A radio frequency power amplifier

Abstract

This invention discloses a radio frequency (RF) power amplifier, comprising: a DC power supply module including a first filter capacitor connected between the output terminal and ground of the DC power supply module; an analog switch module including an analog switch and a second filter capacitor; the input terminal of the analog switch being connected to the output terminal of the DC power supply module, and the second filter capacitor being connected between the input terminal of the analog switch and ground; and a gate DC channel module connected between the output terminal of the analog switch and the bias input terminal of the RF power amplifier module. The technical solution provided by this invention can shorten the transient response time of the RF power amplifier when it is turned on or off by using the second filter capacitor at the input terminal of the analog switch, thereby reducing the intermodulation distortion of the RF power amplifier output signal. It is suitable for RF power amplifiers with ultrashort echo time series in magnetic resonance systems, and also applicable to RF power amplifiers in other applications.

Description

Technical Field

[0001] This invention relates to the field of medical magnetic resonance imaging technology, and more particularly to a radio frequency power amplifier. Background Technology

[0002] With the development of wireless technology, radio frequency power amplifiers are widely used in fields such as medical magnetic resonance imaging, wireless communication base stations, radar, and electronic countermeasures. Among them, the ultra-short echo time (UTE) in magnetic resonance systems is generally required to be in the range of 8µs-500µs, and its echo time is limited by the on or off time of the radio frequency power amplifier.

[0003] Currently, RF power amplifiers and their bias circuits mainly use low-frequency intermodulation distortion to feed into the input section of an operational amplifier connected to the gate of a field-effect transistor, replacing the decoupling capacitor to achieve lower-power intermodulation distortion decoupling.

[0004] Operational amplifiers have weak driving capability for capacitors, which can easily cause ringing; the settling time increases, affecting the transient response time of the RF power amplifier; and the ability to inject intermodulation distortion generated by high-power amplifiers deteriorates, resulting in severe intermodulation distortion in the output signal of the RF power amplifier. Summary of the Invention

[0005] This invention provides a radio frequency power amplifier that can shorten the transient response time of the radio frequency power amplifier and reduce the intermodulation distortion of the output signal of the radio frequency power amplifier.

[0006] This invention provides an RF power amplifier, comprising: a DC power supply module, the DC power supply module including a first filter capacitor connected between the output terminal and ground terminal of the DC power supply module, the output terminal of the DC power supply module outputting a DC voltage; an analog switch module including an analog switch and a second filter capacitor; the input terminal of the analog switch is connected to the output terminal of the DC power supply module, and the second filter capacitor is connected between the input terminal and ground terminal of the analog switch; wherein the capacitance value of the second filter capacitor is less than the capacitance value of the first filter capacitor; a gate DC channel module connected between the output terminal of the analog switch and the bias input terminal of the RF power amplifier module, used to process the signal output from the analog switch module and output a bias voltage to the RF power amplifier module; the gate DC channel module and the analog switch module are disposed close to the RF power amplifier module; the RF power amplifier module is used to amplify the RF pulse signal and output it.

[0007] Optionally, the capacitance of the first filter capacitor is 10-100 times the capacitance of the second filter capacitor.

[0008] Optionally, the analog switch module further includes a first resistor, comprising: the input terminals of the analog switch include a first input terminal and a second input terminal; the first input terminal of the analog switch is connected to the output terminal of the DC power supply module; a second filter capacitor is connected between the first input terminal of the analog switch and the ground terminal; and the first resistor is connected between the second input terminal of the analog switch and the ground terminal.

[0009] Optionally, the gate DC channel module includes a second resistor, a first inductor, a decoupling capacitor, and an overvoltage protection diode; the first end of the first inductor is connected to the output terminal of the analog switch, the second end of the first inductor is connected to the first end of the second resistor, and the second end of the second resistor is connected to the bias input terminal; the overvoltage protection diode is connected to the first end of the first inductor, the first end of the decoupling capacitor is connected between the overvoltage protection diode and the first end of the first inductor, and the second end of the decoupling capacitor is connected to the ground terminal.

[0010] Optionally, the gate DC channel module includes a second resistor, a first inductor, a decoupling capacitor, and an overvoltage protection diode; the first end of the first inductor is connected to the output terminal of the analog switch, the second end of the first inductor is connected to the first end of the second resistor, and the first end of the second resistor is connected to the bias input terminal; the overvoltage protection diode is connected between the ground terminal and the first end of the first inductor; the decoupling capacitor is connected between the ground terminal and the second end of the second resistor.

[0011] Optionally, the capacitance value of the decoupling capacitor is less than the capacitance value of the first filter capacitor.

