System and methods for extraction of threshold and mobility parameters in AMOLED displays
A system and method for 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 system and method determine the biasing voltage of an internal node of the pixel circuit during a driving cycle for a desired measurement level, and modify voltages of the pixel circuit that do not affect said biasing voltage to eliminate unwanted cross talk. In different implementations, the biasing voltage is determined by measuring the voltage at an internal node, or by calculating the voltage at the internal node.
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:
determining the biasing voltage of an internal node of the pixel circuit during a driving cycle for a desired measurement level,
modifying voltages of the pixel circuit that do not affect said biasing voltage to eliminate unwanted cross talk, and
extracting a parasitic capacitance from said pixel circuit.
2. The method of claim 1 in which said biasing voltage is determined by measuring the voltage at said internal node.
3. The method of claim 2 in which said biasing voltage is controlled by the light emitting device during the driving cycle, and by a monitor line during the measuring, and the voltage of the light emitting device is determined during the driving cycle for a given current.
4. The method of claim 3 in which the light emitting device is an organic light emitting diode (OLED), and the OLED voltage is determined by extracting an OLED voltage for a known current from an OLED model.
5. The method of claim 3 in which the light emitting device is an organic light emitting diode (OLED), and the OLED voltage is determined by applying a known current to the OLED , and measuring the resulting voltage.
6. The method of claim 1 in which said biasing voltage is determined by calculating the voltage at said internal node.
7. The method of claim 1 which includes removing unwanted signals that affect an unwanted measurement signal by double sampling.
8. The method of claim 1 in which a measured parameter is a current in said pixel circuit.
9. The method of claim 1 in which a measured parameter is a charge in said pixel circuit.