Abstract:
One embodiment is a method for adjusting impedance of a power amplifier system comprising combining an output of a first power amplifier with an output of a second power amplifier via a coupler that couples an output connection of the first power amplifier with an output connection of the second power amplifier, wherein a prematching impedance network coupled to the second power amplifier adjusts a system impedance to a first value when the second power amplifier is not actuated, and wherein the prematching impedance network adjusts the system impedance to a second value when the second power amplifier is actuated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of copending U.S. utility application entitled, “DYNAMIC BIAS FOR A POWER AMPLIFIER,” having Ser. No. 09/818,285, filed Mar. 27, 2001, now issued as U.S. Pat. No. 6,639,465 B2, granted on Oct. 28, 2003, which is entirely incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention is generally related to power amplifiers and, more particularly, is related to adjusting impedance of a power amplifier system. 
     2. Related Art 
     With the increasing power efficiency demands from users of mobile communication devices, such as cell phones and the like, mobile communication device manufacturers are continually searching for ways to improve power consumption efficiency within the mobile communication device, thereby increasing the useful operating period that a mobile communication device gets from a single charge of the power source, such as, but not limited to, a battery or fuel cell. During a normal voice conversation by a person using the mobile communication device, the transmitting function consumes a very large amount of available power. As such, energy conservation in transmitters is of paramount importance. 
     Conventional mobile communication devices typically consume large amounts of power as a voice signal is converted into a communication signal and amplified to a power level necessary for transmission from the mobile communication device to a base station. Within the communication industry, significant efforts continue to attempt to minimize power consumption. Therefore, there is an ongoing need to continue to reduce energy consumption in mobile communication devices. 
     SUMMARY 
     The invention provides for adjusting impedance of a power amplifier system. One embodiment is a method for adjusting impedance of a power amplifier system comprising combining an output of a first power amplifier with an output of a second power amplifier via a coupler that couples an output connection of the first power amplifier with an output connection of the second power amplifier, wherein a prematching impedance network coupled to the second power amplifier adjusts a system impedance to a first value when the second power amplifier is not actuated, and wherein the prematching impedance network adjusts the system impedance to a second value when the second power amplifier is actuated. 
     In another embodiment, a system that adjusts impedance of a power amplifier system comprises a first power amplifier amplifying a communication signal; a bias controller for outputting a control signal, the bias controller coupled to a node in a communication device such that the communication signal is sensed; a second power amplifier responsive to the control signal, such that the bias controller activates the second power amplifier when an amplitude of the communication signal is at least equal to a predetermined amplitude, and such that the bias controller deactivates the second power amplifier when the amplitude of the communication signal is less than the predetermined amplitude; and a prematching impedance network coupled to at least the second power amplifier such that when the bias controller activates the second power amplifier the prematching impedance network adjusts a system impedance to a first value when the first power amplifier is activated, and such that when the bias controller deactivates the second power amplifier the prematching impedance network adjusts the system impedance to a second value when the first power amplifier and the second power amplifier are activated. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
     FIG. 1 is a simplified block diagram of a mobile communication device communicating with a base station. 
     FIG. 2 is a block diagram illustrating selected transmitter components of the mobile communication device of FIG.  1 . 
     FIG. 3 is a block diagram of the dynamic bias controller residing in the mobile communication device of FIG.  1 . 
     FIG. 4 is a block diagram showing components residing in an embodiment of the dynamic bias controller of FIG.  3 . 
     FIG. 5 is a block diagram showing selected components of an exemplary embodiment of the dynamic bias controller of FIG.  4 . 
     FIG. 6 is a graph of the output power of the power amplifiers of FIG. 3 when controlled by the dynamic bias controller of FIGS. 3 and 4. 
     FIG. 7 is a block diagram of an embodiment of the dynamic bias controller having alternative configurations of the rectifying circuit and reference voltage generator. 
     FIG. 8 is a block diagram of an embodiment of a dynamic bias controller controlling a plurality of second power amplifiers in a multiple stage power amplifier. 
     FIG. 9 is a block diagram of an embodiment of a dynamic bias controller controlling a plurality of power amplifiers residing in a single-stage, multiple power amplifier unit. 
     FIG. 10 is a block diagram of an embodiment of the dynamic bias controller controlling a second stage amplifier and a prematching impedance network. 
     FIG. 11 is a block diagram of an embodiment of the dynamic bias controller comprising a prematching impedance network at the input of the first and second amplifiers. 
     FIG. 12 is a block diagram of an embodiment of the dynamic bias controller comprising a prematching impedance network at the input of the first and second amplifiers and at the output of the second amplifier. 
