Abstract:
A phase modulation apparatus and method are provided. The phase modulation apparatus includes a storage to store phase modulation setting values corresponding to various communication modes; a phase modulation setting value selector to select, when a communication mode is changed, phase modulation setting values corresponding to the changed communication mode among the phase modulation setting values stored in the storage; and a phase modulator to modulate a phase of a transmission signal using the phase modulation setting values selected by the phase modulation setting value selector. According to the phase modulation apparatus, since a frequency characteristic of a loop filter in a PLL circuit is changed depending on a transmission mode of a communication apparatus and phase modulation is performed using appropriate bandwidths according to various transmission modes, it is possible to prevent noise characteristics from degrading when a PLL bandwidth changes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119(a) of a Korean Patent Applications Nos. 10-2009-0126242, filed on Dec. 17, 2009, and 10-2010-0036024, filed on Apr. 19, 2010, the entire disclosures of which are incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relates to a phase modulation technique, and more particularly, to a phase modulation apparatus and method which reflects a communication mode to apply a variable specification. 
     2. Description of the Related Art 
     A variable bandwidth Phase Locked Loop (PLL) is applied to a phase modulation apparatus which is generally used in a communication apparatus. Phase modulation using a variable bandwidth PLL has advantages of low cost, low power consumption, excellent noise characteristics, high modulation precision, etc. 
     In order to achieve high modulation precision, a PLL has to have a wider frequency bandwidth than that of a modulation signal. This is because a high reference frequency reduces a division ratio N to widen the bandwidth of a loop filter and also shorten a PLL lock time. However, a wide bandwidth of PLL degrades noise characteristics. 
     In order to solve the problem, a 2-point modulation method has been proposed which sets a modulation bandwidth of a PLL to be narrower than a modulation bandwidth and performs modulation within a PLL band and modulation outside of a variable PLL band at two different points. 
     According to the 2-point modulation method, since no control signal is transferred to a loop filter when a communication mode is a narrow-band mode, effectively only a 1-point modulation is performed. When the communication mode is a wide-band mode, control signals are transferred to individual communication apparatuses to modulate signals outside of the PLL band. 
     With development of cognitive access techniques and software defined radios (SDR) terminals, demands for a communication apparatus capable of supporting multiple modes are increasing, however, existing phase modulation techniques have limitations in satisfying these demands. 
     SUMMARY 
     The following description relates to a phase modulation apparatus and method that can perform phase modulation adaptively depending on a communication mode. 
     In one general aspect, there is provided a phase modulation apparatus including: a storage to store phase modulation setting values corresponding to various communication modes; a phase modulation setting value selector to select, when a communication mode is changed, phase modulation setting values corresponding to the changed communication mode among the phase modulation setting values stored in the storage; and a phase modulator to modulate a phase of a transmission signal using the phase modulation setting values selected by the phase modulation setting value selector. The phase modulation setting values include at least one of a reference frequency, a division ratio and a modulation bandwidth value. 
     In one general aspect, there is provided a phase modulation method including: deciding, when a communication mode is changed, phase modulation setting values using pre-stored information; and performing phase modulation according to the decided phase modulation setting values. The phase modulation setting values include at least one of a reference frequency, a division ratio and a modulation bandwidth value. 
     Accordingly, the frequency characteristics of a loop filter in a Phase Locked Loop (PLL) change depending on a transmission mode of a communication apparatus and an appropriate bandwidth is used according to a transmission modes to perform phase modulation, thereby preventing noise characteristics from degrading when the bandwidth of the PLL changes. 
     Also, since a reference frequency of a PLL can be changed and a division ratio can be automatically changed, a phase modulation apparatus and a data transmission apparatus is to which various communication specifications can be applied are implemented. 
     Furthermore, since the frequency response, reference frequency and division ratio of the loop filter in the PLL can be set to appropriate values automatically according to a transmission mode, load to other circuits can be reduced. In addition, since an appropriate PLL band of a phase modulation bandwidth can be selected according to a communication mode, noise out of the PLL band is reduced and noise characteristics are improved, which leads to performance improvement of a communication apparatus. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a phase modulation apparatus. 
