Abstract:
A synchronizing circuit synchronizes a predetermined code with first and second codes different in phase, include: a code generating part outputting phase-shifted code shifted in phase by a predetermined number of chips from the predetermined code; a first correlation detecting part detecting a correlation between the phase-shifted code from the code generating part and the first code; a second correlation detecting part detecting a correlation between the phase-shifted code from the code generating part and the second code; and a code shifting part shifting the phase of the phase-shifted code from the code generating part by a predetermined number of chips according to the detection results of the first and second correlation detecting parts.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a synchronizing circuit which renders a synchronization between externally provided codes and internal codes. 
   2. Description of the Related Art 
     FIG. 1  shows a block configuration of one exmaple of a GPS receiving apparatus in the related art. 
   The GPS receiving apparatus  1  shown in the figure includes a receiving antenna  3 , a receiving unit  4 , an information processing device  5  and a display device  5 . 
   The receiving antenna  2  receives GPS signals from GPS satellites 2-1 through 2-n. The GPS signals are signals of 1575.42 MHz. The GPS signals received by the receiving antenna  2  are provided to the receiving unit  4 . 
   The receiving unit  4  extracts C/A codes (pseudo-random codes) from the GPS signals, and outputs data according to time difference between different C/A codes. The data output from the receiving unit  4  is provided to the information processing device  5 . 
   The information processing device  5 , according to the output data of the receiving unit  4 , obtains information of latitude, longitude, altitude, time and so forth. The information processing device  5 , accordintg to the thus-obtained information, drives the display device  6 . The display device  6  displays the information of latitude, longitude, altitude, time and so forth obtained by the information processing device  4 . 
   The receiving unit  4  will now be described. 
     FIG. 2  shows a block configuration of the receiving unit  4  shown in FIG.  1 . 
   The receiving unit  4  includes a radio-frequency circuit  11 , a receiving circuit  12 , a CPU  13  and a RAM  14 . 
   A received signal is provided to the radio-frequency circuit  11  from the antenna  3 . The radio-frequency circuit  11  renders frequency conversion on the thus-provided received signal into a signal in a predetermined frequency band. 
     FIG. 3  shows a block configuration of the radio-frequency circuit  11 . 
   The radio-frequency circuit  11  includes frequency converting parts  21  and  22 , and an oscillating circuit  23 . An oscillation signal of 18.414 MHz is provided to the oscillating circuit  23  from the receiving circuit  12 . The oscillating circuit  23  includes a PLL (Phase Locked Loop) circuit, generates an oscillation signal of 1555.983 MHz from the thus-provided oscillation signal of 18.414 MHz, and provides the thus-generated signal to the frequency converting part  21 . 
   The received signal having a carrier frequency of 1575.42 MHz is provided to the frequency converting circuit  21  from the antenna  3 , and also, the oscillation signal of 1555.983 MHz is provided to the frequency converting circuit  21  from the oscillating circuit  23 . The frequency converting part  21  multiplies the received signal with the oscillation signal of 1555.983 MHz, and converts the carrier frequency of the received signal into 19.437 MHz. 
   The received signal having thus undergone the frequency conversion by the frequency converting circuit  21  is provided to the frequency converting circuit  22 . The oscillation signal of 18.414 MHz is provided to the frequency converting circuit  22  from the receiving circuit  12 . The frequency converting circuit  22  multiplies the received signal from the frequency converting circuit  21  with the oscillation signal from the receiving circuit  12 , and converts the received signal into a signal having a carrier frequency of 1.023 MHz. The signal obtained through the conversion by the frequency converting circuit  22  is provided to the receiving circuit  12 . 
   The receiving circuit  12  extracts a satellite code according to the signal provided from the radio-frequency circuit  11 . 
     FIG. 4  shows a block configuration of the receiving circuit  12 . 
   The receiving circuit  12  includes a C/A-code generating circuit  31 , multipliers  32  through  37 , an oscillating circuit  38 , a first detecting circuit  39 , a second detecting circuit  40 , a third detecting circuit  41  and a fourth detecting circuit  42 . 
