Electroluminescent display with initial nonuniformity compensation

A method of compensating for differences in characteristics of a plurality of electroluminescent (EL) subpixels, comprising:

• (a) providing for each of a plurality of EL subpixels a drive transistor with a first electrode, a second electrode, and a gate electrode;
• (b) providing a first voltage source and a first switch for selectively connecting the first voltage source to the first electrode of each drive transistor;
• (c) providing an EL emitter for each EL subpixel connected to the second electrode of the respective drive transistor, and a second voltage source and a second switch for selectively connecting each EL emitter to the second voltage source;
• (d) providing for each EL subpixel a readout transistor having a first electrode and a second electrode, and connecting the first electrode of each readout transistor to the second electrode of the respective drive transistor;
• (e) providing a current source and a third switch for selectively connecting the current source to the second electrode of each readout transistor;
• (f) providing a current sink and a fourth switch for selectively connecting the current sink to the second electrode of each readout transistor;
• (g) selecting an EL subpixel and its corresponding drive transistor, readout transistor and EL emitter;
• (h) providing a test voltage to the gate electrode of the selected drive transistor and providing a voltage measurement circuit connected to the second electrode of the selected readout transistor;
• (i) closing the first and fourth switches and opening the second and third switches, and using the voltage measurement circuit to measure the voltage at the second electrode of the selected readout transistor to provide a corresponding first signal representative of characteristics of the selected drive transistor;
• (j) opening the first and fourth switches, closing the second and third switches, and using the voltage measurement circuit to measure the voltage at the second electrode of the selected readout transistor to provide a corresponding second signal representative of characteristics of the selected EL emitter;
• (k) repeating steps g through j for each remaining EL subpixel in the plurality of EL subpixels;
• and
• (l) using the first and second signals for each subpixel to compensate for differences in characteristics of the plurality of EL subpixels.