PREDISTORTER

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit of Singapore Patent Application No. 10201702678 W, entitled "Method For Tuning A RF Predistorter" and filed on March 31 , 2017, which is expressly incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] Various aspects of this disclosure generally relate to wireless communication, and more particularly, to tuning a radio frequency predistorter.

BACKGROUND

[0003] In order to satisfy the demand for increasing data rate for wireless communication, a wireless communication system requires higher bandwidth and higher order, non-constant envelope modulations to increase the data link capacity. Modulations schemes like quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM) have high peak to average ratios and put linearity constraints on the radio frequency (RF) power amplifier (PA). As such, a power amplifier requires linearization techniques to improve the efficiency and linearity. RF predistortion (PD) is a technique suitable for broadband power amplifier linearization. However, due to the highly non-linear characteristic of the power amplifier, the parameters setting for the predistortion needs to be optimized across the frequency band of operation.

[0004] The power amplifier operates across many channels in the allocated frequency spectrum. For each frequency channel, the predistortion linearizer needs to be adjusted to fit the power amplifier characteristic for broadband linearization. In order to assess the performance of the linearizer and automatically adjust to compensate for the change of operating frequency channel, the signal at the output of the power amplifier needs to be monitored. [0005] Some traditional linearization approaches do not include any compensation for operating across different frequency channels and do not have any detector for monitoring the power amplifier. Some traditional linearization approaches handle limited bandwidth, and require high computation power and high-speed analog-to- digital converters (ADCs) for the detector. Some traditional linearization approaches need to digitize signals using ADCs. When the modulated signal is a wideband signal, the ADCs need to sample at very high speed, which consumes more power.

[0006] It may be desirable to provide a linearization technique for a RF predistorter that is suitable for broadband signals, in particular, in satellite communications, and have a predistorter that is adjustable to cater to different frequency channels.

SUMMARY

[0007] The following presents a simplified summary in order to provide a basic understanding of various aspects of the disclosed invention. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. The sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0008] In one aspect of the disclosure, an apparatus for optimizing the bias setting of a RF predistortion linearizer for a power amplifier to operate across different frequency channels is provided. The apparatus may include a radio frequency power amplifier. The apparatus may include a radio frequency predistortion linearizer that predistorts a radio frequency signal and passes the predistorted radio frequency signal to the radio frequency power amplifier for amplification. The radio frequency predistortion linearizer may be configured based on a set of bias control settings for different operating frequencies. The apparatus may include a filtering and detection component configured to monitor performance of the radio frequency power amplifier and fine-tune the set of bias control settings based on the monitored performance of the radio frequency power amplifier.

[0009] In another aspect of the disclosure, a method of optimizing the bias setting of a RF predistortion linearizer for a power amplifier to operate across different frequency channels is provided. The method may include predistorting a radio frequency signal based on a set of bias control settings for different operating frequencies. The method may include passing the predistorted radio frequency signal to a radio frequency power amplifier for amplification. The method may include coupling a fraction of radio frequency power from the amplified radio frequency signal to obtain a feedback signal. The method may include down converting the feedback signal. The method may include monitoring performance of the radio frequency power amplifier based on the down-converted feedback signal. The method may include adjusting the set of bias control settings based on the monitored performance of the radio frequency power amplifier.

[0010] In another aspect of the disclosure, a radio frequency power monitor for tuning a predistortion linearizer for power amplification is provided. The radio frequency power monitor may include a coupler configured to obtain a feedback signal based on an amplified radio frequency signal provided by a power amplifier. The radio frequency power monitor may include an IQ down-converter configured to split in- phase (I) and quadrature (Q) signals based on the feedback signal and down-convert the I and Q signals. The radio frequency power monitor may include a filter configured to filter the down-converted I and Q signals. The radio frequency power monitor may include a power detector configured to detect the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals. A bias setting value for an operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals.

[0011] In yet another aspect of the disclosure, a method of tuning a predistortion linearizer for power amplification is provided. The method may include obtaining a feedback signal based on an amplified radio frequency signal provided by a power amplifier. The method may include splitting I and Q signals based on the feedback signal and down-converting the I and Q signals. The method may include filtering the down-converted I and Q signals. The method may include detecting the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals. A bias setting value for an operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals.

