Abstract:
The present disclosure relates to the efficient transmission of voice and data signals using mobile terminals, and in particular to optimizing the power added efficiency (PAE) of a power amplifier (PA) by controlling the amplifier&#39;s load impedance over a range of radio frequency (RF) output power levels. A power amplifier having a first power level and at least a second power level is provided along with a first impedance matching network section with an output. A second impedance matching network section and at least a third impedance network section in communication with the output are selectably coupled to a load network by switches that are opened and close in response to various power levels of operation for the load switch circuit.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser. No. 61/225,441, filed Jul. 14, 2009, provisional patent application Ser. No. 61/243,387, filed Sep. 17, 2009, and provisional patent application Ser. No. 61/301,789, filed Feb. 5, 2010, the disclosures of which are hereby incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to the efficient transmission of voice and data signals using mobile terminals, and in particular to optimizing the power added efficiency (PAE) of a power amplifier (PA) by controlling the PA&#39;s load impedance over a range of radio frequency (RF) output power levels. 
     BACKGROUND OF THE DISCLOSURE 
     The European Information and Communications Industry Association (EICTA), which was rebranded DIGITALEUROPE in March of 2009 was formed from a consolidation of the European Telecommunications and Professional Electronics Industry (ECTEL) and the European Association of Manufacturers of Business Machines and Information Technology (EUROBIT). This disclosure refers to standards enacted by ECTEL. The ECTEL standards include talk time and standby time for Global System for Mobile Communications (GSM) mobile terminals. GSM mobile terminals operating in the 900 MHz band have defined power levels.  FIG. 1  is a table showing GSM power level (PWL) numbers with corresponding power output levels delivered to a GSM mobile terminal&#39;s antenna. 
     ECTEL talk time is measured at power level  7  (PWL  7 ) which is defined as 29 dBm of output power delivered to a mobile terminal&#39;s antenna. However, due to a typical antenna trace loss of 0.3 dBm, the output power of a PA is preferably increased to 29.3 dBm. In another example, a GSM mobile terminal operating in the extended E-GSM-900 band that spans 880-915 MHz within the European Union (EU) includes a low band (LB) power amplifier (PA) that needs to provide at least 32.5 dBm of output power at the mobile terminal&#39;s antenna. However, the PA is typically designed for 34.2 dBm because of an antenna trace loss and a preferred production margin. Power losses such as the antenna trace loss affect a figure of merit for PAs known as power added efficiency (PAE). A relatively low PAE reduces talk time for a mobile terminal. 
     As such, a goal of an optimal PAE for typical power levels should be focused on PA output circuitry design. 
     The relationship between power added efficiency (PAE), output power (P o ) and maximum output power (P MAX ) can roughly be calculated as: 
     
       
         
           
             
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       FIG. 2  illustrates the relationship between PAE and P o . Typically, a PA design specification requires the PA to be able to deliver P MAX . Yet, the PA is most often operated at a lower power than P MAX . As a result, PAE is reduced to undesirable percentages when the PA is operated at lower levels such as PWL  7 ,  8 , etc. 
     As shown in  FIG. 2 , a PA achieving 45% PAE when operated at 34 dBm will only achieve a PAE of around 26% when the PA is operated at 29 dBm. 
       FIG. 3  is a schematic diagram of a prior art mobile terminal output stage  10  that includes a PA  12  with a load switch  14  for switching in and out impedance elements of an impedance matching network  16  that is coupled to PA  12 . The impedance matching network  16  is selectively in communication with an antenna  18  through a transmit and receive (T/R) switch  20  and a filter  22 . The prior art load switch and impedance matching network of  FIG. 3  is commonly used to improve PAE when the PA  12  is operated at lower power levels than P MAX . A goal of the load switch concept illustrated in  FIG. 3  is to design an output impedance matching network that includes two impedance matching states. A first impedance matching state is for PWL  5  and PWL  6 , in which the PA  12  may provide a maximum power of 34.2 dBm. A second impedance matching state is for PWL  7  as well as lower power levels and provides a lower output power, but yields an improved PAE. 
