Patent GB-934418-A (GB)
Title: Improvements in or relating to circuit arrangements comprising a controlling cross-bar system
IPC: H04N3/14
Filed: 1960-09-30
Abstract: 934,418. Semi-conductor devices. PHILIPS ELECTRICAL INDUSTRIES Ltd. Sept. 30, 1960 [Oct. 2, 1959], No. 33634/60. Class 37. [Also in Groups XXXIX, XL (a), XL (b) and XL (c)] General.-Relates to a circuit arrangement, Fig. 3, comprising a controlling cross-bar system consisting of at least two groups X and Y of crossing conductors, a writing circuit associated with each crossing of the conductors, which circuit includes a ferro-electric or other storage element 11 in which information fed to the cross-bar system in the form of electric signals is stored periodically for the crossing concerned so that the impedance of the storage element is changed and a reading circuit associated with each crossing which circuit includes an electro-luminescent reproducing element 12 connected to the storage element but included in a separate circuit adapted to provide continuous activation from an A.C. source 13. In accordance with the invention, the circuit is characterized in that at each crossing a unilaterally conducting element 16 is connected between a conductor of the X-group and the storage element, whilst in order to block the element 16 a D.C. voltage source 6 is connected to each via an individual resistance element 17, means 9 being provided for switching sequentially the conductors of the Y-group so that the blocking voltage for the elements associated with the switched conductor is removed for the writing period of the storage elements. The invention is described more particularly as applied to a television receiver display panel although other applications are envisaged. The received video signals Vd for each picture line are distributed to the X-group conductors by a device 4 and are released simultaneously to control the conductor potentials by a pulse Vp from a source 5. At the same instant, switch means 9 earths the Y conductor for the appropriate picture line for 10Á secs. to unblock elements 16 and allow the video potentials to influence the ferro-electric or other elements 11 and change their capacitance values correspondingly. Thereafter the electroluminescent elements are energized from source 13 at a level determined by the potential distribution in the capacitive network formed of elements 11 and 12 and a further capacitive element 20 whose value is approximately one-tenth of C 11  and C 12 . Synchronizing pulses separated from the received signal in stage 7 establish the correct time relation between switch means 9 and pulse source 10. The pulses also establish the correct frequency and phase relationship in A.C. source 13 in order to prevent undesired unblocking of elements 16 as described in Specification 934,419. In a second embodiment, Fig. 1 (not shown), the unilateral conducting elements are blocked by a potential derived from a tapping on D.C. source 6 and applied to each element via an individual resistance element. Unblocking is effected by arranging switch means 9 to connect the positive of the source to the Y conductors. The circuit at each crossing of the bar system requires an additional resistance or unilaterally conducting element. In connection with this embodiment there are described modifications to permit operation with video signals of either polarity. Reference is also made to an arrangement in which the video signals are distributed to the X conductors sequentially. The Specification discusses the choice of biasing conditions to obtain optimum capacitance change in the ferroelectric storage elements, and in connection with Fig. 3 reference is made to the use of the non-linearity of capacitance-voltage characteristic of the ferro-electric elements to limit the amount of gamma convection necessary in the video signal. A modification for colour television is described in which the X conductors are in groups of three, one conductor for controlling rod luminescent elements, one for green and one for blue. Constructional details.-A panel having a circuit as described in connection with Fig. 3, is constructed as shown in Fig. 5. On a transparent glass support 23 are first provided. transparent conductors Y, the conductors being formed by laying down an Al 2 O 3  mass to function as a binder, and then spraying on SnO 2  for the actual conductor material and finally heating the assembly to 550 C. to burn away the binder. The storage elements 11, reproducing elements 12 and resistive elements 17 are applied on the Y conductors in strips. The ferro-electric elements 11 comprise a mixture of Ba Ti O 3  and Sr Ti O 3  which is applied as a paste on a layer of carbon embedded in enamel and then hardened by heating and polished to flatness. The electro-luminescent elements 12 consist of ZnS activated with 10<SP>-3</SP> Cu atoms and 9Î10<SP>-4</SP> Al atoms per molecule of ZnS, the strips being applied by printing using a mixture of 40% of ZnS and 60% of enamel with an organic binder which is subsequently removed by heating. The resistive strips 17 are formed of a mixture of carbon and enamel. Connecting strips 24 for joining elements 11, 12 and 17 in parallel are formed in the same manner as strips 17 but using a mixture with more carbon. Alternatively, the strips may be made of Al or Ag paste. Between strips 24 and extending completely across the screen surface are provided insulating ribs 25 formed of enamel with a filler of quartz powder. The X conductors, which may be Al or Ag, are deposited on top of the ribs, and material to form the unilaterally conducting elements 16 is deposited on one face. The material comprises CdS with an electret added to establish suitable rectifying characteristics and 2x10<SP>-4</SP> Cu and 2x10<SP>-4</SP> Ga atoms per molecule of CdS added to give the material photo-conductive properties. To function properly the elements require continuous exposure to radiation. The assembly is completed by a filler 26 of polystyrene and conductors of Al or Ag disposed above strips 24 to form capacitors 22. Filler 26 is transparent to permit exposure of elements 16 which is effected by a separate continuously energized electroluminescent plate arranged over the whole panel and formed of ZnSe activated with 10<SP>-3</SP> Cu atoms and 10<SP>-3</SP> Al atoms per molecule of ZnSe. The radiation is not visible. If ribs 25 and strips 24 are made opaque, visible radiation may be used since it will not reach the viewing side of the panel. Elements 12 may be formed of a material with luminescences in response to the radiation from the ZnSe panel and whose luminescence is controllable extinguished in response to applied voltage. As an alternative to ferro-electric material, storage elements 11 may be formed of germanium or silicon and utilize the variable capacitance effect at a diode junction. The construction of a panel using the second embodiment referred to above is briefly described. Specification 829,255 also is referred to.