Abstract:
A power management system for a multi-carriers transmitter is disclosed. The power management system includes a first switcher having a control input and a power output, and a second switcher having a control input and a power output. Also included is a mode switch having a mode control input, wherein the mode switch is adapted to selectively couple the power output of the first switcher to the power output of the second switcher in response to a mode control signal received by the mode control input. Further included is a control system adapted to generate the mode control signal. The control system is coupled to the mode control input of the mode switch.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application Ser. No. 61/431,264, filed Jan. 10, 2011, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a power management system for a communications system. 
     BACKGROUND 
     Future cellular equipment types such as handsets, notebook computers, and tablet computers will require simultaneous transmission of signals at two different frequencies, referred to as multi-carriers. These multi-carriers require a wide bandwidth for each carrier. Each of the multi-carriers typically require up to 20 MHz of bandwidth. Long term evolution (LTE-Advanced) as currently defined allows for the possibility of multi-carrier transmission in a single band or in different bands. As a result, LTE-Advanced customers will be afforded relatively large data rates. 
       FIG. 1  is a spectrum diagram that demonstrates a peak data rate increase via a bandwidth increase. In this case, five multi-carriers each having a 20 MHz bandwidth can yield up to 100 MHz of total bandwidth for a given user. 
       FIG. 2  is a spectrum diagram depicting intra band component carriers (CC) that are contiguous within a band A. For this case, the multi-carriers are aggregated in the spectrum allocated to band A. Therefore, a typical power management system having a modern fast power converter referred to herein as a switcher can be used to drive a single power amplifier (PA) for transmitting multi-carriers that are contiguous within the band A. However, bandwidth requirements for the typical power management system can be exceeded even while using intra band component carriers (CC) that are contiguous within a single band. 
       FIG. 3  is a spectrum diagram depicting intra band CC that are non-contiguous within the band A. In this case, the problem of increased bandwidth requirement for a power management system is made even worse since the spectrum is not used in a contiguous manner. 
       FIG. 4  is a spectrum diagram depicting inter band CC within the band A and within a band B. The bandwidth requirement for a power management system is even greater in this case since multi-carriers are spread among the band A and the band B. 
       FIG. 5  depicts a related art power management system  10  that drives a single power amplifier (PA)  12  for multi-carriers. The power management system  10  includes a full size switcher  14  that converts power from an energy source such as a battery (not shown) to power levels that are appropriate for the single PA  12 . 
     An output filter  16  that is coupled to an output node  18  of the second switching power supply is continuously coupled between the full size switcher  14  and a power supply node  20  of the single PA  12 . The output filter  16  is an LC type filter for reducing output ripple voltage that is a component of a dynamic voltage output from the full size switcher  14 . The output filter  16  includes an inductor LLINEAR coupled between the output terminal  18  and the power supply node  20  of the single PA  12 . A capacitor CLINEAR is coupled between the inductor LLINEAR and a fixed voltage node such as ground GND. Typically, the inductor LLINEAR has an inductance value of a few nH, while the CLINEAR capacitor has a capacitance value of a few nF. For example, the inductor LLINEAR has an inductance value that ranges from about 1 nH to 10 nH, and the first capacitor CLINEAR has a capacitance value that ranges from about 1 nF to 10 nF. 
     An operational amplifier (OPAMP)  22  drives the full size switcher in response to an analog control signal VRAMP coupled to a first OPAMP input  24 . An output  26  of the OPAMP  22  is coupled to a control input  28  of the full size switcher  14 . Alternating current AC components are passed from the output  26  of the OPAMP  22  through an output capacitor COUT that is coupled between the output  26  and the power supply node  20 . A sample of a common collector voltage (VCC) pseudo envelope following (PEF) signal is coupled from the power supply node  20  to a second OPAMP input  30 . An enable signal EN is usable to enable and disable the single PA  12 . 
       FIG. 6  is a spectrum diagram that depicts a VCC bandwidth (BW) of the full size switcher  14  for dual carriers that provide modulation for the single PA  12 . In particular, the modulation bandwidth of the full size switcher  14  is a function of an offset frequency Df between a carrier # 1  and a carrier # 2 . Therefore, the higher the offset frequency Df between the carrier # 1  and the carrier # 2 , the higher the modulation bandwidth must be. At some point, the offset frequency Df is large enough that related art approaches for modulating the VCC PEF via the full size switcher  14  are no longer practical. Moreover, even if the offset frequency Df is equal to zero between two adjacent carriers having a 20 MHz bandwidth each, a resulting 50 MHz VCC BW is too large for efficient modulation of the VCC PEF via the full size switcher  14 . 