       FIG. 4  depicts the improvement in PAE by activation of the load switch  14 . When the load switch  14  is deactivated, the PA  12  may deliver power at the PWL  5  and PWL  6  power levels through the impedance matching network  16  at the first impedance matching state. Conversely, when the load switch  16  is activated, the PA  12  may deliver power at the PWL  7  power level and below through the impedance matching network  16  at the second impedance matching state. As shown in  FIG. 4 , activating the load switch  14  improves the PAE of the PA  12  from about 26% to about 40% for PWL  7 . Consequently, the talk time of a mobile terminal incorporating the load switch  14  and impedance matching network  16  is significantly increased for PWL  7  and below. 
     A traditional design of a load switch circuit comes from classical power amplifier textbook theory, which is briefly described below.  FIG. 5  is a schematic diagram of a typical load switch circuit having PA with a transistor  24  and output impedance matching network  26  that was designed in accordance with the classical power amplifier textbook theory. The task of designing the output impedance matching network  26  is primarily to convert an antenna impedance (Z ant ) to a lower impedance level at the collector of the transistor  24 . The lower impedance level (R Opt ) is generally given as: 
     
       
         
           
             
               
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     where P o  is the maximum output power in Watts plus the impedance matching loss, V cc  is the battery supply voltage and V knee  is a transistor parameter for the transistor  24 . Note that the values calculated from the above equation may need to be adjusted for a practical PA, because the above equation assumes a pure sinusoidal collector voltage, which is usually an incorrect assumption for modern PA circuitry. Nevertheless, the equation serves the purpose of showing that the optimum load impedance as seen from the collector is dependent upon the desired output power. Generally, a lower collector load impedance is required for a given higher output power. As such, the design of a load switch circuit may be redefined as designing an impedance matching network that will present a collector of a PA output transistor with a relatively low impedance of around two and one-half Ohms for PWL  5 , and a relatively higher impedance of around seven Ohms to seven and one-half Ohms for PWL  7 . 
     The PAE of a PA typically depends on three criteria.
         The impedance presented to the collector of the PA&#39;s output transistor. This impedance needs to be designed such that the PA can provide a desired output power, but no more than the desired output power.   The minimization of energy losses due to the output impedance matching network.   The harmonic termination seen from the collector of the PA&#39;s output transistor, which is to a large degree associated with the class of the PA (i.e., class AB, F, E, and so on).
 
A well designed load switch circuit with an output impedance matching network ensures that all three criteria are met. Unfortunately, designing a load switch circuit with an output impedance matching network needed to provide a desired output power, but no more than the desired output power while minimizing energy losses due to the output impedance matching network is a particularly difficult challenge.
       

     In  FIG. 6A , a series of load-pull contours depicting power consumption for a typical PA is shown overlaying a Smith Chart. Notice that the load-pull contours depicting power consumption are more or less centered around fifty Ohms, which is at the center of the Smith Chart. 
       FIG. 6B  provides an example in which a PA&#39;s output current is significantly lower in the upper right quadrant of a series of PA output current contours shown overlaying a Smith chart. A load impedance, which in this case is an antenna impedance, is represented by a load impedance arrow that extends from the center of the Smith Chart. The mobile terminal circuit board designer will attempt to rotate the load impedance arrow to an angle that yields minimum PA current draw. The angle of minimum PA current draw is referred to as a sweetspot in RF engineering vernacular. For the purpose of this disclosure, the sweetspot of an impedance match is the load impedance such as an antenna impedance (Z ant ) that is presented to the PA for a given VSWR such that the electrical current draw of the PA is minimized. The location of the sweetspot primarily depends upon an output impedance matching network in communication with the PA. 
     Typically, an antenna designer is not able to design an antenna for a mobile terminal with fifty Ohms of impedance. Instead, the antenna impedance is typically located within a 3:1 Voltage Standing Wave Ratio (VSWR) circle. A mobile terminal circuit board designer typically attempts to rotate the load impedance arrow for the best compromise between power and current consumption for the PA. 