[0012] Optionally, the DC power supply module includes a linear regulator chip, an input filter capacitor, a third resistor, a fourth resistor, a fifth resistor, and a sixth resistor; the input terminal of the linear regulator chip is connected to the first power supply, and the output terminal of the linear regulator chip is connected to the first filter capacitor; the input filter capacitor is connected to the input terminal of the linear regulator chip; the third, fourth, fifth, and sixth resistors are connected in series between the output terminal and the ground terminal of the linear regulator chip, and the common connection terminal of the fifth and sixth resistors is connected to the feedback input terminal of the linear regulator chip; the fourth resistor is an adjustable resistor, and the fifth resistor is a thermistor.

[0013] Optionally, the DC power supply module includes an operational amplifier, a first input filter capacitor, a transistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor; the first input filter capacitor is connected to the non-inverting input terminal of the operational amplifier; the seventh, eighth, and ninth resistors are connected in series between the first power supply and the ground terminal, and the common terminal of the eighth and ninth resistors is electrically connected to the non-inverting input terminal of the operational amplifier to provide a reference voltage for the non-inverting input terminal of the operational amplifier; the eighth resistor is an adjustable resistor, and the ninth resistor is a thermistor; the tenth resistor is connected between the inverting input terminal of the operational amplifier and the ground terminal; the eleventh resistor is connected between the emitter of the transistor and the first terminal of the tenth resistor; the base of the transistor is connected to the output terminal of the operational amplifier, the collector of the transistor is connected to the first power supply, and the emitter of the transistor is connected to the first filter capacitor.

[0014] Optionally, the RF power amplifier module includes an input matching and DC isolation circuit, an output matching and DC isolation circuit, a field-effect transistor (FET), and a second inductor. The input matching and DC isolation circuit is connected between the RF pulse signal input terminal and the gate of the FET. The second inductor is connected between the first terminal of the FET and the second power supply. The output matching and DC isolation circuit is connected between the RF pulse signal output terminal and the first terminal of the FET. The second terminal of the FET is connected to the ground terminal, and the gate of the FET serves as the bias input terminal.

[0015] Optionally, the radio frequency pulse signal includes pulses with a fixed sequence and pulses with a variable sequence.

[0016] The technical solution of this invention addresses the issue that the on-resistance and peak current of the analog switch affect the transient response time of the RF power amplifier. By setting a second filter capacitor at the input of the analog switch, the decoupling capacitance at the output of the analog switch can be reduced, thereby shortening the transient response time of the RF power amplifier and enabling rapid turn-on or turn-off. Furthermore, by setting the capacitance value of the second filter capacitor to be smaller than that of the first filter capacitor, the first and second filter capacitors can filter out waveforms of different frequencies, reducing intermodulation distortion of the RF output signal.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a radio frequency power amplifier provided by the present invention;

[0020] Figure 2 This is a schematic diagram of another radio frequency power amplifier provided by the present invention;

[0021] Figure 3 This is a schematic diagram of another radio frequency power amplifier provided by the present invention;

[0022] Figure 4 This is a schematic diagram of another radio frequency power amplifier provided by the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] Figure 1 This is a schematic diagram of a radio frequency power amplifier provided by the present invention. This embodiment can be applied to the case of radio frequency power amplification.

[0026] like Figure 1 As shown, the RF power amplifier 1 includes:

[0027] The DC power supply module 10 includes a first filter capacitor C1, which is connected between the output terminal and the ground terminal GND of the DC power supply module 10. The first filter capacitor C1 is the output filter capacitor of the DC power supply module 10, and the output terminal of the DC power supply module 10 outputs a DC voltage.

[0028] The DC power module 10 can be a temperature-compensated, voltage-adjustable, and low-noise DC regulated power supply module. Optionally, the temperature compensation function of the DC power module 10 can be used to compensate for drift caused by temperature changes in the RF power amplifier module 40. The noise range of the DC power module 10 can be between 0.8uVrms and 20uVrms. The model of the DC power module 10 can be various. For example, the DC power module 10 can be LP38798, or LT3045, etc.

[0029] The analog switch module 20 includes an analog switch U1 and a second filter capacitor C2. The input terminal of the analog switch is connected to the output terminal of the DC power supply module 10, and the second filter capacitor C2 is connected between the input terminal of the analog switch U1 and the ground terminal GND. The capacitance of the second filter capacitor C2 is smaller than that of the first filter capacitor C1. The second filter capacitor C1 is positioned closer to the input terminal of the analog switch U1 than the first filter capacitor C1. In other words, the second filter capacitor C1 is connected in parallel with the first filter capacitor C1, and the input terminal of the analog switch U1 and the DC power supply module 10 share the second filter capacitor C2. Due to the different self-resonant frequencies of the actual capacitors, the parallel connection of the first filter capacitor C1 and the second filter capacitor C2 achieves low impedance from hundreds of hertz to several megahertz, improving the filtering effect.

