Multiband envelope tracking power amplifier

An apparatus relates generally to multiband power modulation. In such an apparatus, there is a first power supply and a second power supply. The first power supply and the second power supply are each narrow-banded. A digital predistorter is coupled to provide separate bands of a modulation signal for respective input of a first band of the bands to the first power supply and a second band of the bands to the second power supply. The first power supply generates a first power at a first center frequency. The second power supply generates a second power at least at a second center frequency spaced apart from the first center frequency for a wide-band configuration. The second power output from the second power supply is coupled to the first power output from the first power supply to provide a multiband power modulation output.

FIELD OF THE INVENTION

The following description relates to communications. More particularly, the following description relates to a multiband envelope tracking power amplifier.

BACKGROUND

For two bands or carriers separated in frequency by a sufficient amount such that their in-band intermodulation distortion (“IMD”) does not overlap means that a high sample rate or a large bandwidth is used to provide a cavity filter response enveloping both bands as well as both in-band IMD terms. In the past, systems may employ envelope tracking (“ET”) by a single power supply for feeding a drain current to a power amplifier to improve efficiency in such power amplifier for a single band. However, providing a single power supply with sufficient bandwidth to cover a large cavity filter response adds a substantial amount of cost. For example, bandwidth for drain modulation, such as for supplying a drain current to a power amplifier, generally is at least twice the instantaneous bandwidth (“IBW”) of a signal. Because of bandwidth demands in more recent communication systems, such demand has in some instances precluded use of envelope tracking in power provided to a power amplifier.

Others have used wide band switching power supplies to provide a drain current to a power amplifier for envelope tracking. Again, as bandwidth for such switching power supplies is at least twice total bandwidth of a signal, for instances with widely spaced carriers a high degree of complexity and cost is added to provide such switching power supplies. Furthermore, efficiency of such switching power supplies may be depressed for configurations with wide separation of two or more carriers. Thus, system efficiency is affected by efficiency of having a single switching power supply to provide envelope tracking, as well as reduced efficiency of a power amplifier provided with less efficient or closeness of envelope tracking by a drain current associated with widely separated carriers.

Accordingly, it would be useful and desirable to provide envelope tracking which overcomes one or more of the above-described limitations.

SUMMARY

An apparatus relates generally to a multiband envelope tracking power amplifier. In such an apparatus, there is a first power supply and a second power supply. The first power supply and the second power supply are each narrow-banded. A digital predistorter is coupled to provide separate bands of a modulation signal for respective input of a first band of the bands to the first power supply and a second band of the bands to the second power supply. The first power supply generates a first power at a first center frequency. The second power supply generates a second power at least at a second center frequency spaced apart from the first center frequency for a wide-band configuration. The second power output from the second power supply is coupled to the first power output from the first power supply to provide a multiband power modulation output.

Another apparatus relates generally to a multiband envelope tracking power amplifier. In such an apparatus, there is a first power supply, a second power supply, and a third power supply. The first power supply, the second power supply and the third power supply are each narrow-banded. A digital predistorter is coupled to provide separate bands of a modulation signal for corresponding inputs to the first power supply, the second power supply, and the third power supply. The first power supply generates a first power at a first center frequency. The second power supply generates a second power at a second center frequency spaced apart from the first center frequency. The third power supply generates a third power at a third center frequency spaced apart from both the first center frequency and the second center frequency for a wide-band configuration. The second power output from the second power supply and the third power output from the third power supply are each coupled to the first power output from the first power supply to provide a multiband power modulation output.

A method relates generally to operation of a multiband envelope tracking power amplifier. In such a method, a modulation signal is generated with a digital predistorter. A first band and a second band of the modulation signal are respectively provided to a first power supply and a second power supply. First power at a first center frequency is generated with the first power supply for envelope tracking responsive to the first band of the modulation signal. Second power at a second center frequency is generated with the second power supply for envelope tracking responsive to the second band of the modulation signal. The first power supply and the second power supply are each narrow-banded. The second center frequency is spaced apart from the first center frequency for a wide-band configuration. The second power is coupled to the first power to provide a multiband power modulation output.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide a more thorough description of the specific examples described herein. It should be apparent, however, to one skilled in the art, that one or more other examples and/or variations of these examples may be practiced without all the specific details given below. In other instances, well known features have not been described in detail so as not to obscure the description of the examples herein. For ease of illustration, the same number labels are used in different diagrams to refer to the same items; however, in alternative examples the items may be different.

Before describing the examples illustratively depicted in the several figures, a general introduction is provided to further understanding.

