Symbol-based envelope tracking and crest factor reduction

Abstract

The invention relates to symbol-based envelope tracking and crest factor reduction. Aspects of the present disclosure relate to symbol-based envelope tracking. The voltage modulator circuit may generate an output bias voltage that tracks a root-mean-square symbol power of the radio frequency signal. A crest factor reduction circuit in a signal path providing a radio frequency signal may adjust a crest factor reduction threshold such that the crest factor reduction threshold corresponds to an output bias voltage.

Description

[0001] Cross-reference priority application

[0002] This application claims priority to U.S. Provisional Application No. 63 / 512,041, filed on July 5, 2023, entitled “SYMBOL-BASED ENVELOPE TRACKING,” the disclosure of which is incorporated herein by reference in its entirety for all purposes. Technical Field

[0003] Embodiments of the present disclosure are directed to systems for generating bias voltages for power amplifiers with sign-based envelope tracking. Background Art

[0004] The radio system may send and receive signals in the form of electromagnetic waves having a frequency in the range of approximately 30 kilohertz (kHz) to 300 gigahertz (GHz). The radio system may be used for wireless communications, such as cellular communications and / or other wireless network communications.

[0005] Radio systems that transmit signals typically include power amplifiers to amplify radio frequency (RF) signals for transmission via one or more antennas. In such systems, power amplifiers may consume a large amount of power. Power-efficient power amplifiers are desirable for various applications. Summary of the invention

[0006] Each of the innovations described in the claims has several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the claims, some of the prominent features of the disclosure will now be briefly described.

[0007] One aspect of the present disclosure is a power amplifier system with symbol-based envelope tracking, including a voltage modulator circuit, a power amplifier, and a signal path. The voltage modulator circuit is configured to generate an output bias voltage that tracks the root mean square symbol power of a radio frequency signal. The voltage modulator circuit is configured to adjust the output bias voltage on a symbol boundary. The power amplifier is configured to receive the output bias voltage and amplify the radio frequency signal. The signal path is configured to provide the radio frequency signal to the power amplifier. The signal path includes a crest factor reduction block, and the crest factor reduction module is configured to adjust a crest factor reduction threshold so that the crest factor reduction threshold corresponds to the output bias voltage.

[0008] The power amplifier system may include a quantizer configured to determine a symbol-based envelope tracking state based on a transmit signal power. The voltage modulator circuit may generate an output bias voltage based on the symbol-based envelope tracking state. The crest factor reduction block may adjust the crest factor reduction threshold based on the symbol-based envelope tracking state. The signal path may include a digital predistortion system coupled between the crest factor reduction block and the digital-to-analog converter. The digital predistortion system may adjust the digital predistortion based on the symbol-based envelope tracking state. The quantizer may receive a composite transmit symbol power associated with a plurality of carriers.

[0009] The signal path may include a digital-to-analog converter coupled between an output of the crest factor reduction block and an input of the power amplifier.

[0010] The power amplifier system may be operated in a discontinuous transmission state. The power amplifier transistor of the power amplifier system may have an output terminal connected to ground in the discontinuous transmission state. The power amplifier transistor of the power amplifier system may have an output terminal that is floating in the discontinuous transmission state.

[0011] The radio frequency signal may include at least two carriers having different symbol lengths. The voltage modulator circuit may adjust the output bias voltage corresponding to a symbol boundary of a carrier among the at least two carriers having the shortest symbol period.

[0012] The power amplifier may include a main power amplifier transistor coupled to a voltage modulator circuit and a peak power amplifier transistor coupled to a fixed voltage source. The power amplifier may include a main power amplifier transistor coupled to a voltage modulator circuit and a peak power amplifier transistor coupled to a voltage modulator circuit. The power amplifier may include a main power amplifier transistor coupled to a voltage modulator circuit and a peak power amplifier transistor coupled to a second voltage modulator circuit.

[0013] The voltage modulator circuit may switch the output bias voltage between discrete voltage levels within a time range between 5 nanoseconds and 200 nanoseconds.

[0014] The voltage modulator circuit may switch the output bias voltage between discrete voltage levels of at least 4 discrete voltage levels on symbol boundaries.

[0015] A base station may include a power amplifier system.

[0016] Another aspect of the present disclosure is a method for amplifying a radio frequency signal using symbol-based envelope tracking. The method includes: determining a symbol-based envelope tracking state based on a transmitted signal power; switching an output bias voltage between a plurality of discrete voltage levels on a symbol boundary of a radio frequency signal based on the symbol-based envelope tracking state, wherein the output bias voltage is provided to a power amplifier; adjusting a crest factor reduction threshold of a crest factor reduction block based on the symbol-based envelope tracking state, wherein the crest factor reduction block is in a signal path providing the radio frequency signal to the power amplifier; and amplifying the radio frequency signal with the power amplifier.

[0017] The method may include adjusting digital predistortion in the signal path based on a symbol-based envelope tracking state.

[0018] The method may include operating a power amplifier system including a power amplifier in a discontinuous transmission state.

[0019] The radio frequency signal may include two carriers with different symbol periods. The switching of the output voltage may occur at a symbol boundary of one of the two carriers with the shorter symbol period.

[0020] Another aspect of the present disclosure is a system with symbol-based envelope tracking. The system includes a device for generating an output bias voltage that tracks the root mean square symbol power of a radio frequency signal on a symbol-by-symbol basis, and a signal path configured to provide the radio frequency signal. The signal path includes a crest factor reduction block that is configured to adjust a crest factor reduction threshold so that the crest factor reduction threshold corresponds to the output bias voltage.

[0021] Another aspect of the present disclosure is a power amplifier system with symbol-based envelope tracking, including a voltage modulator circuit, a power amplifier, and a signal path configured to provide a radio frequency signal to the power amplifier. The voltage modulator circuit is configured to generate an output bias voltage based on a symbol-based envelope tracking state, so that the output bias voltage tracks the root mean square symbol power of the radio frequency signal symbol by symbol. The power amplifier is configured to receive the output bias voltage and amplify the radio frequency signal. A digital predistortion system is included, which is configured to adjust the digital predistortion based on the symbol-based envelope tracking state.

