Abstract:
An intelligent light source for use with the test of a digital camera module provides a plurality of shapes of light. A fast light pulse is created with turn-on and turn-off transitions less than or equal to one microsecond. Other waveform shapes comprise a ramp and a sinusoid, and all shapes can be made to occur once or repetitively. The magnitude of the light has a range from 0.01 LUX to 1000 LUX, and the ramp has a ramp time that has a range from microseconds to 100 ms. The light comprises of a plurality of colors created by serial connected strings of LED devices, where the LED devices in a string emit the same color. The light emanating from the light source is calibrated using a photo diode and the control of a tester by adjusting offset voltages of a DAC controlling a current through the LED strings.

Description:
RELATED PATENT APPLICATION  
       [0001]     This application is related to U.S. patent application docket number DS04-022, Ser. No. ______, filed on ______, and assigned to the same assignee as the present invention.  
         [0002]     This application is related to U.S. patent application docket number DS04-023, Ser. No. ______, filed on ______, and assigned to the same assignee as the present invention.  
         [0003]     This application is related to U.S. patent application docket number DS04-025, Ser. No. ______, filed on ______, and assigned to the same assignee as the present invention.  
         [0004]     This application is related to U.S. patent application docket number DS04-026, Ser. No. ______, filed on ______, and assigned to the same assignee as the present invention.  
         [0005]     This application is related to U.S. patent application docket number DS04-027, Ser. No. ______, filed on ______, and assigned to the same assignee as the present invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0006]     1. Field of Invention  
         [0007]     The present invention is related to a light source, and in particular to an intelligent light source used to test a digital camera module that is synchronized with the digital camera module.  
         [0008]     2. Description of Related Art  
         [0009]     The digital camera is becoming a ubiquitous device. Not only are digital cameras replacing the traditional film camera, digital camera devices are being used in many other applications, such as small electronic devices, such as PDA (personal data assistant) and cellular phones. With the explosion of cellular phones, the ability to take a picture and then send that picture to another individual using a second cellular phone comes the need to produce inexpensive digital camera modules and efficiently test these modules in large quantities. This is further complicated by the many different module configurations that are emerging as a result of the many different application requirements, including fixed focus, manual focus and automatic focus as well as physical size. Some of these modules are very small and others have signal leads in the form of a flex filmstrip. The testing time for digital camera module, which can have mega-pixel capability, has traditionally been a relatively long process (approximately sixty seconds for a module with 0.3 megapixels) to insure the integrity and picture quality of the camera. Quality testing at a low cost has become the utmost of importance. This necessitates a testing capability that is fast and insures the integrity and specification of the digital camera module while testing a large quantity of modules.  
         [0010]     A patent application, Ser. No. 10/417,316 dated Apr. 16, 2003, is related to miniature cameras and their manufacturing methods that are used as built-in modules in hand held consumer electronics devices such as mobile phones and PDA&#39;s. In a second patent application, Ser. No. 10/434,743 dated May 18, 2003, a test system is described for digital camera modules used as built-in modules for consumer electronics, which performs electrical tests, adjustment of focus and sealing of the lens barrel with glue.  
