WO2015131385A1

WO2015131385A1 - Method and apparatus for modulating power supply

Info

Publication number: WO2015131385A1
Application number: PCT/CN2014/073025
Authority: WO
Inventors: Zhancang WANG
Original assignee: Nokia Technologies Oy; Nokia (China) Investment Co., Ltd.
Priority date: 2014-03-07
Filing date: 2014-03-07
Publication date: 2015-09-11
Also published as: EP3114742A1; EP3114742A4

Abstract

A method and an apparatus for modulating a power supply are provided. The method comprises linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator. The method further comprises selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage. With the claimed inventions, the extra power may be saved and circuitry complex may be reduced, which may lead to low cost, energy saving and device miniaturization.

Description

METHOD AND APPARATUS FOR MODULATING POWER SUPPLY

FIELD OF THE INVENTION [0001] Example embodiments of the present disclosure generally relate to generating a power supply for a power amplifier. More particularly, example embodiments of the present disclosure relate to a method and an apparatus for modulating a power supply for a radio frequency power amplifier ("RFPA"). BACKGROUND OF THE INVENTION

[0002] The following description of background art may include insights, discoveries, understandings or disclosures, or associations together with disclosures not known to the relevant art prior to the present disclosure but provided by the present disclosure. Some such contributions of the present disclosure may be specifically pointed out below, while other such contributions of the present disclosure will be apparent from their context.

[0003] With the development of the emerging wireless communication standards, such as the Fourth Generation ("4G") Long Term Evolution-Advanced ("LTE-A"), the number of data services are increasing dramatically, which results in more and more complex modulation schemes being used to gain rapid transmission of various data signals in mobile environments.

[0004] The 4G communication provides a higher transmission rate while suffering from amplification efficiency degradation due to a high peak-to-average-power ratio ("PAPR") issue on the signal character, which causes a rather low efficiency during a signal amplification process in devices or equipments. An Envelope Tracking ("ET") and envelope elimination and restoration ("EE&R") are seen as promising techniques to keep high efficiency power amplification for high PAPR advanced signals, which both may have a high-efficient power supply modulator to provide dynamic supply output according to RF envelope into the RF power amplifier ("PA") component.

SUMMARY OF THE INVENTION

[0005] The following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects of the present disclosure. It should be noted that this summary is not an extensive overview of the present disclosure and that it is not intended to identify key/critical elements of the present disclosure or to delineate the scope of the present disclosure. Its sole purpose is to present some concepts of the present disclosure in a simplified form as a prelude to the more detailed description that is presented later.

[0006] According to an aspect of the present disclosure, there is provided a method.

The method comprises linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator. The method also comprises selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage.

[0007] In one embodiment, the selecting comprises selecting to output the amplified radio frequency envelope signal to the radio frequency power amplifier when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and selecting to output the amplified radio frequency envelope signal to the switcher stage when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0008] In another embodiment, the method further comprises bypassing and powering off the switcher stage when selecting to output the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

[0009] In yet another embodiment, the linear regulator stage is powered by a low voltage fixed direct current power supply and the switcher stage is powered by a high voltage fixed direct current power supply.

[0010] In a further embodiment, the method further comprises powering off the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and powering on the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0011] In one embodiment, the linear regulator stage is a linear amplifier that provides sourcing function and sinking function for the envelope power of the radio frequency power amplifier.

[0012] In another embodiment, the switcher stage is a switching mode power supply that provides a high side source supply for the envelope power of the radio frequency power amplifier.

[0013] In a further embodiment, the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier.

[0014] In an additional embodiment, the envelope threshold is adjustable.

[0015] According to an aspect of the present disclosure, there is provided an apparatus. The apparatus comprises a linear regulator stage for linearly amplifying a radio frequency envelope signal. The apparatus also comprises an envelope threshold detector for detecting whether a level of the amplified radio frequency envelope signal is lower or higher than an envelope threshold. The apparatus further comprises a switcher stage connected in series with the linear stage. In the apparatus, the linear regulator stage outputs directly to a radio frequency power amplifier or outputs to the switcher stage based on a judgment result of the envelope threshold detector.

