Abstract:
Provided is a pulse density modulation value converter, comprising: a pulse density modulation reference point storage for storing a plurality of pulse density modulation reference points, each pulse density modulation reference point comprising a linear pulse density modulation value, an actual pulse density modulation value and/or an integral non-linear error value, wherein the integral non-linear error value is the difference between the actual pulse density modulation value and the linear pulse density modulation value; and a pulse density modulation value calculator for receiving a linear pulse density modulation value, searching the pulse density modulation reference point storage for a pair of pulse density modulation reference points closest to the linear pulse density modulation value, obtaining an actual pulse density modulation value corresponding to the linear pulse density modulation value through linear interpolation on the basis of the pair of pulse density modulation reference points, and outputting the actual pulse density modulation value.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a pulse density modulation (PDM) value converter and an application thereof, and more particularly to a PDM modulation value converter; an automatic gain controller (AGC) using PDM, an automatic frequency controller (AFC) using PDM and a mobile terminal using PDM, and a method thereof. 
       BACKGROUND ART 
       [0002]    As a technology of signal control, pulse density modulation (PDM) is widely applied in electronic circuits, such as communication devices, power control devices, and tuning units. Particularly, PDM can be used in an automatic gain controller (AGC) and/or an automatic frequency controller (AFC) in mobile terminals for transmission power control and tuning control respectively. 
         [0003]    For example, when using PDM for automatic gain control, in order to control a transmission power to a target power value, a corresponding PDM value needs to be set. In practice, only the PDM values of several points calibrated in advance are generally stored. As the target power value is not necessarily on these points, a corresponding PDM value needs to be calculated through linear interpolation. 
         [0004]    However, the relationship between the PDM value of an actual chip and the corresponding power value is not an ideal linear one. That is, an integral non-linear (INL) error exists. Therefore, when automatic gain control is conducted using a PDM value calculated through linear interpolation, an error of the actual power value is caused by the INL error, thus leading to a relatively long ping-pong time, that is, it requires a plurality of adjustments for the PDM value to finally reach the target power value. 
         [0005]    For automatic frequency control, a similar problem also exists that an error of an actual frequency value is caused when using PDM tuning and that it requires a plurality of adjustments for PDM before reaching a target frequency value. The above-mentioned problems caused by INL errors are not limited to AGC and AFC, but will affect any circuits using a PDM value. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, in order to solve the above-mentioned problems, the present invention provides a pulse density modulation (PDM) value converter; an automatic gain controller (AGC) using PDM, an automatic frequency controller (AFC) using PDM and a mobile terminal using PDM, and a method thereof, wherein the linearity of a PDM value is improved by correcting an integral non-linear (INL) error. 
         [0007]    According to one embodiment of the present invention, provided is a pulse density modulation (PDM) value converter comprising: a PDM reference point storage to store a plurality of PDM reference points, each PDM reference point comprising a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, wherein the INL error value is the difference between the actual PDM value and the linear PDM value; and a PDM value calculator to receive a linear PDM value, look up a pair of PDM reference points closest to the linear PDM value in the PDM reference point memory, obtain an actual PDM value corresponding to the linear PDM value through linear interpolation based on the pair of PDM reference points, and output the actual PDM value. 
         [0008]    According to an embodiment, the PDM value calculator may linearly interpolate the PDM values of the pair of PDM reference points to obtain an actual PDM value corresponding to the linear PDM value. 
         [0009]    According to an embodiment, the PDM value calculator may linearly interpolate the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear PDM value, and obtain an actual PDM value corresponding to the linear PDM value based on the linear PDM value and the INL error value. 
         [0010]    According to another embodiment of the present invention, provided is a method of pulse density modulation (PDM) value conversion, the method comprising: receiving a linear PDM value; looking up a pair of PDM reference points closest to the linear PDM value among a plurality of PDM reference points, wherein each PDM reference point comprises a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, the INL error value being the difference between the actual PDM value and the linear PDM value; obtaining an actual PDM value corresponding to the linear PDM value through linear interpolation based on the pair of PDM reference points; and outputting the actual PDM value. 
         [0011]    According to an embodiment, obtaining an actual PDM value corresponding to the linear PDM value through linear interpolation may comprise: linearly interpolating the PDM values of the pair of PDM reference points to obtain an actual PDM value corresponding to the linear PDM value. 
         [0012]    According to an embodiment, obtaining an actual PDM value corresponding to the linear PDM value through linear interpolation may comprise: linearly the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear PDM value; and obtaining an actual PDM value corresponding to the linear PDM value based on the linear PDM value and the INL error value. 