         [0011]     In addition there are a number of other prior art patents that are directed to testing of digital cameras: US 20040032496A1 (Eberstein et al.) is directed to a method of camera calibration and quality testing; EP 1389878A1 (Bednarz et al.) is directed to a method of camera calibration and testing camera quality; US 20040027456A1 (pierce) directed to the use of calibration targets; EP 1382194A1 (Baer) is directed to dark current subtraction; JP 2003259126 (Keisuke) is directed to removing noise of an image; US 20030146976A1 (Liu) is directed to a digital camera system enabling remote monitoring; JP 2003219436 (Fuminori) is directed to adjustment of a pixel shift camera; US 2003142374 (Silverstein) is directed to calibrating output of an image output device; JP 2003179949 (Hidetoshi) is directed to a luminance level inspection apparatus; JP 2003157425 (Vehvilainen) is directed to improving image quality produced in a mobile imaging phone; JP 2003101823 (Kenichi) is directed to specifying a picture data area; EP 1286553 A2 (Baer) is directed to a method and apparatus for improving image quality; US 20030030648 (Baer) is directed to a method and apparatus for improving image quality in digital cameras; U.S. Pat. No. 6,512,587 (Dilella et al.) is directed to measurement method and apparatus of an imager assembly; US 20030002749 (Vehvilainen) is directed to a method and apparatus for improving image quality; US 20020191973 A1 (Hofer et al.) is directed to a method and apparatus for focus error reduction; WO 2002102060 A1 (Baer) is directed to a method and apparatus for smear in digital images using a frame transfer sensor; JP 2002290994 (Hidetoshi) is directed to a method and apparatus to detect foreign matter on the surface of a lens; JP 200223918 (Yanshinao) is directed to an image inspection device and method for a camera module; JP 2002077955 (Keisuke) is directed to a method and apparatus for evaluating camera characteristics; JP 2001292461 (Keisuke) is directed to a system and method for evaluating a camera; U.S. Pat. No. 6,219,443 B1 (Lawrence) is directed to a method and apparatus for inspecting a display using a low resolution camera; U.S. Pat. No. 6,201,600B1 (Sites et al.) is directed to a method and apparatus for inspection of optically transmissive objects having a lens; U.S. Pat. No. 5,649,258 (Bergstresser et al.) is directed to an apparatus and testing of a camera; EP 0679932 B1 (Kobayashi et al.) is directed to testing an electronically controlled camera; U.S. Pat. No. 5,179,437 ( Katsumi et al.) is directed to an apparatus for color correction of image signals of a color television camera; JP 03099376 (Hiroshi) is directed to the quality of a display screen; U.S. Pat. No. 4,612,666 (King) is directed to a pattern recognition apparatus; and U.S. Pat. No. 4,298,944 Stoub et al.) is directed to a method and apparatus for distortion correction for scintillation cameras  
       SUMMARY OF THE INVENTION  
       [0012]     It is an objective of the present invention to produce a light source in which a pulse of light has a controlled intensity and rise and fall times that are less than a microsecond.  
         [0013]     It is also an objective of the present invention to produce a magnitude of the light source ranging from 0.01 LUX to 1000 LUX.  
         [0014]     It is also an objective of the present invention to synchronize a light pulse with a digital camera module under test.  
         [0015]     It is still an objective of the present invention to control the light pulse as a single pulse or a repetitive pulse.  
         [0016]     It is further an objective of the present invention to vary the shape and intensity of the light source comprising a ramp of light and a sinusoidal shaped light.  
         [0017]     It is further an objective of the present invention to produce a ramp with a ram time ranging from microseconds to 100 ms.  
         [0018]     It is still further an objective of the present invention to produce a light source with a plurality of colors each being controlled for intensity, light shape and repetition.  
         [0019]     It is also still further an objective of the present invention to provide calibration for each color in the light source.  
         [0020]     In the present invention a light source is controlled by a tester for the purpose of testing a digital camera module. The light source is configured from a plurality of serially connected strings of LED (light emitting diodes) devices, each of which produces a light color. There is a plurality of LED strings producing a plurality of colors comprising red, blue, green and infrared. Each LED string produces a different color, and each of the LED strings is powered separately by a current source driven by a DAC (digital to analog converter). The light emanating from the LED strings can be turned on and turned off rapidly with a turn on transition and a turn off transition of 1us or faster. Different pulse shapes are produced comprising a sinusoidal varying light and a light in which the turn-on transition is a ramp of variable length of time. The ramp time is controlled in a plurality of time range than have a maximum ramp time of 100us, 1 ms, 10 ms and 100 ms. The amplitude of the light source is controlled in a plurality of ranges where, for example, the maximum comprise 10 LUX, 100 LUX and 1000 LUX, and the light from the light source can be made to be repetitive or only one pulse.  
         [0021]     A tester provides controls for selecting color, intensity, shape and repetitiveness of the light pulse. Within the tester is a frame grabber function, which synchronizes the light source with a clock of a digital camera under test (MUT). When the light source is turned on, the MUT captures a digital image of the light, and the frame grabber couples the image into a memory of a computational unit within the tester for analysis.  
