US2805363A - Electric counting circuits - Google Patents

Description

p 1957 G. T. BAKER ETAL 2,805,363

ELECTRIC COUNTING CIRCUITS Filed Aug. 9, 1955 FIGJ.

+5ov +50v +50v W HI HI Hl HI- +50V W2 W3 -y 4 FIG.3.

United States Patent 2,805,363 Patented Sept. 3, 1957 ice George Thomas Baker, deceased, Taplow, and Wincenty Bezdel, London, England, assignors to British Telecommunications Research Limited, Taplow, England, a British company Application August 9, 1955, Serial No. 527,386

Claims priority, application Great Britain August 11, 1954 4 Claims. (Cl. 315-345) The present invention relates to electrical counting circuits and is more particularly concerned with binary counting circuits employing gas-filled discharge tubes of the cold-cathode type as counting elements. Such circuits are known in which a stage in a binary counter comprises two gas discharge tubes arranged in a bi-stable trigger circuit. In such a circuit, an input pulse extinguishes the conducting tube of the pair and strikes the non-conducting tube. If the output is taken in the form of unidirectional pulses from one tube of the pair, the output will have half the frequency of the input.

It is the object of the invention to provide an improved binary ccunting circuit of the general type mentioned above, which employs a smaller number of components than existing circuits. According to the invention, a single-stage binary counting circuit comprises a gas-filled discharge tube of the cold-cathode type adapted to be connected in circuit with resistors and capacitors of such value that it is rendered alternately conducting and non-conducting by the application of successive similar voltage impulses to one electrode.

The invention will be better understood from the following description of a preferred form which should be taken in conjunction with the accompanying drawings, comprising Figs. 1-3. Of these,

Fig. 1 shows a single-stage binary counting element in accordance with the invention;

Fig. 2 shows the waveform of the output of the counting element, and

Fig. 3 shows a multi-stage binary counting circuit employing a plurality of the elements shown in Fig. 1.

Referring to Fig. 1, VK is a gas-filled discharge tube of the cold-cathode type, arranged as a binary counting element or frequency halver. The anode resistor R1, the anode capacitor C2 and the cathode resistor R2 are chosen so that (a) they do not form a self-quenching circuit, (b) the value of resistor R1 is very much greater than that of resistor R2, and (c) the combination of resistor R2 and capacitor C2 provides an output pulse of suitable shape. The component values necessary to satisfy these conditions will vary somewhat for difierent tubes but satisfactory results have been obtained with R1=68(),0O0 ohms, R2=l5,000 ohms and C2=.01 mfd. The H. T. supply is arranged to have a value between the breakdown and maintaining voltages for the tube and 200 volts was found suitable with the figures pust mentioned.

The tube is controlled via leads and 11. By way of lead it) and resistor R3 a biasing potential is applied to the trigger electrode of the tube. The biasing potential may remain steady or be a controlling waveform, such as a train of rectangular pulses, in which the maximum value of the potential is just too low to ignite the trigger gap. By way of lead 11 and capacitor C1 steepfronted driving pulses are also applied to the trigger electrode. The sum of the pulse potential and the maximum value of the bias potential is high enough to ignite the trigger gap.

The operation is as follows. Assume the tube to be in the non-conducting state and lead 10 to be appropriately biased. A suitable positive pulse applied at lead 11 will cause the trigger gap to conduct, and ionisation of the tube will take place. Capacitor C2, which is already charged to the value of the H. T. supply, will now discharge through the tube.

Reference should now be made to Fig. 2 which shows the output waveform appearing at lead 12. At point a the cathode of the tube is at earth potential when the tube is non-conducting. Point b shows the rapid increase of cathode voltage as capacitor C2 commences to discharge through the tube and cathode resistor R2. The discharge current diminishes until it is substantially zero and hence the current through the tube is that through resistor R1 only. Because the value of resistor R1 is so much greater than that of resistor R2, the output voltage at this stage is very small indeed and is indicated by c in Fig. 2.

