Method and system for writing data to MEMS display elements

• US 8,310,441 B2
• Filed: 09/22/2005
• Issued: 11/13/2012
• Est. Priority Date: 09/27/2004
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Chui, Clarence, Kothari, Manish
• Primary Examiner(s): Moorad, Waseem
• Application Number:
  US11/234,061
• Publication Number:
  US 20060066561A1
• Time in Patent Office: 2,609 Days
• Field of Search: 345/108
• US Class Current: 345/108
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2310/0245 Clearing or presetting the whole screen independently of waveforms, e.g. on power-on G09G2310/063 takes precedence
• CPC Class Codes: G09G 2310/0254 Control of polarity reversal in general, other than for liquid crystal displays
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2340/0435 Change or adaptation of the frame rate of the video stream
• CPC Class Codes: G09G 3/3466 based on interferometric effect

Abstract

Charge balanced display data writing methods use write and hold cycles of opposite polarity during selected frame update periods. A release cycle may be provided to reduce the chance that a given display element will become stuck in an actuated state.

Claims

1. A method of actuating a MEMS display element, said MEMS display element comprising a portion of an array of MEMS display elements, said method comprising:

writing display data to said MEMS display element with a potential difference of a first polarity during a first portion of a display write process;

applying a first bias potential having said first polarity to said MEMS display element during a second portion of said display write process; and

applying a second bias potential having a polarity opposite said first polarity to said MEMS display element during a third portion of said display write process, there being a period of time between said applying said first bias potential and said applying said second bias potential,

wherein a transition time between said applying said first bias potential and said applying said second bias potential is configured such that a state change of said MEMS display element will be avoided when a voltage having a value outside of a hysteresis window of said MEMS display element is applied across said MEMS display element during said period,

wherein the transition time between the first and second bias potentials is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display element determined with reference to physical characteristics of said MEMS display element, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display element.

2. The method of claim 1, further comprising writing display data to said MEMS display element with a potential difference having a polarity opposite said first polarity during a fourth portion of said display write process.

3. The method of claim 2, wherein said first portion of said display write process comprises writing a first frame of display data to said array of MEMS display elements, and wherein said fourth portion of said display write process comprises re-writing said first frame of display data to said array of MEMS display elements.

4. The method of claim 3, wherein said second and third portions of said display write process comprises holding said first frame of display data following said re-writing.

5. The method of claim 4, additionally comprising writing a second frame of display data using said writing, re-writing, applying a first bias potential and applying a second bias potential.

6. The method of claim 2, wherein said first portion of said display write process comprises writing a first row of display data to said array of MEMS display elements, and wherein said fourth portion of said display write process comprises re-writing said first row of display data to said array of MEMS display elements.

7. The method of claim 6, wherein said second and third portions of said display write process comprises holding said first row of display data following said re-writing.

8. The method of claim 7, additionally comprising writing a second row of display data using said writing, re-writing, applying a first bias potential and applying a second bias potential.

9. The method of claim 2, wherein said first, second, third, and fourth portions of said display write process each comprise approximately one-fourth of a time period defined by the inverse of a rate at which frames of display data are received by a display system.

10. The method of claim 2, wherein said first portion of said display write process comprises writing a first frame of display data to said array of MEMS display elements, and wherein said fourth portion of said display write process comprises writing a second frame of display data to said array of MEMS display elements, wherein said second frame comprises different display data than said first frame.

11. The method of claim 10, further comprising applying a third bias potential to said MEMS display element during a fifth portion of said display write process, and applying a fourth bias potential to said MEMS display element during a sixth portion of said display write process, said third and fourth bias potentials having opposite polarities.

12. The method of claim 1, comprising switching from said applying said first bias potential to said applying said second bias potential at a speed sufficient to maintain an RMS potential of said bias potentials within an absolute value of a hysteresis window of said MEMS display element.

