Abstract: An active matrix electroluminescent (EL) display device has a switching circuit for each display pixel which has a drive transistor (30) and a cascode transistor (32) in series with the associated EL display element (20). The switching circuit is operable in two modes, a first mode in which an input current is sampled by the drive transistor (30) and a second mode in which the drive transistor drives a current corresponding to the input current through the EL display element (20). This configuration uses the same transistor for current sampling as for current driving, thereby avoiding the need for matched transistors. The cascode transistor increases the output impedance and ensures that no voltage fluctuations pass to the drive transistor, so that a constant current supply is maintained.

Abstract: Physical barriers (210) are present between neighbouring pixels (200) on a circuit substrate (100) of an active-matrix electroluminescent display device, particularly with LEDs (25) of organic semi conductor materials. The invention forms these barriers (210) with metal or other electrically-conductive material (240), that is insulated (40) from the LEDs but connected to the circuitry within the substrate (100). This conductive barrier material (240) backs-up or replaces at least a part of the drive supply line (140,240) to which the LEDs are connected by a drive element T1. This transfers the problem of line resistance and associated voltage drop from within the circuit substrate (100), where it is severely constrained, to the much freer environment of the pixel barriers (210) on the substrate (100) where the conductive barrier material (240) can provide much lower resistance. Very large displays can be made with low voltage drops along this composite drive supply line (140,240).