Current source circuit and current source of nuclear magnetic resonance system

Abstract

The utility model embodiment discloses a current source circuit and current source of a nuclear magnetic resonance system, wherein the circuit includes: a signal input end and a current output end; an isolation amplifier circuit, a linear adjustment circuit, a drive circuit and a MOS tube output circuit sequentially coupled between the signal input end and the current output end, the output end of the MOS tube output circuit is coupled to the input end of the linear adjustment circuit through a current sampling circuit closed loop; the linear adjustment circuit includes an error amplifier, the error amplifier is configured to control the output current of the MOS tube output circuit to be in a linear relationship with the input voltage signal according to the input voltage signal of the isolation amplifier circuit and the current sampling circuit; the MOS tube output circuit includes a plurality of MOS tubes connected in parallel. Through the utility model embodiment, a linear high-power current source with high duty cycle, high pulse width, small volume and high stable current output is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of current sources, in particular to a current source circuit and a current source of a nuclear magnetic resonance system. Background Art

[0002] Nuclear magnetic resonance technology is a non-destructive testing technology widely used in the fields of analysis and imaging. The principle of nuclear magnetic resonance is a way of inspection based on the signal generated by the atomic nucleus in the magnetic field, which is reconstructed and processed by a computer. The atomic nucleus is equivalent to a small magnet. The distribution and arrangement of the spin axis of the small magnet are disorderly. If placed in a strong magnetic field, these small magnets will be arranged regularly according to the direction of the magnetic field. At this time, a radio frequency pulse that affects the magnetic field is applied, and the atomic nucleus absorbs energy and jumps to a high energy state; after the radio frequency pulse ends, the signal released during the process of the atomic nucleus returning to its initial state is the nuclear magnetic resonance signal.

[0003] Gradient layer selection is widely used as a measurement technology for accurately selecting a certain area. The gradient is a linear change that satisfies mathematical laws in the spatial direction, and is used to spatially locate the nuclear magnetic resonance signal. The gradient system is mainly composed of gradient coils, high-power current sources, analog-to-digital converters, gradient controllers, etc. Its main function is to generate the gradient magnetic field required for layer selection. Among them, the performance of the high-power current source is very important for the quality accuracy of the layer selection signal.

[0004] The traditional current source of the nuclear magnetic resonance system is a pulsed current source. The existing pulsed current source has a small maximum operating duty cycle (about 30%), a short current pulse duration, and requires an external high-power power supply to assist in operation. As a result, the current source is too large and the cost is high. In addition, due to the use of a digital switching mode, the circuit is complex, the current ripple is large, the stray interference frequency is large, and the interference handling measures are difficult. Utility Model Content

[0005] The utility model aims to solve at least one of the technical problems existing in the prior art. To this end, the utility model proposes a current source circuit of a nuclear magnetic resonance system to realize a linear high-power current source with high duty cycle, high pulse width, small volume and high stable current output.

[0006] In a first aspect, the utility model provides a current source circuit of a nuclear magnetic resonance system, comprising:

[0007] Signal input terminal and current output terminal;

[0008] An isolation amplifier circuit, a linear adjustment circuit, a drive circuit and a MOS tube output circuit are sequentially coupled between the signal input terminal and the current output terminal, and the output terminal of the MOS tube output circuit is coupled to the input terminal of the linear adjustment circuit through a current sampling circuit closed loop; wherein,

[0009] The linear adjustment circuit comprises an error amplifier, wherein a first input terminal of the error amplifier is coupled to an output terminal of the isolation amplifier circuit, a second input terminal of the error amplifier is coupled to an output terminal of the current sampling circuit, and the error amplifier is configured to output a control signal to the drive circuit according to an input voltage signal of the isolation amplifier circuit and the current sampling circuit to control an output current of the MOS tube output circuit to have a linear relationship with the input voltage signal;

[0010] The MOS tube output circuit includes a plurality of MOS tubes connected in parallel.

[0011] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0012] The output end of the error amplifier is connected to a plurality of driving circuits, each of the driving circuits correspondingly drives and is connected to a MOS tube output circuit, and the MOS tubes of each MOS tube output circuit are connected in parallel and output to the current output end.

[0013] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0014] An RC regulating circuit is connected in parallel between the second input terminal and the output terminal of the error amplifier, and the time constant of the RC regulating circuit is in millisecond level.