         [0013]    According to another embodiment of the present invention, provided is an automatic gain controller comprising: a power reference point memory to store a plurality of power reference points, each power reference point comprising a power value and a linear pulse density modulation (PDM) value; a PDM value converter to convert a linear PDM value into an actual PDM value; a power PDM value calculator to receive a target power value, look up a pair of power reference points closest to the target power value in the power reference point memory, linearly interpolating the linear PDM values of the pair of power reference points to obtain a linear power PDM value corresponding to the target power value, and convert the linear power PDM value into an actual power PDM value via the PDM value converter; and a PDM modulator to perform automatic gain control based on the actual power PDM value. 
         [0014]    According to an embodiment, the PDM value converter may comprise: a PDM reference point memory to store a plurality of PDM reference points, each PDM reference point comprising a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, wherein the INL error value is the difference between the actual PDM value and the linear PDM value; and a PDM value calculator to receive a linear PDM value, look up a pair of PDM reference points closest to the linear PDM value in the PDM reference point memory, obtain an actual PDM value corresponding to the linear PDM value through linear interpolation based on the pair of PDM reference points, and output the actual PDM value. 
         [0015]    According to an embodiment, the PDM value calculator may linearly interpolate the PDM values of the pair of PDM reference points to obtain an actual PDM value corresponding to the linear PDM value. 
         [0016]    According to an embodiment, the PDM value calculator may linearly interpolate the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear PDM value, and obtain an actual PDM value corresponding to the linear PDM value based on the linear PDM value and the INL error value. 
         [0017]    According to another embodiment of the present invention, provided is a method of automatic gain control, the method comprising: receiving a target power value; looking up a pair of power reference points closest to the target power value among a plurality of power reference points, wherein each power reference point comprises a power value and a linear pulse density modulation (PDM) value; linearly interpolating the linear PDM values of the pair of power reference points to obtain a linear power PDM value corresponding to the target power value; converting the linear power PDM value into an actual power PDM value; and performing automatic gain control based on the actual power PDM value. 
         [0018]    According to an embodiment, converting the linear power PDM value into an actual power PDM value may comprise: looking up a pair of PDM reference points closest to the linear power PDM value among a plurality of PDM reference points, wherein each PDM reference point comprises a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, the INL error value being the difference between the actual PDM value and the linear PDM value; and obtaining an actual power PDM value corresponding to the linear power PDM value through linear interpolation based on the pair of PDM reference points. 
         [0019]    According to an embodiment, obtaining an actual power PDM value corresponding to the linear power PDM value through linear interpolation may comprise: linearly interpolating the PDM values of the pair of PDM reference points to obtain an actual power PDM value corresponding to the linear power PDM value. 
         [0020]    According to an embodiments, obtaining an actual power PDM value corresponding to the linear power PDM value through interpolation may comprise: linearly interpolating the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear power PDM value; and obtaining an actual power PDM value corresponding to the linear power PDM value based on the linear power PDM value and the INL error value. 
         [0021]    According to another embodiment of the present invention, provided is an automatic frequency controller comprising: a frequency reference point memory to store a plurality of frequency reference points, each frequency reference point comprising a frequency value and a linear pulse density modulation (PDM) value; a PDM value converter to convert a linear PDM value into an actual PDM value; a frequency PDM value calculator to receive a target frequency value, look up a pair of frequency reference points closest to the target frequency value in the frequency reference point memory, linearly interpolate the linear PDM values of the pair of frequency reference points to obtain a linear frequency PDM value corresponding to the target frequency value, and convert the linear frequency PDM value into an actual frequency PDM value via the PDM value converter; and a PDM modulator to perform automatic frequency control based on the actual frequency PDM value. 
         [0022]    According to an embodiment, the PDM value converter may comprise: a PDM reference point memory to store a plurality of PDM reference points, each PDM reference point comprising a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, wherein the INL error value is the difference between the actual PDM value and the linear PDM value; and a PDM value calculator to receive a linear PDM value, look up a pair of PDM reference points closest to the linear PDM value in the PDM reference point memory, obtain an actual PDM value corresponding to the linear PDM value through linear interpolation based on the pair of PDM reference points, and output the actual PDM value. 
         [0023]    According to an embodiment, the PDM value calculator may linearly interpolating the PDM values of the pair of PDM reference points to obtain an actual PDM value corresponding to the linear PDM value. 