[0030] The enable terminal of analog switch U1 is used to control the on / off state of the output voltage signal of DC power module 10. Analog switch U1 can be an integrated circuit with normally open and normally closed (NOC) functions, or it can be a circuit with NOC functions built from discrete transistors. For example, analog switch U1 can be a TMU6219, or it can be an ADG1419, ADG1459, ADG849, or a similar switch built from transistors. The on / off time of analog switch U1 affects the on / off time of RF power amplifier 1, and the on-resistance and peak current of analog switch U1 affect the charging transient response time of RF power amplifier 1. Analog switch U1 has good RF performance, low insertion loss, and provides a good path to the second filter capacitor C2 for spurious and low-frequency intermodulation distortion.

[0031] This invention, through the addition of a new second filter capacitor C2, achieves decoupling of low-frequency intermodulation distortion. Specifically, since all capacitors possess parasitic inductance, the larger the capacitance, the greater the parasitic inductance. Furthermore, the parasitic inductance is connected in series with the capacitor, forming an LCR resonant circuit. Here, L is the inductance related to the lead length, R is the lead resistance, and C is the capacitance. The resonant circuit has a resonant frequency point, where the impedance is lowest. As the operating frequency of the RF power amplifier varies, the characteristics of the capacitor also change. When the operating frequency is below the resonant frequency, the capacitor is generally capacitive; when the operating frequency is above the resonant frequency, the capacitor is generally inductive. At this point, the capacitor loses its decoupling function. The capacitance value is generally chosen based on the capacitor's resonant frequency. Different capacitance values ​​and different packages of capacitors can filter out signals of different frequencies. By setting the capacitance value of the second filter capacitor C2 to be smaller than that of the first filter capacitor C1, the first filter capacitor C1 can be used to filter out waves in the range of tens of Hz (Hertz) to hundreds of kHz (kilohertz); the second filter capacitor C2 can be used to filter out waveforms near or below one-tenth of the center operating frequency of the RF pulse signal. For example, when the center operating frequency of the RF pulse signal is 210 MHz (megahertz), the second filter capacitor C2 can be used to filter out waveforms in the range of 1 MHz to 20 MHz.

[0032] The main charge / discharge real constant of the transient response of RF power amplifier 1 and the switching speed of analog switch U1 determine the turn-on or turn-off time of RF power amplifier 1. When the second filter capacitor C2 is placed at the output of analog switch U1, the charging time increases after passing through analog switch U1 due to the on-resistance of analog switch U1, and the main charge real constant of the transient response of RF power amplifier 1 becomes larger. By placing the second filter capacitor at the input of analog switch U1, the transient response time of RF power amplifier 1 can be shortened, achieving rapid turn-on or rapid turn-off of RF power amplifier 1.

[0033] The gate DC channel module 30 is connected between the output terminal of the analog switch U1 and the bias input terminal of the RF power amplifier module 40. It processes the signal output from the analog switch module 20 and outputs a bias voltage to the RF power amplifier module 40. The RF power amplifier module 40 amplifies the RF pulse signal before outputting it. The gate DC channel module 30 ensures that the RF power amplifier 1 does not experience self-oscillation during operation, reducing ringing in the RF power amplifier module 40.

[0034] Radio frequency (RF) pulse signals include fixed-sequence pulses and variable-sequence pulses. In other words, the DC power supply module 10, the analog switch module 20, and the gate DC channel module 30 constitute the DC bias circuit of the RF power amplifier 1. This DC bias circuit can be applied not only to RF power amplifiers with fixed-sequence narrow-pulse modulation, but also to RF power amplifiers with variable-sequence pulse modulation of variable pulse width and variable period, especially the ultra-short echo time (UTE) sequence in magnetic resonance systems, and can also be used in commonly used RF power amplifiers.

[0035] The specific working process of the RF power amplifier 1 is as follows: The DC power supply module 10 adjusts the output DC voltage according to the requirements of the RF power amplifier module 40, providing a suitable static operating current for the RF power amplifier module 40 and determining a suitable DC voltage for the static operating point. The first filter capacitor C1 and the second filter capacitor C2 filter out RF pulse signals of different operating frequencies and input them to the analog switch U1. The pulse signal at the enable terminal of the analog switch U1 controls the conduction and turn-off of the analog switch U1, thereby controlling the on and off of the RF pulse signal. When the analog switch U1 is on, the gate DC channel module 30 processes the signal output from the analog switch module 20 and outputs a bias voltage to the RF power amplifier module 40. The gate DC channel module 30 and the analog switch module 20 are set close to the RF power amplifier module 40, which is used to amplify the RF pulse signal before outputting it.

