Abstract:
A phase measurement method is disclosed, which includes inputting a predetermined voltage to the photodiode; receiving an optical signal and transforming into an electrical signal; generating a sampled signal with a signal transforming process; determining whether the amplitude value of the sampled signal in a predetermined range or not; if the amplitude of the sampled signal is not in the predetermined amplitude range, adjusting the predetermined voltage and receiving the optical signal and judging again until the amplitude value falls into the predetermined amplitude range; if the amplitude of the sampled signal is in the predetermined amplitude range, calculating the first phase value; and judging whether the predetermined voltage adjusted or not. If the predetermined voltage has been adjusted, calculating the compensating phase value and the second phase value in accordance with the adjusted predetermined voltage.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is based on, and claims priority from, Taiwan Application Serial Number 95106980, filed Mar. 02, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a distance measurement system, and more particularly to a phase measurement method. 
         [0004]    2. Description of Related Art 
         [0005]    Refer to  FIG. 1 .  FIG. 1  illustrates a conventional phase-shift laser distance measurement system  100 . The emitter  10  emits two optical signals T(t) wherein one of the optical signals T(t) is received by the first receiver  20 A and another of the optical signals T(t) is emitted to the target object  5  to generate a reflective optical signal received by the second receiver  20 B. The optical signal T(t) received by the first receiver  20 A is mixed with the mixed signal H(t) to provide a reference signal Ref(t). The reflective optical signal received by the second receiver  20 B is mixed with the mixed signal H(t) to provide a target signal Sig(t) wherein the mixed signal H(t) might come from a mixer. The first phase detector  30 A detects the phase of the reference signal Ref(t), and the second phase detector  30 B detects the phase of the target signal Sig(t). The processing unit  40  calculates the distance between the target object  5  and the measurement system  100  by the phase difference between the reference signal Ref(t) and the target signal Sig(t). 
         [0006]    In the prior art, the avalanche photodiode (APD) is used to be the photoelectric converter of the first receiver  20 A and the second receiver  20 B such that the received optical signal is converted into a corresponding outputted electric signal. However, the luminous intensity received by the avalanche photodiode may vary with ambient conditions, such as the reflection of the target object surface, the distance, the temperature, the atmosphere etc. Therefore, the amplitude of the corresponding outputted electric signal, generated by the light beam signal received by the avalanche photodiode, is too unstable to measure the distance accurately. 
       SUMMARY 
       [0007]    A phase measurement method is provided. The method includes inputting a predetermined voltage to a photoelectric converter; receiving an optical signal and converting the optical signal into an electrical signal; mixing the electrical signal with a mixed signal to provide an output signal; filtering the output signal to generate an IF (Intermediate Frequency) signal; sampling the IF signal to generate a sampled signal; determining whether the amplitude value of the sampled signal falls within the predetermined amplitude range or not; adjusting the predetermined voltage and re-receiving the optical signal until the amplitude value falls within the predetermined amplitude range when the amplitude value does not fall within the predetermined amplitude range; calculating a first phase value in accordance with the sampled signal when the amplitude value falls within the predetermined amplitude range; determining whether the predetermined voltage is adjusted or not; calculating the compensating phase value in accordance with the adjusted predetermined voltage when the predetermined voltage has been adjusted; and summing the first phase value and the compensating phase value to generate a second phase value. 
         [0008]    A phase measurement circuit including a receiver and a feedback calculator is provided wherein the receiver has a photoelectric converter. The photoelectric converter in the receiver receives an optical signal and converts the optical signal into an electrical signal. The electrical signal is mixed with a mixed signal, generated by a mixer, to generate an output signal wherein the photoelectric converter is in a reverse bias with the predetermined voltage. The feedback calculator calculates a sampled signal with an amplitude value in accordance with the output signal. When the amplitude value does not fall within the predetermined amplitude range, adjusting the predetermined voltage to make the receiver re-receive the optical signal until the amplitude value falls within the predetermined amplitude range; when the amplitude value falls within the predetermined amplitude range, calculating a first phase value in accordance with the sampled signal and compensating the phase value in accordance with whether the predetermined voltage has been adjusted or not. 
