Abstract:
A mixing apparatus and related methods are provided. The mixing apparatus can filter out unwanted harmonic orders according to demands, to thereby increase circuit attribute performance. Regardless of the type of mixing circuit used for the mixing apparatus, the harmonic interfering phenomenon can be substantially improved.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of Application No. 096105393 filed in Taiwan, R.O.C. on Feb. 14, 2007, and Application No. 096127026, filed in Taiwan, R.O.C. on Jul. 25, 2007, under 35 U.S.C. §119; the entire contents of all of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a mixer, particularly to a mixer for harmonic rejection. 
         [0004]    2. Brief Description of the Related Art 
         [0005]    A mixer is an important component in many data communication circuits. A mixer is used for mixing a received signal with a clock signal LO. The above-mentioned process generates not only the expected mixing signal but also the unexpected harmonic orders, thereby interfering the transmitted data, greatly reducing signal-to-noise ratio (SNR), and decreasing the efficiency of the receiver. 
         [0006]      FIG. 1  shows a function block diagram illustrating the prior art for overcoming the harmonic problem. The function block diagram  100  comprises an antenna  102 , a low noise amplifier (LNA)  104 , a mixer  105 , a filter  106 , a filter  107 , and a frequency synthesizer  108 , wherein the frequency synthesizer  108  provides a clock signal LO. The signal processing method as illustrated in the above-mentioned  FIG. 1 , uses the filter  107  to filter out the unwanted harmonic and finally generates an intermediate frequency/IF signal I without the hamonic or a baseband frequency B. 
         [0007]    Traditionally, the filter  107  is generally implemented by filters, such as LC filter, Gm-C filter, and OP-RC filter, and so forth. If the filter  107  is implemented by the LC filter and is made as part of the chip, the chip area and the chip cost will be increased due to the quite big value of the conductance L. And, if the L is made on the outside of the chip, the cost will also increase. If the filter  107  is implemented by the Gm-C filter or the OP-RC filter, the noise figure increases to make the linearity decrease and the overall circuit performance get worse. However, no matter how good the filter is adopted, the the chip area and the chip cost increase inevitably. 
         [0008]    In light of the above-mentioned description, not only the cost is expensive according to the prior art, but also the circuit attribute cannot achieve the standard of the harmonic interference cancellation that those who are skilled in the art wants to reach. Therefore, an invention for solving the long existing problems in the above-mentioned field is needed urgently. 
       SUMMARY OF THE INVENTION 
       [0009]    One object of the present invention is to provide a harmonic rejecting mixing apparatus for solving the above-mentioned problem. 
         [0010]    One object of the present invention is to provide a harmonic rejecting mixing apparatus for solving the harmonic interference of various frequencies according to the demand. 
         [0011]    The present invention provides an equivalent function block structure of a mixing apparatus that can filter out the harmonic orders according to design requirement so as to increase the performance of the circuit. Also, no matter what type and style of the mixing circuit is adopted by the mixing apparatus, the phenomenon of harmonic interference will be greatly improved according to the present invention. The chip designer can also design the circuit to filter out the harmonic orders according to the individual requirement. The circuit design is therefore more flexible. According to the above-mentioned description, the present invention is a novel invention. 
         [0012]    Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
           [0014]      FIG. 1  shows a function block diagram illustrating the prior art for overcoming harmonic interference. 
           [0015]      FIG. 2  shows a function block diagram illustrating the mixing apparatus according to one embodiment of the present invention. 
           [0016]      FIG. 3(   a ) shows a function block diagram illustrating the mixing apparatus according to one embodiment of the present invention. 
           [0017]      FIG. 3(   b ) shows a function block diagram illustrating the mixing apparatus according to one embodiment of the present invention. 
           [0018]      FIG. 3(   c ) shows a function block diagram illustrating the mixing apparatus according to one embodiment of the present invention. 
           [0019]      FIG. 3(   d ) shows a function block diagram illustrating the mixing apparatus according to one embodiment of the present invention. 
           [0020]      FIG. 4  shows a circuit implementation diagram according to one embodiment of  FIG. 2 ,  FIG. 3(   a ), and  FIG. 3(   b ). 
           [0021]      FIG. 5  shows a circuit implementation diagram according to another embodiment of  FIG. 2 ,  FIG. 3(   a ), and  FIG. 3(   b ). 
           [0022]      FIG. 6  shows a circuit implementation diagram according to one embodiment of  FIG. 2 ,  FIG. 3(   c ), and  FIG. 3(   d ). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    In the past, a filter is used to filter out the harmonic waves that induces interference. However, the present invention provides a mixing apparatus, wherein at least one harmonic of the mixing output signal in the output of the mixing apparatus is eliminated in the mixing apparatus. Therefore, using at least one filter to filter out the harmonic can be omitted. Herein, not only the chip area is reduced, but also the chip cost is relatively reduced to increase the price competability. Besides, the harmoic orders to be filtered can be decided according to the requirement of design objectives. Therefore, the design is extremely flexible. Compared to the prior art, the chip area, the price, and the design flexibility have been greatly improved. 
         [0024]    The principle of the present invention can be illustrated by Fourier Series for thorough comprehension. According to the inference of the Fourier Series, the signal LO(t) is actually composed of sinusoidal series of the first order, third order, fifth order, seventh order, and so forth, as illustrated in the following equation: 
         [0000]    
       
