CN104579192B - Use the radiofrequency signal amplification system and method for feedback control - Google Patents
Use the radiofrequency signal amplification system and method for feedback control Download PDFInfo
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- 238000003199 nucleic acid amplification method Methods 0.000 title claims abstract description 27
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- 230000010363 phase shift Effects 0.000 claims abstract description 6
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- 230000033228 biological regulation Effects 0.000 description 6
- 238000002595 magnetic resonance imaging Methods 0.000 description 4
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/189—High-frequency amplifiers, e.g. radio frequency amplifiers
- H03F3/19—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only
- H03F3/195—High-frequency amplifiers, e.g. radio frequency amplifiers with semiconductor devices only in integrated circuits
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Abstract
A kind of radio frequency amplification system, the modulator including the feedback control that is used for modulating initial radio frequency signal and generating modulated radiofrequency signal, the amplifier for being used for amplifying the modulated radiofrequency signal and the radio frequency output signal for generating amplification connected with the modulator and the device for generating I/Q signal with the radio frequency output signal of the amplification.The radio frequency amplification system further includes phase feedback loop, the amplification radio frequency output signal compared with the target phase shift φ of local oscillator not equal in the case of 90 or 270 degree, based on to I withComparison adjust the phase of the initial radio frequency signal, alternatively,In the case of equal to 90 or 270 degree, the phase of the initial radio frequency signal is adjusted based on the comparison to Q and 0.The radio frequency amplification system further includes amplitude feedback loop, detects the amplitude characteristic of the radio frequency output signal of the amplification, and the amplitude of the initial radio frequency signal is adjusted based on the difference between the amplitude characteristic and reference amplitude.
Description
Technical Field
The present invention relates to a radio-frequency (RF) signal amplification system and method, and more particularly, to a RF signal amplification system and method using feedback control.
Background
Many forms of wireless communication employ radio frequency transmission. A radio frequency carrier signal may be modulated to carry information. The modulated radio frequency carrier signal may be amplified and transmitted. In order to prevent distortion of the information carried by the modulated radio frequency carrier signal, it is generally desirable to maintain relative linearity of the amplification process.
For example, Magnetic Resonance Imaging (MRI) systems typically use a radio frequency amplifier to drive a radio frequency coil located within its primary magnetic structure. The rf amplifier receives as its input a series of pulses generated by an external rf source and generates as its output a series of pulses of increased power that are transmitted and used to drive the rf coil. The increased image quality requirements result in greater magnetic induction (in tesla) of the magnets used, which requires greater rf amplifier output power. However, the greater output power may introduce non-linearities in the gain and phase of the radio frequency amplifier into the system, resulting in distortion of the MRI image. To avoid such a situation, it is necessary to correct a non-linearity factor introduced during radio frequency amplification to maintain linearity.
An effective way to maintain linearity is to control the modulator with a feedback signal to correct for non-linearity of the amplified radio frequency signal. However, in current control methods, such as Cartesian Loop (Cartesian Loop) feedback methods, the amplitude and phase are coupled to each other, which reduces the response speed of the feedback. For the polar loop feedback method, additional components (e.g., a phase-locked loop or a detector) are needed to detect the amplitude and phase, which limits the bandwidth of the whole system due to the slow response of the phase detector. In the digital control approach, when input in Direct Digital Synthesis (DDS), it is necessary to sample the phase information and "translate" it into a phase shift of the DDS. Further, other limitations and disadvantages of existing systems will become apparent to one of skill in the art upon examination of the following drawings in which several aspects of the invention are described.
Disclosure of Invention
One aspect of the invention relates to a radio frequency amplification system comprising a feedback controlled modulator for modulating an initial radio frequency signal based on a feedback correction control signal and producing a modulated radio frequency signal, an amplifier in communication with the modulator for amplifying the modulated radio frequency signal and producing an amplified radio frequency output signal, and means for producing an IQ signal with the amplified radio frequency output signal. The radio frequency amplification system further comprises a phase feedback loop that shifts a phase of the amplified radio frequency output signal relative to a target of a local oscillatorNot equal to 90 or 270 degrees, based on the sum of ITo adjust the phase of said initial radio frequency signal, or, inEqual to 90 or 270 degrees, the phase of the initial radio frequency signal is adjusted based on a comparison of Q and 0. The RF amplification system further includes an amplitude feedback loop that detects an amplitude characteristic of the amplified RF output signal and adjusts the initial RF signal based on a difference between the amplitude characteristic and a reference amplitudeThe amplitude of the signal.