         [0024]    According to an embodiment, the PDM value calculator may linearly interpolate the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear PDM value, and obtain an actual PDM value corresponding to the linear PDM value based on the linear PDM value and the INL error value. 
         [0025]    According to another embodiment of the present invention, provided is a method of automatic frequency control, the method comprising: receiving a target frequency value; looking up a pair of frequency reference points closest to the target frequency value among a plurality of frequency reference points, wherein each frequency reference point comprises a frequency value and a linear pulse density modulation (PDM) value; linearly interpolating the linear PDM values of the pair of frequency reference points to obtain a linear frequency PDM value corresponding to the target frequency value; converting the linear frequency PDM value into an actual frequency PDM value; and performing automatic frequency control based on the actual frequency PDM value. 
         [0026]    According to an embodiment, converting the linear frequency PDM value into an actual frequency PDM value may comprise: looking up a pair of PDM reference points closest to the linear frequency PDM value among a plurality of PDM reference points, wherein each PDM reference point comprises a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, the INL error value being the difference between the actual PDM value and the linear PDM value; and obtaining an actual frequency PDM value corresponding to the linear frequency PDM value through linear interpolation based on the pair of PDM reference points. 
         [0027]    According to an embodiment, obtaining an actual frequency PDM value corresponding to the linear frequency PDM value through linear interpolation may comprise: linearly interpolating the PDM values of the pair of PDM reference points to obtain an actual frequency PDM value corresponding to the linear frequency PDM value. 
         [0028]    According to an embodiment, obtaining an actual frequency PDM value corresponding to the linear frequency PDM value through linear interpolation may comprise: linearly interpolating the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear frequency PDM value; and obtaining an actual frequency PDM value corresponding to the linear frequency PDM value based on the linear frequency PDM value and the INL error value. 
         [0029]    According to another embodiment of the present invention, provided is a mobile terminal comprising an automatic gain controller according to embodiments of the present invention. 
         [0030]    According to another embodiment of the present invention, provided is a mobile terminal comprising an automatic frequency controller according to embodiments of the present invention. 
         [0031]    According to another embodiment of the present invention, provided is a mobile terminal comprising a PDM value converter according to embodiments of the present invention. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  shows a block diagram of a pulse density modulation (PDM) value converter according to an embodiment of the present invention; 
           [0033]      FIG. 2  shows a block diagram of an automatic gain controller according to an embodiment of the present invention; 
           [0034]      FIG. 3  shows a block diagram of an automatic frequency controller according to an embodiment of the present invention; 
           [0035]      FIG. 4  shows a flowchart of a method of PDM value conversion according to an embodiment of the present invention; 
           [0036]      FIG. 5  shows a flowchart of a method of automatic gain control according to an embodiment of the present invention; 
           [0037]      FIG. 6  shows a flowchart of a method of automatic frequency control according to an embodiment of the present invention; and 
           [0038]      FIG. 7  shows a block diagram of a mobile terminal according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    Exemplary embodiments according to the present invention are described in detail below with reference to the accompanying drawings. Throughout the drawings, identical or like reference numerals are granted to components which are substantially structurally and functionally the same, and redundant description on the substantially same components is omitted for conciseness of the description. 
         [0040]    According to the present invention, in order to improve the accuracy of linear interpolation of a pulse density modulation (PDM) value, the linearity of the PDM value needs to be improved, namely, the integral non-linear (INL) error therein is to be eliminated. Here, an INL error eliminated PDM value is referred to as a linear PDM value, and an uncorrected PDM value is referred to as an actual PDM value. 
         [0041]    In order to realize the conversion between a linear PDM value and an actual PDM in practical use, the INL errors on several PDM reference points need to be pre-determined. This process can be conducted before chips leave the factory. 
         [0042]    As the INL errors of the PDM values of chips may be relatively consistent among the same batch, and may be significantly different among different batches, PDM value correction information may generally be produced individually for each batch of chips. For example, sample chips can be extracted from the same batch of chips, and INL tests for PDM values are respectively conducted to obtain INL error values, and the INL error values are averaged to obtain an INL error value of this batch of chips. 
         [0043]    Examples of PDM reference points obtained after sample chip INL tests and averaging are shown in table 1 below. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Serial 
                 Linear PDM  
                 Actual PDM  
                 INL error  
               
