Low noise amplifier for nuclear magnetic resonance radio frequency receiving system

Abstract

The invention discloses a low noise amplifier for a nuclear magnetic resonance radio frequency receiving system, and relates to the technical field of amplifiers. Comprising two cascaded common-source amplifier circuits, the two stages of the common-source amplifier circuits are realized based on an ATF54143 transistor and a BGA616 amplifier respectively, and the common-source amplifier circuits comprise an input matching circuit, an inter-stage matching circuit, an output matching circuit, an output attenuation circuit, an input phase shift circuit and a single-power-supply direct-current biasing circuit; the low-noise amplifier has ultra-low input impedance, and the input impedance at a working center frequency point 64MHz is only 0.003-j * 0.263 which is far lower than the standard, so that the performance effect is excellent; according to the invention, the output noise is extremely low, the performance is more excellent under the working frequency band, the sensitivity is extremely high, the device is suitable for an MR I system and can reach-130dBm, and the whole structure is simple and reliable and is easy to realize.

Description

Technical Field

[0001] The invention relates to the technical field of amplifiers, in particular to a low noise amplifier for a nuclear magnetic resonance radio frequency receiving system. Background Art

[0002] In a 1.5T MRI system, the RF receiving system is one of the key components, and its performance directly affects the quality of imaging and the accuracy of the signal. In this system, the low noise amplifier (LNA) plays a vital role. It is responsible for minimizing the noise interference of the signal as much as possible in the initial stage of receiving the MRI signal and amplifying the signal to the required size in the subsequent stage. Therefore, the design and optimization of the low noise amplifier has become an important part of improving the quality of MRI imaging.

[0003] Nuclear magnetic resonance signals come from the resonance of hydrogen atomic nuclear spins in human tissues in a strong magnetic field. These signals are usually very weak, usually at the microvolt level or lower. Therefore, the receiving system must have extremely high sensitivity to effectively capture these weak signals and amplify them to a level sufficient for subsequent processing. The higher the sensitivity, the more the system can capture weak signals, thereby improving the signal-to-noise ratio (SNR) of the image and providing clearer and more detailed images.

[0004] The performance of a low noise amplifier is usually measured by the noise figure (NF). The lower the noise figure, the less additional noise the amplifier introduces while amplifying the signal. In the RF receiving chain, the low noise amplifier is usually placed at the back end of the receiving coil as the first step of RF signal processing. Since the nuclear magnetic resonance signal is usually very weak, usually at the microvolt level, it is crucial to minimize the introduction of noise during the amplification process. If too much noise is introduced in the early stage of the signal, the subsequent signal processing and amplification will not be able to effectively extract useful information, resulting in a decrease in image quality. Therefore, when designing a 1.5T MRI receiving system, the design goal of the low noise amplifier is to achieve a low noise figure while ensuring sufficient gain and bandwidth to meet the needs of the MRI system. In summary, in a 1.5T nuclear magnetic resonance imaging system, the low noise amplifier is a key component of the RF receiving system, and its design and performance directly affect the quality of imaging. By optimizing the noise performance, gain, sensitivity, and input impedance of the LNA, the overall performance of the MRI system can be significantly improved, thereby providing clearer and more accurate images for clinical diagnosis. To this end, we provide a low noise amplifier for a 1.5T nuclear magnetic resonance radio frequency receiving system. Summary of the invention

[0005] The purpose of the present invention is to provide a low noise amplifier for a nuclear magnetic resonance radio frequency receiving system to solve the problem in the prior art proposed in the background technology that the low noise amplifier for nuclear magnetic resonance is limited by size and external conditions, resulting in difficulty in achieving low noise, low input impedance, high sensitivity and high gain.

[0006] The present invention can be implemented through the following technical scheme: a low-noise amplifier for a nuclear magnetic resonance radio frequency receiving system, comprising a two-stage cascaded common-source amplifier circuit, wherein the two stages of the common-source amplifier circuit are respectively implemented based on an ATF54143 transistor and a BGA616 amplifier, and comprise an input matching circuit, an inter-stage matching circuit, an output matching circuit, an output attenuation circuit, an input phase shift circuit and a single-power supply DC bias circuit, wherein the ATF54143 transistor is arranged between the input matching circuit and the inter-stage matching circuit, and the BGA616 amplifier is cascaded with the ATF54143 transistor through the inter-stage matching circuit.

