 251. Such resistances increase the resistance of the switch between 21 and 22 but prevent any such effect as that described. It will be appreciated that push-pull pulses are required at terminals 26 and 261 and such pulses may be obtained from such a push-pull amplifier as is described in Patent Specification No. 482,740.

According to the modification of the invention the two diode valves 24 and 241 of Fig. 3 can be omitted and the controlling pulses can be applied to the ends of the impedances 27 and 271 in push-pull ; alternatively, the pulses may be applied directly to the cathodes of the valves 23 and 25 and to the anodes of valves 231 and 251, also in reversed phase, from a high impedance push-pull source of pulses in parallel with the impedances 27 and 271, which in effect is equivalent to applying pulses in series with impedances 27 and 271 of slightly lower values.

The device of Fig. 3 may be used for charging a condenser, for example, at 22 to the potential of line 21 during the operative period, the device being capable of charging and discharging the condenser so that no leak resistance is required.

Similarly, the device of Fig. 3 may be used to hold or "clamp" the potential of 21 to a fixed potential applied at 22 for the purpose of carrying out the arrangement described in Patent Specification No. 449,242. In this case referring to Fig. 4 of the prior specification the line 21 (of this application) represents the lead joining condenser 18 to the grid of valve 19, line 22 (of this application) represents the connection to battery 42 and the pulses of 26 and 261 (of this application) are supplied from a pulse generator such as 25 (of the prior specification), except that in the present case push-pull pulses are required.

Dated this 25th day of April 1938

F. W. Cackett

Chartered Patent Agent

COMPLETE SPECIFICATION

Improvements in Electrical Circuits controlled by Pulses, suitable for use in Television

I, ALAN DOWER BLUMLEIN, a British subject, of 37, The Ridings, Ealing, London, W.5, and ERIC LAWRENCE CASLING WHITE, of 7, Vine Lane, Hillingdon, Middlesex, a British Subject, do hereby declare the nature of this invention and in what manner the same is to be performed, to be particularly described and ascertained in and by the following statement:

This invention relates to electrical circuits controlled by pulses.

In the British Patent Specification No. 497,637 there is disclosed a switch which may be employed for a variety of purposes. This arrangement comprises a pair of uni-directional conducting devices which under the operation of controlling impulses act as an uni-directional switch. One of the electrodes of one of said uni-directional devices is connected to a like electrode of the second uni-directional conducting device the common electrodes being connected to a conductive impedance. Switching pulses are applied to one or more of the electrodes of said arrangement so that the switch is rendered conductive or insulting.

The object of the present invention is to provide an improved circuit employing uni-directionally conducting devices which requires controlling pulses of smaller amplitude than those of the aforesaid arrangement and which operates in a quicker and improved fashion.

The circuit described in the aforesaid Specification is a circuit which permits of a voltage equalisation in only one direction and a further object of the present invention is to provide an improved circuit which permits of a bi-directional voltage equalisation.

According to one feature of the present invention an electrical circuit adapted to be controlled by pulses is provided comprising three uni-directional conducting devices having effectively three like electrodes connected together and to a conductive impedance, means being provided for applying controlling impulses to an electrode of one of said devices, said electrode not being directly connected to said impedance, the arrangement being such that when a controlling pulse is applied one or both of the other devices is or are switched from substantially a conducting condition to a non-conducting condition, or vice versa.

According to another feature of the invention an electrical circuit adapted to cause the potential of a first conductor to approach the potential of a second conductor under the control of pulses is provided, comprising tee uni-directionally conducting devices having effectively effectively three like electrodes connected together and to one end of a conductive impedance, the other end of which is connected to a source of potential, another electrode of each device being connected respectively to said first conductor, to said second conductor and to a source of controlling pulses, the arrangement being such that when a pulse is applied to the device connected to said source of pulses the potential of said common electrodes changes in such sense that one or both of the other devices is or are changed from a non-conducting to a conducting condition.

In one form of the invention the three cathodes of three diode valves may be connected together and the controlling pulses may be applied to an anode of one of the diodes, if desired, from a further valve. Alternatively, three diode valves with their anodes connected together may be used, the pulses being applied to the cathode of one of the diodes. In another form of the invention triode or other multi-electrode valves may be used with the cathodes connected together. This last arrangement has the advantage that as the controlling potentials are applied to the control electrode, or electrodes, of the valve or valves, the device places substantially no load on the controlling pulse circuit.

