Analog pulse width modulation of video data

• US 6,590,549 B1
• Filed: 12/21/1999
• Issued: 07/08/2003
• Est. Priority Date: 12/30/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Marshall, Stephen W.
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US09/468,980
• Time in Patent Office: 1,295 Days
• Field of Search: 345/84, 345/108, 345/205, 345/208, 345/690-691, 345/770-771, 345/581, 345/589, 345/617
• US Class Current: 345/84
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2310/0224 Details of interlacing
• 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 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 3/001 using specific devices not provided for in groups G09G3/02 - G09G3/36, e.g. using an intermediate record carrier such as a film slide; Projection systems; Display of non-alphanumerical information, solely or in combination with alphanumerical information, e.g. digital display on projected diapositive as background slide projectors per se G03B23/00 = 42 HP
• 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 3/346 based on modulation of the reflection angle, e.g. micromirrors micromirrors devices per se G02B26/0833
• CPC Class Codes: H04N 9/312 Driving therefor driving of electronic spatial light modulators in displays other than projection devices G09G3/34, G09G3/36; control of liquid crystal elements G02F1/133; control of micromechanical modulators G02B26/08

Abstract

A micromirror capable of analog pulse width modulation, and method thereof A capacitor (406) in each micromirror element stores a charge representative of one pixel of image data. A comparator (414) compares the image data signal stored on the capacitor (406) to a reference signal from a reference signal generator (416). Depending on the results of the comparison, the address electrodes (418) of the micromirror are biased to deflect the micromirror (412). As either the image data charge stored on the capacitor (406), or the reference voltage changes, the output of the comparator (414) changes to alter the position of the micromirror (412).

Claims

1. A method of operating an element of a spatial light modulator, said method comprising the steps of:

providing a pixel data signal to said element of said spatial light modulator;

providing a reference signal to said element of said spatial light modulator;

comparing said pixel data signal and said reference signal during at least one frame period as at least one of said pixel data signal and said reference signal change;

operating said element of said spatial light modulator according to the results of said comparing step to form an image; and

altering said reference signal after at least one frame period to alter at least one image parameter selected from the group consisting of image brightness and image contrast in said image formed by said operating step.

2. The method of claim 1, said step of providing said pixel data signal further comprising providing said pixel data signal once each field.

3. The method of claim 1, further comprising the step of decaying said pixel data signal during a frame time.

4. The method of claim 1, said step of providing a reference signal further comprising providing a changing reference signal.

5. The method of claim 1, said step of providing a reference signal further comprising providing a gradually increasing reference signal.

6. The method of claim 1, said step of providing a reference signal further comprising providing a gradually decreasing reference signal.

7. The method of claim 1, said step of providing a reference signal further comprising providing a gradually increasing then gradually decreasing reference signal.

8. The method of claim 1, further comprising the step of selecting a global reset waveform upon a change in an output of said comparing step.

9. The method of claim 1, further comprising the step of generating a reset waveform upon a change in an output of said comparing step.

10. A micromirror device comprising:

at least two address electrodes;

a deflectable mirror element suspended above said at least two address electrodes;

a capacitor for storing charge representing an image data signal;

a reference voltage generator for generating a reference voltage, said reference voltage generator operable to alter said reference voltage to adjust at least one image parameter selected from the group consisting of image brightness and image contrast; and

a comparator receiving said image data signal and said reference voltage, said comparator for comparing said reference voltage input with said image data signal for at least one frame period, and for providing address voltages to said at least two address electrodes to cause a deflection of said deflectable mirror element, wherein said alteration of said reference voltage after said at least one frame period adjusts said at least one parameter.

11. The micromirror device of claim 10, said micromirror cell further comprising an edge detector to detect a change in the output of said comparator.

12. The micromirror device of claim 11, said micromirror cell further comprising a switch for enabling a global reset signal when said edge detector detects a change in the output of said comparator.

13. The micromirror device of claim 11, said micromirror cell further comprising a reset generator for outputting a reset signal when said edge detector detects a change in the output of said comparator.

14. A micromirror cell comprising:

at least two address electrodes;

a deflectable mirror element suspended above said at least two address electrodes;

a capacitor for storing charge representing an image data signal;

a reference voltage generator for generating a reference voltage, said reference voltage generator operable to alter said reference voltage to adjust at least one image parameter selected from the group consisting of image brightness and image contrast; and

a comparator receiving said image data signal and said reference voltage, said comparator comparing said reference voltage and said image data signal for at least one frame period, and providing address voltages to said at least two address electrodes to cause a deflection of said deflectable element, wherein said alteration of said reference voltage after said at least one frame period adjusts said at least one parameter.

15. The micromirror cell of claim 14, further comprising an edge detector to detect a change in the output of said comparator.

16. The micromirror cell of claim 15, further comprising a switch for enabling a global reset signal when said edge detector detects a change in the output of said comparator.

17. The micromirror cell of claim 15, further comprising a reset generator for outputting a reset signal when said edge detector detects a change in the output of said comparator.

18. A display system comprising:

a light source for providing a beam of light along a light path;

an array of micromirror cells on said light path, each micromirror cell operable to selectively reflect incident light along a projection path, each said micromirror cell comprising;

at least two address electrodes;

a deflectable mirror element suspended above said at least two address electrodes;

a capacitor for storing charge representing an image data signal;

a reference voltage generator for generating a reference voltage, said reference voltage generator operable to alter said reference voltage to adjust at least one image parameter selected from the group consisting of image brightness and image contrast; and

a comparator receiving said image data signal and said reference voltage for at least one frame period, said comparator comparing said reference voltage input and said image data signal providing address voltages to said at least two address electrodes to cause a deflection of said deflectable element, wherein said alteration of said reference voltage after said at least one frame period adjusts said at least one parameter;

a controller providing said image data signal to said micromirror array; and

projection optics on said projection path, said projection optics operable to focus said selectively reflected incident light on an image plane.