Patent Publication Number: US-11664906-B2

Title: Method for calibrating transmitter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of Taiwan application No. 109139980 filed on Nov. 16, 2020, which is incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present application relates to a calibration method; in particular, to a method capable of calibrating the local oscillator leakage in a transmitter. 
     BACKGROUND 
     When the local oscillator is not perfectly isolated from the mixer and low-noise amplifier at the transmitting end, leakage of the local oscillator signal may occur, which may interfere with the transmission signal. One conventional approach handles this issue by analyzing the components mixed from an original signal and a local oscillation signal leakage in a real signal generated by the I and Q signals&#39; self-mixing and keep adjusting the compensation value accordingly until the best result is achieved. However, one drawback of this approach is time consuming. Therefore, how to compensate for the local oscillation signal leakage fast and accurately has become an essential issue in the field of communication systems. 
     SUMMARY OF THE INVENTION 
     The present application discloses a method for calibrating a transmitter, wherein the transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path includes a first low pass filter, the second signal path includes a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path includes thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: setting the first compensation value to zero and the second compensation value to a first preset value, and passing a single-frequency signal through the transmitter to generate a first transmission signal; looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result; setting the first compensation value to zero and the second compensation value to a second preset value, and passing the single-frequency signal through the transmitter to generate a second transmission signal; looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result; reversing signs of gains of the first low pass filter and the second low pass filter, setting the first compensation value to zero and the second compensation value to the first preset value, and passing the single-frequency signal through the transmitter to generate a third transmission signal; looping back the third transmission signal and performing a spectrum analysis on the third transmission signal to obtain a third spectrum analysis result; reversing signs of gains of the first low-pass filter and the second low-pass filter, setting the first compensation value to zero and the second compensation value to the second preset value, and passing the single-frequency signal through the transmitter to generate a fourth transmission signal; looping back the fourth transmission signal and performing a spectrum analysis on the fourth transmission signal to obtain a fourth spectrum analysis result; and optimizing the second compensation value based on the first spectrum analysis result, the second spectrum analysis result, the third spectrum analysis result; the fourth spectrum analysis result, the first preset value, and the second preset value to generate an optimal second compensation value. 
     The present application discloses a method for calibrating a transmitter, wherein the transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path comprises a first low pass filter, the second signal path comprises a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path include thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: setting the first compensation value to a first preset value and the second compensation value to zero, and passing a single-frequency signal through the transmitter to generate a first transmission signal; looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result; setting the first compensation value to a second preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a second transmission signal; looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result; reversing signs of gains of the first low pass filter and the second low pass filter, setting the first compensation value to the first preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a third transmission signal; looping back the third transmission signal and performing a spectrum analysis on the third transmission signal to obtain a third spectrum analysis result; reversing signs of gains of the first low-pass titter and the second low-pass filter, setting the first compensation value to the second preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a fourth transmission signal; looping back the fourth transmission signal and performing a spectrum analysis on the fourth transmission signal to obtain a fourth spectrum analysis result; and optimizing the first compensation value based on the first spectrum analysis result, the second spectrum analysis result, the third spectrum analysis result, the fourth spectrum analysis result, the first preset value, and the second preset value to generate an optimal first compensation value. 
     The present application discloses a method for calibrating a transmitter, wherein the transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path comprises a first low pass filter, the second signal path comprises a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path include thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: configuring gains of the first low pass filter and the second low pass filter as a first gain, and setting the first compensation value to zero and the second compensation value to a first preset value, and passing a single-frequency signal through the transmitter to generate a first transmission signal; looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result; configuring gains of the first low pass filter and the second low pass filter as the first gain, and setting the first compensation value to zero and the second compensation value to a second preset value, and passing the single-frequency signal through the transmitter to generate a second transmission signal; looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result; and optimizing the second compensation value based on the first spectrum analysis result, the second spectrum analysis result, the first preset value, and the second preset value to generate a first leading optimal value. 
