CN104579192B - Use the radiofrequency signal amplification system and method for feedback control - Google Patents

Abstract

A radio frequency amplification system comprising a feedback controlled modulator for modulating an initial radio frequency signal and producing a modulated radio frequency signal, in communication with said modulator for amplifying said modulated radio frequency signal and producing an amplified radio frequency output An amplifier for a signal, and means for generating an IQ signal from said amplified radio frequency output signal. The radio frequency amplification system also includes a phase feedback loop based on a pair of I and comparison to adjust the phase of the initial RF signal, or, in When it is equal to 90 or 270 degrees, the phase of the initial radio frequency signal is adjusted based on the comparison between Q and 0. The RF amplification system also includes an amplitude feedback loop that detects an amplitude characteristic of the amplified RF output signal and adjusts the amplitude of the initial RF signal based on a difference between the amplitude characteristic and a reference amplitude.

Description

Radio Frequency Signal Amplification System and Method Using Feedback Control

technical field

The present invention relates to a radio-frequency (radio-frequency, RF) signal amplification system and method, and more particularly, to a radio-frequency signal amplification system and method using feedback control.

Background technique

Many forms of wireless communication employ radio frequency transmissions. A radio frequency carrier signal can be modulated to carry information. The modulated RF carrier signal can be amplified and transmitted. In order to prevent the information carried by the modulated radio frequency carrier signal from being distorted, generally, it is necessary to maintain the relative linearity of the amplification process.

For example, a magnetic resonance imaging (MRI) system typically uses an RF amplifier to drive an RF coil within its primary magnetic structure. The radio frequency amplifier receives a series of pulses generated by an external radio frequency source as its input signal, and generates a series of pulses with enhanced power as its output signal, which is transmitted and used to drive the radio frequency coil. The higher the requirement for image quality, the greater the magnetic induction (unit: Tesla) of the magnet used, which will require a larger output power of the RF amplifier. However, greater output power may introduce gain and phase nonlinearity of the RF amplifier into the system, resulting in MRI image distortion. In order to avoid such a situation, it is necessary to correct the nonlinear factors introduced in the process of RF amplification to maintain linearity.

An effective way to maintain linearity is to use a feedback signal to control the modulator to correct the nonlinearity of the amplified RF signal. However, in current control methods, such as the Cartesian Loop feedback method, the magnitude and phase are coupled to each other, which reduces the response speed of the feedback. For the polar loop feedback method, additional components (such as a phase-locked loop or a detector) are required to detect the amplitude and phase, and the slow response of the phase detector will limit the bandwidth of the entire system. In the digital control method, when the input is in direct digital synthesis (DDS), the phase information needs to be sampled and "translated" into the phase shift of the DDS. Furthermore, other limitations and deficiencies in existing systems will become apparent to those skilled in the art after comparing existing systems with aspects of the present invention described hereinafter with reference to the accompanying drawings.

Contents of the invention

One aspect of the present 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 generating a modulated radio frequency signal, a communication device in communication with the modulator for amplifying the An amplifier for generating an amplified radio frequency output signal from the modulated radio frequency signal, and means for generating an IQ signal from the amplified radio frequency output signal. The radio frequency amplification system also includes a phase feedback loop that operates at a target phase shift of the amplified radio frequency output signal relative to a local oscillator not equal to 90 or 270 degrees, based on the I and comparison to adjust the phase of the initial RF signal, or, in When it is equal to 90 or 270 degrees, the phase of the initial radio frequency signal is adjusted based on the comparison between Q and 0. The RF amplification system also includes an amplitude feedback loop that detects an amplitude characteristic of the amplified RF output signal and adjusts the amplitude of the initial RF signal based on a difference between the amplitude characteristic and a reference amplitude.