     What is needed is a power management system that meets the VCC BW requirements for a multi-carriers transmitter that uses envelope tracking or pseudo envelope following for intra band component carriers (CC) that are contiguous or non-contiguous within the band A and for inter band CC within the band A and within the band B. In particular, there is a need for a power management system that includes a switcher type power supply that extends the use of envelope tracking or pseudo envelope following for a modulation bandwidth greater than 20 MHz such as 2×20 MHz required for high data rate applications like those allowed with LTE-Advanced. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a power management system for a multi-carriers transmitter that includes a switcher type power supply that extends the use of envelope tracking or pseudo envelope following for a modulation bandwidth greater than 20 MHz such as 2×20 MHz required for high data rate applications like those allowed with LTE-Advanced. In particular, the power management system includes a first switcher having a control input and a power output, and a second switcher having a control input and a power output. Also included is a mode switch having a mode control input, wherein the mode switch is adapted to selectively couple the power output of the first switcher to the power output of the second switcher in response to a mode control signal received by the mode control input. Further included is a control system adapted to generate the mode control signal. The control system is coupled to the mode control input of the mode switch. 
     In one embodiment, the power management system further includes an analog multiplexer having a control input coupled to the control system, a first analog input, a second analog input, a first analog output, and a second analog output. Also further included is a first operational amplifier (OPAMP) having a first input for receiving a first analog control signal, a second input communicatively coupled to the power output of the first switcher, and an output coupled to the first analog input to provide feedback to the control input of the first switcher and/or to provide feedback to the control input of the second switcher through the analog multiplexer in response to the mode control signal generated by the control system. The feedback provided by the first OPAMP corresponds to an output voltage provided at the power output of the first switcher. 
     Also further included is a second OPAMP having a first input for receiving a second analog control signal, a second input communicatively coupled to the power output of the second switcher, and an output coupled to the second analog input to provide feedback to the control input of the first switcher and/or to provide feedback to the control input of the second switcher through the analog multiplexer in response to the mode control signal generated by the control system. The feedback provided by the second OPAMP corresponds to an output voltage provided at the power output of the second switcher. 
     Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure. 
         FIG. 1  is a spectrum diagram that demonstrates a peak data rate increase via a bandwidth increase. 
         FIG. 2  is a spectrum diagram depicting intra band component carriers (CC) that are contiguous within a band A. 
         FIG. 3  is a spectrum diagram depicting intra band CC that are non-contiguous within the band A. 
         FIG. 4  is a spectrum diagram depicting inter band CC within the band A and within a band B. 
         FIG. 5  is a schematic diagram of a related art single power amplifier (PA) power management system for multi-carriers. 
         FIG. 6  is a spectrum diagram for a common collector (Vcc) bandwidth (BW) for a power supply of the related art single transmitter PA power management system for multi-carriers shown in  FIG. 5 . 
         FIG. 7  is a schematic diagram of a dual transmitter PA power management system for multi-carriers that in accordance with the present disclosure is shown operating in a first mode. 
         FIG. 8  is a schematic diagram of the dual transmitter PA power management system for multi-carriers that in accordance with the present disclosure is shown operating in a second mode. 
         FIG. 9  is a schematic diagram of the dual transmitter PA power management system for multi-carriers that in accordance with the present disclosure is shown operating in a third mode. 
         FIG. 10  is a schematic diagram of the dual transmitter PA power management system for multi-carriers that in accordance with the present disclosure is shown operating in a fourth mode. 
         FIG. 11  is a schematic diagram of the dual transmitter PA power management system for multi-carriers that in accordance with the present disclosure is shown operating in a fifth mode. 
         FIG. 12  is a block diagram of a mobile terminal that incorporates the dual transmitter PA power management system for multi-carriers of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the disclosure and illustrate the best mode of practicing the disclosure. Upon reading the following description in light of the accompanying drawings, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
       FIG. 7  depicts a multi-band power management system  30  for multi-carriers that is in accordance with the present disclosure. The multi-band power management system  30  includes a full size power converter  32  that converts power from an energy source such as a battery (not shown) to power levels that are appropriate for a first PA  34  and a second PA  36 . The full size power converter  32  includes a first ½ size switcher  38  and a second ½ size switcher  40 . The first ½ size switcher  38  and the second ½ size switcher  40  can each be a buck, buck/boost, or a buck/boost with charge pump type switcher. Moreover, the first ½ size switcher  38  is coupled to an output filter made up of a first inductor LLINEAR 1  and a first capacitor CLINEAR  1 . Similarly, the second ½ size switcher  40  is coupled to an output filter made up of a second inductor LLINEAR 2  and a second capacitor CLINEAR 2 . 
     A first OPAMP  42  and a second OPAMP  44  control the first ½ size switcher  38  and the second ½ size switcher  40 . A control system  46  drives an analog multiplexer  48  with three mode bits A, B, and C to control the modes of the multi-band power management system  30  and a mode switch  50 . Preferably, the mode switch  50  is a field effect transistor (FET) with a gate, source and drain. Other switches such as micro-electromechanical mechanical systems (MEMS) switches may also be used for the mode switch  50 . Table 1 below lists the modes of the multi-band power management system  30 . 
     