[0012] To the accomplishment of the foregoing and related ends, the aspects disclosed include the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail illustrate certain features of the aspects of the disclosure. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a chart illustrating the typical characteristic of a power amplifier.

[0014] FIG. 2 is a block diagram of an apparatus for optimizing the bias setting of the radio frequency predistortion linearizer in accordance with some embodiments of the disclosure.

[0015] FIG. 3 is a block diagram of a radio frequency predistortion linearizer with independent control of gain and phase responses and adaptive biasing.

[0016] FIG. 4 is a diagram illustrating the schematic of an adaptive bias circuit.

[0017] FIGS. 5A and 5B show the response of the radio frequency predistortion linearizer with the adaptive bias circuits.

[0018] FIG. 6 is a block diagram showing a filter and detection component.

[0019] FIG. 7 is a chart illustrating a power spectral density curve of a signal and the filter responses to the signal.

[0020] FIG. 8 is a flowchart of a method of wireless communication.

[0021] FIG. 9 is a flowchart of a method of tuning a predistortion linearizer for power amplification.

DETAILED DESCRIPTION

[0022] The detailed description set forth below in connection with the appended drawings is intended as a description of various possible configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0023] Several aspects of tuning a radio frequency predistorter will now be presented with reference to various apparatus and methods. The apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as "elements"). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0024] FIG. 1 is a chart illustrating the typical characteristic of a power amplifier. As shown, the gain response of the power amplifier changes with frequency. As such, the predistortion of the power amplifier needs to be optimized for different operating frequency channels.

[0025] In the disclosure, the bias setting of a RF predistortion linearizer may be optimized for a power amplifier to operate across different frequency channels. FIG. 2 is a block diagram of an apparatus 200 for optimizing the bias setting of the RF predistortion linearizer in accordance with some embodiments of the disclosure. As shown, the apparatus 200 may include a power amplifier 204, a RF predistorter 206, a coupler 208, a down converter 210, a filtering and detection component 214, and a controller 216.

[0026] The power amplifier 204 may be initially calibrated off-line to obtain a set of bias control settings 218 for different operating frequencies. The bias control settings 218 may be stored in a lookup table (LUT) for quick setting for the RF predistorter 206. In some embodiments, the lookup table may be part of the controller 216. The RF input may be predistorted by the RF predistorter 206 and passed to the power amplifier 204 for amplification. The coupler 208 may couple some RF power from the output of the power amplifier 204 for feedback. The feedback signal may be down converted by the down converter 210, and passed through the filtering and detection component 214. The controller 216 may process the output of the filtering and detection component 214 to fine-tune the bias control setting 218.

[0027] In some embodiments, an apparatus (e.g., the apparatus 200) for wireless communication is provided. The apparatus may include a radio frequency power amplifier (e.g., the power amplifier 204). The apparatus may include a radio frequency predistortion linearizer (e.g., the RF predistorter 206) configured to predistort a radio frequency signal and pass the predistorted radio frequency signal to the radio frequency power amplifier for amplification. The radio frequency predistortion linearizer may be configured based on a set of bias control settings (e.g., the bias control setting 218) for different operating frequencies. The apparatus may include a filtering and detection component (e.g., the filtering and detection component 214) configured to monitor performance of the radio frequency power amplifier and fine-tune the set of bias control settings based on the monitored performance of the radio frequency power amplifier.

[0028] In some embodiments, the radio frequency predistortion linearizer may be optimally set across a plurality of channels based on the set of bias control settings. In some embodiments, the filtering and detection component may include a power detector. The frequency of the output signal of the power detector may be substantially lower than the frequency of the radio frequency signal.

[0029] In some embodiments, the apparatus may further include a coupler (e.g., the coupler 208) configured to couple a fraction of radio frequency power from the amplified radio frequency signal to obtain a feedback signal. In some embodiments, the apparatus may further include a down converter (e.g., the down converter 210) configured to down-convert the feedback signal and pass the down-converted feedback signal to the filtering and detection component.

