Push-pull gradient power amplifier

Abstract

The present application relates to a kind of push-pull gradient power amplifiers, belong to the field of electronic devices.The power amplifier includes linear push-pull amplification module, drive amplification module, current detection module, circuit protection module, thermal protection module, power module.The present application adopts multistage parallel push-pull linear amplification structure, avoids the switching noise in circuit, reduces the electromagnetic radiation noise of overall circuit, greatly reduces gradient power amplifier output current noise, realizes the highest 50A peak current output, greatly reduces the volume and weight of gradient power amplifier under the requirement of low-field magnetic resonance imaging sequence, applicable to portable mobile magnetic resonance imaging equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of magnetic resonance, and relates to a push-pull type gradient power amplifier. BACKGROUND

[0002] Magnetic resonance imaging technology plays an important role in the field of medical imaging and is applied more and more widely. As a core component of a magnetic resonance imaging device, a gradient power amplifier mainly provides a gradient magnetic field with high linearity, fast switching and switching for an imaging process, and the performance of the gradient power amplifier is closely related to the imaging quality. In a traditional high-field magnetic resonance imaging system, a human body needs to be imaged as a whole, so the gradient power amplifier required by the system has a large output current and high power, and the device has a large volume and needs to be installed in a separate device room.

[0003] In a low-field magnetic resonance imaging system, the whole system needs to be reduced to realize miniaturization and portability, so the volume and weight of the gradient power amplifier need to be greatly reduced. In the low-field magnetic resonance system, the main magnetic field is more than one order of magnitude lower than that in the traditional magnetic resonance, which causes the image signal-to-noise ratio to also decrease. In order to ensure the image signal-to-noise ratio, the output current noise of the gradient system needs to be as low as possible. Compared with the traditional switch-type gradient power amplifier, the linear gradient power amplifier has no switching noise and has extremely low output current noise.

[0004] At the same time, if the traditional switch-type gradient power amplifier is used in an open magnetic resonance system, when the gradient power amplifier is close to the magnet system, the electromagnetic noise generated by the gradient power amplifier will seriously reduce the image signal-to-noise ratio of the imaging image. SUMMARY

[0005] Therefore, the purpose of the application is to provide a push-pull type gradient power amplifier.

[0006] In order to achieve the above purpose, the application provides the following technical scheme.

[0007] A push-pull type gradient power amplifier, the power amplifier comprising:

[0008] A linear push-pull amplification module controls the stability of the output current of the system;

[0009] A drive amplification module converts a differential gradient signal into a single-ended voltage signal and amplifies and filters the signal;

[0010] A current detection module detects the size of the output current in real time and is connected to a circuit protection module;

[0011] The circuit protection module is set to close the output when the protection value reaches a certain value to prevent the circuit from being damaged due to overload;

[0012] A thermal protection module monitors the working temperature of the device in real time and also transmits the overheating signal to the circuit protection module;

[0013] a power module, which supplies power for the drive amplification module, the linear push-pull amplification module and the current detection module;

[0014] the drive amplification module is electrically connected with the linear push-pull amplification module;

[0015] the linear push-pull amplification module is electrically connected with the current detection module;

[0016] the circuit protection module is electrically connected with the drive amplification module, the linear push-pull amplification module and the current detection module, respectively;

[0017] the current detection module and the circuit protection module are electrically connected.

[0018] Optionally, the linear push-pull amplification module comprises:

[0019] a push-pull module, which is composed of a first push-pull circuit, a second push-pull circuit and a third push-pull circuit in parallel, and each of the first push-pull circuit, the second push-pull circuit and the third push-pull circuit is composed of a MOS tube and a resistor in series;

[0020] a drive module, which is composed of a first resistor R4, a second resistor R16 and a first operational amplifier U1 in series, the first resistor and the second resistor are used to adjust the voltage difference of the MOS tube VGS, the first operational amplifier is used as a comparator, and the output is changed by comparing and feeding back the voltage signal and the input voltage signal, so that the power current is different, the voltage difference of the first resistor and the second resistor is different, and the output current of the MOS tube is finally stabilized;

[0021] a feedback module, which is composed of a second operational amplifier U2 and a sampling resistor R24, amplifies the voltage signal of the sampling resistor, provides high input impedance and reduces sampling error;

[0022] a filter module, which is composed of three or more than three filter circuits in series, and each of the filter circuits is composed of a capacitor C4 and a resistor R22, a capacitor C6 and a resistor R26, and a capacitor C5 and a resistor R23, and is used to filter the voltage noise at both ends of the resistor and improve the collection accuracy;

