Digital driving circuits, methods and systems for display devices

• US 9,852,702 B2
• Filed: 04/22/2014
• Issued: 12/26/2017
• Est. Priority Date: 01/14/2010
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Van Ess, David, Keeser, Christopher Corson, Murphy, Robert LeRoy, Wright, David G.
• Primary Examiner(s): Lee, Benjamin C
• Assistant Examiner(s): Zheng, Xuemei
• Application Number:
  US14/258,905
• Publication Number:
  US 20140267216A1
• Time in Patent Office: 1,344 Days
• Field of Search: 345212, 345 34, 345 50, 340324, 330300
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• CPC Class Codes: G09G 3/04 for presentation of a single character by selection from a plurality of characters, or by composing the character by combination of individual elements, e.g. segments using a combination of such display devices for composing words, rows or the like, in a frame with fixed character positions
• CPC Class Codes: G09G 3/18 using liquid crystals
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/36 using liquid crystals
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

A method may include generating display driver signals that vary between only two levels and applying the display driver signals to opposing electrodes of a display segment within a display device. An intrinsic capacitance of the display device filters the display driver signals to generate different analog signal levels at the display segment of the display device. The method varies the pulse density of the display driver signals to select or de-select the display segment based on an average voltage magnitude across the display segment over a time period. The display segment is activated when the average voltage magnitude exceeds a threshold value.

Claims

1. A method comprising:

generating display driver signals that vary between only two levels and vary in pulse density, wherein the display driver signals are digital signals and comprise common driver signals and segment driver signals;

applying, by a driver circuit, the display driver signals to opposing electrodes of a display element within a display device, wherein the driver circuit comprises an output resistance, wherein the output resistance, an intrinsic resistance, and an intrinsic capacitance of the display device form a low pass filter with respect to a modulating frequency of the display signals, wherein the low pass filter filters the display driver signals to generate different analog signal levels at the display element of the display device, wherein the modulating frequency is outside of a pass band of the low pass filter, wherein the low pass filter transforms display driver signals having a variable pulse density into variable voltage levels of a voltage across the display element;

in a first mode, varying the pulse density of the display driver signals to select or de-select the display element based on a first average voltage magnitude of the voltage across the display element over a first time period, wherein the display element is activated in the first mode when the first average voltage magnitude exceeds a first threshold value; and

in a second mode, varying a correlation between the common drive signals and the segment drive signals to select or de-select the display element based on a second average voltage magnitude of the voltage across the display element over a second time period, wherein the display element is activated in the second mode when the second average voltage magnitude exceeds a second threshold value.

2. The method of claim 1, wherein the varying the pulse density of the display driver signals comprises generating a plurality of common driver signals that each includes frames of N timeslots, including one selection time slot and N−

1 de-selection timeslots, the one selection timeslot being different for each common driver signal.

3. The method of claim 2, wherein the varying the pulse density of the display driver signals comprises generating at least one segment driver signal having frames of N timeslots corresponding to the common driver signals, wherein the display element is activated when the average voltage magnitude applied to the opposing electrode of the display element due to correlating corresponding common and segment driver signals exceeds a voltage threshold in a timeslot.

4. The method of claim 2, further comprising

generating at least one segment driver signal having frames of N timeslots corresponding to the frames of N timeslots of each of the plurality of common driver signals, the at least one segment driver signal varying a correlation to at least one common driver signal in response to display data.

5. The method of claim 1, further comprising switching between the first mode and the second mode in response to a mode indication.

6. The method of claim 5, wherein the second mode is a low power mode and the first mode is a higher power mode.

7. The method of claim 5, further comprising:

generating a plurality of time division multiplexed common driver signals and segment driver signals that vary substantially between the two levels;

in the second mode, activating display elements by varying a correlation between common and segment driver signals connected to such display elements; and

in the first mode, activating display elements by at least varying voltage levels of a common driver signal as received by the display elements.

8. The method of claim 7, further comprising:

in the second mode,

generating common driver signals that vary according to a predetermined sequence; and

generating segment driver signals that selectively correlates with at least one common driver signal in response to display data to exceed a minimum average voltage over a time period, wherein a display element is activated or not activated depending upon whether a voltage exceeds the minimum average voltage over the time period.

