WO2020206246A1

WO2020206246A1 - DIGITAL ENVELOPE TRACKER FOR mmWAVE SYMBOL POWER TRACKING AND DIGITAL ENVELOPE TRACKER FOR MULTIPLE-TX CHANNELS WITH SHARED-RESOURCE VOLTAGE REGULATOR

Info

Publication number: WO2020206246A1
Application number: PCT/US2020/026569
Authority: WO
Inventors: Stephan Henzler; Christian Kranz; Otto Schumacher; Bernhard Sogl; Alexander Belitzer; Holger Wenske; Andreas Langer; Thomas Eichler
Original assignee: Apple Inc.
Priority date: 2019-04-03
Filing date: 2020-04-03
Publication date: 2020-10-08

Abstract

Systems, methods, and circuitries are described for generating an envelope tracking supply voltage for a power amplifier. In one example, a method includes: generating a level select signal based on a transmit signal indicative of a baseband transmit signal; regulating the tracking supply voltage based on a source voltage, a feedback signal related to the tracking supply voltage, and the level select signal, wherein the tracking supply voltage is carried in a supply line of the power amplifier; and selectively disposing one or more pre-charged capacitors in a parallel signal path with respect to the power amplifier supply line, to modulate the tracking supply voltage based on the level select signal.

Description

DIGITAL ENVELOPE TRACKER FOR mmWAVE SYMBOL POWER TRACKING AND DIGITAL ENVELOPE TRACKER FOR MULTIPLE-TX CHANNELS WITH SHARED-RESOURCE VOLTAGE REGULATOR

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to US Provisional Patent Application Number 62/828,633 filed on April 3, 2019, entitled“DIGITAL ENVELOPE TRACKER FOR MULTIPLE-TX CHANNELS WITH SHARED-RESOURCE VOLTAGE REGULATOR AND SLIM SINGLE CHANNEL DIGITAL ENVELOPE TRACKER FOR mmWAVE SYMBOL POWER TRACKING,” which is incorporated herein by reference for all purposes.

BACKGROUND

[0002] Envelope tracking is a technique by which the bias or supply voltage (e.g., Vcc) and current of a power amplifier (PA) in a transmit chain is controlled based on the radio frequency (RF) signal envelope of the transmit signal being amplified by the power amplifier. The idea is to operate the power amplifier close to or slightly in compression and to lower the PA supply voltage when the instantaneous signal amplitude is low, thereby boosting the efficiency of the power amplifier and its supply generation.

Further, envelope tracking improves the linearity of the power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] FIG. 1 is a block diagram of an exemplary transmitter architecture that includes a digital envelope tracking system for a power amplifier, in accordance with various aspects described.

[0004] FIG. 1 A illustrates an exemplary mapping of an envelope of an RF transmit signal to tracking supply voltages as performed by the system of FIG. 1 .

[0005] FIG. 2 is a block diagram of an exemplary digital envelope tracking system that includes tracking supply voltage circuitry that includes a selector switch in power amplifier supply line. [0006] FIG. 3 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry that modulates the tracking supply voltage by adjusting a voltage across a capacitor in parallel with the power amplifier, in accordance with various aspects described.

[0007] FIG. 4 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[0008] FIG. 5 is a block diagram of an exemplary reconfigurable capacitor circuitry, in accordance with various aspects described.

[0009] FIG. 6 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00010] FIG. 7 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00011] FIG. 8 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00012] FIG. 9 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00013] FIG. 10 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00014] FIG. 1 1 is a block diagram of an exemplary digital envelope tracking system that includes reconfigurable capacitor circuitry, in accordance with various aspects described.

[00015] FIG. 12 is a flow diagram outlining an exemplary method for generating a tracking supply voltage for a power amplifier, in accordance with various aspects described. [00016] FIG. 13 is a block diagram of an exemplary digital envelope tracking system , in accordance with various aspects described.

[00017] FIG. 14 is a block diagram of the exemplary digital envelope tracking system of FIG. 13, that includes predistortion circuitry that predistorts a baseband transmit signal based on an estimated power amplifier supply voltage and current, in accordance with various aspects described.

[00018] FIG. 15 is a block diagram of one example of the digital envelope tracking system of FIG. 14, in accordance with various aspects described.

[00019] FIG. 16 is a block diagram of one example of the digital envelope tracking system of FIG. 14 including predistortion functions, in accordance with various aspects described.

DETAILED DESCRIPTION

[00020] The present disclosure will now be described with reference to the

attached figures, wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures and devices are not necessarily drawn to scale.

[00021] Some transmitters that employ envelope tracking techniques generate the supply voltage for the power amplifier using an analog control loop. Within the loop, the power amplifier supply voltage is sensed, compared to a target voltage that tracks the envelope of the signal being amplified, and the difference is used to steer a continuous actuator such as an amplifier to correct the power amplifier supply voltage. This analog- based envelope tracking solution suffers from several problems. For example, the realization of the analog control loop becomes difficult for increasing envelope signal bandwidth while maintaining reasonable system efficiency. Further, the alternating current (AC) signal path used to generate and control the supply voltage to be equal to the target voltage and the direct current (DC) signal path used to determine the target voltage are normally separated into two supply chains, which yields an unattractively large solution area on the printed circuit board (PCB). The analog control loop for supply voltage control is feasible low and medium carrier aggregation in the cellular context. For higher levels of carrier aggregation in cellular applications and for

WLAN/WiFi applications, the analog control loop solution does not scale.

[00022] Throughout this description, components that are exemplary versions of a same or analogous component are assigned reference characters having the same value for the last two digits while the initial digit(s) of reference characters are assigned based on the FIG. number in which they are first introduced.

[00023] FIG. 1 illustrates an exemplary transmitter architecture 100 that includes a transmitter chain 1 10 and an exemplary feedforward digital envelope tracking system 120. The transmitter chain 1 10 processes a digital baseband transmit signal to generate an RF transmit signal. The RF transmit signal is amplified by a PA to generate an uplink signal that is transmitted by an antenna or cable (not shown). The exemplary transmit chain 1 10 includes transmit digital processing circuitry 1 15, which operates on a digital baseband transmit signal to convert the signal into amplitude and phase components. The amplitude and phase components are converted into the analog RF transmit signal by transmit analog processing circuitry 1 18. The transmit digital processing circuitry 1 15 may also include digital pre-distortion circuitry (DPD) (see FIGs.12-17) that operates to pre-distort the transmit data to account for non-linearities in the analog processing circuitry 1 15, the envelope tracking system 120, and the PA.

[00024] The envelope tracking system 120 includes envelope circuitry 125 to generate a level select signal 127, which is used to control a tracking supply voltage circuitry 130 to supply a selected or“tracking” supply voltage to the PA. The envelope circuitry 125 samples the baseband transmit signal to project an envelope of the RF transmit signal that will be amplified by the PA to generate the uplink signal. FIG. 1 A illustrates an exemplary RF transmit signal and a projected envelope that bounds the RF transmit signal. The envelope circuitry 125 determines the envelope of the RF transmit signal and generates the level select signal 127 to control the tracking supply voltage circuitry 130 to provide a PA supply voltage that closely matches the envelope.