[0030] In some embodiments, the set of bias control settings may be stored in a lookup table. In some embodiments, the set of bias control settings may be retrieved from the lookup table and directed to the radio frequency predistortion linearizer to adaptively compensate non-linearity when an operating frequency changes. In some embodiments, the set of bias control settings stored in the lookup table may be searched to obtain an optimal ratio between channel spectrum power and spectral regrowth.

[0031] FIG. 3 is a block diagram of a RF predistortion linearizer 300 with independent control of gain and phase responses and adaptive biasing. In some embodiments, the RF predistortion linearizer 300 may include the RF predistorter 206 described above with reference to FIG. 2.

[0032] The RF input signal may be passed through a 3 dB hybrid coupler 302 and divided into two paths - one path to the power splitter 312, the other path to the power splitter 332. Each path is again split further into another two paths. The outputs of power splitter 312 form the conventional predistorter 310. The conventional predistorter 310 includes a linear branch and a non-linear branch. The linear branch includes a phase shifter 314, an attenuator 316, and a delay line 318. The non-linear branch includes an attenuator 320, a non-linear generator 322, and a delay line 324. A power combiner 326 combines the outputs of the linear branch and the non-linear branch. The attenuator 320 may limit the power going into the non-linear generator 322 so that it will not be overdriven by the input signal.

[0033] The outputs of the power splitter 332 go to the adaptive bias circuits 334 and 346. The output of the adaptive bias circuit 334 may be provided to the non-linear generator 322. The output of the adaptive bias circuit 346 may be provided to a nonlinear phase shifter 340, which may include an amplifier 344 and a phase shifter 342. The phase shifter 342 receives the output of the power combiner 326 and generates the output of the RF predistortion linearizer 300.

[0034] FIG. 4 is a diagram illustrating the schematic of an adaptive bias circuit 400. In some embodiments, the adaptive bias circuit 400 may be the adaptive bias circuit 334 or 346 described above with reference to FIG. 3. As shown, the adaptive bias circuit 400 may include capacitors 402, 406, 408, inductors 412, 416, and a diode 410. The output signal of the adaptive bias circuit 400 may be controlled by VA and VC. When the RF power of the input signal is low, the adaptive bias circuit 400 may have a constant direct current (DC) voltage output. After the RF power of the input signal exceeds a threshold level, as the RF power increases, the voltage of the output signal will increase.

[0035] Referring back to FIG. 3, the adaptive bias circuit 334 controls the shape of the RF predistortion linearizer 300 via VA1 and VC1. Neither the gain nor the phase response is independent. In some embodiments, the gain and phase response of the RF predistortion linearizer 300 may be independently adjusted by the VAs and VCs of the adaptive bias circuit 334 and the adaptive bias circuit 346, respectively. FIG. 5 A shows the response of the RF predistortion linearizer 300 with the adaptive bias circuit 334. As shown in FIG. 5 A, the gain response of the RF predistortion linearizer 300 changes with changing phase response. FIG. 5B shows the response of the RF predistortion linearizer 300 with the adaptive bias circuit 346. As shown in FIG. 5B, the gain response of the RF predistortion linearizer 300 is unchanged with changing phase response.

[0036] In traditional techniques, in order for the digital processor to produce the compensation for the power amplifier, the digital processor requires information from the transmit in-band channel bandwidth plus at least one or more adjacent channels that contain the spectrum regrowth information. Thus, the analog to digital converters (ADCs) require a sampling rate of at least 5 times the channel bandwidth. When the channel bandwidth is large, the ADCs operate at very high sampling rate, resulting in high power consumption. Beside the ADCs, the baseband processor also needs to operate at high speed in order to process the information from the ADCs.

[0037] Some embodiments of the disclosure are also independent of the digital baseband, as the controls are performed in the biasing of the predistortion. In the traditional approaches, the compensations are applied to the transmitter digital signal in the baseband processor.

[0038] Some embodiments of the disclosure may include two techniques: coarse- tuning based on lookup table and fine-tuning based on output monitoring. The two techniques may be combined and used together for the benefits of quick tuning and great accuracy.