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, said modulated radio frequency signal is amplified and an amplified radio frequency signal is generated an output signal, using the amplified radio frequency output signal to generate an IQ signal. The phase shift of the amplified RF output signal relative to the local oscillator target not equal to 90 or 270 degrees, based on the I and comparison to adjust the phase of the initial RF signal, or, in When it is equal to 90 or 270 degrees, the phase of the initial radio frequency signal is adjusted based on the comparison between Q and 0. The amplitude of the initial radio frequency signal is adjusted based on a difference between the amplitude characteristic and a reference amplitude by detecting the amplitude characteristic of the amplified radio frequency output signal.

Description of drawings

By describing the embodiments of the present invention in conjunction with the accompanying drawings, the present invention can be better understood. In the accompanying drawings:

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.

The schematic in Figure 3 shows an example of converting the feedback signal into I and Q signals.

Fig. 4 shows a radio frequency signal amplification system using feedback control in another embodiment of the present invention.

Fig. 5 shows a radio frequency signal amplification system using feedback control in another embodiment of the present invention.

FIG. 6 shows a radio frequency signal amplification system using feedback control in another embodiment of the present invention.

The schematic diagram in Figure 7 shows an example of a rotational reference coordinate.

Fig. 8 shows a radio frequency signal amplification system using feedback control in another embodiment of the present invention.

Detailed ways

Unless otherwise defined, the technical terms or scientific terms used in the claims and the description shall have the ordinary meanings understood by those skilled in the technical field to which the present invention belongs. "First", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "A" or "one" and similar words do not indicate a limitation of number, but mean that there is at least one. Words such as "comprises" or "comprises" and similar terms mean that the elements or items listed before "comprises" or "comprises" include the elements or items listed after "comprises" or "comprises" and their equivalent elements, and do not exclude other components or objects. Words such as "connected," "communicating," or "linked" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

An embodiment of the present invention provides a radio frequency signal amplification system, which includes a radio frequency amplifier and a feedback control loop, the feedback control loop can achieve high linearity and high stability under different loads, and obtain a constant gain (referring to the output signal and magnitude ratio between input signals). The feedback control loop includes mutually independent amplitude and phase control loops, which are used to control the amplitude and phase independently of each other, so that the responses of the amplitude and phase can be independently optimized to obtain high bandwidth, for example, meeting the requirements of MRI systems high bandwidth. In this way, the RF amplifier can be compensated with a fast response speed to achieve stability under different load conditions. By using different feedback signals, such as the output power or current of the amplifier, for feedback control, 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 output current of the amplifier can be used as a feedback signal for feedback control. When the output power is used as the feedback signal for control, a stable power gain can be obtained, When the output current is used as the feedback signal to control, a stable current source can be obtained.

FIG. 1 is a block diagram showing a radio frequency amplification system 100 using independent amplitude and phase feedback loops according to an aspect of the present invention. The system 100 modulates and amplifies an RF signal to generate an output signal, such as a power or current output signal. In system 100 as shown, modulator 112 is used to modulate radio frequency signal 102 to produce modulated radio frequency signal 104, and amplifier 114 is used to amplify said modulated radio frequency signal 104 to produce amplified radio frequency output The signal 106 is sent to the sending coil 116 . The modulator 112 and the amplifier 114 can be in any suitable form, and they can be integrated in one device or device, or can be respectively set in different devices or devices, depending on specific applications or needs. In a specific embodiment, the amplifier 114 is a power amplifier. The feedback control loop 120 is used to correct the distortion or nonlinearity introduced by the amplifier 114 , which allows the RF signal 102 to be modulated based on the feedback corrected control signal, thereby correcting the distortion or nonlinearity introduced by the amplifier 114 . As shown in the figure, the feedback control loop 120 includes an amplitude feedback loop 130 and a phase feedback loop 150, which can be used to adjust the amplitude and phase independently of each other. A feedback signal 172 can be obtained by sampling the output signal 106 through the sampling device 170 , which is used 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 used to obtain a power feedback signal, or a sensor (such as a current sensor) used to obtain a current feedback signal.