A second pulse of the same polarity and shape as the first may now be applied to lead 11. The effect of raising the potential of the trigger electrode in a tube in which the current is very small is to transfer enough ionisation from the main gap to the minor gap so that when the input pulse has passed the tube is left in a feebly ionised state not sufiicient to maintain the main gap discharge with the voltage retained on capacitor C2 and is thus extinguished. Because the H. T. supply is lower than the breakdown voltage of the main gap, the tube will remain extinguished. Accordingly on receipt of a second input pulse, the cathode potential will return to that of earth, as indicated at point a, and remain in that condition during the period e until a further pulse is applied to the tube.

During the period c between the first and second input pulses, the anode of the tube is maintained at a potential just greater than the voltage drop in the tube. During period e, the anode assumes the potential of the H. T. supply, as capacitor C2 is able to charge through resistor R1. A third input pulse will now find the circuit in the same condition as did the first pulse, and the same sequence will be repeated for subsequent pulses.

it will be seen that the output pulse frequency is half the input pulse frequency, and the output comprises steep-fronted pulses, b, 7 and so on, as shown in Fig. 2.

In the four-stage binary counting circuit shown in Fig. 3, each stage comprises a binary element of the type shown in Fig. 1. The last three stages each have their input circuit connected to the output circuit of the previous stage, and each tube is continuously primed by connection of a suitable positive voltage shown as 50 volts, to its trigger electrode. The input pulses are applied to tube VKl via lead 13, and pulses are passed from stage to stage at a diminishing frequency, each stage introducing a division by two. In a normal fourstage binary counter, the total count is sixteen, i. e. after sixteen input pulses the pattern of conducting tubes reverts to that existing initially.

A count of sixteen is seldom required in practice, and a more frequent requirement is a count of ten or twelve. These are readily obtained by introducing a simple feedback circuit. The counter shown in Fig. 3 is arranged to provide one way of counting ten. From the anode of tube VK4, feedback paths extend to the cathodes of tubes VK2 and VK3 via capacitors C3 and C4 respectively. Negative pulses will therefore be applied to the cathodes of tubes VK2 and VK3 when tube VK4 is struck. These negative pulses are only slightly delayed with respect to the positive cathode pulses occurring at the cathodes of tubes VKZ and VK3 and cause extra current "through the tubes resulting in the lowering of their anode potentials below the extinction potential. Thus when tube VK4 ignites tubes VK2 and VK3' are extinguished. The pattern of conducting. tubes, there.- fore, 'will'n'otp'roceed in a regular manner, and the-count will, in fact, be reduced to ten conditions.

'The pattern of fired tubes 'in each of the ten stages is asjfollow's, 0 indicating a non-conducting tube and l a conducting tube:

VKl VK2 V K3 VK4 1 -0 O 0 0 0 l 1 1 1 0 0 -1 1 O 1 0 1 0 0 0 1 0 1 1 0 O (l 1 0 O 1 0 0 0 O O 0 0 1 1 1 1 which immediately changes to We claim:

I. A 'single stage binary counting circuit comprising a single cold cathode gas discharge tube in association with a capacitor and at least two resistors, the values of said capacitor and resistors being so chosen that a suitable pulse applied to the trigger electrode causes the tube to strike and continue to pass current after the pulse ceases but of a much smaller value and on the subsequent application of a similar pulse to the trigger electrode the tube isextinguished when the pulse ceases.

2. A single-stage binary counting circuit employing a cold cathode gas discharge tube in which the trigger electrode of the tube is connected to a biassing or priming potential over a resistor and is supplied with input pulses by way of a capacitor, the main discharge path including resistors connected respectively to the anode and cathode, the anode resistor being large compared with the cathode resistor and a capacitor being connected between the anode and the negative pole of the source and the output being taken from the cathode, the values of the different components being so chosen that the tube is rendered alternately conducting and non-conducting by the application of successive similar input pulses to the trigger electrode.

'3. A counting circuit as claimed in claim 2 in which the biassing potential is supplied in the form of pulses.

4. A decimal counting circuit employing four singlesta-ge circuits as claimed in claim 2 in which the required operation is secured by providing feedback from the final stage to the second and third stages.

References 'Citedin the file of this patent UNITED STATES PATENTS

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