Patent Publication Number: US-2007096821-A1

Title: Wide-band amplifier

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims priority from Korean Patent Application No. 10-2005-0105000 filed on Nov. 3, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Apparatuses consistent with the present invention relate to a wide-band amplifier, and more particularly, to a wide-band amplifier that is designed to achieve impedance matching in a wide-band frequency range.  
      2. Description of the Related Art  
      In general, an amplifier is an essential circuit block of an RF device.  FIG. 1  shows an amplifier circuit according to the related art.  
      In  FIG. 1 , a cascade topology representative of an amplifier configuration is shown, and the cascade topology includes a common source N-type Metal Oxide Semiconductor (NMOS) transistor  105  and a common gate NMOS transistor  110 .  
      An inductor  107  for input impedance matching of an amplifier  100  is coupled between a source terminal of the common source NMOS transistor  105  and a ground terminal, and a gate terminal of the common source NMOS transistor  105  is an input terminal.  
      Further, a gate terminal of the common gate NMOS transistor  110  is coupled to a bias voltage source, and a drain terminal of the common gate NMOS transistor  110  is an output terminal. Furthermore, a load inductor  112  is coupled between the drain terminal of the common gate NMOS transistor  110  and a DC voltage source V DD  so as to adjust the output impedance of the amplifier  100 .  
      In  FIG. 1 , if input impedance at the input terminal of the amplifier  100  is set to Z in ; Z in  is expressed by Equation 1: 
               Z   in     =       (       1     j   ⁢           ⁢     wC   gs         +     j   ⁢           ⁢     wL   s         )     +       g   m     ×       L   s       C   gs                   (   1   )             
 
      C gs  represents a capacitance between the gate terminal and the source terminal of the common source NMOS transistor  105 , and g m  represents the transconductance of the common source NMOS transistor  105 .  
      In Equation 1, in order to accomplish input impedance matching at 50 Ω, the following conditions must be satisfied:  
                 1     wC   gs       -     wL   s       =   0                 and   ⁢           ⁢     g   m     ×       L   s       C   gs         =   50             
 