[0036] After the radio frequency pulse signal passes through the radio frequency power amplifier module 40, the intermodulation distortion and spurious signals caused by nonlinear effects and memory effects enter the analog switch through the gate DC channel module 30. The low-frequency band is decoupled by the first filter capacitor C1 and the second filter capacitor C2.

[0037] The generation of radio frequency pulse modulation signals, with output power close to the P1dB compression point, produces nonlinear and memory effects. This process is equivalent to AM modulation, where the modulation signal is a baseband pulse signal. AM modulation shifts the single-sideband spectrum of the baseband signal onto the radio frequency carrier, resulting in two symmetrical sidebands. Radio frequency pulse modulation generates more sidebands and spurious signals.

[0038] The Fourier transform of a radio frequency pulse modulated signal can be written as:

[0039]

[0040] In the formula, τ and T are the pulse width and pulse period of the radio frequency pulse signal, respectively. and Let n be the repetition frequency and carrier frequency of the radio frequency pulse signal, respectively, where n is any integer.

[0041] From this Fourier transform, we can see that the frequency components contained in the radio frequency pulse signal are: Theoretically, it has an infinite number of frequency components. Because the signal is periodic, its spectrum is discrete, with the frequency interval between adjacent spectral lines being Ω, and the Sa(x) function determining the amplitude of each spectral line.

[0042] Discrete multiple spectra, after passing through the nonlinear and memory effects of the RF high-power amplifier, generate more harmonics, intermodulation distortion, and spurious signals at various frequencies—all of which are unwanted interference signals. Variable pulse width and period cause changes in the frequency bands of intermodulation distortion and spurious signals generated by the RF power amplifier. Decoupling through the first filter capacitor C1 and the second filter capacitor C2 can reduce the intermodulation distortion and spurious signals of the output RF pulse signal.

[0043] The technical solution of this invention addresses the issue that the on-resistance and peak current of the analog switch affect the transient response time of the RF power amplifier. By setting a second filter capacitor at the input of the analog switch, the decoupling capacitance at the output of the analog switch can be reduced, thereby shortening the transient response time of the RF power amplifier and enabling rapid turn-on or turn-off. Furthermore, by setting the capacitance value of the second filter capacitor to be smaller than that of the first filter capacitor, the first and second filter capacitors can filter out waveforms of different frequencies, reducing intermodulation distortion and spurious signals in the RF output signal.

[0044] Figure 2 This is a schematic diagram of another radio frequency power amplifier provided by the present invention.

[0045] like Figure 2 As shown, optionally, the capacitance value of the first filter capacitor C1 is 10-100 times the capacitance value of the second filter capacitor C2. By setting the capacitance value of the first filter capacitor C1 to be 10-100 times the capacitance value of the second filter capacitor C2, the filtering effect can be improved.

[0046] The DC power supply module 10 includes a linear regulator chip U2, an input filter capacitor C4, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6. The input terminal IN of the linear regulator chip U2 is connected to the first power supply VCC, and the output terminal OUT of the linear regulator chip U2 is connected to the first filter capacitor C1. The input filter capacitor C4 is connected to the input terminal of the linear regulator chip U2. The third resistor R3, the fourth resistor R4, the fifth resistor R5, and the sixth resistor R6 are connected in series between the output terminal OUT of the linear regulator chip U2 and the ground terminal GND. The common connection terminal of the fifth resistor R5 and the sixth resistor R6 is connected to the feedback input terminal FB of the linear regulator chip U2. The fourth resistor R4 is an adjustable resistor, and the fifth resistor R5 is a thermistor. The ground terminal GND1 of the linear regulator chip U2 is grounded.

[0047] In this circuit, the output voltage Vout of the linear regulator chip U2 is calculated as Vref * (1 + (R2 + R4 + R5) / R6), where Vref is the internal reference voltage value of the linear regulator chip U2. The third resistor R3 is a fixed resistor, and the fourth resistor R4 is an adjustable resistor used to adjust the DC output voltage, thus meeting the bias voltage requirements of the field-effect transistor in the RF power amplifier module 40. The fifth resistor R5 is a thermistor; based on the temperature coefficient of the RF power amplifier 1, an inverting thermistor is used to reduce current changes caused by temperature variations, thereby ensuring the stability of the output current and meeting the stability requirements of the field-effect transistor's static operating current.

[0048] The analog switch module 20 also includes a first resistor R1. The analog switch U1 has two input terminals: a first input terminal IN1 and a second input terminal IN2. The first input terminal IN1 of the analog switch U1 is connected to the output terminal of the DC power supply module 10. A second filter capacitor C2 is connected between the first input terminal IN1 of the analog switch U1 and the ground terminal GND. The first resistor R1 is connected between the second input terminal IN2 of the analog switch U1 and the ground terminal GND. The first resistor R1 is a discharge resistor.