Another aspect of the present invention relates to a radio frequency amplification method in which an initial radio frequency signal is modulated based on a feedback correction control signal and a modulated radio frequency signal is generated, the modulated radio frequency signal is amplified and an amplified radio frequency output signal is generated, and an IQ signal is generated with the amplified radio frequency output signal. Target phase shift at the amplified RF output signal relative to a local oscillatorNot equal to 90 or 270 degrees, based on the sum of ITo adjust the phase of said initial radio frequency signal, or, inEqual to 90 or 270 degrees, the phase of the initial radio frequency signal is adjusted based on a comparison of Q and 0. Adjusting the amplitude of the initial radio frequency signal based on a difference between the amplitude characteristic and a reference amplitude by detecting an amplitude characteristic of the amplified radio frequency output signal.
Drawings
The invention may be better understood by describing embodiments of the invention in conjunction with the following drawings, in which:
fig. 1 shows a radio frequency signal amplification system using feedback control in one embodiment of the present invention.
Fig. 2 shows a radio frequency signal amplification system using feedback control in another embodiment of the present invention.
An example of the conversion of the feedback signal into I and Q signals is shown in the schematic diagram of fig. 3.
Fig. 4 shows a radio frequency signal amplification system using feedback control in yet another embodiment of the present invention.
Fig. 5 shows a radio frequency signal amplification system using feedback control in yet another embodiment of the present invention.
Fig. 6 shows a radio frequency signal amplification system using feedback control in yet another embodiment of the present invention.
An example of a rotational reference coordinate is shown schematically in fig. 7.
Fig. 8 shows a radio frequency signal amplification system using feedback control in yet another embodiment of the present invention.
Detailed Description
Unless otherwise defined, technical or scientific terms used in the claims and the specification should have the ordinary meaning as understood by those of ordinary skill in the art to which the invention belongs. The use of "first," "second," and similar terms in the description and claims of the present application do not denote any order, quantity, or importance, but rather the terms are used to distinguish one element from another. The terms "a" or "an," and the like, do not denote a limitation of quantity, but rather denote the presence of at least one. The word "comprise" or "comprises", and the like, means that the element or item listed before "comprises" or "comprising" covers the element or item listed after "comprising" or "comprises" and its equivalent, and does not exclude other elements or items. The terms "connected," "communicating," or "coupled" and the like are not restricted to physical or mechanical connections, but may include electrical connections, whether direct or indirect.
The embodiment of the invention provides a radio frequency signal amplification system, which comprises a radio frequency amplifier and a feedback control loop, wherein the feedback control loop can realize high linearity and high stability under different loads and obtain constant gain (namely magnitude proportion between an output signal and an input signal). The feedback control loop comprises mutually independent amplitude and phase control loops for controlling amplitude and phase independently of each other such that the amplitude and phase responses can be independently optimized to achieve a high bandwidth, e.g. a high bandwidth that meets the requirements of an MRI system. In this way, the RF amplifier can be compensated and stabilized with a fast response speed under different load conditions. By feedback controlling using different feedback signals, e.g. the output power or current of the amplifier, a stable power gain or a stable current source can be obtained. More specifically, in the system or method described herein, the output power or the output current of the amplifier can be used as a feedback signal for feedback control, and when the output power is used as the feedback signal for control, a stable power gain can be obtained, and when the output current is used as the feedback signal for control, a stable current source can be obtained.
