Patent Publication Number: US-11641215-B2

Title: Power tracker for multiple transmit signals sent simultaneously

Description:
BACKGROUND 
     I. Related Applications 
     This application is a continuation of U.S. patent application Ser. No. 15/916,101 filed on Mar. 8, 2018, now U.S. Pat. No. 11,133,833 issued on Sep. 28, 2021, which is a continuation of U.S. patent application Ser. No. 15/444,083 filed on Feb. 27, 2017, which is a continuation of U.S. patent application Ser. No. 13/764,328 filed on Feb. 11, 2013, now U.S. Pat. No. 9,608,675 issued on Mar. 28, 2017. 
     II. Field 
     The present disclosure relates generally to electronics, and more specifically to techniques for generating a power supply voltage for a circuit such as an amplifier. 
     III. BACKGROUND 
     A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may transmit and receive data for two-way communication. The wireless device may include a transmitter for data transmission and a receiver for data reception. For data transmission, the transmitter may process (e.g., encode and modulate) data to generate output samples. The transmitter may further condition (e.g., convert to analog, filter, amplify, and frequency upconvert) the output samples to generate a modulated radio frequency (RF) signal, amplify the modulated RF signal to obtain an output RF signal having the proper transmit power level, and transmit the output RF signal via an antenna to a base station. For data reception, the receiver may obtain a received RF signal via the antenna and may amplify and process the received RF signal to recover data sent by the base station. 
     The transmitter typically includes a power amplifier (PA) to provide high transmit power for the output RF signal. The power amplifier should be able to provide high transmit power and have high power-added efficiency (PAE). 
     SUMMARY 
     Techniques for generating a power tracking supply voltage for a circuit (e.g., a power amplifier) that processes multiple transmit signals sent simultaneously are disclosed herein. The multiple transmit signals may comprise transmissions sent simultaneously on multiple carriers at different frequencies. 
     In one exemplary design, an apparatus includes a power tracker and a power supply generator. The power tracker determines a power tracking signal based on inphase (I) and quadrature (Q) components of a plurality of transmit signals being sent simultaneously, as described below. The power supply generator generates a power supply voltage based on the power tracking signal. The apparatus may further include a power amplifier that amplifies a modulated RF signal based on the power supply voltage and provides an output RF signal. 
     Various aspects and features of the disclosure are described in further detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    shows a wireless device communicating with a wireless system. 
         FIGS.  2 A to  2 D  show four examples of carrier aggregation. 
         FIG.  3    shows a block diagram of the wireless device in  FIG.  1   . 
         FIG.  4    shows a transmit module comprising a separate power amplifier with separate power tracking for each transmit signal. 
         FIGS.  5  and  6    show two designs of a transmit module comprising a single power amplifier with power tracking for all transmit signals. 
         FIGS.  7 A and  7 B  show power tracking for two and three transmit signals, respectively. 
         FIGS.  8  and  9    show a design of a power supply generator with power tracking. 
         FIG.  10    shows a process for generating a power supply voltage with power tracking. 
     
    
    
     DETAILED DESCRIPTION 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other designs. 
     Techniques for generating a power tracking supply voltage for a circuit (e.g., a power amplifier) that processes multiple transmit signals sent simultaneously are disclosed herein. The techniques may be used for various electronic devices such as wireless communication devices. 
       FIG.  1    shows a wireless device  110  communicating with a wireless communication system  120 . Wireless system  120  may be a Long Term Evolution (LTE) system, a Code Division Multiple Access (CDMA) system, a Global System for Mobile Communications (GSM) system, a wireless local area network (WLAN) system, or some other wireless system. A CDMA system may implement Wideband CDMA (WCDMA), CDMA 1X, Time Division Synchronous CDMA (TD-SCDMA), or some other version of CDMA. For simplicity,  FIG.  1    shows wireless system  120  including two base stations  130  and  132  and one system controller  140 . In general, a wireless system may include any number of base stations and any set of network entities. 
     Wireless device  110  may also be referred to as a user equipment (UE), a mobile station, a terminal, an access terminal, a subscriber unit, a station, etc. Wireless device  110  may be a cellular phone, a smartphone, a tablet, a wireless modem, a personal digital assistant (PDA), a handheld device, a laptop computer, a smartbook, a netbook, a cordless phone, a wireless local loop (WLL) station, a Bluetooth device, etc. Wireless device  110  may be capable of communicating with wireless system  120 . Wireless device  110  may also be capable of receiving signals from broadcast stations (e.g., a broadcast station  134 ), signals from satellites (e.g., a satellite  150 ) in one or more global navigation satellite systems (GNSS), etc. Wireless device  110  may support one or more radio technologies for wireless communication such as LTE, WCDMA, CDMA 1X, TD-SCDMA, GSM, 802.11, etc. 
     Wireless device  110  may be able to operate in low-band (LB) covering frequencies lower than 1000 megahertz (MHz), mid-band (MB) covering frequencies from 1000 MHz to 2300 MHz, and/or high-band (HB) covering frequencies higher than 2300 MHz. For example, low-band may cover 698 to 960 MHz, mid-band may cover 1475 to 2170 MHz, and high-band may cover 2300 to 2690 MHz and 3400 to 3800 MHz. Low-band, mid-band, and high-band refer to three groups of bands (or band groups), with each band group including a number of frequency bands (or simply, “bands”). Each band may cover up to 200 MHz and may include one or more carriers. Each carrier may cover up to 20 MHz in LTE. LTE Release 11 supports 35 bands, which are referred to as LTE/UMTS bands and are listed in 3GPP TS 36.101. 