[0007] A further technical improvement of the present invention is that the input matching circuit adopts a π-type matching method, the input end is initially connected to capacitor C1, the other end of capacitor C1 is connected to capacitor C2, the other end of capacitor C2 is connected to the gate of ATF54143, and there are two parallel inductors L1 and L2 between capacitor C1 and capacitor C2, and the other ends of inductor L1 and inductor L2 are grounded respectively.

[0008] A further technical improvement of the present invention is that the inter-stage matching circuit adopts a T-type matching method, the drain of ATF54143 is connected to capacitor C3, the other end of capacitor C3 is connected to capacitor C4, the other end of capacitor C4 is connected to the input end of BGA616, an inductor L3 is connected in parallel between capacitors C3 and C4, and the other end of inductor L3 is grounded.

[0009] A further technical improvement of the present invention is that the output matching circuit adopts a π-type matching method, the output end of BGA616 is connected to capacitor C5, the other end of capacitor C5 is connected to capacitor C6, the other end of capacitor C6 is connected to resistor R2, and two inductors L4 and L5 are connected in parallel between capacitor C5 and capacitor C6, and the other ends of inductor L4 and inductor L5 are grounded respectively.

[0010] A further technical improvement of the present invention is that the output attenuation circuit adopts a T-type attenuation network, the capacitor C6 in the output matching circuit 3 is connected to the resistor R2, the two ends of the resistor R2 have parallel resistors R1 and R3, and the other ends of the resistor R1 and R3 are grounded respectively.

[0011] A further technical improvement of the present invention is that the input phase shift circuit is arranged at the front end of the input matching circuit, and the input phase shift circuit adopts a phase shift network, a phase shifter or a phase shift line.

[0012] The further technical improvement of the present invention is that: the single power supply DC bias circuit adopts a resistor voltage division method to supply power to ATF54143 and BGA616 respectively, one end of the DC power supply is connected to the resistor R4, and the other end is grounded, a capacitor C7 is connected in parallel between the DC power supply and the resistor R4, and the other end of the capacitor C7 is grounded, the resistors R4, R5 and R6 are connected to form a T-type structure, the other end of the resistor R5 is connected to the inductor L6, and the other end of the inductor L6 is connected to the output end of the BGA616 to supply power to it;

[0013] The other end of resistor R6 is connected to inductor L7, the other end of inductor L7 is connected to resistor R7, resistor R7 is connected to resistor R8 and inductor L9 to form a T-type structure, the other end of inductor L9 is connected to the drain of ATF54143, a capacitor C8 is connected in parallel between inductor L9 and resistor R7, and the other end of capacitor C8 is grounded; resistor R8, resistor R9 and resistor R10 are connected to form a T-type structure, the other end of resistor R9 is grounded, the other end of resistor R10 is connected to inductor L8, capacitor C9 is connected in parallel between resistor R10 and inductor L8, the other end of capacitor C9 is grounded, and the other end of inductor L8 is connected to the gate of ATF54143.

[0014] A further technical improvement of the present invention is that the operating frequency band of the low noise amplifier is set to 54 MHz to 74 MHz.

[0015] The further technical improvement of the present invention is that the input matching circuit and the input phase shift circuit transform the input impedance of 50 ohms to the input impedance of 0.003-j*0.263

[0016] A further technical improvement of the present invention is that the output attenuation circuit enables the gain to reach 33.8dB, and the gain flatness is within 2dB.

[0017] A further technical improvement of the present invention is that within the working frequency band, the output noise of the low noise amplifier is less than 0.25, S22 is below 25dB, and the stability coefficient is greater than 1.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The low noise amplifier of the present invention has an ultra-low input impedance. At the working center frequency of 64 MHz, the input impedance is only 0.003-j*0.263, while the general default input impedance only needs to be less than 5. The amplifier of the present invention is far lower than this industry standard and has excellent performance.