[00025] In one example, the target voltage signal generated by the envelope circuitry includes voltage domain information that may be a control word, a bus link, or voltage that communicates the desired supply voltage or a selection setting from the plurality of voltage levels to the tracking supply voltage circuitry 130. In addition, the target voltage signal may include time domain information that communicates when or a time during which the desired supply voltage should be provided to the PA. For example, the level select signal 127 may specify voltage domain information Vs2 and time domain information stn to cause the tracking supply voltage circuitry 130 to change the PA supply voltage from Vsi to Vs2 at the switching time stn as shown in FIG. 1 A. The time domain information may also include a duration of time until a next voltage level and switching time will be communicated.

[00026] In order to reduce noise, the envelope circuitry 125 may determine a switching time that will coincide with a relatively low RF transmit signal. In one example,“relatively low” means that the RF transmit signal is lower or equal to a predetermined threshold. In an alternate implementation the envelope circuitry 125 may choose a switching time when the instantaneous envelope signal is low, (i.e., when the instantaneous signal power is low). In this case the next selected voltage is an upper bound of all instantaneous target voltages which occur until another low phase is reached. At the next low phase another voltage is selected and so on. Thus the switching time may be selected based on either a zero crossing of the RF signal or a close to zero condition of the envelope signal.

[00027] It can be seen in FIG. 1 that the there is no control loop in the generation of the PA supply voltage. The output PA supply voltage is delivered from pure voltage sources instead of a regulated stage. Thus the PA supply voltage may be more accurate and less load dependent especially at high frequencies and during fast switching. The illustrated tracking supply voltage circuitry 130 separates the analog task of voltage level generation from the control of voltage selection, which is digital.

[00028] It can be seen in FIG. 1 A that the PA supply voltage provided by the tracking supply voltage circuitry 130 varies in a stepwise fashion to approximate the envelope. While analog envelope tracking PA power supply solutions may also be able to closely follow the envelope, recall that analog solutions have limited applicability in high frequency applications and present the other drawbacks discussed above. The feed forward digital envelope tracking provides effective envelope tracking in a manner that scales for higher frequencies and presents a small package size. [00029] The tracking supply voltage circuitry 130 is capable of producing any number of voltage levels. To leverage this feature the tracking supply voltage circuitry 130 may receive transmitter operation conditions or parameters that include, for example, a transmit power level, a mode of operation, and or an estimated or measured saturation level of the power amplifier. The tracking supply voltage circuitry 130 may use this information to control or scale the voltage levels that are produced by the tracking supply voltage circuitry 130. For example, if the transmit power level is relatively small, the set of voltages for selection may span a smaller range so that the PA supply voltage can more closely follow the envelope or the number of voltages for selection may be reduced to a smaller set. In contrast, if the transmit power level is large, the set of voltages for selection may span a larger range to cover the variation in the envelope.

[00030] FIG. 2 illustrates an example transmitter 200 with a digital envelope tracking system 220 that includes envelope circuitry 125 and a tracking supply voltage circuitry 230 that includes a selector switch 290 in a supply line 145 of the power amplifier. The supply voltage circuitry 230 includes multi-level voltage generation circuitry 270 and the selector switch 290. The multi-level voltage generation circuitry 270 is an analog circuit that generates a regulated output voltage from the battery voltage VBAT. The multi-level voltage generation circuitry 270 generates a plurality of output voltages (e.g., Vsi , ..., Vs4) having differing levels.

[00031] The selector switch 290 is a switching circuit that connects one of these output voltages to the output of the tracking supply voltage circuitry 230.

The output of the tracking supply voltage circuitry 230 (i.e. , the PA supply voltage) is connected to a supply input (not shown) of the PA. One

disadvantage to the tracking supply voltage circuitry 230 of FIG. 2 is that the switching of the PA supply voltage occurs in the supply line, causing voltage droop, losses, transients, and other interference that degrades the quality of the tracking supply voltage and also preventing ultra-fast modulation of the PA supply voltage.

[00032] In digital envelope tracker for 5G and mmWave applications where a small bill of material (BOM) is key and no multiple parallel channels are needed it is important to provide an ultra-fast modulation of the PA supply voltage. For this reason neither the digital envelope tracking system described in FIG. 2, nor symbol power tracking is used in mmWave so far. Another disadvantage of the digital envelope tracking system described in FIG. 2 is the equidistant spacing of the discrete voltage levels generated by the multi-level voltage generation circuitry 270. Although lower levels are seldom used (or even never used) they are generated in order to get reasonably low spacing between the upper levels. Further, there is a large overhead for the additional DCDC converter needed for time interleaving and/or pre-charging of the stages of capacitors in the multi-level voltage generation circuitry 270.

[00033] Described herein are systems, methods, and circuitries in which the supply line series switching-based approach to envelope tracking illustrated in FIG. 2 is replaced with reconfigurable capacitor circuitry that moves the PA supply voltage switching or modulation to a parallel path with respect to the supply line, which significantly reduces voltage droop, losses, transients, distortion, and settling time for the supply voltage.

[00034] FIG. 3 illustrates an example transmitter 300 that includes digital envelope tracking system 320. Tracking supply voltage circuitry 330 includes a“slow” voltage regulator circuitry 340, which may be a buck converter, (optionally supplied by a charge pump). The voltage regulator circuitry 340 is provided with the capability of quickly switching its output voltage between arbitrary but discrete levels by a reconfigurable capacitor circuitry 350 coupled in parallel with the supply line.

[00035] The example reconfigurable capacitor circuitry 350 includes charge provisioning circuitry 360 and capacitor circuitry 380. The reconfigurable capacitor circuitry 350 is configured to selectively dispose one or more pre-charged capacitors of the capacitor circuitry 380 (which are pre-charged by the charge provisioning circuitry 360) in a parallel signal path with respect to the power amplifier supply line to modulate the tracking supply voltage based on the level select signal 127. This is conceptually similar to providing a reconfigurable bulk capacitor for a DCDC voltage regulator by swapping out the DCDC bulk cap with appropriately pre-charged capacitors. As will described in the following variations, pre-charging of the capacitors may be achieved by charge pumps, low dropout regulators (LDOs), or DCDC converters. The capacitors of the capacitor circuitry 380 can be fully swapped out or only partially. In one example, a two point modulation scheme keeps the slow voltage regulator control loop calm despite abrupt and fast modulation of the PA supply voltage.

[00036] FIG. 4 illustrates an exemplary“slim” envelope tracking system that includes voltage regulator circuitry 440 and a reconfigurable capacitor circuitry 450. The voltage regulator circuitry 440 (e.g., buck converter) includes control circuitry, step-down circuitry 447, and, optionally, a regulator charge pump circuitry 445. The step-down circuitry 447 includes switches that charge and discharge an inductor 448 to regulate the tracking supply voltage. The controller 443 controls the switches in the step-down circuitry 447 based on the level select signal N and regulated voltage feedback to maintain a desired target voltage. The regulator charge pump circuitry 445 (optional) generates a voltage that is always high enough to run the step-down circuitry 447 in buck mode. In one example, the regulator charge pump circuitry includes a boost charge pump that generates an internal supply voltage equal to or larger than the battery voltage.

