Abstract:
A carrier generator for generating a carrier at a frequency of interest in a wireless communications system comprises an oscillator exhibiting a first impedance, the oscillator comprising an energy storage tank configured to generate a periodic signal, the energy storage tank including at least one inductor and at least one capacitor, and an amplifier coupled with the energy storage tank, the amplifier being configured to amplify an amplitude of the periodic signal, an antenna exhibiting a second impedance smaller than the first impedance, and a network coupled between the oscillator and the antenna, the network including at least one inductor or at least one capacitor and being configured to provide a third impedance such that a resultant impedance of the second impedance and the third impedance as viewed from the oscillator toward the antenna is large enough to facilitate the oscillator to generate the carrier at the frequency of interest.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to a transmitter and, more particularly, to a carrier generator for generating a carrier at a frequency of interest. 
         [0002]    In a wireless communication system, information or data to be transmitted from a transmitter may be conveyed by a carrier generated by the transmitter.  FIG. 1  is a schematic block diagram of a conventional wireless transmitter  10 . Referring to  FIG. 1 , the wireless transmitter  10  may include a quartz crystal  11 , a crystal circuit  12 , a phase-frequency detector (PFD)  13 , a charge pump (CP)  14 , a low pass filter (LPF)  15 , a voltage-controlled oscillator (VCO)  16 , a divider  17 , a power amplifier (PA)  18  and an antenna  19 . The above-mentioned components  13  to  17  may form a phase-locked loop (PLL) circuit of the wireless transmitter  10 . The PA  18 , which may comprise active components, is used to drive an antenna and translate a signal level and may thus require a considerable amount of power during operation. A transmitter with the PA  18  may not satisfy the increasing demand for communication devices with low power consumption and low cost. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    Examples of the present invention may provide a carrier generator for generating a carrier at a frequency of interest in a wireless communications system. The carrier generator comprises an oscillator exhibiting a first impedance, the oscillator comprising an energy storage tank configured to generate a periodic signal, the energy storage tank including at least one inductor and at least one capacitor, and an amplifier coupled with the energy storage tank, the amplifier being configured to amplify an amplitude of the periodic signal, an antenna exhibiting a second impedance smaller than the first impedance, and an LC network coupled between the oscillator and the antenna, the LC network including at least one inductor or at least one capacitor and being configured to provide a third impedance such that a resultant impedance of the second impedance and the third impedance as viewed from the oscillator toward the antenna is large enough to facilitate the oscillator to generate the carrier at the frequency of interest. 
         [0004]    Some examples of the present invention may also provide a carrier generator for generating a carrier at a frequency of interest in a wireless communications system. The carrier generator comprises a first oscillator configured to generate a first periodic signal at a first frequency, a second oscillator exhibiting a first impedance, the second oscillator comprising an energy storage tank configured to generate a second periodic signal based on the first periodic signal through an analog or digital adjustment circuit, the energy storage tank including at least one inductor and at least one capacitor, and an amplifier coupled with the energy storage tank, the amplifier being configured to amplify an amplitude of the second periodic signal, an antenna exhibiting a second impedance smaller than the first impedance, and an LC network coupled between the second oscillator and the antenna, the LC network including at least one inductor or at least one capacitor and being configured to provide a third impedance such that a resultant impedance of the second impedance and the third impedance as viewed from the second oscillator toward the antenna is large enough to facilitate the second oscillator to generate the carrier at the frequency of interest. 
         [0005]    Examples of the present invention may further provide a carrier generator for generating a carrier at a frequency of interest in a wireless communications system. The carrier generator comprises a first oscillator configured to generate the carrier, the first oscillator exhibiting a first impedance, an antenna exhibiting a second impedance smaller than the first impedance, and an LC network coupled between the first oscillator and the antenna, the LC network being configured to provide a third impedance such that a resultant impedance of the second impedance and the third impedance as viewed from the first oscillator toward the antenna facilitates the first oscillator to generate the carrier at the frequency of interest. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The foregoing summary as well as the following detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0007]      FIG. 1  is a schematic block diagram of a conventional wireless transmitter; 
           [0008]      FIG. 2  is a schematic block diagram of a carrier generator consistent with an example of the present invention; 
           [0009]      FIGS. 3A to 3E  are circuit diagrams of exemplary oscillators of the carrier generator illustrated in  FIG. 2 ; 
           [0010]      FIGS. 4A to 4H  are circuit diagrams of exemplary LC networks of the carrier generator illustrated in  FIG. 2 ; 
           [0011]      FIG. 5  is a schematic block diagram of a carrier generator consistent with another example of the present invention; 
           [0012]      FIG. 6  is a schematic block diagram of a transmitter architecture consistent with an example of the present invention; 
           [0013]      FIG. 7A  is a schematic block diagram of a transmitter architecture consistent with another example of the present invention; 
           [0014]      FIG. 7B  is a schematic diagram of an exemplary oscillator and finite state machine (FSM) of the transmitter architecture illustrated in  FIG. 7A ; and 
           [0015]      FIG. 8  is a schematic block diagram of a transmitter architecture consistent with still another example of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Reference will now be made in detail to the present examples of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like portions. 
         [0017]      FIG. 2  is a block diagram of a carrier generator  20  consistent with an example of the present invention. Referring to  FIG. 2 , the carrier generator  20  may include an oscillator  21 , an inductor and capacitor (hereinafter an “LC”) network  22  and an antenna  23 . The oscillator  21  may include an LC tank  21 - 1  and an amplifier  21 - 2 . The LC tank  21 - 1  may serve as an energy storage and may further include one or more inductor and one or more capacitor. Based on the inductance “L” of the one or more inductor and the capacitance “C” of the one or more capacitor, a carrier frequency “f” of interest may be determined in an equation as given below. 
         [0000]    
       