[0039] Referring back to FIG. 2, in some embodiments, the coarse-tuning bias settings for different frequency channels may be obtained during the calibration of the amplification chain. These settings are obtained off-line and stored in a lookup table. When the power amplifier 204 is operating at a particular frequency channel, the controller 216 may retrieve the setting for the power amplifier 204 and quickly adjust to fit the setting.

[0040] For fine-tuning, the spectral regrowth of the modulated signal after the power amplifier 204 may need to be monitored. In some embodiments, the RF signal at the output of the power amplifier 204 may be coupled out and down converted to baseband I and Q signals. The baseband I and Q signals may then be processed by the filtering and detection component 214 before going to the controller 216.

[0041] FIG. 6 is a block diagram showing a filter and detection component 600. In some embodiments, the filter and detection component 600 may be the filter and detection component 214 described above with reference to FIG. 2. In some embodiments, each of the I and Q signals may be split into two paths. For example, the I signal may be split into two paths by the power splitter 610. One of the paths may pass through a low pass filter (LPF) 612 and the other a bandpass filter (BPF) 620. The LPF 612 may only allow the channel spectrum (desired signal) of the I signal to pass through and be detected by a power detector 614. The BPF 620 may only allow the spectral regrowth (undesired signal) of the I signal to pass through and be detected by another power detector 622. [0042] Similarly, the Q signal may be split into two paths by the power splitter 630. One of the paths may pass through a low pass filter 632 and the other a bandpass filter 640. The LPF 632 may only allow the channel spectrum (desired signal) of the Q signal to pass through and be detected by a power detector 634. The BPF 640 may only allow the spectral regrowth (undesired signal) of the Q signal to pass through and be detected by another power detector 642.

[0043] FIG. 7 is a chart 700 illustrating a power spectral density curve 702 of a signal and the filter responses to the signal. The chart 700 shows a LPF function 704 and a BPF function 706. The intersection between the area under the LPF function 704 and the area under the power spectral density curve 702 shows the total signal power at the output of the LPF, which may be the desired signal. The intersection between the area under the BPF function 706 and the area under the power spectral density curve 702 shows the total signal power at the output of the BPF, which may be undesired signal.

[0044] Referring back to FIG. 6, the output of the power detectors 614, 622, 634, 642 may be very low frequency signals compared to the transmitted signals. As such, low speed and low power consumption analog to digital converters (ADCs) 618, 624, 638, 644 may be employed to measure the power level and pass the information to the controller (e.g., the controller 216). The traditional methods require high speed and high power consumption ADCs to detect the entire bandwidth of the desired and undesired signals.

[0045] The measured power levels may be used to monitor the performance of the power amplifier. The ratio of power level between the in-band channel spectrum power and the spectral regrowth may provide an indication on the linearity performance of the power amplifier. It may be desirable to have this ratio as high as possible so that the spectral regrowth is minimized. Referring back to FIG. 2, based on the information of the ratios for I and Q channels, the controller 216 may further fine-tune the bias control settings 218 for the RF predistorter 206 to obtain the optimum ratio between the channel spectrum power and the spectral regrowth.

[0046] The RF predistortion linearizer 300 of FIG. 3 has independent gain and phase response controls. Therefore, the optimization algorithm may first optimize the gain response of the RF predistortion linearizer 300 to compensate for the gain nonlinearity of the power amplifier. Once the search is complete, the optimization algorithm may proceed to optimize the phase response of the RF predistortion linearizer 300 to compensate the phase non-linearity of the power amplifier. This method of optimization is much simpler compare to the algorithms used by digital predistortion (DPD) that require high speed and high complexity of processing. With independent gain and phase response controls in some embodiments of RF predistortion linearizer, it also opens the possibility to implement the optimization algorithm in continuous time to completely avoid the need for ADCs. For the purpose of generating a fine tuning gain or phase-control signal, the gain or phase nonlinear response of the RF predistortion linearizer may be perturbed sinusoidally, resulting in a periodic modulation of the spectral regrowth. The power of the spectral regrowth modulation is detected and used in a feedback arrangement to control the gain and phase-control value. This enables a fully integrated low-cost RF adaptive predistortion linearizer with very wide linearization bandwidth.

