System and Methods of RF Power Transmission, Modulation, and Amplification, Including Control Functions to Transition an Output of a MISO Device
Embodiments of the present invention include a method and system for control of a multiple-input-single output (MISO) device. For example, the method includes partitioning a waveform constellation space into a plurality of regions, where each region of the plurality of regions is associated with one or more control functions of the MISO device. The method also includes transitioning the MISO device between a plurality of classes of operation based on the one or more control functions.
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The present application is a continuation of U.S. application Ser. No. 13/565,007, filed Aug. 2, 2012, now allowed, which is a continuation of U.S. application Ser. No. 13/069,155, filed Mar. 22, 2011, now U.S. Pat. No. 8,410,849, which is a continuation of U.S. patent application Ser. No. 12/236,079, filed Sep. 23, 2008, now U.S. Pat. No. 7,911,272, which is a continuation-in-part of U.S. patent application Ser. No. 12/142,521, filed Jun. 19, 2008, now U.S. Pat. No. 8,013,675, which claims the benefit of U.S. Provisional Patent Application No. 60/929,239, filed Jun. 19, 2007, and U.S. Provisional Patent Application No. 60/929,584, filed Jul. 3, 2007, all of which are incorporated herein by reference in their entireties.
The present application is related to U.S. patent application Ser. No. 11/256,172, filed Oct. 24, 2005, now U.S. Pat. No. 7,184,723 and U.S. patent application Ser. No. 11/508,989, filed Aug. 24, 2006, now U.S. Pat. No. 7,355,470, both of which are incorporated herein by reference in their entireties.
BACKGROUND FieldEmbodiments of the present invention relate generally to RF (radio frequency) power transmission, modulation, and amplification.
BackgroundToday's RF power amplifiers are required to generate complex RF signals with stringent output power and linearity requirements. For example, in order to comply with the requirements of a WCDMA waveform, a power amplifier needs to support approximately 30-40 dB of instantaneous output power dynamic range at a given power output level. This is mainly due to the ACPR (Adjacent Channel Power Ratio) and the ACLR (Adjacent Channel Leakage Ratio) requirements of the WCDMA waveform, which require very deep nulls as the output power waveform crosses zero.
Generally, the ACLR and ACPR that a power amplifier can achieve are related to the linearity of the power amplifier over the output power range of the desired waveform. Modern RF waveforms (e.g., OFDM, CDMA, WCDMA, etc.) are characterized by their associated PAP (Peak-to-Average Power) ratios. As such, in order to generate such waveforms, the power amplifier needs to be able to operate in a largely linear manner over a wide output power range that encompasses the output power range of the desired waveforms.
Outphasing amplification or LINC (Linear Amplification with Nonlinear Components) provides an amplification technique with the desirable linearity to amplify RF waveforms with large PAP ratios. Outphasing works by separating a signal into equal and constant envelope constituents, linearly amplifying the constituents, and combining the amplified constituents to generate the desired output signal. To preserve linearity when combining the amplified constituents, existing outphasing techniques use an isolating and/or a combining element, which provides the needed isolation between the branches of the outphasing amplifier to reduce non-linear distortion.
In several respects, however, existing outphasing techniques are not suitable for implementation in modern portable devices. For example, the isolating and/or combining element that they use causes a degradation in output signal power (due to insertion loss and limited bandwidth) and, correspondingly, low power amplifier efficiency. Further, the typically large size of isolating/combining elements precludes having them in monolithic amplifier designs.
There is a need therefore for outphasing amplification systems and methods that eliminate the isolating/combining element used in existing outphasing techniques, while providing substantially linear amplification over a wide output power dynamic range to support modern RF waveforms.
BRIEF SUMMARYEmbodiments of the present invention relate generally to RF power transmission, modulation, and amplification.