[0016] In one embodiment, the linear regulator stage outputs the amplified radio frequency envelope signal to the radio frequency power amplifier when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and the linear regulator stage outputs the amplified radio frequency envelope signal to the switcher stage when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0017] In another embodiment, the envelope threshold detector drives the switcher stage to be bypassed and powered off and the linear regulator stage outputs the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

[0018] In a further embodiment, the apparatus further comprises a low voltage fixed direct current power supply for powering the linear regulator stage and a high voltage fixed direct current power supply for powering the switcher stage.

[0019] In an additional embodiment, the high voltage fixed direct current power supply is powered off when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and is powered on when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0020] In one embodiment, the linear regulator stage is a linear amplifier that provides both sourcing function and sinking function for envelope power of the radio frequency power amplifier.

[0021] In another embodiment, the switcher stage is a switching mode power supply that provides a high side source supply for envelope power of the radio frequency power amplifier.

[0022] In yet another embodiment, the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier.

[0023] In an additional embodiment, the envelope threshold is adjustable.

[0024] In a further embodiment, the apparatus includes an envelope tracking power supply modulator.

[0025] According to an aspect of the present disclosure, there is provided an apparatus. The apparatus comprises means for linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator. The apparatus further comprises means for selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage.

[0026] The aspects and example embodiments of the present disclosure as described above may be utilized separately or in combination and different combining forms may be constituted to target at least some intentions of the present disclosure as mentioned in the following.

[0027] First, since the linear regulator stage according to some example embodiments of the present disclosure may only take care of the low power portion of envelope signal and have no rigid distortion requirements due to clamped/distorted version of the envelope signal, it can run in more compression or saturation regions to enhance the efficiency.

[0028] Second, since the linear regulator stage according to some example embodiments of the present disclosure may deliver a medium power rather than the full scale power in the prior art, less dissipation of the linear part contributes to the overall ET PA system.

[0029] Third, according to some example embodiments of the present disclosure, only the clamped/distorted version of envelope signal is amplified so as to reduce and keep PAR low for sake of maintaining high amplification efficiency.

[0030] Fourth, since the switcher stage according to some example embodiments of the present invention is allowed to be switched off and bypassed in the low power mode to save power based on the envelope threshold detection, the switcher stage is capable of working constantly or in intervals rather than running all the time; thus, from a perspective of operation intervals, the DC power is saved compared to the prior art. Because the switcher stage in the present disclosure may only provide high side sourcing current rather than the prior art providing both high side source current and low side sink current, the power saving and circuitry complexity reduction may be achieved. Due to the adjustable envelope threshold, the duty cycle of switcher operation may also be adjusted accordingly to compromise the efficiency and linearity design from the systematic perspective.

[0031] Fifth, since the linear regulator stage and switcher stage according to some example embodiments of the present disclosure are arranged in serial to provide outputs directly to a final supply modulator output, there are no timing alignment difficulties between the linear and switcher stages due to the in-series or cascade structure, which could process much wider bandwidth envelope signal for broadband applications. The impacts of delays between stages may be minimized and the linearity and efficiency could be also improved compared to the prior art due to the elimination of the timing mismatches. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The embodiments of the present disclosure that are presented in the sense of examples and their advantages are explained in greater detail below with reference to the accompanying drawings, in which:

[0033] Fig. 1 illustrates an example apparatus for modulating a power supply for an

RFPA according to some example embodiments of the present disclosure;

[0034] Fig. 2 is a flow chart schematically illustrating a method for modulating a power supply for an RFPA according to an embodiment of the present disclosure;

[0035] Fig. 3 is a flow chart schematically illustrating a method for modulating a power supply for an RFPA according to another embodiment of the present disclosure;

[0036] Fig. 4 is a schematic diagram of an example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure;

[0037] Fig. 5 is a schematic time domain waveform illustrating a supply voltage of the power supply modulator in Fig. 1 as compared to the waveform generated by the prior art;

[0038] Fig. 6 is a schematic diagram of another example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure;

[0039] Fig. 7 is a schematic diagram of a further example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure;

[0040] Fig. 8 is an efficiency illustration of continuous wave ("CW") simulation results of efficiency and gain over the output power in an exemplary fixed DC supplied RFPA;

[0041] Fig. 9 is waveform of an 8-tone stimulus RF signal at 700 MHz to emulate modulated high-PAPR signal and its envelope for test by the power supply modulator according to some example embodiments of the present disclosure;