     FIG. 13 is a block diagram of an embodiment of the dynamic bias controller comprising a prematching impedance network at the input and/or at the output of a third amplifier. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a simplified block diagram of a mobile communication device  100  communicating with a base station  102 . Mobile communication device  100  typically has a microphone  104 , a speaker  106 , a transmit/receive unit  108  and an antenna  110 . To initiate a voice conversation, a user actuates keys  112  on a keypad to transmit a destination code, such as a telephone number, to the transmit/receive unit  108 . The user&#39;s voice is transformed into a communication signal by the transmit/receive unit  108  and transmitted to power amplifier  116  via connection  118 . Power amplifier  116 , using energy from power source  120 , amplifies the communication signal and injects the communication signal onto antenna  110  via connection  122 . The amplified communication signal  124  is then transmitted to base station antenna  126 , typically set up on a tower  128  or other similarly situated high point. Non-limiting examples of power source  120  include conventional batteries, fuel cells and solar energy panels. The received communication signal  126  then travels to the base station receiver/transmitter  130  via connection  132 . Once the base station  102  has established connectivity to the destination location (not shown), as defined by the telephone number, a person using mobile communication device  100  carries on a voice telephone conversation with another person at the destination location. 
     FIG. 2 is a block diagram illustrating additional selected transmitter components of the mobile communication device  100 . The transmit/receive unit  202 , in this simplified illustrative example, has at least a processor  204 , a transmit unit  206  and a power amplifier bias controller  208 . Single-stage power amplifier unit  210  employs first stage  212  having two power amplifiers  214  and  216  that amplifies communication signals received from transmit unit  206  via connection  218  (see also FIG.  1 ). The transmit/receive unit  202  and the power amplifier  210  are well known components of a conventional mobile communication device  100 . Detailed operation of the individual components are not described in detail other than to the extent necessary to understand the operation and functioning of these components with respect to the invention. One skilled in the art will realize that the mobile communication device  100  or other similar mobile communicators may have the components shown in FIG. 2 connected in a different order and manner than shown in FIG. 2, or may not include all of the components shown in FIG. 2, or may include additional components connected in some manner with the components shown in FIG.  2 . Any such variations in a mobile communication device  100  or a similar mobile communication device are intended to be within the scope of this disclosure. 
     The single-stage power amplifier unit  210  as shown in FIG. 2 is a simplified illustration of a power amplifier. In one embodiment, power amplifier  210  employs a first power amplifier  214  and a second power amplifier  216 . An input matching impedance and coupler  220  is disposed between the input to the power amplifier  210  (at connection  218 ) and the power amplifiers  214  and  216 . An output matching impedance and coupler  222  is disposed between the power amplifiers  214  and  216 . A communication signal is received by power amplifier  210  from the transmit unit  206  via connection  218 . The communication signal travels through the input matching impedance and coupler  220  to the power amplifiers  214  and  216  via connections  224  and  226 , respectively. After amplification by the power amplifiers  214  and  216 , the communication signal is transmitted to the output matching impedance and coupler  222 , via connections  228  and  230 , respectively. The amplified communication signal is transmitted from the output matching impedance and coupler  222 , via connection  122 , to antenna  110 . Typically, there may be other components between antenna  110  and output matching impedance  222 , but such components are not described here for convenience and because such components are not relevant to the explanation of the operation and functionality of the single-stage power amplifier unit  210  and its components. The degree of amplification of the communication signal by the first power amplifier  214  and the second power amplifier  216  is determined by processor  204  and controlled by the power amplifier bias controller  208  residing in the transmit/receive unit  202 . 
     Processor  204  communicates with the transmit unit  206 , via connection  231 , to specify various parameters associated with the converted output communication signal. For example, the processor  204  may specify the transmission frequencies to be used by the transmit unit  206  when a voice signal is converted to a communication signal suitable for transmission. Processor  204  also controls the amplification levels of the power amplifiers  214  and  216  by providing instructions to the power amplifier bias controller  208 , via connection  232 . The power amplifier bias controller  208  controls the bias of the first power amplifier  214 , via connection  234 , thereby controlling the amount of signal amplification by the first power amplifier  214 . 
     For illustrative purposes, FIG. 2 shows the bias of the second power amplifier  216  controlled by power amplifier bias controller  208 , via connection  236 . This configuration corresponds to a typical conventional system in that the power amplifier bias controller  208  controls the amount of signal amplification by the second power amplifier  216 . 
     FIG. 3 is a block diagram of the dynamic bias controller  302  residing in the mobile communication device  300 . The dynamic bias controller  302  controls the bias applied to the second stage power amplifier  216 , via connection  304 . The dynamic bias controller  302  detects the RF signal on connection  218 , via connection  306 , and activates the second stage power amplifier  216  when the amplitude of the RF signal is such that both the first stage power amplifier  214  and the second stage power amplifier  216  are to be used by the single-stage power amplifier unit  308  to generate the amplified communication signal. Alternatively, dynamic bias controller  302  may detect the RF signal on any other suitable connection (not shown) having a signal having a voltage that is spectrally related to the signal on connection  218 . 