     Wireless device  110  may support carrier aggregation, which is operation on multiple carriers. Carrier aggregation may also be referred to as multi-carrier operation. Wireless device  110  may be configured with up to 5 carriers in one or two bands in LTE Release 11. 
     In general, carrier aggregation (CA) may be categorized into two types—intra-band CA and inter-band CA. Intra-band CA refers to operation on multiple carriers within the same band. Inter-band CA refers to operation on multiple carriers in different bands. 
       FIG.  2 A  shows an example of contiguous intra-band CA. In the example shown in  FIG.  2 A , wireless device  110  is configured with three contiguous carriers in one band in low-band. Wireless device  110  may send and/or receive transmissions on the three contiguous carriers in the same band. 
       FIG.  2 B  shows an example of non-contiguous intra-band CA. In the example shown in  FIG.  2 B , wireless device  110  is configured with three non-contiguous carriers in one band in low-band. The carriers may be separated by 5 MHz, 10 MHz, or some other amount. Wireless device  110  may send and/or receive transmissions on the three non-contiguous carriers in the same band. 
       FIG.  2 C  shows an example of inter-band CA in the same band group. In the example shown in  FIG.  2 C , wireless device  110  is configured with three carriers in two bands in low-band. Wireless device  110  may send and/or receive transmissions on the three carriers in different bands in the same band group. 
       FIG.  2 D  shows an example of inter-band CA in different band groups. In the example shown in  FIG.  2 D , wireless device  110  is configured with three carriers in two bands in different band groups, which include two carriers in one band in low-band and one carrier in another band in mid-band. Wireless device  110  may send and/or receive transmissions on the three carriers in different bands in different band groups. 
       FIGS.  2 A to  2 D  show four examples of carrier aggregation. Carrier aggregation may also be supported for other combinations of bands and band groups. 
       FIG.  3    shows a block diagram of an exemplary design of wireless device  110  in  FIG.  1   . 
     In this exemplary design, wireless device  110  includes a data processor/controller  310 , a transceiver  320  coupled to a primary antenna  390 , and a transceiver  322  coupled to a secondary antenna  392 . Transceiver  320  includes K transmitters  330   pa  to  330   pk , L receivers  380   pa  to  380   pl , and an antenna interface circuit  370  to support multiple bands, carrier aggregation, multiple radio technologies, etc. K and L may each be any integer value of one or greater. Transceiver  322  includes M transmitters  330   sa  to  330   sm , N receivers  380   sa  to  380   sn , and an antenna interface circuit  372  to support multiple bands, carrier aggregation, multiple radio technologies, receive diversity, multiple-input multiple-output (MIMO) transmission, etc. M and N may each be any integer value of one or greater. 
     In the exemplary design shown in  FIG.  3   , each transmitter  330  includes a transmit circuit  340  and a power amplifier (PA)  360 . For data transmission, data processor  310  processes (e.g., encodes and symbol maps) data to be transmitted to obtain modulation symbols. Data processor  310  further processes the modulation symbols (e.g., for OFDM, SC-FDMA, CDMA, or some other modulation technique) and provides I and Q samples for each transmit signal to be sent by wireless device  110 . A transmit signal is a signal comprising a transmission on one or more carriers, a transmission on one or more frequency channels, etc. Data processor  310  provides the I and Q samples for one or more transmit signals to one or more selected transmitters. The description below assumes that transmitter  330   pa  is a transmitter selected to send one transmit signal. Within transmitter  330   pa , transmit circuit  340   pa  converts I and Q samples to I and Q analog output signals, respectively. Transmit circuit  340   pa  further amplifies, filters, and upconverts the I and Q analog output signals from baseband to RF and provides a modulated RF signal. Transmit circuit  340   pa  may include digital-to-analog converters (DACs), amplifiers, filters, mixers, matching circuits, an oscillator, a local oscillator (LO) generator, a phase-locked loop (PLL), etc. A PA  360   pa  receives and amplifies the modulated RF signal and provides an output RF signal having the proper transmit power level. The output RF signal is routed through antenna interface circuit  370  and transmitted via antenna  390 . Antenna interface circuit  370  may include one or more filters, duplexers, diplexers, switches, matching circuits, directional couplers, etc. Each remaining transmitter  330  in transceivers  320  and  322  may operate in similar manner as transmitter  330   pa.    
     In the exemplary design shown in  FIG.  3   , each receiver  380  includes a low noise amplifier (LNA)  382  and a receive circuit  384 . For data reception, antenna  390  receives signals from base stations and/or other transmitter stations and provides a received RF signal, which is routed through antenna interface circuit  370  and provided to a selected receiver. The description below assumes that receiver  380   pa  is the selected receiver. Within receiver  380   pa , an LNA  382   pa  amplifies the received RF signal and provides an amplified RF signal. A receive circuit  384   pa  downconverts the amplified RF signal from RF to baseband, amplifies and filters the downconverted signal, and provides an analog input signal to data processor  310 . Receive circuit  384   pa  may include mixers, filters, amplifiers, matching circuits, an oscillator, an LO generator, a PLL, etc. Each remaining receiver  380  in transceivers  320  and  322  may operate in similar manner as receiver  380   pa.    
