CN107703468A - The drive circuit of NMR gradient power amplifier - Google Patents

Abstract

The invention relates to a driving circuit of a gradient power amplifier of a nuclear magnetic resonance instrument, relating to the gradient power amplifier. It is equipped with a zero-crossing comparator, an adder circuit and a transmission gate; the input terminal of the zero-crossing comparator is connected with the pulse input signal of 0~±5V, and the output terminal of the zero-crossing comparator is connected with the transmission gate control terminal of the positive and negative signal paths The adder circuit is provided with three adders under the positive and negative signal paths, and the non-inverting input terminals of the adders are connected with the input signal; the output terminal of the adder is connected with the input terminal of the transmission gate; There are 3 transmission gates under the channel, the control terminals of the 3 transmission gates are connected to the output terminals of the zero-crossing comparator, and the output of the zero-crossing comparator controls its on-off, and the input terminals of the 3 transmission gates are connected to the adder , the output terminals of the three transmission gates are connected to the IGBT of the amplifying circuit, and the working state of the IGBT is controlled by the output state of the output adder.

Description

Driving Circuit of Gradient Power Amplifier in Nuclear Magnetic Resonance Instrument

technical field

The invention relates to a gradient power amplifier, in particular to a drive circuit for a nuclear magnetic resonance (NMR)/nuclear magnetic resonance imager (MRI) gradient power amplifier.

Background technique

Nuclear Magnetic Resonance (NMR), also known as Magnetic Resonance (MR), is a phenomenon in which atomic nuclei undergo energy level splitting in a static magnetic field and undergo energy level transitions under the excitation of an external radio frequency magnetic field. It is mainly used for the measurement of nuclear magnetic moment, electromagnetic pole moment and spin. MRI (Magnetic Resonance Imaging, MRI) is nuclear magnetic resonance used to determine the molecular structure, analysis of biological tissues and living tissues, pathological analysis, non-destructive testing of products, medical diagnosis, etc. In addition, NMR/MRI can also be used to observe changes in some dynamic processes.

One of the core components of nuclear magnetic resonance NMR/MRI using this technology is the gradient power amplifier, which emits a strong and variable gradient pulse in a very short time (microseconds to milliseconds) The coil load provides a drive current of hundreds of amperes, and the load current follows the computer spectrometer to generate pulse sequence reference signals in the three directions of X-axis, Y-axis, and Z-axis, and generates a magnetic field with variable gradient to realize the dynamic change of the main magnetic field.

IGBT (Insulated Gate Bipolar Transistor), or Insulated Gate Bipolar Transistor, is a dual-mechanism composite device composed of MOSFET (Insulated Gate Field Effect Transistor) and BJT (Bipolar Transistor). It has the advantages of high input impedance of MOSFET and low turn-on voltage drop and low turn-on resistance of GTR. Among them, the driving power of MOSFET is small and the switching speed is fast, but the conduction voltage drop is large and the current carrying density is small. The saturation voltage of GTR is low, and the current carrying density is high, but the driving current is large. The IGBT combines the advantages of the two devices, with low driving power and low saturation voltage. IGBT has great advantages in motor control, medium and high frequency switching power supply, especially in the field of medium and high power and low loss. It can be used in the design of gradient power amplifiers. The amplifying circuit is composed of a push-pull circuit structure. By controlling the working state of the IGBT, the positive and negative voltage signals are converted into current signals of hundreds of amperes. This requires a driving circuit, which can effectively put the IGBT in the required working state under the control of the signal, so as to ensure the normal operation of the push-pull circuit.

Contents of the invention

The object of the present invention is to provide a drive circuit for the gradient power amplifier of the nuclear magnetic resonance instrument in view of the circuit requirements of the gradient power amplifier of the nuclear magnetic resonance instrument.

The invention is provided with a zero-crossing comparator, an adder circuit and a transmission gate;

The zero-crossing comparator is provided with two opposite zero-crossing comparators, the input ends of the two opposite zero-crossing comparators are connected and connected with the pulse input signal of 0 ~ ± 5V, and the two opposite zero-crossing comparators are compared The output terminals of the device are respectively connected to the transmission gate control terminals of the positive and negative signal paths;

The adder circuit is provided with 3 adders under the positive and negative signal paths, and the 3 adders respectively add -20V, -9V, and +5V 3 state voltages to the inverting input of the adder, and the non-inverting input of the adder The input terminals are connected to the input signal; the output terminal of the adder is connected to the input terminal of the transmission gate;

The transmission gate is provided with 3 transmission gates under the positive and negative signal paths, the control terminals of the 3 transmission gates are connected to the output terminals of the zero-crossing comparator, and its on-off is controlled by the output of the zero-crossing comparator. The input terminal of the gate is connected with the adder, and the output terminals of the three transmission gates are connected with the IGBT of the amplifying circuit, and the working state of the IGBT is controlled by the output state of the output adder.