[0049] Optionally, for different models of RF power amplifier 1, the second terminal of the first resistor R1 can be grounded or connected to a negative power supply. For example, when the RF power amplifier 1 is a gallium nitride (GaN) RF power amplifier 1, the second terminal of the first resistor R1 is connected to a negative power supply to turn it off. The pulse signal at the enable terminal of analog switch U1 controls analog switch U1 to connect to the DC power module 10 to enable the RF pulse signal, or the pulse signal at the enable terminal of analog switch U1 controls analog switch U1 to connect to the ground through the first resistor R1 to turn off the RF pulse signal. The on or off time of analog switch U1 affects the on or off time of RF power amplifier 1, and the on-resistance and peak current of analog switch U1 affect the transient response time of charging the input capacitor of the field-effect transistor. After analog switch U1 is turned off, the input capacitor of the field-effect transistor is discharged through the first resistor R1, and the transient response time of the input capacitor discharge affects the off time of the field-effect transistor. The turn-on time of analog switch U1 and the charging time of the input capacitor of the field-effect transistor are the turn-on time of the field-effect RF power amplifier 1; the turn-off time of analog switch U1 and the discharge time of the input capacitor of the field-effect transistor are the turn-off time of the RF power amplifier 1.

[0050] The gate DC channel module 30 includes a second resistor R2, a first inductor L1, a decoupling capacitor C3, and an overvoltage protection diode TVS1. The first end of the first inductor L1 is connected to the output terminal of the analog switch U1, the second end of the first inductor L1 is connected to the first end of the second resistor R2, and the first end of the second resistor R2 is connected to the bias input terminal. The overvoltage protection diode TVS1 is connected to the first end of the first inductor L1, the first end of the decoupling capacitor C3 is connected to the overvoltage protection diode TVS1 and the first end of the first inductor L1, and the second end of the decoupling capacitor C3 is connected to the ground terminal GND.

[0051] The second resistor R2 serves as a stabilizing resistor. The second resistor R2, the first inductor L1, and the decoupling capacitor C3 work together to ensure that the RF power amplifier 1 does not experience self-oscillation during operation. Additionally, the second resistor R2 acts as a damper during the transient response of the field-effect transistor (FET), reducing gate ringing during FET conduction. The first inductor L1 attenuates some energy at the center frequency of the RF pulse signal; the remaining RF energy is decoupled by the decoupling capacitor C3. Intermodulation distortion and harmonics caused by nonlinear and memory effects in the RF power amplifier 1, as well as high-frequency energy, are also decoupled by the decoupling capacitor C3. The decoupling capacitor C3 is selected based on the center frequency of the RF pulse signal; its capacitance value is relatively low, typically in the picofarad (pF) range. The capacitance value of the decoupling capacitor C3 is smaller than that of the first filter capacitor C1, and is primarily determined by the center frequency of the RF pulse signal. For lower frequency bands caused by nonlinear effects and memory effects, the signal is decoupled by the second filter capacitor C2 after passing through analog switch U1. The capacitance value of the second filter capacitor C2 is relatively large, usually in the microfarad (µF) range, thereby reducing the overall intermodulation distortion of the RF pulse signal. Due to the bandwidth (3dB) limitation of analog switch U1, the center operating frequency of the RF pulse signal is usually higher than the bandwidth of analog switch U1. When the center operating frequency of the RF pulse signal is within the bandwidth of analog switch U1, the decoupling capacitor C3 can be omitted. In this case, the first filter capacitor C1 and the second filter capacitor C2 are used for decoupling, further improving the transient response time.

[0052] The second end of the second resistor R2 is also connected to the third power supply VBiss.

[0053] The RF power amplifier module 40 includes an input matching and DC isolation circuit M1, an output matching and DC isolation circuit M2, a field-effect transistor (FET) Q1, and a second inductor L2. The input matching and DC isolation circuit M1 is connected between the RF pulse signal input terminal RF_in and the gate of the FET Q1. The second inductor L2 is connected between the first terminal of the FET Q1 and the second power supply VDD. The output matching and DC isolation circuit M2 is connected between the RF pulse signal output terminal RF_out and the first terminal of the FET Q1. The second terminal of the FET Q1 is connected to the ground terminal GND, and the gate of the FET Q1 serves as the bias input terminal. The second inductor L2 is a choke inductor.

[0054] The RF power amplifier module 40 also includes a fifth filter capacitor C5, which is used to filter out noise from the second power supply VDD, making the output of the second power supply VDD more stable. The fifth filter capacitor is connected between the second power supply VDD and the ground terminal GND.