[00037] Capacitor circuitry 480 includes a main bulk capacitor 483 (that is charged by the voltage regulator circuitry) and a tracking capacitor arrangement 485. In this example, the tracking supply voltage modulation by capacitor switching is done at the ground plate of the main bulk capacitor 483. This may be advantageous because of the possibility of using lower voltage rated switches in charge provisioning circuitry 460.

The charge provisioning circuitry 460 configures the tracking capacitor arrangement 485 to provide a tracking voltage VTRK based on the level select signal N 1 27. The charged tracking capacitor arrangement 485 lifts the ground node of the main capacitor 483 such that the tracking supply voltage can be changed quickly without requiring a fast response of the voltage regulator circuitry 440. The switches are located inside the capacitor circuitry and not in series with the main current path toward the power amplifier.

[00038] Also illustrated in FIG. 4 is an optional differential amplifier A that may be coupled to the supply line to compensate for ripples in the tracking supply voltage. The differential amplifier A has as inputs the output the voltage regulator circuitry 440 and an analog target tracking supply voltage which corresponds to the envelope of the transmit signal (see, e.g., FIG. 1 A). The differential amplifier provides a corrective current parallel to the current provided by the voltage regulator to set the PA supply voltage or some frequency components of the PA supply voltage according to a target derived from the envelope of the transmit signal,

[00039] FIG. 5 illustrates an example reconfigurable capacitor circuitry 540. A tracking capacitor arrangement includes a first capacitor 585A and a second capacitor 585B. Charge provisioning circuitry includes a set of switches 561 -566. A controller 541 controls the switches, based on the level select signal 127, to arrange the capacitors 585A, 585B into one of four arrangements. The switches are also used to pre-charge the capacitors 585A, 585B to a charging voltage. The switches can be controlled to arrange the capacitors such that there is a short circuit path around the capacitors (e.g., by closing switch 566). Switch 565 can be closed to connect the capacitor 585A to a ground node of a main capacitor VMAIN. Switches 563, 562, 564 can be closed to connect capacitor 585B and capacitor 585A in parallel with one another to the ground node of the main capacitor. Switches 563 and 564 can be closed to connect capacitor 585B and capacitor 585A in series to the ground node of the main capacitor.

In this manner, the reconfigurable capacitor circuitry can provide a tracking voltage VTRK of the four voltages: 0, 0.5VAUX, 1 .OVAUX or 2.0VAUX. This means that the tracking supply voltage at the PA is one of VMAIN, VMAIN+0.5VAUX, VMAIN+VAUX, VMAIN+2. OVAUX where VMAIN is the voltage across the main capacitor 583 which is defined by the DCDC control loop.

[00040] In example of FIG. 5, the reconfigurable capacitor circuitry 540 has the optional property that all capacitors 585A, 585B in the tracking capacitor arrangement are always charged. This means that the reconfigurable capacitor circuitry 540 can immediately provide any of the output voltages without re-charging the capacitors. This property provides for efficient operation and enables fast and frequent switching between voltage levels.

[00041] In one example, the tracking capacitor arrangement includes a set of capacitors arranged to be charged to a capacitor voltage corresponding to M/N times the charging voltage. A set of switches is coupled between the capacitors in the set of capacitors. The switches are configurable to connect the capacitors in the set of capacitors into a plurality of linear combinations of the capacitor voltage. A control circuitry is configured to control the set of switches based on the level select signal. In one example, M and N are integers. In one example, the capacitor voltage is

substantially constant.

[00042] FIG. 6 illustrates an example envelope tracking system in which two point modulation is employed in order to keep the regulation quiet while switching the PA supply voltage. An estimated tracking voltage VTRK that estimates the voltage across the tracking capacitor arrangement 685 (e.g., the modulation of the output of the voltage regulator circuitry) can be subtracted from the feedback signal again to determine a setpoint for control circuitry 643. In one example, the estimated VTRK is computed based on the level select signal N 129 multiplied by a voltage increment D between differing voltage levels provided by the reconfigurable capacitor circuitry. The voltage increment D is 0.5VAUX in FIG. 6.

[00043] As the voltage regulator circuitry keeps the voltage across the main capacitor 683 constant at the target voltage, the modulation or variation of VTRK translates directly into a variation of the PA supply voltage according to the level select signal 127. The voltage regulator circuitry will lock directly to this new voltage. Thus, the setpoint for the voltage regulation circuitry should follow the target envelope signal. This is achieved by the two point modulation.

[00044] FIG. 7 illustrates an alternative way to keep the modulation out of the control loop by using an instrumentation amplifier 787 to tap main capacitor 783 differentially for the feedback of the regulated voltage. In this manner, the difference between the regulated output voltage and tracking voltage is generated in an analog way.

[00045] As illustrated in FIG. 8, for good efficiency charge provisioning circuitry 860 can be supplied from the PA supply voltage itself. This makes the charge provisioning circuitry control a bit complicated because the charge provisioning circuitry has to take into account what the charge provisioning circuitry does itself and tune its pump factors accordingly.

[00046] The reconfigurable capacitor circuitry illustrated in FIGs. 4-8 includes a tracking capacitor arrangement to provide a modulated tracking voltage that is added to a main voltage across a main capacitor that remains relatively constant. This provides the advantage that it is that it is not necessary to have equal spacing between the differing levels of tracking supply voltage. In many instances, a lowest PA supply voltage in a range of possible envelope tracking voltages is not often used and it is desirable to having smaller granularity in tracking supply voltages nearer the top of the range. The lowest PA supply voltage can be maintained across the main capacitor whilst a set of smaller incremental voltage levels can be provided by the tracking capacitor arrangement.

[00047] FIG. 9 illustrates an alternative reconfigurable capacitor circuitry 950. In this example, the switching between discrete voltage levels is not done by pushing the ground node of a main capacitor (e.g., DCDC bulk capacitor) as in FIGs 4-8. Instead multiple“bulk capacitors” 987A, 987B (more than two may be used) are operated in a time interleaved manner by way of switches 955A, 955B. The bulk capacitor that is connected is regulated by the DCDC to the target voltage. The other capacitor(s) are kept isolated or actively charged by charge provisioning circuitry 987A or 987B to the respective other tracking supply voltage levels. When the supply voltage shall be changed from one level to another, the capacitors are swapped out by opening one of the switches 955A, 955B and closing the other. In one example, the charge

provisioning circuitry determines the desired charge level for the bulk capacitor 987 based on a target voltage signal related to a predicted tracking supply voltage. The target voltage signal is derived by a predictor looking at upcoming portions of the transmit signal.

[00048] The charge provisioning circuitry 960A, 960B can be directly supplied from the tracking supply voltage itself (as shown in FIG. 9) or from an additional auxiliary supply as shown in other figures. The setpoint of the voltage regulator circuitry should be changed together with the capacitor switching. This is the same 2-point modulation principle which has been previously discussed.

[00049] An example with two tracking supply voltage levels is shown in FIG. 10. Charge provisioning circuitries 1060A, 1060B supply themselves from the output. This reflects in the reciprocal pump factors. For more than two levels more capacitors 1087 and more charge provisioning circuitries 1060 may be added. This comes with an overhead in components but allows that all capacitors always retain their charge and no re-charging losses occur. Thus, the charge is maintained on the capacitors and the voltage across the capacitors does not change when the voltage regulator circuitry output is changed from one level to another level. The charge provisioning circuitry 1060 can charge one of the disconnected capacitors 1087 to an anticipated future tracking supply voltage.