[0042] Fig. 10 is an efficiency plot illustrating efficiencies of the power supply modulator with the 8-tone stimulus RF signal envelope in Fig. 9 as stimulus and its curve fitting with 5^th order polynomial fitting function;

[0043] Fig. 11 is a time domain output waveform comparisons of simulation program with integrated circuitry emphasis ("SPICE") transient simulation results of voltages of key points;

[0044] Fig. 12 is an efficiency plot illustrating power added efficiencies ("PAE") and probability density function histograms of the 8-stone signal in Fig. 9 versus output power; and

[0045] Fig. 13 is a schematic diagram of an apparatus according to some embodiments of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0046] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the present disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Like numbers refer to like elements throughout the specification.

[0047] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The discussion above and below in respect of any of the aspects of the present disclosure is also in applicable parts relevant to any other aspect of the present disclosure.

[0048] As a prior art technique to some example embodiments of the present disclosure, US 2013/0093247A1 appears to disclose a solution related to the envelope tracking technique as mentioned in the background part. In this US patent application, an apparatus comprising a switching mode power supply ("SMPS") module and a linear regulator is disclosed for modulating a supply voltage of a power amplifier. Although the apparatus may provide some advantage in increasing the power amplification efficiency of the power supply modulation amplifier, it does have some drawbacks. First, since the SMPS module and the linear regulator are running in parallel and combined by a summing node, there would be a timing alignment difficulty for that architecture, which brings a difficulty in wider bandwidth operations with high efficiency and good linearity. Second, a sinking part sinking low level pulses into the ground in the SMPS module gives rise to additional power dissipations since there is already a sinking part in the linear regulator. Third, the linear regulator takes charge of high power output for the high frequency and the scenarios when the SMPS module cannot deliver much power to output. Due to inherent low efficiency linear regulator stage, it is unadvisable for the linear regulator to handle existing and potential high power signal, especially for the high PAPR signal, whose peak-to-average-ratio ("PAR") of envelope is even much higher. Since the linear regulator performs the full-scale amplification, the rail-to-rail signal may suffer from serious low efficiency problems for wide band application scenarios. Finally, due to the parallel architecture in the prior art, the output signal combination of SMPS and linear regulator restrict the prior art to use different voltage power supplies to enhance each efficiency because the parallel combination requires proper output levels from each to guarantee the accuracy of envelope power amplification in the power supply modulator in envelope tracking process.

[0049] To better copy with the power supply modulator loss being obvious and serious when the PAPR and modulation bandwidth of the modulated signal are increasing for 4G, for example, LTE-A system, and effectively address the drawbacks existing in the US 2013/0093247A1, the exemplary embodiments of the present disclosure generally propose making the power supply modulator enter into two modes, that is, a lower power linear mode and a high power voltage switching mode, based on the result of an envelope detection and judgment operation. To this end, it is proposed to generate the envelope shape supply voltage and current by cascading a linear regulator stage with a low voltage fixed direct current power supply and a switcher stage with a high voltage fixed direct current supply. Thereby, the supply voltages of the linear mode and the high power voltage switching mode may be split away and the lower linear supply voltage on the linear amplifier (i.e., the linear stage) may boost the peak power efficiency in the low power linear mode whereas the higher switching mode supply voltage on the switch stage may simplify and boost the supply modulator efficiency for high power parts of the signal in the high power voltage switching mode.

[0050] Fig. 1 illustrates an example apparatus 100 for modulating a power supply for an RFPA according to some example embodiments of the present disclosure. As illustrated in Fig. 1, the apparatus 100 according to some embodiments of the present disclosure includes a linear regulator stage 102 for linearly amplifying a radio frequency envelope signal, which may, as shown, be injected into the linear regulator stage 102 with a low voltage supply VL first for linear amplification. The apparatus 100 further includes an envelope threshold detector, which may be exemplarily embodied as a comparator 104, for detecting whether a level of the amplified radio frequency envelope signal is lower or higher than an envelope threshold, which may be embodied as a signal for clamp from an external circuitry. The apparatus 100 additionally includes a switcher stage 108 connected in series with the linear regulator stage 102 via the comparator 104 and a Single-Pole Double-Throw ("SPDT") switch 106 and 109 to perform the path selection function. The SPDT switch 106 and 109 may switch, based on the result of the comparator, the output of the linear regulator stage 102 directly to the RFPA 110 or switch the output of the linear regulator stage 102 via the comparator 104 to the switcher stage 108 upon which the higher power part of the envelope signal may be injected to the RFPA 110.