       FIG.  3    shows an exemplary design of transmitters  330  and receivers  380 . A transmitter and a receiver may also include other circuits not shown in  FIG.  3   , such as filters, matching circuits, etc. All or a portion of transceivers  320  and  322  may be implemented on one or more analog integrated circuits (ICs), RF ICs (RFICs), mixed-signal ICs, etc. For example, transmit circuits  340 , LNAs  382 , and receive circuits  384  may be implemented on one module, which may be an RFIC, etc. Antenna interface circuits  370  and  372  and PAs  360  may be implemented on another module, which may be a hybrid module, etc. The circuits in transceivers  320  and  322  may also be implemented in other manners. 
     Data processor/controller  310  may perform various functions for wireless device  110 . For example, data processor  310  may perform processing for data being transmitted via transmitters  330  and data being received via receivers  380 . Controller  310  may control the operation of transmit circuits  340 , PAs  360 , LNAs  382 , receive circuits  384 , antenna interface circuits  370  and  372 , or a combination thereof. A memory  312  may store program codes and data for data processor/controller  310 . Data processor/controller  310  may be implemented on one or more application specific integrated circuits (ASICs) and/or other ICs. 
     Wireless device  110  may send multiple transmit signals simultaneously. In one design, the multiple transmit signals may be for transmissions on multiple contiguous or non-contiguous carriers with intra-band CA., e.g., as shown in  FIG.  2 A or  2 B . For example, each transmit signal may comprise a transmission sent on one carrier. In another design, the multiple transmit signals may be for transmissions on multiple frequency channels to the same wireless system. In yet another design, the multiple transmit signals may be for transmissions sent to different wireless systems (e.g., LTE and WLAN). In any case, data to be sent in each transmit signal may be processed (e.g., encoded, symbol mapped, and modulated) separately to generate I and Q samples for that transmit signal. Each transmit signal may be conditioned by a respective transmit circuit  340  and amplified by a respective PA  360  to generate an output RF signal for that transmit signal. 
     A PA may receive a modulated RF signal and a power supply voltage and may generate an output RF signal. The output RF signal typically tracks the modulated RF signal and has a time-varying envelope. The power supply voltage should be higher than the amplitude of the output RF signal at all times in order to avoid clipping the output RF signal, which would then cause intermodulation distortion (IMD) that may degrade performance. The difference between the power supply voltage and the envelope of the output RF signal represents wasted power that is dissipated by the PA instead of delivered to an output load. 
     It may be desirable to generate a power supply voltage for a PA such that good performance and good efficiency can be obtained. This may be achieved by generating the power supply voltage for the PA with power tracking so that the power supply voltage can track the envelope of an output RF signal from the PA. 
       FIG.  4    shows a design of a transmit module  400  supporting simultaneous transmission of multiple (K) transmit signals with a separate PA and separate power tracking for each transmit signal. Transmit module  400  includes K transmitters  430   a  to  430   k  that can simultaneously process K transmit signals, with each transmitter  430  processing one transmit signal. Each transmitter  430  includes a transmit circuit  440 , a PA  460 , and a power tracking supply generator  480 . 
     Transmitter  430   a  receives I 1  and Q 1  samples for a first transmit signal and generates a first output RF signal for the first transmit signal. The I 1  and Q 1  samples are provided to both transmit circuit  440   a  and voltage generator  480   a . Within transmit circuit  440   a , the I 1  and Q 1  samples are converted to I and Q analog signals by DACs  442   a  and  443   a , respectively. The I analog signal is filtered by a lowpass filter  444   a , amplified by an amplifier (Amp)  446   a , and upconverted from baseband to RF by a mixer  448   a . Similarly, the Q analog signal is filtered by a lowpass filter  445   a ,amplified by an amplifier  447   a , and upconverted from baseband to RF by a mixer  449   a . Mixers  448   a  and  449   a  perform upconversion for the first transmit signal based on I and Q LO signals (ILO 1  and QLO 1 ) at a center RF frequency of the first transmit signal. A summer  450   a  sums the I and Q upconverted signals from mixers  448   a  and  449   a  to obtain a modulated RF signal, which is provided to PA  460   a.    
     Within voltage generator  480   a , a power tracker  482   a  receives the I 1  and Q 1  samples for the first transmit signal, computes the power of the first transmit signal based on the I 1  and Q 1  samples, and provides a digital power tracking signal to a DAC  484   a . DAC  484   a  converts the digital power tracking signal to analog and provides an analog power tracking signal. A power supply generator  486   a  receives the analog power tracking signal and generates a power supply voltage for PA  460   a . PA  460   a  amplifies the modulated RF signal from transmit circuit  440   a  using the power supply voltage from supply generator  486   a  and provides the first output RF signal for the first transmit signal. 