[0015] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0016] The isolation amplifier circuit comprises an isolation signal amplifier, an input end of the isolation signal amplifier is coupled to the signal input end, and an output end of the isolation signal amplifier is coupled to the first input end of the error amplifier.

[0017] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0018] An adjustable potentiometer is also coupled between the isolation amplifier circuit and the error amplifier, and the adjustable potentiometer is used to adjust the voltage signal output by the isolation signal amplifier.

[0019] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0020] A zero calibration circuit is also coupled between the isolation signal amplifier and the error signal amplifier.

[0021] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0022] The current sampling circuit includes a sampling resistor, a first sampling signal amplifier and a second sampling signal amplifier. One end of the sampling resistor is connected to the current output end, and the other end is grounded. The input end of the first sampling signal amplifier is connected between the current output end and the sampling resistor. The output end of the first sampling signal amplifier is coupled to the input end of the second sampling signal amplifier. The output end of the second sampling signal amplifier is coupled to the second input end of the error amplifier.

[0023] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0024] The circuit also includes an output current monitoring circuit, which includes a third sampling signal amplifier, an input end of the third sampling signal amplifier is coupled to an output end of the second sampling signal amplifier, and an output end of the third sampling signal amplifier is coupled to an external output monitoring end.

[0025] In one embodiment of the current source circuit of the above-mentioned nuclear magnetic resonance system,

[0026] The circuit also includes an input voltage monitoring circuit, which includes a fourth sampling signal amplifier, an input end of the fourth sampling signal amplifier is connected to the output end of the isolation amplifier circuit, and an output end of the fourth sampling signal amplifier is connected to an external input monitoring end.

[0027] In a second aspect, the utility model provides a current source, comprising a plurality of nuclear magnetic resonance system current source circuits as described in any one of the first aspects, wherein outputs of the plurality of nuclear magnetic resonance system current source circuits are connected in parallel through a current combiner and then output.

[0028] One or more of the above embodiments of the present invention have at least one or more of the following beneficial effects:

[0029] In the technical scheme for implementing the utility model, a linear adjustment circuit is used to ensure that the output current and the input voltage are in a linear relationship in the current source circuit topology, so that the current source has a continuous wave output capability, the circuit form is simple and reliable, and through the parallel output of several MOS tubes, the circuit has a high duty cycle, a high pulse width and a high power output capability; based on the circuit topology, it is possible to achieve the maximum output capacity using the MOS tube saturation zone working mode, low power consumption, the larger the output current, the closer the circuit form is to the saturation zone, the higher the efficiency, and the relatively smaller the heat generation, and the internal integration of a high-energy-level small-volume switching power supply form, so that the volume of the current source is greatly reduced, the number of components is greatly reduced compared to the pulse digital switch type, the circuit board layout is compact, and the small volume requirement is achieved; the overall circuit is a unidirectional output circuit, a linear form, high current accuracy, no interference frequency, the circuit is simple and stable, and at the same time, the circuit adopts a high-gain, high common-mode rejection ratio amplifier, so that the circuit output current stability and accuracy are high.

[0030] Additional aspects and advantages of the present invention will be given in part in the following description and in part will become apparent from the following description or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The disclosure of the present invention will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the drawings are used to represent similar components, among which:

[0032] Figure 1 It is a schematic diagram of a current source circuit of a nuclear magnetic resonance system according to an embodiment of the utility model;

[0033] Figure 2 is a circuit diagram of a linear adjustment circuit according to an embodiment of the utility model;

[0034] Figure 3 It is a driving circuit and a MOS tube output circuit diagram according to an embodiment of the utility model;

[0035] Figure 4 is a current source circuit diagram of a magnetic resonance system according to an embodiment of the utility model;