The present invention utilizes a zero-crossing comparator to effectively distinguish voltages from 0 to +5V and voltages from 0 to -5V, and controls the voltage through the adder circuit and the transmission gate in the positive and negative signal paths under these two input signals respectively. The IGBT in the amplifying circuit makes the four IGBTs forming the push-pull bridge structure in the amplifying circuit work in the required state, and completes the function of converting 0~±5V to hundreds of amperes.

Description of drawings

Fig. 1 is the overall structural block diagram of the embodiment of the present invention;

Fig. 2 is the output characteristic curve of the amplifier circuit IGBT transistor;

Fig. 3 is an overall circuit diagram of an embodiment of the present invention connected to an amplifying circuit.

detailed description

Referring to FIG. 1 , the embodiment of the present invention is provided with two opposite zero-crossing comparators 1 to receive input signals, and the output terminals are respectively connected to the transmission gate 3 of the positive signal path and the transmission gate 4 of the negative signal path. When the input signal is a positive voltage, the transmission gate 3 of the positive signal path is turned on, and the output state of the adder circuit 2 of the positive signal path is added to the IGBT of the amplifying circuit 5; when the input signal is a negative voltage, the negative signal path transmits The gate 4 is turned on, and the output state of the adder circuit 2 of the negative signal path is added to the IGBT of the amplifying circuit 5 .

Referring to Figure 2, the output characteristic curve of the IGBT shows that for the IGBT, when the voltage is 20V, it is in the amplified state, when the voltage is 9V, it is in the saturated state, and when the voltage is -5V, it is in the cut-off state.

Referring to Fig. 3, two opposite zero-crossing comparators 1, when the input signal is a positive voltage, the comparator receiving the control signal at the non-inverting input terminal reverses, outputs a 10V voltage, and provides a switching signal for the positive signal path transmission gate 3; when When the input signal is a negative voltage, the comparator receiving the signal at the inverting input end is reversed and outputs a 10V voltage to provide a switching signal for the transmission gate 4 of the negative signal path. The adder circuit 2 of the positive and negative signal paths each has 3 adders, respectively applying voltages of -20V, -9V and +5V to the inverting input terminals of the 3 adders, while the non-inverting input terminals of the 3 adders are connected to the input signal, the state voltage of 20V, 9V, -5V and the input signal can be transmitted to the respectively connected positive signal path transmission gate 3 and negative signal path transmission gate 4 . The amplifier circuit 5 works under the push-pull bridge structure, and the normal working state is that when the input voltage is 0~+5V, the T1 tube is in the amplified state, the T4 tube is saturated, and T2 and T3 are cut off; when the input voltage is 0~-5V At this time, the T2 tube is in the amplified state, the T3 tube is saturated, and the T1 and T4 are cut off. The operation process of the circuit is that when the input signal is 0~+5V, the comparator that receives the signal at the input end of the same direction is reversed, and the output voltage is 10V, the transmission gate 3 of the positive signal path is turned on, and the output state of the adder circuit 2 is respectively added. To the IGBT of the amplifying circuit, the T1 tube is in the amplified state, the T4 tube is saturated, and T2 and T3 are cut off; when the input signal is 0~-5V, the comparator that receives the signal at the inverting input terminal is reversed, and the output voltage is 10V, negative The transmission gate 4 of the signal path is turned on, and the output state of the adder is respectively added to the IGBT of the amplifying circuit, so that the T2 tube is in the amplified state, the T3 tube is saturated, and T1 and T4 are cut off. In this way, the amplifying circuit can work normally and complete the function of converting an input signal of 0-±5V into a current signal of hundreds of amps under the push-pull bridge structure. In Fig. 3, the mark T0 is the gradient coil.

Claims (1)

1. The driving circuit of the nuclear magnetic resonance instrument gradient power amplifier is characterized in that a zero-crossing comparator, an adder circuit and a transmission gate are provided; The zero-crossing comparator is provided with two opposite zero-crossing comparators, the input ends of the two opposite zero-crossing comparators are connected and connected with the pulse input signal of 0 ~ ± 5V, and the two opposite zero-crossing comparators are compared The output terminals of the device are respectively connected to the transmission gate control terminals of the positive and negative signal paths; The adder circuit is provided with 3 adders under the positive and negative signal paths, and the 3 adders respectively add -20V, -9V, and +5V 3 state voltages to the inverting input of the adder, and the non-inverting input of the adder The input terminals are connected to the input signal; the output terminal of the adder is connected to the input terminal of the transmission gate; The transmission gate is provided with 3 transmission gates under the positive and negative signal paths, the control terminals of the 3 transmission gates are connected to the output terminals of the zero-crossing comparator, and its on-off is controlled by the output of the zero-crossing comparator. The input terminal of the gate is connected with the adder, and the output terminals of the three transmission gates are connected with the IGBT of the amplifying circuit, and the working state of the IGBT is controlled by the output state of the output adder.