         
           
             
               LO 
                
               
                 ( 
                 t 
                 ) 
               
             
             = 
             
               
                 sin 
                  
                 
                   ( 
                   
                     
                       ω 
                       0 
                     
                      
                     t 
                   
                   ) 
                 
               
               + 
               
                 
                   sin 
                    
                   
                     ( 
                     
                       3 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 3 
               
               + 
               
                 
                   sin 
                    
                   
                     ( 
                     
                       5 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 5 
               
               + 
               
                 
                   sin 
                    
                   
                     ( 
                     
                       7 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 7 
               
               + 
               
                 
                   sin 
                    
                   
                     ( 
                     
                       9 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 9 
               
               + 
               
                 
                   sin 
                    
                   
                     ( 
                     
                       11 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 11 
               
               + 
               … 
             
           
         
       
       
         
           
             
               wherein 
                
               
                   
               
                
               
                 
                   sin 
                    
                   
                     ( 
                     
                       3 
                        
                       
                           
                       
                        
                       
                         ω 
                         0 
                       
                        
                       t 
                     
                     ) 
                   
                 
                 3 
               
             
             , 
             
               
                 sin 
                  
                 
                   ( 
                   
                     5 
                      
                     
                         
                     
                      
                     
                       ω 
                       0 
                     
                      
                     t 
                   
                   ) 
                 
               
               5 
             
             , 
             
               
                 sin 
                  
                 
                   ( 
                   
                     7 
                      
                     
                         
                     
                      
                     
                       ω 
                       0 
                     
                      
                     t 
                   
                   ) 
                 
               
               7 
             
             , 
             
               
                 sin 
                  
                 
                   ( 
                   
                     9 
                      
                     
                         
                     
                      
                     
                       ω 
                       0 
                     
                      
                     t 
                   
                   ) 
                 
               
               9 
             
             , 
           
         
       
     
         [0000]    and so forth belong to the part of the harmonic orders which will interfere with the signal. Therefore, if the interfering harmonic orders are eliminated, the SNR value can be increased to increase the circuit performance. The present invention adopts this principle to achieve the objective of harmonic rejection accordingly. The following equation can be utilized to eliminate the harmonic orders from the above-mentioned equation LO(t): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       V 
                       out 
                     
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                     
                    
                   
                     
                       
                         R 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                       × 
                       
                         ( 
                         
                           
                             sin 
                              
                             
                               ( 
                               
                                 
                                   ω 
                                   o 
                                 
                                  
                                 t 
                               
                               ) 
                             
                           
                           + 
                           
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   3 
                                    
                                   
                                       
                                   
                                    
                                   
                                     ω 
                                     0 
                                   
                                    
                                   t 
                                 
                                 ) 
                               
                             
                             3 
                           
                           + 
                           
                             
                               sin 
                                
                               
                                 ( 
                                 
                                   5 
                                    
                                   
                                       
                                   
                                    
                                   
                                     ω 
                                     0 
                                   
                                    
                                   t 
                                 
                                 ) 
                               