[0023] an adjustment module, which is composed of three or more than three adjustment circuits in parallel between the source electrodes, and specifically comprises a resistor R1, a resistor R2, a resistor R3, a resistor R17, a resistor R18 and a resistor R19, and is used to adjust the output current balance of each group of MOS tubes, reduce the output current difference of each group of MOS tubes, and improve the stability of the MOS tubes in long-time work;

[0024] a compensation module, which is composed of a third resistor R10 and a capacitor C3 in series, and is used to adjust the overshoot of the output current, stabilize the output of the amplifier and pre-emphasize the gradient signal;

[0025] the drive module is connected with the push-pull module in parallel, and then is electrically connected with the compensation module;

[0026] The feedback module is connected in series with the filter module, and the filter module is connected with the compensation module.

[0027] The adjustment module is connected with the driving module and the feedback module.

[0028] Optionally, the linear push-pull amplifier module further comprises a power inductor L2, a fourth resistor R8 and a capacitor C1 for adjusting loop stability; the power inductor L2 is connected in series at the output end of the linear push-pull amplifier module, and the fourth resistor R8 and the capacitor C1 are connected in series.

[0029] Optionally, the MOS tube comprises a PMOS tube and an NMOS tube, and the size of the MOS tube drain current ID is adjusted by the VGS voltage through the linear relationship of the VGS voltage and the drain current of the PMOS tube and the NMOS tube, so as to stably control the output current of the amplifier.

[0030] The R4 controls the PMOS, the R16 controls the NMOS, the VGS voltage is controlled through the voltage difference of the R4 and the R16, the input signal of the operational amplifier is the gradient signal output after the driving amplifier module is amplified and converted, and the voltage feedback signal after the MOS tube output current flows through the resistance; finally, the operational amplifier U1, the push-pull MOS tube output stage and the operational amplifier U2 constitute a closed-loop control loop, the voltage signal fed back on the sampling resistor is compared with the input voltage signal, the U1 output state is controlled, the corresponding voltage difference on the R4 and the R16 is generated due to the current consumed by the positive and negative power supplies of the U1, the MOSFET amplification state is controlled by the VGS, the output current of the MOSFET reaches a balanced and stable value, and finally the MOS tube output current is stabilized.

[0031] Optionally, the filter circuit is formed by connecting the resistance and the capacitor in parallel.

[0032] Optionally, the two resistors are connected in series to the source of the PMOS tube and the NMOS tube.

[0033] The present application has the following advantages:

[0034] (1) The linear gradient power amplifier is based on the basic principle of the push-pull amplifier, does not have the switching noise of the traditional gradient power amplifier, does not need to increase the LC filter in the output stage to filter out the switching noise, and the inductor in the filter is relatively large in volume and weight under the condition of large current output, and the gradient power amplifier of the present application reduces the volume and weight.

[0035] (2) The traditional gradient power amplifier needs to be placed in a separate equipment cabinet outside the shielded room, and cannot be directly used in a low-field open magnetic resonance system. When placed close to the magnet system, the switching noise generated will seriously affect the signal-to-noise ratio of the magnetic resonance signal. The low-field linear gradient power amplifier of the present application has no switching noise, low overall noise, and can be placed under the magnet system with minimal impact on the magnetic resonance signal, which is beneficial to the integrated design and manufacture of mobile magnetic resonance equipment.

[0036] (3) The traditional gradient power amplifier outputs a series of filters connected to the gradient coil to reduce current ripple. The present application only needs a set of filters to filter out external interference after connecting the gradient connection to the gradient coil in the magnet, simplifying the wiring process and facilitating mass production.

[0037] (4) The present application is designed for low-field mobile magnetic resonance systems, with a maximum output peak current of 50A and a current noise of less than 100uA. The X, Y and Z three-channel gradient amplifiers and power supply are finally housed in a 4U chassis, effectively reducing the overall device volume. The overall weight is less than 20kg.