     The above calibration method calibrates a baseband circuit and a front-end modulation circuit of a transmitter to compensate local oscillator leakage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram illustrating a transmitter according to some embodiments of the present application. 
         FIG.  2    is a schematic diagram illustrating the calculation of an optimal compensation value using linear extrapolation or linear interpolation. 
         FIG.  3    to  FIG.  4    are flow charts illustrating a method for calibrating a transmitter according to a first embodiment of the present application. 
         FIG.  5    to  FIG.  6    are flow charts illustrating a method for calibrating a transmitter according to a second embodiment of the present application. 
         FIG.  7    to  FIG.  8    are flow charts illustrating a method for calibrating a transmitter according to a third embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    is a schematic diagram illustrating a transmitter according to some embodiments of the present disclosure, wherein the transmitter  100  includes a first signal path and a second signal path, wherein one of the two signal paths is an in-phase (I) signal path, and the other of the two signal paths is a quadrature (Q) signal path. 
     As shown in  FIG.  1   , the transmitter  100  includes a transmitting end  104 , a power amplifier  106 , a self-mixer  108 , an analog to digital converter (ADC)  110 , a spectrum analysis unit  112 , a calibration coefficient computing unit  114 , and a control unit  116 , wherein the transmitting end  104  includes a first signal path, a second signal path and an adder  1056 ; for example, the first signal path is an in-phase signal path and passes through a first digital-to-analog converter  1042 , a first low pass filter  1046 , and a first mixer  1050 ; the second signal path is a quadrature signal path and passes through a second digital-to-analog converter  1044 , a second low pass filter  1048 , and a second mixer  1052 . 
     In the present embodiment, after each time the transmitter  100  is restarted (e.g., after power-on or after a system reset) and before the normal data transmission mode is officially started, in order to mitigate the local oscillator leakage caused by the oscillator  1054  so as to reduce the interference to the transmission signal, the transmitter  100  will first enter a calibration parameter computation mode; in other words, in the calibration parameter computation mode, the transmission signal of the transmitter  100  is looped back to the self-mixer  108  and passed through the DAC ADC  110 , the spectrum analysis unit  112 , and the calibration coefficient computing unit  114 , so as to compute an optimal calibration parameter concerning the leakage issue of the oscillator  1054 , and then, the transmitting end  104  enters the normal data transmission mode. In the normal data transmission mode, the transmission signal is no longer looped back to the self-mixer  108 , and the calibration parameter obtained during the calibration parameter computation mode is used for official data transmission and reception. 
     Specifically, the present embodiment additionally incorporates a first calibration unit  102  and a second calibration unit  103  for the transmitting end  104  of the transmitter  100 , wherein the first calibration unit  102  includes adders  1024  and  1026 , which are configured to use a compensation value DBC to compensate for the leakage DB generated by the oscillator  1054  and introduced to the circuit (that is, the corresponding baseband circuit) preceding the first low pass filter  1046  and the second low pass filter  1048 ; the second calibration unit  103  includes adders  1034  and  1036 , which are configured to use a compensation value DMC to compensate for the leakage DM generated by the oscillator  1054  and introduced to the circuit (that is, the corresponding front-end modulation circuit) succeeding the first low pass filter  1046  and the second low pass filter  1048 . It should be noted that, in practice, the adders  1024 ,  1026 ,  1034 , and  1036  can be implemented using ways such as a current digital-to-analog converter (IDAC), and that the leakage and compensation value mentioned in the present disclosure are complex numbers, with the real and imaginary parts corresponding to the I-path and Q-path respectively. 
     The advantage of the present disclosure to compensate for the oscillator leakage of the circuit preceding and succeeding the first low-pass filter  1046  and the second low-pass filter  1048 , respectively, is that the signal generated by the baseband circuit can enter the front-end modulation circuit under the situation that the leakage DB has been compensated, so that the leakage DM in the front-end modulation circuit does not contain the leakage DB component and the leakage DB will not be amplified by the gain of the front-end modulation circuit. The methods for obtaining the optimal value DMCT of the compensation value DMC and the optimal value DBCT of the compensation value DBC are described below. 
     Step  202  to Step  216  are a first embodiment of the present disclosure for computing DMCT and DBCT in the calibration parameter computation mode. Reference is made to  FIG.  1   , in Step  202 , the control unit  116  sets the compensation value DBC of the first calibration unit  102  to 0 and sets the compensation value DMC of the second calibration unit  103  to DMC1; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P1 of Fourier transform (i.e., the energy power at the frequency −w) can be expressed as:
 
 P 1∝ G*DB +( DM+DMC 1)  (1),
 
where G is the gain caused by the first low pass filter  1046  and the second low pass filter  1048  to the single-frequency test signal, the symbol ∝ indicates proportional relation.
 