       
         
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 MODE 
                 MODE 
                 MODE 
                   
                   
               
               
                 MODE 
                 BIT A 
                 BIT B 
                 BIT C 
                 PA 1 
                 PA2 
               
               
                   
               
             
             
               
                 0 
                 0 
                 0 
                 0 
                 ON, ½ POWER 
                 ON, ½ POWER 
               
               
                 1 
                 0 
                 0 
                 1 
                 ON, FULL PWR 
                 OFF 
               
               
                 2 
                 0 
                 1 
                 0 
                 ON, ½ POWER 
                 OFF 
               
               
                 3 
                 0 
                 1 
                 1 
                 OFF 
                 ON FULL PWR 
               
               
                 4 
                 1 
                 0 
                 0 
                 OFF 
                 ON, ½ POWER 
               
               
                   
               
             
          
         
       
     
     As shown in  FIG. 7  and according to Table 1, in a first mode (MODE 0), the first PA  34  and second PA  36  are both enabled via an enable signal EN 1  and an enable signal EN 2 . Mode 0 is useful for supplying power such that dual carriers can be transmitted simultaneously using the first PA  34  to amplify a first carrier and the second PA  36  to amplify a second carrier. The control system  46  commands the analog multiplexer  48  via the control bits A, B, and C to route feedback from the first OPAMP  42  to the first ½ size switcher  38 , and to route feedback from the second OPAMP  44  to the second ½ size switcher  40 . The control system also commands the mode switch  50  open. As a result, the first PA  34  is supplied with half power (−3 dB) by the first ½ size switcher  38  and the second PA  36  is supplied with half power by the second ½ size switcher  40 . 
     As shown in  FIG. 8  and according to Table 1, in a second mode (MODE 1), the second PA  36  is not enabled and is off as indicated by dashed lines. As a result, MODE 1 is a single carrier transmission mode. The second PA  36  is disabled via the enable signal EN 2 . The second OPAMP  44  is also temporarily disabled so that it does not draw power. However, the first ½ size switcher  38  and the second ½ size switcher  40  are both on. The control system  46  commands the analog multiplexer  48  to route feedback from the first OPAMP  42  to both the first ½ size switcher  38  and the second ½ size switcher  40 . The control system  46  also commands the mode switch  50  closed. As a result, the first PA  34  is supplied with full power while the second PA  36  is off. During MODE 1, the efficiency of the multi-band power management system  30  is slightly negatively impacted due to thermal losses that occur in the mode switch  50 . However, it is possible to provide an extra switcher state during the modulation envelope of the VCC PEF in which the mode switch  50  is opened for a relatively short period of time. As a result, a required modulated current is allowed to flow briefly from the first ½ size switcher  38  only. In this way, any reduction in efficiency caused by the mode switch  50  is minimized. However, an engineering tradeoff pertaining to an efficiency cost of charging the gate and the drain and source of the mode switch  50  during each closure of the mode switch  50  should be considered. 
     As shown in  FIG. 9  and according to Table 1, in a third mode (MODE 2), the second PA  36  and the second OPAMP  44  remain off. Moreover, in MODE 2, the second ½ size switcher  40  is off. The control system  46  commands the analog multiplexer  48  to route feedback only from the first OPAMP  42  to the first ½ size switcher  38 . The control system  46  also commands the mode switch  50  open. As a result, the first PA  34  is supplied with half power while the second PA  36  is off. In a practical sense, the MODE 2 is a quasi improved segmentation mode since the second ½ size switcher  40  is off and does not load a first output node LX 1  with relatively large off parasitic capacitances. This is due to a second output node LX 2  having an off parasitic capacitance that is in series with the off parasitic capacitance of the mode switch  50 . 
