Patent Application
20090140670
This disclosure generally relates to control systems, and more particularly to a light beam control system for a spatial light modulator and a method of operating the same.
Spatial light modulators may be used to modulate a light beam into an image. These spatial light modulators may have a number of spatially oriented refractive or reflective elements that are arranged in a two-dimensional configuration. Examples of such light modulators may include liquid crystal display modulators or digital micro-mirror devices (DMDs).
According to one embodiment of the disclosure, a light beam control system includes a positive intrinsic negative diode coupled to a controller circuit. The positive intrinsic negative diode receives a portion of a light beam generated by a light source and converts the portion into a measured intensity. The controller circuit receives the measured intensity, determines an output signal according to the measured intensity and a reference, and adjusts the light beam according to the output signal.
Some embodiments of the invention provide technical advantages. For example, according to one embodiment, the light beam control system regulates the light beams generated by light sources. The light beam control system may, therefore, control light sources, such as light emitting diodes or lasers, that do not have a consistent intensity.
Some embodiments may benefit from some, none, or all of these advantages. Other technical advantages may be readily ascertained by one of ordinary skill in the art.
A more complete understanding of embodiments of the disclosure will be apparent from the detailed description taken in conjunction with the accompanying drawings in which:
A spatial light modulator may modulate a light beam generated by any suitable light source. Examples of such light sources may include light emitting diodes (LEDs) and laser diodes. These light sources may comprise solid-state components. Solid-state components, however, may have characteristics that vary widely due to, for example, changes in operating temperature. These light sources may produce light beams that vary in intensity, which may limit the quality of images produced by spatial light modulators.
Light source 20 generates a light beam 18. Examples of light sources 20 include light emitting diodes or laser diodes, which typically do not generate light beams of consistent intensity. Other examples of light beams 20 include incandescent lamps, sodium vapor lamps, metal halide lamps, xenon lights, high-pressure mercury lamps, fluorescent lamps, and tungsten-halogen lamps.
The spatial light modulator 16 reflects or refracts selected portions of light beam 18. In one embodiment, spatial light modulator 16 may have a plurality of reflective elements corresponding to the arrangement and quantity of pixels to be displayed in image 24. Spatial light modulator 16 may be a digital micro-mirror device (DMD). The digital multi-mirror device has a plurality of reflective surfaces arranged in an M×N configuration that are adapted to selectively reflect light from light source 20 to or away from projecting lens 26. When coordinated together, the reflective surfaces modulate light beam 18 to form image 24. Image 24 may include a plurality of pixels arranged in a N number of rows by a M number of columns, thereby forming the image having height equal to M*(pixel size) and a width equal to N*(pixel size).
Spatial light modulator 16 may have digital circuitry, such as an onboard processing circuit, that manages function of spatial light modulator 16. For example, the digital circuitry may regulate light beam 18. Other examples of spatial light modulators include liquid crystal display modulators.
In one embodiment, positive intrinsic negative diode 12 may be integrally formed with spatial light modulator 16 on a common substrate. That is, positive intrinsic negative diode 12 may be formed on the same surface of a substrate in which spatial light modulator 16 is formed. When light beam 18 is directed to spatial light modulator 16, positive intrinsic negative diode 12 receives a portion of light beam 18 and converts the portion into a measured signal indicative of the intensity of light beam 18.
Controller circuit 14 controls light beam 18 using positive intrinsic negative diode 12. Controller circuit 14 receives an intensity signal from the light beam 18 and adjusts light beam 18 so that light beam 18 may have a relatively consistent intensity. Controller circuit 14 is described in more detail with reference to
In this particular embodiment, controller circuit 14 includes an integrator circuit. Capacitor 28 is coupled between positive intrinsic negative diode 12 and constant voltage source 30. Capacitor 28 may operate in conjunction with the positive intrinsic negative diode 12 to integrate current through positive intrinsic negative diode 12 over a period of time. When reset switch 32 is opened, voltage increases across capacitor 28 proportional to the instantaneous intensity of the light beam 18. The voltage across capacitor 28 represents an amount of light directed to spatial light modulator 16 and indicates a time averaged intensity of light beam 18. Although the present embodiment describes an integrator circuit implemented with capacitor 28, any suitable type of circuit or integrator circuit may be implemented with positive intrinsic negative diode 12.
Reference 36 may be any suitable device that provides a reference signal that indicates a desired time averaged intensity of light beam 18. In one embodiment, reference 36 includes a digital-to-analog converter (DAC) circuit that converts a digital signal into an analog voltage. The digital-to-analog converter circuit may receive digital signals from digital circuitry of spatial light modulator 16 may regulate light beam 18.
Comparator 34 compares the voltage across capacitor 28 with a reference signal provided by reference 36. Comparator 34 has an output 38 that switches according to comparison of reference signal with the voltage across capacitor 28. Output 38 may be active for a period of time that extends from opening of reset switch 32 to when the voltage across capacitor 28 exceeds the reference signal from reference 36.
