Abstract:
A method and an apparatus for analyzing performance of a multi-stage radio frequency amplifier are described. The method simplifies the multi-stage radio frequency amplifier into equivalent input parts, output parts and mid-stage parts. The mid-stage parts are temporarily unset. Therefore, the equivalent input parts and output parts will be adjusted to make best gain performance and the mid-stage parts will be the next targets for analysis. Repeating the above-mentioned methods for decomposing the circuit can systemize the method for analyzing circuits and problems in each part of the circuit may be found more quickly.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present is related to a method and an apparatus for analyzing performance of a multi-stage radio frequency amplifier, and especially to a systematic method for rapidly analyzing stage gain and loss of each amplifier.  
         [0003]     2. Description of Related Art  
         [0004]     Radio frequency amplifiers are important in the design of radio frequency integrate circuits. When circuits are operated under microwave and radio frequencies, circuits with mismatched impedances suffer from decay and loss of power gain.  
         [0005]      FIG. 1  shows a prior art single-stage radio frequency amplifier, which comprises an input power source circuit  010 , an input-stage matching network  030 , a single-stage amplifier  050 , an output-stage matching network  070  and an output circuit  090 . The input power source circuit  010  further includes an input source  012  and an input power source characteristic impedance  014 ; the impedance value of the input power source characteristic impedance  014  is 50 ohms.  
         [0006]     The prior art method for analyzing the single-stage radio frequency amplifier is to find a reflection coefficient Γ S  of a power source terminal, a reflection coefficient Γ L  of the load, an input reflection coefficient Γ IN , and an output reflection coefficient Γ OUT . The four coefficients can be adjusted for acquiring preset gain value.  
         [0007]     Matching methods in producing multi-stage radio integrate circuits are important issues in recent years. Prior art methods for analyzing power gain are designed for single-stage radio frequency amplifiers and microwave amplifiers; effective methods for analyzing power loss of multi-stage radio frequency amplifiers have not yet been successfully proposed. A common method applied for analyzing a multi-stage radio frequency amplifier is trial and error, but this wastes time and is ineffective. Prior art circuit simulation methods are hard to use in accounting for the reason why power gain decays.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is related to a method and an apparatus for analyzing performance of a multi-stage radio frequency amplifier. The apparatus comprises an input-stage matching network, a mid-stage network, an output-stage matching network and an output circuit. The method mainly includes the following steps: targeting a circuit network for analyzing, and treating non-analyzed circuit networks as mid-stage networks.  
         [0009]     Reflection coefficients Γ S  and Γ L  of the targeted circuit network are obtained first, and then a power source matching network maximum gain G Smax  and a load matching network maximum gain G Lmax  are obtained with a Smith chart. A power source matching network maximum gain G SMAX  of the input-stage matching network and a load matching network maximum gain G LMAX  of the output-stage matching network can be made by adjusting the reflection coefficients Γ S  and Γ L .  
         [0010]     Circuit networks will be neglected after analysis, and non-analyzed circuit networks are decomposed into equivalent circuit parts. One part is targeted for analysis; and the remaining parts are all viewed as a mid-stage network.  
         [0011]     Repeating the above-mention steps for analysis will simplify the complexity of the circuit, and the power decays in circuit networks may be found more rapidly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     The foregoing aspects and many of the attendant advantages of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0013]      FIG. 1  shows a prior art circuit;  
         [0014]      FIG. 2  shows a first embodiment according to the present invention;  
         [0015]      FIG. 3  depicts a simplified circuit of the first embodiment according to the present invention;  
         [0016]      FIG. 4A  shows a device for obtaining a reflection coefficient Γ S  of a power source;  
         [0017]      FIG. 4B  shows a device for obtaining a reflection coefficient Γ L  of a load;  
         [0018]      FIG. 5A  shows another simplified circuit of the first embodiment according to the present invention;  
         [0019]      FIG. 5B  shows another simplified circuit of the first embodiment according to the present invention for obtaining a reflection coefficient Γ S  of a power source;  
         [0020]      FIG. 5C  shows another simplified circuit of the first embodiment according to the present invention for obtaining a reflection coefficient Γ L  of a load;  
         [0021]      FIG. 6  shows a second embodiment according to the present invention; and  
         [0022]      FIG. 7  shows a flow chart of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]     The object of the present invention is to provide a method and an apparatus for analyzing a multi-stage radio frequency amplifier, and finding decay in the multi-stage radio frequency amplifier.  