     FIG. 4 is a block diagram showing components residing in an embodiment of the dynamic bias controller  302 . These components include at least attenuator  402 , DC stop  406 , rectifying circuit  408 , low pass filter  410 , switch  412 , reference voltage generator  414  and emitter follower transistor  416 . Dynamic bias controller  302 , via connection  306 , detects the communication signal. Attenuator  402  attenuates the detected communication signal such that portions of the communication signal that exceed a predefined threshold are output by attenuator  402 , via connection  418 . Thus, any portion of the communication signal that is output over connection  418  corresponds to an operating condition where the second stage power amplifier  216  (FIG. 3) should be amplifying the communication signal. Attenuator  402  may be implemented using well known components commonly employed in attenuator and thresholding systems. Thus, a detailed description of the individual components residing in attenuator  402  is not provided since such a description is not necessary to understand the operation and functioning of the dynamic bias controller  302 . One skilled in the art will realize that attenuator  402  may be implemented by a variety of means such that portions of the communication signal that have an amplitude that exceed the predefined threshold is output by the attenuator  402 . Any such embodiments of attenuator  402  utilized in a dynamic bias controller  302  are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     The output of attenuator  402  is coupled to the DC stop  406  via connection  418 . DC stop  406  prevents any direct current (DC) generated within the dynamic bias controller  302  from flowing out of the dynamic bias controller  302  via connection  306 . Such DC currents, if allowed to flow out of the dynamic bias controller  302  over connection  306 , might undesirably interfere with the communication signal being detected by the single-stage power amplifier unit  308  (FIG.  3 ). Since DC stop  406  may be implemented using well known components, such as a capacitor or any other device that is designed to stop the flow of DC current, a detailed description of the individual components residing in DC stop  406  is not provided. All such embodiments of DC stop  406  utilized in a dynamic bias controller  302  are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     Rectifying circuit  408  detects portions of the communication signal that exceeds the predefined threshold. Rectifying circuit  408  rectifies the portions of the communication signal received, and outputs the rectified portions of the communication signal to low pass filter  410 , via connection  422 . Low pass filter  410  filters out any fundamental and harmonic frequency components, such as, but not limited to, alternating current (AC) components, of the detected portions of the communication signal received over connection  422  and outputs the base band portion of the communication signals to switch  412 , via connection  430 . Switch  412 , via connection  432 , controls emitter follower  416 . If base band portions of the communication signal that exceed the predefined threshold are output by low pass filter  410  onto connection  430 , switch  412  activates emitter follower transistor  416 , in a manner described below, such that the second stage power amplifier  216  (FIG. 3) is conducting. If low pass filter  410  does not output any base band signal over connection  430  (the amplitude of the detected communication signal on connection  306  is below the threshold of attenuator  402 ), then switch  412  deactivates emitter follower transistor  416  such that the second stage power amplifier  216  is not conducting. Reference voltage generator  414 , via connection  434  provides an appropriate predefined voltage reference such that switch  412  can control emitter follower transistor  416 . 
     FIG. 5 is a block diagram showing selected components of an exemplary embodiment of the dynamic bias controller  302  (FIGS.  3  and  4 ). One skilled in the art will appreciate that the illustrated components as shown in FIG. 5 may have the elements connected in a different order and manner than shown in FIG. 5, or may not include all of the elements shown in the components of FIG. 5, or may include additional elements within the components connected in some alternative manner. Any such variations in the elements of the components residing in a dynamic bias controller  302  that have the same operation and functionality of the illustrative components shown in FIG. 5 are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     Rectifying circuit  408  of FIG. 5 includes a reference resistor (RREF)  502 , a first transistor (Q 1 )  504 , a second transistor (Q 2 )  506  and a resistor connected to ground (RM)  508 . RREF  502  is shown coupled to a reference voltage (VREF) such that a reference current (IREF) is provided to transistors Q 1   504  and Q 2   506  as shown. Transistor Q 2   506  is coupled to Vcc, via connection  510 , as illustrated. For convenience of illustration, Vcc is shown to be available from a bus  512  that is easily accessible by other components of the dynamic bias controller  302  and other components (not shown) residing in the mobile communication device  300  (FIG.  3 ). As portions of the communication signal that have a magnitude exceeding the predefined threshold are received by the rectifying circuit  408  on connection  418 , are rectified and then passed to the low pass filter  410  over connection  422 . 
     Low pass filter  410  includes a filtering resistor (RF)  514  and a filtering capacitor (CF)  516 . The rectified portions of the communication signal exceeding the threshold are attenuated by RF  514 . Then, at node  518 , the AC components of the portions of the RF signals are filtered by CF  516 . After filtering by low pass filter  410 , a signal is delivered to switch  412  via connection  430 . The signal on connection  430  includes those portions of the communication signal having an amplitude that exceeds the predefined threshold, as defined by attenuator  402  (FIG.  4 ), that have been rectified by the rectifying circuit  408  and that have had the AC components filtered by low pass filter  410 . 