   The signal from the radio-frequency circuit  11  is provided to the multipliers  32  and  33 . The multipliers  32  and  33  are connected to the oscillating circuit  38 . The oscillating circuit  38  provides an oscillation signal accordintg to a carrier frequency of an I-signal to the multiplier  32 , and provides an oscillation signal accordintg to a carrier-frequency of a Q-signal to the multiplier  33 . The phase of the oscillating circuit  38  is controlled by a control signal from the CPU  13 . 
   The C/A-code generating circuit  31  generates  3  types of C/A codes in timing according to the control signal from the CPU  13 . The three types of C/A codes are a 0-chip delayed C/A code without delay, a −½-chip delayed C/A code having a delay of −½ chip from the 0-chip delayed C/A code, and a +½-chip delayed C/A code having a delay of +½ chip from the 0-chip delayed C/A code. The term ‘chip’ is a special term in the GPS technical field, and means a unit of a signal when the signal is divided in time axis. 
   The multiplier  32  multiplies the signal from the radio-frequency circuit  11  with the occultation signal from the oscillating circuit  38 , and extracts the I-signal. The multiplier  33  multiplies the signal from the radio-frequency circuit  11  with the occultation signal from the oscillating circuit  38 , and extracts the Q-signal. 
   The I-signal extracted by the multiplier  32  is provided to the multipliers  34  through  36 . The I-signal is provided to the multiplier  34  from the multiplier  32 , and, also, the −½-chip delayed C/A code is provided to the multiplier  34  from the C/A-code generating circuit  31 . The multiplier  34  multiples the I-signal with the −½-chip delayed C/A code. 
   The I-signal is provided to the multiplier  35  from the multiplier  32 , and, also, the 0-chip delayed C/A code is provided to the multiplier  35  from the C/A-code generating circuit  31 . The multiplier  35  multiples the I-signal with the 0-chip delayed C/A code. 
   The I-signal is provided to the multiplier  36  from the multiplier  32 , and, also, the +½-chip delayed C/A code is provided to the multiplier  36  from the C/A-code generating circuit  31 . The multiplier  36  multiples the I-signal with the +½-chip delayed C/A code. 
   The Q-signal is provided to the multiplier  37  from the multiplier  33 , and, also, the 0-chip delayed C/A code is provided to the multiplier  37  from the C/A-code generating circuit  31 . The multiplier  37  multiples the Q-signal with the 0-chip delayed C/A code. 
   The multiplication result of the multiplier  34  is provided to the first detecting circuit  39 . The multiplication result of the multiplier  35  is provided to the second detecting circuit  40 . The multiplication result of the multiplier  36  is provided to the third detecting circuit  41 . The multiplication result of the multiplier  37  is provided to the fourth detecting circuit  42 . 
   The first detecting circuit  39  counts, from the multiplication result of the multiplier  34 , chips in disagreement between the −½-chip delayed C/A code and I-signal, and, outputs the thus-obtained count value C 1 . The second detecting circuit  40  counts, from the multiplication result of the multiplier  35 , chips in disagreement between the 0-chip delayed C/A code and I-signal, and, outputs the thus-obtained count value C 2 . The third detecting circuit  41  counts, from the multiplication result of the multiplier  36 , chips in disagreement between the +½-chip delayed C/A code and I-signal, and, outputs the thus-obtained count value C 3 . The fourth detecting circuit  42  counts, from the multiplication result of the multiplier  37 , chips in disagreement between the 0-chip delayed C/A code and Q-signal, and, outputs the thus-obtained count value C 4 . 
   The count values C 1 , C 2 , C 3  and C 4  output from the first through fourth detecting circuits  39  through  42  are provided to the CPU  13 . 