[0036] Figure 5 The present invention is a schematic diagram of a plurality of current sources connected in parallel for output according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] See attached Figure 1 , Figure 1 A current source circuit of a nuclear magnetic resonance system according to an embodiment of the utility model comprises: a signal input terminal Vin and a current output terminal I out, and an isolation amplifier circuit, a linear adjustment circuit, a drive circuit and a MOS tube output circuit sequentially coupled between the signal input terminal Vin and the current output terminal I out, wherein the output terminal of the MOS tube output circuit is coupled to the input terminal of the linear adjustment circuit through a current sampling circuit closed loop; wherein the linear adjustment circuit comprises an error amplifier, wherein a first input terminal of the error amplifier is coupled to the output terminal of the isolation amplifier circuit, and a second input terminal of the error amplifier is coupled to the output terminal of the current sampling circuit; wherein the error amplifier is configured to output a control signal to the drive circuit according to an input voltage signal of the isolation amplifier circuit and the current sampling circuit to control the output current of the MOS tube output circuit to be in a linear relationship with the input voltage signal; and the MOS tube output circuit comprises a plurality of MOS tubes connected in parallel. The utility model aims to ensure that the output current and the input voltage are in a linear relationship in the current source circuit topology through a linear adjustment circuit, so that the current source has a continuous wave output capability, the circuit form is simple and reliable, and through the parallel output of a plurality of MOS tubes, the circuit has a high duty cycle, a high pulse width and a high power output capability; based on the circuit topology, it can be realized that the MOS tube saturation region working mode is adopted at the maximum output capacity, the power consumption is small, the larger the output current, the closer the circuit form is to the saturation region, the higher the efficiency, and the relatively smaller the heat generation, and the internal integration of a high-energy-level small-volume switching power supply form makes the volume of the current source machine greatly reduced, the number of components is greatly reduced compared with the pulse digital switch type, the circuit board layout is compact, and the small volume requirement is achieved; the overall circuit is a unidirectional output circuit, a linear form, a high current accuracy, no interference frequency, and a simple and stable circuit. At the same time, the circuit adopts a high-gain, high common-mode rejection ratio amplifier, so that the circuit output current stability and accuracy are high.

[0039] The present invention will be described in detail below through specific embodiments.

[0040] In one embodiment, referring to Figure 2, an error amplifier circuit of a linear adjustment circuit, a first input terminal of the error amplifier (a positive input terminal 3 in the figure) is coupled to the output terminal of the isolation amplifier circuit, a second input terminal of the error amplifier is coupled (an inverting input terminal 2 in the figure) to the output terminal of the current sampling circuit, an output terminal 6 of the error amplifier is connected to a drive circuit, and the error amplifier outputs a control signal to the drive circuit according to an input voltage signal at its input terminal to control the output current of the MOS tube output circuit to be in a linear relationship with the input voltage signal, so as to achieve a current output with high duty cycle, high pulse width, small volume, high stability and high power. Furthermore, an RC regulation circuit is connected in parallel between the second input terminal (inverting input terminal 2) and the output terminal 6 of the error amplifier to form a closed-loop control with the error amplifier. The time constant of the RC regulation circuit is in the millisecond level to achieve a millisecond response time of the circuit. Specifically, the RC regulation circuit includes a resistor R4 and a capacitor C7, and its time constant τ=R4*C7. The time constant τ only needs to meet the millisecond level. For example, when R4 is 10kΩ and C7 is 0.01uF, the response time is 10kΩ*0.01uF=0.1ms, and the error amplifier achieves a millisecond response time through the RC circuit parameters.

[0041] In one embodiment, reference Figure 3 ,The error amplifier U2 can output to several drive circuits at the same time, for example Figure 3 In the figure, the driving circuit adopts drivers U1 and U4, and the input terminals Y1 of the drivers U1 and U4 are commonly connected to the output terminal 6 of the error amplifier. The driver has a voltage conversion function, and converts the control signal output by the error amplifier U2 into a driving voltage with driving capability, and its level changes with the control voltage, thereby controlling the current output of the MOS tube; each driver drives a MOS tube output circuit corresponding to the connection, and the MOS tubes of each MOS tube output circuit are connected in parallel to output to the current output terminal Iout. The MOS tube uses a single MOS power device with small switching loss. For example, in the figure, each MOS tube output circuit includes 5 parallel MOS tubes, and the pin A6 of the driver drives and connects the gate of each MOS tube, and the pin A4 of the driver connects the drain of each MOS tube, and the common output is connected to the current output terminal, that is, the output interface J2; the source of each MOS tube is connected to the external main power supply; two groups of 10 MOS tubes are output, and the maximum output current capacity of a single MOS tube is 10A. In normal use, a high-power current of 60A can be continuously output, and a combined expansion function can be realized according to different application scenarios to increase the current output, that is, multiple groups of drivers and multiple groups of MOS tubes are designed.

[0042] In one embodiment, based on the above Figure 2 and Figure 3 Example, further set the nuclear magnetic resonance system current source circuit as follows Figure 4As shown, a current source circuit in which multiple MOS tubes are connected in parallel and combined with an operational amplifier is used to achieve high duty cycle, high pulse width, high power, low rising and falling edge response time, unidirectional current output, and small volume requirements.