     Switch  412  includes a switching transistor (Q 3 )  520  and a switch resistor (RS)  522  connected to ground. If any signal is provided to switch  412  over connection  430 , as described above, Q 3  is activated. If there is no signal on connection  430  (i.e., the amplitude of the communication signal is less than the threshold as determined by attenuator  402 ) then Q 3  is deactivated. 
     Reference voltage generator  414  includes a first diode (D 1 )  524 , a second diode (D 2 )  526  and a resistor (RG)  528 . Reference voltage generator  414  is coupled to a voltage source (Vcc) on bus  512  via connection  530 , and is coupled to switch  412  via connection  434 . When Q 3   520  is conducting, the voltage on connection  432  is small and insufficient to activate Q 4   532 . When Q 3   520  is not conducting, voltage on connection  432  is equal to the voltage generated by voltage generator  414  and is sufficient to activate Q 4   532 . Diodes D 1  and D 2  may be any suitable conventional diode or a specially fabricated diode. 
     Emitter follower transistor  416  includes a transistor (Q 4 )  532  and a resistor (REF)  534 . Q 4  is connected to the voltage source Vcc at bus  512  via connection  536  as shown. When the voltage on connection  432  is substantially zero, Q 4  is activated (not conducting) and the voltage at node  538  is zero. When the voltage on connection  432  is equal to the voltage provided by reference voltage generator  414  (Q 3   520  is not conducting) then Q 4   532  is activated (conducting). When Q 4  is activated, current flows from bus  512  through Q 4   532  and through REF  534  to ground. Thus, the voltage at node  538  is now equal to (IEF×REF). This non-zero voltage at node  538  is output from the emitter follower transistor  416  via connection  304 . As described above, when the voltage on connection  304  is above the turn-on voltage, the second stage power amplifier  216  (FIG. 3) is activated such that the communication signal is amplified by the second stage power amplifier  216 . One skilled in the art will appreciate that the transistor Q 4   532  and the resistor REF  534  can be sized so that a desired voltage is provided on connection  304  and so that the second stage power amplifier  216  is activated. 
     In summary, the dynamic bias controller  302  (FIGS. 3 and 4) senses the amplitude of a communication signal and automatically determines when the second stage power amplifier  216  residing in the single-stage amplifier  212  is to be activated, thereby amplifying the communication signal that is to be transmitted from the mobile communication device  300  (FIG.  3 ). The dynamic bias controller  302  accomplishes this function by detecting those portions of the communication signal that have an amplitude greater than a predefined threshold value, as determined by attenuator  402  (FIG.  4 ), and by generating a voltage on connection  304  that activates the second stage power amplifier  216 . 
     FIG. 6 is a graph of the output power of the power amplifiers  214  and  216  (FIG. 3) when controlled by the dynamic bias controller  302  (FIGS.  3  and  4 ). The vertical axis of graph  600  is the output bias current, in per unit (p.u.), of the first stage power amp  214  and the second stage power amp  216  (FIG.  3 ). The horizontal axis of graph  600  is the amplitude, in milli-decibels (dBm), of the detected communication signal on connection  306  (FIGS.  3  and  4 ). The output of amplifiers  214  and  216 , as shown on graph  600 , are intended to be illustrative hypothetical outputs of the amplifiers  214  and  216  to facilitate an explanation of the operation and functionality of the dynamic bias controller  302  in response to a detected hypothetical communication signal. Thus, one skilled in the art will appreciate that the output of the two amplifiers in practice can be specified, designed and/or implemented in mobile communication device  300  (FIG. 3) in a manner that provides any desired output level from the two power amplifiers  214  and  216 . 
     Curve  602  represents an example of the output of the first stage power amp  214 . Curve  604  represents the power output of the second stage power amp  216 . When the communication signal amplitude detected on connection  306  is between −10 dBm and 10 dBm, the output of the second stage power amp  216  is zero p.u. That is, the dynamic bias controller  302  has deactivated the second stage power amp  216  when the amplitude of the communication signal is between −10 dBm and 10 dBm. When the communication signal amplitude is between −10 dBm and 10 dBm, only the first stage power amp  214  is required to be activated to provide an adequate amplified communication signal to the antenna  110  (FIG.  1 ). Since second stage power amp  216  is deactivated, power is conserved. 
     When the amplitude of the communication signal reaches 10 dBm, the turn-on point  606  of the second stage power amp  216  is reached and the second stage power amp  216  activates. The output of the second stage power amp  216  increases in a manner that corresponds to the increasing amplitude of the communication signal such that an amplified communication signal of adequate strength for broadcasting is delivered to antenna  110 . In the simplified illustrative example of FIG. 6, the turn-on point  606  is selected to be at a communication signal amplitude equal to 10 dBm. This 10 dBm turn-on point  606  was effected by the threshold point as defined by the attenuator  402  (FIG.  4 ). When the amplitude of the communication signal exceeds 10 dBm, a portion of the communication signal is processed by the dynamic bias controller  302  such that the output of the dynamic bias controller  302  on connection  304  activates the second stage power amp  216 . 
