Abstract:
A broad power band transmitter utilizing a duty cycle modulator achieves 80dB of power range for 3G signals. The present invention greatly improves the efficiency of transmitters used in mobile phones, for example, by using the duty cycle modulator during medium and low power levels of the transmitting power amplifier. The power amplifier operates in three different modes based upon the amplifier power level selected. The power amplifier operates in an EER mode during high power levels, in a DCM ERR mode during medium power levels, and in a DCM mode during low power levels.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to communication transmitters and more specifically to power amplifiers in communication transmitters. 
         [0003]    2. Description of Related Art 
         [0004]    Transmitters used in mobile phones vary their output power when transmitting signals. Although improvements have been made to the efficiency of such transmitters at high power ranges, improvements in efficiency when operating at medium and low power ranges have largely been ignored. While efficiency improvements at high power ranges result in energy savings, such energy savings tend to be minimal due to the relatively shorter periods of time that mobile phones operate at a high power output.  FIG. 1  represents a graph of probability of use of mobile phones, against output power level, in both suburban and urban areas. Mobile phones spend much more time at medium power ranges and low power ranges than at high power ranges. 
         [0005]    There is an unresolved need for an apparatus and method to improve mobile phone efficiency when operating at medium power ranges and low power ranges. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a much more efficient transmitter for mobile phones, by operating the power amplifiers in different modes, depending on the selected power output of the power amplifier. The transmitter changes the operating characteristics of the power amplifier to provide for the greatest amount of efficiency across the entire power band. At high power ranges, the power amplifier is operated in an Envelope Elimination and Restoration (“EER”) mode in the compressed region. In this mode, all the amplitude modulation is provided to the amplifier at the supply port, with the radio frequency (“RF”) input modulator turned off. At medium power ranges, the power amplifier is in a Duty Cycle Modulation Envelope Reduction and Restoration (“DCM ERR”) mode, in the compressed region. In this mode both the supply port and RF input port provide parts of the amplitude modulation required to get full dynamic range. At low power ranges, the power amplifier is operated in a Duty Cycle Modulation (“DCM”) mode, with the supply modulation turned off. Duty cycle modulation used at medium and low power ranges provides a considerable improvement in operating efficiency. The high, medium, and low power ranges are determined on the basis of the specification for Adjacent Channel Leakage Ratio (“ACLR”), like for example, ACLR 5, ACLR 10, and receive band noise at a 45 MHz offset. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The exact nature of this invention, as well as the objects and advantages thereof, will become readily apparent from consideration of the following specification in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein: 
           [0008]      FIG. 1  is a graph illustrating probability density for power consumption of mobile phones in urban and suburban environments; 
           [0009]      FIG. 2  is graph illustrating power efficiency of mobile phones across the used power band using a Duty Cycle Modulation Envelope Reduction and Restoration (“DCM ERR”) mode and Envelope Elimination and Restoration (“EER”) mode; 
           [0010]      FIG. 3  is a graph illustrating the adjustment of the operating characteristic of a power amplifier; 
           [0011]      FIG. 4  is a schematic diagram of a power amplifier operating in an Envelope Reduction and Restoration (“ERR”) mode; 
           [0012]      FIG. 5  is a graph showing how the envelope varying signal at the RF input port and the supply port combine when the amplifier is in the ERR mode; 
           [0013]      FIG. 6  is a block diagram of a power amplifier that operates with an envelope varying signal at both the RF input port and the supply port; 
           [0014]      FIG. 7  is a block diagram of a preferred embodiment according to the present invention; 
           [0015]      FIG. 8  is a graph of the specification for Adjacent Channel Leakage Ratio 5 (ACLR5) showing the use of three operating modes for a power amplifier to match the specification; 
           [0016]      FIG. 9  is a graph of the specification for Adjacent Channel Leakage Ratio 10 (ACLR10) showing the use of three operating modes of a power amplifier to match the specification; 
           [0017]      FIG. 10  is a graph of the specification receive band noise at a 45 MHz offset (Rx 45) showing use of three operating modes of a power amplifier to match the specification; 
           [0018]      FIG. 11  is a block diagram illustrating signal flow in an embodiment of the present invention; 
           [0019]      FIG. 12  is a block diagram illustrating the three basic modes of operation of an amplifier according to the present invention; 
           [0020]      FIG. 13  is a graph comparing supply signal and amplitude dynamic range requirement for three different operating modes; 
           [0021]      FIG. 14  is a graph illustrating separation of a polar coordinate signal into a first and second amplitude component according to the present invention; 
           [0022]      FIG. 15  is a graph illustrating three modes of operation of a power amplifier according to the present invention; 
           [0023]      FIG. 16  is a block diagram of a power amplifier utilizing EER modulation at low power ranges; 
           [0024]      FIG. 17  is a block diagram of a power amplifier according to the present invention operating in a DCM mode at low power ranges; 
           [0025]      FIG. 18  is a graph of power spectral density comparison for a power amplifier operating in the EER mode and in the DCM ERR mode; 
           [0026]      FIG. 19  is a graph of an overall magnitude waveform of a power amplifier at medium and low power ranges; and 
           [0027]      FIG. 20  is a graph of power spectral density comparison for a power amplifier operating in the EER mode and in the DCM ERR mode at low power ranges. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Referring to  FIG. 2 , a power amplifier operating in envelope elimination and restoration (“EER”) mode, also known as polar modulation, is efficient at high power ranges, depicted by region  13 . However, EER modulation sacrifices efficiency at low and medium power ranges, depicted by region  15 . 