         FIG. 2  is an example of a reference table that is used to decide a voltage signal for controlling a loop filter in the phase modulation apparatus illustrated in  FIG. 1 . 
         FIG. 3  is a characteristic graph showing the relationship between a modulation bandwidth and a PLL bandwidth. 
         FIG. 4  is a circuit diagram illustrating an example of a loop filter. 
         FIG. 5  is a flowchart illustrating an example of a phase modulation method. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
       FIG. 1  is a diagram illustrating an example of a phase modulation apparatus. 
     Referring to  FIG. 1 , the phase modulation apparatus includes: a phase modulator  120 , a storage  100 , a phase modulation setting value selector  110 , a switching unit  130 , a filter  132 , a digital-to-analog converter  134  and a modulation signal generator  136 . The phase modulator  120  includes a reference frequency oscillator  122 , a phase comparator  126 , a loop filter  128 , a voltage-controlled oscillator  129  and a frequency divider  124 . 
     The phase modulation apparatus has to determine an appropriate reference frequency, an appropriate division ratio (N) and an appropriate loop bandwidth when a communication mode changes. 
     Conventionally, in the case of a single or multi mode, a reference frequency and a division ratio are both fixed or only a division ratio is changeable. However, a communication apparatus capable of supporting various communication modes, which is to be developed in the future, has to be able to change both a reference frequency and a division ratio. Optimal values of the reference frequency and division ratio may be predetermined. 
     The storage  100  may be a memory, and stores an optimized reference frequency, division ratio and loop bandwidth with respect to various communication modes, in the form of a table. 
     According to an example, the phase modulation setting value selector  110  decides a is modulation bandwidth according to a communication mode based on stored information, and outputs a voltage signal for controlling the loop filter  128  to change a PLL bandwidth. For example, the phase modulation setting value selector  110  decides a reference frequency, a division ratio and a modulation bandwidth, with reference to the table that is stored in the storage  100  and includes information about reference frequencies, division ratios (N) and modulation bandwidths with respect to communication modes. Then, the phase modulation setting value selector  10  transfers the decided reference frequency, division ratio and modulation width to the reference frequency oscillator  122 , the frequency divider  124 , the switching unit  130  and the loop filter  128 . Accordingly, depending on a communication mode, the switching unit  130  is turned on or off to perform 1-point modulation or 2-point modulation, so that a reference frequency, a division ratio and a bandwidth of a PLL circuit are changed. Also, the frequency response of the loop filter  128  is changed. 
     The phase modulation setting value selector  110  outputs, when the modulation bandwidth is set to a narrow-band mode with reference to the table that includes modulation bandwidths with respect to communication modes, a control signal for turning off the switching unit  130 . If the switching unit  130  is turned off, 1-point modulation is performed so as not to perform the modulation out of the PLL band. Then, the phase modulation setting value selector  110  outputs voltage signals V t1  and V t2  to be input to the loop filter  128 , the voltage signals V t1  and V t2  decided according to the decided modulation bandwidth. In the phase modulation apparatus, since the frequency of the loop filter  128  is lowered when the communication mode is a narrow-band mode, a resonance point of the frequency of the loop filter  128  with resistance is lowered to make a bandwidth narrow. 
     Meanwhile, the phase modulation setting value selector  110  transfers a control signal to the switching unit  130  with reference to the table that includes modulation bandwidths with respect to communication modes, thus turning on the switching unit  130 . If the switching unit  130  is turned on, 2-point modulation is performed to perform the modulation out of the PLL band. 
     Also, the phase modulation setting value selector  110  outputs voltage signals V t1  and V t2  to be input to the loop filter  128 , the voltage signals V t1  and V t2  decided according to the decided modulation bandwidth. When the communication mode is a wide-band mode, the frequency of the loop filter  120  is raised and a resonance point of the frequency of the loop filter  128  with resistance is accordingly raised, resulting in an increase of a bandwidth. 
       FIG. 2  is an example of a reference table that is used to decide a voltage signal for controlling the loop filter  128  in the phase modulation apparatus illustrated in  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the phase modulation setting value selector  110  may decide a voltage signal for controlling the loop filter  128  appropriately according to a communication mode, with reference to predetermined table information seen in  FIG. 2 . According to an example, the reference table, which is constructed according to a general PLL design procedure, is made in various forms depending on applications. 