   The CPU  13  obtains correlation values b 1  through b 4  from the count values C 1  through C 4 . The correlation value b 1  is a correlation value between the I-signal and −½-chip delayed C/A code. The correlation value b 2  is a correlation value between the I-signal and 0-chip delayed C/A code. The correlation value b 3  is a correlation value between the I-signal and +½-chip delayed C/A code. The correlation value b 4  is a correlation value between the Q-signal and 0-chip delayed C/A code. 
   The correlation values b 1  through b 4  are obtained by the following formulas assuming that the count value in a case where there is no correlation is ‘a’:
 
 b   1 = C   1 − a   (1)
 
 b   2 = C   2 − a   (2)
 
 b   3 = C   3 − a   (3)
 
 b   4 = C   4 − a   (4)
 
   The CPU  13  obtains a correlation d 0  between the I-signal and Q-signal, and the internally generated code from the correlation value b 2  and correlation b 4  by the following formula (5):
 
 d   0 =( b   2   2   +b   4   2 )  (5)
 
   The CPU  13  compares the correlation d 0  with a threshold. When the correlation d 0  is smaller than the threshold (this means that the correlation between the received signal and internally generated code is small) and also the phase shift amount has reached 1023 chips (a condition in which it is determined that the frequency difference is so large that the predetermined correlation cannot be obtained therebetween although the phase is shifted through the maximum range), the CPU  13  provides a frequency control signal to the oscillating circuit  38 . The oscillating circuit  38  controls the frequency of the oscillation signal provided to the multipliers  32  and  33  accordintg to the frequency control signal from the CPU  13 . The CPU  13  repeats the above-mentioned operation until the correlation d 0  exceeds the threshold (the phase difference therebetween becomes sufficiently small). 
   When the correlation d 0  exceeds the threshold, the CPU  13  performs a lock operation. The lock operation is such that CPU  13  controls the oscillating circuit  38  according to the correlation d 0 , and monitors the correlation between the I-signal and Q-signal, and the internally generated code. The correlation d 0  between the I-signal and Q-signal, and the internally generated code is provided to the information processing device  5 . 
   The information processing device  5  renders a synchronization with the signal from the satellite by using the correlation d 0  between the I-signal and Q-signal, and the internally generated code provided from the CPU  13 , obtains information therefrom, and extracts position information therefrom. A map is displayed by the display device  6 , and, a position according to the thus-extracted position information is displayed on the thus-displayed map. Further, the CPU  13  performs the lock operation according to the correlation value b 1  and correlation value b 3 . With regard to the principle and so forth for obtaining position information and so forth from the GPS signal (signal from satellites), they are well known in the GPS technical field, and detailed description thereof is omitted. 
   However, in such a search method in the related art, only the correlation between one pair of 0-chip delay of I-signal and 0-chip delay of Q-signal is utilized. Accordingly, the C/A-code can be shifted only by one chip every time in the search operation. 
   Thereby, a considerable time is required for the search. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a synchronizing circuit by which it is possible to render a synchronization at high speed with a simple configuration. 
   A synchronizing circuit synchronizing a predetermined code (0-chip delayed C/A code) with first and second codes (I-signal and Q-signal) different in phase, according to the present invention, includes: 
   a code generating part ( 31 ′) outputting phase-shifted code (−1-chip delayed C/A code) shifted in phase by a predetermined number (−1) of chips from the predetermined code; 
   a first correlation detecting part ( 34 ,  39 ) detecting a correlation between the phase-shifted code (−1-chip delayed C/A code) from the code generating part ( 31 ′) and the first code (I-signal); 
   a second correlation detecting part ( 36 ,  41 ) detecting a correlation between the phase-shifted code (−1-chip delayed C/A code) from the code generating part and the second code (Q-signal); and 
   a code shifting part ( 13 ) shifting the phase of the code (0-chip delayed C/A code, −1-chip delayed C/A code, −½-chip delayed C/A code and +½-chip delayed C/A code) generated from the code generating part ( 31 ′) by a predetermined number (2) of chips according to the detection results of the first and second correlation detecting parts ( 34 ,  36 ,  39 ,  42 ). 