An embodiment of the present invention includes a method for control of a multiple-input-single-output (MISO) device. The method can include partitioning a waveform constellation space into a plurality of regions, where each region of the plurality of regions is associated with one or more control functions of a multiple-input-single-output (MISO) device. The method can also include transitioning the MISO device between a plurality of classes of operation based on the one or more control functions.
Another embodiment of the present invention includes a system. The system includes a multiple-input-single-output (MISO) device and a transfer function module. The transfer function module is configured to transition the MISO device between a plurality of classes of operation based on one or more control functions, wherein the one or more control functions are each associated with a region from a plurality of regions partitioned from a waveform constellation space.
Further embodiments, features, and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
The present invention will be described with reference to the accompanying drawings. Generally, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.
DETAILED DESCRIPTIONIn commonly owned U.S. patent(s) and application(s), cross-referenced above, VPA (Vector Power Amplification) and MISO (Multiple-Input-Single-Output) amplification embodiments were introduced. VPA and MISO provide combiner-less RF power amplification, which results in high power amplifier efficiency. At the same time, despite minimal or zero branch isolation, VPA and MISO amplification include innovative amplifier bias functions that effectively result in highly linear amplification over the entire output power range of desired waveforms.
In the following sections, embodiments of a blended control function for operating a MISO amplifier embodiment are provided. The blended control function allows for the mixing of various output power control functions enabled by VPA and MISO, to generate a desired waveform with high accuracy. In Section 2, the relationship between branch isolation (i.e., isolation between the branches of an outphasing amplifier) and output power error is described. This serves as an introduction to the practical limitations of a pure outphasing system, which are described in Section 3. In Section 4, blended control amplification is introduced. In Section 5, design considerations related to blended control amplification are described. Section 6 describes an example blended control function and associated performance results. Finally, Section 7 presents example blended control methods according to embodiments of the present invention.
1. Relationship Between Branch Isolation and Output Power ErrorEquation (1) below describes the sum of two sine waves (or phasors) of equal amplitude, A, and frequency, ωc, but having a differential phase θ:
R sin(ωct+δ)=A sin ωct+A sin(ωct+θ). (1)
The resulting phasor has amplitude R and phase δ. Equation (1) further indicates that any desired phasor of given amplitude and phase can be obtained from the sum of two equal amplitude phasors with appropriate differential phase between the two. The equal amplitude phasors are commonly referred to as the constituents of the desired phasor.
From equation (1), it can be further noted that the amplitude of the resulting phasor is a function of the differential phase, θ, between its constituents, as follows:
Similarly, the phase, δ(θ), of the resulting phasor is a function of the differential phase, θ, between its constituents.
In the context of power amplification, phasor amplitude curve 102 shown in
Therefore, for practical outphasing amplifier designs, a finite isolation between the branches of an outphasing amplifier is to be assumed. This finite isolation results in crosstalk between the branches of the amplifier (i.e., the signal in one branch causes an undesired effect on the signal in the other branch), effectively causing an error signal to appear at the output of the power amplifier.
In the worst case scenario, the crosstalk between the branches of the amplifier is entirely non-linear. The resulting error signal at the output of the power amplifier can therefore be written as:
Rnonlinear sin(ωct+δ)=Aa sin(ωct)·(Ab sin(ωct+θ))+Aa sin(ωct+θ)·Ab sin(ωct) (3)
where Aa represents the desired phase amplitude and Ab represents the amplitude of the crosstalk between the branches of the amplifier.
Aa and Ab are related to each other according to Ab=1−Aa (where the sum of Aa and Ab is normalized to 1). The relative isolation in dB between the branches of the amplifier can be calculated as −20 log (Ab). For example, for Aa=0.5, Ab=0.5 and the relative isolation is −20 log (0.5)=6 dB.