[0051] In some example embodiments, the linear regulator stage 102 outputs the amplified radio frequency envelope signal to the RFPA 110 when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and the linear regulator stage 102 outputs the amplified radio frequency envelope signal to the switcher stage 108 when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold (or threshold value).

[0052] In some example embodiments, the envelope threshold detector drives the switcher stage 108 to be bypassed and powered off and the linear regulator stage 102 outputs the amplified radio frequency envelope signal directly to the RFPA 110.

[0053] In some example embodiments, the apparatus 100 may further comprise a low voltage fixed direct current power supply shown as "VL" in Fig. 1 for powering the linear regulator stage and a high voltage fixed direct current power supply shown as "VH" in Fig. 1 for powering the switcher stage 108. The ratio between VL and VH may be adjustable or programmable to optimize the overall system efficiency and linearity from a systematic perspective. The ratio may also change with the change of the envelope threshold.

[0054] In some example embodiments, the high voltage fixed direct current power supply VH may be powered off when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and may be powered on when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0055] In some example embodiments, the linear regulator stage 102 is a linear amplifier that provides sourcing function and sinking function for envelope power of the radio frequency power amplifier. As a non-limiting example, the linear amplifier herein may be a clamp/distorted version of the linear amplifier wherein the sinking function is intended to absorb the redundant current generated when the sourcing function operates to provide power to the RFPA 110.

[0056] Regarding the envelope power, it should be noted that in the envelope tracking power amplifier system, the drain/collector current and voltage of the power amplifier are not constant/fixed values and they are changing with the shape of envelope. According to fixed DC power supplied PA, the supplied power may be expressed as P_DC=V_DC* I DC, where P DC denotes DC power, V DC denotes DC voltage and I DC denotes DC current. Therefore, in the envelope tracking power amplifier system, the supplied power is changing with the voltage and the current which also change with time, and may be expressed as P_ENV=V_ENV*I_ENV, where P_ENV denotes the instantaneous supplied power (i.e., the envelope power) at the drain/collector of the power amplifier, V_ENV denotes the supplied voltage at the drain/collector, and I ENV denotes the supplied current at the drain/collector.

[0057] In some example embodiments, wherein the switcher stage 108 is a switching mode power supply that may provide a high side source supply for envelope power of the RFPA 110, such as shown in Fig. 4 in a series of rectangular/square waves, and that may be bypassed or connected to final output dependent on the envelope value judgment from the envelope threshold detector.

[0058] In some example embodiments, the switcher stage 108 may be a three-state control circuitry for switching the high voltage fixed direct current power supply VH to the RFPA 110 or switching the amplified radio frequency envelope signal to the RFPA 110, such as shown in Fig. 5 as VLIN.

[0059] In some example embodiments, the envelope threshold may be adjustable or programmable. For example, the threshold value may be adjusted according to PAR of the envelope signal with various modulation schemes. In some example embodiments, wherein the apparatus 100 includes an envelope tracking power supply modulator which may include the linear regulator stage 102 and the switcher stage 108 as discussed above.

[0060] With the apparatus 100 and a number of its variants as set forth in some example embodiments of the present disclosure, the linear regulator stage 102 may run in more compression or saturation regions to enhance the efficiency. Further, since the switcher stage 108 is allowed to be switched off and bypassed in the low power mode to save power based on the envelope threshold detection, it may be capable of working constantly or in intervals rather than running all the time and thus the direct current ("DC") power for powering the switcher stage 108 may be saved compared to the prior art. Because the switcher stage 108 in the present disclosure may only provide the high side sourcing current rather than the prior art providing both the high side source current and low side sink current, the power saving and circuitry complexity reduction may be achieved.

[0061] Additionally, since the linear regulator stage 102 and switcher stage 108 according to some example embodiments of the present disclosure may be arranged in serial to provide outputs directly to a final modulator output, there is no timing alignment difficulties between the linear regulator stage and switcher stage due to the in-series or cascade structure, which may process much wider bandwidth envelope signal. Therefore, the impacts of delays between both stages may be minimized and the linearity and efficiency may be also improved compared to the prior art due to the elimination of the timing mismatches.