9. The method of claim 8, wherein the common and segment driver signals include frames, each having a plurality of timeslots, and the time period comprises one of a plurality of time slots.

10. The method of claim 7, further comprising:

in the first mode,

generating common driver signals having a variable pulse density, and

filtering the common driver signals with a variable pulse density to generate the varying voltage levels received by the display elements.

11. The method of claim 10, wherein the display elements comprise liquid crystal display (LCD) elements, wherein the low pass filter further comprises:

an external resistor coupled between an output node of the driver circuit and an input node of the display device; and

an external capacitor coupled to the input node of the display device and a ground potential.

12. The method of claim 7, further comprising further varying a pulse density of at least the common driver signals or the segment driver signals in response to an intensity value.

13. The method of claim 1, wherein the display device is a liquid crystal display (LCD) device.

14. The method of claim 13, wherein glass of the LCD device forms part of the low pass filter to filter the display driver signals to generate different analog signal levels at the display element of the display device.

15. A method comprising:

generating display driver signals that vary between only two levels, wherein the display driver signals are digital signals and comprise common driver signals and segment driver signals;

applying, by a driver circuit, the display driver signals to electrodes of display elements within a display device, wherein the driver circuit comprises an output resistance, wherein the output resistance, an intrinsic resistance, and an intrinsic capacitance of the display device form a low pass filter with respect to a modulating frequency of the display driver signals, wherein the low pass filter transforms a variable pulse density into varying voltage levels of a voltage across the display element;

in a first mode, varying a pulse density of the display driver signals;

in the first mode, filtering, by the lower pass filter, the display driver signals to provide different analog voltage levels across the display elements that vary according to the variable pulse density, wherein the display element is activated when an average voltage magnitude across the display element over a time period exceeds a threshold value;

in a second mode, varying a correlation between the common drive signals and the segment drive signals to select or de-select the display element based on a second average voltage magnitude of the voltage across the display element over a second time period, wherein the display element is activated in the second mode when the second average voltage magnitude exceeds a second threshold value.

16. The method of claim 15, wherein the display device is a liquid crystal display device, wherein the low pass filter further comprises:

an external resistor coupled between an output node of the driver circuit and an input node of the display device; and

an external capacitor coupled to the input node of the display device and a ground potential.

17. A system comprising:

a plurality of programmable digital blocks to be coupled to display elements of a display device, wherein the plurality of programmable digital blocks are configured into the following circuits;

a first signal generator circuit that generates control signals that vary between substantially only two levels, wherein the control signals are digital signals and comprise common drivers signals and segment driver signals; and

a selection driver circuit coupled to the first signal generator circuit, wherein the selection driver circuit is to apply the control signals to opposing electrodes of the display element elements, wherein the selection driver circuit comprises an output resistance, wherein the output resistance, an intrinsic resistance of the display device, and an intrinsic capacitance of the display device form a low pass filter with respect to a modulating frequency of the control signals, wherein the modulating frequency is outside of a pass band of the low pass filter, wherein the low pass filter transforms a variable pulse density into varying voltage levels of a voltage across the display element, wherein the low pass filter filters the control signals to generate different analog signal levels at the display element of the display device, wherein the selection driver circuit, in a first mode, varies the pulse density of the control signals to select or de-select the display element based on a first average voltage magnitude of the voltage across the display element over a first time period, wherein the display element is activated in the first mode when the

first average voltage magnitude exceeds a first threshold value, and wherein the selection driver circuit, in a second mode, varies a correlation between the common drive signals and the segment drive signals to select or de-select the display element based on a second average voltage magnitude of the voltage across the display element over a second time period, wherein the display element is activated in the second mode when the second average voltage magnitude exceeds a second threshold value.

18. The system of claim 17, wherein the selection driver circuit comprises:

a common section that time division multiplexes the control signals to a plurality of common connection points in a predetermined sequence; and

a segment section that time division multiplexes the control signals to a plurality of common connection points in response to at least display data.

19. The system of claim 17, wherein the display device is a liquid crystal display coupled to the common and segment connection points.

20. The system of claim 19, wherein glass of the LCD device forms part of the low pass filter to filter the display driver signals to generate different analog signal levels at the display element of the display device.