[0022] The digital predistortion system may adjust the digital precompensator by adjusting at least the digital predistortion coefficients. The digital predistortion system may adjust the digital precompensator by adjusting at least the digital predistortion actuator.

[0023] The power amplifier system may include a quantizer configured to determine a symbol-based envelope tracking state based on a transmit signal power. The quantizer may receive a composite transmit symbol power associated with a plurality of carriers. The power amplifier system may include one or more delay blocks coupled between the quantizer and the digital predistortion system.

[0024] The signal path may include a crest factor reduction block configured to adjust a crest factor reduction threshold based on a symbol-based envelope tracking state.

[0025] The power amplifier system may be operated in a discontinuous transmission state.

[0026] The radio frequency signal may include at least two carriers having different symbol lengths. The voltage modulator circuit may adjust the output bias voltage corresponding to a symbol boundary of a carrier among the at least two carriers having the shortest symbol period.

[0027] The voltage modulator circuit may switch the output bias voltage between discrete voltage levels of at least 4 discrete voltage levels on symbol boundaries.

[0028] The power amplifier may be a Doherty power amplifier.

[0029] Another aspect of the present disclosure is a method for amplifying a radio frequency signal using symbol-based envelope tracking. The method includes: determining a symbol-based envelope tracking state based on a transmitted signal power; switching an output bias voltage between a plurality of discrete voltage levels on a symbol boundary of a radio frequency signal according to the symbol-based envelope tracking state, wherein the output bias voltage is provided to a power amplifier; adjusting digital predistortion according to the symbol-based envelope tracking state, wherein a digital predistortion system performing the digital predistortion is in a signal path providing the radio frequency signal to the power amplifier; and amplifying the radio frequency signal with the power amplifier.

[0030] The method may include operating a power amplifier system including a power amplifier in a discontinuous transmission state.

[0031] The radio frequency signal may include two carriers with different symbol periods. An output bias voltage may shift at a symbol boundary of the carrier with the shorter symbol period of the two carriers.

[0032] Another aspect of the present disclosure is a system with symbol-based envelope tracking. The system includes a voltage modulator circuit and a signal path configured to provide a radio frequency signal. The voltage modulator circuit is configured to generate an output bias voltage based on a symbol-based envelope tracking state, so that the output bias voltage tracks the root mean square symbol power of the radio frequency signal symbol by symbol. The signal path includes a digital predistortion system configured to adjust the digital predistortion based on the symbol-based envelope tracking state.

[0033] The system may include a quantizer configured to determine a symbol-based envelope tracking state based on an indication of transmit power. The system may include one or more delay blocks coupled between the quantizer and the digital predistortion system. The quantizer may receive composite transmit symbol powers associated with multiple carriers.

[0034] The signal path may include a crest factor reduction block configured to adjust a crest factor reduction threshold based on a symbol-based envelope tracking state.

[0035] The voltage modulator circuit may switch the output bias voltage between discrete voltage levels of the plurality of discrete voltage levels within a time in a range between 5 nanoseconds and 200 nanoseconds.

[0036] For the purpose of summarizing the present disclosure, certain aspects, advantages, and novel features of the innovations have been described herein. It should be understood that not all of these advantages may be realized according to any particular embodiment. Thus, the innovations may be embodied or implemented in a manner that realizes or optimizes one advantage or a group of advantages taught herein without necessarily realizing other advantages taught or suggested herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Embodiments of the present disclosure will be described by way of non-limiting examples with reference to the accompanying drawings.

[0038] Figure 1 It is a bar chart of the probability of unit resource usage for a relatively large number of base stations over several weeks.

[0039] Figure 2 It is a graph of the RF envelope of a 20 MHz LTE carrier over time, with resource utilization varying from 100% to 1.6%.

[0040] Figure 3A , 3B and 3C are graphs of 5 symbols of the RF signal. Figure 3A A fixed bias voltage is shown. Figure 3B The sign-based envelope tracking bias voltage is shown. Figure 3C The continuous envelope tracking voltage is shown.

[0041] Figure 4is a schematic block diagram of a symbol-based envelope tracking system according to one embodiment.

[0042] Figure 5 is corresponding to Figure 2 EVM plot for each symbol of a 20 MHz LTE carrier.

[0043] Fig. 6A and 6B is an experimental result graph showing the efficiency and power savings using symbol-based envelope tracking.

[0044] Fig. 7A , 7B 7C is a schematic diagram of a Doherty amplifier connected to a sign-based envelope tracking voltage modulator according to an embodiment.

[0045] Figure 8 is a schematic diagram of a power amplifier transistor connected to a sign-based envelope tracking voltage modulator according to one embodiment. DETAILED DESCRIPTION

[0046] The following detailed description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein may be embodied in a variety of different ways, for example, as defined and covered by the claims. In this specification, reference is made to the accompanying drawings in which similar reference numerals may indicate identical or functionally similar elements. It should be understood that the elements shown in the figures are not necessarily drawn to scale. In addition, it will be understood that certain embodiments may include more elements than the elements shown in the figures and / or a subset of the elements shown. In addition, some embodiments may combine any suitable combination of features from two or more of the drawings. The headings provided herein are for convenience only and do not necessarily affect the scope or meaning of the claims.

[0047] introduction

[0048] Desirable characteristics of a cellular wireless base station include maximizing data throughput, minimizing energy consumption, minimizing acquisition cost, minimizing the number of sites, and minimizing size and weight.

[0049] Achieving these aspirations simultaneously is challenging. Over the past 20 years, it has been difficult to introduce energy-saving measures that had a measurable impact on initial equipment cost (capex). Any increase in equipment cost has largely paralleled increases in throughput. However, this has been gradually changing, and recent significant increases in global energy prices and the ongoing, incremental shift toward a green economy are finally tipping the equation in favor of lower operating costs through reduced energy consumption, even if this results in a slightly higher initial purchase cost.

[0050] Radio frequency (RF) power amplifiers (PAs) can be the main energy consumer in wireless base stations, and remain so despite evolutions such as massive multiple-input multiple-output (mMIMO). Therefore, PAs can be an important component of base station design when it comes to energy reduction methods.