     In Step  204 , the control unit  116  sets the compensation value DBC of the first calibration unit  102  to 0 and sets the compensation value DMC of the second calibration unit  103  to a DMC2 that is different from DMC1; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P2 can be expressed as:
 
 P 3∝− G*DB +( DM+DMC 1)  (3)
 
     In Step  208 , reverse signs of gains of the first low pass filter  1046  and the second low pass filter  1048 , and repeat Step  204 ; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P4 can be expressed as:
 
 P 4∝− G*DB +( DM+DMC 2)  (4)
 
     In Step  210 , the calibration coefficient computing unit  114  sums up P1 and P3, and sums up P2 and P4, thereby respectively obtaining:
 
( P 1+ P 3)∝( DM+DMC 1)  (5)
 
( P 2+ P 4)∝( DM+DMC 2)  (6)
 
     Since the leakage DM that the oscillator  1054  causes in the front-end modulation circuit is a fixed value, DMC1, DMC2 and (P1+P3),(P2+P4) in equations (5) and (6) are in linear relation. Therefore, the calibration coefficient computing unit  114  can estimate the optimal compensation value DMCT using linear extrapolation or linear interpolation. As shown in  FIG.  2   , one can obtain a straight line by connecting the two points of DMC1, DMC2, (P1+P3) and (P2+P4) in the two-dimensional coordinate; then, extend the straight line to the X-axis, and the intersecting point is the DMCT. It should be noted that in  FIG.  2   , the concept of this embodiment is simplified to two dimensions to facilitate the understanding, whereas the actual situation is four dimensions. 
     In Step  212 , the control unit  116  sets the compensation value DMC of the second calibration unit  103  to DMCT so as to compensate for the leakage DM in the front-end modulation circuit perfectly, and sets the compensation value DBC of the first calibration unit  102  to DBC1; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P5 can be expressed as:
 
 P 5∝ G *( DB+DBC 1)  (7)
 
     In Step  214 , the control unit  116  sets the compensation value DMC of the second calibration unit  103  to DMCT, and sets the compensation value DBC of the first calibration unit  102  to DBC2 that is different from DBC1; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P1 can be expressed as:
 
 P 6∝ G *( DB+DBC 2)  (8)
 
     In Step  216 , since the leakage DB that is caused by the oscillator  1054  in the baseband circuit is a fixed value, DBC1, DBC2 and P5, P6 in equations (7) and (8) are in linear relation. Therefore, the calibration coefficient computing unit  114  can compute the optimal compensation value DBCT using linear extrapolation or linear interpolation. 
     Step  302  to Step  316  are a second embodiment of the present application for computing DMCT and DBCT in the calibration parameter computation mode. The difference between the second embodiment and the first embodiment is that in the second embodiment, DBCT is computed before DMCT. Reference is made to  FIG.  1   , in Step  302 , the control unit  116  sets the compensation value DMC of the second calibration unit  103  to 0 and sets DBC of the first calibration unit  102  to DBC3; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P7 can be expressed as:
 
 P 7 ∝G *( DB+DBC 3)+ DM   (9)
 
     In Step  304 , the control unit  116  sets the compensation value DMC of the second calibration unit  103  to 0, and sets the compensation value DBC of the first calibration unit  102  to DBC4 that is different from DBC3; after that, the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P8 can be expressed as:
 
 P 8∝ G *( DB+DBC 4)+ DM   (10)
 
     In Step  306 , reverse signs of gains of the first low pass filter  1046  and the second low pass filter  1048 , and repeat Step  302 ; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P9 can be expressed as:
 
 P 9∝− G *( DB+DBC 3)+ DM   (11)
 