13. A method of maintaining a frame of display data on an array of MEMS display elements, said method comprising alternately and sequentially applying approximately equal bias potentials of opposite polarities to said MEMS display elements, wherein said applying comprises switching between the bias potentials of opposite polarities at a rate sufficient to maintain an RMS potential of said bias potentials within an absolute value of a hysteresis window of said MEMS display elements, wherein a transition time between the bias potentials is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display element determined with reference to physical characteristics of said MEMS display element, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display element.

14. A method of writing frames of display data to an array of MEMS display elements at a rate of one frame per defined frame update period, said method comprising:

writing display data to said MEMS display elements, wherein said writing takes less than said frame update period; and

after said writing said display data, applying a series of bias potentials of alternating polarity to said MEMS display elements for the remainder of said frame update period,

wherein an RMS potential of said series of bias potentials is within an absolute value of a hysteresis window of said MEMS display elements, wherein a transition time between consecutive bias potentials of the series is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display element determined with reference to physical characteristics of said MEMS display element, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display element.

15. The method of claim 14, wherein said series comprises an application of a first polarity during approximately half of said remainder of said frame update period, and an application of a second opposite polarity during approximately half of said remainder of said frame update period.

16. A microelectromechanical systems (MEMS) display device comprising an array of MEMS display elements and configured to display images at a frame update rate, said frame update rate defining a frame update period, said display device comprising a column driver circuit configured to apply a polarity balanced sequence of bias voltages to substantially all columns of said array for portions of at least one frame update period, wherein a root-mean-square (RMS) voltage of said sequence is between an absolute value of a release voltage of said MEMS display elements and an absolute value of an actuation voltage of said MEMS display elements, said RMS voltage being calculated from a first voltage in the sequence and a last voltage in the sequence and all voltages applied to the columns between the first voltage and the last voltage, wherein said driver circuit is configured to switch between applying said bias voltages such that a transition time between consecutive ones of the bias voltages of the sequence is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display elements determined with reference to physical characteristics of said MEMS display elements, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display elements.

17. The MEMS display device of claim 16, wherein said driver circuit is configured to apply the same voltage to substantially all columns of said display array during a portion of said frame update period.

18. The MEMS display device of claim 16, wherein said driver circuit is further configured to write display data to said array with a potential difference of a first polarity during a first portion of said frame update period, and to re-write said display data to said array with a potential difference of a second polarity during a second portion of said frame update period.

19. A method of actuating a MEMS display element, said MEMS display element comprising a portion of an array of MEMS display elements, said method comprising:

writing display data to said MEMS display element with a potential difference of a first polarity during a first portion of a display write process;

applying a first bias potential having said first polarity to said MEMS display element during a second portion of said display write process; and

applying a second bias potential having a polarity opposite said first polarity to said MEMS display element during a third portion of said display write process,

wherein a transition time between said applying said first bias potential and said applying said second bias potential is configured to avoid state change of said MEMS display element, and

wherein said transition time is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display element determined with reference to physical characteristics of said MEMS display element, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display element.

20. The method of claim 19, wherein said physical characteristics comprise at least one of a thickness of an electrode of said MEMS display element, a dielectric material of said MEMS display element, a material of the electrode, a geometry of a deformable layer of said MEMS display element, a tensile stress of a material of the deformable layer, and a placement of damping holes in a reflective layer of the MEMS display element.

21. A MEMS display device comprising an array of MEMS display elements and configured to display images at a frame update rate, said frame update rate defining a frame update period, said display device comprising a column driver circuit configured to apply a polarity balanced sequence of bias voltages to substantially all columns of said array for portions of at least one frame update period, wherein an RMS voltage of said sequence is between an absolute value of a release voltage of said MEMS display elements and an absolute value of an actuation voltage of said MEMS display elements, wherein said driver circuit is configured to switch between applying said bias voltages such that a transition time between each bias voltage is less than or equal to τ

_iMoD+τ

_RC, wherein τ

_iMoD comprises a constant of said MEMS display elements determined with reference to physical characteristics of said MEMS display elements, and wherein τ

_RC comprises a constant related to electrical characteristics of said MEMS display elements.