[0051] Cellular networks are also dominated by newer wireless standards of the fourth generation (4G) (Long Term Evolution) and fifth generation (5G) (New Radio), while phasing out older technologies of the third generation (3G) (Wideband Code Division Multiple Access) and second generation (2G) (Global System for Mobile Communications). It looks like 3G will be phased out first, with 2G remaining in limited frequency bands in some continents, such as Europe to support existing machine-to-machine (M2M) communications infrastructure. Either way, most new equipment installed in the future will be pure 4G and 5G using compatible orthogonal frequency division multiplexing (OFDM) modulation schemes.

[0052] The operating mode of cellular wireless networks is to provide users with a good experience. This usually means that if users suddenly have a demand for network resources, these network resources are immediately available. In access networks, these network resources include RF power and bandwidth. This usually means that the wireless access network has idle capacity most of the time.

[0053] This can be seen in data taken day and night over a period of several weeks from a large network of base stations. Figure 1 is a bar chart of the probability of unit resource usage for a large number of base stations over several weeks. Figure 1 The average resource usage is 18% of the maximum capacity. Figure 1 , unit resource usage may correspond to the root mean square (RMS) RF output power. Figure 1 Indicates a low probability of 100% resource usage and maximum RMSRF power.

[0054] Even taking into account the low usage at night, the base station is at a high percentage of utilization for a relatively short period of time. This provides an opportunity to save energy by adjusting the efficiency of the RF PA at a lower RF power output rather than at its maximum RF power.

[0055] Both Long Term Evolution (LTE) and New Radio (NR) use OFDM modulation in the modulation of the RF signal. This means that both LTE and NR are symbol-based transmission methods. Within the period of one symbol, which is approximately 70μs for LTE and 70 / (2^N)μs for NR (where N is the number 0, 1, 2…4), the RMS power of the waveform is a constant because it transmits the sum of thousands of sinusoids of different frequencies and relative phases. In the next symbol, there may be a different sum of sinusoids, or just a few if there is not much data to transmit. Within one symbol, these sinusoids add together to produce a peak waveform with a peak-to-average ratio of approximately 11 decibels (dB), which can be clipped to approximately 8 dB through crest factor reduction (CFR) with little loss in data integrity. This can be achieved in a variety of signal processing techniques. Figure 2 As can be seen in FIG. 1 , for a 10 millisecond (ms) long LTE transmission waveform, the percentage of usage of the available sine wave varies from 100% to 1.6%.

[0056] Figure 2 20 is a graph of the RF envelope of a 20 megahertz (MHz) LTE carrier over time, with resource utilization varying from 100% to 1.6%. The y-axis of the graph is the RF envelope (or amplitude). The x-axis of the graph is time in 491.52 MHz clock samples. The graph includes instantaneous amplitude (peak) 202, a trace 204 of the RMS level, a trace 206 of the CFR clipping level, and a waveform envelope 208 after clipping at 8 dB peak-to-average power ratio (PAR).

[0057] Symbol-based envelope tracking (SBET) can take advantage of the significantly reduced RF peak power involved in transmitting these symbols in low-power symbols, and can be provided by the same RF transistor operating at a significantly reduced drain voltage. The reduced drain voltage can result in significantly reduced energy consumption. The drain voltage can be quickly switched from one value to another at symbol boundaries in 10 nanoseconds (ns).

[0058] Description of Certain Embodiments

[0059] Figure 3A , 3B and 3C are the drain voltage diagrams for 5 symbols of the RF signal. Figure 3A A fixed bias voltage is shown. Figure 3B The sign-based envelope tracking bias voltage is shown. Figure 3C The continuous envelope tracking voltage is shown. Figure 3A , 3BFigures 3 and 3C graphically illustrate the concept of envelope tracking. This waveform is what a single RF PA transistor produces at its output. The waveform is symbol-based, with symbol boundaries at 0, 1, 2, 3, 4, and 5 on the x-axis, corresponding to time. Therefore, the RMS power of the waveform varies on each symbol boundary (where a symbol is typically 10 microseconds long in LTE and NR).

[0060] If the system is restricted to have Figure 3A The fixed drain voltage shown in FIG. 3 supports the maximum RF peak power that can be generated. The fixed drain voltage line 302 is as shown in FIG. Figure 3A This is how most cellular wireless base station RF power amplifiers are configured. Slow changes in drain voltage (seconds or more) can be implemented to accommodate situations where the likelihood of high traffic is minimal, such as at night.

[0061] In sign-based envelope tracking (SBET), the voltage at the output of the power amplifier transistor (e.g., the drain voltage) may change only on symbol boundaries, e.g. Figure 3B The drain voltage can support the maximum peak power within that symbol. This improves PA efficiency because the same RF power is produced in the symbol, but operating at a lower drain voltage as shown by the symbol-based envelope tracking line 304.

[0062] Figure 3C A more efficient mode of operation using full envelope tracking is shown. Figure 3C Each peak of the waveform envelope in . Figure 3C As shown, the drain voltage curve 306 tracks each peak on the waveform envelope. However, this efficiency gain may come at the expense of having to change the drain voltage 1000s several times faster than SBET. Figure 3C This full envelope tracking in is an order of magnitude more complex than the SBET embodiments disclosed herein and involves complex digital pre-distortion (DPD) and analog switches (e.g., gallium nitride (GaN) switches) that are faster than SBET. As the instantaneous bandwidth of the RF signal increases, full envelope tracking may find it difficult or impossible to track every peak and valley. In this case, full envelope tracking can begin to skip valleys to reduce complexity, at the expense of some efficiency performance. This is different from the disclosed embodiments of SBET, in which the drain voltage only offsets a value on symbol boundaries. In SBET, the drain voltage can have a roughly constant voltage level for the entire symbol, while the waveform envelope has multiple peaks and valleys for a symbol.

[0063] In the case of NR (5G) mixed digital symbol bearers, the symbol length is shorter for higher digital symbols. In this case, in some cases, SBET can switch at the symbol boundary of the highest digital bearer. Alternatively, in some other cases, SBET can switch at the symbol boundary of the lowest digital bearer.

