Adaptive temporal modulation of periodically varying light sources

• US 6,285,491 B1
• Filed: 12/21/1999
• Issued: 09/04/2001
• Est. Priority Date: 12/28/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Perry, Roger P., Doherty, Donald B., Marshall, Stephen W.
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): MAGEE, JOHN J
• Application Number:
  US09/467,816
• Time in Patent Office: 623 Days
• Field of Search: 345/148, 345/84, 348/743, 359/292, 359/291, 359/239
• US Class Current: 359/292
• CPC Class Codes: G09G 2320/0266 Reduction of sub-frame artefacts
• CPC Class Codes: G09G 2320/04 Maintaining the quality of display appearance
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/2033 with splitting one or more sub-frames corresponding to the most significant bits into two or more sub-frames
• CPC Class Codes: G09G 3/34 by control of light from an independent source
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• 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 9/3114 by using a sequential colour filter producing one colour at a time
• CPC Class Codes: H04N 9/3123 using pulse width modulation
• CPC Class Codes: H04N 9/3155 for controlling the light source light source control per se H05B35/00 – H05B47/00; control of an illumination source for displays in general G09G3/3406

Abstract

A controller (800) for a pulse width modulated display system. The controller (800) periodically determining the output of a light source by sampling the output of a light detector (808) an creating a smoothed approximation of the periodic waveform of the light source. A processor (806) in the controller (800) reads a base bit split sequence from a read only memory (804) and modifies the sequence by lengthening or shortening the bit periods described therein in order to compensate for the periodic variations of the light source. The modified bit split sequence is stored in two-port random access memory (802) where it is later accessed by both the processor (806) and a sequencer (304). The sequencer (304) reads the modified bit split sequence from the two-port random access memory (802) to determine when to load each bit of image data into a modulator an-ay. The processor (806) periodically reads the two-port random access memory (802) and further modifies the modified sequence contained therein to reflect additional waveform data collected by the detector (808).

Claims

1. A method of temporally modulating a light beam, said method comprising:

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

providing a light modulator on said light path, said light modulator comprising an array modulator elements, each modulator element operable to selectively relay light incident said modulator element to an image plane in response to an image signal;

detecting the quantity of light provided by said light source and providing a signal representing said light output; and

providing a controller for receiving image data words and controlling the operation of said light modulator, said controller serially providing each bit of said image data words to said light modulator for a separate time period in a frame period, wherein the quantity of light output during the time period for each bit represents the relative weight of said each bit in said image data word.

2. The method of claim 1, said step of detecting comprising a photodetector in said light path.

3. The method of claim 1, said step of detecting comprising a current detector for measuring the current supplied to said light source.

4. The method of claim 1, said step of detecting comprising a photodetector detecting reflected light.

5. A display system comprising:

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

a modulator array in said light path;

a means for detecting the amount of light provided to said modulator array by said light source; and

a controller electrically connected to said modulator array, said controller operable to receive image data and to control said modulator array, said image data comprising multiple bits of image data for each element in said modulator array, said controller providing said bits of image data to said modulator array elements such that the total quantity of light directed by each modulator element to an image plane is proportional to the weight of said image data bit.

6. The display system of claim 5, said controller comprising;

memory for storing at least one base bit split sequence and for storing at least one modified bit split sequence;

a processor for receiving samples representing the output of said light source and for calculating a smoothed estimate of the periodic output of said light source, said processor modifying said base bit split sequences and for storing said modified bit split sequences in memory;

a sequencer for reading said modified bit split sequence from memory and for controlling the operation of said modulator array based on said modified bit split sequence.

7. The display system of claim 6, said memory comprising a read only memory for storing said at least one base bit split sequence.

8. The display system of claim 6, said memory comprising a two port random access memory for storing said at least one modified bit split sequence.

9. The display system of claim 6, said processor flier modifying said modified bit split sequence each frame period.

10. The display system of claim 6, said periodically varying beam of light having a periodically varying intensity and further comprising:

at least two sequentially alternating primary color periods, wherein said periodically varying beam of light is a unique primary color beam of light during each said color period; and

wherein at least two of said primary color beams of light have a different total intensity, said processor modifying said base bit split sequences to equalize the total quantity of light directed by each modulator element to an image plane during all said primary color periods in response to equal-weight image data bits.

11. The display system of claim 5, said controller comprising an analog to digital converter for digitizing an output from said means for detecting.

12. The display system of claim 5, said means for detecting the output of said light source comprising a current sensor.

13. The display system of claim 5, said means for detecting the output of said light source comprising a light detector.

14. The display system of claim 5, said means for detecting the output of said light source comprising a light detector in said illumination path.

15. The display system of claim 5, said periodically varying beam of light having a periodically varying intensity and further comprising:

at least two sequentially alternating primary color periods, wherein said periodically varying beam of light is a unique primary color beam of light during each said color period; and

wherein at least two of said primary color beams of light have a different total intensity, said controller providing said bits of image data to said modulator array elements such that the total quantity of light directed by each modulator element to an image plane is proportional to the weight of said image data bit during all said primary color periods.