For amplitude adjustment, in the amplitude adjustment loop 130 , an amplitude detector 132 is used to detect the output amplitude of the amplifier 114 from the feedback signal 172 . Typically, the magnitude detector includes a rectifier and a low pass filter. Then, the output amplitude of the amplifier 114 is compared with 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 magnitude and the reference magnitude is considered an error, which is used by the input controller 136 to control the input of the amplifier 114 . The controller 136 may include a filter (such as 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 implementations, the gain of the filter and the parameters of the PID controller can be adjusted to optimize the transient response of the system.

For phase adjustment, in the phase feedback loop 150, as shown in FIG. filters (such as low-pass filters) 157 and 158 to convert the vector of the feedback signal 172 into a quadrature scalar to generate the IQ signal as shown in Figure 3, where I and Q represent the in-phase component and the positive-phase component of the waveform, respectively. Hand in weight.

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°. In the quadrature system, the phase error can be expressed as in is the target phase shift of the amplifier output relative to the local oscillator, which can also be any value between 0 and 360°.

if not equal to 90° or 270°,

If higher-order errors are ignored,

when Phase error = 0, indicating no phase error.

Therefore, it is possible to determine whether (i.e. judging whether ) to determine whether there is a phase error. think when There is no phase error when There is a phase error. because is a predeterminable constant that can be easily and conveniently compared to I and A comparison is made, and based on the comparison result, it is judged whether there is a phase error.

In a specific embodiment, It can be preset to 45°, so that it can be judged whether (That is, to judge whether I=Q) to judge whether there is a phase error. A comparator can be used to compare I and Q. If I=Q, it is judged that there is no phase error, and if I≠Q, it is judged that there is a phase error.

if is equal to 90° or 270°, then it can be judged whether there is a phase error by judging whether Q is equal to 0. A comparator can be used to compare Q and 0. If Q=0, it is judged that there is no phase error, and if Q≠0, it is judged that there is a phase error.

For example, if is not equal to 90° or 270°, as shown in Figure 1, in the phase feedback loop 150, the product function 159 is used to combine Q and multiplied to get Comparator 162 is used to compare I and If I is not equal to It is judged that there is a phase error. The integrator 164 and the phase shifter 166 are used to accumulate the phase error and gradually adjust the phase in response to the phase error until I is equal to In this way, the output phase of the amplifier can be adjusted to a constant phase relative to the local oscillator. For example, if I/Q is kept at 1 (ie I=Q), the output phase of the amplifier can be maintained at a relative local oscillator. The machine oscillator has a phase shift of 45°.

if It is equal to 90° or 270°, and certain changes can be made to the phase feedback loop. For example, in a system 200 similar to the system 100 shown in FIG. 2, there is a When the phase feedback loop is equal to 90° or 270°, its other parts are the same as or similar to the system 100 except the phase feedback loop. exist Where equal to 90° or 270°, system 200 may be used. In the system 200, the phase feedback loop 250 includes a comparator 262 for comparing Q and 0 to determine that there is a phase error when Q is not equal to 0. The integrator 264 and the phase shifter 266 can be used to accumulate the phase error and gradually adjust the phase in response to the phase error until Q is equal to zero, respectively.

The system described in this paper can control the amplitude and phase independently of each other. Since there is no need for phase locking, no additional hardware is needed to lock the phase, and a faster response can be obtained. The system can be integrated in firmware, such as that of an MRI exciter, for better performance amplifier compensation without the need to turn the amplifier during manufacturing. An amplifier with the described system can directly drive various loads to achieve constant gain.

The aforementioned amplitude feedback loop can be implemented through different implementations. For example, in the system 300 shown in FIG. 4 , an amplitude feedback loop 330 including an amplitude function 331 and a filter (such as a low-pass filter) is adopted. Wherein, the amplitude function 331 obtains the feedback amplitude from the IQ signal obtained from the feedback signal The feedback magnitude is compared to a reference magnitude to determine an error for magnitude adjustment. exist Other than 90° or 270°, the rest of the system 300 can be the same or similar to the system 100 . exist Equal to 90° or 270°, the remainder of the system 300 may be the same or similar to the system 200 .