         [0029]    In contrast, a power amplifier according to the present invention, utilizes a combination of EER modulation and Duty Cycle Modulation Envelope Reduction and Restoration (“DCM ERR”) modulation, as depicted by region  11 . The power amplifier operates at the high efficiency of the EER mode at high power ranges, and a much higher efficiency than the EER mode, at low and medium power ranges. 
         [0030]      FIG. 3 , a graph of input power at the RF input port versus output power of a conventional power amplifier, shows a normal power characteristic curve  21 . The power amplifier can operate in quadrature mode in its linear region  24 . However, at high power ranges at the RF input port, the conventional power amplifier will operate in the saturation region  22  and compressed region  20 . 
         [0031]    The characteristic power curve  21  does not follow the ideal power curve  23  at medium to high power ranges. By pre-processing the input characteristics of the amplifier to generally follow the curve  25 , the ideal performance of curve  23 , can be approached. 
         [0032]    A conventional power amplifier  41 , as seen in  FIG. 4 , normally receives an amplitude modulated signal at a supply port  27  and a modulated RF signal at an RF input port  29  to generate an output signal  40 . An envelope varying signal  31 , must be processed by the amplifier  41 . The signal  31  contains an amplitude component  33  and a phase component  35 . The envelope  33  sweeps above and below the amplifier saturation levels  36  and  38 . 
         [0033]    The Pin versus Pout graph inside power amplifier  41  shows the characteristic. Curve  26  is the actual characteristic of the amplifier  41 . Curve  28  is an ideal characteristic. To fit within the dynamic range of the amplifier, the magnitude of the RF input port signal  31  must be decomposed, as shown in  FIG. 5 . For example, the magnitude of an ideal signal  42  can be decomposed into an RF input port signal  44  and a supply port signal  46 . The RF input port signal  44  tracks the ideal signal  42  until the magnitude of the ideal signal  42  is above a predetermined maximum. At this predetermined maximum, the RF input port signal  44  will stop tracking the ideal signal and maintain a constant level. In contrast, the supply port signal  46  maintains a constant level until the magnitude of the ideal signal  42  is above the maximum magnitude of the RF input port signal. The supply port signal  46  tracks the ideal signal  42  when it is above the maximum magnitude of the RF input port signal. 
         [0034]    The ideal signal  42  is thereby decomposed into two signals, RF input port signal  44  and supply port signal  46 , with the RF input port signal  44  tracking the ideal signal  42  below its maximum magnitude, and the supply port signal  46  tracking the ideal signal  41  above the RF maximum magnitude. 
         [0035]    A conventional ERR transmitter  50  is shown in  FIG. 6 . A signal decomposer  47  receives a rectangular coordinate signal including an in-phase component  56  and a quadrature-phase component  58  and converts it into a polar coordinate signal including an amplitude component and a phase-component. The signal decomposer  47  transmits the amplitude component above a predetermined maximum level as the first component  53 . The signal decomposer  47  converts the amplitude component below the predetermined maximum level and the phase-component into a modified rectangular coordinate signal as the second component  55 . 
         [0036]    A supply modulator  49  receives the first component  53 , modulates it, and sends the resulting supply signal to the power amplifier  51 . The second component  55  is sent to the RF input port of the amplifier  51 . The power amplifier  51  thus generates the wide power band output signal  57 . 