[0055] The input matching and DC isolation circuit M1 matches the RF input signal and the field-effect transistor Q1 in the operating frequency band and isolates the DC bias of the gate of the field-effect transistor Q1; the output matching and DC isolation circuit M2 matches the RF output signal and the output of the field-effect transistor Q1 and isolates the second power supply VDD connected to the second terminal of the field-effect transistor Q1.

[0056] The secondary power supply VDD of a field-effect transistor (FET) is typically high, and the overvoltage protection diode TVS1 ensures that the FET's gate is at a safe voltage. In kilowatt-level RF power amplifiers, the parasitic capacitance of the FET cannot be ignored, resulting in a large input capacitance (Ciss). This generates significant spurious harmonics and high power, making it unsuitable to use operational amplifiers for gate input current sinking decoupling. Instead, capacitors are typically used for decoupling to reduce spurious harmonics at the output.

[0057] The input capacitance Ciss of the field-effect transistor Q1 is equal to Cgs + Cgd. Here, Cgs is the parasitic capacitance between the gate and source, and Cgd is the parasitic capacitance between the gate and drain. The main charging real constants of the transient response of RF power amplifier 1 are: τ1 = R2 * Ciss, τ4 = Ru2 * C2. Here, Ru2 is the on-resistance of analog switch U1, typically less than a few ohms. The main discharging real constants of the transient response of RF power amplifier 1 are: τ2 = (R1 + R2) * Ciss, τ3 = R1 * C3. The charging and discharging real constants and the switching speed of analog switch U1 determine the turn-on or turn-off time of RF power amplifier 1. The total value of the first filter capacitor C1 and the second filter capacitor C2 is much larger than the input capacitance of the field-effect transistor and the decoupling capacitor C3. By placing the second filter capacitor C2 before analog switch U1, compared to the filter capacitor typically placed after analog switch U1, there is a significant improvement in both the turn-on and turn-off times. The main difference lies in the charging constant, which changes from Ru2*(C2+C3) to Ru2*C2. The difference in transient response time can be observed on an oscilloscope. On the oscilloscope, from the fifth filter capacitor C5 terminal, it is clear to observe the reduction in the amplitude of the spurious AM modulation signal envelope produced by adding and not adding the second filter capacitor C2 before analog switch U1; alternatively, using a spectrum analyzer and attenuator, the power of the spurious signal is reduced at the RF pulse signal output terminal RF_out. The short on / off time of the RF power amplifier is beneficial for the transmission of RF hard pulses. The on / off time of conventional RF power amplifiers is 10µs to 20µs, which cannot meet the requirements of ultra-short echo time of 8µs to 500µs in magnetic resonance systems. The RF power amplifier of this invention has an on / off time of 40ns to 300ns, which meets the requirements of UTE sequence RF hard pulse RF transmission and also meets the pulse sequence requirements of other functions.

[0058] Furthermore, the second filter capacitor C2 is positioned close to the field-effect transistor Q1. By positioning the second filter capacitor C2 close to the field-effect transistor Q1, the influence of PCB traces can be reduced, and the decoupling performance of the second filter capacitor C2 can be improved.

[0059] In this embodiment of the invention, the RF high-power amplifier used is a MRFX1K80N field-effect transistor. When the center operating frequency of the RF pulse signal is 210MHz, the capacitance value of the decoupling capacitor C3 is generally 510pF, the capacitance value of the second filter capacitor C2 is generally 1uF, and the capacitance value of the first filter capacitor C1 is generally 10uF. The second resistor R2 is 6.2 ohms, the first inductor L1 is 22nH, the first resistor R1 is 100 ohms, the second power supply VDD is 75V, the saturated output power of the RF pulse signal is 2400W, and the turn-on or turn-off time of the RF power amplifier is 40ns-300ns, meeting the requirements of UTE sequence RF hard pulse RF transmission. This invention, verified through experiments, demonstrates that with a 210MHz operating frequency and a 2kW P1dB output power RF power amplifier at the test center, for an AM modulation signal with a period of 100ms, a pulse width of 200µs, and a maximum low-frequency amplitude of 2.9MHz, adding a 1µF second filter capacitor at the analog switch input resulted in a reduction in the AM modulation signal output amplitude from -43dBc to -50dBc, as detected by a spectrum analyzer at the output. For an AM modulation signal with a period of 1s, a pulse width of 1ms, and a maximum intermodulation frequency amplitude of 7.3MHz, adding the second filter capacitor resulted in an output amplitude below -51dBc. For different periods and pulse widths, resulting in different low-frequency intermodulation signals, this solution consistently provides an improvement of over 6dB.

