Abstract:
A method for generating a modulated RF signal with high dynamic range is disclosed, which electrically combines average output power adjustment and instantaneous output power adjustment to improve the dynamic range of output power of an RF signal. Compared to the single control mechanism in the traditional method for generating a modulated RF signal, the method for generating a modulated RF signal proposed by the present invention can be applied to produce a variety of highly efficient RF transmitters with high dynamic range.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to methods for generating a radio-frequency (RF) signal, and, more particularly, to a method for generating a modulated RF signal with high dynamic range. 
       BACKGROUND OF THE INVENTION 
       [0002]    Advanced cellular mobile communication standards, such as CDMA2000, WCDMA and the like, use dynamic power control to improve spectral efficiency. Through dynamic power control, when a cellular phone is close to a base station, the output power of the radio-frequency (RF) transmitter of the cellular phone is reduced, whereas when the cellular phone is far from the base station, the output power of its RF transmitter is increased. In communication standards, such as CDMA2000 and WCDMA, the dynamic range of the output power is approximately 80 dB in an attempt to reduce interference between users and prolong the time in which the phone is operable. 
         [0003]    Traditionally, an RF transmitter is implemented with a linear power amplifier. By adjusting the input power of this power amplifier, the RF transmitter can obtain a power output with a dynamic range of 80 dB. However, this linear power amplifier is not efficient such that the efficiency will drop rapidly when backed off from the maximum output power level and severely reduce the operational time of the phone. 
         [0004]    Prior art has disclosed a power-level tracking technique, which essentially adds a DC-DC converter between the power supply of the RF transmitter and the linear power amplifier, so that the power supply voltage of the linear power amplifier can be adjusted by the DC-DC converter. By dynamically adjusting the power supply voltage, the efficiency of the linear power amplifier can be improved significantly, when compared to a conventional RF transmitter. However, since a linear power amplifier is employed, its efficiency is still relatively low. 
         [0005]    The envelope elimination and restoration (EER) transmission technique described in “L-band transmitter using Kahn EER technique” (IEEE Trans. Microwave Theory Tech., vol. 46, no. 12, pp. 2220-2225, December 1998, E H. Raab, B. E. Sigmon, R. G. Myers, and R. M. Jackson) can significantly increase the efficiency of the RF transmitter when operated close to the maximum power level. However, a transmitter adopting the EER technique only has a single control mechanism, wherein both the fast-varying instantaneous output power level and the slow-varying average output power level are controlled concurrently by the information detected by the envelope detector. The single control mechanism is limited by the difference of the maximum and the minimum power supply voltages, which limits the dynamic range of the transmitted RF signals to less than 20 dB. As a result, the dynamic range does not comply with the regulations on the dynamic range of output power specified in the aforementioned communication standards. 
         [0006]    In summary, a dynamic range of 80 dB for the power output can be obtained with the use of a linear power amplifier, but efficiency of the power output is poor; and, although said EER method mitigates poor efficiency, the dynamic range of the power output is inevitably reduced to below 20 dB. 
         [0007]    Thus, there is a need for a method for generating a modulated RF signal that solves the prior art shortcomings, specifically, by not compromising either the average output efficiency or the dynamic range of output power. 
       SUMMARY OF THE INVENTION 
       [0008]    In the light of forgoing drawbacks, an objective of the present invention is to provide a method for generating a modulated RF signal with high dynamic range and to provide high average output efficiency while maintaining the output power in a range that complies with that specified by current communication standards such as CDMA2000, WCDMA and the like. 
         [0009]    In accordance with the above and other objectives, the present invention provides a method for generating a modulated radio-frequency (RF) signal, comprising the steps of: generating a pulse modulation control signal, a gain control signal, and an average power control signal; receiving a constant-envelope modulated RF signal and the gain control signal by a variable gain module, and the variable gain module adjusting an amplifying gain of the constant-envelope modulated RF signal according to the gain control signal that sets the amplitude of the constant-envelope modulated RF signal to generate an constant-envelope modulated RF signal with an adjusted amplitude, and adjusting the DC supply voltage of a DC power supply to be output to a power amplification module according to the average power control signal to generate a power amplifier with adjusted average power, and receiving and modulating the constant-envelope modulated RF signal with an adjusted amplitude by an instantaneous power adjusting module according to the pulse modulation control signal to generate a pulse modulated RF signal carrying phase information; and receiving the pulse modulated RF signal carrying phase information and the power amplifier with adjusted average power by the power amplification module, and adjusting the output power of the received pulse modulated RF signal carrying phase information in its envelope by the power amplification module according to the power amplifier with adjusted average power, so as to output/generate a pulse modulated RF signal with adjusted power and carrying phase information. 
