Abstract:
The present invention relates an optical three-dimensional coordinate sensor system and method thereof. A plurality of light-emitting modules produce a plurality of light signals, and then a plurality of reflected light signals reflected by an object are received by a plurality of photodetectors. After receiving the reflected light signals, the photodetectors generate a plurality of photocurrents. A plurality of active pixel circuits receive the photocurrents and transform the photocurrents to a plurality of reflective optical voltages. A plurality of differential amplifier circuits (DAC) compare the reflective optical voltages and the background voltages, and then output a plurality of DAC output voltages of the reflected light signals. Afterward, a processing module detects the DAC output voltages and uses an algorithm to calculate the top three of the DAC output voltages to determine the three-dimensional coordinate of the object.

Description:
FIELD OF THE INVENTION 
     The exemplary embodiment(s) of the present invention relates to a sensor system and the method thereof. More specifically, the exemplary embodiment(s) of the present invention relates to an infrared optical three-dimensional coordinate sensor system and the method thereof. 
     BACKGROUND OF THE INVENTION 
     In recent years, the LED technology has big progress in the efficiency of brightness, and many applications for displays appear continuously. Also, the optical proximity sensor (OPS) is commonly used in wireless communications, bio-molecular sciences, environmental monitoring, and displays. The OPS is developed based on the light signal received by the photo-detector (PD) via the reflections of the measured object. The PD transfers the light signal to the electrical signal. By detecting the intensity of the electrical signal, the OPS can calculate the distance of measured object. 
     The conventional OPS is used mostly for switches; however, there are limited applications for OPS. Also, the OPS needs to comply with the specific color or shape to effectively detect the object, and it is easily affected by the ambient light or the dark current, which results in a wrong detection. In addition, the OPS has at most two-dimensional detection range (i.e. single plane detection range). Thus, it can not do a three-dimensional coordinate sensing of an object. 
     SUMMARY 
     A primary object of the present invention is to provide an infrared optical three-dimensional coordinate sensor system and the method thereof, so as to improve the previous drawbacks of the conventional OPS and provide a better three-dimensional coordinate sensor system. 
     According to an object of the present invention, an optical three-dimensional coordinate sensor system is provided, comprising a plurality of light-emitting modules, a plurality of sensing modules, and a processing module. The light-emitting modules emit a plurality of light signals to an object. The sensing modules are formed from a plurality of photodetectors, a plurality of active pixel circuits (APCs), a plurality of sampling circuits, and a plurality of differential amplifier circuits (DACs). The photodetectors absorb a plurality of reflected light signals reflected by the object to generate a plurality of photocurrents. Each of the APCs comprises at least one active transistor within a pixel unit cell; the APCs connected to the photodetectors receive the photocurrents and transform the photocurrents to a plurality of reflective optical voltages. Each of the sampling circuits comprises a sampling transistor and a capacitor; the sampling circuits connected to the APCs sample and store the reflective optical voltages. The DACs connected to the sampling circuits receive the reflective optical voltages. Each of the DACs subtracts the reflective optical voltage from a background voltage and multiply a differential gain to the difference. Then, the DACs output a plurality of DAC output voltages of the reflected light signals. Next, the processing module connected to the sensing modules detects the DAC output voltages and uses an algorithm to calculate the top three of the DAC output voltages to determine the three-dimensional coordinate of the object. 
     To achieve this object, a optical three-dimensional coordinate sensing method according to the present invention comprises the steps of emitting a plurality of light signals to an object by a plurality of light-emitting modules; absorbing a plurality of reflected light signals reflected by the object and generating a plurality of photocurrents by a plurality of photodetectors; receiving the photocurrents and transforming the photocurrents to a plurality of reflective optical voltages by a plurality of active pixel circuits (APCs); sampling and storing the reflective optical voltages by a plurality of sampling circuits; subtracting the reflective optical voltages from a plurality of background voltages and multiplying differential gains to output a plurality of DAC output voltages of the reflected light signals by a plurality of differential amplifier circuits (DACs); and detecting the DAC output voltages and using an algorithm by a processing module to calculate the top three of the DAC output voltages to determine the three-dimensional coordinate of the object. 
     Herein the APC may be a 2-transistor-APC (2T-APC). The 2T-APC comprises a reset transistor, a row select transistor and a storage capacitor. The source of the reset transistor is connected to a Vdd, the drain of the reset transistor is connected to the drain of the row select transistor, and the source of the row select transistor is connected to the storage capacitor. 
     Herein the 2T-APC operates in three modes sequentially: reset, integration, and readout. In the reset mode, the reset transistor is switched ON and pre-charges the node Va to 3.3V. At the same time, the row select transistor is switched ON. In the integration mode, the reset transistor is switched OFF and the node Va drops because of the photo-carriers discharging a photocurrent capacitor C PD . In the readout mode, the row select transistor is switched OFF and an output voltage of the row select transistor is readout. 
     In summary of the aforementioned descriptions, the optical three-dimensional coordinate sensor system and the method thereof according to the present invention feature one or more of the following advantages: 
     (1) The sensing modules have the storage capability; they can reduce the incorrect positioning due to the influence of the background light or charge injection (charge injection). 
     (2) The system and method thereof reduce the cost of the sensor circuit. It only needs fewer APC to reach a larger area of detection. 
     (3) The algorithm significantly shortens the reaction time, thereby increases the speed of reaction to reach the required rapid rate of reaction of a wide range. 
     (4) The system and method thereof achieve low-cost, three-dimensional positioning, and low noise, which is practical for application. 
     With these and other objects, advantages, and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the detailed description of the invention, the embodiments and to the several drawings herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exemplary embodiment(s) of the present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments, but are for explanation and understanding only. 
         FIG. 1  is the architecture of optical proximity sensor; 
         FIG. 2  is a block diagram of the optical three-dimensional coordinate sensor system according to the present invention; 
         FIG. 3  is a space side view of sensor and light source according to the present invention; and 
         FIG. 4  is a relationship of the position of the object and space coordinates. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention are described herein in the context of the optical three-dimensional coordinate sensor system and method thereof. 
     Please refer to  FIG. 1  which is the architecture of the optical proximity sensor (OPS) according to the present invention. As shown, the OPS comprises light-emitting diodes (LEDs)  10  and polymer photo-detectors (PPDs)  12 . The LEDs  10  and the PPDs  12  are disposed side by side in the same plane to form the OPS. Light emitted by the LEDs  10  is reflected from the measured object  11  back onto the PPD pixels. 
     Please refer to  FIG. 2  which is a block diagram of the optical three-dimensional coordinate sensor system according to the present invention. As shown, the readout circuit of the OPS comprises an active pixel circuit (APC)  20 , a sampling circuit  21 , a differential amplifier circuit (DAC)  22  and row decoders. 
     An APC  20  is defined as a sensor that has one or more active transistors within the pixel unit cell. In the embodiment, the 2-transistor-APC (2T-APC)  20  comprises a polymer photodiode (PPD), a reset transistor (M 1 ), a row select transistor (M 2 ) and a storage capacitor. M 1  and M 2  adopt PMOS structure. The 2T-APC  20  operates in three modes:
     (1) Reset mode: The reset transistor (M 1 ) is switched ON and pre-charges the node Va to 3.3V. The 2T-APC  20  with the storage capacitor can increase the electrical charge and storage ability. At the same time, the row select transistor (M 2 ) is switched ON.   (2) Integration mode: After reset, M 1  is switched OFF for an integration period (T t ). During T t , photodiode voltage (Va) drops because of the photo-carriers discharging C PD .   (3) Readout mode: After integration, the M 2  is switched OFF and the V out  is readout. Because the M 2  acts as an ideal switch (V DS2 =0), Va is equal to the output voltage of the M 2 . At the end of integration, the output voltage of the M 2  can be expressed as   

