System and methods for extraction of parasitic parameters in AMOLED displays
A system reads a desired circuit parameter from a pixel circuit that includes a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal. One embodiment of the extraction system extracts a parasitic capacitance value from a pixel circuit by measuring at least one parameter of the pixel circuit when in a first state having a first set of operating voltages and currents, measuring at least one parameter of the pixel circuit when in a second state having a second set of operating voltages and currents different from the first set, and extracting the value of a selected parasitic capacitance from the measurements.
1. A method of extracting a parasitic capacitance value from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:
measuring at least one parameter of the pixel circuit when in a first state having a first set of operating voltages and currents,
measuring at least one parameter of the pixel circuit when in a second state having a second set of operating voltages and currents different from said first set,
modeling the effect of parasitic capacitance on measured parameters at different sets of operating conditions, said modeling being done before or after said measuring of said parameters of the pixel circuit when in said first and second states, and
extracting the value of a selected parasitic capacitance from said measurements and said modeling.
2. The method of claim 1 in which said measured parameter is a current in said pixel circuit.
3. The method of claim 1 in which said measured parameter is a charge in said pixel circuit.
4. A method of extracting a parasitic capacitance value from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:
measuring at least one parameter of the pixel circuit when in a first state having a first set of operating voltages and currents,
measuring at least one parameter of the pixel circuit when in a second state having a second set of operating voltages and currents different from said first set,
determining the difference between the two measurements, and
measuring at least one parameter of the pixel circuit when in a third state having a known set of operating voltages and currents, and modifying this measurement by a gain based on said determined difference.
5. The method of claim 4 in which said pixel circuit is part of a display having a prescribed specification, and said gain is adjusted to make said pixel circuit match said prescribed specification.