     The 10 dBm turn-on point  606  illustrated in the graph  600  of FIG. 6 was selected as a convenience for explaining the operation and functionality of a dynamic bias controller  302  implemented in a mobile communication device  300  (FIG.  3 ). The turn-on point  606  could be designed to be at any value of the communication signal amplitude depending upon the particular needs of the mobile communication device  300 . The turn-on point  606  can be specified by the appropriate determination of the various components of the dynamic bias controller  302 . For example, the threshold of attenuator  402  could be modified. Alternatively, VREF in the rectifying circuit  408  (FIG. 5) and/or the reference resistor RREF  502  could be selected such that the turn-on point  606  could be adjusted to a different value. Additionally, the turn-on voltage of transistor Q 3   520  residing in switch  412  could be specified such that the turn-on point  606  could be adjusted. One skilled in the art will appreciate that other components residing in the dynamic bias controller  302  might be defined in a similar manner to adjust the turn-on point  606 . Any such variations in the components residing in the dynamic bias controller  302 , and/or any variations in the elements residing in those components, are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     FIG. 7 is a block diagram of an embodiment of the dynamic bias controller  700  having an alternative configuration of the rectifying circuit  702  and reference voltage circuit  704 . Generally, when compared to the configuration of the components residing in the dynamic bias controller  302  of FIG. 5, the components of the dynamic bias controller  700  are generally similar. Low pass filter  410 , switch  412  and emitter follower transistor  416 , are substantially the same as in the embodiment as shown in FIG.  5 . Furthermore, the individual components are coupled together in substantially the same manner. That is, rectifying circuit  702  is coupled to the low pass filter  410  via connection  422 . Low pass filter  410  is coupled to switch  412  via connection  430 . Switch  412  is coupled to emitter follower transistor  416  via connection  432 . The emitter follower is coupled to the voltage source Vcc via connection  536  and the output of the emitter follower transistor  416  is output at connection  304 . 
     Rectifying circuit  702  employs different elements as compared to the rectifying circuit  408  in FIG.  5 . Here, a rectifying circuit  702  employs a first transistor (Q 5 )  706 , a second transistor (Q 6 )  708  and a reference resistor (RREF 1 )  710 . RREF 1  is coupled to a reference voltage VREF via connection  712 . Reference voltage circuit  704  is also coupled to the same VREF via connection  714 . Reference voltage circuit  704  includes a transistor (Q 7 )  716 , a transistor (Q 8 )  718 , a reference resistor (RREF 2 )  720  and a resistor (RG)  722  connected to ground. Here, RREF 1   710  and RREF 2   720  have been selected such that corresponding reference currents, IREF 1  and IREF 2  are provided to the rectifying circuit  702  and the reference voltage circuit  704 , respectively. The dynamic bias controller  700  operates in substantially the same manner as explained above for the dynamic bias controller  302  illustrated in FIG.  5 . Here, an attenuator (not shown) employs a predefined threshold to define the turn-on point of the dynamic bias controller  700 . Rectifying circuit  702  rectifies those portions of the communication signal greater than the predefined threshold, low pass filter  410  filters out the AC components of the portions of the communication signal rectified by rectifying circuit  702 , and the output of low pass filter  410  activates the switch  412  when portions of the rectified/filtered communication signal are present or deactivates the switch when the rectified/filtered portions of the signal are absent. Similar to the embodiment according to FIG. 5, the emitter follower transistor  416  will either activate or deactivate according to the status of switch  412 . 
     FIG. 8 is a block diagram of an embodiment of a dynamic bias controller  802  controlling a plurality of second power amplifiers  804 ,  806  and  808  residing in a multiple stage power amplifier unit  810 . Multiple stage power amplifier unit  810  employs three stages; N−1 stage  812 , Nth stage  814  and N+1 stage  816 . A first power amplifier (amp)  818  resides in each stage  812 ,  814  and  816 . Typically, a multiple stage power amplifier unit  810  employs a plurality of impedance matching and coupler circuits  820 . The communication signal enters the multiple stage power amplifier unit  810  on connection  822  and is amplified to a desired amplified communication signal and output to antenna  110  via connection  122 . 
     Dynamic bias controller  802  senses the communication signal on connection  826 . When the amplitude of the communication signal is less than the turn-on point, the multi-stage power amplifier unit  810  amplifies the communication signal with only the plurality of first power amplifiers  818  residing in the three stages  812 ,  814  and  816 . When the amplitude of the communication signal exceeds the turn-on point, the dynamic bias controller  802  activates each of the second power amplifiers  804 ,  806  and  808  via connection  824 . 
     One skilled in the art will realize that each of the impedance matching and coupler circuits  820  of FIG. 8 are likely to have different elements residing in each circuit  820 , and that FIG. 8 is intended to be a simplified illustration of the manner in that components might be coupled in a multiple stage power amplifier unit. Thus, variations in the components of a multiple stage power amplifier unit  810  employing the dynamic bias controller  802  may vary from one specific application to another without substantially affecting the operation and functionality of the dynamic bias controller  802  that is activating or deactivating the second power amplifiers  804 . 