     In Step  308 , reverse signs of gains of the first low pass filter  1046  and the second low pass filter  1048 , and repeat Step  304 ; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P4 can be expressed as:
 
 P 10∝− G *( DB+DBC 4)+ DM   (12)
 
     In Step  310 , the calibration coefficient computing unit  114  subtracts P9 from P7, and subtracts P10 from P8, thereby respectively obtaining:
 
( P 7− P 9)∝2 G ( DB+DBC 3)  (13)
 
( P 8− P 10)∝2 G ( DB+DBC 4)  (14)
 
     The calibration coefficient computing unit  114  can compute the optimal compensation value DBCT using linear extrapolation or linear interpolation. 
     In Step  312 , the control unit  116  sets the compensation value DBC of the first calibration unit  102  to DBCT to compensate for the leakage DB in the baseband circuit perfectly, and sets the compensation value DMC of the second calibration unit  103  to DMC3; after that the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P11 can be expressed as:
 
 P 11∝( DM+DMC 3)  (15)
 
     In Step  314 , the control unit  116  sets the compensation value DBC of the first calibration unit  102  to DBCT to compensate for the leakage DB in the baseband circuit perfectly, and sets the compensation value DMC of the second calibration unit  103  to DMC4 that is different from DMC3; after that the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P12 can be expressed as:
 
 P 12∝( DM+DMC 4)  (16)
 
     In Step  316 , the calibration coefficient computing unit  114  can compute the optimal compensation value DMCT using linear extrapolation or linear interpolation. 
     Step  402  to Step  416  are a third embodiment of the present disclosure for computing DMCT and DBCT in the calibration parameter computation mode. Reference is made to  FIG.  1   , in Step  402 , the control unit  116  sets the gain of the first low pass filter  1046  and the second low pass filter  1048  to G1, and sets the compensation value DBC of the first calibration unit  102  to 0, and sets the compensation value DMC of the second calibration unit  103  to DMC5; after that the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P13 can be expressed as:
 
 P 13∝ G 1* DB+DM+DMC 5  (17)
 
     In Step  404 , the control unit  116  sets the gain of the first low pass filter  1046  and the second low pass filter  1048  to G1, and sets the compensation value DBC of the first calibration unit  102  to 0, and sets the compensation value DMC of the second calibration unit  103  to DMC6 that is different from DMC5; after that the control unit  116  inputs a single-frequency test signal with a frequency w; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P14 can be expressed as:
 
 P 14∝ G 1* DB+DM+DMC 6  (18)
 
     In Step  406 , since DM and DB that the oscillator  1054  causes are fixed values, DMC5, DMC6 and P13, P14 in equations (17) and (18) are in linear relation. Therefore, by using linear extrapolation or linear interpolation, the calibration coefficient comput unit  114  can estimate a compensation value DM, referred to as a leading optimal value DMPT1, that compensates for DB and DM simultaneously when the gain of the first low pass filter  1046  and the second low pass filter  1048  is G1, and causes:
 
 G 1* DB +( DM+DMPT 1)=0  (19)
 
     In Step  408 , the control unit  116  sets the gain of the first low pass filter  1046  and the second low pass filter  1048  to G2, and the remaining step is the same as Step  402 ; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P15 can be expressed as:
 
 P 15 ∝ G 2* DB+DM+DMC 5  (20)
 
     In Step  410 , the control unit  116  sets the gain of the first low pass filter  1046  and the second low pass filter  1048  to G2, and the remaining step is the same as Step  404 ; then the spectrum analysis unit  112  performs Fourier transform with respect to −w, and the result P16 can be expressed as:
 
 P 16∝ G 2* DB+DM+DMC 6  (21)
 
     In Step  412 , by using linear extrapolation or linear interpolation, the calibration coefficient comput unit  114  can estimate a compensation value DM, referred to as a leading optimal value DMPT2, that compensates for DB and DM simultaneously when the gain of the first low pass filter  1046  and the second low pass filter  1048  is G2, and causes:
 
 G 2* DB +( DM+DMPT 2)=0  (22)
 
