Patent GB-1264491-A (GB)
IPC: G06G7/163
Filed: 1969-01-23
Abstract: 1,264,491. Cathode-ray tube displays; transistor switching and multi-stable circuits. TEKTRONIC Inc. 23 Jan., 1969 [26 Jan., 1968], No. 3958/69. Headings H3T and H4T. [Also in Divisions G4, H1 and H2] A resistive device for conversion between electrical and positional information comprises a medium providing a resistive surface with input and output connection means at predetermined locations on the surface so that, for example, the location of an input connection determines the proportion of output current or voltage reaching each of a plurality of output connections, or the proportion of input voltage or current applied to each of a plurality of input connections selects the location of an output connection. As shown, planar resistive medium 10 has four edge output electrodes 12, 14, 16, 18 and input voltages are applied at spaced points P 1 , P 2  defining a character on the resistive area by connection means 38, 40 so that a division of current takes place between electrodes 12, 14, 16, 18 according to the position of points P 1 , P 2 . Electrodes 12, 14 are connected to vertical deflection plates 24, 26 of a cathode-ray tube and electrodes 16, 18 to horizontal deflection plates 34, 36. By gradually decreasing the voltage at P 1  and increasing that at P 2  a continuous line 46 is displayed on the tube. The device can accordingly act as an alpha-numeric character generator by using a sufficient number of input points (e.g. Fig. 7, not shown), the gradual change in inputs being achieved by an apparatus producing triangular wave outputs, or a device according to the invention having a current steering application may be coupled to a second device functioning as a character generator (Figs. 37 to 39, not shown). The resistive medium may be resistive paper but preferably is semi-conductive, forming part of a more complex arrangement, e.g. transistors may be included for input and output coupling to the resistive medium. In the simplest semi-conductive device (Fig. 2, not shown) the medium is a N-type epitaxial layer on a P-type substrate and the connections are N-type emitters. Individual P-type base diffusions may be provided between emitters and the epitaxial semiconductive layer (Fig. 3, not shown) or a single common one (Fig. 4, not shown). The semiconductive layer may constitute the collector of a transistor (Fig. 7, not shown). Manufacturing steps for a semi-conductor device are described briefly (Figs. 10 to 14, not shown). Fig. 19 illustrates a current steering application of the device which can function as an analogue to one out of five switch. Complementary input voltages xV and (1-x)V are applied to the base electrodes of transistors 146, 148 and by varying x the voltage distribution on the surface 124<SP>1</SP> changes to select one of outputs 132<SP>1</SP> which will permit current supplied to one of the common emitter electrodes of transistors 134<SP>1</SP> to 138<SP>1</SP> to be delivered to the corresponding one of the collector electrodes. To improve selectivity or increase the number of outputs, additional transistors in a cascade arrangement providing wave-shaping may be employed (Fig. 20, not shown) or reverse connected diodes (170), (172) may be connected between each pair of output terminals and between the end output terminals and the input terminals (Fig. 21, not shown). In Fig. 22 the resistive medium is constituted by P-type semi-conductive layer 176 overlying N-type layer 174. The output transistors are integral with the device and comprise N-type emitters 178, layers 176 and 174. Additional transistors are provided by P-type diffusions 190, layer 174 and P-type elements 188 (cf. arrangement of Fig. 20, not shown). Complementary currents supplied to inputs 180, 182 select which emitter 178 will conduct current I 2 . This current passes through layer 174 to contact 186 setting up a voltage differential in the layer, and causes conduction of current I 3  through one PNP transistor 188, 174, 190. PNP transistors 190, 174, 176 permit feedback to layer 176 giving complete and rapid switching. Each collector 190 may be divided into separate elements (Fig. 23, not shown) each of which is connected to an NPN transistor, the collector of which is connected to a collector line to produce selected outputs on these lines (Fig. 24, not shown). The lines may be energized in accordance with a binary code designating the location selected by the resistive medium. In a modification of the Fig. 22 arrangement, functioning as a memory device (Fig. 35, not shown), the P-type diffusions 190 are replaced by an underlying P-type layer (246). The input value x can be stored by raising current I 3  to the regeneration level to intensify feedback and the selected emitter can now continue to inject current in the absence of control from the inputs 180, 182. Emitters 178 can be located on peninsulas of layer 176 (Fig. 36, not shown), to aid ensuring that the voltage generated by the feedback current is greater than any voltage change at the inputs, e.g. when the input value x is allowed to swing through a scanning waveform. In the embodiment illustrated in Fig. 25 a planar epitaxial N-type collector layer 198 has end contacts 200 and a superposed base layer 202 is the resistive medium. Complementary input currents x1 and (1 - x)1 determine the location of a maximum voltage underneath continuous emitter 204 and current supplied to 204 will enter at this location and divide between contacts 200. The device can function as a potentiometer or as an analogue multiplier since the product of x and the current applied to 204 is shown to be proportional to the differential output currents at 200. In a modification (Figs. 27, 28, not shown) the arrangement of Fig. 25 is doubled and complementary currents applied to two continuous emitters corresponding to 204 provide a value y which can be multiplied by x. In another modification of the Fig. 25 arrangement (Fig. 32, not shown), emitter 204 lies along the straight side and linear variation of input x provides an inversed cosine function between contacts 200. Alternatively (Fig. 33, not shown), the distance between the selected position of maximum voltage on the emitter and a shaped collector contact varies with the shape of the contact, again providing a function generator. A shaped buried semi-conductive layer produces the same effect. Fig. 34 illustrates a device for generating a sine wave. A saw-tooth wave is applied to the base of transistor 240 and the current provided the emitters of transistors 240 and 242 is low enough to ensure only partial switching of output transistors 238 driven by output connections 236. The phase of the sine wave generated at the output may be adjusted by potentiometer 244.