[0062] Fig. 2 is a flow chart schematically illustrating a method 200 for modulating a power supply for an FPA according to an embodiment of the present disclosure. As illustrated in Fig. 2, the method 200 comprises, at S201, linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator, for example the linear regulator stage 102 illustrated in Fig. 1. The method 200 further comprises, at S202, selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage. The switcher stage herein may be the switcher stage 108 as illustrated in Fig. 1.

[0063] In some example embodiments, the selecting at S202 may comprise selecting to output the amplified radio frequency envelope signal to the RFPA when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and selecting to output the amplified radio frequency envelope signal to the switcher stage when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0064] In some example embodiments, the method 200 further comprises bypassing and powering off the switcher stage when selecting to output the amplified radio frequency envelope signal directly to the radio frequency power amplifier. In some other example embodiments, the linear regulator stage may be powered by a low voltage fixed direct current power supply and the switcher stage may be powered by a high voltage fixed direct current power supply.

[0065] In some example embodiments, the method 200 may further comprise powering off the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and powering on the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0066] In some example embodiments, the linear regulator stage is a linear amplifier that may provide sourcing function and sinking function for the radio frequency power amplifier. In some other embodiments, the switcher stage may be a switching mode power supply that provides a high side source supply for the radio frequency power amplifier.

[0067] In some example embodiments, the switcher stage may be a three-state control circuitry for switching the high voltage fixed direct current power supply to the RFPA or switching the amplified radio frequency envelope signal to the RFPA. In some other example embodiments, the envelope threshold may be adjustable, for example, programmed according to PAR of the envelope signal with various modulation schemes.

[0068] By virtue of the method 200 and a number of its variants discussed in the above example embodiment, efficiency for the linear regulator stage may be improved since it is able to run more compression or saturation region. Further, since the switcher stage may only provide the high side sourcing current without low side sinking current, the extra power is saved and circuitry complex may be reduced, which may lead to the low cost, energy saving and device miniaturization.

[0069] Fig. 3 is a flow chart schematically illustrating a method 300 for modulating a power supply for an RFPA according to another embodiment of the present disclosure. To facilitate a better understanding of the present disclosure, the discussion with regards to the method 300 would be made with reference to Fig. 4, which is a schematic diagram of an example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure.

[0070] Referring to Fig. 4 first, the shown example circuitry could be treated as a relatively simplified version of the apparatus illustrated in Fig. 1 , wherein the linear regulator stage includes an operational amplifier 402, which is connected in series with an input of the comparator 404 whose main function is to detect whether the amplified envelope signal VLIN is higher or lower than the envelope threshold to provide pulse input to the switcher stage, and the switcher stage herein is connected in series with the output of the comparator 404 and includes a 3 -state control circuitry, which is shown by a block for illustrative purposes and whose main function is to switch the VH or VLIN to the RFPA based on the output of the comparator 404.

[0071] Returning back to Fig. 3, the example circuitry as shown in Fig. 4 may follow the operational flow of the method 300. The method 300 may start at S302 and proceed to S304, at which the linear amplification may be carried out by a closed loop operational amplifier 402 included in the linear regulator stage to provide linear output voltage and current with low fixed supply VL. Then, the method 300 proceeds to S306, at which a comparator 404 with its reference equal to the envelope threshold voltage detects (or compares) whether the envelope voltage VLIN is higher than the envelope threshold voltage. If this is the case, the flow advances to S308, at which the method 300 connects and powers on the switcher stage and disconnects the linear regulator stage bypass path as shown in Fig. 4 by the comparator's drive. Then, at S312, the VH branch is turned on and the VH would be output to the RFPA as the VOUT, placing the switcher stage into the high power voltage switching mode as mentioned before. If the result of S306 is "NO," then the flow switches to S310, at which the method 300 provides the output of the linear regulator stage and bypasses and powers off the switcher stage. In other words, the linear regulator stage bypass path would be turned on and the VLIN would be output as VOUT directly to the RFPA while the branch connecting the VH and VOUT would be turned off temporarily, placing the linear regulator stage into the lower power linear mode as mentioned before. After that, the method ends at S314.

