Patent GB-907119-A (GB)
Title: Improvements in or relating to bi-stable electric circuit arrangements and apparatusfor intelligence storage embodying such arrangements
Inventor: HYMAN ROBERT ANTHONY
IPC: H03K17/58
Filed: 1961-03-17
Abstract: 907,119. Sensing record cards; digital data storage. STANDARD TELEPHONES & CABLES Ltd. March 17, 1961, No. 9847/61. Class 106 (1). [Also in Groups XXXVI and XL (c)] A bi-stable electric circuit device comprises as a unitary structure a photo-voltaic element connected in a closed current path with a negativeresistance element and serving as a source of power therefor so that, by suitably energizing the photo-voltaic element with incident light, the negative-resistance element can be so biased that it can be made to adopt either of two stable states. The device comprises a semi-conductor block a portion of which functions as a photoelectric generator and a further portion of which functions as a tunnel diode. A plurality of such bi-stable devices may be combined to provide an intelligence store as shown in Figs. 1 and 2. The store comprises a plurality of rectangular section bars 13 of N-type silicon arranged one above the other and separated by insulating strips 14. Each bar 13 has a thin P-type layer formed by diffusion on its front surface, so that an E.M.F. may be generated within the bar by shining light on to its front surface. A central portion 18 of each bar is converted to be of degenerate N-type, this portion 18 extending in depth through the whole thickness of the bar. Pellets 19 of aluminium are alloyed at intervals along the length of each bar to the degenerate central portion each forming therewith a tunnel diode. Each tunnel diode is effectively in a closed circuit with a photo-voltaic cell provided by the corresponding bar 13 and its P-type surface layer; these circuits are interconnected by means of row conductors 12, there being one conductor 12 to each bar 13 passing along the length of the region 18 and soldered to it, and column conductors 11 which interconnect corresponding positioned aluminium pellets in different bars. By illuminating the bars 13 with light of a suitable spectral composition and intensity each of the tunnel diodes can be biased to a point on the low-voltage portion of its characteristic. By then applying a current pulse in the correct polarity between a pair of conductors 11 and 12 the tunnel diode situated at the intersection of these conductors can be switched to a stable point on the high-voltage portion of its characteristic. A subsequent current pulse in the opposite direction, or an interruption in the illumination restores the original low-voltage condition. The circuit for the store, Fig. 4 (not shown), comprises two access selectors, one common to the column conductors 11 and the other common to the row conductors 12. One access selector scans each of the conductors 11 in turn and the other steps to a new conductor 12 after all the conductors 11 have been scanned. Read-in is effected by applying pulses of one polarity to the conductors and read-out by applying pulses of opposite polarity. In a modified arrangement for reading information from punched cards, Fig. 5, the surface of the bars 13 is removed between the aluminium pellets, as shown at 50, to a level beneath the P-type layer. Thus each device comprises a photovoltaic cell individual to its tunnel diode, instead of a cell common to the whole bar 13, so that different ones of the device along any bar may either be energized or not according to whether there is a corresponding hole in the card 53 placed in front of the assembly.