System and methods for extraction of threshold and mobility parameters in AMOLED displays
A system to improve the extraction of transistor and OLED parameters in an AMOLED display includes a pixel circuit having an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide the programming signal, and a storage device to store the programming signal. A charge-pump amplifier has a current input and a voltage output. The charge-pump amplifier includes an operational amplifier in negative feedback configuration. The feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier. A common-mode voltage source drives the non-inverting input of the operational amplifier. An electronic switch is coupled across the capacitor to reset the capacitor. A switch module including the input is coupled to the output of the pixel circuit and an output is coupled to the input of the charge-pump amplifier.
1. A method of determining the mobility of a drive transistor in a pixel circuit based on transient settling of the pixel circuit, the method comprising:
setting the output of the drive transistor to a reset voltage;
disconnecting the reset voltage and allowing the output voltage to be adjusted by the drive transistor;
sampling the transient output voltage of the drive transistor at a fixed time interval; and
calculating the mobility of the drive transistor from the sampled output voltage of the drive transistor.
2. The method of claim 1 wherein the threshold voltage of the drive transistor is compensated prior to calculating the mobility of the drive transistor.
3. A method of determining the mobility of a drive transistor in a pixel circuit based on transient settling of the pixel circuit, the method comprising:
setting the output of the drive transistor to a reset voltage;
disconnecting the reset voltage and allowing the output voltage to be adjusted by drive transistor;
sampling the output voltage of the drive transistor at a fixed time interval; and
calculating the mobility of the drive transistor from the sampled output voltage of the drive transistor,
wherein the transient voltage is sampled at a plurality of different timing intervals and mobility is extracted from the sampled voltages.
4. A method of determining the mobility of a drive transistor in a pixel circuit based on transient settling of the pixel circuit, the method comprising:
setting the output of the drive transistor to a reset voltage;
disconnecting the reset voltage and allowing the output voltage to be adjusted by drive transistor;
sampling the output voltage of the drive transistor at a fixed time interval; and
calculating the mobility of the drive transistor from the sampled output voltage of the drive transistor,
wherein the output voltage is amplified before sampling.
5. A method of extracting mobility from a drive transistor in a pixel circuit based on the transient settling of the drive transistor comprising:
measuring the current of the drive transistor over a constant interval by converting the current into voltage by integration; and sampling the output voltage at constant interval; and
calculating the mobility of the drive transistor from the measured current.
6. A method of extracting mobility from a drive transistor in a pixel circuit based on the transient settling of the drive transistor comprising:
measuring the current of the drive transistor at a constant interval at a plurality of different timing intervals and mobility is extracted from the sampled currents.