[0047] In some embodiments, a radio frequency power monitor for tuning a predistortion linearizer for power amplification is provided. The radio frequency power monitor may include a coupler (e.g., the coupler 208) configured to obtain a feedback signal based on an amplified radio frequency signal provided by a power amplifier (e.g., the power amplifier 204). The radio frequency power monitor may include an IQ down- converter (e.g., the down converter 210) configured to split I and Q signals based on the feedback signal and down-convert the I and Q signals. The radio frequency power monitor may include a filter (e.g., the LPFs 612, 632, the BPFs 620, 640) configured to filter the down-converted I and Q signals. The radio frequency power monitor may include a power detector (e.g., the power detectors 614, 622, 634, 642) configured to detect a power level of channel spectrum and a power level of spectral regrowth in each of the filtered I and Q signals. The bias setting value for an operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals.

[0048] In some embodiments, the filter may include, for each signal of the I and Q signals, a power splitter (e.g., the power splitter 610, 630) configured to split the signal. The filter may include, for each signal of the I and Q signals, a low pass filter (e.g., the LPF 612 or 632) configured to filter a first portion of the channel spectrum of the signal based on the operating frequency. The filter may include, for each signal of the I and Q signals, a bandpass filter (e.g., the BPF 620 or 640) configured to filter a second portion of the channel spectrum of the signal based on the operating frequency.

[0049] In some embodiments, the power detector may detect the power level of the first portion of the channel spectrum of each of the I and Q signals, and the power level of the second portion of the channel spectrum of each of the I and Q signals. In some embodiments, the power level of the first portion of the channel spectrum of each of the I and Q signals and the power level of the second portion of the channel spectrum of each of the I and Q signals may be differentiated to provide a bias signal. The bias signal may provide an indication of linearity performance of the power amplifier. In some embodiments, the filtered first portion of the channel spectrum of the signal represents channel spectrum power, and the filtered second portion of the channel spectrum of the signal represents the spectral regrowth.

[0050] In some embodiments, the bias setting value may be stored in a lookup table for the operating frequency. In some embodiments, a range of bias setting values may be stored for a range of operating frequencies. In some embodiments, the bias setting values may be retrieved from the lookup table and directed to a predistortion component to adaptively compensate non-linearity when the operating frequency changes. In some embodiments, the bias setting values stored in the lookup table may be searched to obtain an optimal ratio between channel spectrum power and spectral regrowth.

[0051] Below is an example of the enhancement provided by the RF predistortion linearizer of some embodiments for a Ka-band power amplifier with 25W (44dBm) RF output power. Without the RF predistortion linearizer, the efficiency of the power amplifier may be 1 1 %, the DC power consumption may be 230W, and the power to dissipate by heatsink may be 205W. With the RF predistortion linearizer of one embodiment, the backoff of the power amplifier may improve by 3 dB, the efficiency of the power amplifier may be improved to 17%, the DC power consumption may be reduced to 149W, the power to dissipate by heatsink may be reduced to 124W. Therefore, the power saving caused by the RF predistortion linearizer may be 81 W, and the efficiency improvement may be 55%.

[0052] In one aspect of the disclosure, a linear transmit architecture with RF predistortion linearizer is provided. The architecture may use a LUT to achieve quick tuning of bias settings for different frequency channels and a low power consumption filter and detector block to obtain performance monitoring and automatic fine-tuning of bias settings for further performance optimization. The predistortion linearizer of the power amplifier may be optimally set across various frequency channels. The performance of the power amplifier may be monitored and optimized with a low power detector.

[0053] In another aspect of the disclosure, a RF power monitor for tuning a predistortion linearizer for power amplification is provided. The RF power monitor may include a coupler for receiving the amplified RF signal from the power amplifier and obtaining a feedback signal based on the amplified RF signal. The RF power monitor may include an IQ downconverter for splitting I and Q signals and down converting the I and Q signals to provide a pair of modulated signals. The RF power monitor may include a filter for receiving the I and Q signals. The RF power monitor may include a (power) detector configured for detecting power level of the channel spectrum of the I and Q signals, and power level of spectral regrowth in each of the I and Q signals, to provide a bias setting value to be stored in a LUT for an operating frequency. A range of bias setting values may be stored for a range of operating frequencies.