     The design practice of rotating the load impedance arrow to an angle that yields minimum PA current draw plays a significant, but often overlooked role in the load switch circuit. For the load switch circuit to provide an increase in PAE, the sweetspots of PWL  5  and PWL  7  matches are preferably located relatively close to each other.  FIGS. 7A and 7B  illustrate a problem of not having properly aligned sweetspots. Rotating the load impedance arrow for PWL  5  to the upper left quadrant of a series of PA output current contours shown overlaying a Smith chart in  FIG. 7A  results in a poor antenna impedance rotation for PWL  7  having a series of PA output current contours shown overlaying a Smith chart in  FIG. 7B . Consequently, the benefit of the load switch is jeopardized. 
     The requirements for the load switch circuit can be summarized as follows.
         The output impedance matching network must be able to present optimized antenna impedance to the PA&#39;s collector for both power levels PWL  5  and PWL  7 .   The energy loss due to the output impedance matching network must be low for both power levels whether the output impedance matching network is designed for a fifty Ohm antenna load or other antenna impedances located within a VSWR circle. Therefore, it is preferred that the load impedance arrow representing antenna impedance be rotated to the sweetspot for electrical current contours on the Smith Chart.   The harmonics must be properly terminated in power levels PWL  5  and PWL  7 .   The sweetspot must be aligned such that the load impedance arrow may be rotated into the region where the PA has minimum current draw in power levels PWL  5  and PWL  7 .       

       FIG. 8  is a schematic diagram of a typical PA having a transistor  28  and output impedance matching network  30  that was designed in accordance with the classical power amplifier textbook theory. The traditional approach of implementing a load switch is to switch in an extra capacitor in the matching network either at C 1 , C 2 , or C 3  by way of switches S 3 , S 4  and S 5 , respectively. In general, it is most cost efficient to implement just one of the switches S 3 , S 4  and S 5 . Other implementations of load switch circuits have been proposed in the prior art. Some examples include: “Efficiency Enhancement Method for High-Power Amplifiers using a Dynamic Load Adaptation Technique,” by H. T. Jeong et al., Microwave Symposium Digest, 2005 IEEE MTT-S International, pp 2059-2062; “A MEMS Reconfigurable Quad-Band Class-E Power Amplifier for GSM Standard,” by L. Larcher et al., Proceedings of the 22nd IEEE International Conference on Micro Electro Mechanical Systems MEMS 2009, Sorrento, Italy, 25-29 Jan. 2009, pp 864-867; “A Novel Reconfigurable Power Amplifier Structure for Multi-Band and Multi-Mode Portable Wireless Applications using a Reconfigurable Die and a Switchable Output Matching Network,” by C. Zhang and A. E. Fathy, Microwave Symposium Digest, 2009. MTT &#39;09. IEEE MTT-S International, pp 913-916; and “MEMS-Based Reconfigurable Multi-band BiCMOS Power Amplifier,” by A. J. M. de Graauw et al., Bipolar/BiCMOS Circuits and Technology Meeting, 2006, pp 1-4, the disclosures of which are incorporated herein by reference in their entireties. 
     The traditional approach of designing load switch circuits has two primary deficiencies:
         The component that is switched into the output matching network exhibits a poor quality factor (Q-factor) because of the loss coming from the switch. A poor Q-factor may be avoided by using Micro-electromechanical Systems (MEMS) devices. However, MEMS devices are expensive and often require additional circuitry. The poor Q-factor of a component switched into an impedance matching network results in a high energy loss for the impedance matching network, which results in a degraded PAE.   Since the sweetspots of the PWL  5  and PWL  7  match are not well aligned, it is not possible to rotate the load impedance arrow to an optimum angle for both power levels. However, this deficiency can be solved by using more than a single load switch such that multiple components are switched at a time. In general, having multiple load switches in an output impedance matching network is not a desirable solution because any additional switches will increase the energy loss, which reduces PAE. Further still, multiple load switches and associated components add financial cost to manufacturing a mobile terminal circuit board.       