      Therefore, one matching circuit is not enough to make a frequency bandwidth, in which input impedance matching is achieved for more than 10% of a center frequency.  
      The output impedance of the output terminal is determined by the output resistance of the common gate NMOS transistor  110  and the load inductor  112 .  
      Assuming that the output impedance is Zout, Zout can be expressed as: Zout=(r o ∥jwL L ). When r o  is very large, Z out  becomes jwL L , and as a result, wide-band matching is difficult.  
      In other words, since the input impedance and the output impedance are determined on the basis of frequencies, a matching frequency band, in which the S-parameter S 11  corresponding to the input impedance and the S-parameter S 22  corresponding to the output impedance are both less than −10 dB, is narrow, as shown in  FIG. 2 .  
       FIG. 2  is a graph showing a simulation result of the circuit shown in  FIG. 1 . In  FIG. 2 , the center frequency is 2.35 GHz, and the matching frequency band in which the S-parameters S 11  and S 22  are both less than −10 dB at the input and output terminals is about 10% of the center frequency.  
      Further, according to the related art shown in  FIG. 1 , the inductor  107  is provided at the source terminal of the common source NMOS transistor  105  for matching of the circuit, and the inductor  112  is used as a load in order to obtain a gain. Therefore, the layout size of the whole circuit increases, and thus the cost increases.  
      For this reason, an amplifier is required that can achieve matching in a wider frequency band without increasing the size of the entire circuit.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention is to provide an amplifier that achieves impedance matching in a wide frequency band.  
      Another aspect of the present invention is to provide an amplifier that achieves wide-band impedance matching and enough gain without using elements such as an inductor.  
      Aspects of the present invention are not limited to those mentioned above, and other aspects of the present invention will be apparently understood by those skilled in the art through the following description.  
      In order to achieve the above and other aspects, according to an exemplary embodiment of the present invention, a wide-band amplifier includes a first n-type metal oxide semiconductor (NMOS) transistor which receives an input signal; a second NMOS transistor which buffers a signal amplified by the first NMOS transistor; a third NMOS transistor which amplifies a signal supplied from a source of the first NMOS transistor; and an output terminal which outputs a signal obtained by combining the signal buffered by the second NMOS transistor with the signal amplified by the third NMOS transistor.  
      Further, according to another exemplary embodiment of the present invention, a wide-band amplifier includes an input module which receives an input signal to be amplified, and provides signals corresponding to the input signal through different terminals, and an output terminal which combines the signals supplied from the input module through different circuit paths. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other aspects, of the present invention will become more apparent by describing in detail certain exemplary embodiments thereof with reference to the attached drawings, in which:  
       FIG. 1  is a circuit diagram showing the configuration of an amplifier according to the related art;  
       FIG. 2  is a graph showing the simulation result of the circuit of  FIG. 1 ;  
       FIG. 3  is a block diagram showing an example of a wide-band amplifier according to an exemplary embodiment of the present invention;  
       FIG. 4  is a circuit diagram showing the configuration of the wide-band amplifier according to an exemplary embodiment of the present invention; and  
       FIG. 5  is a graph showing a simulation result of the wide-band amplifier according to an exemplary embodiment of the invention. 
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION  
      Advantages and features of the present invention and methods of accomplishing the same may be understood more readily by reference to the following detailed description of exemplary embodiments of the present invention and the accompanying drawings. The present inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concept of the invention to those skilled in the art, and the present invention will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.  
      The present inventive concept is described hereinafter with reference to flowchart illustrations of user interfaces, methods, and computer program products according to exemplary embodiments of the invention. It will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks.  
      These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks.  
      The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.  
      And each block of the flowchart illustrations may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.  
       FIG. 3  is a block diagram showing an example of a wide-band amplifier according to an exemplary embodiment of the present invention.  
      Referring to  FIG. 3 , a wide-band amplifier  200  according to an exemplary embodiment of the present invention includes an input module  210 , a first output module  220 , and a second output module  230 .  
      The term “module”, as used herein, means, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on an addressable storage medium and configured to execute on one or more processors. Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules.  
      The input module  210  receives an input signal to be amplified, and outputs signals corresponding to the input signal to the first output module  220  and the second output module  230  through two different terminals, respectively.  
      The first output module  220  and the second output module  230  output signals corresponding to the signals provided from the input module  210 . The output signals of the first and second output modules  220  and  230  are combined to form one output signal of the wide-band amplifier  200 .  
      In other words, in the wide-band amplifier  200  according to an exemplary embodiment of the present invention, two signals corresponding to an input signal pass through two different paths to be combined into one signal, and the combined signal is then output as an amplified signal.  
       FIG. 4  is a circuit diagram showing the configuration of the wide-band amplifier according to the exemplary embodiment of the present invention shown in  FIG. 3 .  
      Referring to  FIG. 4 , a wide-band amplifier  300  includes an NMOS transistor M 1  simultaneously performing functions of a common source and a common drain; a common drain NMOS transistor M 2  for buffering a signal amplified by the NMOS transistor M 1 ; and an NMOS transistor M 3  for amplifying a signal supplied from a source of the NMOS transistor M 1 .  
      Further, the wide-band amplifier  300  includes a current source  340  for operating the NMOS transistor M 1  and an NMOS transistor M 4  that is connected in the form of a diode connection to sink a current flowing from the current source  340  to the NMOS transistor M 1 .  
      Furthermore, in  FIG. 4 , V DD  denoting a DC power source voltage, a signal input terminal  360 , and a signal output terminal  370  are shown.  
      Comparing the circuit of  FIG. 4  with the configuration of  FIG. 3 , the input module  210 , the first output module  220 , and the second output module  230  of  FIG. 3  may correspond to the NMOS transistor M 1 , the common drain NMOS transistor M 2 , and the NMOS transistor M 3  of  FIG. 4 , respectively.  
      The wide-band amplifier  300  of  FIG. 4  has two signal paths, similar to the wide-band amplifier of  FIG. 3 .  
      The first signal path is a common source-common drain signal path formed by the NMOS transistor M 1  and the common drain NMOS transistor M 2 , which is based on a common source-source follower configuration.  
      The second signal path is a common drain-common source signal path formed by the NMOS transistor M 1  and the NMOS transistor M 3 , which is based on a source follower-common source configuration.  
      The two paths are joined together at the output terminal  370 . The phases of the signals output from the two paths are equal to each other, and thus the signal gain at the output terminal  370  becomes twice.  
      Assuming that the output impedance of the output terminal  370  of the wide-band amplifier  300  shown in  FIG. 4  is Z out , Z out  can be expressed as follows: Zout=(r o ∥1/g m ).  
      Here, r o  denotes a resistance component when looking at the drain terminal side of the NMOS transistor M 3  from the output terminal  370 , 1/g m  represents a resistance component when looking at the source terminal side of the common drain NMOS transistor M 2  from the output terminal  370 , and g m  represents the transconductance of the common drain NMOS transistor M 2 .  
      In this case, when r o  is very large, Z out  can be expressed by Equation 2:  
                     Z   out     ≅       ⁢     1     g   m                   ≅       ⁢     50   ⁢           ⁢   Ω                   (   2   )             
 