For another example, in a system 400 as shown in FIG. 5 , an amplitude feedback loop 430 including a band-pass filter 431 , an absolute value function 432 and a low-pass filter 433 is adopted. When using this amplitude feedback loop, after the feedback signal is filtered by the pass filter 431, the absolute value is obtained by the absolute value function 432, and then the absolute value is further filtered by the low-pass filter 433, and then the further filtered value Used to compare with the reference amplitude. Similar to system 200 , the remainder of system 400 may be the same as or similar to system 100 or 200 . Here, the absolute value function can be defined as f(x)=|x|, where:

In some embodiments, to enhance small signal phase stability, a coordinate adjustment loop may be added to the system described herein. As 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 between the feedback signal and the local oscillator α and the predetermined value at the time of initial operation equal. For example, in a specific embodiment, as shown in Figure 7, if the If it is set to 45°, the reference coordinate can be rotated so that α is equal to 45°. In this way, whether there is a phase error can be judged by judging whether I is equal to Q. In other embodiments, the predetermined value It can also be set to any angle within the range of 0 to 360°, such as 30° or 60°.

Referring to FIG. 6 again, the coordinate adjustment loop 580 communicates with the integrator 564 through a changeover switch 582, the switch 582 can be switched between a first position 583 and a second position 584, and the phase feedback loop is turned on at the first position 550, turn on the coordinate adjustment loop 580 when in the second position. The coordinate adjustment loop 580 is a loop that connects the comparator 562 and the integrator 564 to the modulator 512 through the local oscillator 552 and the phase shifter 504 . During initial operation, the coordinate adjustment loop 580 is turned on so that the reference coordinates can be turned to a suitable position to ensure that α is equal to a predetermined value . Switch 582 is then switched to close the phase feedback loop 550 to achieve phase feedback control. Similarly, such coordinate regulation loops may also be added to system 200 .

In some embodiments, a feed-forward loop can also be added to the system described herein, so that the system can obtain a faster response speed. The feed-forward loop inverts the gain and phase characteristics of the analog amplifier, introducing "predistortion" at the input of the amplifier to counteract any non-linearities the amplifier may have. 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 possible amplitude non-linearity of the amplifier. The amplitude feedforward loop may include a feedforward predistortion look-up table or predistortion circuit to receive a reference amplitude to determine accordingly how much "amplitude predistortion" needs to be introduced to the input of the amplifier. For example, as shown in FIG. 8, in a system 700 similar to system 100, a feed-forward pre-distortion look-up table is added between the reference amplitude and the adder 794 connected between the PID controller 738 and the modulator 712 At 792 , an amplitude feedforward loop 790 is formed. The feed-forward pre-distortion look-up table 792 receives the reference amplitude to determine how much "amplitude pre-distortion" needs to be introduced accordingly, so that an appropriate amount of "amplitude pre-distortion" can be introduced in the front stage of the amplifier to pre-compensate the possible abnormalities of the amplifier. linear.

Similarly, a phase feed-forward loop can be added to allow the system to respond faster. In addition, the aforementioned coordinate adjustment loop and/or feedforward loop can also be added to the system 200 .

Although the present invention has been described in conjunction with specific embodiments, those skilled in the art will appreciate that many modifications and variations can be made to the present invention. It is, therefore, to be realized that the intent of the appended claims is to cover all such modifications and variations as are within the true spirit and scope of the invention.