         [0037]    A transmitter  100 , utilizing the present invention, is shown in  FIG. 7 . A baseband chip  164  receives a baseband information signal  162  from a base station (not shown). The baseband chip  164  extracts power level information from the baseband information signal  162  to generate a power level signal  181  indicating a desired power output of a power amplifier  177 . For example, when the baseband chip initially communicates with the base station, the baseband information signal  162  could indicate that the desired power output for the power amplifier  177  is 20 dBm. Subsequently, the base station could indicate in the baseband information signal  162  to increment or decrement the power output of the power amplifier  177 . 
         [0038]    The baseband chip also receives a data signal  158  from a data unit (not shown) representing the desired data to be transmitted such as voice information or image information. The baseband chip  164  generates rectangular coordinate signals including an in-phase component  56  and a quadrature-phase component  58  from the data signal  158 . 
         [0039]    A power controller  165  receives the power level signal  181  from the baseband chip  164 , to indicate the desired power output of power amplifier  177 . The power level signal  181  can be a digital signal and can indicate a low, medium, or high power range based on the desired power output of the power amplifier  177 . 
         [0040]    The baseband chip determines the power level signal  181  by communicating with a base station. For example, a base station can instruct a mobile phone containing the transmitter  100  to vary the power output of the power amplifier  177  based on a distance between the base station and the transmitter  100 . Thus, if the mobile phone is located a large distance from the base station, then the base station can instruct the baseband chip to transmit the power level signal  181  indicating the high power range. However, if the mobile phone is located a short distance from the base station, then the base station can instruct the baseband chip to transmit the power level signal  181  indicating the low or medium power range. 
         [0041]    Likewise, the base station can instruct the mobile phone to vary the power output of the power amplifier  177  based on the quality of the communications channel between the mobile phone and the base station. If the communications channel between the mobile phone and the mobile station is degraded, then the base station can instruct the baseband chip to transmit the power signal  181  indicating the high power range. However, if the communications channel between the mobile phone and the mobile station is acceptable or extremely clear, then the baseband chip can instruct the base station can instruct the baseband chip to transmit the power level signal  181  indicating the low or medium power range. 
         [0042]    Responsive to the power level signal  181 , the power controller  165  determines a threshold signal  183  for a signal decomposer  163 , an amplification signal  199  for variable gain amplifier  173 , and a gain signal  197  for supply modulator  175 . The power controller determines the threshold signals and the gain signals by use of a look-up table (not shown) as directed by the power level signal  181 . The power level signal  181  also determines a first predetermined power threshold and a second predetermined power threshold, which will be described later. 
         [0043]    The signal decomposer  163  receives rectangular coordinate signals including an in-phase component  56  and a quadrature-phase component  58  and converts these signals into polar coordinate signals having an amplitude component and a phase component. The signal decomposer  163  decomposes the amplitude component into a first amplitude component  185  which is above a predetermined amplitude threshold, and a second amplitude component  191 , which is below the predetermined amplitude threshold, and a phase component  189 . Thus, the signal decomposer  163  prepares the first amplitude component  185 , the second amplitude component  191 , and the phase component  189 , based on the in-phase component  56  and the quadrature-phase component  58 . The predetermined amplitude threshold is established by threshold signal  183  supplied to decomposer  163  by power controller  165  based on the selected power output of the power amplifier  177 . 
         [0044]    The signal decomposer  163  transmits the first amplitude component  185  to a supply modulator  175 . The supply modulator  175  receives the first amplitude component  185  and modulates it with a gain signal  197  from the power controller  165  to produce a supply signal  176 . When the supply modulator  175  is active, such as when the power level signal  181  indicates that power output of the power amplifier  177  should be above the second predetermined power threshold, the supply modulator output signal  176  is a modulated supply signal. However, when the supply modulator is inactive, such as when the power level signal  181  indicates that output power of the power amplifier  177  should be below the second predetermined power threshold, the supply modulator output signal  176  is merely a constant level signal since the first amplitude component  185  is a constant level signal. 
         [0045]    A constant envelope signal generator  167  receives the phase component  189  of the polar coordinate signal from the signal decomposer  163  and generates a constant envelope phase indicating signal  193  which is transmitted to a combining unit  171 , which may be an AND gate. 
         [0046]    The duty cycle modulator  169  receives the second amplitude component  191  of the polar coordinate signal from the signal decomposer  163  and modulates the second amplitude component  191  on to a pulse signal to produce a duty cycle modulator output signal  170  which is transmitted to the combining unit  171 . The duty cycle modulation could be, for example, a type of pulse width density modulation such as ΔΣ modulation wherein the amplitude variations of signal  191  is represented by the pulse widths of the output signal  170 . When the power level signal  181  indicates that power output of the power amplifier  177  should be below the first predetermined power threshold, the duty cycle modulator is active. When the power level signal  181  indicates that power output of the power amplifier  177  should be above the first predetermined power threshold, the duty cycle modulator is inactive. The duty cycle modulator output signal  170  is then a constant level signal. 
