Abstract:
Method and device for light signal reception. This device can selectively execute a comparison mode or a gain mode. In the device, a transmitter transmits a light beam to a target. A receiver receives the light beam reflected from the target and outputs a corresponding received signal. In the comparison mode, it is determined whether a pulse in the received signal is higher than a reference voltage level. When the pulse is higher the reference voltage level, the pulse is outputted. The gain mode is executed and the received signal is amplified and output when no pulse is higher than the reference voltage level in the received signal. The method and device of the present invention can be applied to range finders, the comparison mode is executed during short-distance measurement and the gain mode is executed during long-distance measurement thereby measuring the target distance from several meters to a thousand meters.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to light signal receiving method, and more particularly, the invention relates to a light signal receiving method and device thereof applicably to range finders, and capable of both long-distance measurement and short-distance measurement. 
   2. Description of the Related Art 
   In conventional pulse laser range finders, current noise is produced during measurement. After conversion into time domain, the location of the current noise is at location distance 7˜10 meters from the ranger finders meaning noise and true signals cannot be differentiated between when the distance from the target to the range finder is within 10 meters. To address this problem, small signal noise can be eliminated using a high reference voltage level provided by a single comparator. However, this method also eliminates the small signal pulse needed for long distance measurement, hence a long distance target cannot be measured. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide method and device for light signal reception applicable to range finders, capable of both long-distance measurement and short-distance measurement. 
   According to the above mentioned object, the present invention provides a method for light signal reception. First, a first light beam is transmitted to a target. The light beam reflected from the target is then received and a corresponding first received signal is output by a receiver. It is then determined whether a pulse in the first received signal is higher than a reference voltage level. When the pulse is higher than the reference voltage level, the pulse is output. A second light beam is transmitted to the target, and a second received signal is output according to the light beam reflected from the target again, when no pulse in the first received signal is higher than the reference voltage level. Finally, the second received signal is amplified non-linearly and output. 
   According to the above mentioned object, the present invention also provides another method for light signal reception. In this method, a comparison/gain device is applied to execute a comparison mode and a gain mode. First, the comparison/gain device executes the comparison mode, and a light beam is transmitted to a target by a transmitter. The light beam reflected from the target is then received and a first received signal is output by a receiver. In the comparison mode, the comparison/gain device compares pulses in the first received signal with a reference voltage level, and outputs the pulse higher than the reference voltage level. In this method, the gain mode is executed when all pulses in the first received signal are smaller than the reference voltage level. In the gain mode, the transmitter transmits another light beam to the target again, and the light beam reflected from the target is received and a second received signal is output by the receiver. Finally, the comparison/gain device amplifies and outputs the second received signal non-linearly. 
   According to the above mentioned object, the present invention also provides another method for light signal reception. In this method, a channel selection circuit is applied to select a comparison circuit or a gain circuit. First, the channel selection circuit selects the comparison circuit, and a light beam is transmitted to a target by a transmitter. The light beam reflected from the target is then received and a first received signal is outputted by a receiver. The comparison circuit compares pulses in the received signal with a reference voltage level, and outputs the pulse higher than the reference voltage level. In this method, the gain mode is executed when all pulses in the received signal are smaller than the reference voltage level. Consequently, the transmitter again transmits a light beam to the target, and the light beam reflected from the target is received and a second received signal is output by the receiver. Finally, the comparison/gain device amplifies and outputs the second received signal non-linearly. 
   The feature of the present invention resides in that the comparison mode is applied to measure the short distance target, and the gain mode is applied to measure the long distance target. The operation mode of the comparison/gain device is switched by a mode switching circuit. 