Claims (20)

1. A radio frequency amplification system, comprising: a feedback-controlled modulator that modulates an initial radio frequency signal based on a feedback correction control signal and produces 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 from said amplified radio frequency output signal; phase feedback loop, where the amplified RF output signal is phase shifted relative to the local oscillator target not equal to 90 or 270 degrees, based on the I and comparison to adjust the phase of the initial RF signal, or, in In the case of being equal 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 detects an amplitude characteristic of the amplified RF output signal and adjusts the amplitude of the initial RF 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 magnitude feedback loop adjust phase and magnitude independently of each other. 3. A system as claimed in claim 1, wherein, like not equal to 90 or 270 degrees, the phase feedback loop consists of a Q and multiplied to get Product function for comparing I and A comparator, and is used when I is not equal to a phase shifter that adjusts the phase; or, like Equal to 90 or 270 degrees, the phase feedback loop includes: a comparator used to compare Q with 0, and a phase shifter used to adjust the phase when Q is not equal to 0. 4. The system of claim 1, wherein the magnitude feedback loop comprises: amplitude detection means for detecting amplitude characteristics of said amplified radio frequency output signal; a comparator for comparing said magnitude signature to a reference magnitude; and control means for adjusting the amplitude based on the difference between said amplitude characteristic and a reference amplitude. 5. The system of claim 4, wherein the magnitude feedback loop includes an absolute value function to obtain an absolute value of the reference magnitude with which the magnitude characteristic is compared . 6. The system according to claim 4, wherein said amplitude detecting means comprises generating an amplitude component signal based on said IQ signal The function. 7. The system of claim 4, wherein the amplitude detection means comprises: a bandpass filter for filtering a feedback signal sampled from said amplified radio frequency output signal; an absolute value function for obtaining the absolute value of said 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 so that the phase difference α between the feedback signal sampled from the amplified RF output signal and the local oscillator is equal to 9. A system as claimed in claim 8, further comprising: a switch switchable between a first position and a second position, which closes the phase feedback loop in the first position and connects the phase feedback loop in the second position. through the coordinate adjustment loop. 10. The system of claim 1, further comprising: a feed-forward loop for inversely simulating the gain and phase characteristics of the amplifier and introducing predistortion to the input of the amplifier to pre-compensate possible non-linearity of the amplifier. 11. The system of claim 10, wherein the feedforward loop comprises an amplitude feedforward loop comprising a feedforward predistortion look-up table or predistortion circuit between the reference amplitude and the modulator , the pre-distortion look-up table or pre-distortion circuit may receive a reference magnitude and accordingly determine how much pre-distortion needs to be introduced. 12. A radio frequency amplification method, comprising: modulating the initial radio frequency signal based on the 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; The phase shift of the amplified RF output signal relative to the local oscillator target not equal to 90 or 270 degrees, based on the I and comparison to adjust the phase of the initial RF signal, or, in In the case of being equal to 90 or 270 degrees, adjusting the phase of the initial radio frequency signal based on a comparison of Q and 0; and A magnitude characteristic of the amplified radio frequency output signal is detected, and the magnitude of the initial radio frequency signal is adjusted based on a difference between the magnitude characteristic and a reference magnitude. 13. The method of claim 12, wherein the phase and amplitude are adjusted independently of each other. 14. The method of claim 12, wherein at I is not equal to Or adjust the phase of the initial radio frequency signal when Q is not equal to 0. 15. The method of claim 12, further comprising obtaining an absolute value of the reference magnitude, the magnitude characteristic being compared to the absolute value of the reference magnitude. 16. The method of claim 12, wherein the amplitude characteristics of the amplified radio frequency output signal are obtained by: generating an amplitude component signal based on the IQ signal; and The amplitude component signal is filtered. 17. The method of claim 16, wherein the magnitude component signal is in the form of Indicates the magnitude of the feedback. 18. The method of claim 12, wherein the amplitude characteristics of the amplified radio frequency output signal are obtained by: filtering a feedback signal sampled from said amplified radio frequency output signal with a bandpass filter; using an absolute value function to obtain the absolute value of the filtered feedback signal; 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 so 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 inversely simulating gain and phase characteristics of an amplifier and introducing predistortion to an input of the amplifier to pre-compensate for possible non-linearities of the amplifier.