         [0047]    The combining unit AND gate  171  receives the duty cycle modulator output signal  170  and the signal  193  from the constant envelope generator  167  to form a signal  195 . The signal  195  is high or “ON” during a period when both the constant envelope signal  193  and the duty cycle modulator output signal  170  are high or “ON.” The combined signal  195  is low or “OFF” during the period that one of the input signals is low. If the duty cycle modulator output signal  170  is constantly high, or “ON” because the duty cycle modulator  169  is inactive, then the signal  195  from combined AND gate  171  is merely the constant envelope signal  193 . The signal  195  is transmitted to a variable gain amplifier  173 . 
         [0048]    The variable gain amplifier  173  amplifies the signal  195  based on the amplification signal  199  from the power controller  165  to generate an amplified signal  201 . The amplification of signal  195  is adjusted to the desired power range as directed by amplification signal  199  from power controller  165 . The amplified signal  201  is supplied to a power amplifier  177 . 
         [0049]    The power amplifier  177  includes a supply port  178  and an RF input port  180 . The supply port  178  receives the supply signal  176  from supply modulator  175 . The RF input port  180  receives the amplified signal  201  from the variable gain amplifier  173 . The power amplifier  177  uses signal  201  at the RF input port and the supply signal  176  at the supply port to form a power output signal  203 . 
         [0050]    The path from the signal decomposer  163  to the supply port  178  of power amplifier  177  is the amplitude path. The path taken from the signal decomposer  163  to the RF input port  180  of the power amplifier  177  is an RF input port path. 
         [0051]    The power amplifier  177  is set up to operate in three modes, the EER mode, the DCM ERR mode, and the DCM mode, depending on the selected power output of the power output signal  203  as indicated by the power level signal  181 . The power amplifier  177  operates in the EER mode when the power level signal  181  indicates the high power range. The power level signal  181  causes the power controller to direct when the power amplifier operates in the EER mode. The power amplifier  177  operates in the DCM ERR mode when the power level signal  181  indicates the medium power range. The power level signal  181  causes the power controller to direct when the power amplifier operates in the DCM ERR mode. The power amplifier  177  operates in the DCM mode when the power level signal  181  indicates the low power range. The power level signal  181  causes the power controller to direct when the power amplifier operates in the DCM mode. 
         [0052]    When the power amplifier  177  is operating in the EER mode during high power ranges, the supply modulator  175  is active and the duty cycle modulator  169  is inactive. With only the supply modulator  175  active, only supply signal  176  is provided to the power amplifier  177  at supply port  178 . The supply signal  176  contains the entire amplitude component. The amplified signal  201  at the RF input port of power amplifier  177 , at high power ranges, is a constant envelope signal, as the result of the constant envelope signal  193  being passed through combiner unit  171 . When the duty cycle modulator  169  is inactive, the duty cycle output signal  170  is a constant high or “ON.” With a high at one of its inputs the combiner AND gate unit  171  passes the constant envelope signal  193  on its other input to amplifier  173  unaltered. During high power ranges, the power amplifier  177  operates in the compressed region using polar modulation. This provides low, out of band noise. Because the duty cycle modulator  169  is inactive, a surface acoustic wave (“SAW”) filter which is normally required to reduce interference to external electronic devices is not needed. 
         [0053]    When power output of the power amplifier  177  is selected to be at medium power ranges, the DCM ERR mode is used. In this mode, the supply modulator  175  and the duty cycle modulator  169  are both active. The output signal  176  from supply modulator  175  is provided to supply port  178  of the power amplifier  177 . With the duty cycle modulator  169  active, the amplified combined signal  201  received by the power amplifier at the RF input port  180  includes the constant envelope signal  193  and the duty cycle modulated signal  170 . 
         [0054]    When the power amplifier  177  is operating in the DCM mode wherein power output of the power amplifier  177  is selected to be at low power ranges, the supply modulator  175  is inactive and the duty cycle modulator  169  is active. With the supply modulator  175  inactive, the output signal  176  is a constant level signal. Since the duty cycle modulator  169  is active, the amplified combined signal  201  includes components of both the duty cycle modulated signal  170  and the constant envelope signal  193 . 