[0064] SBET system architecture

[0065] Various aspects of the present disclosure relate to a power amplifier system with symbol-based envelope tracking. The power amplifier system may include a voltage modulator circuit for generating an output bias voltage that tracks an RMS symbol power of an RF signal that varies on a symbol-by-symbol basis, and a power amplifier configured to receive the output bias voltage and amplify the RF signal. The power amplifier transmitter system may include a crest factor reduction circuit that adjusts a crest factor reduction threshold on a symbol boundary. The power amplifier-transmitter system may include a DPD system that accounts for the output bias voltage in the DPD.

[0066] The SBET state can be determined based on the RMS power of the transmitted signal per symbol. In some applications, the transmitted signal can be a composite transmitted signal including multiple carriers. The voltage modulator can adjust the output bias voltage based on the SBET state. The crest factor reduction circuit can adjust the crest factor reduction threshold based on the SBET state. The DPD system can adjust the DPD according to the SBET state.

[0067] In applications where there is a composite transmit signal comprising two or more carriers with different symbol lengths, the SBET state can be transitioned based on the shortest symbol length. In some other applications, where there is a composite transmit signal comprising two or more carriers with different symbol lengths, the SBET state can be transitioned based on the longest symbol length.

[0068] In response to detecting the absence of power in the transmit signal, the power amplifier system can operate in a discontinuous transmit state. In the discontinuous transmit state, the output of the power amplifier transistor (e.g., a field effect power amplifier transistor) can be connected to ground (short circuit) or at a floating potential (open circuit).

[0069] Figure 44 is a schematic block diagram of an SBET system 400 according to one embodiment. The SBET system 400 is a power amplifier system including a power amplifier. As shown, the SBET system 400 includes a voltage modulator 402, a supply voltage circuit 404, and a power amplifier 406. The SBET system 400 has 4 SBET voltages that can be selected for the drain of the power amplifier transistor, and the waveform consists of 3 individual carriers. Any other suitable number of SBET voltages and / or any other suitable number of individual carriers may be used in some other applications.

[0070] Voltage modulator 402 selects 1 of N fixed voltages from supply voltage circuit 404 to provide power amplifier 406. In the illustrated power amplifier 406, the selected voltage is provided to the drain of power amplifier transistor 407. Each voltage from supply voltage circuit 404 corresponds to SBET state 1 to N. There may be any suitable number of SBET states for a particular application. For example, in some applications, there are 2 SBET states, such as Figure 4 There are 4 SBETs, 8 SBETs, or 16 SBETs shown. The voltage modulator 402 can generate an output bias voltage that tracks the envelope of the RF signal symbol by symbol. The output bias voltage can track the envelope of the RF signal for a group of symbols and / or each individual symbol. The output bias voltage can have a transition time of 10s nanoseconds. In some applications, the voltage modulator 402 can convert the output bias voltage between discrete voltage levels within a time range between 5 nanoseconds and 200 nanoseconds. In some applications, the voltage modulator 402 can convert the output bias voltage between discrete voltage levels within a time range between 5 nanoseconds and 50 nanoseconds. The output bias voltage can step significantly on the symbol boundary (e.g., from 25 volts (V) to 50 volts).

[0071] The SBET system 400 also has a state known as a discontinuous transmission (DTX) mode in which no RF power can be transmitted in a symbol. In this case, either no voltage is connected to the common side of the switch (open circuit), or the drain of the power amplifier transistor 407 is connected to ground via the switch. The PA output bias voltage can be discharged so that it is close to zero volts (e.g., ground) in the DTX state. In the DTX state, the RF PA 406 is off and should consume negligible power.

[0072] The voltage modulator 402 can provide a constant voltage for the entire symbol and switch states on symbol boundaries. The voltage modulator 402 can select from a plurality of discrete voltages (e.g., V1, V2, V3, V4) based on the SBET state to provide as an output bias voltage. The voltage modulator 402 can switch the output bias voltage between these discrete voltages on symbol boundaries. In some applications, the voltage modulator 402 can provide a constant voltage for a group of symbols and change the state on symbol boundaries.

[0073] In some applications, when the composite transmit signal includes carriers with different symbol lengths, the voltage modulator 402 can only switch states on the symbol boundary of the carrier with the shortest symbol period (the highest value in NR). For example, in the SBET system 400, if one carrier has a symbol length that is half the symbol length of the other two carriers, the quantizer 408 can determine the SBET state at or near the symbol boundary of the symbol with half the length of the other symbols. In this example, for two different symbols with shorter symbol lengths, the RMS power of the symbols of the other two carriers can remain the same value.

[0074] In some applications, when the composite transmit signal includes carriers with different symbol lengths, the voltage modulator 402 can only switch states on the symbol boundary of the carrier with the longest symbol period (the lowest value in NR). For example, in the SBET system 400, if the first carrier has a longer symbol length than the second and third carriers, the quantizer 408 can determine the SBET state at or near the symbol boundary of the symbol of the first carrier of the composite signal. The maximum RMS power of each individual symbol of the second carrier corresponding to a symbol of the first carrier can be used to determine the SBET state. Similarly, the maximum RMS power of each individual symbol of the third carrier corresponding to a symbol of the first carrier can be used to determine the SBET state. Therefore, in this example, the SBET state can be determined and set for the peak RMS power of the composite symbol of the length of the longest length symbol.

[0075] Capacitor C RF and C SNUB The capacitors C1 to C1 are relatively small (e.g., having a capacitance of less than 1 nanofarad) to reduce and / or minimize the switching / settling time of the drain voltage of the power amplifier transistor 407. N ( Figure 4 C1 to C4 in can be larger (e.g., microfarad-sized) decoupling capacitors.

[0076] The fixed voltage V1 to V1 provided by the power supply voltage circuit 404 NThe maximum voltage V1 can be selected so that it supports the highest peak RF power after applying crest factor reduction (CFR) (typically Ppk(max)=Prms(max)+8dB or so). N (Right now Figure 4 V4 in the figure may be limited by the reduced gain caused by the lower drain voltage. The minimum voltage V N Can depend on the PA transistor technology. In some cases, V N ≈1 / 2V1, the gain is reduced by about 6dB. If the gain is reduced too much, the benefits of SBET may begin to diminish. Each SBET state can have an associated and different CFR threshold level so that each SBET state supports a different RF peak power. In some applications, subsets of SBET states can have different CFR threshold levels to support different RF peak powers.