[0020] 2. The output noise of the present invention is extremely low, and the performance is more excellent in the working frequency band;

[0021] 3. The present invention has extremely high sensitivity and is suitable for use in MRI systems, and can reach -130dBm. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0023] Figure 1 is a circuit schematic diagram of the present invention;

[0024] Figure 2 is the output noise diagram of the present invention;

[0025] Figure 3 is a gain diagram of the present invention;

[0026] Figure 4 is the S parameter diagram of the present invention;

[0027] Figure 5 is the stability coefficient diagram of the present invention;

[0028] Figure 6 This is the Smith chart of the S11 input characteristic curve of the present invention.

[0029] In the figure: 1. Input matching circuit; 2. Inter-stage matching circuit; 3. Output matching circuit; 4. Output attenuation circuit; 5. Input phase shift circuit; 6. Single power supply DC bias circuit. DETAILED DESCRIPTION

[0030] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0031] See also Figure 1-6 As shown, a low noise amplifier for a nuclear magnetic resonance radio frequency receiving system is specifically a two-stage cascade form, the first stage is implemented based on ATF54143, and ATF54143 is a low noise enhancement mode pseudo electron high mobility transistor (E-PHEMT); the second stage is implemented based on BGA616, BGA616 is a silicon germanium (SiGe) broadband MM IC amplifier, forming a two-stage common source amplifier circuit;

[0032] Specifically, the two-stage common source amplifier circuit includes an input matching circuit 1, an inter-stage matching circuit 2, an output matching circuit 3, an output attenuation circuit 4, an input phase shift circuit 5 and a single power supply DC bias circuit 6;

[0033] Among them, the input matching circuit 1 adopts a π-type matching method, the input end is connected to the capacitor C1 at the beginning, the other end of the capacitor C1 is connected to the capacitor C2, the other end of the capacitor C2 is connected to the gate of ATF54143, and there are two parallel inductors L1 and L2 between the capacitors C1 and C2, and the other ends of L1 and L2 are grounded respectively; in short, the input matching circuit 1 includes two capacitors C1 and C2, two inductors L1 and L2, one end of the entire input matching circuit 1 is connected to the input end, and the other end is connected to the gate of ATF54143;

[0034] Preferably, in the input matching circuit 1, C1=6100pF, the capacitor C1 is not only the first stage of input matching, but also serves as a DC blocking capacitor protection circuit to prevent DC signals at the input end, C2=6000pF, L1=180nF, L2=730nF.

[0035] The inter-stage matching circuit 2 adopts a T-type matching method. The drain of ATF54143 is connected to capacitor C3, the other end of capacitor C3 is connected to capacitor C4, the other end of capacitor C4 is connected to the input end of BGA616, an inductor L3 is connected in parallel between capacitors C3 and C4, and the other end of inductor L3 is grounded; in short, the inter-stage matching circuit 2 includes two capacitors C3 and C4, an inductor L3, one end of the entire inter-stage matching circuit 2 is connected to the drain of ATF54143, and the other end is connected to the input end of BGA616;

[0036] Preferably, in the inter-stage matching circuit 2, C3=5300pF, C4=320pF, and L3=6100nF.

[0037] The output matching circuit 3 adopts a π-type matching method, the output end of BGA616 is connected to capacitor C5, the other end of capacitor C5 is connected to capacitor C6, the other end of capacitor C6 is connected to resistor R2, and there are two parallel inductors L4 and L5 between capacitor C5 and capacitor C6, and the other ends of inductor L4 and inductor L5 are grounded respectively; in short, the output matching circuit 3 includes two capacitors C5 and C6, two inductors L4 and L5, and one end of the entire output matching circuit 3 is connected to the output end of BGA616, and the other end is connected to R2;

[0038] Preferably, in the output matching circuit 3, C5=3700pF, C6=7200pF, L4=4500nF, and L5=1600nF.