         [0055]    The supply modulator  175  operates similar to open loop polar supply modulation at high and medium power ranges. During low power ranges, the supply modulator  175  provides a constant level voltage signal to power amplifier  177 . The level of the voltage signal depends on power indicator signal  181 . During low power ranges, the dithering frequency of duty cycle modulator  169  is a function of the power level signal  181 . During low power ranges, the variable gain amplifier  173  and the power amplifier  177  function similar to attenuators. 
         [0056]    The predetermined amplitude threshold and the first and second predetermined power thresholds are controlled by threshold indicating signal  183  from power controller  165 . The variable amplification amount is controlled by the amplification signal  199 . The gain signal  197  is controlled by the first and second predetermined power thresholds based on performance matrices regarding the adjacent channel leakage ratio specifications (“ACLR”) and received band (“Rx”) noise specifications. For example, the first and second predetermined power thresholds can be based on performance matrices regarding ACLR 5, ACLR 10, and Rx noise specifications at a 45 MHz offset (“Rx 45”). 
         [0057]    ACLR is the ratio of a root-raised cosine (“RRC”) filtered mean power centered on an assigned channel frequency to the RRC filtered power centered on an adjacent channel frequency. The ACLR 5 and the ACLR 10 measure a relative power at ±5 MHz and ±10 MHz offsets from an uplink channel such as output signal  203 . ACLR measurements and more specifically ACLR 5 and ACLR 10 measurements are defined in the 3rd Generation Partnership Project (“3GPP”) Technical Specification (“TS”) 34.121, sections 5.10 and 5.10A, which is incorporated herein in its entirety. Rx 45 is the receive band noise specification at a 45 MHz offset to avoid desensitization of the receiver. Since a mobile phone utilizing the transmitter  100  may spend most of its time at medium power ranges, the energy savings at the medium power range can be a large amount of energy savings. 
         [0058]    The following Table 1 discloses noise level when comparing EER to DCM ERR at a power output level of 6 dBm for power amplifier  177 . 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 ACLR 5 
                 ACLR 10 
                 Rx 45 
               
               
                   
                 (dBc) 
                 (dBc) 
                 (dBm/100 KHz) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 3GPP 
                 −33 
                 −43 
                 (N/A) 
               
               
                 Target Specification 
                 −46 
                 −52 
                 −66.8 
               
               
                 EER mode 
                 −46.2 
                 −52.8 
                 −93.3 
               
               
                 DCM ERR mode 
                 −50.7 
                 −67.0 
                 −79.8 
               
               
                   
               
             
          
         
       
     
         [0059]    From Table 1, the EER mode and the DCM ERR mode are both below the target specification and the 3GPP specification. Both the EER mode and DCM ERR mode are thus acceptable modulation modes for the power amplifier  177 . However, at some power level, the EER mode will have an unacceptable noise level as compared to the DCM ERR mode. The power amplifier  177  switches to operate in the DCM ERR, before the EER mode reaches an unacceptable noise level. Similar tables to Table 1 can be created for a spectrum of power output ranges to determine the transition points for the power amplifier  177 , from the EER mode to the DCM ERR mode, and to the DCM mode. 
         [0060]    In  FIG. 8 , an ACLR 5 target specification is compared to operation of the power amplifier in the EER mode, the DCM ERR mode, and the DCM mode. The target specification, represented by curve  265  is matched as closely as possible by operating the power amplifier in the EER mode  263  at high power ranges, operating the amplifier in the DCM ERR mode  267  at medium power ranges, and operating the power amplifier in the DCM mode  269  on low power ranges. 
         [0061]    In  FIG. 9 , an ACLR 10 target specification is compared to operation of the amplifier in the EER mode, the DCM ERR mode, and the DCM mode. The target specification represented by curve  273  is matched as closely as possible by operating the power amplifier in the EER mode  271 , at high power ranges, operating the power amplifier in the DCM ERR mode  275  at medium power ranges, and operating the power amplifier in the DCM mode  277  at low power ranges. 
         [0062]    In  FIG. 10  an Rx 45 target specification is compared to operation of the amplifier in EER mode, DCM ERR mode, and DCM mode. The target specification represented by curve  281  is matched as closely as possible by operating the power amplifier in the EER mode  287  at high power ranges, operating the power amplifier in the DCM ERR mode  283  at medium power ranges, and operating the power amplifier in the DCM mode  285  at low power ranges. 
         [0063]    Based on  FIG. 8 ,  FIG. 9 ,  FIG. 10 , and Table 1, transition points for switching between EER mode, DCM ERR mode, and DCM mode of operation for the power amplifier can be selected so the power amplifier operates within the specification. For example, the point for the DCM ERR mode to transition to the EER mode can be selected to be between 6 dBm to 24 dBm because the EER mode has an ACLR 5, ACLR 10, and Rx 45 noise below the target specification in that power range. Below 6 dBm, however, the EER mode has an ACLR 5 and ACLR 10 noise above the target specification. Although the EER mode still has acceptable noise for the specification, the EER mode should preferably have acceptable noise levels in the ACLR 5, and the ACLR 10 specifications as well. 