Buffer 40 isolates the input impedance of comparator 34 from capacitor 28. Buffer 40 may not be needed if the input impedance of comparator 34 is sufficiently high.
Positive intrinsic negative diode 12 may include a high frequency biasing source 42 and a parasitic capacitance modeled by parasitic capacitor 44. High frequency biasing source 42 causes positive intrinsic negative diode 12 to have a resistance that varies according the light intensity of light beam 18. Parasitic capacitor 44 may be a inherent consequence caused by the junctions of the positive, intrinsic, and negative portions of positive intrinsic negative diode 12.
Modifications, additions, or omissions may be made to light beam control system 10 without departing from the scope of the invention. The components of light beam control system 10 may be integrated or separated. For example, positive intrinsic negative diode 12 and spatial light modulator 16 may be integrally formed on the same surface of a substrate, or may be formed on a different surface or substrate. Moreover, the operations of light beam control system 10 may be performed by more, fewer, or other components. For example, controller circuit 14 may include buffer 40 that buffers the input of comparator 34 from capacitor 28, or comparator 34 may be directly coupled to the terminals of capacitor 28. Additionally, operations of controller circuit 14 may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
A reference voltage plot 54 shows the voltage level of reference 36. In this case, reference 36 remains at a relatively constant level. As time progresses from time t1 to time t2, the capacitor voltage shown by capacitor voltage plot 52 continually increases until it exceeds the reference voltage. At time t2, comparator 34 switches state in which output 38 of comparator 34 becomes inactive and light beam 18 is prevented from illuminating image 24. Output 38 may prevent illumination using any suitable approach. In one embodiment, output 38 may instruct the elements of spatial light modulator 16 to turn off. In another embodiment, power to light source 20 may be turned off.
In act 102, positive intrinsic negative diode 12 receives a portion of light beam 18 modulated by spatial light modulator 16. In one embodiment, positive intrinsic negative diode 12 and spatial light modulator 16 may be formed on the same surface of a substrate such that positive intrinsic negative diode 12 may intercept a portion of light beam 18 directed onto spatial light modulator 16.
In act 104, positive intrinsic negative diode 12 converts the portion of light beam 18 into a measured intensity signal. The measured intensity signal may indicate the instantaneous intensity of light beam 18. In act 106, controller circuit 14 receives the measured intensity signal from positive intrinsic negative diode 12. In one embodiment, controller circuit 14 receives the measured intensity signal as a current level that varies according to the light intensity of light beam 18.
In act 108, controller circuit 14 determines an output signal according to the measured intensity signal and a reference signal from reference 36. In one embodiment, the reference signal is indicative of a desired time averaged intensity of light beam 18. Controller circuit 14 may determine the output signal by comparing the time averaged intensity of light beam 18 with reference 36.
In act 110, controller circuit 14 adjusts light beam 18 according to the output signal. In the example, if the time averaged intensity of the measured intensity signal is less than that indicated by the reference signal, controller circuit 14 may adjust light beam 18 to increase the time averaged intensity of light beam 18. Conversely, if the time averaged intensity of the measured intensity signal is greater than that indicated by the reference signal, controller circuit 14 may adjust light beam 18 to decrease the time averaged intensity of light beam 18.
In one embodiment, controller circuit 14 adjusts light beam 18 by decreasing the amount of time light beam 18 illuminates image 24. For example, controller circuit 14 may turn off the elements of the spatial light modulator 16 or turn off light source 20. In another embodiment, controller circuit 14 adjusts light beam 18 by adjusting the instantaneous intensity of light beam 18. The instantaneous intensity of light source 20 may be adjusted by proportionally adjusting power to light source 20.
The previously described process continues throughout operation of light beam control system 10. When control of light beam 18 is no longer needed or desired the process may be halted in act 112.
Modifications, additions, or omissions may be made to the method without departing from the scope of the invention. The method may include more, fewer, or other acts. For example, digital circuitry of spatial light modulator 16 may adjust the reference signal provided to comparator 34 to adjust the overall intensity of image 24.
In one embodiment, a positive intrinsic negative diode 12 and an associated controller circuit 14 may be provided for each of the reset zones 58. Certain embodiments incorporating a controller circuit 14 and associated positive intrinsic negative diode 12 for each reset zone 58 may provide enhanced control of the image's brightness by individually regulating light beam 18 modulated by each reset zone 58 of spatial light modulator 16.
In the particular embodiment shown, reference 36 provides a common signal to multiple controller circuits 14. In other embodiments, one or more controller circuits 14 may receive reference signals from dedicated references 36. In this manner, intensity of light beam 18 may be individually controlled from each reset zone 58.
Although the present invention has been described with several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, variations, alterations, transformation, and modifications as they fall within the scope of the appended claims.