         [0010]    In another implementation aspect of the method for generating an RF signal with high dynamic range of the present invention, the method includes: generating an instantaneous power control signal, a gain control signal, and an average power control signal; receiving an constant-envelope modulated RF signal and the gain control signal by a variable gain module, having the variable gain module adjust the amplifying gain of the constant-envelope modulated RF signal according to the gain control signal to adjust the amplitude of the constant-envelope modulated RF signal to generate an constant-envelope modulated RF signal with an adjusted amplitude, and then adjust the average power the DC supply voltage of a DC power supply to be output to a plurality of power amplification modules according to the average power control signal to generate a power amplifier with adjusted average power, and receiving and modulating the constant-envelope modulated RF signal with adjusted amplitude by each of a plurality of instantaneous power adjusting modules according to the instantaneous power control signal to simultaneously generate a plurality of modulated RF signals carrying phase information; receiving the plurality of modulated RF signals carrying phase information and the power amplifier with adjusted average power by the plurality of power amplification modules, and then simultaneously adjusting the output powers of the received modulated RF signals carrying phase information by the power amplification modules according to the power amplifier with adjusted average power, so as to output/generate a plurality of modulated RF signals with adjusted power and carrying phase information; and combining the plurality of modulated RF signals with adjusted power and carrying phase information in their envelopes to output/generate an RF signal with high dynamic range. 
         [0011]    Compared to the prior art, the method for generating an RF signal with high dynamic range of the present invention adopts two power adjustment mechanisms to increase the dynamic range of output power. That is, on the one hand, adjustment of average output power can be achieved through the controlling of the DC power supply input of the RF amplifying module; on the other hand, fast adjustment of average output power can also be achieved through the adjustment of the amplitude of the constant-envelope modulated RF signal and pulse modulation (pulse width or duty cycle) of the constant-envelope modulated RF signal. Compared to the single control mechanism of the prior art, the method for generating an RF signal with high dynamic range of the present invention achieves a higher average power output efficiency while allowing the dynamic range of output power to comply with those required by current communication standards such as CDMA2000 and WCDMA. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention can be more fully understood by reading the following detailed description of the preferred embodiments, with reference made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a schematic diagram depicting a circuit for carrying out a method for generating a modulated RF signal with high dynamic range of the present invention; 
           [0014]      FIG. 2  is a schematic diagram depicting another circuit for carrying out the method for generating a modulated RF signal with high dynamic range of the present invention; 
           [0015]      FIGS. 3A and 3B  are diagrams depicting signal waveforms of an input constant-envelope modulated RF signal and an output pulse modulated RF signal with adjusted power and carrying phase information using the circuitry shown in  FIG. 1 ; 
           [0016]      FIGS. 4A and 4B  are diagrams depicting signal waveforms of an input constant-envelope modulated RF signal and an output RF signal with high dynamic range using the circuitry shown in  FIG. 2 ; 
           [0017]      FIG. 5  is a chart depicting a curve of power added efficiency obtained with an RF transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention; 
           [0018]      FIG. 6  is a chart depicting relationships between input and output powers obtained with an RF transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention; 
           [0019]      FIG. 7  is a chart depicting ACPR 1  and ACPR 2  (Adjacent Channel Power Ratio) curves obtained with an RF transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention; 
           [0020]      FIG. 8  is a chart illustrating a comparison between the efficiencies of a polar coordinated transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention and a commercial linear power amplifier within 40 dB dynamic range; 
           [0021]      FIG. 9  is a flowchart illustrating a method for generating a modulated RF signal with high dynamic range according to an embodiment of the present invention; and 
           [0022]      FIG. 10  is a flowchart illustrating a method for generating a modulated RF signal with high dynamic range according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    The present invention is described by the following specific embodiments. Those with ordinary skills in the art can readily understand other advantages and functions of the present invention after reading the disclosure of this specification. The present invention can also be implemented with different embodiments. Various details described in this specification can be modified based on different viewpoints and applications without departing from the scope of the present invention. 