         [0064]    The point for the DCM mode or the EER mode to transition to the DCM ERR mode can be selected to be between −22 dBm to 12 dBm because during those ranges the DCM ERR mode is below the target specification in the ACLR 5, ACLR 10, and Rx 45 noise specification. The point for the DCM ERR mode to transition to the DCM mode can be selected to be between −50 dBm to −22 dBm since the DCM mode operates below the target specification at that range in the ACLR 5, ACLR 10, and Rx 45. 
         [0065]    Thus, the first predetermined power threshold for operating in the high power ranges can be selected to be greater than 6 dBm, with a range between 6 dBm to 24 dBm. The power amplifier operates in the EER mode above this power threshold. The power amplifier  177  operates in the DCM mode when power output of the power amplifier is selected to be below a second predetermined power threshold in the low power range. The second predetermined power threshold can be selected to be less than −22 dBm, with a range between −50 dBm to −22 dBm. At low power ranges, receive (“Rx”) band noise is not an issue and power is conserved to meet ACLR 5 and ACLR 10 requirements. 
         [0066]    The power amplifier  177  operates in the DCM ERR mode when the power output of the power amplifier is selected to be at medium power ranges between the first predetermined power threshold and the second predetermined power threshold. In this range, the power output of the power amplifier is in the range of about −22 dBm to 12 dBm. 
         [0067]    During medium power ranges, the RX band noise requirement is relaxed and the supply modulator  175  has a reduced dynamic range when compared to the high power ranges. Also, the power amplifier  177  can provide a good fit to ACLR 5 and ACLR 10 specifications when it operates with limited dynamic range from the supply modulator  175 . 
         [0068]    In the above described example, the 3GPP specification was used to determine the transition points for the EER mode, the DCM ERR mode, and the DCM mode of the power amplifier  177 . However, other specifications for Global System for Mobile Communications (“GSM”), Enhanced Data Rate for GSM Evolution (“EDGE”), Code division multiple access (“CDMA”), Time division multiple access (“TDMA”), and other wireless specifications may be used to determine the transition points for the EER mode, the DCM ERR mode, and the DCM mode of the power amplifier  177 . Furthermore, the predetermined amplitude threshold is selected such that when the power level signal  181  indicates a low power range wherein power output of the power amplifier  177  is selected to be below the second predetermined power threshold, the first amplitude component  185  is a constant level signal; and when the power level signal  181  indicates a high power range, wherein power output of the power amplifier  177  is selected to be above the first predetermined power threshold, the second amplitude component  191  is a constant signal. 
         [0069]      FIG. 11  is a block diagram illustrating signal flow for a preferred embodiment of a transmitter  200  according to the present invention. A rectangular coordinate signal generator  97  generates a rectangular coordinate signal  113  which is transmitted to a signal decomposer  99 . 
         [0070]    The signal decomposer  99  converts the rectangular coordinate signal into a polar coordinate signal, including an original amplitude component and a phase component  123 . The signal decomposer  99  separates the original amplitude component into a first amplitude component  115  which is above a predetermined amplitude threshold, and a second amplitude component  121  which is below the predetermined amplitude threshold. The first amplitude component  115  is provided to a supply modulator  101 . The second amplitude component  121  is provided to a duty cycle modulator  107 . The phase component  123  is provided to a constant envelope generator  105 . 
         [0071]    The supply modulator  101  provides a supply signal  119  to the power amplifier  111 . When the supply modulator  101  is active, the supply signal  119  is a modulated signal. When the supply modulator  101  is inactive, the supply signal  119  is a constant level signal. 
         [0072]    A duty cycle modulator  107  provides a duty cycle modulated signal  125  to a combining unit  109 . When the duty cycle modulator  107  is active, the signal  125  is a modulated signal. When the duty cycle modulator  107  is inactive, the signal  125  is a constant high level, or “ON.” 
         [0073]    A constant envelope signal generator  105  receives the phase component signal  123  and generates a constant envelope phase indicating signal  127 , which is transmitted to the combining unit  109 . The combining unit  109  receives the duty cycle signal  125  and the constant envelope signal  127  and forms a combined signal  129 . The combined signal  129  is provided to the RF input port of the power amplifier  111 . The power amplifier  111  receives the supply  119  and the combined signal  129  and generates a power output signal  131 . 