     The multiple stage power amplifier  810  illustrated in FIG. 8 employs three amplification stages  812 ,  814  and  816  for convenience of illustration purposes. The dynamic bias controller  802  could equally be applicable to a multiple stage power amplifier unit having only two amplification stages, or a multiple stage power amplifier units having more than three amplification stages. One aspect of the invention is the ability of the dynamic bias controller  802  to enable the control of a plurality of second power amplifiers based upon a single turn-on point. 
     For convenience of illustration, the plurality of second power amplifiers  804 ,  806  and  808  are shown controlled by a single connection  824 . Alternatively, each of the plurality of second power amplifiers  804 ,  806  and  808  could be controlled over an individual connection (not shown) without departing substantially from the operation and functionality of the dynamic bias controller  802 . Individual connections would be applicable if multiple stage power amplifier unit  810  employs different rated second power amplifiers ( 804 ,  806  and/or  808 ), each having a different turn-on signal requirement. In this situation, the dynamic bias controller  802  would have a means for providing the required unique turn-on signal to each of the second power amplifiers. For example, additional components could be added to the dynamic bias controller  802  such that the required signal is uniquely provided to each of the second power amps  804 ,  806  and  808  via the individual connections. 
     FIG. 9 is a block diagram of an embodiment of a dynamic bias controller  902  controlling a plurality of power amplifiers  904  and  906  residing in a single-stage, multiple power amplifier unit  908 . With the single-stage, multiple power amplifier unit  908 , a communication signal is provided on connection  910 . The amplified communication signal is output to antenna  110  over connection  122 . Matching impedance and coupler circuits  912  may be employed for the plurality of power amplifiers  904 ,  906  and  914 . For convenience of illustration, the single-stage multiple power amplifier unit  910  is illustrated having three power amplifiers, a first power amplifier  914 , a second power amplifier  904  and an Nth power amplifier  906 . Dynamic bias controller  902  controls the second power amplifier  904  via connection  916 . Dynamic bias controller  902  controls the Nth power amplifier  906  via connection  918 . 
     The communication signal is detected by the dynamic bias controller  902  on connection  920 . When the amplitude of the communication signal is below the first turn-on point, dynamic bias controller  902  deactivates the second power amplifier  904  and the Nth power amplifier  906 . With this operating condition, the communication signal is amplified only by the first power amplifier  914 . 
     When the amplitude of the communication signal exceeds a first turn-on point, the dynamic bias controller  902  activates the second power amplifier  906 . The communication signal is then amplified by the first power amplifier  914  and the second power amplifier  904 . (For this operating condition, it is assumed that the amplitude of the communication signal is less than a second turn-on point, as described below.) 
     When the amplitude of the communication signal exceeds a second turn-on point, the dynamic bias controller  902  activates the Nth power amplifier  904 . Thus, the communication signal being amplified by the single-stage, multiple power amplifier unit  908 , is amplified by all three power amplifiers  914 ,  904  and  906  during this operating condition. 
     Alternatively, the dynamic bias controller  902  may have deactivated the second power amplifier  904  in conjunction with the activation of the Nth power amplifier  906 , assuming that the Nth power amplifier  906  was larger than the second power amplifier  904 . Then, at a third turn-on point, the dynamic bias controller  902  could activate the second power amplifier  904 . Furthermore, an optional connection  922  could have been provided to control the first power amplifier  914 . A plurality of turn-on points could be defined within the dynamic bias controller  902  such that any one or any combination of the power amplifiers  914 ,  904  and  906  could be activated depending on a particular amplitude of the communication signal. Thus, a hand-held communication device (not shown) employing a single-stage, multiple power amplifier unit  908  with the dynamic bias controller  902 , could be designed to operate in a highly efficient manner, thus conserving the limited power supply and optimizing operation time of the mobile communication device. 
     The dynamic bias controller  902  can easily be designed to control four or more such power amplifiers (not shown). However, the single-stage, multiple power amplifier unit  908  having three power amplifiers  914 ,  904  and  906  is used to explain the functionality and operation of the embodiment of the dynamic bias controller  902 . 
     Yet another alternative embodiment of the dynamic bias controller may have fewer components than the dynamic bias controller  302  (FIGS. 3 and 4) or  700  (FIG.  7 ). For example, in some applications the emitter follower transistor  416  (FIG. 7) may be omitted. The transistor Q 3   520  residing in switch  412  may be configured such that the output of switch  412  alone, over connection  432 , is sufficient to control a power amplifier. Alternatively, the reference voltage circuit  704  may not be required. A suitable voltage could be provided from another component (not shown) residing in the mobile communication device  300  (FIG.  3 ). Another alternative embodiment of a dynamic bias controller could provide a control signal (turn-on/turn-off) to a power amplifier that already has its own controller switch. All such alternative embodiments of a dynamic bias controller are intended to be within the scope of this disclosure and be protected by the accompanying claims. 