[0077] Intermediate drain voltage levels (e.g. Figure 4 V2 and V3 in (V2 and V3 in) can be between the maximum and minimum voltages. There is a tradeoff in selecting the number of discrete voltages, with more discrete voltages generally corresponding to higher efficiency improvements, but at the expense of increased cost and board area. In some applications, typical values ​​of N range from 2 to 4. The voltage modulator 402 can implement a DTX state. In the DTX state, all switches of the voltage modulator 402 can be disconnected, or one or more switches can be grounded.

[0078] The SBET system 400 may include a digital predistortion (DPD) block 412 to compensate for the nonlinearity of the power amplifier 406. The DPD block 412 is a DPD system. The DPD block 412 may include a DPD actuator and a DPD adaptive circuit. For the power amplifier 406, the RF PA nonlinear response may be a function of the drain voltage. Therefore, the DPD performed in the DPD block 412 may also be a function of the SBET state. In the SBET system 400, the SBET state is fed to the DPD block 412 after a matching delay. As shown in FIG. Figure 4 As shown, quantizer 408 may output an SBET state, and delay blocks 414 and 416 may add matching delays such that the SBET state received by DPD block 412 corresponds to an input signal to DPD block 412 .

[0079] The DPD can be adjusted based on the DPD SBET state. Adjusting the DPD can include adjusting the DPD coefficients and / or adjusting the DPD actuator. In some implementations, the DPD model coefficients can be switched on the symbol boundary. Alternatively or additionally, the DPD actuator can be adjusted by enabling and / or disabling certain functions and / or by adjusting the topology of the DPD actuator. This can adjust the DPD model to correspond to the SBET state. For example, the model can be adjusted by adjusting the connection of the signal path in the DPD actuator including a nonlinear gain block (e.g., a lookup table) and / or by adjusting the connection of the artificial neural network of the DPD actuator. Each SBET state or output bias voltage level can have its own DPD model / coefficient, which can be switched simultaneously in one clock cycle when the symbol data boundary passes through the DPD block 412.

[0080] To simplify the implementation of DPD, no effort may be made to accurately correct PA distortion during the switching transition when the drain voltage is between two set voltages. However, the switching duration may be minimized to nanoseconds of 10s to minimize the spectral distortion contribution of the switching on average. Distortion may be relatively high during the transition time, but on average can be reduced by approximately 1:1000, which is the approximate ratio of the voltage transition time to the symbol period. The output of the DPD block 412 may be provided to a digital-to-analog converter (DAC) 417 to generate an analog transmit signal.

[0081] The analog signal generated by DAC 417 may be filtered by filter 452, amplified by amplifier 453, and split by hybrid splitter 454. Hybrid splitter 454 may provide an RF signal to main power amplifier transistor 407 and peak power amplifier transistor 462 of power amplifier 406. Hybrid splitter 454 may also provide a phase shift such that there is a 90 degree phase shift between the output signals provided by hybrid splitter 454. Power amplifier 406 of SBET system 400 is a Doherty power amplifier as shown.

[0082] The error vector magnitude (EVM) impact due to drain voltage transitions may be less of a concern since the transition occurs during the cyclic prefix period of most symbols, although it can appear mid-symbol in the case of mixed numerology.

[0083] The CFR threshold for limiting the peak power of the digital signal can be a function of the SBET state. In the SBET system 400, the SBET state is fed to the CFR block 418 after a matching delay. Figure 4As shown, quantizer 408 can output an SBET state, and delay block 414 can add a matching delay so that the SBET state received by CFR block 418 corresponds to the input signal of CFR block 418. CFR block 418 can adjust the CFR threshold based on the SBET state. Therefore, the CFR threshold can correspond to the output bias voltage provided to power amplifier 406. CFR block 418 can be implemented by any suitable circuit. The digital circuit of a digital signal processor can implement CFR block 418. A transceiver integrated circuit can implement CFR block 418, for example.

[0084] Adjusting the CFR threshold based on the SBET state may be important for the energy-saving performance of the SBET system 400. By having a different CFR threshold for each SBET state (e.g., drain voltage), a peak RF power is defined for each SBET level. The lower the CFR threshold, the greater the energy savings, but the higher the signal distortion and EVM, which in turn increases the bit error rate (BER). The trade-off is to ensure that the PAR of any symbol in any SBET state remains greater than or equal to the threshold. An example threshold is 8dB.

[0085] Figure 5 is corresponding to Figure 2 Figure 2. EVM per symbol for a 20MHz LTE carrier. Figure 2 The EVM of 140 symbols in the waveform is as follows Figure 5 The RMS EVM of the reduced power symbols is below 1%, except for 1 symbol where the CFR clipping is the most peaky.

[0086] refer to Figure 4 , the SBET state is carried by the SBET+DTX bit output from the n-level quantizer 408. Figure 4 In FIG. 4 , the n-level quantizer 408 is a 4-level quantizer because the voltage modulator circuit 402 provides 4 SBET voltages. The SBET+DTX bit can change state on each symbol boundary. These bits are appropriately delayed so that they arrive at the CFR block 418, the DPD block 412, and the voltage modulator 402, and when the transmit data passes through the SBET system 400 (in the case of the voltage modulator 402, it is an analog signal through the field effect transistor of the power amplifier 406), these bits become the configuration for the new SBET state. Delay blocks 414, 416, and 419 provide such delays for the SBET state bits.

[0087] The appropriate SBET state can be determined by effectively calculating the composite transmit RMS signal power of each complete symbol at the input of the CFR block 418. The quantizer 408 can determine the composite transmit RMS signal power. The composite transmit signal can be formed by multiple carriers. In the SBET system 400, each carrier can be received as a frequency domain signal; transformed to the time domain by a corresponding inverse fast Fourier transform (iFFT) block 442A, 442B, 442C; a cyclic prefix (CP) can be added by a corresponding CP block 444A, 444B, 444C, and up-converted by a corresponding digital up converter (DUC) 446A, 446B, 446C. The outputs of the DUC 446A, 446B, 446C can be combined to form a composite transmit signal provided to the CFR block 418.