         
           
             f 
             = 
             
               1 
               
                 2 
                  
                 
                     
                 
                  
                 π 
                  
                 
                     
                 
                  
                 
                   LC 
                 
               
             
           
         
       
     
         [0018]    In one example, the oscillator  21  may generate a carrier signal at a frequency ranging from approximately 300 to 400 megahertz (MHz) but the value may change to suit different applications. 
         [0019]    The amplifier  21 - 2  may be configured to amplify the amplitude of the carrier signal. The oscillator  21  may further include one or more trimming pin  211  to adjust the carrier frequency, and a modulation pin  212  to receive a modulation signal from a modulator (not shown). A carrier signal from the oscillator  21  may be modified based on a modulation scheme of the modulator to convey a message to be transmitted via the antenna  23 . 
         [0020]    The LC network  22  may include one or more inductor, one or more capacitor or both. The LC network  22  may be configured to provide an impedance large enough to facilitate oscillation of the oscillator  21 . In general, the antenna  23  may exhibit a resistance of, for example, approximately 50 ohms, which is a relatively low impedance. In the absence of the LC network  22 , there may be an input impedance of about 50 ohms at an output of the oscillator  21  as viewed from the oscillator  21  toward the antenna  23 . However, the oscillator  21  may itself exhibit a relatively high impedance. If the oscillator  21  is directly connected to the antenna  23 , the low-impedance antenna  23  may attenuate the gain of the oscillator  21  such that the oscillator  21  may not be able to oscillate. By electrically coupling the LC network  22  between the oscillator  21  and the antenna  23 , a resultant impedance “Z” viewed from the output of the oscillator  21  toward the antenna  23  may be given as follows. 
         [0000]    
       
      
       Z=R+jX  
      
     
         [0021]    Where the reactance “X” is the imaginary part of the resultant impedance, which may be contributed by the LC network  22 . The impedance Z may be equal to (R+jX L ) if the LC network  22  is comprised of one or more inductor, X L =2π f L. Likewise, the impedance Z may be equal to (R+jX C ) if the LC network  22  is comprised of one or more capacitor, 
         [0000]    
       
         
           
             
               X 
               C 
             
             = 
             
               
                 
                   - 
                   1 
                 
                 
                   2 
                    
                   
                       
                   
                    
                   π 
                    
                   
                       
                   
                    
                   f 
                    
                   
                       
                   
                    
                   C 
                 
               
               . 
             