[0038] Other advantages, objects and features of the present application will be set forth in part in the following specification taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art from a consideration of the following specification and drawings, or can be learned from the practice of the present application. The objects and other advantages of the present application can be realized and attained by the below description. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to make the purpose, technical scheme and advantages of the present application clearer, the preferred detailed description of the present application will be combined with the drawings as follows, wherein:

[0040] Fig. 1 Structure block diagram of the push-pull gradient power amplifier of the present application;

[0041] Fig. 2 Structure circuit structure schematic diagram of the push-pull gradient power amplifier of the present application;

[0042] Fig. 3 MOS characteristic curve of the linear gradient power amplifier of the present application. DETAILED DESCRIPTION

[0043] Following specific examples illustrate the embodiments of the present application, and other advantages and purposes of the present application can be easily understood by those skilled in the art from the disclosure of this specification. The present application can also be implemented or applied by other different specific embodiments, and various modifications or changes can be made to the details in this specification based on different views and applications without departing from the spirit of the present application. It should be noted that the diagrams provided in the following examples only illustrate the basic concepts of the present application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0044] The accompanying drawings are only used for illustrative purposes, and the representations are only schematic diagrams, not physical diagrams, and should not be understood as limitations of the present application; in order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual size of the product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0045] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for illustrative purposes, and should not be understood as limitations of the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0046] Please refer to Figs. 1-3 , which is a push-pull type gradient power amplifier, comprising a linear push-pull amplification module, a drive amplification module, a current detection module, a circuit protection module, a thermal protection module and a power supply module.

[0047] As Fig. 2 shown, the linear push-pull amplification module mainly consists of three groups of MOSFETs Q1 and Q4, Q2 and Q5, Q3 and Q6 to form a push-pull output stage, and the MOSFETs work in the linear amplification zone, so the conduction loss is large during work, and three groups of push-pull structure are used in parallel output to improve the output capacity and reduce the loss on each MOSFET.

[0048] Fig. 2In the embodiment, R1, R2, R3, R17, R18 and R19 are adjusting resistors for reducing transistor difference and balancing output current. R10 and C3 are compensation circuits for stabilizing amplifier output. U1, R4 and R16 are driving modules. RP1 is an adjustable resistor. J1 is a voltage input signal. U2 is a feedback module. R26 and C6, C4 and R22, and R23 and C5 are filter structures. R24 is a sampling resistor. The circuit composed of R5, R6, R7, R12, R13, R14, Q1, Q2, Q3, Q4, Q5 and Q6 is a push-pull output stage.

[0049] The MOS transistor includes PMOS and NMOS. In the embodiment, Q1, Q2 and Q3 are PMOS, and Q4, Q5 and Q6 are NMOS. The linear relationship between VGS voltage and drain current ID of the MOS transistor is utilized to adjust the size of the drain current ID by controlling the VGS voltage, wherein R4 controls PMOS and R16 controls NMOS. The VGS voltage is controlled by the voltage difference between R4 and R16. The operational amplifier U1 is used as a comparator to compare the feedback voltage signal and the input voltage signal, change the output, and control the voltage difference between R4 and R16. The input signal of the operational amplifier is the gradient signal output by the driving amplifier module after amplification and conversion, and the voltage feedback signal of the output current of the MOS transistor flowing through the resistor. Finally, the operational amplifier U1, the push-pull MOS transistor output stage and the operational amplifier U2 form a closed-loop control circuit. By comparing the voltage signal fed back on the sampling resistor with the input voltage signal, the output state of U1 is controlled to change the current consumed by the positive and negative power supplies of U1, generate a corresponding voltage difference on R4 and R16, and control the MOSFET amplification state through VGS to control the output current to a balanced and stable value, and finally stabilize the output current of the MOS transistor. The two resistors R4 and R16 and the first operational amplifier U1 are connected in series to form a driving module. The operational amplifier U2 mainly amplifies the voltage signal of the sampling resistor and provides high input impedance to reduce sampling error. The capacitors C4 and R22, the capacitors C6 and R26, and the capacitors C5 and R23 are connected in parallel and then connected in series to form a filter circuit. In order to prevent the output current from overshooting, R10 and C3 are connected in series in the embodiment to form a compensation circuit for stabilizing the amplifier output. L2, R8 and C1 are used to adjust the loop stability of the entire linear push-pull amplification structure and improve the small signal bandwidth of the amplifier. The adjustable resistor RP1 can be used to adjust the output current bias of the amplifier. The conventional push-pull amplification structure will produce crossover distortion when outputting, but the push-pull topology can adjust the resistors R4 and R16 to change the conduction state of the MOSFET and eliminate the crossover distortion. The linear push-pull amplification module has a simple structure and does not require a filter circuit, which reduces the size of the entire gradient power amplifier.