         [0022]     Data for controlling the DAC is loaded into a data memory (1K×16 bits) and is coupled to a 12-bit DAC under the control of a controller. The controller comprises a FPGA (field programmable gate array), which allows for easy upgrading of the controller operation. The data in the data memory is used to control the light source and is coupled to the DAC, which feeds a V/I converter (voltage to current converter). The V/I converter pulls a current through a selected string of LED devices that turns the resulting light on. The current is controlled such as to produce a fast on-off light pulse or a light having a defined shape, e.g. sinusoidal, ramp or stair step. A particular light shape or pulse can be set to be repetitive.  
         [0023]     A photo diode is used to calibrate the light source and maintain a consistency between the strings of LCD devices that produce the different colors of light. The photo diode signal is coupled to an ADC (analog to digital converter), which couples a digital value of the photo diode signal to the tester. The DAC that controls the current source (V/I converter) for a particular LED string is then adjusted to maintain a similar light intensity between the LED strings that produce the different colors of light. This calibration capability also allows for adjustments resulting from aging of the LED diodes and maintains consistency between the different colors of light produced by the LED strings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     This invention will be described with reference to the accompanying drawings, wherein:  
         [0025]      FIG. 1  is a block diagram of the control of the light source of the present invention,  
         [0026]      FIG. 2  is a diagram of the DAC controlling V/I converter of the present invention with attached calibration DAC converters,  
         [0027]      FIG. 3  is a block diagram of the present invention showing the relationship of the frame grabber, the light source and the digital camera under test,  
         [0028]      FIG. 4  is a schematic diagram of the present invention showing the current source that controls the light emanating from an LED string,  
         [0029]      FIG. 5A through 5G  are waveform diagrams of light produced by an LED string of the present invention,  
         [0030]      FIG. 6  is a flow diagram of the present invention for setup and control of light from an LED string, and  
         [0031]      FIG. 7  is a flow diagram of the present invention for the calibration of light emanating from an LED string.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0032]     In  FIG. 1  is shown is a block diagram of the present invention showing the control of a light source  26 . The light source  26  is contained in a test station used to test a digital camera module (MUT)  27 . A tester  20  provides control to a controller  21  and the tester  20  receives back digital picture data from the MUT  27 . The controller comprises a FPGA (field programmable gate array), which allows easy reconfiguration of the control of the light source and provides loop control to produce repetitive light waveforms. The controller  21  controls a data memory  22  containing the data (16-bits×1K) necessary to control the output of the DAC  24  coupled to the V/I converter and range switch  25 . Data used to control the DAC is loaded into the memory  22  from an USB bus  23 .  
         [0033]     The DAC is a 12-bit digital to analog converter that controls the V/I converter and range switch  25  to provide a current to turn-on the light source  26 . The V/I converter  25  has a current capacity that allows a full-scale light output of the light source for a plurality of light intensity ranges comprising 1000LUX, 100LUX and 10LUX. Each range of light is driven with a 12-bit resolution of the DAC  24 . The 12-bit resolution of the DAC allows the creation of a light intensity of 0.01 LUX in the 10LUX range. The range switch in the V/I converter  25  allows a plurality of maximum range of currents to be produced by the V/I converter  25 , comprising currents of approximately 50 ma, 20 ma, 2 ma and 200ua. The maximum current of 50 ma is dependent only upon the LED devices, which make up the light source; therefore the maximum current is established by the LED device used. The light source is switched on and off by the V/I converter with a rise and the fall time of the light emanating from the light source of approximately 1us or faster.  
         [0034]     Continuing to refer to  FIG. 1 , the V/I converter and range switch  25  drives the light source  26 , which comprises a plurality of serial connected strings of LED devices. Each serial connected string of LED devices produces a different light color comprising red, blue, green and infrared. There are spare strings of LED devices that can be used to repeat the colors used in the light source, or provide additional light colors. A separate DAC  24  and V/I converter  25  drives each LED device string. Any combination of LED device strings can be turned-on, and off, by a plurality of DAC and V/I converters simultaneously. The light source produces a light  30  that is received by a photo diode  28  for the purpose of calibrating the light  30  and maintaining the calibration throughout the life of the LED devices. The calibration includes setting and maintaining the light intensity between the various colors produced by the LED device string for the various light ranges, 1000LUX, 100LUX and 10LUX.  