[0072] Fig. 5 is a schematic time domain waveform illustrating a supply voltage of the power supply modulator in Fig. 1 as compared to the waveform generated by the prior art. As illustrated in Fig. 5, the VTH denotes the programmable envelope threshold, the VL denotes a low voltage fixed direct current power supply for powering the linear regulator stage and VH denotes a high voltage fixed direct current power supply for powering the switcher stage. As can be seen from the Fig. 5, at the lower power part where the voltage of the envelope signal is lower than the VTH, the prior art output as shown by the dotted line is the same as the output obtained and shown as solid line according to example embodiments of the present disclosure, although they are depicted separately for easy observation. In the case the voltage of the envelope signal is higher than the VTH, the output of the some embodiments of the present disclosure is notably different from the output of the prior art. As depicted, the prior art would output the peaks of the envelope signal. In contrast, the peaks of the envelope signal are replaced with the pulse high level fixed supply by the switcher stage according to some embodiments of the present disclosure, as exemplarily shown in three rectangular waves. Since the high level pulse does not cut off the RF envelope and RF signal, no obvious distortion would be incurred by this kind of waveform changes. Furthermore, to eliminate a scenario where many peak clusters over the envelope threshold in the local waveform generate many narrow pulses which may bring about the serious switching loss in the switcher stage, a hysteresis comparison may be used to reserve the main pulse for the switcher stage to optimize the overall switcher performance.

[0073] Fig. 6 is a schematic diagram of another example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure. As illustrated in Fig. 6, the power supply modulator mainly includes two parts, i.e., the linear regulator stage 602 and the switcher stage 604. Different from what is shown in Fig. 4, the linear regulator stage 602 herein includes a gain stage 606 and a medium power stage 608, which may use the lower supply voltage to drive and provide most of the low power component of the envelope signal to drive the switcher stage 604. Further, the switcher stage 604 herein is exemplarily and particularly embodied as including a level shifter 610 for a further signal amplification biasing adaption and matching, a hysteresis comparator 612 for determining whether or not to enable the switcher stage into the high power voltage switching mode, and a 3 -state control circuitry 614 for controlling the output to switch between the V+ or V-, which is coupled to a current sourcing switch/source follower 616. The current sourcing switch/source follower 614 would provide the final output to the RFPA. At 616, the dot shading area exemplarily represents the PA power saved due to the envelope tracking.

[0074] Fig. 7 is a schematic diagram of a further example circuitry implementation of the power supply modulator according to some embodiments of the present disclosure. As illustrated in Fig. 7, the power supply modulator may include two parts, i.e., a linear regulator stage 702 and a switcher stage 704. The linear regulator stage 702 may include a bias network- 1 for providing a proper voltage for an operational amplifier- 1, which, together with an operational amplifier-2, may serve as the gain stage 606 as shown in Fig. 6. The linear regulator stage 702 may also include a medium power buffer amplifier for providing high current source and sink as medium power stage 608 as shown in Fig. 6. The switcher stage 704 may include a level shifter for shifting linear output level for the switcher stage, a threshold generator for generating the envelope threshold voltage VTH for comparing, a switcher including a comparator, 3-state control circuitry and a MOSFET driver which are incorporated together, a power MOSFET acting as a power switch and for performing the pulse mode switch and analog linear mode source follow amplifier. The final output of the power MOSFET may be injected into the collector/drain of the RFPA. [0075] Fig. 8 is an efficiency versus fundamental output power illustration of continuous wave ("CW") simulation results of efficiency and gain over the output power for a fixed DC supplied RFPA as an example. As illustrated in Fig. 8, the horizontal axis denotes fundamental output power, i.e., output power of the fundamental wave, the left vertical axis denotes power added efficiencies ("PAE") and the right vertical axis denotes RFPA gains. From the illustrated efficiency curve, it can be seen the fixed direct current power supply in this example may provide approximately 10W (40dBm) output power with 53% peak efficiency. Further, it can be seen that the PAE goes steadily up as the output power increases. However, the PAE may drop as output power back off with high-PAPR modulated signals such as those for 3G and 4G communication. For example, with PAPR=10dB LTE-A signal, the PAE of such an RFPA with fixed DC supply is around 18% average efficiency, which may be less efficient as compared to the present disclosure, depending on specific RFPA design scenarios. The following will evaluate the efficiency that may be obtained using the power supply modulator according to some example embodiments of the present disclosure with reference to Figs. 9-12.