         [0024]    Referring to  FIG. 1 , a schematic diagram depicting a circuit for carrying out a method for generating a modulated RF signal with high dynamic range of the present invention is shown. The present invention is capable of producing higher dynamic range for the transmitted power of RF signals. This dynamic range complies with the 80 dB requirement specified by current communication standards (e.g. CDMA2000 and WCDMA). 
         [0025]    As shown in  FIG. 1 , a variable gain module  103  receives a constant-envelope modulated RF signal  102  and a gain control signal  104 . The variable gain module  103  adjusts the amplifying gain of the constant-envelope modulated RF signal  102  according to the gain control signal  104 . Specifically, the variable gain module  103  adjusts the amplitude of the constant-envelope modulated RF signal  102  to generate a constant-envelope modulated RF signal with an adjusted amplitude  112 . 
         [0026]    Then, an average power adjusting circuit  101  adjusts the average power of the supply voltage of a DC power supply to be output to a power amplification module  107  according to an average power control signal  108  to generate a DC supply voltage with the adjusted average power  110 . Thereafter, an instantaneous power adjusting module  105  receives the constant-envelope modulated RF signal with the adjusted amplitude  112 , and modulates the constant-envelope modulated RF signal with the adjusted amplitude  112  according to a pulse modulation control signal  106  to generate a pulse modulated RF signal carrying phase information  122 . 
         [0027]    After the pulse modulated RF signal carrying phase information  122  is generated, the power amplification module  107  may receive the pulse modulated RF signal carrying phase information  122  and the DC supply voltage with the adjusted average power  110 , and then the power amplification module  107  may adjust the power of the received pulse modulated RF signal carrying phase information  122  correspondingly according to the DC supply voltage with the adjusted average power  110 , so as to output/generate a pulse modulated RF signal with the adjusted power and carrying phase information  132 . 
         [0028]    It should be noted here that the frequency (or duty cycle) of the constant-envelope modulated RF signal with the adjusted amplitude  112  may be modulated by the instantaneous power adjusting module  105 . 
         [0029]    Moreover, in another aspect of the present invention, the power amplification module  107  is an RF power amplifier. 
         [0030]    Further, in another aspect of the present invention, the variable gain module  103  is a variable gain amplifier. 
         [0031]    Referring to  FIG. 2 , a diagram depicting another circuit for carrying out the method for generating a modulated RF signal with high dynamic range of the present invention is shown. As shown in  FIG. 2 , a variable gain module  203  receives a constant-envelope modulated RF signal  202  and a gain control signal  204 . The variable gain module  203  adjusts the amplifying gain of the constant-envelope modulated RF signal  202  according to the gain control signal  204 . Specifically, the variable gain module  203  adjusts the amplitude of the constant-envelope modulated RF signal  202  to generate a constant-envelope modulated RF signal with adjusted amplitude  212 . 
         [0032]    Then, an average power adjusting circuit  201  adjusts the average power of the DC supply voltage of a DC power supply to be output to a plurality of power amplification modules  207  according to an average power control signal  208  to generate a DC supply voltage with the adjusted average power  210 . 
         [0033]    Thereafter, each of a plurality of instantaneous power adjusting modules  205  receive an constant-envelope modulated RF signal with the adjusted amplitude  212 , and modulates the constant-envelope modulated RF signal with the adjusted amplitude  212  according to an instantaneous power control signal  206  to simultaneously generate a plurality of modulated RF signals carrying phase information  222 . In other words, the instantaneous power adjusting modules  205  achieve adjustment of the instantaneous power by controlling the frequency or duty cycle of the signals. 
