Patent GB-919213-A (GB)
Title: Improvements in or relating to a switching arrangement
IPC: H03K3/027
Filed: 1959-07-31
Abstract: 919,213. Gating circuits. SIEMENS & HALSKE A.G. July 31, 1959 [July 31, 1958], No. 26350/59. Class 40 (6). In an exclusive-OR circuit having more than two voltage inputs each of which may assume a working potential -Ua or a rest potential +Ur, means are provided which ensure that the working potential is applied to one input of a switching element (e.g. a transistor) and the rest potential is applied to a second input of the switching element to cause it to deliver a predetermined output only when one and only one of the voltage inputs assumes the working potential, the application of working potential to any one input suppressing the appearance of the rest potential at all except one of the other inputs so that if working potential is applied to two inputs, rest potential is suppressed at all other inputs and hence cannot be applied to said second input of the switching element. Thus in the circuit of Fig. 5 if one of the voltage sources Q1-Q4 assumes the working potential -Ua, the base of the transistor is held at a voltage which is negative to that at the emitter and the transistor conducts. However, the assumption of working potential by any one source (e.g. Q1 or Q2) inhibits the appearance of rest potential at two others of the sources (in this case Q3 and Q4) so that if any other source also takes up working potential no source will be left at rest potential and the emitter of the transistor will no longer be biased positively to render it conducting. When Q1 or Q2 are at potential -Ua a negative potential is applied through diodes 1G3, 1G4 to switch off diodes Gh3, Gh4 so that a potential +Ur cannot be established at sources Q3, Q4. Similarly if either of sources Q3, Q4 is at potential -Ua, positive potential +Ur can no longer appear at sources Q1, Q2. Thus the transistor is switched only when one and only one source assumes the working potential. In a second embodiment, Fig. 7, the establishment of working potential -Ua at any one of sources Q1-Q5 causes a corresponding one of diodes 2G32, 2G42, 2G52, 2G62 and 2G73 to conduct and bias the base of the transistor negatively. Similarly, rest potential is applied from another of the sources Q2-Q5 through 3G23, 3G32, 3G42 and 3G52, or failing that from an auxiliary source Q<SP>1</SP>6. However, the existence of working potential at any one source inhibits the production of rest potential at all succeeding sources except the immediately adjacent one. Thus if Q1 is at -Ua it operates through diode 3G32 and thereafter through diodes 1G42, 1G52 and 1G62 to render sources Q3, Q4, Q5 and Q<SP>1</SP>6 non-effective. Similarly such a source operates on all preceding sources to prevent the production of rest potential thereat. Thus, if Q5 is at - Ua, it operates through diodes 2G41, 1G31, 1G21 and 1G11 to prevent sources Q1-Q4 from being effective. Hence the only source capable of supplying rest potential to energize the emitter of the transistor is that immediately following the source at working potential; if more than one source is at working potential no source of rest potential can exist. Two-input circuit, Fig. 2. Potential sources Q1, Q2 normally assume the rest potential Ur, but on the closing of a switch ql, q2 they assume the working potential -Ua. When one, and only one, of the switches q<SP>1</SP>, q2 is closed, the positive potential +Ur is applied through one of diodes Gr to the emitter of the transistor while the negative potential -Ua causes one of diodes Ga to conduct so that the voltage established at the junction of voltage-dividing resistors Wv, Wa is more negative than +Ur and the transistor conducts. When, however, the potentials at Q1 and Q2 are the same, none of the diodes conducts and the voltage +Uv being more positive than +Ur the transistor remains switched off. Specification 832,588 is referred to.