[0054] In some embodiments, the filter may include a power splitter for splitting each I and Q signals. The filter may include a LPF for filtering a first portion of the channel spectrum of the signal based on the operating frequency, and a BPF for filtering a second portion of the channel spectrum of the signal based on the operating frequency.

[0055] In some embodiments, the (power) detector may detect the power level of the first portion of the channel spectrum of the signal, the power level of the second portion of the channel spectrum (spectral regrowth) of the signal. The (power) detector may differentiate these power levels to provide a bias signal, which may provide an indication of linearity performance of the power amplifier.

[0056] In some embodiments, the filtered first portion of the channel spectrum of the signal may represent channel spectrum power, and the filtered second portion of the channel spectrum of the signal may represent the spectral regrowth. In some embodiments, the bias setting values may be retrieved from the LUT and directed to the predistortion linearizer to adaptively compensate non-linearity when the operating frequency changes. This may be referred to as coarse tuning. Further, the bias setting values stored in the LUT may be searched to obtain the optimal ratio between the channel spectrum power and the spectral regrowth. This may be referred to as fine- tuning, as described above with reference to FIGS. 3-5. [0057] FIG. 8 is a flowchart 800 of a method of wireless communication. In some embodiments, the method may optimize the bias setting of a RF predistortion linearizer so that a power amplifier may operate across different frequency channels. In some embodiments, the method may be performed by the apparatus 200 described above with reference to FIG. 2. At 802, the apparatus may predistort a radio frequency signal based on a set of bias control settings for different operating frequencies. In some embodiments, the radio frequency predistortion linearizer may be optimally set across a plurality of channels based on the set of bias control settings. In some embodiments, the set of bias control settings may be stored in a lookup table.

[0058] At 804, the apparatus may pass the predistorted radio frequency signal to a radio frequency power amplifier for amplification.

[0059] At 806, the apparatus may couple a fraction of radio frequency power from the amplified radio frequency signal to obtain a feedback signal.

[0060] At 808, the apparatus may down-convert the feedback signal.

[0061] At 810, the apparatus may monitor the performance of the radio frequency power amplifier based on the down-converted feedback signal. In some embodiments, the performance of the radio frequency power amplifier may be monitored with a power detector. In some embodiments, the frequency of the output signal of the power detector may be substantially lower than the frequency of the radio frequency signal.

[0062] At 812, the apparatus may adjust the set of bias control settings based on the monitored performance of the radio frequency power amplifier. In some embodiments, the set of bias control settings may be adjusted based on the down-converted feedback signal. In some embodiments, the set of bias control settings maybe retrieved from the lookup table and directed to the radio frequency predistortion linearizer to adaptively compensate non- linearity when the operating frequency changes. In some embodiments, the set of bias control settings stored in the lookup table may be searched to obtain the optimal ratio between channel spectrum power and spectral regrowth.

[0063] FIG. 9 is a flowchart 900 of a method of tuning a predistortion linearizer for power amplification. In some embodiments, the method may be performed by the apparatus 200 described above with reference to FIG. 2 or the filter and detection component 600 described above with reference to FIG. 6. At 902, the apparatus may obtain a feedback signal based on an amplified radio frequency signal provided by a power amplifier. [0064] At 904, the apparatus may split I and Q signals based on the feedback signal. The apparatus may further down-convert the I and Q signals.

[0065] At 906, the apparatus may filter the down-converted I and Q signals. In some embodiments, to filter the down- converted I and Q signals, the apparatus may split each of the I and Q signals into two paths. One path of the signal may pass through a low pass filter, which may filter a first portion of the channel spectrum of the signal based on the operating frequency. The other path of the signal may pass through a bandpass filter, which may filter a second portion of the channel spectrum of the signal based on the operating frequency. In some embodiments, the filtered first portion of the channel spectrum of the signal represents channel spectrum power, and the filtered second portion of the channel spectrum of the signal represents the spectral regrowth.

[0066] At 908, the apparatus may detect the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals. A bias setting value for the operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals.