               
                   
                 number 
                 value 
                 value 
                 value 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 
                 28 
                 0 
                 −28 
               
               
                   
                 1 
                 128 
                 104 
                 −24 
               
               
                   
                 2 
                 256 
                 236 
                 −20 
               
               
                   
                 3 
                 384 
                 368 
                 −16 
               
               
                   
                 4 
                 512 
                 500 
                 −12 
               
               
                   
                 5 
                 640 
                 633 
                 −7 
               
               
                   
                 6 
                 768 
                 764 
                 −4 
               
               
                   
                 7 
                 896 
                 896 
                 0 
               
               
                   
                 8 
                 1024 
                 1027 
                 3 
               
               
                   
                 9 
                 1152 
                 1158 
                 6 
               
               
                   
                 10 
                 1280 
                 1288 
                 8 
               
               
                   
                 11 
                 1408 
                 1419 
                 11 
               
               
                   
                 12 
                 1536 
                 1549 
                 13 
               
               
                   
                 13 
                 1664 
                 1680 
                 16 
               
               
                   
                 14 
                 1792 
                 1810 
                 18 
               
               
                   
                 15 
                 1920 
                 1939 
                 19 
               
               
                   
                 16 
                 2048 
                 2068 
                 20 
               
               
                   
                 17 
                 2176 
                 2192 
                 16 
               
               
                   
                 18 
                 2304 
                 2316 
                 12 
               
               
                   
                 19 
                 2432 
                 2441 
                 9 
               
               
                   
                 20 
                 2560 
                 2567 
                 7 
               
               
                   
                 21 
                 2688 
                 2692 
                 4 
               
               
                   
                 22 
                 2816 
                 2818 
                 2 
               
               
                   
                 23 
                 2944 
                 2943 
                 −1 
               
               
                   
                 24 
                 3072 
                 3069 
                 −3 
               
               
                   
                 25 
                 3200 
                 3195 
                 −5 
               
               
                   
                 26 
                 3328 
                 3321 
                 −7 
               
               
                   
                 27 
                 3456 
                 3447 
                 −9 
               
               
                   
                 28 
                 3584 
                 3575 
                 −9 
               
               
                   
                 29 
                 3712 
                 3701 
                 −11 
               
               
                   
                 30 
                 3840 
                 3829 
                 −11 
               
               
                   
                 31 
                 3968 
                 3956 
                 −12 
               
               
                   
                 32 
                 4095 
                 4083 
                 −12 
               
               
                   
               
             
          
         
       
     