         [0024]      FIG. 2  shows a first embodiment of the present invention. The multi-stage radio frequency amplifier of the present invention includes an input power source circuit  100 , an input-stage matching network  110 , a first-stage amplifier  120 , a mid matching network  130 , a second-stage amplifier  140 , an output-stage matching network  150 , and an output circuit  160  (may be an impedance with 50 ohms). The input power source circuit  100  comprises a power generating device  102  and an input characteristic impedance  104  (usual value of the impedance is 50 ohms). The mid matching network  130  is provided between a first-stage amplifier  120  and a second-stage amplifier  140 .  
         [0025]     Reference is made to  FIG. 3 . The above-mentioned first-stage amplifier  120 , the second-stage amplifier  140  and the mid matching network  130  are combined into a mid-stage amplifier  135 ; therefore, the complexity of amplifier analysis can be simplified. A reflection coefficient Γ S  of the input-stage matching network  110  and a loading reflection coefficient Γ L  of the output-stage matching network  150  will be obtained; the reflection coefficient Γ S  of the input-stage matching network  110  is then adjusted to be Γ S,max  for conjugate matching with an input reflection coefficient Γ IN  of the mid-stage amplifier  135 . The loading reflection coefficient Γ L  of output-stage matching network  150  is adjusted to be Γ L,max  for conjugate matching with an output reflection coefficient Γ OUT  of the mid-stage matching network.  
         [0026]     Two formulas are provided for obtaining a power source gain G S  of input-stage matching network and loading gain G L . Reflection coefficient Γ S , the reflection coefficient Γ L , the input reflection coefficient Γ IN , and the output reflection coefficient Γ OUT  are used as parameters.  
         G   S     =             1   -     |     Γ   S     ⁢     |   2         |     1   -       Γ   S     ⁢     Γ   IN         ⁢     |   2         ⁢           ⁢     G   L       =         1   -     |     Γ   L     ⁢     |   2         |     1   -       Γ   OUT     ⁢     Γ   L         ⁢     |   2               
 
         [0027]     A power source maximum gain G Smax  and a loading maximum gain G Lmax  can be obtained by adjusting the reflection coefficient Γ S  and the reflection coefficient Γ L ; a power circle of a Smith chart will show the value of G Smax  and G Lmax . Thus, the best power transferring rate and lowest gain loss will be made. Further, the difference between the power source gain G S  and the power source maximum gain G Smax  is the loss of power gain due to unmatched input-stage impedance; and the difference between loading gain G L  and loading maximum gain G Lmax  is loss of power gain due to unmatched output-stage impedance.  
         [0028]     Reference is made to  FIG. 4A , it shows the method for obtaining the above-mentioned reflection coefficient Γ S  of the input-stage matching network  110 , wherein an input characteristic impedance  300  and an output characteristic impedance  310  are both 50 ohms. Incident wave intensity and reflection wave intensity may be measured at first, and the reflection coefficient Γ S  of the power source will be gained by calculating the ratio of them.  
         [0029]     Reference is made to  FIG. 4B , which shows the method for obtaining the above-mentioned reflection coefficient Γ L  of the output-stage matching network  150 . An input characteristic impedance  300  and an output characteristic impedance  310  are both given as 50 ohms. Incident wave intensity and reflection wave intensity may be measured at first, and the reflection coefficient Γ L  of the power source will be gained by calculating the ratio thereof.  
         [0030]     Reference is made to  FIG. 5A ; after analyzing  FIG. 2 , the mid-stage amplifier is restored to the original first-stage amplifier  120 , the mid matching network  130 , and the second-stage amplifier  140 . The matched input-stage matching network  110  and the matched output-stage matching network  150  are neglected. This method is undisclosed in prior art method for analyzing radio frequency and microwave amplifiers.  
         [0031]     Gain of the first-stage amplifier  120  is a fixed value G 01  (gain S 21  (dB) is measured when impedances at two terminals are both 50 ohms, where S 21  is the ratio of output power and input power); and gain of the second stage amplifier  140  is a fixed value G 02  (gain S 21  (dB) is measured when impedances at two terminals are both 50 ohms). Because the mid matching network  130 , the second-stage amplifier  140  and the output circuit  160  can be viewed as an output load of the first-stage amplifier, the reflection coefficient Γ L  of the load is obtained by the method shown in  FIG. 5C . Similarly, the mid matching network  130 , the first-stage amplifier  120  and the output circuit  100  can be treated as an input load of the second-stage amplifier, and the reflection coefficient Γ S  of the power source is obtained by the method shown in  FIG. 5B . Thus, the corresponding load matching network gain G L  and the power source matching network gain G S  can be obtained by applying above-mentioned two methods.  