     Each remaining transmitter  430  may similarly process I and Q samples for a respective transmit signal and may provide an output RF signal for the transmit signal. Up to K PAs  460   a  to  460   k  may provide up to K output RF signals at different RF frequencies for up to K transmit signals being sent simultaneously. A summer  462  receives the output RF signals being sent simultaneously, sums the output RF signals, and provides a final output RF signal, which is routed through a duplexer  470  and transmitted via an antenna  490 . 
     As shown in  FIG.  4   , power tracking may be used to improve the efficiency of PAs  460   a  to  460   k . Each transmit signal may be processed by a respective transmitter  430  using a separate sets of mixers  448  and  449  and PA  460 . Multiple transmit signals may be sent on different frequencies (e.g., different carriers) and hence may have increased envelope bandwidth. The increased envelope bandwidth may be addressed by using a separate transmitter  430  for each transmit signal. Each transmitter  430  may then handle the envelope bandwidth of one transmit signal. However, operating multiple transmitters  430  concurrently for multiple transmit signals may result in more circuits, higher power consumption, and increased cost, all of which are undesirable. 
     In an aspect of the present disclosure, a single PA with power tracking may be used to generate a single output RF signal for multiple transmit signals being sent simultaneously. A single power supply voltage may be generated for the PA to track the power of all transmit signals being sent simultaneously. This may reduce the number of circuit components, reduce power consumption, and provide other advantages. 
       FIG.  5    shows a design of a transmit module  500  supporting simultaneous transmission of multiple (K) transmit signals with a single PA and power tracking for all transmit signals. Transmit module  500  performs frequency upconversion separately for each transmit signal in the analog domain and sums the resultant upconverted RF signals for all transmit signals. Transmit module  500  includes K transmit circuits  540   a  to  540   k  that can simultaneously process K transmit signals, with each transmit circuit  540  processing one transmit signal. Transmit module  500  further includes a summer  552 , a PA  560 , a duplexer  570 , and a power tracking supply generator  580 . 
     Transmit circuit  540   a  receives I 1  and Q 1  samples for a first transmit signal and generates a first upconverted RF signal for the first transmit signal. The I 1  and Q 1  samples are provided to both transmit circuit  540   a  and voltage generator  580 . Within transmit circuit  540   a , the I 1  and Q 1  samples are converted to I and Q analog signals by DACs  542   a  and  543   a , respectively. The I and Q analog signals are filtered by lowpass filters  544   a  and  545   a ,amplified by amplifiers  546   a  and  547   a , upconverted from baseband to RF by mixers  548   a  and  549   a , and summed by a summer  550   a  to generate the first upconverted RF signal. Mixers  548   a  and  549   a  perform upconversion for the first transmit signal based on I and Q LO signals at a center RF frequency of the first transmit signal. 
     Each remaining transmit circuit  540  may similarly process I and Q samples for a respective transmit signal and may provide an upconverted RF signal for the transmit signal. Up to K transmit circuits  540   a  to  540   k  may provide up to K upconverted RF signals at different RF frequencies for up to K transmit signals being sent simultaneously. A summer  552  receives the upconverted RF signals from transmit circuits  540   a  to  540   k , sums the upconverted RF signals, and provides a modulated RF signal to PA  560 . 
     Within voltage generator  580 , a power tracker  582  receives I 1  to I K  samples and Q 1  to Q K  samples for all transmit signals being sent simultaneously. Power tracker  582  computes the overall power of all transmit signals based on the I and Q samples for these transmit signals and provides a digital power tracking signal to a DAC  584 . DAC  584  converts the digital power tracking signal to analog and provides an analog power tracking signal for all transmit signals. Although not shown in  FIG.  5   , a lowpass filter may receive and filter an output signal from DAC  584  and provide the analog power tracking signal. A power supply generator  586  receives the analog power tracking signal and generates a power supply voltage for PA  560 . 
     PA  560  amplifies the modulated RF signal from summer  552  using the power supply voltage from supply generator  586 . PA  560  provides an output RF signal for all transmit signals being sent simultaneously. The output RF signal is routed through duplexer  570  and transmitted via antenna  590 . 
       FIG.  6    shows a design of a transmit module  502  supporting simultaneous transmission of multiple (K) transmit signals with a single PA and power tracking for all transmit signals. Transmit module  502  digitally upconverts each transmit signal to an intermediate frequency (IF) in the digital domain, sums the resultant upconverted IF signals for all transmit signals, and performs frequency upconversion from IF to RF for all transmit signals together in the analog domain. Transmit module  502  includes a digital modulator  520 , a transmit circuit  540 , PA  560 , duplexer  570 , and power tracking supply generator  580 . 
     Digital modulator  520  receives I and Q samples for all transmit signals and generates a modulated IF signal for all transmit signals. Within digital modulator  520 , the I 1  and Q 1  samples for the first transmit signal are upconverted to a first IF frequency by multipliers  522   a  and  523   a , respectively, based on CH and CO digital LO signals. The I and Q samples for each remaining transmit signal are upconverted to a different IF frequency by multipliers  522  and  523 , respectively, for that transmit signal. The IF frequencies of the K transmit signals may be selected based on the final RF frequencies of the K transmit signals. A summer  524  sums the outputs of all K multipliers  522   a  to  522   k  and provides an I modulated signal. Similarly, a summer  525  sums the outputs of all K multipliers  523   a  to  523   k  and provides a Q modulated signal. The I and Q modulated signals from summers  524  and  525  form the modulated IF signal for all transmit signals. 