         [0009]    A distance measurement system including an emitter, a first phase measurement circuit and a second phase measurement circuit is provided. The emitter emits a reference signal to the first phase measurement circuit and emits an optical signal to the target object. The first phase measurement circuit receives the reference signal to calculate a first phase value. The second phase measurement circuit receives the optical signal reflected by the target object to calculate a second phase value. Therefore, the distance between the distance measurement system and the target object is calculated in accordance with the phase difference between the first phase value and the second phase value. 
         [0010]    The second phase measurement circuit includes a receiver and a feedback calculator wherein the receiver has a photoelectric converter. The receiver is operable to receive the optical signal and convert into an electrical signal. The electrical signal is mixed with a mixed signal to generate an output signal wherein the predetermined voltage initially supplies the photoelectric converter. The feedback calculator calculates a sampled signal with an amplitude value in accordance with the output signal. When the amplitude value does not fall within the predetermined amplitude range, adjusting the predetermined voltage to make the receiver re-receive the optical signal until the amplitude value falls within the predetermined amplitude range; when the amplitude value falls within the predetermined amplitude range, calculating a third phase value in accordance with the sampled signal and compensating the phase value in accordance with whether the predetermined voltage is adjusted or not. 
         [0011]    The feedback calculator calculates a second phase value in accordance with the third phase value and the compensating phase value. Therefore, the distance between the distance measurement system and the target object is calculated by the phase difference between the first phase value and the second phase value. 
         [0012]    These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the embodiments of the invention, which are further described below in conjunction with the accompanying Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
           [0014]      FIG. 1  is a block diagram of a conventional phase-shift laser distance measurement system; 
           [0015]      FIG. 2  is a curve chart exhibiting the relationship between the reverse bias and the gain of photoelectric converter under various temperatures; 
           [0016]      FIG. 3  is block diagram of the embodiment of the phase measurement circuit; 
           [0017]      FIG. 4  is a circuit diagram of the embodiment of the sample unit; 
           [0018]      FIG. 5  is a curve chart exhibiting the relationship between the predetermined voltage and the compensating voltage of the avalanche photodiode; 
           [0019]      FIG. 6  is a curve chart exhibiting the relationship between the predetermined voltage and the compensating phase value of the avalanche photo diode; 
           [0020]      FIG. 7  is a flow chart of the phase measurement method of the present invention; and 
           [0021]      FIG. 8  is a block diagram of the embodiment of the distance measurement system. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0023]    While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the figures, in which like reference numerals are carried forward. 
         [0024]    In general, the photoelectric converter, such as the avalanche photodiode (APD), is served as a receiver of the optical signal transceiver. The photoelectric converter generates a corresponding signal in accordance with the luminous intensity of the received optical signal. A reverse bias is added to the photoelectric converter during the operation. Refer to  FIG. 2 . The curve chart illustrates the relationship between the reverse bias and the gain of photoelectric converter wherein a higher reverse bias has the larger gain. For example, the avalanche photodiode has a reverse bias range from 80V to 140V. The luminous intensity received by the photoelectric converter may be vary with ambient conditions, such as the reflection of the target object surface, the distance, the temperature, the atmosphere etc. such that an error in measurement may occur. Therefore, the present invention provides method of compensating for the phase variation and adjusting the reverse bias to solve the above problem and carry out an accurate measurement. In addition, the reverse bias of the photoelectric converter is a predetermined voltage in the embodiment. 
         [0025]    Refer to  FIG. 3 .  FIG. 3  is block diagram of the embodiment of the phase measurement circuit. A phase measurement circuit  200  includes a receiver  210  and a feedback calculator  220 . The feedback calculator  220  includes a filter  221 , an analog-to-digital converter  223 , a processing unit  225 , a sample unit  227  and a high-voltage generator  229 . 