As described below in additional detail, a multiband power supply module is provided having a plurality of narrow band power supplies to collectively cover a wide-band configuration of multiple carriers. Each of these power supplies involves substantially less complexity than a single power supply, including without limitation a single switching power supply, spanning a comparable wide-band configuration. Furthermore, such collection of narrow band power supplies may produce outputs which are coupled to one another to provide drain modulation for a power amplifier, and such coupled outputs may provide a higher degree of accuracy of envelope tracking than drain modulation from a single switching power supply covering a comparable wide-band configuration.

With the above general understanding borne in mind, various configurations for a transmitter or a transmitter portion of a transceiver are generally described below.

Because one or more of the above-described examples are described herein using a particular type of IC, a detailed description of such an IC is provided below. However, it should be understood that other types of ICs may benefit from one or more of the techniques described herein.

Each programmable tile typically includes both programmable interconnect and programmable logic. The programmable interconnect typically includes a large number of interconnect lines of varying lengths interconnected by programmable interconnect points (“PIPs”). The programmable logic implements the logic of a user design using programmable elements that can include, for example, function generators, registers, arithmetic logic, and so forth.

Another type of PLD is the Complex Programmable Logic Device, or CPLD. A CPLD includes two or more “function blocks” connected together and to input/output (“I/O”) resources by an interconnect switch matrix. Each function block of the CPLD includes a two-level AND/OR structure similar to those used in Programmable Logic Arrays (“PLAs”) and Programmable Array Logic (“PAL”) devices. In CPLDs, configuration data is typically stored on-chip in non-volatile memory. In some CPLDs, configuration data is stored on-chip in non-volatile memory, then downloaded to volatile memory as part of an initial configuration (programming) sequence.

As noted above, advanced FPGAs can include several different types of programmable logic blocks in the array. For example,FIG. 1illustrates an FPGA architecture100that includes a large number of different programmable tiles including multi-gigabit transceivers (“MGTs”)101, configurable logic blocks (“CLBs”)102, random access memory blocks (“BRAMs”)103, input/output blocks (“IOBs”)104, configuration and clocking logic (“CONFIG/CLOCKS”)105, digital signal processing blocks (“DSPs”)106, specialized input/output blocks (“I/O”)107(e.g., configuration ports and clock ports), and other programmable logic108such as digital clock managers, analog-to-digital converters, system monitoring logic, and so forth. Some FPGAs also include dedicated processor blocks (“PROC”)110.

Some FPGAs utilizing the architecture illustrated inFIG. 1include additional logic blocks that disrupt the regular columnar structure making up a large part of the FPGA. The additional logic blocks can be programmable blocks and/or dedicated logic. For example, processor block110spans several columns of CLBs and BRAMs.

Before proceeding further with the detailed description, a more complete description of a problem is provided by an example for purposes of clarity with reference toFIG. 2A.FIG. 2Ais a graphical diagram depicting an exemplary conventional multiband base station RF output200. Cavity filter response210is for a bandwidth that encompasses two operating bands, as generally indicated as carrier stack201and carrier stack202in an RF band. In this example, each operating band205and206respectively of carrier stacks201and202is 20 MHz. These non-overlapping operating bands205and206are separated by a difference frequency207, which may generally be regarded as a guard bandwidth or guard band207. In this example, guard band207from center frequency251-to-center frequency252respectively of carrier stack201and carrier stack202is 120 MHz, which is substantially larger than the bandwidth of each of operating bands205and206. It should be understood that these and other numerical examples used herein are for purposes of clarity and not limitation, and accordingly these or other bandwidths may be used unless expressly indicated otherwise.

FIG. 2Bis a block diagram depicting an exemplary conventional envelope tracking power amplifier (“ET PA”)220. ET PA220includes an amplitude detector221, an amplitude amplifier223, a delay line224, and a linear mode power amplifier (“PA”)225. An RF input222is provided as a signal input to amplitude detector221and as a signal input to delay line224. Bandwidth of amplitude detector determines whether ET PA220responds to a long-term average of an envelope (AET or Auxiliary Envelope Tracking) or instantaneous variations in an envelope (WBET or Wide-Bandwidth Envelope Tracking). Detected amplitude of RF input222output from amplitude detector221is provided as a signal input to amplitude amplifier223. An amplified detected amplitude signal227output from amplitude amplifier223is provided as a control signal to a linear mode PA225, which may for example be a class A, AB, or B amplifier. Output from delay line224is provided as a delayed version of RF input222, namely delayed RF input228, as a signal input to linear mode PA225. Timing of input of delayed RF input228to linear mode PA225corresponds to timing of application of amplitude signal227for envelope tracking by linear mode PA225, as is known, for outputting an RF output226from linear mode PA225. However, a significant challenge in construction of an ET PA225is providing a high efficiency wideband power supply for amplitude amplifier223for such envelope tracking.