         [0035]     Continuing to refer to  FIG. 1 , a frame grabber function within the tester  20  synchronizes the light from the light source  26  with the clock of the MUT  27  so that the MUT can capture a digital image of the light  30  that is being turned on and off rapidly by the DAC  24  and the V/I converter  25 . The MUT  27  provides picture data  31 , an Hsync signal  32 , a Vsync signal  33  and a clock signal  34  to the tester  20  for use by the frame grabber. The picture data  31 , which is a digital image of the picture taken by the MUT  27 , is stored in a memory of the computation unit of the test system by the frame grabber. The Hsync signal is the horizontal synchronization signal of the digital image from the MUT  27 , which allows scanning out of the picture data by pixel row, and the Vsync signal  33  is the vertical synchronization signal, which allows the picture data to be scanned out by pixel column. The clock  34  is an internal clock of the MUT  27  that is synchronized with the turning on of the light source to allow capture of an image of the light. The frame grabber in the test system  20  synchronizes the turning on of light source  26  with the clock of the MUT  27  to allow a picture of the light of narrow time duration emanating from the light source to be captured by the MUT.  
         [0036]     In  FIG. 2  is shown calibration digital to analog converters, CDAC 1  ( 41 ) and CDAC 2  ( 42 ) that are used to calibrate the DAC  24 , which is used to drive the V/I converter and range switch  25  to provide current to turn on a light color from a serial connected string of LED devices within the light source  26 . A calibration signal  40  is provided by the tester  20  ( FIG. 1 ). The calibration signal  40  is derived from a measurement by the photo diode  28  and a controlled adjustment by the tester to provide a same calibrated intensity of light for each color. Each color string of LED devices is controlled by a separate combination of a DAC  24  connected to a V/I converter and range switch  25 . The calibration CDAC 1  adjusts the DAC  24  to calibrate the maximum value of a range of light intensity and the CDAC 2  adjusts DAC  24  to calibrate the minimum value of a range of light intensity. There are four intensity ranges and two calibration digital to analog converters CDAC 1  ( 41 ) and CDAC 2  ( 42 ) for each color and each range of light within a color produced by the light source. Each color comprising a string of LED devices is coupled to a separate combination of the DAC  24  and V/I converter  25  resulting in eight calibration digital to analog converters connected to the DAC  24  for each color. An alternative to using calibration digital to analog converters is to perform a software calibration and storing the calibration values in memory.  
         [0037]     In  FIG. 3  is shown a block diagram of the present invention showing the interaction of the frame grabber  50  with the light source  26  and the MUT  27 . When a picture is to be taken with the MUT  27 , the frame grabber  50  synchronizes  52  the turning on of the light source  26  with the clock of the digital camera MUT, which takes the picture of the light  51  emanating from the light source  26 . The speed at which the light  51  from the light source  26  is turned on and off (microseconds) requires that the MUT  27  and the light source  26  be synchronized in order to obtain a valid picture.  
         [0038]     In  FIG. 4  is shown a schematic diagram of the circuitry used to turn on and off a serial connected string of LED devices  60  producing a single color of light. A DAC  24  is coupled to a positive input of a differential amplifier  62  within the V/I converter  25  producing a current I 1 . The differential amplifier  62  is connected in a current follower mode, where the voltage applied to the differential amplifier  62  by the DAC  24  is developed across a resistor R 1   64  when switch S 1   65  is closed. The differential amplifier  62  controls the transistor device  63  to conduct a current I 1  until the voltage across R 1   64  approximately equals the output voltage of the DAC  24  and creating a first range of current. Similarly when switch S 2  is closed (S 1 , S 3  and S 4  open), the voltage across R 2  causes a second range of current, when S 3  is closed (S 1 , S 2  and S 4  open) the voltage across R 3  causes a third range of current, and when S 4  is closed (S 1 , S 2  and S 3  open), the voltage across R 4  causes a fourth range of current.  