           
         
       
     
         [0000]    Moreover, the impedance Z may be equal to [R+j(X L +X C )] if the LC network  22  includes one or more inductor and one or more capacitor. 
         [0022]      FIGS. 3A to 3E  are circuit diagrams of exemplary oscillators  31  to  35  of the carrier generator  20  illustrated in  FIG. 2 . Referring to  FIG. 3A , the oscillator  31  may include an LC tank comprising an inductor L and capacitors C 1  and C 2 , and an amplifier comprising metal-oxide-semiconductor (MOS) transistors M 1  and M 2 . At least one of the capacitors C 1  and C 2  may include a variable capacitor to ensure that the oscillator  31  may generate a carrier frequency of interest. The oscillator  31  has an output terminal V O  coupled to the LC network  22  and may be called a “single-ended” oscillator. 
         [0023]    Referring to  FIG. 3B , the oscillator  32  may include an LC tank comprising inductors L 1  and L 2  and a variable capacitor C, and an amplifier comprising MOS transistors M 3 , M 4  and M 5 . The oscillator  32  has output terminals V O1  and V O2  each being coupled to an LC network such as the LC network  22  illustrated in  FIG. 2  and may be called a “fully-differential” oscillator. 
         [0024]    Referring to  FIG. 3C , the oscillator  33  may include an LC tank comprising inductors L 1  and L 2  and a variable capacitor C, and an amplifier comprising n-type MOS (NMOS) transistors MN 1  and MN 2 . The oscillator  33  may be called an NMOS-type oscillator. 
         [0025]    Referring to  FIG. 3D , the oscillator  34  may include an LC tank comprising inductors L 1  and L 2  and a variable capacitor C, and an amplifier comprising p-type MOS (PMOS) transistors MP 1  and MP 2 . The oscillator  34  may be called a PMOS-type oscillator. 
         [0026]    Referring to  FIG. 3E , the oscillator  35  may include an LC tank comprising an inductor L and a variable capacitor C, and an amplifier comprising NMOS transistors MN 1  and MN 2  and PMOS transistors MP 1  and MP 2 . The oscillator  35  may be called a complementary MOS (CMOS)-type oscillator. 
         [0027]      FIGS. 4A to 4H  are circuit diagrams of exemplary LC networks  22 - 1  to  22 - 6  of the carrier generator  20  illustrated in  FIG. 2 . Referring to  FIG. 4A , the LC network  22 - 1  may include a capacitor C coupled between the oscillator  21  and the antenna  23 , and an inductor L coupled in parallel with the oscillator  21 . The oscillator  21  may include a single-ended oscillator. 
         [0028]    Referring to  FIG. 4B , the LC network  22 - 2  may include an inductor L between the oscillator  21  and the antenna  23 , and a capacitor C coupled in parallel with the oscillator  21 . 
         [0029]    Referring to  FIG. 4C , the LC network  22 - 3  may include a capacitor C coupled between the oscillator  21  and the antenna  23 , and inductors L 1  and L 2  coupled in parallel with the oscillator  21 . 
         [0030]    Referring to  FIG. 4D , the LC network  22 - 4  may include an inductor L coupled between the oscillator  21  and the antenna  23 , and capacitors C 1  and C 2  coupled in parallel with the oscillator  21 . 
         [0031]    Referring to  FIG. 4E , the LC network  22 - 5  may include capacitors C 1  and C 2  coupled in series between the oscillator  21  and the antenna  23 , and an inductors L coupled in parallel with the oscillator  21 . 
         [0032]    Referring to  FIG. 4F , the LC network  22 - 6  may include inductors L 1  and L 2  coupled in series between the oscillator  21  and the antenna  23 , and a capacitor C coupled in parallel with the oscillator  21 . Skilled persons in the art will understand that a wide range of LC networks may be available for the LC network  22  illustrated in  FIG. 2 . For example, the LC network  22  may include only one inductor  22 - 7  as illustrated in  FIG. 4G  or only one capacitor  22 - 8  as illustrated in  FIG. 4H . In other examples, the LC network  22  may include two or more capacitors and two or more inductors. 
         [0033]      FIG. 5  is a schematic block diagram of a carrier generator  50  consistent with another example of the present invention. Referring to  FIG. 5 , the carrier generator  50  may include a fully-differential oscillator such as the oscillator  32  described and illustrated with reference to  FIG. 3B . The oscillator  32  may have a first output V O1  coupled to a first LC network  52 - 1  and a second output V O2  coupled to a second LC network  52 - 2 . Each of the first LC network  52 - 1  and the second LC network  52 - 2  may include one of the LC networks  22 - 1  to  22 - 8  described and illustrated with reference to  FIGS. 4A to 4H , respectively. 