         [0044]    In table 1, each row corresponds to one PDM reference point. The PDM reference points in table 1 comprise a linear PDM value, an actual PDM value and an INL error value, wherein the INL error value is the difference between the actual PDM value and the linear PDM value. However, this is merely an example, and the present invention is not limited in this regard. According to an embodiment, the PDM reference points may also be in another form, for example, may comprise only two of the linear PDM value, the actual PDM value and the INL error value, or the like. 
         [0045]      FIG. 1  shows a block diagram of a pulse density modulation (PDM) value converter 100 according to an embodiment of the present invention. 
         [0046]    Referring to  FIG. 1 , the PDM value converter  100  comprises a PDM reference point memory  101  and a PDM value calculator  102 . The PDM reference points obtained through the tests before chips leave the factory can be pre-stored in the PDM reference point memory  101 , for example, as shown in table 1 above. 
         [0047]    The PDM value calculator  102  receives a linear PDM modulation value, and looks up a pair of PDM reference points closest to the linear PDM modulation value in the PDM reference point memory  101 . On the basis of the pair of PDM reference points, the PDM value calculator  102  obtains an actual PDM value corresponding to the PDM modulation value through linear interpolation and outputs the actual PDM value. 
         [0048]    Particularly, when a PDM reference point comprises a linear PDM value and a corresponding actual PDM value, the PDM value calculator  102  may linearly interpolate the actual PDM values of the pair of pulse density modulation reference points to obtain an actual PDM value corresponding to the linear PDM value directly. 
         [0049]    Alternatively, when a PDM reference point comprises a linear PDM value and a corresponding INL error value, the PDM value calculator  102  may linearly interpolate the INL error values of the pair of PDM reference points to obtain an INL error value corresponding to the linear PDM value, and obtain an actual PDM value corresponding to the linear PDM value based on the linear PDM value and the INL error value. 
         [0050]    Although the PDM value converter  100  of  FIG. 1  receives a linear PDM modulation value and converts it into a corresponding actual PDM value, the present invention is not limited in this regard. According to an embodiment, an actual PDM modulation value may also be received and converted into a corresponding linear PDM value; the operation method thereof is similar and will not be further described. 
         [0051]      FIG. 2  shows a block diagram of an automatic gain controller  200  according to an embodiment of the present invention. 
         [0052]    Referring to  FIG. 2 , the automatic gain controller  200  comprises a power reference point memory  201 , a power PDM value calculator  202 , a PDM value converter  203  and a PDM modulator  204 . 
         [0053]    A plurality of power reference points can be pre-stored in the power reference point memory  201 , with each power reference point comprising a power value and a corresponding linear PDM value. Generally, power reference points are pre-produced through calibration and stored during production. 
         [0054]    Examples of power reference points pre-stored in the power reference point memory  201  are shown in table 2 below, in which the linear PDM value can be obtained by correcting the actual PDM value based on the INL error value. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Power value 
                 Linear PDM value 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 4.08412 
                 2772 
               
               
                   
                 9.962472 
                 2922 
               
               
                   
                 14.92162 
                 3049 
               
               
                   
                 17.74155 
                 3121 
               
               
                   
               
             
          
         
       
     