   Another feature of the present invention resides in that the comparison circuit is applied to measure the short distance target, and the gain circuit is applied to measure the long distance target. In this case, the comparison circuit and the gain circuit are electrically connected to a processor selectively by a channel selection circuit. Therefore, the light signal receiving method of the present invention enables measurement of the target distance from several meters to thousand meters. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by the subsequent detailed description and examples with reference made to the accompanying drawings, wherein: 
       FIG. 1  is a flowchart of the light signal reception method according to the present invention; 
       FIG. 2  is another flowchart of the light signal reception method according to the present invention; 
       FIG. 3   a  is a block diagram of light signal reception device according to the flowchart shown in  FIG. 1 ; 
       FIG. 3   b  is another block diagram of light signal receiving device according to the flowchart shown in  FIG. 2 ; 
       FIG. 4   a  is a timing chart output from the comparison circuit; 
       FIG. 4   b  is a timing chart output from the gain circuit; 
       FIG. 5  is a circuit diagram of the channel selection circuit shown in  FIG. 3   a;    
       FIG. 6   a  is a timing chart output from the comparison/gain device; 
       FIG. 6   b  is another timing chart output from the comparison/gain device; and 
       FIG. 7  is a circuit diagram of the light signal receiving device shown in  FIG. 3   b.    
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The method and device for light signal reception of the present invention applicable to range finders is described in the following. 
     FIG. 1  is a flowchart of the method for light signal reception according to the present invention. First, a channel selection circuit is set to enable a comparison circuit to compare a received signal and a reference voltage level in step S 102 . The reference voltage level is slightly higher than the spike noise voltage. The spike noise is produced simultaneously when the pulse signal transmitted by a transmitter. Consequently, the spike noise is eliminated by the comparison circuit. Next, in step S 104 , the transmitter transmits a pulse light beam to a target, and the target reflects the pulse light beam. The pulse light beam reflected from the target is received and a first received signal is output to the comparison circuit and the gain circuit by a receiver in step S 106 . In step S 108 , the comparison circuit then determines whether a pulse is higher than the reference voltage level, in the first received signal. Next, in step S 110 , the comparison circuit outputs pulses higher than the reference voltage level to a processor when the received signal includes pulses higher than the reference voltage level. Consequently, the flight distance of the pulse light beam between the target and the range finder can be calculated by processing the pulse higher than the reference voltage level with a processor. In step S 112 , the gain circuit is enabled by the channel selection circuit to process another pulse light beam when no pulse is higher than the reference voltage level in the first received signal. Next, in step S 114 , the gain circuit amplifies a second received signal. Finally, in step S 116 , the second received signal is amplified and output to the processor for calculation of the flight distance of the pulse light beam between the target and the range finder. 
     FIG. 2  is flowchart of another method for light signal reception according to the present invention. First, in step S 202 , a mode switching circuit sets a comparison/gain device to a comparison mode to compare a received signal and a reference voltage level. Next, in step S 204 , the transmitter transmits a pulse light beam to a target, and the target reflects the pulse light beam. The pulse light beam reflected from the target is received and a first received signal is output to the comparison/gain device by a receiver in step S 206 . In step S 208 , the comparison/gain device then determines whether the pulse in the first received signal is higher than the reference voltage level. Next, in step S 210 , the comparison/gain device outputs the pulse higher than the reference voltage level to a processor when the first received signal includes pulses higher than the reference voltage level. Consequently, the flight distance of the pulse light beam between the target and the range finder can be calculated by processing the pulse higher than the reference voltage level with a processor. In step S 212 , the comparison/gain device is switched to gain mode to process another pulse light beam when no pulse in the first received signal is higher than the reference voltage level. Next, in step S 214 , the comparison/gain device amplifies a second received signal in gain mode. Finally, in step S 216 , the second received signal is amplified and output to the processor to calculate the flight distance of the pulse light beam between the target and the range finder. 
     FIG. 3   a  is a block diagram of light signal reception device according to the flowchart shown in  FIG. 1 . As shown in  FIG. 3   a , the light signal receiving device  300  includes a transmitter  302 , a receiver  304 , a comparison circuit  306 , a gain circuit  308  and a channel selection circuit  310 . The transmitter  302  transmits pulse light beams to a target, and the target reflects the pulse light beams. The receiver  304  receives the pulse light beams reflected from the target, and outputs corresponding received signals to the comparison circuit  306  and the gain circuit  308 . 