         [0074]    A transmitter  300 , according to the present invention, specifically operates in the manner illustrated in  FIG. 12 . A signal transformation unit  288  receives a rectangular coordinate signal with an in-phase component  297  and a quadrature-phase component  299 . The signal transformation unit  288  converts the rectangular coordinate signal into a polar coordinate signal and separates the polar coordinate signal into a first signal  301  and a second signal  303 . The first signal  301  is transmitted to the supply port of a power amplifier  295 . The second signal  303  is transmitted to an EER function unit  289 , a DCM ERR function unit  291 , and the DCM function unit  293 . The first signal  301  can be either a modulated first amplitude component of the polar coordinate signals above a predetermined power threshold or a constant level signal. The second signal  303  includes the second amplitude component of the polar coordinate signal below the predetermined threshold and the phase component of the polar coordinate signal. 
         [0075]    At high power ranges, the signal transformation unit  288  transmits the first signal  301  to the supply port of the power amplifier and the EER function unit  289  transmits a constant envelope signal  305  to the RF input port  315  of power amplifier  295 . At high power ranges, the first signal  301  is a modulated first amplitude component. 
         [0076]    At medium power ranges, the signal transformation unit  288  transmits the first signal  301  to the supply port  313  of the power amplifier  295 , and the DCM ERR function unit  291  transmits a combined signal  307  to the RF input port  315  of the power amplifier  295 . At medium power ranges, the first signal  301  is a modulated first amplitude component and the combined signal  307  includes the phase component of the signal  303  and a duty cycle modulated second amplitude component. 
         [0077]    At low power ranges, the signal transformation unit  288  transmits the first signal  301  to the supply port  313  of the power amplifier  295 , and the DCM function unit  293  transmits the combined signal  309  to the RF input port  315  of the power amplifier  295 . The first signal  301  is a constant level signal. The combined signal  309  includes the phase component of the signal  303  and a duty cycle modulated second amplitude component. 
         [0078]    Advantageously, the present invention allows for a greater amplitude dynamic range when compared with a conventional EER or polar approach.  FIG. 13  depicts various supply voltages plotted as power input versus power output. A power amplifier utilizing only polar or pure EER modulation has an operation curve shown by plot  85  and a corresponding amplitude dynamic range shown by plot  91 . The amplitude dynamic range is limited by the dynamic range of the supply port at the power amplifier. A power amplifier utilizing ERR modulation, such as the conventional power amplifier  51  discussed above, uses an operational curve as shown by plot  89  with the corresponding amplitude dynamic range shown by line  93 . Although the amplitude dynamic range is achievable, a feedback loop is required to ensure proper signal combination while transitioning the power amplifier between the compressed region and the linear region. As seen by the curve  89  between the origin and the last line of the supply voltage, the power amplifier operates in the linear region. A power amplifier utilizing DCM ERR mode, such as the power amplifier  177  ( FIG. 7 ) or the power amplifier  295  ( FIG. 12 ) of the present invention, discussed above, uses a supply signal shown by the plot  87  with an amplitude dynamic range shown by line  95 . The lower part of the amplitude signal and subsequently the lower part of the dynamic amplitude range is achieved through duty cycle modulation by a duty cycle modulator. The power amplifier  177  is either in a compressed region or inactive as indicated by the dotted line between the origin and the last line of the supply voltage. Thus, the power amplifier  177  is operating either in the compressed mode, or is inactive. This is highly efficient for power amplifier operation. 
         [0079]    A signal decomposer in a transmitter, such as the signal decomposer  163  in the transmitter  100  ( FIG. 7 ) and/or a signal transformation unit such as the signal transformation unit  288  in the transmitter  300  ( FIG. 12 ), can include a filter to filter the amplitude component of the polar coordinate signal and generate the first amplitude component and the second amplitude component. As seen in  FIG. 14 , curve  135  which is similar to curve  87  ( FIG. 13 ) has a transition region  137 . At transition region  137 , an amplitude component  139  of the polar coordinate signal can be represented as a first amplitude component  143  and a second amplitude component  141 . 
         [0080]    The amplitude component  141  represents the amplitude component  139  below transition point  145 . Amplitude component  143  represents the amplitude component  139  above the transition point  145 . The transition point  145  is a predetermined amplitude threshold. The amplitude component  141  and the amplitude component  143  are curved in the transition area where the amplitude component  139  intersects with the transition point  145 . This allows for smooth transition between the amplitude component  141  and the amplitude component  143 . By having a smooth transition, the bandwidth required for the amplitude component  141  and the amplitude component  143  can be reduced which also reduces the over-sampling rate. 