         [0055]    Although a power reference point stored in the power reference point memory  201  of  FIG. 2  comprises a power value and a corresponding linear PDM value, the present invention is not limited in this regard. According to an embodiment, a power reference point may also comprise a power value and a corresponding actual PDM value. 
         [0056]    The power PDM value calculator  202  receives a target power value, looks up a pair of power reference points closest to the target power value in the power reference point memory  201 , linearly interpolates the linear PDM values of the pair of power reference points to obtain a linear power PDM value corresponding to the target power value, and converts the linear power PDM value into an actual power PDM value via the PDM value converter  203 . 
         [0057]    Alternatively, when a power reference point comprises a power value and a corresponding actual PDM value, the power PDM value calculator  202  may convert an actual PDM value in a power reference point into a corresponding linear PDM value via the PDM value converter  203  for linear interpolation. 
         [0058]    The PDM value converter  203  may be the PDM value converter  100  of  FIG. 1  for conversion between a linear PDM value and an actual PDM value. 
         [0059]    The PDM modulator  204  performs automatic gain control based on the actual power PDM value produced by the power PDM value calculator  202 . 
         [0060]    As the power PDM value calculator  202  uses an INL error corrected linear PDM value in the linear interpolation calculation, a more accurate actual power PDM value may finally be produced for power control. Thus, the reciprocating ping-pong time can be reduced, accelerating the automatic gain control. 
         [0061]      FIG. 3  shows a block diagram of an automatic frequency controller  300  according to an embodiment of the present invention. 
         [0062]    Referring to  FIG. 3 , the automatic frequency controller  300  comprises a frequency reference point memory  301 , a frequency PDM value calculator  302 , a PDM value converter  303  and a PDM modulator  304 . 
         [0063]    A plurality of frequency reference points can be pre-stored in the frequency reference point memory  301 , with each frequency reference point comprising a frequency value and a corresponding linear PDM value. Generally, frequency reference points are pre-produced through calibration and stored during production. 
         [0064]    Although a frequency reference point stored in the frequency reference point memory  301  of  FIG. 3  comprises a frequency value and a corresponding linear PDM value, the present invention is not limited in this regard. According to an embodiment, a frequency reference point may also comprise a frequency value and a corresponding actual PDM value. 
         [0065]    The frequency PDM value calculator  302  receives a target frequency value, looks up a pair of frequency reference points closest to the target frequency value, linearly interpolates the linear PDM values of the pair of frequency reference points to obtain a linear frequency PDM value corresponding to the target frequency value, and converts the linear frequency PDM value into an actual frequency PDM value via the PDM value converter  303 . 
         [0066]    Alternatively, when a frequency reference point comprises a frequency value and a corresponding actual PDM value, the frequency PDM value calculator  202  may convert a actual PDM value in a frequency reference point into a corresponding linear PDM value via the PDM value converter  203  for linear interpolation. 
         [0067]    The PDM value converter  303  may be the PDM value converter  100  of  FIG. 1  for conversion between a linear PDM value and an actual PDM value. 
         [0068]    The PDM modulator  304  performs the automatic gain control based on the actual frequency PDM value produced by the frequency PDM value calculator  302 . 
         [0069]    As the frequency PDM value calculator  302  uses an INL error corrected linear PDM value in the linear interpolation calculation, a more accurate actual frequency PDM value can finally be produced for tuning control. Thus, the reciprocating ping-pong time can be reduced, accelerating the automatic frequency control. 
         [0070]      FIG. 4  shows a flowchart of a method of PDM value conversion according to an embodiment of the present invention. 
         [0071]    Referring to  FIG. 4 , at step S 401 , a linear PDM value is received. 
         [0072]    At step S 402 , a pair of PDM reference points closest to the linear PDM value are looked up among a plurality of pre-stored PDM reference points, wherein each PDM reference point comprises a linear PDM value, an actual PDM value and/or an integral non-linear (INL) error value, the INL error value being the difference between the actual PDM value and the linear PDM value. The plurality of pre-stored PDM reference points mentioned above can be obtained through tests before chips leave the factory, for example, as shown in table 2 above. 
         [0073]    At step S 403 , an actual PDM value corresponding to the linear PDM value is obtained through linear interpolation based on the pair of PDM reference points found. 
         [0074]    Particularly, when a PDM reference point comprises a linear PDM value and a corresponding actual PDM value, the actual PDM values of the pair of pulse density modulation reference points can be linearly interpolated to obtain an actual PDM value corresponding to the linear PDM value directly. 
         [0075]    Alternatively, when a PDM reference point comprises a linear PDM value and a corresponding INL error value, the INL error values of the pair of PDM reference point can be linearly interpolated to obtain an INL error value corresponding to the linear PDM value, and an actual PDM value corresponding to the linear PDM value can be obtained based on the linear PDM value and the INL error value. 
         [0076]    At step S 404 , the actual PDM value is output. 
         [0077]    Although in the method of PDM value conversion of  FIG. 3  a linear PDM modulation value is received and converted into a corresponding actual PDM value, the present invention is not limited in this regard. According to an embodiment, an actual PDM modulation value can also be received and converted into a corresponding linear PDM value; the operation method thereof is similar and will not be further described. 
         [0078]      FIG. 5  shows a flowchart of a method of automatic gain control according to an embodiment of the present invention. 
         [0079]    Referring to  FIG. 5 , at step S 501 , a target power value is received. 
         [0080]    At step S 502 , a pair of power reference points closest to the target power value are looked up among a plurality of power reference points, wherein each power reference point comprises a power value and a linear PDM value. Generally, a power reference point is pre-produced through calibration and stored during production, for example, as shown in table 2. 