         [0034]    After the plurality of modulated RF signals carrying phase information  222  are generated, the plurality of power amplification modules  207  may each receive a corresponding modulated RF signal carrying phase information  222  and the DC supply voltage with the adjusted average power  210 , and then the plurality of power amplification modules  207  may simultaneously adjust the power of each received modulated RF signal carrying phase information  222  according to the DC supply voltage with the adjusted average power  210 , so as to output/generate a plurality of modulated RF signals with adjusted power and carrying phase information. 
         [0035]    Finally, the plurality of modulated RF signals with the adjusted power and carrying phase information can be combined to output/generate an RF signal with high dynamic range  232 . 
         [0036]    It should be noted that the functions of the instantaneous power adjusting modules  205  and the power amplification modules  207  can be realized by a power digital-to-analog converter (DAC). 
         [0037]    As shown in  FIGS. 3A and 3B , diagrams depicting signal waveforms of a received input signal (e.g. constant-envelope modulated RF signal  102 ) and an output RF signal (e.g. pulse modulated RF signal with adjusted power and carrying phase information  132 ) are provided in conjunction with the circuitry shown in  FIG. 1 , wherein the waveforms depict an exemplary input signal  102  and output RF signal  132 , respectively. 
         [0038]    In addition, as shown in  FIGS. 4A and 4B , diagrams depicting signal waveforms of the received input signal (e.g. constant-envelope modulated RF signal  202 ) and an output RF signal (e.g. an RF signal with high dynamic range  232 ) are provided in conjunction with the circuitry shown in  FIG. 2 , wherein the waveforms depict an exemplary input signal  202  and output RF signal  232 , respectively. 
         [0039]    Compared to the single control mechanism of the EER method in the prior art, the present invention adopts two power adjustment mechanisms to increase the dynamic range of the output power. On the one hand, slow adjustment of the average power in the millisecond timeframe can be achieved, while, on the other hand, fast adjustment of the average power in the microsecond timeframe can also be achieved, allowing the dynamic range of output power to comply with those required by current communication standards, such as CDMA2000 and WCDMA. 
         [0040]    When the method for generating a modulated RF signal with high dynamic range of the present invention is applied to a polar coordinated transmitter, the output power efficiency of the polar coordinated transmitter is increased while exhibiting high dynamic range. In order to more clearly understand this, please refer to  FIG. 5 , which is a plot depicting a curve of power added efficiency. 
         [0041]    Moreover, as shown in  FIG. 6 , by using the method for generating a modulated RF signal with high dynamic range of the present invention, the dynamic range of the output power can be further improved to meet the 80 dB requirement specified by the current communication standards. 
         [0042]    In addition, it is known from the CDMA2000 communication standard that the Adjacent Channel Power Ratio (ACPR 1 ) should be lower than −42 dBc under a measuring bandwidth of 30 KHz or that the power should be lower than −54 dBm under a measuring bandwidth of 1.23 MHz, and that the Alternate Channel Power Ratio (ACPR 2 ) should be lower than −54 dBc under a measuring bandwidth of 30 KHz or the power should be lower than −54 dBm under a measuring bandwidth of 1.23 MHz. 
         [0043]      FIG. 7  is a plot depicting the RF output signal obtained using the method for generating a modulated RF signal with high dynamic range of the present invention by a spectrum analyzer. It can be seen from  FIG. 7 , when the output power varies within the 80 dB dynamic range, the ACPR 1  and the ACPR 2  both comply with the CDMA2000 communication standard. In  FIG. 7 , the curve consisting of small squares indicates the performance of ACPR 1 , and the curve consisting of small circles indicates the performance of ACPR 2 . 
         [0044]    Referring now to  FIG. 8 , a comparison between the efficiencies of a polar coordinated transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention and a commercial linear power amplifier within a 40 dB dynamic range is shown. As can be seen in  FIG. 8 , compared to curve  802  (using the commercial linear power amplifier), curve  801 , which indicates the efficiency of the polar coordinated transmitter using the method for generating a modulated RF signal with high dynamic range of the present invention, has an improved power output efficiency when the output power is close to the maximum output power. 