         [0039]     Continuing to refer to  FIG. 4 , the resulting current I 1  is pulled from a second current source  62  biased to a voltage Vb, which produces a current I 2 , and the current ID through the string of LED devices  60 , such that I 1 =I 2 +ID. The magnitude of the current ID determines the intensity of light emanating from the LED devices  60 . The serial connected string of LED devices  60  is biased with approximately 24V and is shunted by a capacitor  61  to allow a quick discharge of current flowing through the LED devices  60  when the light is turned off. A Zener diode ZD 1  clamps the voltage of node N 1  to approximately 12 volts to prevent saturation and provide a path for the current I 2  when I 1  is turned off. The purpose of the current  12  from the current source  68  is to force the string of LED devices  60  to quickly and completely turn off by starving the LED devices  60  from a source of current from parasitic impedances and the V/I converter  25 .  
         [0040]     In  FIG. 5A through 5G  are shown various light waveforms produce by the present invention. In  FIG. 5A  is shown a fast light pulse produced by the circuitry in  FIG. 4  in terms of LUX versus time, where a LUX is a unit of illumination equal to one lumen (a unit of light) per square meter. The rise time of the light pulse is t2−t1≦1us, and the fall time is t4−t3≦1us. The steady state time of the light pulse is t3−t4≧0 and is dependent upon the requirements of the test being performed.  FIG. 5B  shows the range of the amplitude of light measured in LUX that is produced by the circuitry of  FIG. 4 . Each of the light pulses  70 ,  71  and  72  has a rise time and a fall time of ≦1us. In the lowest range, a light pulse  70  has a full-scale value is 10 LUX. Using the 12-bit DAC shown in  FIG. 4 , a resolution of 0.01 LUX can be attained. The medium range light pulse  71  has a full-scale value of 100 LUX and the highest range light pulse  72  has a full-scale value of 1000 LUX. Any light amplitude can be chosen within each range  70 ,  71  and  72  between the maximum and minimum value of the range.  
         [0041]     In  FIG. 5C  is shown four linear light ramps  75 ,  76 ,  77 , and  78 . The ramp-time of the ramp with the shortest ramp  75  ranges from approximately 10us to 100us. The ramp-time of the longest ramp  78  ranges from 10 ms to 100 ms, and there are two intermediate ramps  76  and  77  having a ramp time range of 100us to 1 ms and 1 ms to 10 ms, respectively. Any ramp time that falls within the ramps  75 ,  76 ,  77 , and  78  can be created with the circuitry shown in  FIG. 4 .  
         [0042]     In  FIG. 5D  is a sinusoidal shaped light waveform  80 . This sinusoidal waveform can be approximated by a light waveform of small steps  81 . As the step size is reduced, the waveform of the light will approach the ideal shape of the sinusoidal waveform  80 . The average value La of the sinusoidal shaped light and the maximum value Lm can be chosen such that the light emanating from a string of LED devices in the light source  26  never turns off or turns off during a portion of the sinusoidal waveform.  
         [0043]     In  FIG. 5E  is a light waveform, which has a raising ramp  84  and a falling ramp  85 . Similar to the approximation of the sinusoid in  FIG. 5D , the ramps  84  and  85  can be approximate by a series of steps controlled by the DAC  24  and V/I converter  25  shown in  FIG. 4 . The falling ramp can be replaced by a fast turn-off transition  87  forming a ramped light pulse similar to those shown in  FIG. 5C . Similar the approximation of the sinusoid using small light steps, the ideal ramp shape can be approached as the steps  86  become smaller. The ramps cannot become any faster than the transition time of a light pulse rise and fall time shown in  FIG. 5A .  