   The first and second codes (I-signal and Q-signal) may be different in phase by ½ chips; and 
   the code generating part ( 31 ′) may generate the phase-shifted code (−1-chip delayed C/A code) shifted in phase by one chip from the predetermined code (0-chip delayed C/A code). 
   The circuit may further include: 
   a third correlation detecting part ( 35 ,  40 ) detecting a correlation between the predetermined code (0-chip delayed C/A code) and the first code (I-signal); and 
   a fourth correlation detecting part ( 37 ,  42 ) detecting a correlation between the predetermined code (0-chip delayed C/A code) and the second code (Q-signal). 
   The code generating part may further generates first and second fraction-shifted codes (−½-chip delayed C/A code and +½-chip delayed C/A code) shifted from the predetermined code by an interval (½ chip) smaller than one chip in opposite directions (plus and minus); and 
   the circuit further comprises a switch part ( 101 ,  102  and  103 ) switching so that the first correlation detects part ( 34 ,  39 ) detecting a correlation between the first fraction-shifted code (−½-chip delayed C/A code) and the first code (I-signal), and the second correlation detecting part ( 36 ,  41 ) detects a correlation between the second fraction-shifted code (+½-chip delayed C/A code) and the first code (I-signal). 
   A GPS receiving apparatus according to the present invention includes: 
   a receiving unit ( 4 ) extracting C/A codes from given GPS signals, and outputting data according to time difference between the different C/A codes; and 
   an information processing device ( 5 ), according to the output data of the receiving unit, obtaining position information, 
   wherein the receiving unit synchronizes a predetermined code with first and second codes different in phase derived from each of the GPS signals, comprises: 
   a code generating part ( 31 ′) outputting phase-shifted code shifted in phase by a predetermined number of chips from the predetermined code; 
   a first correlation detecting part ( 34 ,  39 ) detecting a correlation between the phase-shifted code from the code generating part and the first code; 
   a second correlation detecting part ( 36 ,  41 ) detecting a correlation between the phase-shifted code from the code generating part and the second code; and 
   a code shifting part ( 13 ) shifting the phase of the phase-shifted code from the code generating part by a predetermined number of chips according to the detection results of the first and second correlation detecting parts. 
   Thereby, by detecting the correlation using not only the predetermined code (0-chip delayed C/A code) but also the phase-shifted code (−1-chip delayed C/A code) shifted by an integral number of chips for search operation, it is possible to reduce the number of times of code shifting needed for the search operation. Accordingly, it is possible to render high-speed synchronization of the predetermined code to the given codes (I-signal and Q-signal). 
   Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block configuration of one exmaple of a GPS receiving apparatus in the related art; 
       FIG. 2  shows a block configuration of a receiving unit shown in  FIG. 1 ; 
       FIG. 3  shows a block configuration of a radio-frequency circuit shown in  FIG. 2 ; 
       FIG. 4  shows a block configuration of a receiving circuit shown in  FIG. 2 ; 
       FIG. 5  shows a block configuration of a receiving circuit in one embodiment of the present invention; and 
       FIG. 6  shows a flow chart of operation rendered by a CPU in the first embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of the present invention will now be described with reference to figures. 
     FIG. 5  shows a block configuration of a receiving circuit (corresponding to the receiving circuit  12  in the related art shown in  FIG. 4 ) of the embodiment of the present invention. In  FIG. 5 , the same reference numerals are give to the parts/components same as those in  FIG. 4 , and description thereof is omitted. Further, a GPS receiving apparatus according to the present invention is similar to the GPS receiving apparatus in the related art described above with reference to  FIGS. 1 through 3 , but the receiving circuit is changed from the receiving circuit  12  described above with reference to  FIG. 4  into the receiving circuit  100  which will now be described with reference  5 . 
   The receiving circuit  100  of the embodiment of the present invention is different from the receiving circuit  12  described above by the following points: the C/A codes output from the C/A-code generating circuit  31 ′ (corresponding to the above-described C/A-code generating circuit  31 ) are four types thereof, and, also, three switches  101 ,  102  and  103  are newly provided. 
