Apparatus configured to provide drive transistor control signals to the gate electrodes of drive transistors in a plurality of EL subpixels in an electroluminescent, EL, panel, including a first voltage supply, a second voltage supply, and a plurality of EL subpixels in the EL panel; each EL subpixel including a drive transistor configured to apply current to an EL emitter in each EL subpixel, each drive transistor having a first supply electrode electrically connected to the first voltage supply and a second supply electrode electrically connected to a first electrode of the EL emitter; and each EL emitter including a second electrode electrically connected to the second voltage supply, the apparatus comprising: (a) a sequence controller configured to select one or more of the plurality of EL subpixels; (b) a test voltage source electrically connected to the gate electrodes of the drive transistors of the one or more selected EL subpixels; (c) a voltage controller configured to control voltages of the first voltage supply, second voltage supply and test voltage source to operate the drive transistors of the one or more selected EL subpixels in a linear region; (d) a measuring circuit configured to measure the current passing through the first and second voltage supplies (211, 206) to provide respective status signals for each of the one or more selected EL subpixels representing the characteristics of the drive transistor and EL emitter of those subpixels, wherein the measuring circuit is adapted to measure the current while the drive transistors of the one or more selected EL subpixels are operated in the linear region; (e) means configured to provide a linear code value for each subpixel; (f) a compensator configured to change the linear code values in response to the status signals to compensate for variations in the characteristics of the drive transistor and EL emitter in each subpixel; and (g) a source driver configured to produce the drive transistor control signals in response to the changed linear code values for driving the gate electrodes of the drive transistors, characterised in that the measuring circuit includes: (i) a current to voltage converter configured to produce a voltage signal; and (ii) a correlated double-sampling unit responsive to the voltage signal used in providing the status signal to the compensator, and wherein the apparatus further comprises a plurality of second voltage supplies, wherein the second electrode of each EL emitter is electrically connected to only one second voltage supply. (a) a sequence controller configured to select one or more of the plurality of EL subpixels; (b) a test voltage source electrically connected to the gate electrodes of the drive transistors of the one or more selected EL subpixels; (c) a voltage controller configured to control voltages of the first voltage supply, second voltage supply and test voltage source to operate the drive transistors of the one or more selected EL subpixels in a linear region; (d) a measuring circuit configured to measure the current passing through the first and second voltage supplies (211, 206) to provide respective status signals for each of the one or more selected EL subpixels representing the characteristics of the drive transistor and EL emitter of those subpixels, wherein the measuring circuit is adapted to measure the current while the drive transistors of the one or more selected EL subpixels are operated in the linear region; (e) means configured to provide a linear code value for each subpixel; (f) a compensator configured to change the linear code values in response to the status signals to compensate for variations in the characteristics of the drive transistor and EL emitter in each subpixel; and (g) a source driver configured to produce the drive transistor control signals in response to the changed linear code values for driving the gate electrodes of the drive transistors, characterised in that the measuring circuit includes: (i) a current to voltage converter configured to produce a voltage signal; and (ii) a correlated double-sampling unit responsive to the voltage signal used in providing the status signal to the compensator, and wherein the apparatus further comprises a plurality of second voltage supplies, wherein the second electrode of each EL emitter is electrically connected to only one second voltage supply. (i) a current to voltage converter configured to produce a voltage signal; and (ii) a correlated double-sampling unit responsive to the voltage signal used in providing the status signal to the compensator, and wherein the apparatus further comprises a plurality of second voltage supplies, wherein the second electrode of each EL emitter is electrically connected to only one second voltage supply.