       FIG. 3  is a characteristic graph showing the relationship between a modulation bandwidth and a PLL bandwidth. 
     As seen in  FIG. 3 , if a PLL band  1  denoted in a solid line is narrowed, its bandwidth H(s) is also narrowed. However, the bandwidth H(s) of the PLL band  1  is still wider than a transmission bandwidth of a communication mode  1  which is a narrow-band mode. By preventing an output signal from being positioned outside a modulation band of a modulation signal, it is possible to reduce degradation of modulation precision and suppress power consumption. 
     Meanwhile, referring to  FIGS. 1 and 3 , when the communication mode  1  is a wide-band mode, the frequency of the loop filter  128  is raised due to input voltage signals V t1  and V t2  of the loop filter  128  which are decided by the phase modulation setting value selector  110 , and a resonance point of the frequency of the loop filter  128  with resistance is also raised, which increases a bandwidth. 
     As seen in  FIG. 3 , the bandwidth of a PLL circuit is widened from the PLL band  1  to a PLL band  2 . 
     In a wide-band modulation mode, when the switching unit  130  is controlled to be turned on, 2-point modulation is performed, a resonance point of the loop filter  128  is changed and a PLL bandwidth H(s) is wider than in a narrow-band mode. Also, if a communication mode bandwidth is further widened when 2-point modulation is performed, the resonance point of the frequency of the loop filter  128  with resistance is further raised due to the input voltage signals V t1  and V t2  of the loop filter  128 , which are decided according to a modulation bandwidth. 
     Accordingly, as seen in  FIG. 3 , the bandwidth of the PLL circuit is widened from the PLL band  2  to a PLL band N. 
     In other words, in the wide-band modulation mode, by varying the resistance value of the loop filter  128 , it is possible to reduce the outer region of the PLL band. Accordingly, characteristic degradation due to sensitivity and linearity of a voltage-controlled oscillator (VCO) may be reduced. In addition, the VCO may be allocated a noise margin, which relieves a design specification. 
       FIG. 4  is a circuit diagram illustrating an example of a loop filter. As illustrated in  FIG. 4 , the loop filter may be implemented with various configurations that use variable resistors and variable capacitors to change a PLL bandwidth in order to support various communication modes. A plurality of pin diodes pd 1 , . . . , pdM is are arranged to implement variable resistance to thus widen a variable range of resistance. Also, a varactor diode vd 1  may be provided to form a variable capacitor. However, the configuration of the loop filter is not limited to this. 
       FIG. 5  is a flowchart illustrating an example of a phase modulation method. 
     A phase modulation apparatus decides, when determining that a communication mode has been changed (operation  500 ), phase modulation setting values according to the changed communication mode (operation  510 ). At this time, the phase modulation apparatus has to decide an appropriate reference frequency, division ratio (N) and loop bandwidth according to the changed communication mode. The phase modulation setting values are decided with reference to a pre-stored table. Then, the phase modulation setting values are applied to a phase modulator (operation  520 ). 
     In detail, application of the phase modulation setting values is to provide reference frequency information to a reference frequency oscillator, a division ratio value to a s frequency divider, filter bandwidth information to a loop filter and an on/off control signal to a switching unit. 
     According to an example, when a modulation bandwidth is set to a narrow-band mode with reference to a table that includes modulation bandwidths with respect to communication modes, a control signal for turning off the switching unit is output. If the switching unit  130  is tuned off, 1-point modulation is performed so as not to perform the modulation out of a PLL band. 
     Then, voltage signals V t1  and V t2  to be input to the loop filter are output according to the set modulation bandwidth. In the phase modulation apparatus, since the frequency of the loop filter  128  is lowered when the communication mode is a narrow-band mode, a is resonance point of the frequency of the loop filter with resistance is lowered to make a bandwidth narrow. 
     A phase modulator may perform phase modulation based on the phase modulation setting values (operation  530 ). 
     The processes, functions, methods and/or software described above may be recorded, stored, or fixed in one or more computer-readable storage media that includes program instructions to be implemented by a computer to cause a processor to execute or perform the program instructions. The storage includes magnetic media, optical media and the like. 
     A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.