US2266509A - Electric signal pulse controlling circuits - Google Patents

Description

Patented Dec. 16, 1941 E ELECTRIC SIGN t; PULSE. eoN'raor-ilme CIRCUITS of Great Britain Application March 8, 1938; Serial No. I4542 In- Gl' a/t Blitain March 1851937 3 Claims.

This invention relates to electric signal-pulse controlling -circuits=- and is of general application in circuits which inputsig nal pulses control output potentials to provide,- for example, synehr'onising pulses in television systems, automatic gain con-trolling potentials, a beat frequency-resulting'dromtwo difierent input frequencies-or signals a multiplex signalling-sys tem.-

According to thepresen-t invention an electric signalpulse controllingor mixing circuit a unidirectional conducting device or devices providetwo currentpaths having a common pole connected-tonne end of animpedance whichmay be'the loadimpedance-and the application of suitable control pulses between the other end of said impedance and the other pole of one of said unidirectional conducting devices will allow or prevent-the passage of signals through the second unidirectional conducting device. The current paths may be constituted by the anode/cathode paths in a thermionic valve or valves which may be of the diode type. The effect of .the control pulses applied between the common pole and the other pole of one of the unidirectional conducting devices may be determined by biassing potentials applied to said common pole or said other pole or to both said poles.

In order that the invention may be more clearly understood and readily carried into efiect two pulse controlling circuits embodying the invention will now be more fully described by way of example with reference to the accompanying drawing in which:

Figures 1 and 2 show such alternative forms of circuit, and

Figure 3 represents a television picture signal and synchronising pulse waveform which may be applied to the circuit of Figure 1, for example.

Referring to Figure 1 of the drawing, a double diode valve l is provided with one pair of input terminals 2, 3 between an anode 4 and biassing battery 5 and another pair of input terminals 5, 1 between a resistance 8 in the lead to the cathode 9 and earthed line Ill. The biassing battery 5 is also connected to the line [0. Output terminals ll, l2 are connected to the anode I3 and earthed line l0 respectively, and a condenser I4 and resistance l5, both shown in dotted lines, are used in certain applications of the circuit.

Assuming the circuit of Figure 1 is to be used for selecting a signal for a specified period, this signal is applied to the input terminals 6, 1.

The battery" 5 applies" to= the anodel, a positive bias potential which is less a;negativepulse appliedto the terminals 2, 3- while the signallis appliedto terminals- 6; 1; Until the negative pulse isappliedto the anode-' 4, the positive potential applied to this anode causes cuirent to flow throughthe diode, the cathode ll-becoming positive with respectto the anode 13. Thus no current can now tothear-iode l3 and there is no output fro-m the'circuit. When the: negative pulse is applied the anode' 4' this anode ceases to take currentand the cathode potential falls to such a: value that theanode l-3 't'alse's current and allows the signalapplied to the'terminals 6,: 1 to :passto the output terminals l-l l2;

If desired; during'th'e absence ofthe negative pulse applied toterminals 2 and 3,v these terminals may be used as output terminals-for the signalapplied to the terminals 6-,, 1-. Again',. 1the biassing potential applied by battery 5 to the anode 4 may be in the negative sense, the pulse applied to the terminals land 3 being positive and of greater magnitude than the negative voltage applied by battery 5. The pulse is, of course, applied during instants at which no output from the terminals 2 and 3 is required.

In an alternative application of the circuit, pulses of opposite sign may be applied to the anodes 4 and I3 respectively, and the output taken from anode 4 or l3. In such a case the insertion of the resistance 8 in the cathode lead is not essential.

In the arrangement shown in Figure 2, the resistance is omitted from the cathode lead and a resistance I6 is inserted in the lead to the anode l3. The signal input is applied to terminals l1, 18 connected to the anode l3 and line Ill respectively and output terminals l9 and 20 are connected in the cathode lead of the diode.

It is assumed that the signals to be controlled or modified are applied between the terminals l1 and I8, the insertion of vthe resistance l6 between the anode l3 and terminal I! not being essential. The controlling signals or pulses are applied between the terminals 2 and 3 and the output is taken from the cathode between the terminals 19 and 20. It is further assumed that any apparatus connected between the terminals I9 and 20 will constitute a load impedance and that it is not necessary therefore to include in the cathode lead a resistance corresponding with the resistance 8 in Figure 1.

The anode 4 is normally biased positively so that current will flow from the cathode 9 to the anode 4. When the controlling or switching pulse of negative potential is applied to the anode 4, this anode ceases to take current and the potential of the cathode falls to such an extent that a current flows to the anode I3 and. the signals applied to the terminals l1, l8 provide an output at terminals 19, 20. g g

The vision signal waveform shown in Figure 3 may be used in conjunction with the circuit of Figure 1 to provide automatic gain controlling voltages, the circuit including the condenser l4 and resistance l5 having values of 1 microfarad and 1 megohm respectively. Thus, in order to obtain automatic gain control itis required to produce a steady voltage equal to the voltage V (Fig. 3). The signal waveform with the synchronising pulses in the positive sense is applied to the terminals 6, I and a negative pulse which may be derived from the return stroke of the frame 'frequency blocking oscillator is applied to the terminals 2, 3. During the instants that the negative pulse is applied there will be an output from the anode l3 which will be smoothed by the condenser l4 and resistance I5 and will provide a gain controlling potential which will vary in accordance with the mean amplitude of the voltage V. V

The circuit of Figure 2 may be applied to a multiplex signalling system of the kind described in the specification of United States Patent 2,172,354 dated September, 12, 1939. Thus, U

insteadof the hexode signal, distributing valves shown in. certain circuit arrangements described in that specification, double diode valves operated in accordance with the presentrinvention may be employed. In a receiver the anodes 4 of a the case of a transmitter, the outputs are connected along a delay network and pulses applied simultaneously to all the anodes 4.

While a double diode valve has been described as providing the two unidirectionally conducting devices, it will be understood that equivalent devices may be employed. Thus two separate diodes or other valves may be employed or contact rectifier devices may be used instead of thermionic valves. We claim: 1. An electrical signal developing means comprising a thermionic tube having a cathode source of electrons and at least a first and a second electron collecting member contained within the envelope of said tube, means for biasing the first of said electron collecting members to a predeterminable bias Value relatively to the cathode, a common terminal member for said electron collecting members, an input circuit connected between said cathode and said common terminal member, impedance means connected serially with said cathode and said com- .mon terminal member, and an output circuit connected between said common terminal and said second electron collecting member.

2. Apparatus in accordance with claim 1, wherein there is provided in addition additional input terminal means connected between the first electron collecting member and the common terminal of the electron collecting members.

3. Apparatus in accordance with claim 1,

wherein there is provided in addition a time con- WILLIAM SPENCER PERcIvAL. ERIC LAWRENCE ,CASLING WHITE.

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