   The comparison circuit  306  has a reference voltage level V ref . The reference voltage level is slightly higher than spike noise voltage level. The spike noise is produced simultaneously when pulse signal is transmitted from the transmitter  302 . Consequently, the spike noise is eliminated by the comparison circuit  306 .  FIG. 4   a  is a timing chart output from the comparison circuit  306 . As shown in  FIG. 4   a , the signal  321  is a pulse signal transmitted to the target from the transmitter  302  at time T 0 . The received signal  322  has a spike noise  325  after time T 0 . The comparison circuit  306  receives the received signal  322  and outputs the signal  323 . Namely, the signal  323  is the output wave of the comparison circuit  306  after receiving the received signal  322 . In the comparison circuit  306 , pulses smaller than the reference voltage level V ref  can be eliminated when the distance between the target and the range finder is within 30 meters. Consequently, the signal  323  only includes pulse  326  without spike noise  325 . The pulse light beam reflected from the target can maintain considerable energy intensity if the distance between the target and the range finder is within 30 meters exactly. Thus, the received signal  322  output from the receiver  304  may has a target pulse  324  higher than the reference voltage level V ref . 
   Initially, the channel selection circuit  310  connects to the comparison circuit  306  such that the signal  323  output from comparison circuit  306  can be transferred to a processor  400 . Consequently, the processor  400  determines whether a reflected pulse light beam from the target is received by the receiver  304  during time T a , and calculates the distance between the target and the range finder. The processor  400  enables the channel selection circuit  310  to connect to the gain circuit  308  when the channel selection circuit  310  has no output or the processor  400  cannot obtain the distance between the target and the range finder. 
   The gain circuit  308  has a feedback voltage level V feedback , wherein the feedback voltage level V feedback  is provided from the output of the gain circuit  308 , and the feedback voltage level V feedback  is smaller than the reference voltage level V ref . The gain circuit  308  amplifies pulses therethrough non-linearly.  FIG. 4   b  is a timing chart output from the gain circuit  308 . The flight time of pulse light beam between the target and the range finder would exceed time T a  when the distance between the target and the range finder exceeds 30 meters. As shown in  FIG. 4   b , the signal  341  is a pulse signal transmitted to the target from the transmitter  302  at time T 0 . The received signal  342  has spike noise  346  in the proximity of time T 0 , and the pulses  349 ,  345  and  350  occur in the received signal sequentially at time T′ 1 , T′ 2  and T′ 3 . The pulse  349  is eliminated by the gain circuit  308  because the peak voltage of the pulse  349  is smaller than the feedback voltage level V feedback  when the received signal  342  goes through the gain circuit  308 . The pulses  345  and  350  and spike noise  346  are amplified non-linearly by the gain circuit  308 . The gain circuit  308  receives the received signal  342  and outputs the signal  343 . Namely, the signal  343  is the output wave of the gain circuit  308  after receiving the received signal  342 . The square waves  348 ,  347  and  351  are amplification of the spike noise  346  and the pulses  345  and  350 , wherein the square waves  348 ,  347  and  351  have the same peak voltage level. The signal  343  output from gain circuit  308  can be transferred to the processor  400  to calculate the distance between the target and the range finder. In the present invention, the processor  400  accumulates the amplified signal  343  corresponding to the pulse light beams by statistical operation so as to distinguish between the pulse light beam reflected from the target and environment light. During the statistical operation, the processor  400  eliminates the square wave produced before time Ta automatically, such as square wave  348 , and calculates the signal  344 . 
     FIG. 5  is a circuit diagram of the channel selection circuit shown in  FIG. 3   a . As shown in  FIG. 3   a , the channel selection circuit includes NAND gates  602 ,  604 ,  606  and  608 . The NAND gate  602  has two input terminals I 602   a  and I 602   b , and an output terminal O 602 , wherein the input terminal I 602   a  is coupled to a first channel input terminal  610 , and the input terminal I 602   b  is coupled to the channel selection signal input terminal  614 . The NAND gate  604  has two input terminals I 604   a  and I 604   b  coupled to the channel selection signal input terminal  614 , and an output terminal O 604 . The NAND gate  606  has two input terminals I 606   a  and I 606   b , and an output terminal O 606 , wherein the input terminal I 606   a  is coupled to a second channel input terminal  612 , and the input terminal I 606   b  is coupled to the output terminal O 604  of the NAND gate  604 . 