     Transmit circuit  540  receives I and Q modulated signals from digital modulator  520  and generates a modulated RF signal for all transmit signals. Within transmit circuit  540 , the I and Q modulated signals are converted to I and Q analog signals by DACs  542  and  543 , respectively. The I and Q analog signals are filtered by lowpass filters  544  and  545 , amplified by amplifiers  546  and  547 , upconverted from IF to RF by mixers  548  and  549 , and summed by a summer  550  to generate the modulated RF signal. Mixers  548  and  549  perform upconversion for the modulated IF signal based on I and Q LO signals at a suitable frequency so that the K transmit signals are upconverted to their proper RF frequencies. 
     Power tracking voltage generator  580  receives the I 1  to I K  samples and the Q 1  to Q K  samples for all transmit signals being sent simultaneously. Voltage generator  580  generates a power supply voltage for PA  560  based on the I and Q samples. PA  560  amplifies the modulated RF signal from transmit circuit  540  using the power supply voltage from supply generator  580 . PA  560  provides an output RF signal for all transmit signals being sent simultaneously. The output RF signal is routed through duplexer  570  and transmitted via antenna  590 . 
       FIGS.  5  and  6    show two exemplary designs of a transmit module supporting simultaneous transmission of multiple transmit signals with a single PA and power tracking for all transmit signals. Multiple transmit signals may also be sent with a single PA and power tracking in other manners. For example, polar modulation may be used instead of quadrature modulation, which is shown in  FIGS.  5  and  6   . 
     Power tracker  582  may compute the digital power tracking signal based on the I and Q samples for all transmit signals in various manners. In one design, the digital power tracking signal may be computed as follows: 
                       p   ⁡     (   t   )       =       K     ·           I   1   2     ⁡     (   t   )       +       Q   1   2     ⁡     (   t   )       +   …   +       I   K   2     ⁡     (   t   )       +       Q   K   2     ⁡     (   t   )               ,           Eq   ⁢           ⁢     (   1   )                 
where I k  (t) and Q k  (t) denote the I and Q samples for the k-th transmit signal in sample period t, for k=1, . . . , K, and
 
     p(t) denotes the digital power tracking signal in sample period t. 
     The quantity I k   2 (t)+Q k   2  (t) denotes the power of the k-th transmit signal in sample period t. In the design shown in equation (1), the powers of all transmit signals are summed to obtain an overall power. The digital power tracking signal is then obtained by taking the square root of the overall power. The scaling factor of √{square root over (K)} accounts for conversion between power and voltage. 
     In another design, the digital power tracking signal may be computed as follows: 
     
       
         
           
             
               
                 
                   
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                   Eq 
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     The quantity √{square root over (I k   2 (t)+Q k   2 (t))} denotes the voltage of the k-th transmit signal in sample period t. In the design shown in equation (2), the voltage of each transmit signal is first computed, and the voltages of all transmit signals are then summed to obtain the digital power tracking signal. 
     Equations (1) and (2) are two exemplary designs of computing the digital power tracking signal based on the I and Q samples for all transmit signals being sent simultaneously. The digital power tracking signal computed in equation (1) or (2) has a bandwidth that approximates the bandwidth of the widest transmit signal (instead of the overall bandwidth of all transmit signals being sent simultaneously). Having the bandwidth of the power tracking signal being smaller than a modulation bandwidth may allow for a more efficient power tracking circuitry and may also result in less noise being injected into PA  560  via the power supply. 
     The digital power tracking signal may also be computed based on the I and Q samples of the transmit signals in other manners, e.g., based on other equations or functions. In one design, the digital power tracking signal may be generated based on the I and Q samples for all transmit signals, without any filtering, e.g., as shown in equation (1) or (2). In another design, the digital power tracking signal may be filtered, e.g., with a lowpass filter having similar characteristics as lowpass filters  544  and  545  in transmit circuit  540 . 
     In one design, the digital power tracking signal may be computed in the same manner (e.g., based on the same equation) regardless of the number of transmit signals being sent simultaneously. In another design, the digital power tracking signal may be computed in different manners (e.g., based on different equations) depending on the number of transmit signals being sent simultaneously. The digital power tracking signal may also be computed in different manners depending on other factors such as the transmit power levels of different transmit signals. 
     The techniques described herein for generating a power tracking supply voltage for multiple transmit signals may be used for various modulation techniques. For example, the techniques may be used to generate a power tracking supply voltage for multiple transmit signals sent simultaneously using orthogonal frequency division multiplexing (OFDM), SC-FDMA, CDMA, or some other modulation techniques. The techniques may also be used to generate a tracking power supply voltage for any number of transmit signals being sent simultaneously. 