[0067] In some embodiments, to detect the power level of channel spectrum of each of the filtered I and Q signals, the apparatus may detect the power level of the first portion of the channel spectrum of each of the I and Q signals, and the power level of the second portion of the channel spectrum of each of the I and Q signals. In some embodiments, the power level of the first portion of the channel spectrum of each of the I and Q signals and the power level of the second portion of the channel spectrum of each of the I and Q signals may be differentiated to provide a bias signal. The bias signal may provide an indication of linearity performance of the power amplifier.

[0068] In some embodiments, the bias setting value may be stored in a lookup table for the operating frequency. In some embodiments, a range of bias setting values may be stored for a range of operating frequencies. In some embodiments, the bias setting values may be retrieved from the lookup table and directed to a predistortion linearizer to adaptively compensate non-linearity when the operating frequency changes. In some embodiments, the bias setting values stored in the lookup table may be searched to obtain an optimal ratio between channel spectrum power and spectral regrowth.

[0069] In the following, various aspects of this disclosure will be illustrated:

[0070] Example 1 is an apparatus for wireless communication. The apparatus may include a radio frequency power amplifier. The apparatus may include a radio frequency predistortion linearizer configured to predistort a radio frequency signal and pass the predistorted radio frequency signal to the radio frequency power amplifier for amplification. The radio frequency predistortion linearizer may be configured based on a set of bias control settings for different operating frequencies. The apparatus may include a filtering and detection component configured to monitor performance of the radio frequency power amplifier and fine-tune the set of bias control settings based on the monitored performance of the radio frequency power amplifier.

[0071] In Example 2, the subject matter of Example 1 may optionally include that the radio frequency predistortion linearizer may be optimally set across a plurality of channels based on the set of bias control settings.

[0072] In Example 3, the subject matter of any one of Examples 1 to 2 may optionally include that the filtering and detection component may include a power detector, the frequency of the output signal of the power detector being substantially lower than the frequency of the radio frequency signal.

[0073] In Example 4, the subject matter of any one of Examples 1 to 3 may optionally include that the apparatus may further include a coupler configured to couple a fraction of radio frequency power from the amplified radio frequency signal to obtain a feedback signal.

[0074] In Example 5, the subject matter of Example 4 may optionally include that the apparatus may further include a down converter configured to down-convert the feedback signal and pass the down-converted feedback signal to the filtering and detection component.

[0075] In Example 6, the subject matter of any one of Examples 1 to 5 may optionally include that the set of bias control settings may be stored in a lookup table.

[0076] In Example 7, the subject matter of Example 6 may optionally include that the set of bias control settings may be retrieved from the lookup table and directed to the radio frequency predistortion linearizer to adaptively compensate non-linearity when an operating frequency changes.

[0077] In Example 8, the subject matter of Example 6 may optionally include that the set of bias control settings stored in the lookup table may be searched to obtain an optimal ratio between channel spectrum power and spectral regrowth.

[0078] Example 9 is a method of wireless communication. The method may include: predistorting a radio frequency signal based on a set of bias control settings for different operating frequencies; passing the predistorted radio frequency signal to a radio frequency power amplifier for amplification; monitoring performance of the radio frequency power amplifier; and adjusting the set of bias control settings based on the monitored performance of the radio frequency power amplifier.

[0079] In Example 10, the subject matter of Example 9 may optionally include that the monitoring may be performed with a power detector, the frequency of the output signal of the power detector being substantially lower than the frequency of the radio frequency signal.

[0080] In Example 1 1 , the subject matter of any one of Examples 9 to 10 may optionally include that the method may further include coupling a fraction of radio frequency power from the amplified radio frequency signal to obtain a feedback signal.

[0081] In Example 12, the subject matter of Example 1 1 may optionally include that the method may further include down-converting the feedback signal, wherein the monitoring and the adjusting are performed based on the down-converted feedback signal.