         [0045]    It can be seen from above  FIGS. 3 to 6  that the method for generating a modulated RF signal with high dynamic range of the present invention provides an RF signal with high efficiency and high dynamic range (80 dB) for output power through two simultaneous power adjusting mechanisms, namely, pulse width/amplitude modulation and dynamic voltage regulation of the drain of the power amplifier. 
         [0046]    The processes of the method for generating a modulated RF signal with high dynamic range according to an embodiment of the present invention are now further described in conjunction with the system architecture shown in  FIG. 1 .  FIG. 9  is a flowchart illustrating a method for generating a modulated RF signal with high dynamic range  900  of the present invention. In step S 902 , a pulse modulation control signal, a gain control signal, and an average power control signal are generated. Then, proceed to step S 904 . 
         [0047]    In step S 904 , a constant-envelope modulated RF signal and the gain control signal are received by a variable gain module, which adjusts the amplifying gain of the constant-envelope modulated RF signal according to the gain control signal; specifically, the amplitude of the constant-envelope modulated RF signal is adjusted to generate an constant-envelope modulated RF signal with an adjusted amplitude; and then, an average power of the DC supply voltage of a DC power supply to be output to a power amplification module is adjusted according to the average power control signal to generate a DC supply voltage with the adjusted average power; thereafter, the constant-envelope modulated RF signal with the adjusted amplitude is received and modulated by an instantaneous power adjusting module according to the pulse modulation control signal to generate a pulse modulated RF signal carrying phase information. Then, proceed to step S 906 . 
         [0048]    In step S 906 , the pulse modulated RF signal carrying phase information and the DC supply voltage with the adjusted average power are received by the power amplification module, and then the power of the received pulse modulated RF signal carrying phase information is adjusted by the power amplification module according to the DC amplifier with the adjusted average power, so as to output/generate a pulse modulated RF signal with adjusted power and carrying phase information, and the processes of the method for generating a modulated RF signal with high dynamic range of the present invention are complete. 
         [0049]    The steps of the method for generating a modulated RF signal with high dynamic range according to another embodiment of the present invention are further described in conjunction with the system architecture shown in  FIG. 2 .  FIG. 10  is a flowchart illustrating a method for generating a modulated RF signal with high dynamic range  1000  according to the present invention. In step S 1002 , an instantaneous power control signal, a gain control signal, and an average power control signal are generated. Then, proceed to step S 1004 . 
         [0050]    In step S 1004 , an constant-envelope modulated RF signal and the gain control signal are received by a variable gain module, which adjusts the amplifying gain of the constant-envelope modulated RF signal according to the gain control signal; specifically, the amplitude of the constant-envelope modulated RF signal is adjusted to generate an constant-envelope modulated RF signal with an adjusted amplitude; and then, the average power of the supply voltage from a DC power supply to be output to a plurality of power amplification modules is adjusted according to the average power control signal to generate a DC supply voltage with the adjusted average power; thereafter, the constant-envelope modulated RF signal with the adjusted amplitude is received and modulated by each of a plurality of instantaneous power adjusting modules according to the instantaneous power control signal to simultaneously generate a plurality of modulated RF signals carrying phase information. Then, proceed to step S 1006 . 
         [0051]    In step S 1006 , the plurality of modulated RF signals carrying phase information and the DC supply voltage with the adjusted average power are received by the plurality of power amplification modules, and then the powers of the received modulated RF signals carrying phase information are simultaneously adjusted by the power amplification modules according to the DC supply voltage with the adjusted average power, so as to output/generate a plurality of modulated RF signals with adjusted power and carrying phase information. Then, proceed to step S 1008 . 
         [0052]    In step S 1008 , the plurality of modulated RF signals with adjusted power and carrying phase information are combined to output/generate an RF signal with high dynamic range, and the steps of the method for generating a modulated RF signal with high dynamic range of the present invention are complete. 
         [0053]    The above embodiments are provided to illustrate the principles of the present invention, and they should not be construed as to limit the present invention in any way. The above embodiments can be modified by those with ordinary skills in the arts without departing from the scope of the present invention as defined in the following appended claims.