     As a result of these deficiencies, there is a need for a load switch circuit to optimize PAE through aligning the load impedance arrows for the sweetspots of various power levels, while minimizing the energy losses due to the output impedance matching network of a load switch circuit. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure provides a load switch circuit having aligned sweetspots for operation at various power levels. Moreover, switches in the load switch circuit are dual function in that the switches serve as impedance matching network selectors as well as transmit and receive switches. Therefore, no additional energy loss is introduced by the use of the switches. 
     In general, the present disclosure describes a load switch circuit having a power amplifier for amplifying a radio frequency signal to provide an amplified radio frequency signal having a first power level and a second power level. A first impedance matching network section is in electrical communication with the power amplifier to receive the amplified radio frequency signal. A second impedance matching network section is in electrical communication with the first impedance matching network section to receive the amplified radio frequency signal and includes an output for the amplified radio frequency signal. The output of the second impedance matching network section is selectively placed in electrical communication with a load network by way of a first switch during transmission of the amplified radio frequency signal at the first power level. A third impedance matching network section is also in electrical communication with the first impedance matching network section to receive the amplified radio frequency signal. The third impedance matching network section has an output for the amplified radio frequency signal that is selectively placed in electrical communication with the load network by way of a second switch during transmissions of the amplified radio frequency signal at the second power level. 
     A switch control system is coupled to the first switch and the second switch and is adapted to selectively place the second impedance matching network section in electrical communication with the load network during transmission of the amplified radio signal at the first power level by opening the second switch and closing the first switch. The switch control system is also adapted to selectively place the third impedance matching network section in electrical communication with the load network during transmission of the amplified radio signal at the second power level by opening the first switch and closing the second switch. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures 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 table showing power level (PWL) numbers for the GSM 900 MHz band with corresponding power output levels delivered to a GSM mobile terminal&#39;s antenna. 
         FIG. 2  is a graph that illustrates the relationship between PAE and P o . 
         FIG. 3  is a schematic diagram of a prior art mobile terminal output stage. 
         FIG. 4  is a graph that depicts an improvement in PAE by activation of a load switch. 
         FIG. 5  is a schematic diagram of a typical PA that was designed in accordance with the classical power amplifier textbook theory. 
         FIG. 6A  is a Smith Chart with a series of overlaying load-pull contours depicting power consumption for a typical PA. 
         FIG. 6B  is a Smith Chart with a series of overlaying load-pull contours depicting output current contours having a sweetspot denoted by a load impedance arrow. 
         FIG. 7A  is a Smith Chart with a series of overlaying load-pull contours for the output current of a PA operating at PWL  5 . 
         FIG. 7B  is a Smith Chart with a series of overlaying load-pull contours for the output current of a PA operating at PWL  7 . 
         FIG. 8  is a schematic diagram of a typical prior art PA having an output impedance matching network with a plurality of load switches. 
         FIG. 9  is a schematic representation of a mobile terminal configured to an embodiment of the present disclosure. 
         FIG. 10A  is a general schematic representation of a load switch circuit according to the present disclosure. 
         FIG. 10B  is a general schematic representation of the load switch circuit of  FIG. 10A  wherein the switches are depicted as electronic switches. 
         FIG. 11  is a detailed schematic representation of an embodiment of a load switch circuit according to the present disclosure. 
         FIG. 12  is a schematic representing the operation of the load switch circuit at ECTEL power level PWL  7 . 
         FIG. 13  is a schematic representing the operation of the load switch circuit at ECTEL power level PWL  5 . 
         FIG. 14A  depicts load-pull contours for a PA operating at PWL  5  in a module that implements a load switch circuit according to the present disclosure. 
         FIG. 14B  depicts load-pull contours for a PA operating at PWL  7  in a module that implements a load switch circuit according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice embodiments of the disclosure and illustrate the best mode of practicing the principles of the disclosure. Upon reading the following description in light of the accompanying drawing figures, 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. 