         [0081]      FIG. 15 , includes various supply voltages plotted as a power input (“Pin”) versus power output (“Pout”) when a power amplifier is operating according to the present invention. With the power amplifier utilizing the EER modulation mode at high power ranges, the supply signal is shown as a curve  151  and the corresponding amplitude dynamic range is shown by line  152 . During high power ranges, the power amplifier of the present invention utilizes a conventional polar operation where high efficiency is achieved by operating the power amplifier in the compressed region. This produces low out-of-band noise, because the duty cycle modulator is inactive. With the duty cycle modulator inactive, there is little to no interference with third party electronic devices which removes the need for using a SAW filter. 
         [0082]    With a power amplifier operating in the DCM ERR mode, at medium power ranges, as in the present invention, the operation curve is shown by curve  153  and the corresponding amplitude dynamic range is shown by a line  159 . In this mode, the transmitter is highly efficient because it is operating either in a compressed region or is inactive. Only low absolute out-of-band noise can occur because the power output of the amplifier is relatively low. 
         [0083]    With a power amplifier operating in DCM mode at low power ranges, as in the present invention, the operation curve is shown by curve  155  and the amplitude dynamic range is shown by line  161 . High efficiency is achieved at low power by deactivating the supply modulator and only utilizing the duty cycle modulator with a constant envelope generator. The duty cycle modulator dither frequency can be further reduced when the power output ranges are low. 
         [0084]      FIG. 16  shows a conventional transmitter  210  at low power ranges. In the conventional transmitter  210  a DC-DC converter  207  receives a battery voltage  219  and a power level  217  and outputs a DC signal  208  to a low drop-out regulator (“LDO”)  209 . A digital-to-analog converter (“DAC”)  211  transmits an amplitude component  215  to the LDO  209  in an amplitude path. The LDO  209  receives the amplitude component  215  and the DC signal  208  and outputs a signal  221  to the supply port of power amplifier  205 . The power amplifier  205  receives a phase component  213  at an RF input port. The power amplifier  205  then utilizes the supply signal  221  and the phase component  213  to generate an output signal  222 . 
         [0085]      FIG. 17  depicts a model of a transmitter  230  in a DCM mode according to the present invention, at low power ranges. A DC-DC converter  225  receives a battery voltage  231  and a power level  229  and outputs a DC signal  226  to the supply port of the power amplifier  223 . The power amplifier  223  also receives a combined signal  228  at the RF input port. The combined signal  228  can include both amplitude and phase components  227 . The amplitude component of the combined signal  228  is duty cycle modulated. The power amplifier  223  generates an output signal  232  from the DC signal  226  and the combined signal  228 . 
         [0086]    The transmitter  230  of the present invention utilizes less power than a conventional transmitter  210 , even if the power amplifier  223  were to operate in its linear region at low power ranges because the amplitude path in the transmitter  230  would be shut down. Furthermore, the signal received at the supply port of the power amplifier  223  is a constant voltage. The constant voltage is directly provided by a highly efficient DC-DC converter  225 . Thus, no LDO is required, eliminating the power loss associated with use of an LDO. 
         [0087]    At medium power ranges, the power amplifier of the present invention operates in a DCM ERR mode. This is more efficient than conventional transmitters using power amplifiers operating in pure EER mode. As seen in a graph of power spectral density (“PSD”) over frequency in  FIG. 18 , a PSD curve  239  of the power amplifier of the present invention exhibits lower PSD distribution over a larger number of frequencies as compared to a PSD curve  237  of the EER power amplifier. The improvement is shown, for example, by an arrow  291  indicating the difference in PSD distributions. 
         [0088]    This lower power usage is also confirmed in a graph of overall magnitude of an output signal of a power amplifier of the present invention at medium power ranges. In  FIG. 19 , the magnitude of the output signal is plotted over time as shown by curve  247 . At points  249 , for example, the power amplifier is operating either in the compressed region or is inactive. At power ranges above a transition point, a predetermined power level, the power amplifier is operating in a DCM ERR mode as indicated by the curve  247 . However, at low power range, below the predetermined power level, the power amplifier is operating in a DCM mode as indicated by the points  249 . 
         [0089]    A comparison of the amplifier operating according to an Rx 45 noise specification shows the great improvement of the present invention. In  FIG. 20  a plot of PSD, curve  255  shows a power amplifier operating in the DCM ERR mode. Curve  257  shows the power amplifier operating in an EER modulation mode.