     Another embodiment of a dynamic bias controller system is shown in FIG.  10 . FIG. 10 is a block diagram of an embodiment of the dynamic bias controller  302  controlling a second stage amplifier  216  and a prematching impedance network  1002  employed in a mobile communication device  1000 . One skilled in the art will appreciate that system performance may be optimized by having an output matching impedance and coupler  1004 , which is optimized for an operating condition where only the first stage power amplifier  214  is operating (second stage power amplifier  216  is off). System performance could be further optimized if the output matching impedance is modified when both the first stage power amplifier  214  and the second stage power amplifier  216  are operating. 
     When the second stage power amplifier  216  is controlled by the dynamic bias controller  302 , a prematching impedance network  1002 , coupled between the second stage power amplifier  216  and the output matching impedance and coupler  1004  (FIG.  10 ), can be used to modify the output impedance when both the first stage power amplifier  214  and the second stage power amplifier  216  are operating. When the dynamic bias controller  302  has deactivated the second stage power amplifier  216 , the prematching impedance network  1002  does not affect the output matching impedance because no power flows from the second stage power amplifier  216 , through the prematching impedance network  1002 , to the output matching impedance and coupler  1004 . 
     When the dynamic bias controller  302  has activated the second stage power amplifier  216 , the prematching impedance networks  1002  and  1012  match the output matching impedance because power flows from the second stage power amplifier  216 , over connection  1006 , through the prematching impedance network  1002 , over connection  1008 , to the output matching impedance and coupler  1004 . 
     In another embodiment, dynamic bias controller  302  may be coupled to the prematching impedance network  1002  with connection  1010 . Dynamic bias controller  302  could provide an auxiliary signal, via connection  1010 , to one or more switches (not shown) residing in or coupled to prematching impedance network  1002 . When the dynamic bias controller  302  has deactivated the second stage power amplifier  216 , the one or more switches are actuated by dynamic bias controller  302  to isolate the prematching impedance network  1002  such that the output matching impedance is not affected. When the dynamic bias controller  302  has activated the second stage power amplifier  216 , the one or more switches are actuated by dynamic bias controller  302  to couple the prematching impedance network  1002  such that the output matching impedance is affected. 
     Prematching impedance network  1002 , and any associated switches, may be implemented using well known components commonly employed in matching impedance systems and switching systems. Thus, a detailed description of the individual components residing in prematching impedance network  1002  or any associated switches are not described since such a description is not necessary to understand the operation and function of the dynamic bias controller  302 . One skilled in the art will realize that the prematching impedance networks  1002  and  1012 , and associated switches, may be implemented by a variety of means such that the output matching impedance is adjusted to a desired value when the dynamic bias controller  302  has activated the second stage power amplifier  216 . All such embodiments of prematching impedance network  1002  utilized with a dynamic bias controller  302  are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     Alternatively, the prematching impedance network  1012  could be coupled to the input of the second stage power amplifier  216  as illustrated in FIG.  10 . Also, the dynamic bias controller  302  could be coupled to the prematching impedance network  1012 , via connection  1014 , such that switches (not shown) residing in prematching impedance network  1012  are actuated to uncouple and recouple the prematching impedance network  1012  in a manner similar to that described above for the prematching impedance network  1002 . 
     Yet another embodiment may employ two prematching impedance networks  1002  and  1012 . The prematching impedance networks  1002  and  1012  may also employ switches (not shown) controlled by the dynamic bias controller  302  as described above. 
     Furthermore, prematching impedance network  1002  and/or prematching impedance network  1012  may be coupled to the output and/or the input, respectively, of the first stage power amplifier  214  and controlled as described above. Prematching impedance network  1002  is coupled to the output of the first stage power amplifier  214  at a convenient location on connection  228 . Similarly, prematching impedance network  1012  is coupled to the input of the first stage power amplifier  214  at a convenient location on connection  1016 . 
     Up to four prematching impedance networks could be employed in a single-stage power amplifier unit  308 . A prematching impedance network could be coupled to the input and/or the output of either, or both, the first stage power amplifier  214  and the second stage power amplifier  216 . Dynamic bias controller  302  provides the appropriate control signals to the first stage power amplifier  214  and/or the second stage power amplifier  216 , and to any of the prematching impedance networks employed in the single-stage power amplifier unit  308 . 