         [0026]    The receiver  210  includes a photoelectric converter  211  to convert a received optical signal T(t) into an electrical signal wherein the received optical signal T(t) is the laser beam signal emitted by an emitter and reflected by an object. Thus, the electrical signal is mixed with a mixed signal H(t) to generate a corresponding output signal S 1 . 
         [0027]    The feedback calculator  220  calculates a sampled signal S 3  with an amplitude value in accordance with the output signal S 1  from the receiver  210 . When the amplitude value of the sampled signal does not fall within the predetermined amplitude range, adjusting the predetermined voltage supplied to the photoelectric converter  211  to make the receiver  210  re-receive the optical signal T(t) until the amplitude value falls within the predetermined amplitude range. When the amplitude value falls within the predetermined amplitude range, calculating a first phase value in accordance with the sampled signal S 3  and compensating the phase in accordance with whether the predetermined voltage is adjusted or not. The predetermined amplitude range value for the sampled signal S 3  is in the range, but not limited to the range, 0.3V-3.3V. Decreasing the predetermined amplitude range values increases the measurement accuracy but decreases the measurement speed. 
         [0028]    The filter  221 , a band-pass filter, is coupled with the receiver  210  to filter the output signal S 1  generated by the receiver  210  and generates a corresponding IF (Intermediate Frequency) signal S 2 . The frequency of the mixed signal is the central frequency of the band-pass filter, and the predetermined band is, but not limited to, 2 KHz. The analog-to-digital converter  223  is coupled with the filter  221  to sample the IF signal S 2  generated by the filter  221  and generates a corresponding sampled signal S 3 . 
         [0029]    The high-voltage generator  229  is coupled between the processing unit  225  and the receiver  210  to supply the voltage to the photoelectric converter  211  in accordance with the control signal of the processing unit  225 . In the embodiment, the high-voltage generator  229  initially supplies a predetermined voltage V 1  to the photoelectric converter  211 . The sample unit  227  is coupled with the high-voltage generator  229  to sample the outputted voltage from the high-voltage generator  229  and output the sampled voltage value to the processing unit  225 . 
         [0030]    The processing unit  225  is coupled between the analog-to-digital converter  223  and the high-voltage generator  229  to receive the sampled signal S 3  from the analog-to-digital converter  223  and start the phase and gradient calibration so as to generate a corresponding phase value. In the embodiment, the processing unit  225  generates a control signal SC in accordance with the reference list LUT 1  and the amplitude value of the sampled signal S 3  to make the high-voltage generator  229  adjust the outputted voltage. Thus, the reverse bias of the photoelectric converter  211  is modified to alter the gain. In other words, when the received luminous intensity of the photoelectric converter  211  are varied with the ambient conditions, such as the reflection of the target object surface, the distance, the temperature, the atmosphere etc., the outputted voltage generated by the high-voltage generator  229  is modified to carry out accurate measurement. In addition, the processing unit  225  generates a compensating phase in accordance with the reference list LUT 2  and the voltage value of the outputted voltage to compensate the phase difference resulting from the variable reverse bias of the avalanche photodiode  211 . There, phase compensation is achieved. 
         [0031]    Refer to  FIG. 3  and  FIG. 4 .  FIG. 4  is a circuit diagram of the embodiment of the sample unit. The sample unit  227  includes a resistance R 1 , a resistance R 2 , an operational amplifier  231  and an analog-to-digital converter  233 . The sample unit  227  is coupled with a node N 1  to receive the voltage supplied to the photoelectric converter  211 . The resistance R 1  and the resistance R 2  are cascaded between the node N 1  and the ground. The operational amplifier  231  includes a non-negative input, a negative input, and an output wherein the non-negative input is coupled with a node N 2  and the negative input is coupled with the output of the operational amplifier  231 . The analog-to-digital converter  233  is coupled between the output of the operational amplifier  231  and the processing unit  225  to output the sampled voltage signal. 