         [0034]      FIG. 6  is a schematic block diagram of a transmitter architecture  60  consistent with yet another example of the present invention. Referring to  FIG. 6 , the transmitter architecture  60  may comprise the carrier generator  20  described and illustrated with reference to  FIG. 2 , a first oscillator  61  and an adjustment circuit  63 . The first oscillator  61  may be configured to generate a first periodic signal at a first frequency of, for example, approximately 1 MHz. In the present example, the first oscillator  61  may include a quartz crystal  61 - 1  and a crystal circuit  61 - 2  as illustrated. 
         [0035]    The adjustment circuit  63  may include an analog circuit, which further includes a phase-frequency detector (PFD)  63 - 1 , a charge pump (CP)  63 - 2 , a low pass filter (LPF)  63 - 3  and a frequency divider  63 - 4 . The PFD  63 - 1  may receive the first periodic signal from the first oscillator  61  and a feedback signal from the oscillator  21  via the frequency divider  63 - 4  as inputs and generate an output voltage based on the inputs to adjust the carrier frequency through the CP  63 - 2  and LPF  63 - 3 . The oscillator  21  may be configured to generate a second periodic signal, i.e., a carrier, based on the first periodic signal. 
         [0036]      FIG. 7A  is a schematic block diagram of a transmitter architecture  70  consistent with another example of the present invention. Referring to  FIG. 7A , the transmitter architecture  70  may be similar to the transmitter architecture  60  described and illustrated with reference to  FIG. 6  except that, for example, an adjustment circuit  73  replaces the adjustment circuit  63 . The adjustment circuit  73  may include a digital circuit, which further includes a PFD  73 - 1 , a finite state machine (FSM)  73 - 2  and a frequency divider  73 - 4 . The PFD  73 - 1  may include but is not limited to an exclusive-or (XOR) gate, and the FSM  73 - 2  may include logic gates and flip-flops. The FSM  73 - 2  may a number of “N” outputs to adjust the carrier frequency of the oscillator  21 . In other examples, a time-to-digital converter (TDC) may be used in the transmitter architecture  70  to replace the PFD  73 - 1 . 
         [0037]      FIG. 7B  is a schematic diagram of an exemplary oscillator  33 - 1  and FSM  73 - 2  of the transmitter architecture  70  illustrated in  FIG. 7A . Referring to  FIG. 7B , the oscillator  33 - 1 , which may be similar to the oscillator  33  described and illustrated with reference to  FIG. 3C , may be adjusted based on a control signal from the FSM  73 - 2  for frequency selection. Specifically, the control signal may be transmitted via the N outputs B 1  to B N , each of which may have a logic one or a logic zero value. Furthermore, the oscillator  33 - 1  may include a number of N sets of capacitors C 1  to C N  coupled in parallel to one another, each of which may further include capacitors coupled in series. As an example of the first capacitor C 1 , a first capacitor C 12  and a second capacitor C 12  may be coupled in series and a point between the first capacitor C 11  and the second capacitor C 12  may be coupled to the first bit B 1 . Given a carrier frequency ranging from 300 to 400 MHz to be generated by the oscillator  33 - 1  and an 8-bit control signal, i.e., N=8, the value 11111111 from the FSM  73 - 2  may control the oscillator  33 - 1  to generate a carrier frequency of 400 MHz and the value 00000000 to generate a carrier frequency of 300 MHz. 
         [0038]      FIG. 8  is a schematic block diagram of a transmitter architecture  80  consistent with still another example of the present invention. Referring to  FIG. 8 , the transmitter architecture  80  may comprise the carrier generator  20 , a digital control circuit  82  and a memory  81 . The memory  81  may store predetermined frequency selection signals and modulation data. The digital control circuit  82 , electrically connected between the carrier generator  20  and the memory  81 , may be configured to retrieve the frequency selection signals from the memory  81  and send the same through the trimming pin  211  to the oscillator  21 . In the memory  81 , the predetermined frequency selection signals may include, for example, 8-bit digital signals such as 00000000 for a carrier frequency of approximately 300 MHz, 11111111 for a carrier frequency of approximately 400 MHz and other values between 00000000 and 11111111 for a carrier frequency between 300 and 400 MHz. Moreover, the predetermined modulation data may be retrieved from the memory  81  by the digital control circuit  82  and sent in digital bits to the oscillator  21  through the modulation pin  212  for modulation operation. 
         [0039]    It will be appreciated by those skilled in the art that changes could be made to the examples described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular examples disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.