     For convenience of explaining the operation and functionality of the various embodiments of the dynamic bias controller illustrated in FIGS. 3-10, the communication signal detected by the dynamic bias controller was illustrated and described as being received from transmit unit  206  (FIG.  3 ). However, the dynamic bias controller  302  (and alternative embodiments of the dynamic bias controller) operates satisfactorily when the communication signal is provided from any of the components (not shown) residing in the mobile communication device  300  (FIG.  3 ). The dynamic bias controller requires only that the delivered communication signal have a sufficient bandwidth as to provide meaningful detection of amplitude and a meaningful specification of the operating turn-on point(s). Depending upon the particular mobile communication device  300  in which a dynamic bias controller is installed, the dynamic bias controller has elements defined such that the delivered communication signal can be adequately detected such that the appropriate turn-on/turn-off signals can be delivered to the power amplifiers. All such variations in the source of the communication signal delivered to a dynamic bias controller and the associated components (and their elements) are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     Furthermore, for convenience of illustration and the explanation of the operation and function of a dynamic bias controller, the components (attenuator  402 , DC stop  406 , rectifying circuit  408 , low pass filer  410 , switch  412 , reference voltage generator  414  and the emitter follower transistor  416 ) are shown residing in the dynamic bias controller  302  (see FIG.  4 ). Alternatively, these components may reside in other convenient locations outside of the dynamic bias controller  302  without adversely affecting the operation and functionality of the dynamic bias controller  302 . Also, the necessary reference voltages and supply voltages Vcc could be provided from any convenient location within the mobile communication device  300  and at any convenient value. All such alternative embodiments of the dynamic bias controller are intended to be within the scope of this disclosure and to be protected by the accompanying claims. 
     FIG. 11 is a block diagram of an embodiment of the dynamic bias controller  1100  comprising a prematching impedance network  1102  with portions at the input of the first power amplifier  214  and second power amplifier  216 . The prematching impedance network  1102  comprises a first impedance network  1104  coupled to the input of the first power amplifier (amp)  214 , via connection  1108 . The prematching impedance network  1102  further comprises a second impedance network  1108  coupled to the input of the second power amplifier  216 , via connection  1110 . The first impedance network  1104  and the second impedance network  1108  are coupled to the input matching impedance and coupler  220  via connections  1016  and  1112 , respectively. 
     By design, the components (not shown) residing in the first impedance network  1104  are selected to provide a desirable net input impedance seen by the first power amplifier  214  when the second power amplifier  216  is deactivated by the dynamic bias controller  302 . The components residing in the first impedance network  1104  are comprised, in one embodiment, of passive elements such as, but not limited to, resistors and/or reactances (inductors and/or capacitors). Accordingly, any desirable impedance and/or phase angle characteristics may be achieved by configuration of the components of the first impedance network  1104 . 
     Similarly, by design, the components (not shown) residing in the second impedance network  1108  are selected to provide a desirable net input impedance seen by the second power amplifier  216  when the second power amplifier  216  is activated by the dynamic bias controller  302  and concurrently operating with the first power amplifier  214 . Accordingly, the net impedance seen by the 1st stage  212  is configured at a first impedance and/or first phase angle when only the first power amplifier  214  is operating, and is configured at a second impedance and/or second phase angle when both the first power amplifier  214  and the second power amplifier  216  are operating. 
     The components residing in the second impedance network  1108  are comprised, in one embodiment, of passive elements such as, but not limited to, resistors and/or reactances (inductors and/or capacitors). In another embodiment, active switching elements may be included as described above. Accordingly, any desirable impedance and/or phase angle characteristics may be achieved by configuration of the components of the second impedance network  1108 . 
     FIG. 12 is a block diagram of an embodiment of the dynamic bias controller  1200  comprising a prematching impedance network  1202  with portions at the input of the first power amplifier  214  and the second power amplifier  216 , and another portion at the output of the second power amplifier  216 . This embodiment, similar to the embodiment described above and illustrated in FIG. 11, further comprises a third impedance network  1204  coupled to the output of the second power amplifier  216 , via connection  1206 . The third impedance network  1204  is coupled to the output matching impedance and coupler  1004  via connection  1208 . 
     Components (not shown) residing in the third impedance network  1204  are selected to provide a desirable net input impedance, in combination with the impedance of the second impedance network  1108 , seen by the second power amplifier  216  when the second power amplifier  216  is activated by the dynamic bias controller  302  and concurrently operating with the first power amplifier  214 . Accordingly, any desirable impedance and/or phase angle characteristics may be achieved by configuration of the components of the third impedance network  1204 . 
     In an alternative embodiment, the second impedance network  1108  is omitted. Accordingly, any desirable net impedance and/or phase angle characteristics may be achieved by configuration of the components of the third impedance network  1204 . 
     FIG. 13 is a block diagram of an embodiment of the dynamic bias controller  1300  comprising a prematching impedance network  1302  with portions at the input and/or at the output of the third amplifier  1304 . In this embodiment, a first stage power amplifier (AMP) network  1306  comprises a plurality of serially connected amplifiers, illustrated for convenience as the first power amplifier  1308  and the second power amplifier  1310 . Embodiments of the prematching impedance network  1302  comprise the above-described first impedance network  1108  and/or the second impedance network  1204 . Furthermore, an input impedance (not shown) may be coupled to the input and/or output of the first stage power amplifier network  1306  to achieve desired impedance and/or phase angle characteristics. 
     While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this invention.