[00050] In one example, the charge on the capacitors 1087 may be changed depending on the level select signal. This saves components because the two capacitors can be operated in a tick-tock fashion. However, each re-charging comes with power losses which means that this variant is less efficient. Alternatively two charge provisioning circuitries 1060 may be operated tick tock, but with such a structure that the voltage across the internal capacitors does not change. Yet another alternative example uses LDOs instead of charge pumps to set the voltage of the capacitors 1087 which are currently not connected to the voltage regulator.

[00051] A linear amplifier A may be added to the voltage regulator output (e.g., the tracking supply voltage) as shown in FIG. 1 1 . This amplifier reduces the voltage ripple of the regulator and so noise at the power amplifier.

[00052] It can be seen from the foregoing description that the described methods, circuitries, and systems provide a bill of material (BOM) optimized envelope tracker especially for symbol power tracking. A single buck mode only inductor magnetic switcher can be used with the coil shifted to lower current location. As compared to full blown digital envelope tracking the described envelope tracker is slim, including one coil and smaller charge pumps (compared to the switching based system of FIG. 2) and no voltage selection switch. Further, the lowest voltage level does not have to be equally spaced with all others.

[00053] Following are several flow diagrams outlining example methods. In this description and the appended claims, use of the term“determine” with reference to some entity (e.g., parameter, variable, and so on) in describing a method step or function is to be construed broadly. For example,“determine” is to be construed to encompass, for example, receiving and parsing a communication that encodes the entity or a value of an entity. “Determine” should be construed to encompass accessing and reading memory (e.g., lookup table, register, device memory, remote memory, and so on) that stores the entity or value for the entity. “Determine” should be construed to encompass computing or deriving the entity or value of the entity based on other quantities or entities. “Determine” should be construed to encompass any manner of deducing or identifying an entity or value of the entity. [00054] As used herein, the term identify when used with reference to some entity or value of an entity is to be construed broadly as encompassing any manner of determining the entity or value of the entity. For example, the term identify is to be construed to encompass, for example, receiving and parsing a communication that encodes the entity or a value of the entity. The term identify should be construed to encompass accessing and reading memory (e.g., device queue, lookup table, register, device memory, remote memory, and so on) that stores the entity or value for the entity.

[00055] As used herein, the term select when used with reference to some entity or value of an entity is to be construed broadly as encompassing any manner of determining the entity or value of the entity from amongst a plurality or range of possible choices. For example, the term select is to be construed to encompass accessing and reading memory (e.g., lookup table, register, device memory, remote memory, and so on) that stores the entities or values for the entity and returning one entity or entity value from amongst those stored. The term select is to be construed as applying one or more constraints or rules to an input set of parameters to determine an appropriate entity or entity value. The term select is to be construed as broadly encompassing any manner of choosing an entity based on one or more parameters or conditions.

[00056] FIG. 12 illustrates a flow diagram of an example method 1200 to generate a tracking supply voltage for a power amplifier. The method includes, at 1210, generating a level select signal based on a transmit signal indicative of a baseband transmit signal. The method includes, at 1220, regulating the tracking supply voltage based on a source voltage, a feedback signal related to the tracking supply voltage, and the level select signal, wherein the tracking supply voltage is carried in a supply line of the power amplifier. The method includes, at 1230, selectively disposing one or more pre-charged capacitors in a parallel signal path with respect to the power amplifier supply line, to modulate the tracking supply voltage based on the level select signal.

[00057] In one example, the level select signal is updated on a transmit symbol by symbol basis according to a power level of the upcoming symbol. In one example, the level select signal is updated at predefined time instances according to a power level of the TX signal in an upcoming transmission interval.

[00058] Multiple simultaneously active TX channels are important for transceiver products due to carrier aggregation. Traditionally, each TX chain has its own voltage regulator (analog envelope tracking). This comes with high silicon overhead, overhead of passive components and overhead in PCB area. Referring back to FIG. 2, the digital envelope tracking system 220 may be extended to allow multiple PAs to share a single multi-level voltage generation circuitry 230 by providing a selector switch 290 for each PA that receives the multiple derived output voltages from the shared multi-level voltage generation circuitry 270. The ability to share a single the shared multi-level voltage generation circuitry for all TX channels is an important advantage of digital envelope tracking. However, the shared multi-level voltage generation circuitry is not ideal and the level voltages may droop with the PA current. This causes an immanent cross-talk path between the different TX channels. This cross talk path deteriorates RF performance in case of dual TX operation or may disallow the sharing of the shared multi-level voltage generation circuitry at all.

[00059] Dual TX operation currently requires that the voltage levels used for digital envelope tracking are programmed to their maximum possible value. This compromises overall system efficiency in case of dual TX operation significantly. The reason is that today’s digital envelope tracking solutions work only with a static setting of the voltage regulator. The described systems, circuitries and methods extend digital pre-distortion such that it can work with a dynamically varying shared multi-level voltage generation circuitry and allow a more flexible and more optimum programming of the level voltages.

[00060] Modern dual TX operation with envelope tracking is based on the assumption that the voltage level variation caused by the respective other channel is small enough that sufficient RF performance is achieved. The resulting performance degradation is mitigated by increased capacitive decoupling.

[00061] The described systems, methods and circuitries determine an accurate estimation of the actual tracking supply voltages. This knowledge is used for digital pre distortion. This is important under low RB and dual-TX conditions where the assumption of constant levels is not justified. To this end, the dynamic behavior of the voltage regulator is modeled inside a digital pre-distortion block. An observer for the multi-level voltage generation circuitry and the remaining power train blocks (e.g. selector switch) is used to track the level voltages by means of model based control. The estimated power amplifier (PA) currents of all active PAs are summed up per level (which is momentarily connected). This estimated current is fed to the observer model. As a result the digital pre-distortion has access to the more accurate level voltages.

Therewith, it can increase the quality of the pre-distortion which leads to overall better linearity of the TX path(s).

[00062] An exemplary envelope tracking system is shown in FIG. 13. The envelope tracking system includes a multi-level voltage generation circuitry 270 that provides a set of discrete voltages. The multi-level voltage generation circuitry 270 includes one or several voltage regulators and one or several voltage splitters (see FIG. 15). The splitters derive voltages from the regulated voltages. The selector switch 290 can forward one of the voltages provided by the multi-level voltage generation circuitry 270 to the power amplifier via a supply filter 1395. In a digital pre-distortion block of the transceiver 1305 the selected level is also applied to a digital model of this supply filter 1310. The supply filter model 1310 estimates the instantaneous supply voltage of the power amplifier. This estimation is used as an input to an inverse gain model of the power amplifier 1330. Inverse model means that the model outputs the reciprocal gain of the power amplifier. After the transmit data is multiplied (e.g., using mixer 1339) by the reciprocal (estimated) gain, the transmit data then experiences a multiplication by the actual power amplifier gain, so that the gain cancels out and the transmit chain is equalized.