   The NAND gate  608  has two input terminals I 608   a  and I 608   b , and an output terminal O 608 , wherein the input terminal I 608   a  is coupled to the output terminal O 602  of the NAND gate  602 , the input terminal I 606   b  is coupled to the output terminal O 604  of the NAND gate  606 , and the output terminal O 608  serves as the output terminal  616  of the channel selection circuit. 
   The first channel input terminal  610  is coupled to the gain circuit  308  and the second channel input terminal  612  is coupled to the comparison circuit  306  as shown in  FIG. 3   a . The channel selection circuit  310  connects the first channel input terminal  610  to the gain circuit  308  or connects the second input terminal  612  to the comparison circuit  306  according to the channel selection signal at the channel selection input terminal  614 . The output terminal  616  of channel selection circuit  310  is coupled to a processor  400  to estimate distance between the target and the range finder by the output signal through the output terminal  608 . 
     FIG. 3   b  is another block diagram of light signal receiving device according to the flowchart shown in  FIG. 2 . As shown in  FIG. 3   b , the light signal receiving device  300  includes a transmitter  302 , a receiver  304 , a mode switching circuit  311  and a comparison/gain device  313 . The transmitter  302  transmits pulse light beams to a target, and the target reflects the pulse light beams. The receiver  304  receives the pulse light beams reflected from the target, and outputs corresponding received signals to the comparison/gain device  313  through the mode switching circuit  311 . 
   Initially, the range finder using the light receiving device assumes that the distance between the target and the device is within 30 meters. The mode switching circuit  311  sets the comparison/gain device to operate in a comparison mode, and provides a reference voltage V ref  to the comparison/gain device  313 . Thus, the received signal output from the receiver  304  is transferred to the comparison/gain device  313  operating in the comparison mode through the mode switching circuit  311 . The mode switching circuit  311  enables comparison/gain device  313  to operate in a gain mode and to process the received signal output from the receiver  304  when the distance between the range finder and the target cannot be measured in the comparison mode. During operation in comparison mode, the mode switching circuit  311  provides a reference V ref  to the comparison/gain device  313 . 
   The channel selection circuit  310  connects to the comparison circuit  306  such that the signal  323  output from comparison circuit  306  can be transferred to a processor  400 . Consequently, the processor  400  determines whether a reflected pulse light beam from the target is received by the receiver  304  during time T a , and calculates the distance between the target and the range finder. The processor  400  enables the channel selection circuit  310  to connect to the gain circuit  308  when the channel selection circuit  310  has no output or the processor  400  cannot obtain the distance between the target and the range finder. The reference voltage level V ref  is slightly higher than spike noise. The spike noise is produced when pulse signal transmitted from the transmitter  302 . Consequently, the spike noise can be eliminated by the comparison/gain device  313 .  FIG. 6   a  is a timing chart output from the comparison/gain device. 
   As shown in  FIG. 6   a , the signal  621  is a pulse signal transmitted to the target from the transmitter  302  at time T 0 . The received signal  622  has a spike noise  325  after time T 0 . The comparison/gain device  313  receives the received signal  622  and outputs the signal  623 . Namely, the signal  623  is the output wave of the comparison/gain device  313  after receiving the received signal  622 . In the comparison mode  312 , the pulses smaller than the reference voltage level V ref  can be eliminated by the comparison/gain device  313  when the distance between the target and the range finder is within 30 meters. Consequently, the signal  623  only includes pulse  624  without spike noise  625 . The pulse light beam reflected from the target can maintain considerable energy intensity if the distance between the target and the range finder is within 30 meters exactly. Thus, the received signal  622  output from the receiver  304  may have a target pulse  624  higher than the reference voltage level V erf . 
   Initially, the mode switching circuit  311  enables the comparison/gain device  313  to operate in a comparison mode  312  and to output the signal  623  to a processor  400 . Consequently, the processor  400  determines whether a reflected pulse light beam from the target is received by the receiver  304  during time T a , and calculates the distance between the target and the range finder. The processor  400  enables the comparison/gain device  313  to operate in a gain mode  314  when the comparison/gain device  313  has no output or the processor  400  cannot obtain the distance between the target and the range finder. 