As described below in additional detail, by processing power by band, total bandwidth provided by a power supply module may be at least substantially reduced. Moreover, by processing individual carriers where occupied bandwidth (“BW”) therefor is small compared to a total bandwidth, a more economical result may be obtained by processing power each individual band. For example, in some multi-carrier GSM (“MC-GSM”) systems, for example where a carrier BW is approximately 200 KHz and two or more carriers are spaced 1 MHz or more from each other on a regular channelization scheme, a significant savings may be obtained by processing each power band separately, as described below in additional detail, and performance advantages by envelope tracking for providing a drain current to a power amplifier may be obtained. MC-GSM is just one example, and other communication protocols may be used. However, continuing the MC-GSM example, there may be six carriers in 30 MHz of bandwidth, where occupied bandwidth is 6*200 KHz=1.2 MHz. This may be only 4% of the total bandwidth for such MC-GSM example.

Even though each of the following processing steps may be implemented in an FPGA, such description is not limited to implementation in an FPGA. Along those lines, each of the following digital predistorters may be implemented in any IC, including without limitation another type of SoC, an ASIC, an ASSP, or the like, whether a monolithic IC or an SiP.

FIG. 3is a graphical diagram depicting an exemplary linear multiband power supply response300for envelope tracking. Such envelope tracking may be for a wide band multiband carrier configuration. By wide-band multiband carrier configuration or wide-band configuration, it is generally meant having at least two center frequencies of at least two corresponding bands or carrier stack bandwidths widely spaced apart compared to each band's bandwidth. For two or more widely separated carriers, drain current power supply power spectral density (“PSD”)301for drain modulation may have a plurality of power bands spaced apart from one another. For purposes of clarity by way of example and not limitation, it shall be assumed that there are two carriers or bands; however, in other configurations there may be more than two bands. As generally indicated along a horizontal axis399for frequency, a power band or power311may be at a center frequency321of 0 Hz, namely centered at DC, and powers312and313may be centered at different carrier difference frequencies corresponding to the second order intermodulation products of each composite signal to be transmitted in operating bands205and206. Returning toFIG. 2, a carrier difference frequency207is such a carrier difference frequency.

Powers312and313are respectively centered at plus and minus carrier difference frequencies322and323on either side of center frequency321. Bandwidths331through333respectively of each frequency zone of powers311through313are equal to or approximately equal to twice the maximum bandwidth of signals in each band of such bands.

Drain modulation may be provided as a sum of two or more different sources that each have a bandwidth equal to or approximately equal to twice the maximum bandwidth of signals in each band of such bands. In this example, power311is provided from a “low frequency” power supply, and powers312and313are provided from a “high frequency” power supply.

FIG. 4is a block diagram depicting an exemplary portion of a transmitter400. Transmitter400includes a digital predistorter (“DPD”)420, a multiband power supply module430, a digital-to-analog converter440, an RF modulator450, and a power amplifier410. Power amplifier410, DPD420, and multiband power supply module430may be components of a multiband envelope tracking power amplifier. A digital filter bank (“DFB”)421, which may be incorporated into DPD420, or separate therefrom, may be included, as described below in additional detail. For purposes of clarity by way of example and not limitation, it shall be assumed that DFB421is external to DPD420. Some known components of transmitter400have not been illustratively depicted for purposes of clarity and not limitation.

DPD420, DFB421, and/or DAC440may be incorporated into a same IC or multiple ICs, such as with one or more ASICs, ASSPs, and/or FPGAs. For example, for an FPGA implementation, multiple DSP blocks or slices106of FPGA100ofFIG. 1may be used for implementation of DPD420, DFB,421, and/or DAC440.

FIG. 5is a block diagram depicting an exemplary multiband power supply module430. Multiband power supply module430includes a “low frequency” or “LF” power supply (“PS”)501and a “high frequency” or “HF” power supply502. Multiband power supply module430may include more than two power supplies, such as power supplies501through503for example to handle more than two bands. Along those lines, power supplies501to503may be coupled to respectively receive an input modulation signal402-N on an input side and commonly inductively coupled on an output side to provide a drain modulation signal405. Power supplies501through503may respectively be coupled to windings521through523. Transformer windings of the composite transformer with windings521through523may be respectively coupled to receive output powers or power bands511through513, and transformer windings521through523may be proximately positioned with respect to one another to inductively couple output powers511through513to provide drain modulation signal405, as an analog signal. Power supplies501through503are switching power supplies, and these high frequency power supplies may be implemented as a class E, F or other high efficiency RF power source. Furthermore, power supplies501through503each only cover a narrow band. By narrow band or narrow-banded, it is generally meant a band or carrier stack signal bandwidth that is 40 MHz or less in bandwidth. For purposes of clarity, it shall be assumed that only two bands are to be processed, and thus only power supplies501and502may be present. However, from the following description, it should be understood that more than two bands may be processed.