[0060] The technical solution of this invention can be applied to a variable sequence pulse power amplifier to achieve rapid turn-on or turn-off of the variable sequence pulse power amplifier, especially for ultrashort echo time sequences in magnetic resonance systems. Since the on-resistance and peak current of the analog switch affect the transient response time of the RF power amplifier, by setting a second filter capacitor and positioning it at the input of the analog switch, the decoupling capacitance at the output of the analog switch can be reduced, thereby shortening the transient response time of the RF power amplifier and achieving rapid turn-on or turn-off. Furthermore, by setting the capacitance value of the second filter capacitor to be smaller than that of the first filter capacitor, the first and second filter capacitors can filter out out-of-frequency components. The waveform of the frequency response is optimized to reduce intermodulation distortion of the RF output signal. Decoupling capacitors filter out residual RF energy at the center operating frequency of the RF pulse signal, reducing intermodulation distortion and high-frequency harmonic energy caused by nonlinear and memory effects. An adjustable fourth resistor allows for adjustable DC output voltage, ensuring the output DC voltage meets the bias voltage requirements of the MOSFET gate. A thermistor as the fifth resistor reduces drift caused by MOSFET temperature changes, ensuring output current stability. The second resistor, first inductor, and decoupling capacitors ensure stable operation of the RF power amplifier across the entire frequency band, preventing self-oscillation and reducing MOSFET gate ringing. The RF power amplifier of this invention has an on / off time of 40ns–300ns, meeting the requirements of ultra-short echo time sequences in magnetic resonance imaging and can also be used in commonly used RF power amplifiers.

[0061] Figure 3 This is a schematic diagram of another radio frequency power amplifier provided by the present invention.

[0062] like Figure 3 As shown, the gate DC channel module 30 includes a second resistor R2, a first inductor L1, a decoupling capacitor C3, and an overvoltage protection diode TVS1. The first end of the first inductor L1 is connected to the output terminal of the analog switch U1, the second end of the first inductor L2 is connected to the first end of the second resistor R2, and the first end of the second resistor R2 is connected to the bias input terminal. The overvoltage protection diode TVS1 is connected between the ground terminal and the first end of the first inductor L1. The decoupling capacitor C3 is connected between the ground terminal GND and the second end of the second resistor R1 to achieve stable reduction of coupling.

[0063] Optional, Figure 3 The DC power supply module 10, analog switch module 20, and RF power amplifier module 40 include Figure 2 The structure shown is illustrated as an example. This RF power amplifier 1 possesses the beneficial effects of any of the embodiments of the present invention described above.

[0064] Figure 4 This is a schematic diagram of another radio frequency power amplifier provided by the present invention.

[0065] like Figure 4 As shown, the DC power supply module 10 includes an operational amplifier U3, a first input filter capacitor C6, a transistor Q2, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, and an eleventh resistor R11. The first input filter capacitor C6 is connected to the non-inverting input terminal IN+ of the operational amplifier U3. The seventh resistor R7, the eighth resistor R8, and the ninth resistor R9 are connected in series between the first power supply VCC and the ground terminal GND. The common terminal of the eighth resistor R8 and the ninth resistor R9 is electrically connected to the non-inverting input terminal IN+ of the operational amplifier U3 to provide a reference voltage for the non-inverting input terminal IN+ of the operational amplifier U3. The eighth resistor R8 is an adjustable resistor, and the ninth resistor R9 is a thermistor. The tenth resistor R10 is connected between the inverting input terminal IN- of the operational amplifier U3 and the ground terminal GND; the eleventh resistor R11 is connected between the emitter of the transistor Q2 and the first terminal of the tenth resistor R10; the base of the transistor Q2 is connected to the output terminal of the operational amplifier U3, the collector of the transistor Q2 is connected to the first power supply VCC, and the emitter of the transistor Q2 is connected to the first filter capacitor C1.

[0066] The technical solution of this invention uses an operational amplifier (which does not require conversion rate and bandwidth) to add transistors to increase the drive current, thereby forming a low-noise, low-cost DC power supply module 10.

[0067] Optional, Figure 4 The analog switch module 20, the gate DC channel module 30, and the RF power amplifier module 40 include Figure 2 The structure shown is illustrated as an example. This RF power amplifier 1 possesses the beneficial effects of any of the embodiments of the present invention described above.

[0068] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A radio frequency power amplifier, characterized by, The application relates to a direct-current power supply module, an analog switch module and a gate direct-current channel module. The direct-current power supply module comprises a first filter capacitor connected between an output end and a ground end of the direct-current power supply module, and the output end outputs a direct-current voltage. The analog switch module comprises an analog switch and a second filter capacitor, wherein an input end of the analog switch is connected to the output end of the direct-current power supply module, and the second filter capacitor is connected between the input end of the analog switch and the ground end. The gate direct-current channel module is connected between an output end of the analog switch module and a bias input end of a radio frequency power amplifier module, and is used for outputting a bias voltage to the radio frequency power amplifier module after processing a signal output by the analog switch module. The gate direct-current channel module and the analog switch module are arranged close to the radio frequency power amplifier module, and the radio frequency power amplifier module is used for amplifying and outputting a radio frequency pulse signal.