Fig. 1 is a block diagram illustrating a radio frequency amplification system 100 using mutually independent amplitude and phase feedback loops in accordance with an aspect of the present invention. The system 100 modulates and amplifies a radio frequency signal to produce an output signal, such as a power or current output signal. In the system 100 as shown, the radio frequency signal 102 is modulated by a modulator 112 to produce a modulated radio frequency signal 104, and the modulated radio frequency signal 104 is amplified by an amplifier 114 to produce an amplified radio frequency output signal 106 that is fed to a transmit coil 116. The modulator 112 and amplifier 114 may be in any suitable form, and they may be integrated in one apparatus or device, or may be separately provided in different apparatuses or devices, depending on the particular application or need. In a particular embodiment, the amplifier 114 is a power amplifier. The feedback control loop 120 is used to correct for distortion or non-linearity introduced by the amplifier 114, which allows the rf signal 102 to be modulated based on a feedback corrected control signal, so that the distortion or non-linearity introduced by the amplifier 114 can be corrected. As shown, the feedback control loop 120 includes an amplitude feedback loop 130 and a phase feedback loop 150, which may be used independently of each other to adjust amplitude and phase, respectively. A feedback signal 172 is obtained by sampling the output signal 106 by means of a sampling device 170 for amplitude and phase adjustment in the amplitude feedback loop 130 and the phase feedback loop 150. The sampling device 170 may be a coupler for obtaining a power feedback signal or a sensor (e.g., a current sensor) for obtaining a current feedback signal.
For amplitude regulation, the amplitude of the output of the amplifier 114 is detected from the feedback signal 172 in the amplitude regulation loop 130 by an amplitude detector 132. Generally, the amplitude detector comprises a rectifier and a low-pass filter. The output amplitude of the amplifier 114 is then compared to a reference amplitude by a comparator 134. The comparator may be a processor, a computer or an analog comparator, etc. The difference between the output amplitude and the reference amplitude is treated as an error and is used by the input controller 136 to control the input of the amplifier 114. The controller 136 may include a filter (e.g., a low pass filter) to stabilize the system, and a proportional-integral-derivative (PID) controller to improve response speed and eliminate static errors. In some embodiments, the gain of the filter and the parameters of the PID controller may be adjusted to optimize the transient response of the system.
For phase adjustment, in the phase feedback loop 150, as shown in fig. 1, a Local Oscillator (LO) 152, modulators 154 and 155, and a 90 ° phase shifter 156, or further two filters (e.g., low pass filters) 157 and 158 may be included to convert the vector of the feedback signal 172 into a quadrature scalar to generate an IQ signal as shown in fig. 3, where I and Q represent the in-phase component and the quadrature component of the waveform, respectively.
Since I/Q = tan (α), where α is the phase difference between the feedback signal and the local oscillator, it can be any value between 0 and 360 °WhereinIt may also be any value between 0 and 360 deg. for a target phase shift of the amplifier output relative to the local oscillator.
If it is notNot equal to 90 or 270,
if the high-order errors are ignored,
when in usePhase error =0, indicating no phase error.
Therefore, it is possible to determine whether or not(i.e., determining whether or not to) To determine if there is a phase error. Is believed to be whenWithout phase error whenThere is a phase error. Due to the fact thatIs a predetermined constant, and can be easily and conveniently compared with I and I by a comparatorA comparison is made and based on the comparison it is determined whether there is a phase error.
In a particular embodiment of the present invention,can be preset to 45 degrees, so that whether the angle is larger or not can be judged(i.e., whether I = Q) to determine whether there is a phase error. A comparator may be used to compare I and Q, and if I = Q, it is determined that there is no phase error, and if I ≠ Q, it is determined that there is a phase error.
If it is notEqual to 90 deg. or 270 deg., it can be determined whether there is a phase error by determining whether Q is equal to 0. A comparator may be used to compare Q and 0, and if Q =0, it is determined that there is no phase error, and if Q ≠ 0, it is determined that there is a phase error.
For example, ifNot equal to 90 or 270, as shown in fig. 1, in the phase feedback loop 150, Q is multiplied by the product function 159Multiplication to obtainComparing I and I with comparator 162If I is not equal toAnd judging that the phase error exists. Integrator 164 and phase shifter 166 are used to accumulate phase error and gradually adjust the phase in response to the phase error until I equalsIn this way the output phase of the amplifier can be adjusted to a constant phase with respect to the local oscillator, e.g. if I/Q is kept at 1 (i.e. I = Q), the output phase of the amplifier can be kept at a phase shifted by 45 ° with respect to the local oscillator.
