Methods for measuring electrical properties of electro-optic displays
A method for driving electro-optic displays including electro-optic material disposed between a common electrode and a backplane. The backplane includes an array of pixel electrodes, each coupled to a transistor. A display controller applies waveforms to the pixel electrodes. The method includes applying first measurement waveforms to a first portion of the pixel electrodes. During each frame of the first measurement waveforms, the same time-dependent voltages are applied to each pixel electrode of the first portion of pixel electrodes. The method includes determining the impedance of the electro-optic material in proximity to the first portion of pixel electrodes based on a measurement of the current flowing through a current measurement circuit and the time-dependent voltages applied to each pixel electrode during the first measurement waveforms, and selecting driving waveforms based on the impedance of the electro-optic material in proximity to the first portion of pixel electrodes.
1. A method for driving an electro-optic display, the electro-optic display comprising an electrophoretic display medium disposed between a first common electrode and an array of pixel electrodes, wherein each pixel electrode is coupled to a first terminal of a storage capacitor, wherein a second terminal of each storage capacitor is coupled to second common electrode, and wherein a display controller circuit is configured to apply time-dependent voltages to the first common electrode and the second common electrode independent of one another, the method for driving comprising:
concurrently activating pixel transistors associated with a first portion of pixel electrodes;
toggling a first switch to disconnect the first common electrode from the display controller circuit and to connect the first common electrode to a first terminal of an impedance measurement circuit;
toggling a second switch to disconnect the second common electrode from the display controller circuit and to connect the second common electrode to a second terminal of the impedance measurement circuit;
injecting measurement waveforms voltages from the impedance measurement circuit into the first common electrode, the measurement waveforms comprising time-dependent voltages;
measuring a first current flowing through the impedance measurement circuit based on the measurement waveforms;
determining a first impedance of the electro-optic material in proximity to the first portion of pixel electrodes based on the first current flowing through the impedance measurement circuit and the time-dependent voltages applied to the first common electrode during the measurement waveforms;
selecting first driving waveforms to apply to each pixel electrode of the first portion of pixel electrodes based on the first impedance of the electro-optic material in proximity to the first portion of pixel electrodes;
toggling the first switch to disconnect the first common electrode from the impedance measurement circuit and to connect the first common electrode to the display controller circuit;
toggling the second switch to disconnect the second common electrode from the impedance measurement circuit and to connect the second common electrode to the display controller circuit; and
applying the first driving waveforms to the first portion of pixel electrodes, wherein the first driving waveforms comprise time-dependent voltages sufficient to change an optical state of the electro-optic display in proximity to the first portion of pixel electrodes.
2. The method of claim 1 wherein the measurement waveforms comprise periodic square or sinusoidal voltage waveforms.
3. The method of claim 1 wherein the measurement waveforms comprise voltages having an amplitude insufficient to change an optical state of the electro-optic display in proximity to the first portion of pixel electrodes.
4. The method of claim 3 wherein the measurement waveforms comprise voltages having an amplitude less than one volt.
5. The method of claim 1 wherein the measurement waveforms comprise oscillating voltage waveforms having a plurality of frequencies.
6. The method of claim 1 wherein the first portion of pixel electrodes comprises pixel electrodes located in proximity to an outer perimeter of the array of pixel electrodes.