         [0081]    As an example, a pre-stored power reference point may comprise a power value and a corresponding linear PDM value, but the present invention is not limited in this regard. According to an embodiment, a power reference point may also comprise a power value and a corresponding actual PDM value. 
         [0082]    At step S 503 , the linear PDM values of the pair of power reference points are linearly interpolated to obtain a linear PDM modulation value corresponding to the target power value. 
         [0083]    Alternatively, when a power reference point comprises a power value and a corresponding actual PDM value, the actual PDM value of the power reference point can be converted into a corresponding linear PDM value for linear interpolation. 
         [0084]    At step S 504 , the linear power PDM value is converted into an actual power PDM value. 
         [0085]    The process of conversion between a linear PDM value and an actual PDM value can be carried out with reference to steps S 401  to S 404 . 
         [0086]    At step S 505 , automatic gain control is performed based on the actual power PDM value. 
         [0087]    As an INL error corrected linear PDM value is used in the linear interpolation calculation, a more accurate actual power PDM value can thus finally be produced for power control. Thus, the reciprocating ping-pong time can be reduced, accelerating the automatic gain control. 
         [0088]      FIG. 6  shows a flowchart of a method of automatic frequency control according to an embodiment of the present invention. 
         [0089]    Referring to  FIG. 6 , at step S 601 , a target frequency value is received. 
         [0090]    At step S 602 , a pair of frequency reference points closest to the target frequency value are looked up among a plurality of pre-stored frequency reference points, wherein each frequency reference point comprises a frequency value and a linear PDM value. Generally, a frequency reference point is pre-produced through calibration and stored during production. 
         [0091]    As an example, a pre-stored frequency reference point may comprise a frequency value and a corresponding linear PDM value, but the present invention is not limited in this regard. According to an embodiment, a frequency reference point may also comprise a frequency value and a corresponding actual PDM value. 
         [0092]    At step S 603 , the linear PDM values of the pair of frequency reference points are linearly interpolated to obtain a linear PDM modulation value corresponding to the target frequency value. 
         [0093]    Alternatively, when a frequency reference point comprises a frequency value and a corresponding actual PDM value, the actual PDM value of the frequency reference point may be converted into a corresponding linear PDM value for linear interpolation. 
         [0094]    At step S 604 , the linear frequency PDM value is converted into an actual frequency PDM value. 
         [0095]    The process of conversion between a linear PDM value and an actual PDM value can be carried out with reference to steps S 401  to S 404 . 
         [0096]    At step S 605 , automatic frequency control is performed based on the actual frequency PDM value. 
         [0097]    As an INL error corrected linear PDM value is used in the linear interpolation calculation, a more accurate actual frequency PDM value can thus finally be produced for tuning control. Thus, the reciprocating ping-pong time can be reduced, accelerating the automatic frequency control. 
         [0098]      FIG. 7  shows a block diagram of a mobile terminal  700  according to an embodiment of the present invention. 
         [0099]    Referring to  FIG. 7 , a mobile terminal  700  comprises an automatic gain controller  701 , an automatic frequency controller  702 , a PDM converter  703  and a PDM modulator  704 . Wherein, the automatic gain controller  701  may be the automatic gain controller  200  of  FIG. 2 , the automatic frequency controller  702  may be the automatic frequency controller  300  of  FIG. 3 , and the PDM converter  703  may be the PDM converter  100  of  FIG. 1 . 
         [0100]    Although the PDM converter  703  and the PDM modulator  704  are shown as separate components, the present invention is not limited in this regard. The PDM converter  703  and/or the PDM modulator  704  may also be implemented as internal components of the automatic gain controller  701  and/or the automatic frequency controller  702  as describe in the above embodiments. 
         [0101]    Although the mobile terminal  700  in  FIG. 7  comprises an automatic gain controller  701  and an automatic frequency controller  702 , the present invention is not limited in this regard. According to an embodiment, the mobile terminal  700  may comprise a PDM converter  703  and any other circuits using a PDM value. 
         [0102]    With the PDM value converter, the automatic gain controller using PDM, the automatic frequency controller using PDM and the mobile terminal using PDM, and the method thereof according to the present invention, the accuracy of the PDM value may be increased and the reciprocating ping-pong time in an AGC or AFC process can be reduced by correcting the INL error to improve the linearity of a PDM value, thus improving the performance of power control and tuning control. 
         [0103]    Features of many embodiments are described above, so that those of general knowledge in the art can clearly understand the forms of the description clearly. Those of general knowledge in the art can understand that he/she can accomplish the same objectives as the above-mentioned embodiments and/or achieving the same advantages as the above-mentioned embodiments by designing or modifying other processes and structures based on the disclosure of the present invention. Those of general knowledge in the art can also understand that equivalent structures not departing from the spirit and scope of the present invention may be modified, replaced and embellished in any way without departing from the spirit and scope of the present invention, so that those of general knowledge in the art can clearly understand forms of the description. Features of many embodiments are described above, so that those of general knowledge in the art could understand the form of the description clearly. Those of general knowledge in the art can understand that he/she can accomplish the same objectives as the above-mentioned embodiments and/or achieving the same advantages as the above-mentioned embodiments by designing or modifying other processes and structures based on the disclosure of the present. Those of general knowledge in the art can also understand that equivalent structures not departing from the spirit and scope of the present invention may be modified, replaced and embellished in any way without departing from the spirit and scope of the present invention.