Active Matrix Organic Light Emitting Diode (AMOLED) displays, novel pixel circuits therefor, and methods of programming the pixel circuit and measuring the current of the pixel circuit and OLED thereof are disclosed. One pixel circuit includes four TFT transistors, a storage capacitor and an OLED device and is programmed with use of voltage supplied through a data line. One method measures currents of the OLED and the pixel circuit through the data line by a readout circuit.