If it is notEqual to 90 deg. or 270 deg., some modification may be made to the phase feedback loop. For example, a system 200 similar to system 100, shown in FIG. 2, has one suitable for useEqual to 90 deg. or 270 deg., which is the same or similar to system 100 except for the phase feedback loop. In thatEqual to 90 deg. or 270 deg., system 200 may be used. In system 200, phase feedback loop 250 includes a comparator 262 for comparing Q to 0, and it can be determined that a phase error exists when Q is not equal to 0. Integrator 264 and phase shifter 266 may be used to accumulate phase error and adjust the phase stepwise in response to the phase error until Q equals 0, respectively.
The system described herein can control amplitude and phase independently of each other, and since no phase lock is necessary, no additional hardware is required to lock the phase, and a faster response can be obtained. The system can be integrated into firmware, such as that of an MRI exciter, to achieve better performance amplifier compensation without the need to rotate the amplifier during manufacture. An amplifier with the system can directly drive various loads to obtain a constant gain.
The amplitude feedback loop may be implemented in different embodiments, for example, in the system 300 shown in fig. 4, an amplitude feedback loop 330 including an amplitude function 331 and a filter (e.g., a low pass filter) is used. Wherein the amplitude function 331 obtains the feedback amplitude from the IQ signal obtained from the feedback signalThe feedback amplitude is compared to a reference amplitude to determine an error for amplitude adjustment. In thatThe remainder of the system 300 may be the same as or similar to that of system 100, not equal to 90 or 270. In thatEqual to 90 ° or 270 °, the remainder of the system 300 may be the same as or similar to that of system 200.
For another example, in a system 400 as shown in fig. 5, an amplitude feedback loop 430 is employed that includes a band pass filter 431, an absolute value function 432, and a low pass filter 433. With such an amplitude feedback loop, the feedback signal is filtered by a pass filter 431, the absolute value is taken by an absolute value function 432, the absolute value is further filtered by a low pass filter 433, and the further filtered value is then used to compare with a reference amplitude. Similar to system 200, the remainder of system 400 may be the same as or similar to that of system 100 or 200. Here, the absolute value function may be defined as f (x) = | x |, where:
in some embodiments, to enhance small signalsAs shown in FIG. 6, in a system 500 similar to system 100, a coordinate adjustment loop 580 is added to the phase feedback loop 550 to rotate the reference coordinate so that the phase difference α between the feedback signal and the local oscillator is at a predetermined value from the initial operationAre equal. For example, in one particular embodiment, as shown in FIG. 7, if one is to do soSet at 45 deg., the reference coordinate may be rotated so that α equals 45 deg., so that it can be determined whether a phase error exists by determining whether I equals QAny angle in the range of 0 to 360, such as 30 or 60, etc., may be set.
Referring again to FIG. 6, the coordinate regulation loop 580 communicates with the integrator 564 through a switch 582, the switch 582 is switchable between a first position 583, in which the phase feedback loop 550 is closed, and a second position 584, in which the coordinate regulation loop 580 is closed, the coordinate regulation loop 580 is a loop connecting the comparator 562 and the integrator 564 to the modulator 512 through the local oscillator 552 and the phase shifter 504, in initial operation, the coordinate regulation loop 580 is closed so that the reference coordinate may be rotated to an appropriate position to ensure α is equal to the predetermined value. Switch 582 is then switched to close the phase feedback loop 550 to achieve phase feedback control. Similarly, such coordinate adjustment loops may also be added to the system 200.
In some embodiments, a feed forward loop may also be added to the system described herein to allow the system to achieve a faster response speed. The feed forward loop may reverse the gain and phase characteristics of the analog amplifier, introducing "predistortion" into the input of the amplifier to counteract possible non-linearities of the amplifier. This reduces distortion and enhances the overall linearity of the system.