From equation (3) above, the amplitude of the error signal at the output of the amplifier is a function of the differential phase, θ, and can be described as:
In equation (4), Aa=1 or equivalently Ab=0 corresponds to infinite isolation between the branches of the amplifier. The error amplitude would thus be zero as illustrated in
For Aa=0.9 or equivalently Ab=0.1, the branch isolation is 20 dB (−20 log (0.1)) and the error amplitude as a function of θ is as described by error amplitude curve 302 in
From the resulting error amplitude curve 302 of
As shown in
In
Increasing the branch isolation to 25 dB would further increase the output power control range that can be achieved using only a pure outphasing system. This is shown in
The differential phase range over which a pure outphasing system can be used exclusively (while matching the performance of an ideal outphasing system) can be further determined by examining the derivative of the error amplitude as a function of the differential phase. This is illustrated for 25 dB and 30 dB of branch isolation respectively in
It should be noted that the analysis above represents a worst case scenario because it assumes that the crosstalk error is entirely nonlinear. In practice, a portion of the crosstalk error will be linear, which further increases the differential phase range over which pure outphasing can be used with no additional calibration or, alternatively, allows for lower branch isolation to be used. What can be further noted is that a pure outphasing system can be used to generate a portion of the output power range of a desired waveform with comparable performance to an ideal outphasing system. For waveforms with small output power dynamic range, pure outphasing may be used exclusively to generate such waveforms. However, for waveforms with larger output power dynamic range, practical limitations (i.e., finite branch isolation, crosstalk, etc.) may preclude the use of a pure outphasing solution when highly accurate, distortion-free amplification is desired.
3. Blended Control AmplificationIn this section, a blended control amplification approach according to an embodiment of the present invention will be presented. The blended approach combines pure outphasing with bias and/or amplitude control to yield an accurate, practical, and producible system with substantially comparable performance to that of an ideal outphasing system, but without the extreme isolation and accuracy requirements of outphasing alone. The blended approach provides a high degree of control over the constituent phasors (whether in terms of amplitude and/or phase) in order to generate the desired phasor. This allows for a reduction in both the branch isolation requirements and the phase/amplitude accuracy requirements (as related to the constituent phasors) as compared to a pure outphasing or ideal outphasing system.
A comparison between the blended approach of the present invention and pure outphasing with respect to the level of control over constituent phasors is provided in
As shown in
On the other hand, using the blended approach of the present invention, the constituent phasors can be varied both in terms of phase and amplitude to generate the desired waveform. As a result, not only can any desired phasor be generated without having the differential phase exceed a given amount (e.g., limiting the differential phase to the range over which the error is negligible), but also the amplitude of the constituent phasors can be reduced at given output levels, which increases the operational output power range and repeatability of the overall system.
In
As a result of the blended approach of the present invention, the accuracy requirements in terms of phase/amplitude of the constituent phasors can be significantly reduced, which accommodates the branch isolations, vector accuracy, and phase accuracy that can be practically expected. For example, in an embodiment of the blended approach of the present invention, when the desired output power tends to zero, the constituent phasors are also driven to zero amplitude, which essentially eliminates any accuracy requirements regarding the differential amplitude and phase between the constituent phasors or, in other words, entirely reduces the system's sensitivity to branch phase imbalance, for that particular output power range.
Another advantage of the blended approach of the present invention can also be gleaned from
According to an embodiment of the present invention, the shaping of the constituent phasors in phase and/or amplitude, as described above, is performed substantially instantaneously or in real time in accordance with the desired waveform output power trajectory. In an embodiment, this is performed using a combination of phase, bias, and amplitude controls, with the control combination (or blend) dynamically changing according to the desired waveform output power trajectory. An example amplification system according to an embodiment of the present invention, which may be used to implement a blended control approach as described above, is now presented with reference to
Referring to
According to an embodiment, which shall now be described, system 1000 includes a blended control implementation, which is implemented as a combination of phase, bias, and amplitude controls. For example, phase control (i.e., control of the phases of the constituent phasors) in system 1000 can be performed using one or more of transfer function module 1006 and vector modulators 1008 and 1010. Bias control, which includes biasing power amplifiers 1620 and 1622 within MISO amplifier 1018 to affect the amplitude of the desired phasor, is done via bias control signal 1024 generated by transfer function module 1006. Note also that bias control can be affected at drivers 1014 and 1016 via driver bias control signal 1026. Amplitude control, which includes controlling the input signals into MISO amplifier 1018 in order to affect the amplitude of the constituent phasors, can be performed using one or more of transfer function module 1006 and drivers 1014 and 1016, for example.