         [0032]    Refer to  FIG. 5 , the reference list LUT 1  shows the relationship between the predetermined voltage and the compensating voltage in the photoelectric converter  211 . Refer to  FIG. 6 , the reference list LUT 2  shows the relationship between the predetermined voltage and phase difference in the photoelectric converter  211 . In this embodiment, the reference list LUT 1  and the reference list LUT 2  are stored in, but not limited in, the processing unit  255 . However, the reference list LUT 1  and the reference list LUT 2  can be stored in other memory units out of the processing unit  225 . 
         [0033]    Refer to  FIG. 3  and  FIG. 7 .  FIG. 7  is a flow chart of the phase measurement method of the present invention. 
         [0034]    In step S 710 , a predetermined voltage V 1  is inputted to the photoelectric converter  211  to enact the photoelectric converter  211 . 
         [0035]    In step S 712 , an optical signal T(t) is received by the receiver  210  and converted into an electrical signal. The electrical signal is mixed with a mixed signal H(t) to generate an output signal S 1 . In this embodiment, the received optical signal T(t) is reflected by the object or emitted from the emitter. 
         [0036]    In step S 714 , the output signal S 1  is filtered by the filter  221  to generate an IF signal S 2 . The filter  221  is a band-pass filter which can generate the IF signal S 2  with a phase value. 
         [0037]    In step S 716 , the IF signal S 2  is sampled by the analog-to-digital converter  223  to generate a sampled signal S 3  with an amplitude value. 
         [0038]    In step S 718 , the processing unit  225  determines whether the amplitude value of the sampled signal S 3  falls into the predetermined amplitude range or not. In this embodiment, the predetermined amplitude range is, but not limited in, 0.3V-3.3V. Decreasing the predetermined amplitude range values increases the measurement accuracy but decreases the measurement speed. 
         [0039]    In step S 720 , the processing unit  225  adjusts the predetermined voltage V 1  and makes the receiver  210  re-receive the optical signal T(t) until the amplitude value of the sampled signal S 3  falls within the predetermined amplitude range when the amplitude value does not fall within the predetermined amplitude range. In this way, the reverse bias of the photoelectric converter  211  is modified. Therefore, the amplitude value of the sampled signal S 3  is adjusted to fall within the predetermined amplitude range by modifying the outputted voltage of the high-voltage generator  229  when the received optical signal is varied because of the ambient conditions, such as the reflection of the target object surface, the distance, the temperature, the atmosphere etc. 
         [0040]    The processing unit  225  calculates a compensating voltage (ΔV) in accordance with the voltage V 1  received by the photoelectric converter  211  and the reference list LUT 1 , and outputs a corresponding control signal SC. Therefore, the high-voltage generator  229  modifies the voltage V 1  to another voltage V 1 ′ in accordance with the control signal SC. In this embodiment, the voltage V 1 ′ is the sum of the voltage V 1  and the compensating voltage (ΔV). 
         [0041]    Repeat step S 712  to step S 718  to generate an amplitude value of the sampled signal falling within the predetermined amplitude range. For example, the receiver  210  re-receives the optical signal T(t) to convert the optical signal into an electrical signal when the voltage V 1 ′ is supplied to the photoelectric converter  211 . The electrical signal is mixed with the mixed signal H(t) to generate another output signal S 1 ′. The output signal S 1 ′ is filtered by the filter  221  to generate an IF signal S 2 ′. The IF signal S 2 ′ is sampled by the analog-to-digital converter  223  to generate another sampled signal S 3 ′ whose the amplitude value falls within the predetermined amplitude range. 
         [0042]    In step S 722 , the processing unit  225  determines whether the voltage V 1  received by the photoelectric converter  211  has been modified or not. The sample unit  227  samples the IF voltage signal to output the sampled voltage to the processing unit  225  such that the processing unit  225  can determine whether the voltage received by the photoelectric converter  211  has been modified or not. Starting with step S 724  when the voltage received by the photoelectric converter  211  has not been modified, and starting with step S 726  when the voltage received by the photoelectric converter  211  has been modified. In this embodiment, the voltage V 1  has not been modified and the voltage V 1 ′ has been modified. 