[00063] A high level view of an exemplary digital pre-distortion system that includes a multi-level voltage generation model circuitry 1480 and selector model circuitry 1495 is illustrated in FIG. 14. The models 1480, 1495 are receiving the same input signals as their analog counter parts 270, 290. Additionally they receive selected signals from the analog blocks which describe state variables and/or outputs of the analog multi-level voltage generation circuitry 270. These signals are used to form digital observers of the analog blocks. The output of the observer and associated models 1480, 1495 are then coupled to the original signal chain such that the input voltage levels to the filter mode 1410 which have been idealized so far are now replaced by actual estimations of the real tracking supply voltages.

[00064] Exemplary tracking supply voltage model circuitry (including components in heavy line) is illustrated in FIG. 15. This describes the analog power train components of the envelope tracker: A voltage regulator 1572 converts the battery voltage to a programmable voltage VREG. This voltage is divided by a voltage splitter 1574 into multiple voltages VLN which can be higher or lower than the voltage VREG. A set of level selectors 1590A-1590N accesses these voltage levels. In response to a voltage level selector signal (specific to each level selector) one level can be selected at a time and is forwarded to the power amplifier via a supply filter 1595. Alternatively, the model of the voltage splitter and the voltage selector can be replaced by a digital model of reconfigurable capacitor circuitry. In this manner an estimate of the tracking supply voltage that takes into consideration dynamic effects of the step down circuitry and the optional regulator charge pump circuitry can be generated and can be considered in the predistortion circuitry.

[00065] A voltage regulator model circuitry includes a digital observer of the voltage regulator 1582. The digital observer/model 1582 is a discrete time dynamic model of the dynamics of the voltage regulator 1572. The digital observer/model 1582 responds to set point changes and load current changes in approximately the same way as the analog voltage regulator 1572. As the model is never perfect correction terms are added to the model (observer). Therefore the output of the observer/model 1582 and the measured output of the voltage regulator 1572 (output of ADC) are compared and fed to an observer failure input of the observer/model 1582. A summing node 1589 can be also implicit in the dynamic model. In this case only the VREG~ measurement is fed to the error input.

[00066] The voltage regulator observer/model 1582 uses measurements of the actual battery voltage and of the current voltage of the voltage regulator 1572. Both can be brought to the observer via ADCs. The ADCs can be located either in a tracker IC or a transceiver IC.

[00067] A digital model of the voltage splitter 1584 is connected to the output of the voltage regulator observer/model 1582. The splitter model 1584 receives as inputs the voltage VREG and the estimated currents I LN~ taken from each level. In response the splitter model 1574 provides the estimated level voltages VLN~. Digital models of the selectors 1597 are used to calculate an estimate of the output voltage VOUT~ of the selectors 1590 in response to the estimated level voltages VLN~, level selector signals, and an estimate of the PA current. The estimate of the PA current is provided either by a PA model 1555 or by a PA model filtered through a supply filter model. Besides the output voltage VOUT the selector model 1597 provides also the estimated currents i_pa~ taken from each level. The current estimates of all selector models 1597 are summed up and provided to the voltage splitter model circuitry 1584 as total estimated current IVR~. The training module circuitry 1 51 5 represents a circuitry that calibrates the model parameters in the various models, e.g. the voltage splitter model circuitry 1584, and so on. Therefore one or more of the level voltages are monitored and compared to the model prediction. A search algorithm can tune the model parameters (e.g. RNk) until a good correlation is achieved. This coefficient tuning can be done once during system characterization, during production, in regular calibration intervals or permanently in the background.

[00068] Exemplary models of the different sub-blocks of FIG. 15 are given below. The models may be implemented discrete time.

[00069] An exemplary digital observer of voltage regulator model circuitry 1582:

dx / dt = Ax + B (VBAT-, IVR~ , target voltage)¹ + L(VREG - VREG~) x is the state vector of the voltage regulator observer

A is dynamic kernel of voltage regulator model/observer

B is stimulus coupling matrix to voltage regulator model

L is the observer matrix/function

VREG = C X + D (VBAT-, lvR~, target voltage)¹ EQ. 1

[00070] The dynamic model is discretized and can be implemented in digital.

Alternative models, e.g. more complicated non-linear models are possible as well.

[00071] An exemplary voltage splitter model circuitry 1584 can be a full difference equation model of the voltage splitter 1574. The splitter model 1584 can also be a simplified model, e.g:

[00072] An exemplary selector model 1597 calculates the output of the selector 1590 by the selected input voltage VIN minus the I R drop of the currently active path resistance times the actual output current. [00073] Referring to FIG. 16, the estimated output voltage VOUT of the selector models 1697 can serve as input to a supply filter model which is already present in many DPD systems. Some examples may combine the supply filter model with sub-models. A single combined model, e.g. a large set of differential equations may be possible as well. While the digital pre-distortion techniques described herein are with reference to the supply line switching based envelope tracking system of FIG. 2, a similar approach may be used to perform digital predistortion based on a modulated supply voltage generated by any digital envelope tracking system or analog envelop tracking system.

[00074] It can be seen from the foregoing description that digital pre-distortion can be performed in which voltage levels are not assumed constant but rather the real dynamic variation is approximated. This increases the quality of the digital pre-distortion. The output voltage of the voltage regulator can be dynamically changed with high flexibility and the instantaneous output voltage is considered in the pre-distortion properly. The output voltage of the voltage splitter and the level selector is dynamically considered which improves the quality of the pre-distortion further.

[00075] As utilized herein, terms“module”,“component,”“system,”“circuit,”

“element,”“slice,”“circuitry,” and the like are intended to refer to a set of one or more electronic components, a computer-related entity, hardware, software (e.g., in execution), and/or firmware. For example, circuitry or a similar term can be a processor, a process running on a processor, a controller, an object, an executable program, a storage device, and/or a computer with a processing device. By way of illustration, an application running on a server and the server can also be circuitry.

One or more circuits can reside within the same circuitry, and circuitry can be localized on one computer and/or distributed between two or more computers. A set of elements or a set of other circuits can be described herein, in which the term “set” can be interpreted as“one or more.”

[00076] As another example, circuitry or similar term can be an apparatus with specific functionality provided by mechanical parts operated by electric or electronic circuitry, in which the electric or electronic circuitry can be operated by a software application or a firmware application executed by one or more processors. The one or more processors can be internal or external to the apparatus and can execute at least a part of the software or firmware application. As yet another example, circuitry can be an apparatus that provides specific functionality through electronic components without mechanical parts; the electronic components can include one or more processors therein to execute executable instructions stored in computer readable storage medium and/or firmware that confer(s), at least in part, the functionality of the electronic components.

[00077] It will be understood that when an element is referred to as being“connected” or“coupled” to another element, it can be physically connected or coupled to the other element such that current and/or electromagnetic radiation (e.g., a signal) can flow along a conductive path formed by the elements. Intervening conductive, inductive, or capacitive elements may be present between the element and the other element when the elements are described as being coupled or connected to one another. Further, when coupled or connected to one another, one element may be capable of inducing a voltage or current flow or propagation of an electro-magnetic wave in the other element without physical contact or intervening components. Further, when a voltage, current, or signal is referred to as being“applied” to an element, the voltage, current, or signal may be conducted to the element by way of a physical connection or by way of capacitive, electro-magnetic, or inductive coupling that does not involve a physical connection.