According to embodiments of the present invention, system 1000 may use one or more of phase, bias, and amplitude control with varying degrees of weight given to each type of control according to the desired waveform. Example blended control functions according to the present invention are described below in Section 6.
As would be understood by a person skilled in the art based on the teachings herein, the optimum combination of controls as well as the degrees of weight given to each type of control within an amplification system according to the present invention will depend on both the characteristics of the system itself (e.g., branch isolation, phase/amplitude branch imbalance, etc) and design consideration such as the desired waveform output power. Therefore, it is important in order to design a system with such optimum combination and use of controls to understand the practical effects of system characteristics on the output performance (i.e., accuracy of the output waveform) of the system.
In the following, the effects of phase and amplitude branch imbalance on the output performance of an example amplification system according to the present invention are examined. For ease of analysis and illustration, it is assumed that the constituent phasors (A1 and A2) are constrained to the first and fourth quadrants of the unit circle, and that they are designed to be of equal amplitude and symmetrical to each other with respect to the cosine axis, as illustrated in
Note from the assumptions above that if phasors A1 and A2 are indeed equal in amplitude and symmetrical to each other with respect to the cosine axis (i.e., no amplitude/phase imbalance between the branches of the amplifier), the resulting phasor will be perfectly aligned with the cosine axis (i.e., zero phase error in the output waveform). The power output associated with such resulting phasor will be as illustrated in
In practice, however, phase/amplitude branch imbalance cannot be entirely reduced to zero for a variety of reasons, including finite branch isolation for example, and will affect the choice of combination of controls. In the analysis below, phase/amplitude branch imbalance is introduced into an example amplification system according to the present invention, and the output performance of the system is examined. The example amplification system uses phase control only.
In
As can be seen from
The results from
Nonetheless, phase control only would not be able on its own to achieve output power control ranges of 30-40 dB, as desired for complex waveforms, without degrading the accuracy of the desired waveform at low output powers. Therefore, one or more additional types of control (e.g., bias control, amplitude control) may be needed as used in embodiments of the present invention to enable a practical, accurate amplifier design for complex waveforms.
5. Example Blended Control Function and Performance ResultsAn example blended control function according to an embodiment of the present invention will now be presented. The example blended control function is designed to optimize the output performance (i.e., power output accuracy) of an amplification system according to an embodiment of the present invention for a QPSK waveform output. The example blended control function is illustrated in
In an embodiment, the blended control function determines the type of control or controls used depending on the instantaneous power of the desired output waveform. For example, as would be understood by a person skilled in the art, a QPSK signal moves from one constellation point to another to encode information. However, although all four constellation points correspond to equal power, the signal does not move instantaneously from one constellation point to another and thus will have to traverse the trajectory connecting the constellation points, as shown in
In an embodiment, the example blended control function of
In an embodiment, the example blended control function of
As would be understood by persons skilled in the art, control regions 1602, 1604, and 1606 in
As shown in
Note from
In an embodiment, when bias control is applied, variations occur in the S (reverse isolation) parameters of the amplifiers of the system, resulting in an associated phase error at the output. Fortunately, this can be easily compensated for by applying a rotational transform at the vector modulators of the system.