In some embodiments, an amplitude feed forward loop may be added to introduce "amplitude predistortion" to the input of the amplifier to pre-compensate for amplitude non-linearities that may be present in the amplifier. The amplitude feed forward loop may include a feed forward predistortion look up table or predistortion circuit to receive the reference amplitude to determine accordingly how much "amplitude predistortion" needs to be introduced into the input of the amplifier. For example, as shown in FIG. 8, in a system 700 similar to system 100, a feed forward predistortion look-up table 792 is added between the reference amplitude and a summer 794 coupled between the PID controller 738 and the modulator 712 to form an amplitude feed forward loop 790. The feedforward predistortion look-up table 792 receives the reference amplitude to determine accordingly how much "amplitude predistortion" needs to be introduced, so that an appropriate amount of "amplitude predistortion" can be introduced in the amplifier front-end to pre-compensate for possible amplifier non-linearities.
Similarly, a phase feed forward loop can be added to allow the system to achieve a faster response speed. In addition, the aforementioned coordinate adjustment loop and/or feed forward loop may also be added to the system 200.
While the invention has been described in conjunction with specific embodiments thereof, it will be understood by those skilled in the art that many modifications and variations may be made to the invention. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.
Claims (20)
1. A radio frequency amplification system, comprising:
a feedback controlled modulator that modulates the initial radio frequency signal based on the feedback correction control signal and generates a modulated radio frequency signal;
an amplifier in communication with the modulator for amplifying the modulated radio frequency signal and producing an amplified radio frequency output signal;
means for generating an IQ signal with said amplified radio frequency output signal;
a phase feedback loop for outputting signal at the amplified radio frequencyTarget phase shift of signal relative to local oscillatorNot equal to 90 or 270 degrees, based on the sum of ITo adjust the phase of said initial radio frequency signal, or, inEqual to 90 or 270 degrees, adjusting the phase of the initial radio frequency signal based on a comparison of Q and 0; and
an amplitude feedback loop that detects an amplitude characteristic of the amplified radio frequency output signal and adjusts an amplitude of the initial radio frequency signal based on a difference between the amplitude characteristic and a reference amplitude.
2. The system of claim 1, wherein the phase feedback loop and the amplitude feedback loop adjust phase and amplitude independently of each other.
3. A system as recited in claim 1,
if it isNot equal to 90 or 270 degrees, the phase feedback loop comprises: for mixing Q withMultiplication to obtainProduct function of, for comparing I andand a comparator forAt I not equal toA phase shifter for time-adjusting a phase; or,
if it isEqual to 90 or 270 degrees, the phase feedback loop comprising: a comparator to compare Q and 0, and a phase shifter to adjust the phase when Q is not equal to 0.
4. The system of claim 1, wherein the amplitude feedback loop comprises:
amplitude detection means for detecting an amplitude characteristic of said amplified radio frequency output signal;
a comparator to compare the amplitude signature with a reference amplitude; and
control means for adjusting the amplitude based on a difference between the amplitude characteristic and a reference amplitude.
5. A system as in claim 4, wherein the amplitude feedback loop comprises an absolute value function to obtain an absolute value of the reference amplitude, the amplitude characteristic being compared to the absolute value of the reference amplitude.
6. The system of claim 4, wherein the amplitude detection means comprises generating an amplitude component signal based on the IQ signalAs a function of (c).
7. The system of claim 4, wherein the amplitude detection means comprises:
a band pass filter for filtering a feedback signal sampled from the amplified radio frequency output signal;
an absolute value function to obtain an absolute value of the filtered feedback signal; and
a low pass filter for further filtering the absolute value of the filtered feedback signal.
8. The system of claim 1 further comprising a coordinate adjustment loop for rotating a reference coordinate such that a phase difference α between a feedback signal sampled from the amplified radio frequency output signal and a local oscillator is equal to
9. A system as recited in claim 8, further comprising: a switch switchable between a first position to switch on the phase feedback loop in the first position and a second position to switch on the coordinate adjustment loop in the second position.
10. The system of claim 1, further comprising: a feed forward loop, which is used to inversely model the gain and phase characteristics of the amplifier, introduces predistortion into the input of the amplifier to pre-compensate for possible non-linearities of the amplifier.