         [0044]     In  FIG. 5F  is show a repetitive light waveform using the light pulses of  FIG. 5A . The length of the repetitive waveform can be any length that can be accommodated by the total allowable test time of the MUT. Similar to the repetitive waveform of the light pulses shown in  FIG. 5F , a repetitive light waveform of ramps of light is shown in  FIG. 5G . These repetitive light waveforms can be of any light amplitude and time length that can be accommodated by the circuitry of  FIG. 4 . However, there is no fundamental limit to the shape and sizes of the light waveforms presented in  FIGS. 5A, 5B ,  5 C,  5 D,  5 E,  5 F and  5 G exclusive of the laws of physics and the requirements of the particular circuitry used to produce the light for use in the test of the digital camera module of the present invention.  
         [0045]     In  FIG. 6  is shown a flow diagram of the control of a light pulse and waveform produce by the present invention. The repetition of the light is selected  100  by the controller  21  ( FIG. 1 ), which selects a single shape of light or a light waveform repeating that shape for a plurality of cycles. The shape of the light is selected  101 , which comprises a pulse with fast rise and fall times, and a ramp and a sinusoid or stepped approximations thereof. The shape of the light is controlled by data stored in the data memory  22  ( FIG. 1 ). The intensity of light, measured in LUX, is set for each color of light to be selected  102 . The intensity can range from a maximum of approximately 1000 LUX to approximately the finest resolution, 0.01LUX, of the lowest intensity range and is controlled by the amount of current coupled by the voltage to current converter  25  to a serial connected string of LED devices in the light source  26  ( FIG. 1 ). A light color is selected  103 , which selects one or any combination of serial connected strings of LED devices contained within the light source  26 . Each individual string of LED devices is separately powered from a voltage to current converter  25  and each individual string of LED devices provides a light of a same color, comprising the colors of red, blue, green and infrared. A selection of a combination of a plurality of LED device strings will produce a composite light having a composite color of the selected LED device strings.  
         [0046]     Continuing to refer to  FIG. 6 , the light source is synchronized with the clock of the digital camera module under test (MUT)  104  using a frame grabber function within the tester. This allows the MUT to capture a digital image  105  of the light, which is turned on and off in microseconds, and transfer the captured digital image to a computational unit in the tester. If a change in light color is required, then a next light color is selected  106 , and the subsequent process steps  103  through  106  are repeated. If no color change is required  107 , a next intensity setting of the light is selected  108 , and the subsequent process steps  102  through  108  are repeated. If no additional change in light intensity is required  109  and if a light shape change is required  110 , a next light shape is selected  101  and the subsequent process steps  101  through  110  are repeated. If no additional shape change  111  is required and if the repetition of a particular light set up is required to be changed for the next test of the MUT, a next repetition is selected  112  and the subsequent process steps  100  through  112  are repeated. If the no additional repetition is required of the particular light set up  113 , the process ends, It should be noted that repetition as used here relates to the selection of a single pulse or a repetition of a single pulse, where the single pulse is a fast pulse ( FIG. 5A ), a ramp ( FIGS. 5C and 5E ), and a sinusoid ( FIG. 5D ), and the repetition of a single pulse is shown in  FIGS. 5D, 5F  and  5 G.  
         [0047]     In  FIG. 7 a  process flow for the calibration of the light source of the present invention is shown. A light color is selected  120 , which selects a serial connected string of LED devices, where all LED devices in the selected string produce the same color of light. A light intensity of the selected string of LED devices is selected  121  and the light of the selected string is turned on  122  by pulling a current through the serial connected LED devices using the voltage to current converter  25  ( FIG. 1 ). The light emanating from the LED string is measured  123  using a photo diode and the light is calibrated  104  by adjusting the current flowing through the LED string until the photo diode measures a predetermined calibrated value. The calibration digital to analog converters, CDAC 1  and the CDAC 2  ( FIG. 2 ), under the control of the tester  20  ( FIG. 1 ) are used to adjust the DAC  24  ( FIG. 2 ) until the photo diode measures the predetermined calibration value. If the calibration of another light intensity of the same color of light is required  125 , the next intensity of light is selected  121  and the subsequent process steps  122  through  125  are repeated. If no additional light intensity settings for the light color are required and if the last light color has not been calibrated  127 , a next light color is selected  120  and subsequent process steps  121  through  127  are repeated. If the last light color has been calibrated  128 , the process ends.  
         [0048]     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.