The invention may be applied in one form to provide a uni-directional voltage equalising device and another feature of the invention is the provision of a circuit which acts as a bi-directional voltage equalising device. A uni-directional voltage equalising device means, according to this Specification, a circuit which causes the potential of one conductor to be equalised to the potential of another conductor, the equalisation, however, only taking place by moving the potential of one of the conductors in one direction only. A bi-directional voltage equalising device means a circuit in which voltage equalisation can occur by moving the potential of one of the conductors in either direction. The term "equalisation" does not exclude cases in which after equalisation there is a difference of potential between the two conductors such as may arise as a result of the use of standing biasses on the elements of the circuits.

In the case of a bi-directional voltage equalising device two sets of three valves may be employed, the cathodes of one of said sets being connected together, whilst the anodes of the other set are similarly connected together, the two sets being connected as hereinafter described. Controlling pulses are applied to the cathode of one valve of one set and similar controlling pulses reversed in phase are applied to the anode of one valve of the other set.

In a modification of this bi-directional equalising arrangement instead of applying the controlling pulses through the two diodes, these diodes are omitted and the controlling pulses are applied through suitable impedances.

In order that the said invention may be clearly understood and readily carried into effect it will now be more fully described with reference to the drawings accompanying the Provisional Specification No. 12342/38 the three Figures of which illustrated particular embodiments according to the invention.

Fig. 1 shows an arrangement forming a uni-directional voltage equalising circuit using three thermionic diode rectifiers 23, 24 and 25 (which may be a triple-diode valve) the cathodes of which are joined to a resistance 27 connected to a source of negative potential (not shown). Any other form of rectifier may be used, but if high speeds of operation are required rectifiers of low capacity are desirable. The three diodes are adapted to connect the line 22 with that of line 21 over the diodes 23, 25 under the control of controlling pulses applied to terminal 32 and thus effectively at point 26. The anode of diode 23 is connected to the line 21 and the anode of valve 25 is connected to line 22. The terminal 32 is associated with the control grid of valve 28 to which it is coupled by a suitable condenser and grid leak. The cathode of valve 28 is taken to a suitable negative potential and the anode of the valve is connected to a positive source of potential via resistance 29. The resistance of 29 is preferably lower in value than the impedance 27, which latter may be inductive, its function being to take a constant current from the diode cathodes to a negative potential. If the potential of point 26 is made more positive than the potentials of 21 and 22 then all the current in impedance 27 flows through diode 24. Should point 26 now be made negative the current in the impedance 27 tends to make diodes 23 and 25 conduct, thus providing a conducting path between lines 21 and 22. If 21 and 22 are greatly different in potential the current in the impedance 27 will only flow through one or the other of diodes 23 or 25, but this current will tend to draw the lines 21 and 22 together in potential.

In a particular application it may be necessary to charge a condenser 30 (shown connected between line 22 and earth) to a potential which is representative of the potential of the line 21 during certain periods of time when the device is made operative. In this case the anode of diode 24 is normally maintained positive by means of the resistance 29. The current form impedance 27 then flows through diode 24 and the diodes 23 and 25 insulate, since the anode of diode 24 and consequently the cathode of 24 makes the cathodes of diodes 23 and 25 positive with respect to their anodes. The valve 28 is arranged to make the anode point 26 negative when a positive controlling pulse is applied to the grid of valve 28. When point 26 becomes negative the anode of diode 24 and therefore its cathode also become negative. The cathode potential of diode 24 falls negatively until diode 23 or 25 conducts and robs diode 24 of the current flowing in impedance 27. Suppose, for instance, that during the operative period the potential of 21 is less than the potential of 22. The diode 25 will conduct and charge condenser 30 negatively until the anode of diode 25 drops in potential to the same potential as the anode of diode 23. This latter diode will then conduct and if 21 is connected to a low impedance potential source (the potential of which may be varying), the charging of condenser 30 will cease and 21 and 22 will have been effectively joined. If the potential of 22 is negative of 21 however, and if 21 is connected to a low impedance source of potential so that the current through impedance 27 cannot bring the potential of line 21 to that of line 22, the two lines will not be joined. A leak resistance 31 from a source of positive potential is therefore connected to line 22 in order to make the potential of condenser 30 positive, so that each time the device is operative a negative charge is applied to condenser 30, so that the potential of line 22 follows that of line 21 during the operative period.

The diodes of Fig. 1 may, if desired be connected in a reverse sense so as to charge 30 positively instead of negatively. With all three diodes reversed, i.e., with the cathodes separate and the anodes connected together, the impedance 27 must be taken to a source of positive potential and resistance 31 to a source of negative potential. The valve 28 will then require a negative pulse to be applied to its grid in order to switch the device into the operative condition.