         [0043]    In step S 724 , the processing unit  225  calculates a first phase value in accordance with the sampled signal S 3  and terminated without compensation. 
         [0044]    In step S 726 , the processing unit  25  calculates a compensating phase value (Δφ) in accordance with the modified voltage V 1 ′. The processing unit  225  calculates a first phase value in accordance with the sampled signal S 3 ′ and generates a compensating phase value (Δφ) in accordance with the reference list LUT 2  and the voltage value sampled by the sample unit  227 . The phase difference caused by the voltage modification is compensated to correct the phase. Therefore, the processing unit  225  calculates a second phase value by summing up the first phase value and the compensating phase value (Δφ). 
         [0045]    In this embodiment of the present invention, the optical signal is received by the photoelectric converter and converted into an electrical signal. The reverse bias of the photoelectric converter is modified to correct the phase in accordance with the variation between the reverse bias and the gain. Through this method, the measurement circuit calculates an accurate measurement value under variable measurement parameters. 
         [0046]    Refer to  FIG. 8 .  FIG. 8  is a block diagram of the embodiment illustrating the distance measurement system. The distance measurement system  800  includes an emitter  810 , a signal generator  820 , a first phase measurement circuit  830  and a second phase measurement circuit  840 . 
         [0047]    The emitter  810  emits an optical signal T(t) to the target object  5  and the signal generator  820  provides a mixed signal H(t). In this embodiment, the signal generator  820  is a frequency synthesizer. 
         [0048]    The first phase measurement circuit  830  receives the optical signal T(t) from the emitter  810  to calculate a first phase value. The second measurement circuit  840  receives the optical signal reflected from the target object  5  to calculate a second phase value. Therefore, the distance between the distance measurement system  800  and the target object  5  is calculated in accordance with the difference between the first phase value and the second phase value. The phase measurement circuit  200  in  FIG. 3  can be applied to one of the first phase measurement circuit  830  or the second measurement circuit  840 . In this embodiment, the second measurement circuit  840  is the phase measurement circuit  200  in  FIG. 3 . 
         [0049]    The second measurement circuit  840  includes a receiver  210  and a feedback calculator  220 . The receiver  210  includes a photoelectric converter  211  to convert a received optical signal T(t) reflected by the target object  5  into an electrical signal. Thus, the electrical signal is mixed with the mixed signal H(t) to generate an output signal S 1 . The photoelectric converter  211  inputs a predetermined voltage V 1  to provide an initial reverse bias. The feedback calculator  220  calculates a sampled signal S 3  with an amplitude value in accordance with the output signal S 1  from the receiver  210 . When the amplitude value of the sampled signal S 3  does not fall within the predetermined amplitude range, adjusting the predetermined voltage supplying to the photoelectric converter  211  to make the receiver  210  re-receive the optical signal T(t) reflected by the target object  5  until the amplitude value falls within the predetermined amplitude range. When the amplitude value falls within the predetermined amplitude range, calculating a third phase value. Calculating a compensating phase value (Δφ) in accordance with whether the predetermined voltage of the photoelectric converter  211  has been modified or not to start the phase compensation. 
         [0050]    When the predetermined voltage V 1  has been modified, the processing unit  225  calculates the compensating phase value (Δφ) in accordance with the modified voltage V 1 ′ and generates a second phase value by summing up the third phase value and the compensating phase value (Δφ). When the predetermined voltage V 1  has not been modified, the compensating phase value (Δφ) is zero and the second phase value is the same as the third phase value. 
         [0051]    As a result, the feedback calculator  220  calculates the distance between the measurement system  800  and the target object  5  in accordance with the phase difference between the first phase value and the second phase value. The first phase value measurement circuit  830  and the second phase value is generated by the second phase measurement circuit  840 . 
         [0052]    Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. Therefore, their spirit and scope of the appended claims should no be limited to the description of the preferred embodiments contained herein. 
         [0053]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.