Patent GB-1203647-A (GB)
Title: Improvements in or relating to electrical display devices
IPC: H04N3/14
Filed: 1967-09-22
Abstract: 1,203,647. Electroluminescence. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 22 Sept., 1967 [30 Sept., 1966], No. 43269/67. Heading C4S. [Also in Division G5] A display device comprises a display panel 4 including a matrix of luminescent elements located at the intersections of groups of crossed conductors, means 10 for generating sequential control pulses of short duration during a recurrent scanning period, each pulse being fed successively to one of a plurality of gate circuits 7 associated with one group of conductors 1, the gate circuits also having an input signal applied to them in common as that each gate circuit when opened by a control pulse passes an output signal corresponding to the instantaneous value of the input signal to a storage element 6 and between each element 6 and the associated conductor 1 a pulse generator 5 which produces pulses of constant amplitude with a duration dependent on the magnitude of the signal from the element 6. The panel comprises two groups of parallel conductors 2, 3 and a third perpendicular group 1. Located at the intersections of conductors 1, 2, 3 are Ne discharge lamps or elements of electroluminescent material, the intensity of luminescence being proportional to the duration of the applied potential. Conductors 1 are each connected to a Schmitt trigger pulse generator circuit controlled from the storage element 6 to which an input signal on terminals 8, 9 is applied through the gate circuit 7. The gate circuits 7 are controlled by short sequential pulses from a shift register 10 fed with synchronizing signals through terminal 11. These signals are also fed to shift registers 12, 13 which supply pulses of one scanning period to conductors 2, 3 180 degrees out of phase. With no control pulse the register 10 applies a positive potential to the base of transistor 16 such that transistor 20 is cut off since its emitter potential is so high. When a negative pulse is applied transistor 16 is cut off permitting the collector of transistor 20 to reach a potential corresponding to the instantaneous value of the input signal. This is passed via transistors 21, 22 to a discharge storage capacitor 23. This is normally maintained at a positive potential above the reverse level of the pulse generator by a constant current source comprising transistor 24 and a Zener diode 26 which subsequently recharges the capacitor to normal potential. The capacitor is connected to the Schmitt circuit and when its potential is above the reverse level of this circuit transistors 30, 32 will be cut off and conductor 1 will be at a high supply potential V 3 . When the voltage of the capacitor falls transistor 29 is cut off permitting transistors 30, 31 to conduct and the potential to conductor 1 to fall for the whole period that the capacitor is below the reversal level, i.e. the recharging period which is proportional to the instantaneous value of the input signal. By dividing the horizontal conductors into two groups and delaying pulses to conductors 3 by half a scanning period the duration of luminescence of any element is up to half a scanning period. In another embodiment only one group of horizontal conductors may be used and storage circuits 6 are duplicated, each being supplied with synchronized square-wave pulses of opposite polarity. Integrated circuits may be used and the Schmitt circuits replaced by controlled Si rectifiers. The devices are used for radar and alpha-numeric character display and for colour TV, when the conductors are triplicated and the discharge lamps coated with red, green or blue-emitting phosphor.