With simultaneous reference toFIGS. 3 to 5, transmitter400is further described. A DPD420may be coupled to receive input samples signal401. More particularly, input samples signal401may be two or more different input signals for two or more corresponding different bands for a wide-band configuration. DPD420may be configured to provide a modulation signal402output and a digital predistorted signal403, which is a digital predistorted version of input samples signal401as known.

DFB421may be coupled on an input side to receive modulation signal402to parse such signal into separate bands. Along those lines, DFB421may include a plurality of digital filters422-N, for N an integer number of such bands or power supplies. Digital filters422-N may be commonly coupled to receive modulation signal402to respectively provide N band specific modulation signals thereof, namely corresponding modulation signals402-N. Power supply501and power supply502of multiband power supply module430may be respectively coupled on an input side for receiving a modulation signal of modulation signals402-N from DFB421. Optionally, modulation signals402-N may be provided to corresponding optional DACs504-N of multiband power supply module430for conversion of modulation signals402-N from respective band specific digital signals to corresponding analog versions thereof for respective input to power supplies501and502. Thus, for example, band specific digital modulation signals402-1and402-2for separate bands, such as an LF band and an HF band, may be respectively input to optional DACs504-1and504-2to provide corresponding analog modulation signals402-1and402-2to HF PS502and LF PS501. However, for purposes of clarity by way of example and not limitation, it shall be assumed that power supplies501and502are each configured to receive a respective input digital signal and provide a corresponding analog power output signal; even though, in other configurations each of power supplies501and502may be configured to receive an analog input signal. For purposes of clarity and not limitation, modulation signal402is generally described below as being provided to multiband power supply module430with the understanding that such modulation signal402may be represented as band specific modulation signals402-N output from DFB421.

Power supply501is configured to generate a power511at a center frequency for a first narrow band. As power supply501is a “low frequency” power supply as between power supplies501and502, such center frequency may be center frequency321. Power supply502is configured to generate a power512at another center frequency therefor for a second narrow band, which may or may not be equal in bandwidth to such first narrow band. As power supply502is a “high frequency” power supply as between power supplies501and502, such other center frequency may be center frequency322or323. At least one narrow band centered at either of center frequency322or323may be produced by power supply502. Thus, each of power supplies501and502is narrow banded, though collectively power supplies501and502may support a wide-band configuration.

Again, center frequency322or323is spaced apart from center frequency321. Center frequency321, in addition to being a center frequency of a narrow power band of power511, may be considered to be at an overall center of a spectral distribution of power from multiband power supply module430. Center frequencies322and323, which are effectively frequency negatives of one another and so both may be generated from a same source, are center frequencies with respect to their corresponding narrow power bands of output power512.

Power512output from power supply502may be inductively coupled to power511output from power supply501to provide a multiband power modulation output, which may be drain modulation405. Drain modulation405may have a linear multiband power supply response300for envelope tracking of each band of input samples signal401. More particularly, drain modulation405provides a modulation associated with modulation signal402and thus may be for envelope tracking of an RF analog signal404input to PA410, where such RF analog signal404is an analog version of digital predistorted signal403after passing through DAC440. Such analog signal output from DAC440may be input to a modulator450to produce an RF analog signal404. An amplified version, namely transmission signal406, of RF analog signal404may be provided as a power modulated signal responsive to drain modulation405. In other words, power amplifier410envelope tracks RF analog signal404using drain modulation405to provide transmission signal406, which envelope tracking may improve efficiency of power amplifier410in amplifying RF analog signal404to provide transmission signal406. It should further be appreciated that such envelope tracking is for each of a plurality of bands of RF analog signal404.

Drain modulation405may be a drain current. Power amplifier410may be coupled to receive such drain current to a supply port444of power amplifier410for envelope tracking of RF input404to power amplifier410. Generally, power amplifier410may be coupled to receive an analog signal associated with a converted form of a digital predistorted signal output from DPD420and an analog multiband power modulation signal to envelope track such analog signal input.

Power supply501in this example provides power511at DC for center frequency321. Power supply501may have a supply bandwidth331of at least twice a maximum bandwidth of a largest signal bandwidth of signals in a band205of carrier stack201, which is a narrow band as compared with a wide-band configuration of multiple bands. Again, carrier signal or stack201is one of a plurality of carrier signals, such as for example carrier signals201and202, for multiband power modulation output.