                             
                             5 
                           
                           + 
                           … 
                         
                         ) 
                       
                     
                     - 
                     
                       
                         1 
                         3 
                       
                        
                       
                         R 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                       × 
                     
                   
                 
               
             
             
               
                 
                     
                    
                   
                     ( 
                     
                       
                         sin 
                          
                         
                           ( 
                           
                             3 
                              
                             
                                 
                             
                              
                             
                               ω 
                               0 
                             
                              
                             t 
                           
                           ) 
                         
                       
                       + 
                       
                         
                           sin 
                            
                           
                             ( 
                             
                               9 
                                
                               
                                   
                               
                                
                               
                                 ω 
                                 0 
                               
                                
                               t 
                             
                             ) 
                           
                         
                         3 
                       
                       + 
                       
                         
                           sin 
                            
                           
                             ( 
                             
                               15 
                                
                               
                                   
                               
                                
                               
                                 ω 
                                 0 
                               
                                
                               t 
                             
                             ) 
                           
                         
                         5 
                       
                       + 
                       … 
                     
                     ) 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       R 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                     × 
                     
                       ( 
                       
                         
                           sin 
                            
                           
                             ( 
                             
                               
                                 ω 
                                 0 
                               
                                
                               t 
                             
                             ) 
                           
                         
                         + 
                         
                           
                             sin 
                              
                             
                               ( 
                               
                                 5 
                                  
                                 
                                     
                                 
                                  
                                 
                                   ω 
                                   0 
                                 
                                  
                                 t 
                               
                               ) 
                             