         [0032]     A power source maximum gain G Smax  and a loading maximum gain G Lmax  can be obtained by adjusting the power source reflection coefficient Γ S  of the mid matching network of the second-stage amplifier and the loading reflection coefficient Γ L  of the mid matching network of first-stage amplifier; an optimal gain may be acquired by Smith chart. The difference between the power source gain G S  and the power source maximum gain G Smax  is the loss of power gain due to the first-stage amplifier  120  being unmatched by mid matching network  130 ; and the difference between loading gain G L  and loading maximum gain G Lmax  is loss of power gain due to the second-stage amplifier  140  being unmatched with the mid matching network  130 . So, adjusting the mid matching network  130  can obtain the maximum gain and least loss.  
         [0033]     Reference is made to  FIG. 6 , which shows another embodiment of the present invention where the circuit may be analyzed by using the methods provided in  FIG. 4A ,  FIG. 4B ,  FIG. 5B ,  FIG. 5C . An input power source circuit  500  depicted in  FIG. 6  includes a power generating device  502 , and an input characteristic impedance  504 . An input-stage matching network  510  is connected to the input power source circuit  500  and the first-stage amplifier  520 , a first stage amplifier  520  is connected behind the input-stage matching network  510 , and a first-stage mid matching network  530  is set between the first-stage amplifier  520  and the second-stage amplifier  540 . Each stage amplifier is therefore connected one by one and there is a corresponding mid-stage matching network set between every two stage amplifiers. Finally, an Nth stage amplifier is connected to an output-stage matching network  580  and an output circuit  590 . The output circuit  590  may have a characteristic impedance (50 ohms).  
         [0034]     In this embodiment according to the present invention, gain (G 01 , G 02 , G 03 , to G N ) of each stage amplifier is analyzed with scattering parameters and uses an impedance of 50 ohms. The reflection coefficients Γ S  of the power source terminal of the mid-stage matching network and of each stage amplifier, as well as a reflection coefficient Γ L  of a load, are obtained in sequence by the above-mentioned methods.  
         [0035]     Additionally, the first-stage amplifier  520 , the first-stage mid matching network  530 , the second-stage amplifier  540 , a N−1 th  stage amplifier  550 , a N−1 th  stage mid matching network  560  and a N th  amplifier  570  are all treated as an N th  stage mid stage amplifier. Then, a reflection coefficient Γ S  of a power source of the input-stage matching network  510  is adjusted to be Γ S,max  for conjugate matching with an input reflection coefficient Γ IN  of the first stage amplifier  520  and a loading reflection coefficient Γ L  of an output-stage matching network  580  is adjusted to be Γ L,max  for conjugate matching with an output reflection coefficient Γ OUT  of the N th  amplifier  570 . The maximum gain G Smax  of the input-stage matching network  510  and the maximum gain G Lmax  of output-stage matching network  580  can be obtained with a Smith chart.  
         [0036]     After the maximum gain G Smax  of the input-stage matching network  510  and the maximum gain G Lmax  of output-stage matching network  580  are acquired, the above two matching network will be neglected. Next, the first-stage amplifier  520 , the first-stage mid matching network  530 , the second-stage amplifier  540 , the (N−1) th -stage amplifier  550 , the (N−1) th -stage mid matching network  560  and the N th -stage amplifier  570  will be analyzed. The first-stage mid matching network  530 , the second-stage amplifier  540 , the (N−1) th -stage amplifier  550 , and the (N−1) th -stage mid matching network  560  are again viewed as a mid multi-stage amplifier. A loading reflection coefficient Γ L ′ of the first-stage mid matching network  530  is obtained by regarding the mid multi-stage amplifier as a load of the first-stage amplifier. The power source reflection coefficient Γ S ′ of the (N−1) th -stage mid matching network  560  is obtained by regarding the mid multi-stage amplifier as an input network of the N th -stage amplifier. By adjusting a reflection coefficient Γ S ′ of a power source of the (N−1) th  stage mid matching network to be Γ S ′ max  for conjugate matching with an input reflection coefficient Γ IN  of the N th  stage amplifier  570  and adjusting a loading reflection coefficient Γ L ′ to be Γ L ′ max  for conjugate matching with an output reflection coefficient Γ OUT  of the first amplifier  520 , the input maximum gain G S′max  of the N th -stage amplifier  570  and the loading maximum gain G L′max  of the first-stage matching network  520  can be obtained with a Smith chart.  