[0076] Fig. 9 is waveform of an 8-tone stimulus RF signal at 700 MHz to emulate modulated high-PAPR signal and its envelope for test by the power supply modulator according to some example embodiments of the present disclosure. As illustrated in Fig. 9, the 8-tone stimulus RF signal consists of eight kinds of signals with respectively different frequencies and amplitudes and its envelope signal is illustrated as the dashed line, which is approximately fitting the sharp of the RF signal. Fig. 10 is an efficiency plot illustrating efficiencies of the power supply modulator with the 8-tone stimulus RF signal envelope in Fig. 9 as stimulus and its curve fitting with 5^th order polynomial fitting function. It can be seen from Fig. 10 that the efficiency of the power supply modulator according to some example embodiments of the present disclosure may reach over 90% and keep a wide operational range. The transient simulation results are shown in Fig. 11 with the output voltages of the power supply modulator according to the present disclosure, the linear modulator output voltages and the RFPA output voltages. Therefore, based on the 8-tone signal simulation, it can be seen that the average efficiency achieved by the present disclosure may be much higher than the traditional fixed supplied RFPA, which is exemplarily illustrated in Fig. 12.

[0077] As seen from Fig. 12, the efficiency as obtained from the present disclosure may be higher than the prior art of fixed DC supplied RFPA. The table 1 below illustrates 8-tone stilumulus simulation results of efficiency with regards to the present disclosure and the prior art. Item PAE, (%) Average Ouput Power (dBm) Error Vector Magnitude ("EVM") (%)

Prior Art 17.8 34.2 2.4

The 27.1 34.1 2.9

present

disclosure

[0078] Fig. 13 is a schematic diagram of an apparatus 1300 according to some embodiments of the present disclosure. As illustrated in Fig. 13, the apparatus 1300 comprises means 1302 for linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator. The apparatus 1300 further comprises means 1304 for selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage.

[0079] In some example embodiments, the means for selecting comprises means for selecting to output the amplified radio frequency envelope signal to the radio frequency power amplifier when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and means for selecting to output the amplified radio frequency envelope signal to the switcher stage when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0080] In some example embodiments, the apparatus 1300 further comprises means for bypassing and powering off the switcher stage when selecting to output the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

[0081] In some example embodiments, the linear regulator stage is powered by a low voltage fixed direct current power supply and the switcher stage is powered by a high voltage fixed direct current power supply.

[0082] In some example embodiments, the apparatus 1300 further comprises means for powering off the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is lower than the envelope threshold and means for powering on the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

[0083] In some example embodiments, the linear regulator stage is a linear amplifier that provides sourcing function and sinking function for envelope power of the radio frequency power amplifier.

[0084] In some example embodiments, the switcher stage is a switching mode power supply that provides a high side source supply for envelope power of the radio frequency power amplifier.

[0085] In some example embodiments, the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier. In some other example embodiments, the envelope threshold is adjustable.

[0086] The techniques described herein may be implemented by various means so that an apparatus implementing one or more functions of a corresponding mobile entity described with an embodiment comprises not only prior art means, but also means for implementing the one or more functions of a corresponding apparatus described with an embodiment and it may comprise separate means for each separate function, or means may be configured to perform two or more functions. For example, these techniques may be implemented in hardware (one or more apparatuses), firmware (one or more apparatuses), software (one or more modules), or combinations thereof. For a firmware or software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in any suitable, processor/computer-readable data storage medium(s) or memory unit(s) or article(s) of manufacture and executed by one or more processors/computers. The data storage medium or the memory unit may be implemented within the processor/computer or external to the processor/computer, in which case it can be communicatively coupled to the processor/computer via various means as is known in the art.

[0087] Many modifications and other embodiments of the disclosures set forth herein will come to mind to one skilled in the art to which these embodiments of the disclosure pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiments of the disclosure are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

WHAT IS CLAIMED IS:

1. A method, comprising:

linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator; and

selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage.

2. The method according to claim 1, wherein the selecting comprises:

selecting to output the amplified radio frequency envelope signal to the radio frequency power amplifier when the level of the amplified radio frequency envelope signal is lower than the envelope threshold; and

selecting to output the amplified radio frequency envelope signal to the switcher stage when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

3. The method according to claim 1, further comprising:

bypassing and powering off the switcher stage when selecting to output the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

4. The method according to any of claims 1-3, wherein the linear regulator stage is powered by a low voltage fixed direct current power supply and the switcher stage is powered by a high voltage fixed direct current power supply.