[00078] As used herein, a signal that is“indicative of” a value or other information may be a digital or analog signal that encodes or otherwise communicates the value or other information in a manner that can be decoded by and/or cause a responsive action in a component receiving the signal. The signal may be stored or buffered in computer readable storage medium prior to its receipt by the receiving component and the receiving component may retrieve the signal from the storage medium. Further, a “value” that is“indicative of” some quantity, state, or parameter may be physically embodied as a digital signal, an analog signal, or stored bits that encode or otherwise communicate the value.

[00079] The term“couple” is used throughout the specification. The term may cover connections, communications, or signal paths that enable a functional relationship consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, in a first example device A is coupled to device B, or in a second example device A is coupled to device B through intervening component C if intervening component C does not substantially alter the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A.

[00080] As used herein, a signal may be transmitted or conducted through a signal chain in which the signal is processed to change characteristics such as phase, amplitude, frequency, and so on. The signal may be referred to as the same signal even as such characteristics are adapted. In general, so long as a signal continues to encode the same information, the signal may be considered as the same signal. For example, a transmit signal may be considered as referring to the transmit signal in baseband, intermediate, and radio frequencies.

[00081] Use of the word example is intended to present concepts in a concrete fashion. The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting of examples. As used herein, the singular forms“a,”“an” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,”“comprising,”“includes” and/or“including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

[00082] In the foregoing description, a plurality of details is set forth to provide a more thorough explanation of the embodiments of the present disclosure. However, it will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present disclosure. In addition, features of the different embodiments described above may be combined with each other, unless specifically noted otherwise.

[00083] While the methods are illustrated and described above as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or examples of the disclosure herein. Also, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. In some examples, the methods illustrated above may be implemented in a computer readable medium using instructions stored in a memory. Many other examples and variations are possible within the scope of the claimed disclosure.

[00084] Examples can include subject matter such as a method, means for performing acts or blocks of the method, at least one machine-readable medium including instructions that, when performed by a machine cause the machine to perform acts of the method or of an apparatus or system for practicing the embodiments and examples described herein.

[00085] Example 1 is an envelope tracking system configured to generate a tracking supply voltage for a power amplifier, the system including envelope circuitry, tracking supply voltage circuitry, and reconfigurable capacitor circuitry. The envelope circuitry is configured to: receive a transmit signal indicative of a baseband transmit signal; and generate a level select signal based on the transmit signal. The tracking supply voltage circuitry includes voltage regulator circuitry including control circuitry configured to regulate the tracking supply voltage based on a source voltage and a feedback signal related to the tracking supply voltage, wherein the voltage regulator circuitry is coupled in series with the source voltage in a supply line of the power amplifier. The

reconfigurable capacitor circuitry is coupled in parallel with the supply line and is configured to dispose one or more pre-charged capacitors in a parallel signal path with respect to the supply line, to modulate the tracking supply voltage based on the level select signal.

[00086] Example 2 includes the subject matter of example 1 , including or omitting optional elements, the voltage regulator circuitry includes a buck converter configured to step the source voltage down.

[00087] Example 3 includes the subject matter of example 1 , including or omitting optional elements, wherein the voltage regulator circuitry includes a boost charge pump coupled to a battery and configured to generate an internal supply voltage equal to or greater than a battery voltage. [00088] Example 4 includes the subject matter of example 1 , including or omitting optional elements, wherein the reconfigurable capacitor circuitry includes: capacitor circuitry including a plurality of capacitors, wherein the plurality of capacitors are arranged in a selectively configurable manner; and charge provisioning circuitry configured to receive a charging voltage and, in turn, charge one or more of the plurality of capacitors.

[00089] Example 5 includes the subject matter of example 4, including or omitting optional elements, wherein the capacitor circuitry includes a main capacitor configured to be charged by the voltage regulator circuitry and tracking capacitor arrangement coupled in series with the main capacitor, the tracking capacitor arrangement including a remainder of the plurality of capacitors, wherein the remainder of the plurality of capacitors are configured to be charged by the charging voltage. The reconfigurable capacitor circuitry is configured to selectively configure the tracking capacitor arrangement to cause a tracking voltage present across the tracking capacitor arrangement combined with a voltage across the main capacitor to provide a desired tracking supply voltage.

[00090] Example 6 includes the subject matter of example 5, including or omitting optional elements, wherein the tracking capacitor arrangement includes a first capacitor and a second capacitor; the charge provisioning circuitry includes a plurality of switches configurable in a first configuration creates a first signal path connecting the main capacitor directly to a reference voltage; a second configuration that creates a second signal path that connects the first capacitor in series between the main capacitor to the reference voltage of the power amplifier; a third configuration that creates a third signal path that connects the first capacitor in parallel with the second capacitor between the main capacitor and the reference voltage; and a fourth configuration that creates a fourth signal path that connects the first capacitor in series with the second capacitor between the main capacitor and the reference voltage; and the reconfigurable capacitor circuitry is configured to control the switches activate one of the signal paths based on the level select signal.

[00091] Example 7 includes the subject matter of example 5, including or omitting optional elements, further including a differential amplifier having as inputs a supply line voltage and a target tracking supply voltage and having an output coupled between the main capacitor and the tracking capacitor arrangement, wherein the target tracking supply voltage is derived from an envelope of the transmit signal.

[00092] Example 8 includes the subject matter of example 5, including or omitting optional elements, further including a differential amplifier having as inputs a supply line voltage and a target tracking supply voltage and having an output coupled to the supply line, wherein the target tracking supply voltage is derived from an envelope of the transmit signal.

[00093] Example 9 includes the subject matter of example 5, including or omitting optional elements, wherein the tracking capacitor arrangement includes a set of capacitors arranged to be charged to a capacitor voltage corresponding to M/N times the charging voltage; a set of switches coupled between the capacitors in the set of capacitors, wherein the switches are configurable to connect the capacitors in the set of capacitors into a plurality of linear combinations of the capacitor voltage; and control circuitry configured to control the set of switches based on the level select signal.

[00094] Example 10 includes the subject matter of example 9, including or omitting optional elements, wherein M and N are integers.

[00095] Example 1 1 includes the subject matter of example 9, including or omitting optional elements, wherein the capacitor voltage is substantially constant.

[00096] Example 12 includes the subject matter of example 4, including or omitting optional elements, wherein the capacitor circuitry includes at least two capacitors each arranged in a respective different parallel signal path between the supply line and a reference voltage, wherein each parallel signal path includes a switch in series with the capacitor; the charge provisioning circuitry includes one or more charge sources, each associated with one or more of the capacitors and configured to charge the one or more of the capacitors to a desired charge level; and the reconfigurable capacitor circuitry is configured to control the switches in the signal paths to connect a selected capacitor to the supply line based on the level select signal.

[00097] Example 13 includes the subject matter of example 12, including or omitting optional elements, wherein the charge provisioning circuitry determines the desired charge level based on a target voltage signal related to a predicted tracking supply voltage. [00098] Example 14 includes the subject matter of example 4, including or omitting optional elements, wherein charge provisioning circuitry is configured to receive the charging voltage from the supply line.