Subsequently, in step 2404, process 2400 includes determining a control point of operation of the power amplifier based on the determined instantaneous power level. In an embodiment, the control point of operation enhances one or more of linearity and accuracy of the power amplifier for the determined instantaneous power level. In an embodiment, referring to
Subsequently, in step 2406, process 2400 includes controlling the power amplifier to operate according to the determined control point of operation. In an embodiment, step 2406 includes performing one or more of (a) controlling the phase of input signals of the power amplifier; (b) controlling the bias of the power amplifier; and (c) controlling the amplitude of the input signals of the power amplifier. In an embodiment, referring to
According to an embodiment, the control point of operation can be within a first, second, or third control regions, depending on the determined instantaneous power level. For example, in an embodiment, the control point of operation is within a first control region when the instantaneous power level is greater than a first threshold; within a second control region when the instantaneous power level is greater than a second threshold but lower than the first threshold; and within a third control region when the instantaneous power level is lower than the second threshold. According to an embodiment, boundaries of the first, second, and third control regions are based on the Complementary Cumulative Density Function (CCDF) of the desired output waveform.
According to an embodiment of the present invention, when the control point of operation is within the first control region, the controlling step 2406 of process 2400 includes performing (a) only, or performing (a), (b), and (c). In the latter case, in an embodiment, step 2406 includes performing (a) more often than (b) or (c). When the control point of operation is within the second control region, the controlling step 2406 includes performing (a), (b), and (c). Further, controlling step 2406 may include performing (b) more often than (a) or (c). When the control point of operation is within the third control region, the controlling step 2406 includes performing (b) and (c) only. In an embodiment, controlling step 2406 further includes performing (c) more often than (b).
According to an embodiment, controlling step 2406 includes performing one or more of (a), (b), and (c) according to respective weights given to (a), (b), and (c). In an embodiment, the respective weights are determined according to one or more of error/system characteristics within the power amplifier (e.g., branch phase imbalance, branch amplitude imbalance, branch isolation) and the instantaneous power level.
Subsequently, in step 2504, process 2500 includes varying one or more weights associated with respective power controls of the power amplifier to cause the required change in power output, wherein the power controls include one or more of (a) control of phase of input signals of the power amplifier, (b) control of bias of the power amplifier, and (c) control of amplitude of the input signals of the power amplifier. In an embodiment, referring to
According to an embodiment, the weights associated with the respective power controls of the power amplifier are determined according to one or more of branch phase imbalance, branch amplitude imbalance, and branch isolation within the power amplifier.
According to an embodiment, varying the weights causes the power amplifier to transition between various classes of operation. For example, in an embodiment, varying the weights causes the power amplifier to transition between class S and class A. In another embodiment, varying the weights causes the power amplifier to transition from linear operation to non-linear operation, and vice versa.
Subsequently, step 2604 includes determining one or more of (a) branch phase imbalance; (b) branch amplitude imbalance; and (c) branch isolation, between branches of the power amplifier. In an embodiment, step 2604 is performed by various error/system measurement modules of the power amplifier, which report measurements to transfer function module 1006.
In step 2606, process 2600 includes calculating one or more weights based on one or more of the determined branch phase imbalance, branch amplitude imbalance, and branch isolation. In an embodiment, referring to
Finally, in step 2608, process 2600 includes applying one or more power controls according to the one or more weights to control the power amplifier to generate the desired power output trajectory. In an embodiment, the power controls include one or more of (a) control of phase of input signals of the power amplifier, (b) control of bias of the power amplifier, and (c) control of amplitude of the input signals of the power amplifier. As noted above, in an embodiment, step 2608 is performed by transfer function module 1006, which controls different power control mechanisms of the power amplifier to apply (a), (b), and (c). For example, to control the phase of the input signals of the power amplifier, transfer function 1006 may control the signals it inputs into vector modulators 1008 and 1010. Similarly, to control the bias of the power amplifier, transfer function 1006 may vary bias signals 1024 and 1026 that it provides to driver amplifiers 1014 and 1016 and MISO amplifier 1018.
7. ConclusionIt is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way.
The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.
The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.