                           
                           5 
                         
                         + 
                         … 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
         [0025]    The above-mentioned equations V out (t) can completely filter out the third order harmonic. Same methods can be used to filter out the fifth order harmonic, the seventh order harmonic, the ninth order harmonic, and so forth. 
         [0026]    Please refer to  FIG. 2 . The function block diagram shows a harmonic rejecting mixing apparatus according to one embodiment of the present invention. 
         [0027]    As shown in  FIG. 2 , the harmonic rejecting mixing apparatus  200  comprises a mixing circuit  201 , a first circuit  202 , a second circuit  203 , a third circuit  204 , and a summation unit  205 . The mixing circuit  201  further comprises a mixing unit  2012 , for receiving a signal S and a f 0  and performing mixing of the signal S and the f 0  via the mixing unit  2012  to generate a signal S 1 . The first circuit  202  further comprises a gain unit  2021  and a mixing unit  2022 , for receiving the signal S and the 3f 0  and performing mixing of the signal S and the 3f 0  via the gain unit  2021  and the mixing unit  2022  to generate a signal S 2 . The second circuit  203  further comprises a gain unit  2031  and a mixing unit  2032 , for receiving the signal S and the 5f 0  and performing mixing of the signal S and the 5f 0  via the gain unit  2031  and the mixing unit  2032  to generate a signal S 3 . The third circuit  204  further comprises a gain unit  2041  and a mixing unit  2042 , for receiving the signal S and the 7f 0  and performing mixing the signal S and the 7f 0  via the gain unit  2041  and the mixing unit  2042  to generate a signal S 4 . The gain units  2021 ,  2031 , and  2041  convert the signals into the signals having the gain value, and the mixing units  2022 ,  2032 , and  2042  mix the two signals for generating the harmonic signals, which want to be eliminated. Finally, the summation unit  205  sums up the signals S 1 , S 2 , S 3 , and S 4  and then outputs the S′. 
         [0028]    Among them, the first circuit (that is, the gain unit  2021  and the mixing unit  2022 ) can be regarded as the third harmonic eliminating circuit; the second circuit (that is, the gain unit  2031  and the mixing unit  2032 ) can be regarded as the fifth harmonic eliminating circuit; and the third circuit (that is, the gain unit  2041  and the mixing unit  2042 ) can be regarded as the seventh harmonic eliminating circuit. Besides, since the signals generated by the third harmonic eliminating circuit comprise the third harmonic, the ninth harmonic, the fifteenth harmonic, and so forth, the ninth harmonic eliminating circuit in the embodiment of the present invention is not needed. In addition,  FIG. 2  shows that one embodiment of the harmonic eliminating circuit is also a mixer. The difference is that the frequency of the clock signal is N times the clock signal of the mixing circuit  201  and its gain value of the clock signal is 1/N times the gain value of the mixing circuit  201 . Besides, f 0 , 3f 0 , 5f 0 , and 7f 0  are generated by a clock signal generator and the embodiments of which can be: frequency synthesizer, phase-locked loop (PLL), and so forth. 
         [0029]    Please refer to  FIGS. 3(   a ),  3 ( b ),  3 ( c ), and  3 ( d ).  FIGS. 3(   a ),  3 ( b ),  3 ( c ), and  3 ( d ) are the function block diagrams illustrating haramonic rejecting mixing apparatus of various embodiments according to the present invention in  FIG. 2 . Since the processing principle of  FIGS. 3(   a ),  3 ( b ),  3 ( c ), and  3 ( d ) is similar to that of  FIG. 2 , the detailed description is omitted hereafter. 
         [0030]    Please refer to  FIG. 4 .  FIG. 4  shows a circuit diagram implementing one embodiment of the present invention. Gilbert mixer is adopted for the implementation of this embodiment and other types of mixers can be applied in the present invention. The functions illustrated in  FIG. 2 ,  FIG. 3(   a ), and  FIG. 3(   b ) are achieved by setting LO 1 (+)=f 0 , LO 1 (−)=−f 0 , LO 2 (+)=3f 0 , LO 2 (−)=−3f 0 , LO 3 (+)=5f 0 , LO 3 (−)=−5f 0 , LO 4 (+)=7f 0 , and LO 4 (−)=−7f 0 . Since Gilbert mixer is a well-known technology for those who are skilled in the art, the description is omitted. 
         [0031]    Please refer to  FIG. 5 .  FIG. 5  illustrates a circuit implementation diagram illustrating another embodiment of  FIG. 2 ,  FIG. 3(   a ), and  FIG. 3(   b ). The single-ended mixer is used for the implementation where the functions illustrated in  FIG. 2 ,  FIG. 3(   a ), and  FIG. 3(   b ) are achieved by setting LO 1 (+)=f 0 , LO 1 (−)=−f 0 , LO 2 (+)=3f 0 , LO 2 (−)=−3f 0 , LO 3 (+)=5f 0 , LO 3 (−)=−5f 0 , LO 4 (+)=7f 0 , and LO 4 (−)=−7f 0 . Since the single-ended mixer is a well-known technology for those who are skilled in the art, the description is omitted. 
         [0032]    Please refer to  FIG. 6 .  FIG. 6  is a circuit implementation diagram illustrating one embodiment of  FIGS. 2 ,  3 ( c ), and  3 ( d ). The Gilbert mixer is adopted for implementation where the functions illustrated in  FIG. 2 ,  FIG. 3(   c ), and  FIG. 3(   d ) are achieved by setting LO 1 (+)=f 0 , LO 1 (−)=−f 0 , LO 2 (+)=3f 0 , LO 2 (−)=−3f 0 , LO 3 (+)=5f 0 , LO 3 (−)=−5f 0 , LO 4 (+)=7f 0 , and LO 4 (−)=−7f 0 . 
         [0033]    In addition, as illustrated in  FIGS. 4 ,  5 , and  6 , one embodiment of the summation unit of  FIG. 2  and  FIGS. 3(   a )˜ 3 ( d ) can be a node. 
         [0034]    In practical applications, if the signal intensity of the harmonic signal is small, the corresponding harmonic eliminating circuit (that is, the gain unit and the mixing unit) can be omitted. For example, since the signal intensity of the higher orders harmonic signal is small, the harmonic eliminating circuit for the fifth order and the orders higher than the fifth order can be omitted. In other words, only the third order harmonic eliminating circuit is remained. Of course, if more precise signal for back-end circuit processing is required, the third order and the fifth order harmonic eliminating circuits can be kept accordingly. 
         [0035]    Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it should not be construed as any limitation on the range of implementation of the invention. Various equivalent changes and modifications of the shape, scope, characteristics, and spirit as described by the claims of the present invention is to be encompassed by the scope of the present invention.