       FIG.  7 A  shows an example of power tracking for two transmit signals sent on two non-contiguous carriers with SC-FDMA, e.g., for non-contiguous intra-band CA shown in  FIG.  2 B . The two transmit signals are sent on two carriers separated by a 25 MHz gap, with each carrier having a bandwidth of 10 MHz. A plot  710  shows an output RF signal comprising the two transmit signals and provided by PA  560  in  FIG.  5  or  6   . A plot  712  shows a power tracking signal provided by power tracker  582  in  FIG.  5  or  6   . The power tracking signal is computed based on I and Q samples for the two transmit signals in accordance with equation (1). As shown in  FIG.  7 A , the power tracking signal closely follows the envelope of the output RF signal. Hence, good performance and high efficiency may be achieved for PA  560 . 
       FIG.  7 B  shows an example of power tracking for three transmit signals sent on three non-contiguous carriers with OFDM, e.g., for non-contiguous intra-band CA. The three transmit signals are sent on three carriers, with each carrier having a bandwidth of 5 MHz and being separated by a 15 MHz gap to another carrier. A plot  720  shows an output RF signal comprising the three transmit signals and provided by PA  560  in  FIG.  5  or  6   . A plot  722  shows a power tracking signal provided by power tracker  582  in  FIG.  5  or  6   . The power tracking signal is computed based on I and Q samples for the three transmit signals in accordance with equation (1). As shown in  FIG.  7 B , the power tracking signal follows the envelope of the output RF signal. Hence, good performance and high efficiency may be achieved for PA  560 . 
     It can be shown that a power tracking supply voltage may also be generated for multiple transmit signals sent on multiple carriers with CDMA. In general, the power tracking supply voltage can closely follow the envelope of the output RF signal when two transmit signals are sent simultaneously, e.g., as shown in  FIG.  7 A . The power tracking supply voltage can approximate the envelope of the output RF signal when more than two transmit signals are sent simultaneously, e.g., as shown in  FIG.  7 B . 
     Power supply generator  586  may generate a power supply voltage for PA  560  based on a power tracking signal in various manners. Power supply generator  586  should generate the power supply voltage in an efficient manner in order to conserve battery power of wireless device  110 . 
       FIG.  8    shows a design of power supply generator  586  in  FIGS.  5  and  6   . In this design, power supply generator  586  includes a power tracking amplifier (PT Amp)  810 , a switcher  820 , a boost converter  830 , and an inductor  822 . Switcher  820  may also be referred to as a switching-mode power supply (SMPS). Switcher  820  receives a battery voltage (V BAT ) and provides a first supply current (I SW ) comprising DC and low frequency components at node A. Inductor  822  stores current from switcher  820  and provides the stored current to node A on alternating cycles. Boost converter  830  receives the V BAT  voltage and generates a boosted supply voltage (V BOOST ) that is higher than the V BAT  voltage. Power tracking amplifier  810  receives the analog power tracking signal at its signal input, receives the V BAT  voltage and the V BOOST  voltage at its two power supply inputs, and provides a second supply current (I PT ) comprising high frequency components at node A. The PA supply current (I PA ) provided to power amplifier  560  includes the I SW  current from switcher  820  and the I PT  current from power tracking amplifier  810 . Power tracking amplifier  810  also provides the proper PA supply voltage (V PA ) at Node A for PA  560 . The various circuits in power supply generator  586  are described in further detail below. 
       FIG.  9    shows a schematic diagram of a design of power tracking amplifier  810  and switcher  820  within power supply generator  586  in  FIG.  8   . Within power tracking amplifier  810 , an operational amplifier (op-amp)  910  has its non-inverting input receiving the power tracking signal, its inverting input coupled to an output of power tracking amplifier  810  (which is node X), and its output coupled to an input of a class AB driver  912 . Driver  912  has its first output (R 1 ) coupled to the gate of a P-channel metal oxide semiconductor (PMOS) transistor  914  and its second output (R 2 ) coupled to the gate of an N-channel metal oxide semiconductor (NMOS) transistor  916 . NMOS transistor  916  has its drain coupled to node X and its source coupled to circuit ground. PMOS transistor  914  has its drain coupled to node X and its source coupled to the drains of PMOS transistors  918  and  920 . PMOS transistor  918  has its gate receiving a C 1  control signal and its source receiving the V BOOST  voltage. PMOS transistor  920  has its gate receiving a C 2  control signal and its source receiving the V BAT  voltage. 
     A current sensor  824  is coupled between node X and node A and senses the I PT  current provided by power tracking amplifier  810 . Sensor  824  passes most of the I PT  current to node A and provides a small fraction of the I PT  current as a sensed current (I SEN ) to switcher  820 . 
     Within switcher  820 , a current sense amplifier  930  has its input coupled to current sensor  824  and its output coupled to an input of a switcher driver  932 . Driver  932  has its first output (S 1 ) coupled to the gate of a PMOS transistor  934  and its second output (S 2 ) coupled to the gate of an NMOS transistor  936 . NMOS transistor  936  has its drain coupled to an output of switcher  820  (which is node Y) and its source coupled to circuit ground. PMOS transistor  934  has its drain coupled to node Y and its source receiving the V BAT  voltage. Inductor  822  is coupled between node A and node Y. 