The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
Claims
1. A method comprising:
- partitioning a waveform constellation space into a plurality of regions, wherein each region of the plurality of regions is associated with one or more control functions of a multiple-input-single-output (MISO) device; and
- transitioning the MISO device between a plurality of classes of operation based on the one or more control functions.
2. The method of claim 1, wherein the partitioning comprises partitioning the waveform constellation space based on an output power level of a desired output waveform from the MISO device.
3. The method of claim 1, wherein the transitioning comprises transitioning the MISO device between the plurality of classes of operation based on one or more of a bias control of the MISO device, a phase control of one or more inputs to the MISO device and an amplitude control of the one or more inputs to the MISO device.
4. The method of claim 1, wherein the transitioning comprises applying the one or more control functions to the MISO device based on a weighted combination, and wherein the weighted combination associates a respective weight to each of the one or more control functions.
5. The method of claim 4, wherein the applying comprises varying each of the respective weights associated with each of the one or more control functions based on one or more of a branch phase imbalance, a branch amplitude imbalance and a branch isolation of the MISO device.
6. The method of claim 1, wherein the transitioning comprises transitioning the MISO device between classes of operation analogous to Class A, Class B, Class C, Class D and Class S amplifier classes of operation.
7. The method of claim 6, wherein the transitioning comprises operating the MISO device in classes of operation analogous to the Class A and Class B amplifier classes of operation at a duration of time shorter than operating the MISO device in classes of operation analogous to the Class C, Class D and Class S amplifier classes of operation.
8. The method of claim 1, wherein the transitioning comprises generating a zero, or a near zero, output current with the MISO device when an output waveform of the MISO device undergoes a zero crossing.
9. A system comprising:
- a multiple-input-single-output (MISO) device; and
- a transfer function module configured to transition the MISO device between a plurality of classes of operation based on one or more control functions, wherein each the one or more control functions is associated with a region from a plurality of regions partitioned from a waveform constellation space.
10. The system of claim 9, further comprising:
- one or more vector modulators coupled to respective one or more inputs to the MISO device, wherein the one or more vector modulators are configured to adjust a phase control to one or more input signals received by the MISO device.
11. The system of claim 9, further comprising:
- one or more pre-driver devices coupled to respective one or more inputs to the MISO device.
12. The system of claim 9, wherein the waveform constellation space is partitioned based on an output power level of a desired output waveform from the MISO device.
13. The system of claim 9, wherein the transfer function module is configured to transition the MISO device between the plurality of classes of operation based on one or more of a bias control of the MISO device, a phase control of one or more inputs to the MISO device and an amplitude control of the one or more inputs to the MISO device.
14. The system of claim 9, wherein the transfer function module is configured to apply the one or more control functions to the MISO device based on a weighted combination, and wherein the weighted combination associates a respective weight to each of the one or more control functions.
15. The system of claim 14, wherein the transfer function module is configured to vary each of the respective weights associated with each of the one or more control functions based on one or more of a branch phase imbalance, a branch amplitude imbalance and a branch isolation of the MISO device.
16. The system of claim 9, wherein the transfer function module is configured to transition the MISO device between classes of operation analogous to Class A, Class B, Class C, Class D and Class S amplifier classes of operation.
17. The system of claim 16, wherein the transfer function module is configured to operate the MISO device in classes of operation analogous to the Class A and Class B amplifier classes of operation at a duration of time shorter than operating the MISO device in classes of operation analogous to the Class C, Class D and Class S amplifier classes of operation.
18. The system of claim 9, wherein the transfer function module is configured to generate a zero, or a near zero, output current with the MISO device when an output waveform of the MISO device undergoes a zero crossing.
19. The system of claim 9, wherein the MISO device is configured to output a radio frequency (RF) waveform.
Type: Application
Filed: Mar 27, 2017
Publication Date: Feb 8, 2018
Applicant: ParkerVision, Inc. (Jacksonville, FL)
Inventors: Gregory S. Rawlins (Chuluota, FL), David F. Sorrells (Middleburg, FL)
Application Number: 15/470,738