     In Step  414 , the calibration coefficient computing unit  114  can obtain the following equations according to equations (19) and (22): 
     
       
         
           
             
               
                 
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                         DMPT 
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                   DBCT 
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                   DMCT 
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                   ) 
                 
               
             
           
         
       
     
       FIG.  3    to  FIG.  4    are flow charts illustrating a method for calibrating a transmitter according to a first embodiment of the present application. The transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path includes a first low pass filter, the second signal path includes a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path includes thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: setting the first compensation value to zero and the second compensation value to a first preset value, and passing a single-frequency signal through the transmitter to generate a first transmission signal, wherein a frequency of the single-frequency signal is w ( 502 ); looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result ( 504 ); setting the first compensation value to zero and the second compensation value to a second preset value, and passing the single-frequency signal through the transmitter to generate a second transmission signal ( 506 ); looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result ( 508 ); reversing signs of gains of the first low pass filter and the second low pass filter, setting the first compensation value to zero and the second compensation value to the first preset value, and passing the single-frequency signal through the transmitter to generate a third transmission signal ( 510 ); looping back the third transmission signal and performing a spectrum analysis on the third transmission signal to obtain a third spectrum analysis result ( 512 ); reversing signs of gains of the first low-pass filter and the second low-pass filter, setting the first compensation value to zero and the second compensation value to the second preset value, and passing the single-frequency signal through the transmitter to generate a fourth transmission signal ( 514 ); looping back the fourth transmission signal and performing a spectrum analysis on the fourth transmission signal to obtain a fourth spectrum analysis result ( 516 ); optimizing the second compensation value based on the first spectrum analysis result, the second spectrum analysis result, the third spectrum analysis result, the fourth spectrum analysis result, the first preset value, and the second preset value to generate an optimal second compensation value ( 518 ); setting the first compensation value to a third preset value and the second compensation value to the optimal second compensation value, and passing the single-frequency signal through the transmitter to generate a fifth transmission signal ( 520 ); looping back the fifth transmission signal and performing a spectrum analysis on the fifth transmission signal to obtain a fifth spectrum analysis result ( 522 ); setting the first compensation value to a fourth preset value and the second compensation value to the optimal second compensation value, and passing the single-frequency signal through the transmitter to generate a sixth transmission signal ( 524 ); looping back the sixth transmission signal and performing a spectrum analysis on the sixth transmission signal to obtain a sixth spectrum analysis result ( 526 ); and optimizing the first compensation value and generating an optimal first compensation value based on the fifth spectrum analysis result, the sixth spectrum analysis result, the third preset value, and the fourth preset value ( 528 ). 
       FIG.  5    to  FIG.  6    are flow charts illustrating a method for calibrating a transmitter according to a second embodiment of the present application. The transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path includes a first low pass filter, the second signal path includes a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path include thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: setting the first compensation value to a first preset value and the second compensation value to zero, and passing a single-frequency signal through the transmitter to generate a first transmission signal, wherein a frequency of the single-frequency signal is w ( 602 ); looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result ( 604 ); setting the first compensation value to a second preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a second transmission signal ( 606 ); looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result ( 608 ); reversing signs of gains of the first low pass filter and the second low pass filter, setting the first compensation value to the first preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a third transmission signal ( 610 ); looping back the third transmission signal and performing a spectrum analysis on the third transmission signal to obtain a third spectrum analysis result ( 612 ); reversing signs of gains of the first low-pass filter and the second low-pass filter, setting the first compensation value to the second preset value and the second compensation value to zero, and passing the single-frequency signal through the transmitter to generate a fourth transmission signal ( 614 ); looping back the fourth transmission signal and performing a spectrum analysis on the fourth transmission signal to obtain a fourth spectrum analysis result ( 616 ); optimizing the first compensation value based on the first spectrum analysis result, the second spectrum analysis result, the third spectrum analysis result, the fourth spectrum analysis result, the first preset value, and the second preset