[00099] Example 15 includes the subject matter of any one of examples 1 -14, including or omitting optional elements, wherein the control circuitry regulates the tracking supply voltage based on a target voltage for the voltage regulator circuitry diminished by the feedback signal related to the tracking supply voltage and an estimated tracking voltage.

[000100] Example 16 includes the subject matter of example 15, including or omitting optional elements, wherein the estimated tracking voltage corresponds to the level select signal multiplied by a voltage increment between differing voltage levels provided by the reconfigurable capacitor circuitry.

[000101] Example 17 includes the subject matter of any one of examples 1 -14, including or omitting optional elements, further including an instrumentation amplifier configured to measure a voltage across a capacitor in the plurality of capacitors to generate the feedback signal related to the tracking supply voltage.

[000102] Example 18 includes the subject matter of any one of examples 4-14, including or omitting optional elements, wherein the charge provisioning circuitry includes a charge pump.

[000103] Example 19 includes the subject matter of any one of examples 4-14, including or omitting optional elements, wherein the charge provisioning circuitry includes a DCDC converter.

[000104] Example 20 includes the subject matter of any one of examples 4-14, including or omitting optional elements, wherein the charge provisioning circuitry includes a low dropout (LDO) regulator.

[000105] Example 21 is a method configured to generate a tracking supply voltage for a power amplifier, including: generating a level select signal based on a transmit signal indicative of a baseband transmit signal; regulating the tracking supply voltage based on a source voltage, a feedback signal related to the tracking supply voltage, and the level select signal, wherein the tracking supply voltage is carried in a supply line of the power amplifier; and selectively disposing one or more pre-charged capacitors in a parallel signal path with respect to the supply line, to modulate the tracking supply voltage based on the level select signal.

[000106] Example 22 includes the subject matter of example 21 , including or omitting optional elements, including: charging a main capacitor to a main voltage using a voltage regulator circuitry; pre-charging a plurality of capacitors in a tracking capacitor arrangement coupled in series with the main capacitor; and selectively configuring the tracking capacitor arrangement to cause a tracking voltage present across the tracking capacitor arrangement combined with the main voltage to provide the tracking supply voltage.

[000107] Example 23includes the subject matter of example 21 , including or omitting optional elements, including: pre-charging at least two capacitors each arranged in a respective different parallel signal path between the supply line and a reference voltage; and selectively connecting one of the at least two capacitors to the supply line based on the level select signal.

[000108] Example 24 includes the subject matter of any one of examples 21 -23, including or omitting optional elements, including pre-charging at least one of the plurality of capacitors with the tracking supply voltage on the supply line.

[000109] Example 25 includes the subject matter of any one of examples 21 -23, including or omitting optional elements, including regulating the tracking supply voltage based on a target voltage for the voltage regulator circuitry modified by the feedback signal related to the tracking supply voltage and an estimated tracking voltage.

[000110] Example 26 includes the subject matter of any one of examples 21 -23, including or omitting optional elements, including measuring a voltage across a capacitor in the plurality of capacitors to generate the feedback signal related to the tracking supply voltage.

[000111] Example 27 includes the subject matter of any one of examples 21 -23, including or omitting optional elements, wherein the level select signal is updated on a transmit symbol by symbol basis according to a power level of an upcoming symbol.

[000112] Example 28 includes the subject matter of any one of examples 21 -23, including or omitting optional elements, where the level select signal is updated at predefined time instances according to a power level of a TX signal in an upcoming transmission interval.

[000113] Example 29 is a pre-distortion system, including tracking supply voltage model circuitry configured to determine an estimated tracking supply voltage based on a source voltage and a target voltage provided to a tracking supply voltage circuitry in a power amplifier envelope tracking system; and pre-distortion circuitry configured to adjust a transmit signal that is amplified by the power amplifier based on the estimated tracking supply voltage.

[000114] Example 30 includes the subject matter of any example 29, including or omitting optional elements, wherein the tracking supply voltage model circuitry includes: a voltage regulator observer that uses a measurement of a source voltage and a target voltage for a voltage regulator in the envelope tracking system to estimate a regulated voltage output by the voltage regulator; a voltage splitter model circuitry configured to determine a set of estimated voltage levels based on the estimated regulated voltage and a sum of estimated power amplifier currents, wherein the estimated power amplifier currents estimate a current draw of respective power amplifiers in the envelope tracking system; and a level selector model circuitry configured to estimate the tracking supply voltage based on a voltage level selection signal for the power amplifier and the set of estimated voltage levels.

[000115] Various illustrative logics, logical blocks, modules, and circuits described in connection with aspects disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other

programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform functions described herein. A general-purpose processor can be a microprocessor, but, in the alternative, processor can be any conventional processor, controller, microcontroller, or state machine. The various illustrative logics, logical blocks, modules, and circuits described in connection with aspects disclosed herein can be implemented or performed with a general purpose processor executing instructions stored in computer readable medium.

[000116] The above description of illustrated embodiments of the subject disclosure, including what is described in the Abstract, is not intended to be exhaustive or to limit the disclosed embodiments to the precise forms disclosed. While specific embodiments and examples are described herein for illustrative purposes, various modifications are possible that are considered within the scope of such embodiments and examples, as those skilled in the relevant art can recognize.

[000117] In this regard, while the disclosed subject matter has been described in connection with various embodiments and corresponding Figures, where applicable, it is to be understood that other similar embodiments can be used or modifications and additions can be made to the described embodiments for performing the same, similar, alternative, or substitute function of the disclosed subject matter without deviating therefrom. Therefore, the disclosed subject matter should not be limited to any single embodiment described herein, but rather should be construed in breadth and scope in accordance with the appended claims below.

[000118] In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a "means") used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the disclosure. In addition, while a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. The use of the phrase“one or more of A, B, or C” is intended to include all combinations of A, B, and C, for example A, A and B, A and B and C, B, and so on.

[000119] It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users.

In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.

Claims

CLAIMS What is claimed is:

1 . An envelope tracking system configured to generate a tracking supply voltage for a power amplifier, the system comprising:

envelope circuitry configured to:

receive a transmit signal indicative of a baseband transmit signal; and generate a level select signal based on the transmit signal; tracking supply voltage circuitry, comprising:

voltage regulator circuitry comprising control circuitry configured to regulate the tracking supply voltage based on a source voltage and a feedback signal related to the tracking supply voltage, wherein the voltage regulator circuitry is coupled in series with the source voltage in a supply line of the power amplifier; and

a reconfigurable capacitor circuitry coupled in parallel with the supply line, the reconfigurable capacitor circuitry configured to dispose one or more pre-charged capacitors in a parallel signal path with respect to the supply line, to modulate the tracking supply voltage based on the level select signal.

2. The envelope tracking system of claim 1 , wherein the voltage regulator circuitry comprises a buck converter configured to step the source voltage down.

3. The envelope tracking system of claim 1 , wherein the voltage regulator circuitry comprises a boost charge pump coupled to a battery and configured to generate an internal supply voltage equal to or greater than a battery voltage.

4. The envelope tracking system of claim 1 , wherein the reconfigurable capacitor circuitry comprises:

capacitor circuitry comprising a plurality of capacitors, wherein the plurality of capacitors are arranged in a selectively configurable manner; and

charge provisioning circuitry configured to receive a charging voltage and, in turn, charge one or more of the plurality of capacitors.