     Switcher  820  operates as follows. Switcher  820  is in an ON state when current sensor  824  senses a high output current from power tracking amplifier  810  and provides a low sensed voltage to driver  932 . Driver  932  then provides a low voltage to the gate of PMOS transistor  934  and a low voltage to the gate of NMOS transistor  936 . PMOS transistor  934  is turned ON and couples the V BAT  voltage to inductor  822 , which stores energy from the V BAT  voltage. The current through inductor  822  rises during the ON state, with the rate of the rise being dependent on (i) the difference between the V BAT  voltage and the V PA  voltage at node A and (ii) the inductance of inductor  822 . Conversely, switcher  820  is in an OFF state when current sensor  824  senses a low output current from power tracking amplifier  810  and provides a high sensed voltage to driver  932 . Driver  932  then provides a high voltage to the gate of PMOS transistor  934  and a high voltage to the gate of NMOS transistor  936 . NMOS transistor  936  is turned ON, and inductor  822  is coupled between node A and circuit ground. The current through inductor  822  falls during the 
     OFF state, with the rate of the fall being dependent on the V PA  voltage at node A and the inductance of inductor  822 . The V BAT  voltage thus provides current to PA  560  via inductor  822  during the ON state, and inductor  120  provides its stored energy to PA  560  during the OFF state. 
     Power tracking amplifier  810  operates as follows. When the power tracking signal increases, the output of op-amp  910  increases, the R 1  output of driver  912  deceases and the R 2  output of driver  912  decreases until NMOS transistor  916  is almost turned OFF, and the output of power tracking amplifier  810  increases. The converse is true when the power tracking signal decreases. The negative feedback from the output of power tracking amplifier  810  to the inverting input of op-amp  910  results in power tracking amplifier  810  having unity gain. Hence, the output of power tracking amplifier  810  follows the power tracking signal, and the V PA  voltage is approximately equal to the power tracking signal. Driver  912  may be implemented with a class AB amplifier to improve efficiency, so that large output currents can be supplied even though the bias current in transistors  914  and  916  is low. 
     In one design, power tracking amplifier  810  operates based on the V BOOST  voltage only when needed and based on the V BAT  voltage during the remaining time in order to improve efficiency. For example, power tracking amplifier  810  may provide approximately 85% of the power based on the V BAT  voltage and only approximately 15% of the power based on the V BOOST  voltage. When a high V PA  voltage is needed for PA  560  due to a large envelope of the output RF signal, the C 1  control signal is at logic low, and the C 2  control signal is at logic high. In this case, boost converter  830  is enabled and generates the V BOOST  voltage, PMOS transistor  918  is turned ON and provides the V BOOST  voltage to the source of PMOS transistor  914 , and PMOS transistor  920  is turned OFF. Conversely, when a high V PA  voltage is not needed for PA  560 , the C 1  control signal is at logic high, and the C 2  control signal is at logic low. In this case, boost converter  830  is disabled, PMOS transistor  918  is turned OFF, and PMOS transistor  920  is turned ON and provides the V BAT  voltage to the source of PMOS transistor  914 . 
     A control signal generator  940  receives the power tracking signal and the V BAT  voltage and generates the C 1  and C 2  control signals. The C 1  control signal is complementary to the C 2  control signal. In one design, generator  940  generates the C 1  and C 2  control signals to select the V BOOST  voltage for power tracking amplifier  910  when the magnitude of the power tracking signal exceeds a first threshold. The first threshold may be a fixed threshold or may be determined based on the V BAT  voltage. In another design, generator  940  generates the C 1  and C 2  control signals to select the V BOOST  voltage for power tracking amplifier  910  when the magnitude of the power tracking signal exceeds the first threshold and the V BAT  voltage is below a second threshold. Generator  940  may also generate the C 1  and C 2  signals based on other signals, other voltages, and/or other criteria. 
     Switcher  820  has high efficiency and delivers a majority of the supply current for PA  560 . 
     Power tracking amplifier  810  operates as a linear stage and has relatively high bandwidth (e.g., in the MHz range). Switcher  820  operates to reduce the output current from power tracking amplifier  810 , which improves overall efficiency. 
       FIG.  9    shows an exemplary design of switcher  820  and power tracking amplifier  810  in  FIG.  1   . Switcher  820  and power tracking amplifier  810  may also be implemented in other manners. For example, power tracking amplifier  810  may be implemented as described in U.S. Pat. No. 6,300,826, entitled “Apparatus and Method for Efficiently Amplifying Wideband Envelope Signals,” issued Oct. 9, 2001. 
     In an exemplary design, an apparatus (e.g., an integrated circuit, a wireless device, a circuit module, etc.) may comprise a power tracker and a power supply generator. The power tracker (e.g., power tracker  582  in  FIG.  5   ) may determine a power tracking signal based on I and Q components (e.g., I and Q samples) of a plurality of transmit signals being sent simultaneously. The power supply generator (e.g., power supply generator  586  in  FIG.  5   ) may generate a power supply voltage based on the power tracking signal. 