      Therefore, the impedance matching of the output impedance of the wide-band amplifier  300  is achieved regardless of a frequency by the current flowing through the common drain NMOS transistor M 2  and the NMOS transistor M 3 . As a result, impedance matching can be achieved in a wider frequency band.  
       FIG. 5  is a graph showing a simulation result of an exemplary embodiment of the present invention. More specifically,  FIG. 5  shows a result obtained by simulating the circuit shown in  FIG. 4  under conditions that the center frequency is 2.35 GHz and the span is 1 GHz. For reference, the voltage applied to the circuit shown in  FIG. 4  is 1.8 V and the current consumption thereof is 5.6 mA.  
      Referring to  FIG. 5 , an S-parameter S 11  corresponding to the input impedance and an S-parameter S 22  corresponding to the output impedance are both smaller than −10 dB in the frequency band of 1 GHz.  
      That is, in the wide-band amplifier  300  according to an exemplary embodiment of the present invention, an input impedance and an output impedance are smaller than −10 dB in a wider frequency band, as compared to the S-parameters S 11  and S 22  shown in  FIG. 2 .  
      As can be seen from  FIGS. 2 and 5 , according to an exemplary embodiment of the present invention, the noise figure is the same, the gain is increased by 4 dB, and the variation of the gain is 2.7 dB in a band of 1 GHz, as compared to the amplifier according to the related art. Further, as can be seen from the Smith charts of  FIGS. 2 and 5 , according to the present invention, the impedance matching is accomplished in the vicinity of 50 Ω.  
      The results of comparing the graphs of  FIGS. 2 and 5  are shown in Table 1:  
                               TABLE 1                                   Present           Parameter   Unit   Related art   Invention   Remark                                                    Matching   MHz   236   1000 or more   Fcenter = 2.35 GHz       Band               S11, S22 &lt;− 10 dB       Power Gain   dB   13.9   16.8   @ Freq. = 2.35 GHz       Noise   dB   2.82   2.85   @ Freq. = 2.35 GHz       Figure                  
 
      Although the present inventive concept has been described in connection with the exemplary embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope and spirit of the invention. Therefore, it should be understood that the above exemplary embodiments are not limitative, but illustrative in all aspects.  
      According to the present inventive concept, a wide-band amplifier can achieve impedance matching in a wide frequency band in which a matching frequency band is 50% or more of a center frequency, thereby capable of being applied to wide-band systems such as a tuner, a Ultra Wide Band (UWB) device, a Wireless Local Area Network (WLAN), or other similar application.  
      Further, according to the present inventive concept, the wide-band amplifier does not use any inductor to obtain impedance matching and gain, thereby reducing the layout size of the amplifier circuit and the cost.  
      Furthermore, according to the present inventive concept, the wide-band amplifier has two signal paths to make the final signals thereof be in phase, thereby increasing the gain.