   The C/A-code generating circuit  31 ′ generates, in addition to the −½-chip delayed C/A code, 0-chip delayed C/A code and +½-chip delayed C/A code, −1-chip delayed C/A code delayed from the 0-chip delayed C/A code by one chip. 
   The −½-chip delayed C/A code and −1-chip delayed C/A code are provided to the switch  101  from the C/A-code generating circuit  31 ′. The switch  101  selects either the −½-chip delayed C/A code or −1-chip delayed C/A code according to a switching control signal from the CPU  13 , and provides the thus-selected code to the multiplier  34 . 
   The multiplication result of the multiplier  32  and the multiplication result of the multiplier  33  are provided to the switch  102 . The switch  102  selects either the multiplication result of the multiplier  32  or the multiplication result of the multiplier  33  according to a switching control signal from the CPU  13 , and provides the thus-selected one to the multiplier  36 . 
   The +½-chip delayed C/A code and −1-chip delayed C/A code are provided to the switch  103  from the C/A-code generating circuit  31 ′. The switch  103  selects either the +½-chip delayed C/A code or −1-chip delayed C/A code according to a switching control signal from the CPU  13 , and provides the thus-selected code to the multiplier  36 . 
   Operation of this embodiment of the present invention will now be described. 
     FIG. 6  shows an operation flow chart of the CPU  13  of the embodiment of the present invention. 
   The CPU  13  executes steps S 1  through S 8 . 
   In the step S 1 , the switches  101  through  103  are switched into states for search operation. In the search operation, the switch  101  is switched so that the −1-chip delayed C/A code from the C/A-code generating circuit  31 ′ is provided to the multiplier  34 . Further, the switch  102  is switched so that the Q-signal from the multiplier  33  is provided to the multiplier  36 . The switch  103  is switched so that the −1-chip delayed C/A code from the C/A-code generating circuit  31 ′ is provided to the multiplier  36 . 
   Then, the step S 2  is executed. In the step S 2 , the count values C 1  through C 4  are input from the first through fourth detecting circuit  39  through  42  to the CPU  13 . 
   The CPU  13  obtains a correlation d 0  and a correlation d 10  from the count values C 1  through C 4  input in the step S 2 . 
   The correlation d 10  is obtained from the count value C 1  from the first detecting circuit  39  and the count value C 3  from through third detecting circuit  41 . 
   First, from the count values C 1  and C 3 , the correlation values b 1  and b 3  are obtained by the above-mentioned formulas (1) and (3). Then, from the correlation values b 1  and b 3 , the correlation d 10  is obtained by the following formula (6):
 
 d   10 =( b   1   2   +b   3   2 )  (6)
 
   The correlation d 0  is obtained from the count value C 2  from the second detecting circuit  40  and the count value C 4  from through fourth detecting circuit  42 . 
   First, from the count values C 2  and C 4 , the correlation values b 2  and b 4  are obtained by the above-mentioned formulas (2) and (4). Then, from the correlation values b 2  and b 4 , the correlation d 0  is obtained by the above-mentioned formula (5). 
   The correlation d 10  corresponds to a correlation between the −1-chip delayed C/A code and the I-signal and a correlation between the −1-chip delayed C/A code and the Q-signal. The correlation d 0  corresponds to a correlation between the 0-chip delayed C/A code and the I-signal and a correlation between the 0-chip delayed C/A code and the Q-signal. 
   After obtaining the correlations d 0  and d 10  in the step S 2 , the CPU  13  executes the step S 3 . In the step S 3 , the CPU  13  determines whether or not the correlations d 0  and d 10  are larger than a threshold. When the correlations d 0  and d 10  are smaller than the threshold, the step S 4  is executed. 