     Turning now to  FIG. 9 , a preferred embodiment of the present disclosure is incorporated in a mobile terminal  32 , such as a mobile telephone, a personal digital assistant, or the like. The basic architecture of the mobile terminal  32  and may include a receiver front end  34 , a radio frequency transmitter section  36 , an antenna  38 , a duplexer or switch  40 , a baseband processor  42 , a control system  44 , a frequency synthesizer  46 , and an interface  48 . The receiver front end  36  receives information bearing radio frequency signals from one or more remote transmitters provided by a base station. A low noise amplifier  50  amplifies the signal. A filter circuit  52  minimizes broadband interference in the received signal, while downconversion and digitization circuitry  54  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  34  typically uses one or more mixing frequencies generated by the frequency synthesizer  46 . 
     The baseband processor  42  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  42  is generally implemented in one or more digital signal processors (DSPs). 
     On the transmit side, the baseband processor  42  receives digitized data, which may represent voice, data, or control information, from the control system  44 , which it encodes for transmission. The encoded data is output to the radio frequency transmitter  36 , where it is used by a modulator  56  to modulate a carrier signal that is at a desired transmit frequency. Power amplifier (PA) circuitry  58  amplifies the modulated carrier signal to a level appropriate for transmission from the antenna  38 . 
     The amplified signal is sent to the switch  40  and antenna  38  through a switchable impedance network  60 , which is configured to set the overall load impedance for the PA circuitry  58  to optimize values based on the power level being transmitted. Typically, the switch  40  and antenna  38  provide a relatively constant load impedance, which is combined with the impedance of the switchable impedance network  60  to establish an overall load impedance for the PA circuitry  58 . A load switch control signal  62  is provided by the control system  44  to select an impedance matching network section, which will vary depending on the power level being transmitted. The structure and operation of impedance matching network sections comprising the switchable impedance network  60  is provided in greater detail below. 
     A user may interact with the mobile terminal  32  via the interface  48 , which may include interface circuitry  64  associated with a microphone  66 , a speaker  68 , a keypad  70 , and a display  72 . The interface circuitry  64  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  42 . 
     The microphone  66  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  42 . Audio information encoded in the received signal is recovered by the baseband processor  42 , and converted into an analog signal suitable for driving speaker  68  by the I/O and interface circuitry  64 . The keypad  70  and the display  72  enable the user to interact with the mobile terminal  32 , input numbers to be dialed, address book information, or the like, as well as monitor call progress information. 
       FIG. 10A  is a general schematic representation of a load switch circuit  74  according to the present disclosure. Load switch circuit  74  includes a power amplifier  76  for amplifying a radio frequency signal to provide an amplified radio frequency signal having a first power level and at least a second power level. A first impedance matching network section  78  is in electrical communication with the power amplifier  76  to receive the amplified radio frequency signal. A second impedance matching network section  80  is in electrical communication with the first impedance matching network section  78  to receive the amplified radio frequency signal, wherein the second impedance matching  80  network has an output  82  for the amplified radio frequency signal that is selectively placed in electrical communication with a load network  84  via a switch S 1  during transmission of the amplified radio frequency signal at the first power level. The load network  84  typically includes a harmonic filter  86  and an antenna  88 . 
     A third impedance matching network section  90  is in electrical communication with the first impedance matching network section  78  to receive the amplified radio frequency signal, wherein the third impedance matching network section  90  has an output  92  for the amplified radio frequency signal that is selectively placed in electrical communication with the load network  84  via a switch S 2  during transmissions of the amplified radio frequency signal at the second power level. Additional impedance matching network sections, such as an Nth impedance matching network section  94  is in electrical communication with the first impedance matching network section  78 , wherein the Nth impedance matching network section  94  has an output  96  that is selectively placed in electrical communication with the load network  84  via a switch SN during transmissions of the amplified radio frequency signal at an Nth power level. It is important to note that the individual closure of any one of the switches S 1 , S 2  and SN creates a series path for the amplified radio frequency signal through the first impedance network section  78 , and the corresponding one of the impedance matching network sections  80 ,  90 , or  94 . In this way, the switches S 1 , S 2  and SN not only function as impedance matching network selectors, but also function as transmit and receive switches. Due to their dual function, the switches S 1 , S 2  and SN do not introduce addition energy losses relative to conventional switching circuitry used to switch impedance matching elements in conventional load switch circuits. 