[0039] The output attenuation circuit 4 adopts a T-type attenuation network. The capacitor C6 in the output matching circuit 3 is connected to the resistor R2. The two ends of the resistor R2 are connected in parallel with the resistor R1 and the resistor R3. The other ends of the resistor R1 and the resistor R3 are grounded respectively. The output attenuation circuit 4 includes three resistors, namely the resistor R1, the resistor R2 and the resistor R3. One end of the entire output attenuation circuit 4 is connected to the capacitor C6 in the output matching circuit 3, and the other end serves as the output end of the entire low noise amplifier.

[0040] Preferably, in the output attenuation circuit 4, R1 = 1000 ohm, R2 = 130 ohm, and R3 = 65 ohm.

[0041] The input phase shift circuit 5 adopts a phase shift device;

[0042] Specifically, the phase shifting device may be a phase shifting network, a phase shifter or a phase shifting line. Preferably, the phase shifting electrical length is 129 degrees.

[0043] The single power supply DC bias circuit 6 uses a resistor voltage divider to supply power to ATF54143 and BGA616 respectively. One end of the DC power supply is connected to the resistor R4, and the other end is grounded. A capacitor C7 is connected in parallel between the DC power supply and the resistor R4, and the other end of the capacitor C7 is grounded. The resistors R4, R5 and R6 are connected to form a T-type structure. The other end of the resistor R5 is connected to the inductor L6, and the other end of the inductor L6 is connected to the output end of the BGA616 to supply power to it; the other end of the resistor R6 is connected to the inductor L7, and the other end of the inductor L7 is connected to the resistor R7. Resistor R7 connects resistor R8 and inductor L9 to form a T-shaped structure, the other end of inductor L9 is connected to the drain of ATF54143, a capacitor C8 is connected in parallel between inductor L9 and resistor R7, and the other end of capacitor C8 is grounded; resistor R8, resistor R9 and resistor R10 are connected to form a T-shaped structure, the other end of resistor R9 is grounded, the other end of resistor R10 is connected to inductor L8, capacitor C9 is connected in parallel between resistor R10 and inductor L8, the other end of capacitor C9 is grounded, and the other end of inductor L8 is connected to the gate of ATF54143;

[0044] Preferably, in the single-power supply DC bias circuit 6, R4=140ohm, R5=9000ohm, R6=40ohm, R7=110ohm, R8=1000ohm, R9=240ohm, R10=200ohm, L6=2400nF, L7=4uF, L8=5uF, C7=6730pF, C8=740pF, C9=2400pF.

[0045] Furthermore, the input matching circuit 1 and the input phase shift circuit 5 transform the input impedance of 50 ohms to an input impedance of 0.003-j*0.263.

[0046] Furthermore, the output attenuation circuit 4 appropriately attenuates the high gain and reduces the gain flatness, so that the gain reaches 33.8 dB and the gain flatness is within 2 dB.

[0047] The input impedance of the above-mentioned low-noise amplifier is kept less than 0.1 in the working frequency band of 54MHz to 74MHz, the output characteristic curve S22 of the output port reaches below 25dB in the working frequency band, the output noise is less than 0.25, and when the working frequency band is 64MHz, the output noise is 0.19 and the sensitivity reaches -130dBm.

[0048] In the working frequency band, the stability coefficient of the low noise amplifier is greater than 1, which meets the requirement of the present invention for unconditional stability in the working frequency band.

[0049] When designing the present invention, a two-stage amplifier circuit is determined according to the design indicators. The low-noise ATF54143 transistor is used for the first stage. However, since the gain of the first stage circuit does not meet the requirements, the high-gain BGA616 is selected for the second stage. After debugging to meet the design requirements, it is found that too high gain may cause self-oscillation and the gain varies greatly in the working frequency band. Therefore, the output attenuation circuit 4 is introduced, so as to optimize the overall debugging to achieve the above performance indicators.