     In one design, the power tracker may determine an overall power of the plurality of transmit signals based on the I and Q components of the plurality of transmit signals, e.g., as I 1   2 (t)+Q 1   2 (t)+ . . . +I K   2 (t)+Q K   2 (t). The power tracker may then determine the power tracking signal based on the overall power of the plurality of transmit signals, e.g., as shown in equation (1). In another design, the power tracker may determine the power of each transmit signal based on the I and Q components of that transmit signal, e.g., as I k   2 (t)+Q k   2 (t) for the k-th transmit signal. The power tracker may then determine the power tracking signal based on the powers of the plurality of transmit signals, e.g., as shown in equation (2). The power tracker may determine a voltage of each transmit signal based on the power of the transmit signal, e.g., as √{square root over (I k   2 (t)+Q k   2 (t))}. The power tracker may then determine the power tracking signal based on voltages of the plurality of transmit signals, e.g., as shown in equation (2). The power tracker may also determine the power tracking signal based on the I and Q components of the plurality of transmit signals in other manners. In one design, the plurality of transmit signals may be sent on a plurality of carriers at different frequencies. The power tracking signal may have a bandwidth that is smaller than an overall bandwidth of the plurality of carriers. 
     In one design, the apparatus may comprise a plurality of transmit circuits and a summer, e.g., as shown in  FIG.  5   . The plurality of transmit circuits (e.g., transmit circuits  540   a  to  540   k ) may receive the I and Q components of the plurality of transmit signals and may provide a plurality of upconverted RF signals. Each transmit circuit may upconvert I and Q components of one transmit signal and provide a corresponding upconverted RF signal. The summer (e.g., summer  552 ) may sum the plurality of upconverted RF signals and provide a modulated RF signal. In another design, the apparatus may comprise a transmit circuit (e.g., transmit circuit  540  in  FIG.  6   ) that may receive a modulated IF signal for the plurality of transmit signals and provide a modulated RF signal. The modulated IF signal may be generated (e.g., by digital modulator  520  in  FIG.  6   ) based on the I and Q components of the plurality of transmit signals. In an exemplary design, the apparatus may further comprise a PA (e.g., PA  560  in  FIGS.  5  and  6   ) that may amplify the modulated RF signal based on the power supply voltage and provide an output RF signal. 
     In an exemplary design, the power supply generator may comprise a power tracking amplifier (e.g., power tracking amplifier  810  in  FIGS.  8  and  9   ) that may receive the power tracking signal and generate the power supply voltage. The power supply generator may further comprise a switcher and/or a boost converter. The switcher (e.g., switcher  820  in 
       FIGS.  8  and  9   ) may sense a first current (e.g., the I PT  current) from the power tracking amplifier and provide a second current (e.g., the I SW  current) for the power supply voltage based on the sensed first current. The boost converter (e.g., boost converter  830  in  FIGS.  8  and  9   ) may receive a battery voltage and provide a boosted voltage for the power tracking amplifier. The power tracking amplifier may operate based on the boosted voltage or the battery voltage. 
       FIG.  10    shows a design of a process  1000  for generating a power supply voltage with power tracking. A power tracking signal may be determined based on I and Q components of a plurality of transmit signals being sent simultaneously (block  1012 ). In one design of block  1012 , an overall power of the plurality of transmit signals may be determined based on the I and Q components of the plurality of transmit signals. The power tracking signal may then be determined based on the overall power of the plurality of transmit signals, e.g., as shown in equation (1). In another design of block  1012 , the power of each transmit signal may be determined based on the I and Q components of the transmit signal. The power tracking signal may then be determined based on the powers of the plurality of transmit signals, e.g., as shown in equation (2). 
     A power supply voltage may be generated based on the power tracking signal (block  1014 ). In one design, the power supply voltage may be generated with a amplifier (e.g., amplifier  810  in  FIG.  9   ) that tracks the power tracking signal. The power supply voltage may also be generated based on a switcher and/or a boost converter. 
     A modulated RF signal may be generated based on the I and Q components of the plurality of transmit signals (block  1016 ). In one design, I and Q components of each transmit signal may be upconverted to obtain a corresponding upconverted RF signal. A plurality of upconverted RF signals for the plurality of transmit signals may then be summed to obtain the modulated RF signal, e.g., as shown in  FIG.  5   . In another design, a modulated IF signal may be generated based on the I and Q components of the plurality of transmit signals, e.g., as shown in  FIG.  6   . The modulated IF signal may then be upconverted to obtain the modulated RF signal. In any case, the modulated RF signal may be amplified with a PA (e.g., PA  560  in  FIGS.  5  and  6   ) operating based on the power supply voltage to obtain an output RF signal (block  1018 ). 
     The power tracker and power supply generator described herein may be implemented on an IC, an analog IC, an RFIC, a mixed-signal IC, an ASIC, a printed circuit board (PCB), an electronic device, etc. The power tracker and power supply generator may also be fabricated with various IC process technologies such as complementary metal oxide semiconductor (CMOS), NMOS, PMOS, bipolar junction transistor (BJT), bipolar-CMOS (BiCMOS), silicon germanium (SiGe), gallium arsenide (GaAs), etc. 
     An apparatus implementing the power tracker and/or power supply generator described herein may be a stand-alone device or may be part of a larger device. A device may be (i) a stand-alone IC, (ii) a set of one or more ICs that may include memory ICs for storing data and/or instructions, (iii) an RFIC such as an RF receiver (RFR) or an RF transmitter/receiver (RTR), (iv) an ASIC such as a mobile station modem (MSM), (v) a module that may be embedded within other devices, (vi) a receiver, cellular phone, wireless device, handset, or mobile unit, (vii) etc. 
     In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.