[0088] However, calculating the transmit power directly at the input of CFR block 418 may not be ideal because it may take at least many microseconds (and ideally an entire symbol) to obtain an accurate result. Such a calculation may be prepared too late because the composite transmit RMS signal symbol power should be known at the beginning of the symbol, not the end. Although a 10 microsecond delay can be added to the transmit signal path to calculate the transmit power at the input of CFR block 418, such a delay is generally undesirable.

[0089] Another method is to calculate the symbol power of each carrier multiplied by the single carrier-related gain from the iFFT input to the CFR input, and then add the single carrier powers. In the SBET system 400, the iFFT gain blocks 432A, 432B and 432C and multipliers 434A, 434B and 434C can create a composite transmit signal symbolPwr at the input of the n-level quantizer 408, which has a power corresponding to the composite transmit signal at the input of the CFR block 418. The iFFT gain blocks 432A, 432B and 432C can provide a gain corresponding to the iFFT blocks 442A, 442B and 442C. The gain applied in each multiplier 434A, 434B and 434C can correspond to the gain of the corresponding DUC in the DUC 446A, 446B and 446C that forms the composite transmit signal input to the CFR block 418. Processing frequency domain data rather than time domain data means that symbol power information may be available before the symbol boundaries of the composite transmit signal are provided to the input of the CFR block 418 .

[0090] The quantizer 408 can determine the SBET state based on the composite transmit signal symbolPwr it receives. The N-level quantizer 408 can be pre-programmed with N thresholds in the manner of a thermometer and output the SBET state as a number from 1 to N. The DTX bit is a special condition when the symbol power is zero (or close to zero) and can be used to disable all switches so the common switch node of the voltage modulator 402 is open, or an additional switch is used to short the drain of the power transistor 407 to ground.

[0091] SBET Performance

[0092] The purpose of adding SBET is to reduce the energy consumption of RF PA in wireless base stations, which will reduce operating expenses. With this reduced energy consumption, the performance of RF PA can be minimally reduced in terms of transmit signal purity (e.g., EVM) and spectral emission. It is also hoped that these goals can be achieved with minimal increase in equipment cost (capital expenditure).

[0093] Fig. 6A and 6B is a graph of experimental results showing the efficiency and power savings using SBET. Fig. 6A The enhancement of drain efficiency using SBET and an off-the-shelf GaN-Doherty PA module targeted at small cell and large MIMO base stations is shown. SBET is compared to using a 31V fixed voltage supply for these PAs. Multiple transmit waveforms were generated for a single 20MHz LTE carrier. Different waveforms were generated such that the number of resource blocks (RBs) used for data (physical downlink shared channel (PDSCH)) varied from 1 to 100 RBs. The other physical channels (RS, physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), and physical downlink control channel (PDCCH)) were the same for all waveforms. This approximately simulates different cell resource usage from 1% to 100% since a 20MHz LTE carrier has a maximum of 100 RBs.

[0094] for Fig. 6A and 6B In the SBET, four voltages are used, with the maximum being 31 V and the minimum being 15.5 V. The drain voltage transition time from one symbol to the next is about 20 nanoseconds.

[0095] exist Figure 6BIn the waveform, the RMS RF output power (averaged over all symbols of a 1ms frame) varies from 0.9 watts (W) at 1RB to 7.5 W at 100RB, where the non-data physical channels in the waveform consume most of the power at 1RB. As the number of data RBs decreases from 100%, the RF output power decreases proportionally, and initially there is no power savings using SBET until the drain voltage first drops to a lower voltage of about 60%. From this point on, SBET significantly saves direct current (DC) power from the drain supply.

[0096] exist Fig. 6A In the 2016 paper, SBET maintained PA drain efficiency in the 45%-50% range over a relatively wide range of RF output powers. The efficiency gains were greatest at lower powers, but here less power needs to be saved. Figure 6B The results show that about 2W of DC power can be saved from about 1% to 60% RB utilization, while no power is saved above about 70% RB utilization. These efficiency figures include relatively small power losses in the modulator. The efficiency of the modulator is about 99% because the frequency of the switching changes is relatively low (low 10s of kHz) and the switching losses are mainly from the on-resistance (Rds) of the switch, which is also relatively low.

[0097] The efficiency enhancements of SBET described above translate into energy savings at the base station, which depends on the fraction of time the base station spends at a particular percentage of resource usage. If the base station is always at 100% usage, there may be no savings from SBET. If the base station usage is always 1%, there may be significant savings.

[0098] Figure 1 Statistics on the resource usage of base stations in the network allow us to estimate the average power savings for the collection of base stations in the network during the day / night and over a week. High resource usage occurs only a small fraction of the time. If we assume that a 64T64R Massive MIMO base station is capable of producing 320W RMS power (maximum), the power consumption will be the same as Fig. 6A That corresponds to about 64 PAs. A base station in this network with an average power of 320 watts would consume about 9 kWh / day of energy at the output stage of its RF PA, whereas if SBET is used, it would only consume about 6.2 kWh / day of energy. This is a significant energy saving.

[0099] Other features

[0100] Other functions of the SBET system will be discussed.Any suitable principles and advantages of these features may be implemented with each other and / or any embodiment disclosed herein.

[0101] Tri-state logic to save logic lines in the modulator

[0102] exist Figure 4 In , the number of logic lines driving the voltage modulator 402 is an upper limit (log2(n)), where n is the number of voltages (or SBET states). Adding a DTX state may add additional logic lines. Therefore, implementing the DTX state as a three-state SBET logic line can save the need for additional logic lines. The three-state driver can have a third state, where it is floating or open circuit for the DTX state. The three-state driver can be implemented in a SBET system with a DTX state.

[0103] Crest factor reduction

[0104] A typical CFR block may have 3 sequential engines that first detect peaks and then correct for them. During detection, the CFR block 418 may record the SBET / threshold level with the peak. The threshold may then be passed to the correction hardware. The correction hardware may reduce the peak to the desired level. There may be a central block that delays the update to each engine so that the threshold changes at the same relative sample for each engine. This may also be extended to non-SBET uses where we can now align threshold and pulse updates to symbol boundaries. Updates may be seamless with these features where previously one engine was disabled at a time to update the threshold. These features may be Figure 4 The CFR block 418 is implemented.