11. A system as claimed in claim 10, wherein the feed forward loop comprises an amplitude feed forward loop comprising a feed forward predistortion look up table or predistortion circuit between the reference amplitude and the modulator, the predistortion look up table or predistortion circuit being operable to receive the reference amplitude and to determine accordingly how much predistortion is required to be introduced.
12. A radio frequency amplification method, comprising:
modulating an initial radio frequency signal based on a feedback correction control signal and generating a modulated radio frequency signal;
amplifying the modulated radio frequency signal and generating an amplified radio frequency output signal;
generating an IQ signal with the amplified radio frequency output signal;
target phase shift at the amplified RF output signal relative to a local oscillatorNot equal to 90 or 270 degrees, based on the sum of ITo adjust the phase of said initial radio frequency signal, or, inEqual to 90 or 270 degrees, adjusting the phase of the initial radio frequency signal based on a comparison of Q and 0; and
an amplitude characteristic of the amplified radio frequency output signal is detected and an amplitude of the initial radio frequency signal is adjusted based on a difference between the amplitude characteristic and a reference amplitude.
13. The method of claim 12, wherein the phase and amplitude are adjusted independently of each other.
14. The method of claim 12, wherein is not equal to IOr adjusting the phase of the initial radio frequency signal if Q is not equal to 0.
15. The method of claim 12, further comprising obtaining an absolute value of the reference amplitude, the amplitude characteristic being compared to the absolute value of the reference amplitude.
16. The method of claim 12, wherein the amplitude characteristic of the amplified radio frequency output signal is obtained by:
generating an amplitude component signal based on the IQ signal; and
filtering the amplitude component signal.
17. The method of claim 16, wherein the amplitude component signal is such thatThe magnitude of the feedback indicated.
18. The method of claim 12, wherein the amplitude characteristic of the amplified radio frequency output signal is obtained by:
filtering a feedback signal sampled from the amplified radio frequency output signal with a band pass filter;
obtaining an absolute value of the filtered feedback signal with an absolute value function; and
the absolute value of the filtered feedback signal is further filtered with a low-pass filter.
19. The method of claim 12, further comprising rotating a reference coordinate such that a phase difference α between a feedback signal sampled from the amplified radio frequency output signal and a local oscillator is equal to。
20. The method of claim 12, further comprising inverting the gain and phase characteristics of the analog amplifier and introducing predistortion into the input of the amplifier to precompensate for possible non-linearities of the amplifier.
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| CN105978501B (en) * | 2016-05-09 | 2018-07-03 | 南阳师范学院 | A kind of digital predistorter for high field MRI high power RF power amplifier |
| CN112285620B (en) * | 2019-07-24 | 2024-09-06 | 通用电气精准医疗有限责任公司 | RF transmitting system and method, MRI system and pre-scanning method thereof, and storage medium |
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| US5118997A (en) * | 1991-08-16 | 1992-06-02 | General Electric Company | Dual feedback control for a high-efficiency class-d power amplifier circuit |
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| US7356315B2 (en) * | 2003-12-17 | 2008-04-08 | Intel Corporation | Outphasing modulators and methods of outphasing modulation |
| US8009765B2 (en) * | 2007-03-13 | 2011-08-30 | Pine Valley Investments, Inc. | Digital polar transmitter |
| US7791413B2 (en) * | 2008-06-05 | 2010-09-07 | Her Majesty The Queen In Right Of Canada | Linearizing technique for power amplifiers |
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| EP0441579A1 (en) * | 1990-02-08 | 1991-08-14 | Gec-Marconi Limited | Circuit for reducing distortion produced by an r.f. power amplifier |
| US5118997A (en) * | 1991-08-16 | 1992-06-02 | General Electric Company | Dual feedback control for a high-efficiency class-d power amplifier circuit |
| CN1148754A (en) * | 1995-09-19 | 1997-04-30 | 富士通株式会社 | Digital frequency control circuit, phase control circuit and PLL circuit |
| EP0998088A2 (en) * | 1998-10-27 | 2000-05-03 | Nokia Mobile Phones Ltd. | Modulation with separate stages for phase and amplitude modulation |
| CN1993882A (en) * | 2004-06-04 | 2007-07-04 | 西利康动力装置公司 | Power amplifier and pulse-width modulated amplifier |
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