[0082] Example 13 is a radio frequency power monitor for tuning a predistortion linearizer for power amplification. The radio frequency power monitor may include: a coupler configured to obtain a feedback signal based on an amplified radio frequency signal provided by a power amplifier; an IQ down-converter configured to split I and Q signals based on the feedback signal and down-convert the I and Q signals; a filter configured to filter the down-converted I and Q signals; and a power detector configured to detect the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals. A bias setting value for an operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals.

[0083] In Example 14, the subject matter of Example 13 may optionally include that the filter may include: for each signal of the I and Q signals, a power splitter configured to split the signal; for each signal of the I and Q signals, a low pass filter configured to filter a first portion of the channel spectrum of the signal based on the operating frequency; and for each signal of the I and Q signals, a bandpass filter configured to filter a second portion of the channel spectrum of the signal based on the operating frequency. [0084] In Example 15, the subject matter of Example 14 may optionally include that the power detector may detect the power level of the first portion of the channel spectrum of each of the I and Q signals, and the power level of the second portion of the channel spectrum of each of the I and Q signals.

[0085] In Example 16, the subject matter of Example 15 may optionally include that the power level of the first portion of the channel spectrum of each of the I and Q signals and the power level of the second portion of the channel spectrum of each of the I and Q signals are differentiated to provide a bias signal, the bias signal providing an indication of linearity performance of the power amplifier.

[0086] In Example 17, the subject matter of any one of Examples 14 to 16 may optionally include that the filtered first portion of the channel spectrum of the signal represents channel spectrum power, and the filtered second portion of the channel spectrum of the signal represents the spectral regrowth.

[0087] In Example 18, the subject matter of any one of Examples 13 to 17 may optionally include that the bias setting value may be stored in a lookup table for the operating frequency, where a range of bias setting values may be stored for a range of operating frequencies.

[0088] In Example 19, the subject matter of Example 18 may optionally include that the bias setting values may be retrieved from the lookup table and directed to a predistortion component to adaptively compensate non-linearity when the operating frequency changes.

[0089] In Example 20, the subject matter of Example 18 may optionally include that the bias setting values stored in the lookup table may be searched to obtain an optimal ratio between channel spectrum power and spectral regrowth.

[0090] Example 21 is a method of tuning a predistortion linearizer for power amplification. The method may include: obtaining a feedback signal based on an amplified radio frequency signal provided by a power amplifier; splitting I and Q signals based on the feedback signal; down-converting the I and Q signals; filtering the down-converted I and Q signals; and detecting the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals. A bias setting value for the operating frequency may be adjusted based on the detected power levels of channel spectrum and spectral regrowth in each of the filtered I and Q signals. [0091] In Example 22, the subject matter of Example 21 may optionally include that, to filter the down-converted I and Q signals, the method may further include: for each signal of the I and Q signals, splitting the signal; for each signal of the I and Q signals, filtering a first portion of the channel spectrum of the signal based on the operating frequency; and for each signal of the I and Q signals, filtering a second portion of the channel spectrum of the signal based on the operating frequency.

[0092] In Example 23, the subject matter of Example 22 may optionally include that, to detect the power level of channel spectrum and the power level of spectral regrowth in each of the filtered I and Q signals, the method may include detecting the power level of the first portion of the channel spectrum of each of the I and Q signals, and the power level of the second portion of the channel spectrum of each of the I and Q signals.

[0093] In Example 24, the subject matter of Example 23 may optionally include that the power level of the first portion of the channel spectrum of each of the I and Q signals and the power level of the second portion of the channel spectrum of each of the I and Q signals may be differentiated to provide a bias signal, the bias signal providing an indication of linearity performance of the power amplifier.

[0094] A person skilled in the art will appreciate that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0095] It is understood that the specific order or hierarchy of blocks in the processes / flowcharts disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes / flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented. [0096] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term "some" refers to one or more. Combinations such as "at least one of A, B, or C," "one or more of A, B, or C," "at least one of A, B, and C," "one or more of A, B, and C," and "A, B, C, or any combination thereof include any combination of

A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as "at least one of A, B, or C," "one or more of A,

B, or C," "at least one of A, B, and C," "one or more of A, B, and C," and "A, B, C, or any combination thereof may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words "module," "mechanism," "element," "device," and the like may not be a substitute for the word "means." As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase "means for."