value to generate an optimal first compensation value ( 618 ); setting the first compensation value to the optimal first compensation value and the second compensation value to a third preset value, and passing the single-frequency signal through the transmitter to generate a fifth transmission signal ( 620 ); looping back the fifth transmission signal and performing a spectrum analysis on the fifth transmission signal to obtain a fifth spectrum analysis result ( 622 ); setting the first compensation value to the optimal first compensation value and the second compensation value to a fourth preset value, and passing the single-frequency signal through the transmitter to generate a sixth transmission signal ( 624 ); looping back the sixth transmission signal and performing a spectrum analysis on the sixth transmission signal to obtain a sixth spectrum analysis result ( 626 ); and optimizing the second compensation value based on the fifth spectrum analysis result, the sixth spectrum analysis result, the third preset value, and the fourth preset value to generate an optimal second compensation value ( 628 ). 
       FIG.  7    to  FIG.  8    are flow charts illustrating a method for calibrating a transmitter according to a third embodiment of the present application. The transmitter includes an oscillator, a first signal path, and a second signal path, wherein one of the first signal path and the second signal path is an in-phase signal path, the other of the first signal path and the second signal path is a quadrature signal path, the first signal path includes a first low pass filter, the second signal path includes a second low pass filter, the oscillator causes a first local oscillator leakage to a portion of the first signal path preceding the first low pass filter and a portion of the second signal path preceding the second low pass filter, the oscillator causes a second local oscillator leakage to a portion of the first signal path succeeding the first low pass filter and a portion of the second signal path succeeding the second low pass filter, and the first signal path and the second signal path include thereon a first calibration unit and a second calibration unit, wherein the first calibration unit is disposed preceding the first low pass filter and the second low pass filter, the first calibration unit is set with a first compensation value, the second calibration unit is disposed succeeding the first low pass filter and the second low pass filter, and the second calibration unit is set with a second compensation value; the method including: configuring gains of the first low pass filter and the second low pass filter as a first gain, and setting the first compensation value to zero and the second compensation value to a first preset value, and passing a single-frequency signal through the transmitter to generate a first transmission signal, wherein a frequency of the single-frequency signal is w ( 702 ); looping back the first transmission signal and performing a spectrum analysis on the first transmission signal to obtain a first spectrum analysis result ( 704 ); configuring gains of the first low pass filter and the second low pass filter as the first gain, and setting the first compensation value to zero and the second compensation value to a second preset value, and passing the single-frequency signal through the transmitter to generate a second transmission signal ( 706 ); looping back the second transmission signal and performing a spectrum analysis on the second transmission signal to obtain a second spectrum analysis result ( 708 ); optimizing the second compensation value based on the first spectrum analysis result, the second spectrum analysis result, the first preset value, and the second preset value to generate a first leading optimal value ( 710 ); configuring gains of the first low pass filter and the second low pass filter as a second gain, and setting the first compensation value to zero and the second compensation value to the first preset value, and passing the single-frequency signal through the transmitter to generate a third transmission signal ( 712 ); looping back the third transmission signal and performing a spectrum analysis on the third transmission signal to obtain a third spectrum analysis result ( 714 ); configuring gains of the first low pass filter and the second low pass filter as the second gain, and setting the first compensation value to zero and the second compensation value to the second preset value, and passing the single-frequency signal through the transmitter to generate a fourth transmission signal ( 716 ); looping back the fourth transmission signal and performing a spectrum analysis on the fourth transmission signal to obtain a fourth spectrum analysis result ( 718 ); and optimizing the second compensation value based on the third spectrum analysis result, the fourth spectrum analysis result, the first preset value, and the second preset value to generate a second leading optimal value, wherein the second leading optimal value is configured to compensate for the first local oscillator leakage and the second local oscillator leakage ( 720 ). 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand various aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of embodiments introduced herein. It should be understood that the steps mentioned in the flowchart of the method of the present application can be adjusted in accordance with the actual needs except for those whose sequences are specifically stated, and can even be executed simultaneously or partially simultaneously. In addition, the above-mentioned modules or method steps can be implemented by hardware, software or firmware according to the designer&#39;s needs. Those skilled in the art should also realize that such equivalent embodiments still fall within the spirit and scope of the present disclosure, and they may make various changes, substitutions, and alterations thereto without departing from the spirit and scope of the present disclosure.