     The control system  44  provides the load switch control signal  62  ( FIG. 9 ) for opening and closing the switches S 1 , S 2 , S 3  and SN. In a receive mode, the control system  44  opens the switches S 1 , S 2 , and SN before closing switch S 3 . While the switch S 3  is closed, RF signals received by antenna  88  are conducted to the receiver front end  34 . 
       FIG. 10B  is a general schematic representation of the load switch circuit of  FIG. 10A  wherein the switches S 1 , S 2 , S 3  and SN are depicted as electronic switches SE 1 , SE 2 , SE 3  and SEN. The electronic switches SE 1 , SE 2 , SE 3  and SEN may be implemented as transistor switches as depicted in  FIG. 10B . In particular, the transistor switches may each be a field effect transistor (FET) or other transistor type that is useable to switch radio frequency signals. The gates of the FET transistors making up switches SE 1 , SE 2 , SE 3  and SEN are each driven by the switch control signal  62  that is provided by the control system  44 . The switch control signal  62  turns the FET transistors either on or off. For example, when the FET making up the switch SE 1  is turned on, the output  82  of the second impedance matching network section  80  is connected to the input of the harmonic filter  86 . When the FET making up the switch SE 1  is turned off, the FET will provide a high impedance or open-circuit condition that disconnects the second impedance matching network section  80  from the input of the harmonic filter  86 . The FETs making up SE 2  and SEN work in a similar fashion. The FET making up switch SE 3  will provide a high impedance or open circuit condition when the switch SE 3  is turned off. In this way, an amplified RF signal meant for transmission from the antenna  88  will be impeded from being received by the receiver front end  34 . However, when the switch SE 3  is turned on a low impedance path for RF signals received by the antenna  88  is provided between the receiver front end  34  and the receiver front end  34 . 
       FIG. 11  is a detailed schematic of an embodiment of a load switch circuit  98  according to the present disclosure. Load switch circuit  98  is useable to increase the PAE of a power amplifier (PA)  100  that is operable at ECTEL power levels PWL  5  and PWL  7 . A first impedance matching network section  102  comprises a traditional L-C-L-C-L circuit with inductive components L 1 , L 2  and L 3 , and capacitive components C 1  and C 2 . A first terminal of L 1  is coupled to an output  104  of the PA  100  in order to receive an amplified radio frequency signal from the PA  100 . A second terminal of L 1  is coupled to a first terminal of L 2  and a first terminal of C 1  at a common node  106 . A second terminal of C 1  is coupled to a ground node  108 . A second terminal of L 2  is coupled to a first terminal of L 3  and a first terminal of C 2  at a common node  110 . A second terminal of C 2  is coupled to the ground node  108 . A second terminal of L 3  is an output node  112  for the first impedance matching network section  102 . 
     A second impedance matching network section  114  has an inductor L 4 , and capacitors C 4  and C 5 . A first terminal of L 4  is coupled to the second terminal of L 3  at the output node  112 . A second terminal L 4  is coupled to a first terminal of C 4  and a first terminal of C 5  at a common node  116 . A second terminal of C 4  is coupled to the ground node  108 . A second terminal of C 5  is an output node  118  for the second impedance matching network section  114 . 
     A third impedance network section  120  has capacitors C 3  and C 6 , and an inductor L 5 . A first terminal of C 3  is coupled to the second terminal of L 3 , and the first terminal of L 4  at the output node  112 . A second terminal of C 3  is coupled to a first terminal of C 6  and a first terminal of L 5  at a common node  122 . A second terminal of C 6  is coupled to the ground node  108 . A second terminal of L 5  is an output node  124  for the third impedance network section  120 . 