[0050] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A low noise amplifier for a nuclear magnetic resonance radio frequency receiving system, characterized in that: The invention comprises a two-stage cascaded common-source amplifier circuit, wherein the two stages of the common-source amplifier circuit are implemented based on an ATF54143 transistor and a BGA616 amplifier respectively, and comprise an input matching circuit (1), an inter-stage matching circuit (2), an output matching circuit (3), an output attenuation circuit (4), an input phase shift circuit (5) and a single-power supply DC bias circuit (6); the ATF54143 transistor is arranged between the input matching circuit (1) and the inter-stage matching circuit (2); and the BGA616 amplifier is cascaded with the ATF54143 transistor via the inter-stage matching circuit (2).

2. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 1, characterized in that: The input matching circuit (1) adopts a π-type matching method, wherein the input end is connected to a capacitor C1 at the beginning, the other end of the capacitor C1 is connected to a capacitor C2, the other end of the capacitor C2 is connected to the gate of the ATF54143, and two inductors L1 and L2 are connected in parallel between the capacitors C1 and C2, and the other ends of the inductors L1 and L2 are grounded respectively.

3. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 2, characterized in that: The inter-stage matching circuit (2) adopts a T-type matching method, the drain of ATF54143 is connected to capacitor C3, the other end of capacitor C3 is connected to capacitor C4, the other end of capacitor C4 is connected to the input end of BGA616, an inductor L3 is connected in parallel between capacitors C3 and C4, and the other end of inductor L3 is grounded.

4. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 3, characterized in that: The output matching circuit (3) adopts a π-type matching method, the output end of BGA616 is connected to capacitor C5, the other end of capacitor C5 is connected to capacitor C6, the other end of capacitor C6 is connected to resistor R2, and two inductors L4 and L5 are connected in parallel between capacitor C5 and capacitor C6, and the other ends of inductor L4 and inductor L5 are grounded respectively.

5. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 4, characterized in that: The output attenuation circuit (4) adopts a T-type attenuation network. The capacitor C6 in the output matching circuit 3 is connected to the resistor R2. The two ends of the resistor R2 have parallel resistors R1 and R3. The other ends of the resistor R1 and R3 are grounded respectively.

6. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 1, characterized in that: The input phase shift circuit (5) is arranged at the front end of the input matching circuit (1), and the input phase shift circuit (5) adopts a phase shift network, a phase shifter or a phase shift line.

7. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 5, characterized in that: The single power supply DC bias circuit (6) uses a resistor voltage divider to supply power to ATF54143 and BGA616 respectively. One end of the DC power supply is connected to the resistor R4, and the other end is grounded. A capacitor C7 is connected in parallel between the DC power supply and the resistor R4, and the other end of the capacitor C7 is grounded. The resistors R4, R5 and R6 are connected to form a T-shaped structure. The other end of the resistor R5 is connected to the inductor L6, and the other end of the inductor L6 is connected to the output end of the BGA616 to supply power to it. The other end of resistor R6 is connected to inductor L7, the other end of inductor L7 is connected to resistor R7, resistor R7 is connected to resistor R8 and inductor L9 to form a T-type structure, the other end of inductor L9 is connected to the drain of ATF54143, a capacitor C8 is connected in parallel between inductor L9 and resistor R7, and the other end of capacitor C8 is grounded; resistor R8, resistor R9 and resistor R10 are connected to form a T-type structure, the other end of resistor R9 is grounded, the other end of resistor R10 is connected to inductor L8, capacitor C9 is connected in parallel between resistor R10 and inductor L8, the other end of capacitor C9 is grounded, and the other end of inductor L8 is connected to the gate of ATF54143.

8. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 1, characterized in that: The operating frequency band of the low noise amplifier is set to 54MHz~74MHz.

9. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 7, characterized in that: When the operating frequency band is 64 MHz, the input matching circuit (1) and the input phase shift circuit (5) transform the input impedance of 50 ohms into an input impedance of 0.003-j*0.

263.

10. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 7, characterized in that: The output attenuation circuit (4) enables the gain to reach 33.8 dB, and the gain flatness is within 2 dB.

11. The low noise amplifier for a nuclear magnetic resonance radio frequency receiving system according to claim 7, characterized in that: In the working frequency band, the output noise of the low noise amplifier is less than 0.25, S22 is below 25dB, and the stability coefficient is greater than 1.

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