   In the gain mode  314 , the comparison/gain device  313  has a feedback voltage level V feedback , wherein the feedback voltage level V feedback  is provided from the output of the comparison/gain device  313 , and the feedback voltage level V feedback  is smaller than the reference voltage level V ref . The comparison/gain device  313  gains the pulses therethrough non-linearly in the gain mode  314 .  FIG. 6   b  is a timing chart output from the comparison/gain device  313 . The flight time of pulse light beam between the target and the range finder will exceed time T a  if the distance between the target and the range finder exceeds 30 meters. As shown in  FIG. 6   b , the signal  641  is a pulse signal transmitted to the target from the transmitter  302  at time T 0 . The received signal  642  has a spike noise  646  in the proximity of time T 0 , and the pulses  649 ,  645  and  650  occur in the received signal at time T′ 1 , T′ 2  and T′ 3  sequentially. The pulse  649  is eliminated by the comparison/gain device  313  because the peak voltage of the pulse  649  is smaller than the feedback voltage level V feedback  when the received signal  642  goes through the comparison/gain device  313 . The pulses  645  and  650  and the spike noise  646  are amplified non-linearly by the comparison/gain device  313 . The comparison/gain device  313  receives the received signal  642  and outputs the signal  643 . Namely, the signal  643  is the output wave of the comparison/gain device  313  after receiving the received signal  642 . The square waves  648 ,  647  and  651  are amplification of the spike noise  646  and the pulses  645  and  650 , wherein the square waves  648 ,  647  and  651  have the same peak voltage level. The signal  643  output from comparison/gain device  313  is transferred to the processor  400  for calculation of the distance between the target and the range finder. In the present invention, the processor  400  accumulates the amplified signal  643  corresponding to the pulse light beams by statistical operation so as to distinguish between the pulse light beam reflected from the target and environment light. During the statistical operation, the processor  400  eliminates the square wave produced before time Ta automatically, such as square wave  648 , and calculates the signal  644 . 
     FIG. 7  is a circuit diagram of the light signal receiving device shown in  FIG. 3   b . As shown in  FIG. 7 , the light signal receiving device includes a photoelectric detector D 401 , amplification circuit AP, a mode switching circuit MS and a comparison/gain device U 401 . The photoelectric detector D 401  receives the light beams reflected from the target, and outputs corresponding received signals to the amplification circuit AP. The amplification circuit AP amplifies and outputs the received signals to the comparison/gain device U 401 . The operating mode of the comparison/gain device U 401  is switched by the mode switching circuit MS. The mode switching circuit MS provides a reference voltage V ref  to the terminal  1  of the comparison/gain device U 401  when the comparison/gain device U 401  is switched to operate in comparison mode. Consequently, the comparison/gain device estimates the pulses smaller than the reference voltage level V erf  in the received signal and outputs only the pulses higher than the reference voltage level V erf  in the received signal. Typically, the mode switching circuit MS provides a reference voltage level V ref  to the comparison/gain device U 401  and enables the comparison/gain device U 401  to operate in comparison mode. The mode switching circuit MS switches the comparison/gain device U 401  to operate in a gain mode  314  when the comparison/gain device U 401  has no output or the processor cannot obtain the distance between the target and the range finder by processing the peak voltage level from the comparison/gain device U 401 . At this time, the mode switching circuit MS stops to provide the reference voltage level to the terminal  1  of comparison/gain device U 401 . The terminal  1  receives a feedback voltage level V feedback  from of the comparison/gain device U 401  when the comparison/gain device U 401  is switched to operate in gain mode. Consequently, the pulses smaller than the feedback voltage level in the received signal can be eliminated in the gain mode, and the remaining pulses in the received signal are amplified non-linearly by the comparison/gain device U 401 . 
   It should be noted that in the above embodiment the range finder is operated in short-distance mode when the target distance from the range finder is within 30 meters, it is to be understood that the invention is not limited to the disclosed embodiments. This distance, however, can be adjusted by the range finder, and different range finders can define different distances to operate in short-distance mode. 
   While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.