[0050] In addition to the linear push-pull amplification module, the rest of the modules also play an important role in the entire device. The drive amplification module is used to convert the differential gradient signal into a single-ended voltage signal and amplify the filter, and then input to the amplification module; The circuit protection module monitors the output current size in real time, and is connected with the circuit protection module, and when the set protection value is 50A, the output is closed to prevent circuit overload damage; The thermal protection module monitors the MOSFET temperature when the device is working, and also transmits the overheating signal to the circuit protection module. The power supply provides energy supply for the entire amplification circuit system.

[0051] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A push-pull gradient power amplifier characterized by: The power amplifier comprises: A linear push-pull amplification module controls the stability of the output current of the system; A drive amplification module converts the differential gradient signal into a single-ended voltage signal and amplifies and filters it; A current detection module detects the output current in real time and is connected to the circuit protection module; A circuit protection module sets a protection value to close the output when it reaches a certain value to prevent circuit overload damage; A thermal protection module monitors the working temperature of the device in real time and also transmits the overheating signal to the circuit protection module; A power supply module supplies power to the drive amplification module, the linear push-pull amplification module, and the current detection module; The drive amplification module is electrically connected to the linear push-pull amplification module; The linear push-pull amplification module is electrically connected to the current detection module; The circuit protection module is electrically connected to the drive amplification module and the linear push-pull amplification module, respectively; The current detection module and the circuit protection module are electrically connected; The linear push-pull amplification module comprises: A push-pull module composed of a first push-pull circuit, a second push-pull circuit, and a third push-pull circuit connected in parallel, wherein the first push-pull circuit, the second push-pull circuit, and the third push-pull circuit are each composed of a MOS tube and a resistor connected in series; A drive module composed of a first resistor R4, a second resistor R16, and a first operational amplifier U1 connected in series, wherein the first resistor and the second resistor are used to adjust the MOS tube VGS voltage difference, and the first operational amplifier serves as a comparator to change the output by comparing the feedback voltage signal and the input voltage signal to make the power current different, thereby controlling the first resistor and the second resistor voltage difference to stabilize the MOS tube output current; A feedback module composed of a second operational amplifier U2 and a sampling resistor R24, used to amplify the voltage signal of the sampling resistor, provide high input impedance, and reduce sampling error; A filter module composed of three or more filter circuits connected in series, used to filter out the voltage noise between the resistors to improve the collection accuracy, wherein the filter circuit is composed of a resistor and a capacitor connected in parallel; An adjustment module, three or more adjustment circuits connected in parallel between the sources, used to adjust the output current balance of each group of MOS tubes to reduce the output current difference of each group of MOS tubes to improve the stability of the MOS tube during long-term operation, wherein the adjustment circuit is composed of two resistors connected in series to the source of the PMOS tube and the NMOS tube; A compensation module composed of a third resistor R10 and a capacitor C3 connected in series, used to adjust the output current overshoot, stabilize the amplifier output, and pre-emphasize the gradient signal; The drive module is connected in parallel with the push-pull module, and then connected with the compensation module; The feedback module is connected in series with the filter module, and then connected with the compensation module; The adjustment module is electrically connected to the drive module and the feedback module.

2. A push-pull gradient power amplifier as claimed in claim 1, characterized in that: The linear push-pull amplification module further comprises a power inductor L2, a fourth resistor R8, and a capacitor C1 for adjusting the stability of the loop; wherein the power inductor L2 is connected in series at the output end of the linear push-pull amplification module, and the fourth resistor R8 is connected in series with the capacitor C1.

3. The push-pull gradient power amplifier of claim 1, wherein: The MOS transistor includes PMOS and NMOS, and the linear relationship of VGS voltage and drain current of the PMOS and NMOS is used to adjust the size of the MOS transistor drain current ID through the VGS voltage, so as to stably control the amplifier output current; R4 controls PMOS, R16 controls NMOS, VGS voltage is controlled through the pressure difference of R4 and R16, the input signal of the operational amplifier is the gradient signal output after the driving amplification module is amplified and converted, and the voltage feedback signal of the MOS transistor output current flowing through the resistance; finally, the operational amplifier U1, the push-pull MOS transistor output stage and the operational amplifier U2 constitute a closed loop control loop, the voltage signal fed back on the sampling resistor is compared with the input voltage signal, the U1 output state is controlled, the current consumed by the positive and negative power supplies of U1 is changed, the corresponding pressure difference on R4 and R16 is generated, the MOSFET amplification state is controlled through VGS, the output current is controlled to a balanced and stable value, and finally the MOS transistor output current is stabilized.

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