[0043] In some specific embodiments, the isolation amplifier circuit includes an isolation signal amplifier U3, the input end of the isolation signal amplifier U3 is coupled to the signal input interface J1, the signal input interface J1 inputs a voltage differential signal, and sends it to the isolation signal amplifier U3 through resistors R3 and R6. The isolation signal amplifier U3 isolates and amplifies the voltage differential signal and outputs it through an adjustable potentiometer R5, and then passes through a zeroing circuit composed of resistors R11 and R12 to calibrate the signal, and then sends it to the first input pin 3 of the error amplifier U2 through resistor R8. The output of the error amplifier U2 is divided into two paths, which are sent to two MOS drivers U1 and U4 respectively. U1 drives MOS tubes Q1-Q5; U4 drives MOS tubes Q6-Q10; 10 MOS tube output stages are connected in parallel and output through the output interface J2; wherein the adjustable potentiometer R5 adjusts the size and bias potential of the output signal, and the zeroing circuits of resistors R11 and R12 perform more precise static error adjustment, including the error caused by the properties of the device itself to the signal.

[0044] In some specific implementations, the current sampling circuit includes a sampling resistor R19 and a first sampling signal amplifier U7, which are connected as follows: Figure 4 As shown, the sampling resistor R19 is connected to the output interface J2 to obtain the output current, the first sampling signal amplifier U7 outputs the sampling signal through the resistor R17 and then sends it to the second sampling amplifier U5, the second sampling amplifier U5 amplifies the signal and outputs it to the second input pin 2 of the error amplifier U2, so that the error amplifier U2 generates a control signal for the driver according to the input voltage error, ensuring that the output current is linearly related to the input voltage signal.

[0045] In some specific embodiments, another path of the output of the first sampling signal amplifier U7 is sent to the third sampling signal amplifier U8 after passing through the resistor R18. The third sampling signal amplifier U8 amplifies the signal and outputs it through the resistor R21 as a current monitoring signal output; further, another path of the output of the isolation signal amplifier U3 is output through the fourth sampling signal amplifier U6 and the resistor R15 as an input voltage monitoring signal output. In this example, the current monitoring signal output and the input voltage monitoring signal output are both for external monitoring functions.

[0046] The current source circuit in the above embodiment has the following effects:

[0047] High duty cycle, high pulse width: The error signal amplifier drives multiple parallel MOS tubes to output high-power current, which is linearly related to the input voltage signal and has a continuous wave output capability circuit topology. The circuit form is simple and reliable, and the parallel output of several MOS tubes increases the high-power output capability;

[0048] Small size, high efficiency, low heat generation: The maximum output capacity of the circuit can adopt the MOS tube saturation zone working mode, with low power consumption. The larger the output current, the closer the circuit form is to the saturation zone, the higher the efficiency, and the relatively lower the heat generation; the internal integration of high-energy-level small-volume switching power supply greatly reduces the size of the whole machine; the circuit principle is simple, the number of components is greatly reduced compared with the pulse digital switch type, and the circuit board layout is compact. The above means can achieve a small size;

[0049] Unidirectional output: Using unidirectional output circuit instead of bidirectional output circuit, the circuit is simple and stable;

[0050] High stability and high accuracy output: Adopt high gain and high common mode rejection ratio operational amplifier, including error amplifier U2, signal isolation amplifier U3, first sampling amplifier U7 and second sampling amplifier U5, etc. High common mode rejection ratio and high gain make the output current stability and accuracy relatively high. Common mode rejection ratio is a key indicator to measure the ability of amplifier or circuit to suppress common mode signal. It is defined as the ratio of the voltage amplification factor of the amplifier to the differential mode signal to the voltage amplification factor of the common mode signal, usually expressed in decibels (dB). The larger the common mode rejection ratio, the stronger the circuit's ability to suppress common mode signals, that is, the circuit can better distinguish and process differential mode signals and common mode signals. Therefore, the larger the common mode rejection ratio, the better. High gain is the sampling output current error signal sent to the comparator. The higher the gain, the smaller the current error and the higher the current accuracy.

[0051] It is important to understand that Figure 2-Figure 4 The circuit diagram is intended to explain the principle concept of the utility model, not to impose specific restrictions on each circuit and the specific design of the peripheral circuits of each device. The specific circuit designs carried out under the circuit topology concept of the utility model should be within the protection scope of the present application, and the peripheral circuits around each specific circuit design in the circuit can be adjusted and adaptively changed in actual application, which should all be within the inventive concept of the present application.