[0105] Digital Pre-Distortion

[0106] DPD can measure and subsequently correct the nonlinear response of an RF power amplifier. As mentioned above, the RF PA nonlinear response can be a function of the drain voltage. Therefore, the nonlinear compensation block in the DPD can be a function of the SBET state, which means that the nonlinear coefficients / model can change with the SBET state and the drain voltage at the symbol boundary. Another complexity of using certain transistors (e.g., GaN RF transistors) in RF PAs is that their charge trapping behavior can change the nonlinear characteristics of the PA on long-term time scales of microseconds to milliseconds. Neural predistortion (NPD) can be used for long-term tracking of RF PA nonlinearities. Compared to a fixed drain voltage, the use of SBET can amplify the long-term dynamic nonlinear behavior, which is particularly evident in GaN RF power transistors.

[0107] Within the NPD input data path, the PA drain voltage (SBET level) can be tracked. Each of the N SBET levels (e.g., Figure 4Each of the 4 SBET levels of the SBET system 400 can be expanded to binary levels, so there are N binary levels passed to the neural network (NN). Some NNs use an 8-bit MAC. For such NNs, there can be 8-bit programmable values ​​to indicate 0 or 1. This allows the NN to learn the best 8-bit values ​​for all levels. These functions can be used in Figure 4 The DPD block 412 is implemented.

[0108] RF Power Amplifier Connections

[0109] Doherty RF amplifiers can be used in wireless infrastructure base stations at RF frequencies below 7 gigahertz (GHz). There are many connection options between the SBET voltage modulator and the 2 (or more) transistors of the RF Doherty amplifier. Fig. 7A , 7B 7C are schematic diagrams of Doherty power amplifiers 406 connected to SBET voltage modulators 402 according to an embodiment. These Doherty power amplifiers 406 include a main power amplifier transistor 407 and a peak power amplifier transistor 462.

[0110] exist Fig. 7A In FIG. 4 , a voltage modulator 402 is connected to the main power amplifier transistor 407, while the peak power amplifier transistor 462 has a fixed supply voltage. Figure 7B In FIG. 4 , the drain of the main power amplifier transistor 407 and the peak power amplifier transistor 462 are connected to the same voltage modulator 402 at a common node or common switch point. It may be desirable to reduce and / or minimize the physical distance between the output node of the voltage modulator 402 and the drain of the power amplifier transistor in the physical layout. Figure 7C In the embodiment, there are two voltage modulators 402A and 402B, one voltage modulator 402A is connected to the drain of the main power amplifier transistor 407, and the other voltage modulator 402B is connected to the drain of the peak power amplifier transistor 462.

[0111] Fig. 7A , 7B There is a trade-off in cost performance between the three configurations shown in 7C and 7C. Each of these three configurations is advantageous in certain applications.

[0112] Using a Doherty amplifier with SBET benefits efficiency at maximum RMS power output as well as at lower RMS output powers.

[0113] SBET can also improve the efficiency of non-Doherty RF amplifier stages, whether used alone or in other configurations such as load-modulated balanced amplifiers (LMBAs). Figure 8An example of a voltage modulator 402 is shown in which the SBET is connected to a single power amplifier transistor 802 .

[0114] Power Amplifier Transistors

[0115] Although the embodiments disclosed herein may be discussed with reference to power amplifier field effect transistors and modulating the drain voltage for sign-based envelope tracking, any suitable principles and advantages disclosed herein may be implemented with a power amplifier having a different type of power amplifier transistor output stage. In some applications, a power amplifier in a sign-based envelope tracking system according to any suitable principles and advantages disclosed herein may include, but is not limited to, a field effect transistor, a complementary metal oxide semiconductor (CMOS) transistor, a bipolar transistor, a heterojunction bipolar transistor, and the like. In the case where the power amplifier includes a bipolar power amplifier transistor, the sign-based envelope tracking may modulate the bias voltage at the collector of the bipolar power amplifier transistor, and / or any other suitable teachings applied to the drain may be applied to the collector. The power amplifier transistor may be implemented by any suitable transistor technology for a particular application. Example power amplifier transistors may include, but are not limited to, GaN transistors, silicon transistors, silicon-on-insulator transistors, SiGe transistors, GaAs transistors, SiC transistors, InP transistors, and the like. In addition, any power amplifier transistor disclosed herein may be implemented by two or more power amplifier transistors.

[0116] Wireless communication standards

[0117] Although the embodiments disclosed herein may be discussed with reference to certain communication standards, any suitable principles and advantages disclosed herein may be implemented with a radio frequency system that transmits radio frequency signals via one or more antennas in accordance with any suitable wireless communication standard. In some applications, a radio frequency system with symbol-based envelope tracking in accordance with any suitable principles and advantages disclosed herein may generate signals in accordance with any suitable wireless communication standard, such as a Wi-Fi standard, another local area network standard, a personal wireless local area network standard, a future cellular technology standard, etc.

[0118] in conclusion

[0119] In the above embodiments, the apparatus, system and method for the power amplifier envelope tracker are described in conjunction with specific embodiments. However, it should be understood that the principles and advantages of the embodiments can be applied to any other system, apparatus or method requiring envelope tracking.

[0120] The principles and advantages described herein can be implemented in various devices. Examples of such devices may include, but are not limited to, communication infrastructure, such as wireless or wired communication infrastructure, consumer electronics, components of consumer electronics, electronic test equipment, vehicle electronics, industrial electronics, etc. Electronic products may include, but are not limited to, base stations, such as cellular base stations, access points, repeaters, repeaters, wireless communication devices, mobile phones (e.g., smart phones), handheld computers, tablet computers, laptops, wearable computing devices, in-vehicle electronic systems, radios, wearable health monitoring devices, Internet of Things (IoT) devices, etc. In addition, devices may include unfinished products.

[0121] Unless the context clearly requires otherwise, throughout the specification and claims, the words "comprises," "including," "having," and the like are to be interpreted in an inclusive sense, rather than an exclusive or exhaustive sense; that is, in the sense of "including but not limited to." The words "coupled" or "connected," as generally used herein, refer to two or more elements, which may be directly connected or connected through one or more intermediate elements. In addition, the words "herein," "above," "below," and words of similar meaning used in this application shall refer to the entirety of this application, rather than to any particular part of this application. Where the context permits, words used in the singular or plural in the detailed description may also include the plural or singular, respectively. When referring to a list of two or more items, the word "or" is intended to cover all of the following interpretations of the word: any item in the list, all items in the list, and any combination of items in the list. All numerical values ​​provided herein are intended to include similar values ​​within measurement error.