5. The method according to claim 4, further comprising:

powering off the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is lower than the envelope threshold; and

powering on the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

6. The method according to claim 1, wherein the linear regulator stage is a linear amplifier that provides sourcing function and sinking function for envelope power of radio frequency power amplifier.

7. The method according to claim 1, wherein the switcher stage is a switching mode power supply that provides a high side source supply for envelope power of the radio frequency power amplifier.

8. The method according to claim 4, wherein the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier.

9. The method according to any of claims 1-8, wherein the envelope threshold is adjustable.

10. An apparatus, comprising:

a linear regulator stage for linearly amplifying a radio frequency envelope signal;

an envelope threshold detector for detecting whether a level of the amplified radio frequency envelope signal is lower or higher than an envelope threshold; and

a switcher stage connected in series with the linear stage,

wherein the linear regulator stage outputs directly to a radio frequency power amplifier or outputs to the switcher stage based on a result of the envelope threshold detector.

11. The apparatus according to claim 10, wherein the linear regulator stage outputs the amplified radio frequency envelope signal to the radio frequency power amplifier when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and the linear regulator stage outputs the amplified radio frequency envelope signal to the switcher stage when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

12. The apparatus according to claim 10, wherein the envelope threshold detector drives the switcher stage to be bypassed and powered off and the linear regulator stage outputs the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

13. The apparatus according to any of claims 10-12, further comprising:

a low voltage fixed direct current power supply for powering the linear stage; and a high voltage fixed direct current power supply for powering the switcher stage.

14. The apparatus according to claim 13, wherein the high voltage fixed direct current power supply is powered off when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is lower than the envelope threshold and is powered on when the envelope threshold detector detects that the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

15. The apparatus according to claim 10, wherein the linear regulator stage is a linear amplifier that provides sourcing function and sinking function for envelope power of the radio frequency power amplifier.

16. The apparatus according to claim 10, wherein the switcher stage is a switching mode power supply that provides a high side source supply for envelope power of the radio frequency power amplifier.

17. The apparatus according to claim 13, wherein the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier.

18. The apparatus according to claim 10, wherein the envelope threshold is adjustable.

19. The apparatus according to any of claims 10-18, wherein the apparatus includes an envelope tracking power supply modulator.

20. An apparatus, comprising:

means for linearly amplifying a radio frequency envelope signal at a linear regulator stage of an envelope tracking power supply modulator; and

means for selecting, based on a comparison of a level of the amplified radio frequency envelope signal with an envelope threshold, to output the amplified radio frequency envelope signal directly to a radio frequency power amplifier or to a switcher stage of the envelope tracking power supply modulator which is connected in series with the linear stage.

21. The apparatus according to claim 20, wherein the means for selecting comprises:

means for selecting to output the amplified radio frequency envelope signal to the radio frequency power amplifier when the level of the amplified radio frequency envelope signal is lower than the envelope threshold; and

means for selecting to output the amplified radio frequency envelope signal to the switcher stage when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

22. The apparatus according to claim 20, further comprising:

means for bypassing and powering off the switcher stage when selecting to output the amplified radio frequency envelope signal directly to the radio frequency power amplifier.

23. The apparatus according to any of claims 20-22, wherein the linear regulator stage is powered by a low voltage fixed direct current power supply and the switcher stage is powered by a high voltage fixed direct current power supply.

24. The apparatus according to claim 23, further comprising:

means for powering off the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is lower than the envelope threshold; and

means for powering on the high voltage fixed direct current power supply when the level of the amplified radio frequency envelope signal is higher than the envelope threshold.

25. The apparatus according to claim 20, wherein the linear regulator stage is a linear amplifier that provides sourcing function and sinking function for envelope power of the radio frequency power amplifier.

26. The apparatus according to claim 20, wherein the switcher stage is a switching mode power supply that provides a high side source supply for envelope power of the radio frequency power amplifier.

27. The apparatus according to claim 23, wherein the switcher stage is a three-state control circuitry for switching the high voltage fixed direct current power supply to the radio frequency power amplifier or switching the amplified radio frequency envelope signal to the radio frequency power amplifier.

28. The apparatus according to any of claims 20-27, wherein the envelope threshold is adjustable.