     An load network  126  is comprised of a harmonic filter  128  and an antenna  130 . An output terminal of the harmonic filter  128  is coupled to an input of the antenna  130 . A switch S 1  for selectively coupling the second impedance matching network section  114  has a first terminal that is coupled to the output node  118 . A second terminal of switch S 1  is coupled to an input terminal of the harmonic filter  128  at a common node  132 . A switch S 2  for selectively coupling the third impedance matching network section  120  has a first terminal that is coupled to the output node  124 . A second terminal of switch S 2  is coupled to the input terminal of the harmonic filter  128  at the common node  132 . As shown in  FIG. 11 , the switches S 1  and S 2  are opened such that the second impedance matching network section  114  and the third impedance network section  120  are decoupled from the load network  126 . In this way, radio frequency signals impinging on antenna  130  may be received by the receiver front end  34  ( FIGS. 9 ,  10 A and  10 B).  FIG. 12  is a schematic representing the operation of the load switch circuit  98  at ECTEL power level PWL  7 . While operating at the PWL  7  power level, the switch S 1  is closed and the switch S 2  is left open. As a result of the switch S 2  being open, the inductor L 5  does not present an impedance matching effect. Thus, L 5  is not shown as part of an equivalent circuit section  134 . However, as shown in the equivalent circuit section  134 , the capacitors C 3  and C 5  are placed in series. 
     Capacitors C 3  and C 6  function as a total capacitive reactance incorporated in the matching network.  FIG. 13  is a schematic representing the operation of the load switch circuit  98  at ECTEL power level PWL  5 . During operation of load switch circuit  98  at the PWL  5  power level, the switch S 2  is closed and the switch S 1  is left open. As a result of the switch S 1  being open, the capacitor C 5  does not present an impedance matching effect. Thus, C 5  is not shown as part of an equivalent circuit section  136 , which places inductor L 4  in series with capacitor C 4 . The inductor L 4  and the capacitor C 4  may be selected such that a resonant frequency for the equivalent circuit section  136  is above the carrier frequency of a radio frequency being amplified by PA  100 . In this way, the equivalent circuit section  136  behaves as a capacitive reactance at the carrier frequency of radio frequency being passed to the load network  126 . 
     Turning back to  FIG. 11 , it is preferred that component values for the inductors L 1 -L 5 , and C 1 -C 6  be selected such that a collector impedance of PA  100  in the approximate range of 7-7.5 Ohms is matched by the first and second impedance matching networks sections  102  and  114  for PWL  7  operation. Likewise, it is preferred that component values for the inductors L 1 -L 5 , and C 1 -C 6  be selected such that a collector impedance of approximately 2.5 Ohms is matched by the first and third impedance network sections  102  and  120  for PWL  5  operation. Additionally, a sweetspot for operating the PA  100  at the PWL  5  power level may be rotated on a Smith Chart to an optimum angle via C 5  and L 5  without affecting an optimum impedance match for the PWL  7  power level. Therefore, an advantage of the load switch circuit  98  is that the alignment of the sweetspots for operation at both the PWL  5  and PWL  7  power levels is realizable. 
       FIGS. 14A and 14B  depict load-pull contours for a PA in a module that implements the load switch circuit  98  ( FIGS. 12 ,  13  and  14 ). The load-pull contours of  FIG. 14A  are for PA  100  operated at the PWL  5  power level. The load-pull contours of  FIG. 14B  are for PA  100  operated at the PWL  7  power level. Notice that the sweetspots for both the PWL  5  and PWL  7  power levels are in the upper right quadrants of a series of PA output current contours shown overlaying a Smith chart for both  FIGS. 14A and 14B . A load impedance for load network  84  is represented by load impedance arrows that extend from the centers of the Smith Charts. As a result, of the method and system of the present disclosure, the load impedance arrows are rotated and aligned into the regions where the PA  100  has minimum current draw in both power levels PWL  5  and PWL  7 . 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. For example, the electronic switches SE 1 , SE 2 , SE 3 , and SEN in  FIG. 10B  may also be implemented using a diode with a diode switching network. The diode may be of the positive-intrinsic-negative (PIN) diode type or other type that is useable to switch radio frequency signals. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.