Power supply502in this example provides a tone with power512at a difference frequency, where such difference frequency is a difference as between center frequency321and either of center frequencies332and333. Power supply502may have a supply bandwidth332and a negative equivalent supply bandwidth323, each of which is a narrow band as compared with a wide-band configuration of multiple carriers. Each such supply bandwidth332and333may be at least twice a maximum bandwidth of a largest signal bandwidth of signals in a band206of carrier stack202. In this example, power supply501has a supply bandwidth331which is equal in width to each of supply bandwidths332and333of power supply502. However, in other configurations, supply bandwidths of power supplies501and502may be different from one another.

If there were a third band or carrier in the above example, then power supplies501through503may be used in multiband power supply module430. In such a configuration, a single DPD420may be commonly coupled to provide a modulation signal402for input to each of such power supplies501through503. Power supplies501and502may be for generating respective narrow-banded powers511and512at corresponding spaced apart center frequencies, as previously described, and additionally power supply503may be for generating a narrow-banded power513at yet another center frequency spaced apart from each of center frequencies321through333. Again, powers511through513respectively from power supplies501through503may be commonly inductively coupled to provide a multiband power modulation output, such as a drain modulation405, to support a wide-band configuration for envelope tracking by a power amplifier410, as previously described. Such power supply503may additionally provide another tone with power513at another difference frequency, where such other difference frequency is between center frequency321and either a plus or minus center frequency of a narrow band of power513.

Along the above lines, if bandwidth of a band or bands is too wide for the frequency response of a power supply, then such band or bands may be subdivided or further subdivided, and power supplies may be added corresponding to each additional band, with each such power supply respectively providing operational power in each band.

FIG. 6is a flow diagram depicting an exemplary power amplifier modulation flow600. Power amplifier modulation flow600is further described with simultaneous reference toFIGS. 3 through 6.

At610, a multiband input for a wide-band configuration of carriers is obtained, such as input samples signal401for example. A modulation path601, which includes operations at621through626may be performed in parallel with a signal processing path602, which includes operations at611through613.

At621, a modulation signal402is generated with a DPD420. In parallel with operation621, at611such DPD420outputs a digital predistorted signal403. At612from611, such digital predistorted signal403may be converted to an RF analog signal404by DAC440and modulator450. Optionally, DPD420may additionally modify an envelope tracking signal, such as a predistorted version of modulation signal402for example, to effectively predistort power supply signals output by power supplies of multiband power supply module430.

At622from621, such modulation signal402may be provided to narrow-banded power supplies501and502of multiband power supply module430. At623from622, power511may be generated by power supply501at a center frequency321of a narrow band for envelope tracking responsive to modulation signal402. In other words, power511envelops and tracks analog signal404for a narrow band centered at center frequency321. Likewise, at624from622and in parallel with623, power512may be generated by power supply502at least at one of center frequencies322and323for envelope tracking responsive to modulation signal402. In other words, power512envelops and tracks analog signal404for a narrow band centered at center frequency322and another frequency band centered at frequency323. Center frequency321is spaced apart from center frequency322and center frequency323at least such that associated bands do not overlap with one another for providing a wide-band configuration. Furthermore, center frequency321may be spaced-apart from center frequency322and center frequency323such that IMD associated with bands of such center frequencies do not overlap with one another for such wide-band configuration. Center frequencies322and323may be the same frequency though with opposite signs. From623and624, at625power512may be coupled, such as inductively coupled for example, to power511to provide a multiband power modulation output, such as drain modulation405for example. At626, such multiband power modulation output may be supplied or otherwise input to a supply port444of power amplifier410.

At613from612, such RF analog signal404may be input to power amplifier410to obtain an amplified version of such analog signal404which is power modulated with such multiband power modulation output obtained by power amplifier410at626. In other words for example, analog signal404is envelope tracked for each of a plurality of bands of analog signal404using drain modulation405supplied at supply port444to increase efficiency of operation of power amplifier410for producing such an amplified version of analog signal404. Thus, in addition to be amplified, analog signal404may be power modulated with drain modulation405to more efficiently provide transmission signal406. At630, transmission signal406may be transmitted after having been power modulated with such multiband power modulation output obtained at626.

While the foregoing describes exemplary apparatus(es) and/or method(s), other and further examples in accordance with the one or more aspects described herein may be devised without departing from the scope hereof, which is determined by the claims that follow and equivalents thereof. Claims listing steps do not imply any order of the steps. Trademarks are the property of their respective owners.