[0122] Additionally, unless specifically stated otherwise or otherwise understood in the context of use, conditional language used herein, such as "may," "might," "could," "for example," "such as," etc., is generally intended to convey that some embodiments include and other embodiments do not include certain features, elements, and / or states.

[0123] The teaching of the present invention provided herein can be applied to other systems, not necessarily the above-mentioned systems. The elements and actions of the various embodiments described above can be combined to provide further embodiments. The actions of the methods discussed herein can be performed in any appropriate order. In addition, the actions of the methods discussed herein can be appropriately performed serially or in parallel.

[0124] Although certain embodiments of the present invention have been described, these embodiments are presented only by way of example and are not intended to limit the scope of the present disclosure. In fact, the novel methods and systems described herein can be embodied in various other forms. In addition, without departing from the spirit of the present disclosure, various omissions, replacements and changes can be made to the form of the methods and systems described herein. For example, although the disclosed embodiments are presented in a given arrangement, alternative embodiments can utilize different components and / or circuit topologies to perform similar functions, and some elements can be deleted, moved, added, subdivided, combined and / or modified. Each of these elements can be appropriately implemented in various different ways. Any appropriate combination of the elements and actions of the various embodiments described above can be combined to provide further embodiments. The attached claims and their equivalents are intended to cover such forms or modifications that fall within the scope and spirit of the present disclosure. Therefore, the scope of the present invention is defined by reference to the claims.

Claims

1. A power amplifier system with sign-based envelope tracking, the power amplifier system comprising: a voltage modulator circuit configured to generate an output bias voltage that tracks a root mean square symbol power of a radio frequency signal, the voltage modulator circuit configured to adjust the output bias voltage on a symbol boundary; a power amplifier configured to receive the output bias voltage and amplify the radio frequency signal; and A signal path is configured to provide the radio frequency signal to the power amplifier, the signal path includes a peak factor reduction block, and the peak factor reduction block is configured to adjust a peak factor reduction threshold so that the peak factor reduction threshold corresponds to the output bias voltage.

2. The power amplifier system of claim 1 , further comprising a quantizer configured to determine a symbol-based envelope tracking state based on a transmit signal power, wherein the voltage modulator circuit is configured to generate the output bias voltage according to the symbol-based envelope tracking state, and the crest factor reduction block is configured to adjust the crest factor reduction threshold according to the symbol-based envelope tracking state.

3. The power amplifier system of claim 2, wherein the signal path comprises a digital predistortion system coupled between the crest factor reduction block and a digital-to-analog converter, wherein the digital predistortion system is configured to adjust digital predistortion according to the symbol-based envelope tracking state. 4 . The power amplifier system of claim 2 , wherein the quantizer is configured to receive composite transmit symbol powers associated with a plurality of carriers.

5. The power amplifier system of claim 1, wherein the signal path comprises a digital-to-analog converter coupled between an output of the crest factor reduction block and an input of the power amplifier.

6. The power amplifier system of claim 1, wherein the power amplifier system is operable in a discontinuous transmission state.

7. The power amplifier system of claim 6, wherein a power amplifier transistor of the power amplifier system has an output terminal connected to ground in the discontinuous emission state.

8. The power amplifier system of claim 6, wherein a power amplifier transistor of the power amplifier system has an output terminal that floats in the discontinuous emission state.

9. The power amplifier system of claim 1 , wherein the RF signal comprises at least two carriers having different symbol lengths, and the voltage modulator circuit is configured to adjust an output bias voltage corresponding to a symbol boundary of a carrier among the at least two carriers having a shortest symbol period.

10. The power amplifier system of claim 1, wherein the power amplifier comprises a main power amplifier transistor coupled to the voltage modulator circuit and a peak power amplifier transistor coupled to a fixed voltage source.

11. The power amplifier system of claim 1 , wherein the power amplifier comprises a main power amplifier transistor coupled to the voltage modulator circuit and a peak power amplifier transistor coupled to the voltage modulation circuit.

12. The power amplifier system of claim 1, wherein the power amplifier comprises a main power amplifier transistor coupled to the voltage modulator circuit and a peak power amplifier transistor coupled to a second voltage modulator circuit.

13. The power amplifier system of claim 1, wherein the voltage modulator circuit is configured to switch the output bias voltage between discrete voltage levels within a time in a range between 5 nanoseconds and 200 nanoseconds.

14. The power amplifier system of claim 1, wherein the voltage modulator circuit is configured to convert the output bias voltage between discrete voltage levels of at least 4 discrete voltage levels on the symbol boundaries.

15. A base station comprising the power amplifier system of claim 1.

16. A method for amplifying a radio frequency signal with symbol-based envelope tracking, the method comprising: determining a symbol-based envelope tracking state based on the transmitted signal power; switching an output bias voltage between a plurality of discrete voltage levels on symbol boundaries of a radio frequency signal based on the symbol-based envelope tracking state, wherein the output bias voltage is provided to a power amplifier; adjusting a crest factor reduction threshold of a crest factor reduction block based on the symbol-based envelope tracking state, the crest factor reduction block being in a signal path providing the radio frequency signal to the power amplifier; and The radio frequency signal is amplified using the power amplifier.

17. The method of claim 16, further comprising adjusting digital predistortion in the signal path based on the symbol-based envelope tracking state.

18. The method of claim 16, further comprising operating a power amplifier system including a power amplifier in a discontinuous transmission state.

19. The method of claim 16, wherein the radio frequency signal comprises two carriers having different symbol periods, and the switching occurs at a symbol boundary of the carrier of the two carriers having a shorter symbol period.

20. A system with symbol-based envelope tracking, the system comprising: means for generating an output bias voltage based on tracking the root mean square symbol power of the radio frequency signal on a symbol-by-symbol basis; and A signal path is configured to provide the radio frequency signal, the signal path includes a peak factor reduction block, the peak factor reduction block is configured to adjust a peak factor reduction threshold so that the peak factor reduction threshold corresponds to the output bias voltage.

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