                     I   =     C   ⁢       ⅆ   v       ⅆ   t           ,           (   1   )                   V   out     =       V   DD     -         T   t       C   in       ⁢     I   PD           ,           (   2   )               
where T t  is the integration time and the capacitance C in  represents the photodiode capacitor in parallel with the equivalent capacitance C MOS  of MOS transistors seen at node A and storage capacitor C S  
 
 C   in   =C   PD   +C   gd1   +C   gd2   +C   S .  (3)
 
     Each sampling circuit  21  comprises a sampling transistor (M 3  or M 4 ) and capacitor (CSHR or CSHR 1 ). At first, the LED is switched OFF in the first reset cycle. The reset transistor (M 1 ) is switched ON and pre-charges Va to 3.3V. At the same time, the row select transistor (M 2 ) is switched ON. After reset, M 1  is switched OFF for an integration period (t=t 1 ). During t 1 , PD generates photo-carriers discharging CPD by ΔQ decreasing Va. Before M 2  is switched OFF, V 1  is sampled onto capacitor CSHR by pulsing M 3  to VDD; V 1  is behalf of the background voltage. Next, the LED is switched ON in the second reset cycle. The reset transistor (M 1 ) is switched ON and pre-charges Va to 3.3V. At the same time, the row select transistor (M 2 ) is switched ON. After reset, M 1  is switched OFF for an integration period (t=t 2 ). During t 2 , PD generates photo-carriers discharging CPD by ΔQ decreasing Va. Before M 2  is switched OFF, V 2  is sampled onto capacitor CSHR 1  by pulsing M 4  to VDD; V 2  is behalf of the background voltage with the voltage of reflective light. 
     The differential amplifier circuit (DAC)  22  is connected to the sampling circuits  21  for subtracting V 2  from V 1  and multiplies a differential gain A d  to output the voltage of reflective light V out ; the voltage of reflective light V out  satisfies the following condition:
 