2. The radio frequency power amplifier of claim 1, wherein, The capacitance value of the first filter capacitor is 10-100 times of the capacitance value of the second filter capacitor.

3. The radio frequency power amplifier of claim 1, wherein, The analog switch module further comprises a first resistor. The input end of the analog switch comprises a first input end and a second input end, the first input end of the analog switch is connected to the output end of the direct-current power supply module, the second filter capacitor is connected between the first input end of the analog switch and the ground end, and the first resistor is connected between the second input end of the analog switch and the ground end.

4. The radio frequency power amplifier of claim 1, wherein, The gate direct-current channel module comprises a second resistor, a first inductor, a decoupling capacitor and an overvoltage protection diode. The first end of the first inductor is connected to the output end of the analog switch, the second end of the first inductor is connected to the first end of the second resistor, and the first end of the second resistor is connected to the bias input end. The overvoltage protection diode is connected to the first end of the first inductor, the first end of the decoupling capacitor is connected between the overvoltage protection diode and the first end of the first inductor, and the second end of the decoupling capacitor is connected to the ground end.

5. The radio frequency power amplifier of claim 1, wherein, The gate direct-current channel module comprises a second resistor, a first inductor, a decoupling capacitor and an overvoltage protection diode. The first end of the first inductor is connected to the output end of the analog switch, the second end of the first inductor is connected to the first end of the second resistor, and the first end of the second resistor is connected to the bias input end. The overvoltage protection diode is connected between the ground end and the first end of the first inductor. The decoupling capacitor is connected between the ground end and the second end of the second resistor.

6. The radio frequency power amplifier of claim 4 or 5, wherein, The capacitance value of the decoupling capacitor is smaller than the capacitance value of the first filter capacitor.

7. The radio frequency power amplifier of any one of claims 1-5, wherein, The direct-current power supply module comprises a linear voltage stabilizing chip, an input filter capacitor, a third resistor, a fourth resistor, a fifth resistor and a sixth resistor. The input end of the linear voltage stabilizing chip is connected to a first power supply, and the output end of the linear voltage stabilizing chip is connected to the first filter capacitor. The input filter capacitor is connected to the input end of the linear voltage stabilizing chip. The third resistor, the fourth resistor, the fifth resistor and the sixth resistor are connected in series between the output terminal of the linear voltage stabilizing chip and the ground terminal, the common connection terminal of the fifth resistor and the sixth resistor is connected to the feedback input terminal of the linear voltage stabilizing chip, the fourth resistor is an adjustable resistor, and the fifth resistor is a thermistor.

8. The radio frequency power amplifier of any one of claims 1-5, wherein, The direct current power supply module comprises an operational amplifier, a first input filter capacitor, a triode, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor and an eleventh resistor. The first input filter capacitor is connected to the non-inverting input terminal of the operational amplifier. The seventh resistor, the eighth resistor and the ninth resistor are connected in series between the first power supply and the ground terminal, the common terminal of the eighth resistor and the ninth resistor is electrically connected to the non-inverting input terminal of the operational amplifier to provide a reference voltage for the non-inverting input terminal of the operational amplifier, the eighth resistor is an adjustable resistor, and the ninth resistor is a thermistor. The tenth resistor is connected between the inverting input terminal of the operational amplifier and the ground terminal. The eleventh resistor is connected between the emitter of the triode and the first terminal of the tenth resistor. The base of the triode is connected to the output terminal of the operational amplifier, the collector of the triode is connected to the first power supply, and the emitter of the triode is connected to the first filter capacitor.

9. The radio frequency power amplifier of any of claims 1-5, wherein, The radio frequency power amplification module comprises an input matching and direct current isolation circuit, an output matching and direct current isolation circuit, a field effect transistor and a second inductor. The input matching and direct current isolation circuit is connected between the radio frequency pulse signal input terminal and the gate of the field effect transistor, the second inductor is connected between the first pole of the field effect transistor and the second power supply, the output matching and direct current isolation circuit is connected between the radio frequency pulse signal output terminal and the first pole of the field effect transistor, the second pole of the field effect transistor is connected to the ground terminal, and the gate of the field effect transistor serves as the bias input terminal.

10. The radio frequency power amplifier of claim 1, wherein, The radio frequency pulse signal comprises fixed sequence pulses and variable sequence pulses.

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