The arrangement of Fig. 1 may be used as an "observing" device the purpose of which is described in British Patent Specification No. 458,585, the potential on condenser 30 being the observed potential of line 21 during periods determined by the controlling pulse applied at terminal 32. The arrangement can also be used in place of the pentode valve 24 shown in Fig. 2 of Patent Specification 449,242, by inserting a condenser prior to 21 with a leak resistance from 21 to a source of positive potential, line 22 being connected to a fixed potential source.

The arrangement illustrated in Fig. 2 is a modification of the circuit of Fig. 1. In this figure the diodes 23 and 24 are replaced by triode valves the grid of valve 23 being connected to line 21 and the grid of valve 24 being taken to point 26. The anodes of the two triodes are taken to suitable sources of positive potentials. The end of the common impedance 27 is taken to a suitable negative potential. The impedance of 27 should preferably be larger than the reciprocal of the mutual conductance of the valves 23 and 24 and thus the cathode potentials of the valves 23 and 24 tend to follow the potentials applied to their grids. For this reason the valves 23 and 24 will be termed "cathode follower rectifiers". The action of this circuit is similar to the three diode arrangement of Fig. 1 except that no load need be thrown on line 21 or on point 26. The condenser 30 will not be charged exactly to the potential of line 21 as there will be a difference of potential representing the grid bias on valve 23 necessary to pass the current through impedance 27. An advantage of this arrangement is that the pulses applied at 26 need not be very large in amplitude and they need not be as large as the signals on line 21. For example, if point 26 is made positive in order to keep the device inoperative, and a large signal on line 21 drives the grid of valve 23 very positive, then 23 will conduct and the current flowing through valve 24 will be reduced. This will not affect the condenser 30 since the cathode of valve 25 will be made positive. If line 21 makes a large negative excursion, it will have no effect on the potential of the cathode of valve 23 or of valve 25. If, however, point 26 is made negative so that valve 24 insulates for any working potential of condenser 30, the current in impedance 27 will charge condenser 30 negatively through diode 25 until the cathode of valve 25 and therefore the cathode of valve 23 falls so low in potential that valve 23 passes all the current through impedance 27. Similar remarks apply to the arrangement of Fig. 1 except that large positive potentials on line 21 will make valve 23 conduct thus loading line 21. Of course, if 21 is fed from a low impedance source this is immaterial. If, however, it is required not to load line 21 when the switch is inoperative, a sufficiently positive potential must be applied to the cathode of valve 23 to prevent it from conducting for any positive potential excursion of line 21.

The arrangement of Fig. 2 may be adapted to be used for "observing devices" as required as Specification No. 458,584 and as switched conductors as in Specification No. 449,242. In the latter case, the diode 25 is connected to the condenser in the signal lead and the grids of valves 23 and 24 to a fixed potential and to the pulse source.

Fig. 3 shows two devices such as are shown in Fig 1 connected as shown to form a two-way or a bi-directional voltage equalising devide. When operative diodes 23, 25, 231 and 251 serve to join lines 21 and 22 for current flow in both directions. Negative and positive potentials are applied to impedances 27 and 271 respectively and to maintain the device inoperative (that is, to open-circuit the switch) positive and negative controlling potentials are applied to terminals 26 and 261 respectively. If terminals 26 and 261 are made respectively negative and positive of the potentials of line 21 and 22, the currents in impedances 27 and 271 are diverted into the diodes 23, 25 and 231 251 in such a direction as to draw the potentials of 21 and 22 together. If the rectifiers differ slightly in the potentials at which they begin conducting there may be a possible potential difference between 21 and 22 where, say 23 and 231 are conducting and 25 and 251 are insulting due to these differences in the rectifiers. This difficulty can be overcome by inserting small resistances directly in series with the rectifiers 23, 25, 231 and 251. Such resistances increase the resistance of the switch between 21 and 22 but prevent any such effect as that described. It will be appreciated that push-pull pulses are required at terminals 26 and 261 and such pulses may be obtained from such a push-pull amplifier as is described in Patent Specification No. 482,740 or by any other suitable form of push-pull pulse generator.

Similarly the arrangement of Figure 2 can be adapted to form a bi-directional voltage equalising device by connecting two such arrangements in a manner similar to that shown in Figure 3.