[0052] Further, refer to Figure 5The utility model provides a current source, including a plurality of current source circuits of the nuclear magnetic resonance system as described above, and the outputs of the plurality of current source circuits of the nuclear magnetic resonance system are connected in parallel by a current combiner and then output. Specifically, the input voltage signal is sent to N current source circuits (also referred to as current source modules) after passing through a signal splitter, and the outputs of the N current source circuits are connected in parallel by a current combiner and then output, and the current source modules are used to expand the output in parallel, increase the power, i.e., the current, and realize the combined expansion function to increase the current output according to different specific application scenarios.

[0053] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the utility model. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0054] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present utility model, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0055] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in the field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A current source circuit for a nuclear magnetic resonance system, characterized in that: include: Signal input terminal and current output terminal; An isolation amplifier circuit, a linear adjustment circuit, a drive circuit and a MOS tube output circuit are sequentially coupled between the signal input terminal and the current output terminal, and the output terminal of the MOS tube output circuit is coupled to the input terminal of the linear adjustment circuit through a current sampling circuit closed loop; wherein, The linear adjustment circuit comprises an error amplifier, wherein a first input terminal of the error amplifier is coupled to an output terminal of the isolation amplifier circuit, a second input terminal of the error amplifier is coupled to an output terminal of the current sampling circuit, and the error amplifier is configured to output a control signal to the drive circuit according to an input voltage signal of the isolation amplifier circuit and the current sampling circuit to control an output current of the MOS tube output circuit to have a linear relationship with the input voltage signal; The MOS tube output circuit includes a plurality of MOS tubes connected in parallel.

2. The current source circuit of the nuclear magnetic resonance system according to claim 1, characterized in that: The output end of the error amplifier is connected to a plurality of driving circuits, each of the driving circuits correspondingly drives and is connected to a MOS tube output circuit, and the MOS tubes of each MOS tube output circuit are connected in parallel and output to the current output end.

3. The current source circuit of the nuclear magnetic resonance system according to claim 1, characterized in that: An RC regulating circuit is connected in parallel between the second input terminal and the output terminal of the error amplifier, and the time constant of the RC regulating circuit is in the millisecond level.

4. The current source circuit of the nuclear magnetic resonance system according to claim 1, characterized in that: The isolation amplifier circuit comprises an isolation signal amplifier, an input end of the isolation signal amplifier is coupled to the signal input end, and an output end of the isolation signal amplifier is coupled to the first input end of the error amplifier.

5. The current source circuit of the nuclear magnetic resonance system according to claim 4, characterized in that: An adjustable potentiometer is also coupled between the isolation amplifier circuit and the error amplifier, and the adjustable potentiometer is used to adjust the voltage signal output by the isolation signal amplifier.

6. The current source circuit of the nuclear magnetic resonance system according to claim 4, characterized in that: A zero calibration circuit is also coupled between the isolation signal amplifier and the error signal amplifier.

7. The current source circuit of the nuclear magnetic resonance system according to claim 1, characterized in that: The current sampling circuit includes a sampling resistor, a first sampling signal amplifier and a second sampling signal amplifier. One end of the sampling resistor is connected to the current output end, and the other end is grounded. The input end of the first sampling signal amplifier is connected between the current output end and the sampling resistor. The output end of the first sampling signal amplifier is coupled to the input end of the second sampling signal amplifier. The output end of the second sampling signal amplifier is coupled to the second input end of the error amplifier.

8. The current source circuit of the nuclear magnetic resonance system according to claim 7, characterized in that: The circuit also includes an output current monitoring circuit, which includes a third sampling signal amplifier, an input end of the third sampling signal amplifier is coupled to an output end of the second sampling signal amplifier, and an output end of the third sampling signal amplifier is coupled to an external output monitoring end.

9. The current source circuit of the nuclear magnetic resonance system according to claim 1, characterized in that: The circuit also includes an input voltage monitoring circuit, which includes a fourth sampling signal amplifier, an input end of the fourth sampling signal amplifier is connected to the output end of the isolation amplifier circuit, and an output end of the fourth sampling signal amplifier is connected to an external input monitoring end.

10. A current source, characterized in that: It comprises a plurality of nuclear magnetic resonance system current source circuits as described in any one of claims 1 to 9, wherein the outputs of the plurality of nuclear magnetic resonance system current source circuits are connected in parallel by a current combiner and then output.

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