   In the step S 4 , it is determined whether or not the phase shift amount of the C/A codes output from the C/A-code generating circuit  31 ′ is such that shift has been rendered for 1023 chips equal to all the chips of the C/A code. When it is determined in the step S 4  that the chip shift of 1023 chips has been rendered, it can be determined that the multiplication results of the multipliers  32  and  33  have an error. Accordingly, the CPU  13  controls the frequency of the oscillation signal provided to the multipliers  32  and  33  from the oscillating circuit  38 . After thus changing the frequency in the step S 4 , the process is returned to the step S 1 , and the search operation is performed again. 
   Further, when the shift amount of the C/A codes has not reached 1023 chips in the step S 4 , the step S 6  is executed. In the step S 6 , a shift control signal is provided to the C/A-code generating circuit  31 ′, and the C/A codes generated from the C/A-code generating circuit  31 ′ are shifted by 2 chips. After the C/A codes are shifted in the step S 6 , the process is returned to the step S 2 , and the operation is continued. 
   When the correlations d 0  and d 10  are equal to or larger than the threshold, it can be determined that the lock (phase lock) operation can be rendered, and, therefore, the step S 7  is executed. 
   In the step S 7 , the switches  101  through  103  are switched to states for the lock operation. 
   The switch  101  is switched so that the −½-chip delayed C/A code is provided to the multiplier  34  from the C/A-code generating circuit  31 ′. The switch  102  is switched so that the multiplication result of the multiplier  32  is provided to the multiplier  36 . The switch  103  is switched so that the +½-chip delayed C/A code from the C/A-code generating circuit  31 ′ is provided to the multiplier  36 . 
   Thereby, the count value C 1  output from the first detecting circuit  39  is a correlation value between the I-signal and −½-chip delayed C/A code. The count value C 2  output from the second detecting circuit  40  is a correlation value between the I-signal and 0-chip delayed C/A code. The count value C 3  output from the third detecting circuit  41  is a correlation value between the I-signal and +½-chip delayed C/A code. The count value C 4  output from the fourth detecting circuit  42  is a correlation value between the Q-signal and 0-chip delayed C/A code. 
   After the switches  101  through  103  are thus switched into the states for the lock operation, the lock operation is performed in the step S 8 . 
   In the lock operation, the CPU  13  obtains the correlation value b 2  and b 4  from the count value C 2  from the second detecting circuit  40  and the count value C 4  from the fourth detecting circuit  42  by the formulas (2) and (4), obtains the correlation d 0  by the formula (5), controls the oscillating circuit  38  so that the correlation d 0  becomes not larger than a threshold, and locks the frequency. At this time, control is rendered such that the correlation value b 4  becomes smaller and the correlation value b 2  becomes larger. 
   Further, the CPU  13  obtains the correlation value b 1  and b 3  from the count value C 1  from the first detecting circuit  39  and the count value C 3  from the third detecting circuit  41  by the formulas (1) and (3), obtains the correlation d 10  by the formula (6), controls the C/A-code generating circuit  31 ′ so that the correlation d 10  becomes not larger than a threshold, and locks the phase. At this time, control is rendered such that the difference between the correlation values b 1  and b 3  becomes smaller. 
   According to the present invention, the correlation between the −1-chip delayed C/A code and the I-signal and the correlation between the −1-chip delayed C/A code and the Q-signal, and, also, the correlation between the 0-chip delayed C/A code and the I-signal and the correlation between the 0-chip delayed C/A code and the Q-signal are obtained, and are utilized in the search operation. Thereby, it is possible to render the search for two chips at once. Accordingly, it is possible to render the search at a speed twice that of the related art, and to perform the search at high speed. 
   At this time, the configuration of the C/A-code generating circuit  31 ′ needs to output −1-chip delayed C/A code additionally in comparison to the related art. Accordingly, increase in circuit scale is within a small amount. Further, by adding the switches  101  through  103 , it is possible to render the lock operation similarly to that in the related art. 
   The switches  101  through  103  may be built in the C/A-code generating circuit  31 ′ integrally. 
   The present invention is not limited to the above-described embodiment, and variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application No. 2000-25771, filed on Feb. 2, 2000, the entire contents of which are hereby incorporated by reference.