 V   out   =A   d ( V   background   −V   background+reflection ).  (3)
 
     Row decoders are used to generate the signals used to scan rows during readout. The array architecture is assumed to be column-parallel so that an entire row can be read out simultaneously. Each column of the array has a column readout amplifier that generates an analog output voltage proportional to the intensity of the incident light. 
     Please refer to  FIG. 3  which is a space side view of sensor and light source according to the present invention. As shown, the LED  10  is assumed to be a Lambertian emitter and the object to be a Lambertian reflecting surface. For a Lambertian emitter, the radiant flux that is detected by PPD  12  is proportional to cos θ×Ω, where Ω=A PPD  cos θ/[d 2 +(x−x*) 2 +(y−y*) 2 ] is the solid angle spanned by the PPD  12  to the object  11 , d is the distance between the object  11  and the sensor, θ is the angle between the PPD  12  and the object  11 , A PPD  is the area of the PPD  12  pixel and α is a proportionality factor. Putting all together, one obtains the following expression for the photocurrent 
                       I   i     ⁡     (       x   *     ,     y   *     ,   d     )       =         α   ⁢           ⁢     d   2           [       d   2     +       (       x   i     -     x   *       )     2     +       (       y   i     -     y   *       )     2       ]     2       .             (   4   )               
The position of the PPD  12  is (x 1 , y 1 , 0) . . . (x 9 , y 9 , 0) in 3×3 PPD  12  array, and the position of the object  11  is (x*, y*, d). When the object  11  approaches any pixel of array, nine pixels of the PPD  12  generate photocurrent. In addition, the current and the distance of the object  11  are inversely proportional. Thus, (x*, y*, d) and the photocurrent related equations are as follows
 
                             I   i     α       ⁡     [       d   2     +       (       x   i     -     x   *       )     2     +       (       y   i     -     y   *       )     2       ]       =   d     ,           (   5   )                   Define   ⁢           ⁢     K   i       =           I   i     α       ⁢           ⁢     (     i   =     1   ~   9       )         ,     
     ⁢         K   i     ⁡     [       d   2     +       (       x   i     -     x   *       )     2     +       (       y   i     -     y   *       )     2       ]       =   d             (   6   )               And   ⁢     
     ⁢         V     out   ,   i       =           A   d     ⁢     T   t         C   in       ⁢     (     I   i     )         ,             (   7   )                   Define   ⁢           ⁢   β     =       α   ⁢           ⁢     A   d     ⁢     T   t         C   in         ,     
     ⁢       V     out   ,       =         β   ⁢           ⁢     d   2           [       d   2     +       (       x   i     -     x   *       )     2     +       (       y   i     -     y   *       )     2       ]     2       .               (   8   )               
The location of the object  11  (x*, y*, d) will fall around the large output voltage of the PPD  12 . However, a photo-detector can only access a dimension of information, and the point of the space has three dimensions of information. Therefore, the positioning of the sensed object  11  needs three photo-detectors, which generate the largest output signals. The relationship of the position of the object and space coordinates shows in  FIG. 4 . The point of the maximum voltage and the remaining two points form a right triangle in the x-y plane. The sensed object  11  locates in the x-axis or y-axis is determined by the second large voltage. Then, it is necessary to calculate Eq. (9), Eq. (10) and Eq. (11) simultaneously in order to determine the location of the object precisely.
 
                       V     out   ,   largest       =       β   ⁢           ⁢     d   2           [       d   2     +       (       x   1     -     x   *       )     2     +       (       y   1     -     y   *       )     2       ]     2         ,           (   9   )                   V     out   ,   second       =       β   ⁢           ⁢     d   2           [       d   2     +       (       x   2     -     x   *       )     2     +       (       y   2     -     y   *       )     2       ]     2         ,           (   10   )                 V     out   ,   third       =         β   ⁢           ⁢     d   2           [       d   2     +       (       x   3     -     x   *       )     2     +       (       y   3     -     y   *       )     2       ]     2       .             (   11   )               
Use these equations to obtain (x*,y*,d). Finally, make use of the other equation to verify the correctness of the location.
 
     In summary, the optical three-dimensional coordinate sensor system and the method thereof according to the present invention achieve low-cost, three-dimensional positioning, and low noise, which is practical for application. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this invention and its broader aspects. Therefore, the appended claims are intended to encompass within their scope of all such changes and modifications as are within the true spirit and scope of the exemplary embodiment(s) of the present invention.