     As shown in  FIG. 10  and according to Table 1, in a fourth mode (MODE 3), the first PA  34  is not enabled and is off. The first OPAMP  42  is also disabled so that it does not draw power. However, both the first ½ size switcher  38  and the second ½ size switcher  40  are both on, and the control system  46  commands the analog multiplexer  48  to route feedback from the second OPAMP  44  to both the first ½ size switcher  38  and the second ½ size switcher  40 . The control system  46  also commands the mode switch  50  closed. As a result, the second PA  36  is supplied with full power while the first PA  34  is off. 
     As shown in  FIG. 11  and according to Table 1, in a fifth mode (MODE 4), the first PA  34  and the first OPAMP  42  remain off. Moreover, in MODE 4, the first ½ size switcher  38  is off and the control system  46  commands the analog multiplexer  48  to route feedback from the second OPAMP  44  to the second ½ size switcher  40  only. The control system  46  also commands the mode switch  50  open. As a result, the second PA  36  is supplied with half power while the first PA  34  is off. 
     Turning now to  FIG. 12 , the multi-band power management system  30  is incorporated in a mobile terminal  52 , such as a cellular handset, a personal digital assistant (PDA), or the like. The basic architecture of the mobile terminal  52  may include a receiver front end  54 , an RF transmitter section  56 , an antenna  58 , a baseband processor  60 , the control system  46 , a frequency synthesizer  62 , and an interface  64 . The receiver front end  54  receives information bearing RF signals from one or more remote transmitters provided by a base station. A low noise amplifier (LNA)  66  amplifies the signal. A filter circuit  68  minimizes broadband interference in the received signal, while downconversion and digitization circuitry  70  downconverts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. The receiver front end  54  typically uses one or more mixing frequencies generated by the frequency synthesizer  62 . 
     The baseband processor  60  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  60  is generally implemented in one or more digital signal processors (DSPs). 
     On the transmit side, the baseband processor  60  receives digitized data, which may represent voice, data, or control information from the control system  46  which it encodes for transmission. The encoded data is output to the RF transmitter section  56 , where it is used by a modulator  72  to modulate a carrier signal that is at a desired transmit frequency. The first PA  34  and the second PA  36  amplify multi-band modulated carrier signals to levels that are appropriate for transmission from the antenna  58 . An RF switch  74  responsive to an RF SWITCH CONTROL signal generated by the control system  46  selectively transfers transmit signals to and from the antenna  58 . 
     A user may interact with the mobile terminal  52  via the interface  64 , which may include interface circuitry  76  associated with a microphone  78 , a speaker  80 , a keypad  82 , and a display  84 . The interface circuitry  76  typically includes analog-to-digital converters, digital-to-analog converters, amplifiers, and the like. Additionally, it may include a voice encoder/decoder, in which case it may communicate directly with the baseband processor  60 . 
     The microphone  78  will typically convert audio input, such as the user&#39;s voice, into an electrical signal, which is then digitized and passed directly or indirectly to the baseband processor  60 . Audio information encoded in the received signal is recovered by the baseband processor  60  and converted into an analog signal suitable for driving the speaker  80  by the interface circuitry  76 . The keypad  82  and the display  84  enable the user to interact with the mobile terminal  52  by inputting numbers to be dialed, address book information, or the like, as well as monitoring call progress information. 
     Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.