5. The envelope tracking system of claim 4, wherein: the capacitor circuitry comprises:

a main capacitor configured to be charged by the voltage regulator circuitry; and

tracking capacitor arrangement coupled in series with the main capacitor, the tracking capacitor arrangement comprising a remainder of the plurality of capacitors, wherein the remainder of the plurality of capacitors are configured to be charged by the charging voltage,

wherein the reconfigurable capacitor circuitry is configured to selectively configure the tracking capacitor arrangement to cause a tracking voltage present across the tracking capacitor arrangement combined with a voltage across the main capacitor to provide a desired tracking supply voltage.

6. The envelope tracking system of claim 5, wherein:

the tracking capacitor arrangement comprises:

a first capacitor; and

a second capacitor;

the charge provisioning circuitry comprises a plurality of switches configurable in:

a first configuration creates a first signal path connecting the main capacitor directly to a reference voltage;

a second configuration that creates a second signal path that connects the first capacitor in series between the main capacitor to the reference voltage of the power amplifier;

a third configuration that creates a third signal path that connects the first capacitor in parallel with the second capacitor between the main capacitor and the reference voltage; and

a fourth configuration that creates a fourth signal path that connects the first capacitor in series with the second capacitor between the main capacitor and the reference voltage; and

the reconfigurable capacitor circuitry is configured to control the switches activate one of the signal paths based on the level select signal.

7. The envelope tracking system of claim 5, further comprising a differential amplifier having as inputs a supply line voltage and a target tracking supply voltage and having an output coupled between the main capacitor and the tracking capacitor arrangement, wherein the target tracking supply voltage is derived from an envelope of the transmit signal.

8. The envelope tracking system of claim 5, further comprising a differential amplifier having as inputs a supply line voltage and a target tracking supply voltage and having an output coupled to the supply line, wherein the target tracking supply voltage is derived from an envelope of the transmit signal.

9. The envelope tracking system of claim 5, wherein:

the tracking capacitor arrangement comprises:

a set of capacitors arranged to be charged to a capacitor voltage corresponding to M/N times the charging voltage;

a set of switches coupled between the capacitors in the set of capacitors, wherein the switches are configurable to connect the capacitors in the set of capacitors into a plurality of linear combinations of the capacitor voltage; and

control circuitry configured to control the set of switches based on the level select signal.

10. The envelope tracking system of claim 9, wherein M and N are integers.

1 1 . The envelope tracking system of claim 9, wherein the capacitor voltage is substantially constant.

12. The envelope tracking system of claim 4, wherein:

the capacitor circuitry comprises at least two capacitors each arranged in a respective different parallel signal path between the supply line and a reference voltage, wherein each parallel signal path comprises a switch in series with the capacitor;

the charge provisioning circuitry comprises one or more charge sources, each associated with one or more of the capacitors and configured to charge the one or more of the capacitors to a desired charge level; and the reconfigurable capacitor circuitry is configured to control the switches in the signal paths to connect a selected capacitor to the supply line based on the level select signal.

13. The envelope tracking system of claim 12, wherein the charge provisioning circuitry determines the desired charge level based on a target voltage signal related to a predicted tracking supply voltage.

14. The envelope tracking system of claim 4, wherein charge provisioning circuitry is configured to receive the charging voltage from the supply line.

15. The envelope tracking system of any one of claims 1 -14, wherein the control circuitry regulates the tracking supply voltage based on a target voltage for the voltage regulator circuitry diminished by the feedback signal related to the tracking supply voltage and an estimated tracking voltage.

16. The envelope tracking system of claim 15, wherein the estimated tracking voltage corresponds to the level select signal multiplied by a voltage increment between differing voltage levels provided by the reconfigurable capacitor circuitry.

17. The envelope tracking system of any one of claims 1 -14, further comprising an instrumentation amplifier configured to measure a voltage across a capacitor in the plurality of capacitors to generate the feedback signal related to the tracking supply voltage.

18. The envelope tracking system of any one of claims 4-14, wherein the charge provisioning circuitry comprises a charge pump.

19. The envelope tracking system of any one of claims 4-14, wherein the charge provisioning circuitry comprises a DCDC converter.

20. The envelope tracking system of any one of claims 4-14, wherein the charge provisioning circuitry comprises a low dropout (LDO) regulator.

21 . A method configured to generate a tracking supply voltage for a power amplifier, comprising:

generating a level select signal based on a transmit signal indicative of a baseband transmit signal;

regulating the tracking supply voltage based on a source voltage, a feedback signal related to the tracking supply voltage, and the level select signal, wherein the tracking supply voltage is carried in a supply line of the power amplifier; and

selectively disposing one or more pre-charged capacitors in a parallel signal path with respect to the supply line, to modulate the tracking supply voltage based on the level select signal.

22. The method of claim 21 , comprising:

charging a main capacitor to a main voltage using a voltage regulator circuitry; pre-charging a plurality of capacitors in a tracking capacitor arrangement coupled in series with the main capacitor; and

selectively configuring the tracking capacitor arrangement to cause a tracking voltage present across the tracking capacitor arrangement combined with the main voltage to provide the tracking supply voltage.

23. The method of claim 21 , comprising:

pre-charging at least two capacitors each arranged in a respective different parallel signal path between the supply line and a reference voltage; and

selectively connecting one of the at least two capacitors to the supply line based on the level select signal.

24. The method of any one of claims 21 -23, comprising pre-charging at least one of the plurality of capacitors with the tracking supply voltage on the supply line.

25. The method of any one of claims 21 -23, comprising regulating the tracking supply voltage based on a target voltage for the voltage regulator circuitry modified by the feedback signal related to the tracking supply voltage and an estimated tracking voltage.

26. The method of any one of claims 21 -23, comprising measuring a voltage across a capacitor in the plurality of capacitors to generate the feedback signal related to the tracking supply voltage.

27. The method of any one of claims 21 -23, wherein the level select signal is updated on a transmit symbol by symbol basis according to a power level of an upcoming symbol.

28. The method of any one of claims 21 -23, where the level select signal is updated at predefined time instances according to a power level of a TX signal in an upcoming transmission interval.

29. A pre-distortion system, comprising:

tracking supply voltage model circuitry configured to determine an estimated tracking supply voltage based on a source voltage and a target voltage provided to a tracking supply voltage circuitry in a power amplifier envelope tracking system; and pre-distortion circuitry configured to adjust a transmit signal that is amplified by the power amplifier based on the estimated tracking supply voltage.

30. The pre-distortion system of claim 29, wherein the tracking supply voltage model circuitry comprises:

a voltage regulator observer that uses a measurement of a source voltage and a target voltage for a voltage regulator in the envelope tracking system to estimate a regulated voltage output by the voltage regulator;

a voltage splitter model circuitry configured to determine a set of estimated voltage levels based on the estimated regulated voltage and a sum of estimated power amplifier currents, wherein the estimated power amplifier currents estimate a current draw of respective power amplifiers in the envelope tracking system; and a level selector model circuitry configured to estimate the tracking supply voltage based on a voltage level selection signal for the power amplifier and the set of estimated voltage levels.