         [0037]     To simplify the complexity of circuit analysis, the first-stage amplifier  520  and the N th  stage amplifier  570  are neglected. the remaining part of the circuit is decomposed into a first-stage mid matching network, a multi-stage amplifier (including the second-stage amplifier  540 , the (N−1) th -stage amplifier  550  and other stage circuits, which are not shown) and a (N−1) th -stage mid matching network.  
         [0038]     A loading reflection coefficient Γ L ″ is obtained by regarding the (N−1) th -stage mid matching network  560  as a load, and the input reflection coefficient Γ S ″ is obtained by regarding the first-stage mid matching network  530  as an input network of the N th -stage amplifier. The reflection coefficient Γ S ″ is adjusted to be Γ S ″ max  for conjugate matching with an input reflection coefficient Γ IN  of the second stage amplifier  540  and the loading reflection coefficient Γ L ″ to be Γ L ″ max  for conjugate matching with an output reflection coefficient Γ OUT  of the (N−1) th -stage amplifier  550 . The input maximum gain G S′max  of the second stage amplifier  540  and the loading maximum gain G L′max  of the (N−1) th -stage amplifier  550  can be obtained with a Smith chart.  
         [0039]     Following the procedure described in conjunction with  FIG. 4A ,  FIG. 4B ,  FIG. 5B , and  FIG. 5C , analysis of the power gain and loss in mid matching network of each amplifier can be completed. At last, a maximum transducer power gain G T,MAX  is made by adjusting the Γ S  and Γ L  of each matching network. Hence, using the above-mentioned methods can speed up the design of a circuit and find the reason why the gain of the circuit decays easily.  
         [0040]      FIG. 7  shows the flow chart of the present invention. A first step S 700  is to identify whether the type of an external network of a multi-stage radio frequency amplifier is a matching stage network or amplifier stage network. Next step S 701  simplifies the multi-stage radio frequency amplifier into a front-stage matching network, mid-stage amplifier, and a back-stage matching network if the external network is a matching network. If the external network is an amplifier network, the multi-stage radio frequency amplifier is simplified into a front-stage amplifier, mid-stage matching network, and a back-stage amplifier.  
         [0041]     When the multi-stage radio frequency amplifier is simplified into the front-stage matching network, the mid-stage amplifier, and the back-stage matching network, a step S 703  will analyze the simplified multi-stage radio frequency amplifier and a load reflection coefficient Γ L  of the back stage matching network is obtained by the method shown in  FIG. 4B . A power source reflection coefficient Γ S  of the front-stage matching network is obtained by the method shown in  FIG. 4A . Next, the reflection coefficient Γ S  is adjusted to be Γ S,max  for conjugate matching with an input reflection coefficient Γ IN  of the mid stage amplifier and the load reflection coefficient Γ L  of an back-stage matching network is adjusted to be Γ L,max  for conjugate matching with an output reflection coefficient Γ OUT  of the mid stage amplifier. The input maximum gain G Smax  of the input-stage matching network and the loading maximum gain G Lmax  of the output-stage matching network can be obtained by analyzing a power circle of a Smith chart.  
         [0042]     When the multi-stage radio frequency amplifier is simplified into the front-stage amplifier, the mid-stage matching network, and the back-stage amplifier, the step S 703  will analyze the simplified multi-stage radio frequency amplifier and a load reflection coefficient Γ L  of the front-stage matching network is obtained by the method shown in  FIG. 5C  (the mid-stage matching network and the back-stage amplifier are viewed as a load for the front-stage amplifier). A power source reflection coefficient Γ S  of the back-stage matching network is obtained by the method shown in  FIG. 5B  (the mid-stage matching network, and the front-stage amplifier are viewed as an power input network for the back-stage amplifier). Next, the input maximum gain G Smax  of the back-stage matching network and the loading maximum gain G Lmax  of the front-stage matching network will be made by regulating the mid-stage matching network.  
         [0043]     After step S 705 , a step S 707  is performed for judging whether all circuits have been analyzed or not. If yes, then the procedure is complete and all the circuit networks can make the input maximum gain G Smax  and the loading maximum gain G Lmax ; the multi-stage radio frequency amplifier can also make a maximum transducer power gain G T,MAX . If not, the procedure will return to the step S 700  for analyzing unset circuits, and all above-mentioned methods are executed again until all circuits are set.