According to the modification of the invention the two diode valves 24 and 241 of Fig. 3 can be omitted and the controlling pulses can be applied to the ends of the impedances 27 and 271 in push-pull; alternatively, the pulses may be applied directly to the cathodes of the valves 23 and 25 and to the anodes of valves 231 and 251 also in reversed phase, from a high impedance push-pull source of pulses in parallel with the impedences 27 and 271, which in effect is equivalent to applying pulses in series with impedances 27 and 271 of slightly lower values.

The device in Fig. 3 may be used for charging a condenser, for example, at 22 to the potential of line 21 during the operative period, the device being capable of charging and discharging the condenser so that no leak resistance is required.

Similarly, the device of Figure 3 may be used to hold of "clamp" the potential of 21 to a fixed potential applied at 22 for the purpose of carrying out the arrangement described in Patent Specification No. 449,242. In this case referring to Figure 4 of the prior specification the line 21 (of this Application) represents the lead joining condenser 18 to the grid of valve 19, line 22 (of this Application) are supplied from a pulse generator such as 25 (of the prior Specification) except that in the present case push-pull pulses are required.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is:

  1. An electrical circuit adapted to be controlled by pulses, comprising three uni-directional conducting devices having effectively three like electrodes connected together and to a conductive impedance, means being provided for applying controlling impulses to an electrode of one of said devices, said electrode not being directly connected to said impedance, the arrangement being such that when a controlling pulse is applied one or both of the other devices is or are switched from substantially a conducting condition to a non-conducting condition or vice versa.
  2. An electrical circuit adapted to cause the potential of a first conductor to approach the potential of a second conductor under the control of pulses, comprising three uni-directional conducting devices having effectively three like electrodes connected together and to one end of a conductive impedance, the other end of which is connected to a source of potential, another electrode of each device being connected respectively to said first conductor, to said second conductor and to a source of controlling pulses, the arrangement being such that when a pulse is applied to the device connected to said source of pulses the potential of said common electrodes changes in such sense that one or both of the other devices is or are changed from a non-conducting to a conducting condition.
  3. An electrical circuit according to claim 1 or 2, wherein the three uni-directional conducting devices are of the thermionic type and constituted by a triple diode valve or separate diode valves.
  4. An electrical circuit according to claim 3, wherein effectively two of said valves are connected across a pair of conductors and one of said valves has at least an anode cathode and control electrode said valve being arranged to function as a cathode follower rectifier and one of said conductors is connected to the control electrode of said valve.
  5. An electrical circuit according to claim 3 or 4, wherein the valve to which the controlling pulses are applied comprises at least cathode, anode and control electrode and is arranged to function as a cathode follower rectifier and the controlling pulses are applied to the control electrode of said valve.
  6. An electrical circuit according to any of the preceding claims, wherein the arrangement in such that said impedance tends to maintain the current flow to said like electrodes substantially constant.
  7. An electrical circuit according to any of the preceding claims 2 to 6, wherein a leakage path of providing associated with one of said conductors and arranged so that in operation the potential of the conductor associated with the leakage path changes in relation to the potential of the other conductor so as to ensure that the potential of the first conductor shall be caused to approach the potential of the second conductor despite drifts in potential of the second conductor in either sense.
  8. An electrical circuit wherein two of the electrical switching circuits according to any of the preceding claims are provided and are so connected that the arrangement serves to permit a bi-directional voltage equalisation between two conductors across which said circuits are connected.
  9. An electrical circuit wherein two of the electrical circuits according to any of the preceding claims 1 to 7 are provided, the three like electrodes which are connected to the impedance of one of said circuits being unlike the three like electrodes which are connected to the impedance of the other of said circuits, said circuits being connected between first and second conductors and serving a permit a bi-directional voltage equalisation between said conductors, the first conductor being connected to an electrode in the first circuit and to an unlike electrode in the second circuit. Whilst the second conductor is connected to another electrode in the first circuit and to an unlike electrode in the second circuit and means of provided for applying controlling pulses in push-pull to electrodes of the devices not directly connected to said conductors.
  10. A modification of the electrical circuit according to claim 8 or 9, wherein the devices previously referred to, and to which said controlling pulses are applied, are omitted, and the controlling pulses are arranged to be applied to the common electrodes of the remaining pairs of uni-directionally conducting devices which are connected to said impedances the latter being such that when the controlling pulses are applied, the momentary change in potential across said impedances produced by said pulses is such as to permit a bi-directional voltage equalisation between said conductors.
  11. An electrical circuit substantially as described with reference to Figure 1, 2 or 3 of the drawings accompanying the Provisional Specification No. 12342/38.

Dated this 13th day of December 1938

F. W. Cackett

Chartered Patent Agent