阅读说明：本技术 一种提升信号动态范围的磁共振接收方法 (Magnetic resonance receiving method for improving signal dynamic range ) 是由 张双 吴林 张涛 余洁 尧德中 于 2021-08-03 设计创作，主要内容包括：本发明公开一种提升信号动态范围的磁共振接收方法,应用于电子信息技术领域,针对现有技术存在的信号失真以及动态范围不理想的问题,本发明通过传统接收装置内部集成的自动增益控制的功能,简化了软件控制流程；并在接收装置数字域对ADC输出的数字信号进行增益补偿,相位补偿以及直流偏直补偿；实现了对幅值较小的信号进行更大的接收增益,对幅值较大的信号进行较小的接收增益的技术效果,并提高了磁共振接收信号的动态范围。(The invention discloses a magnetic resonance receiving method for improving the dynamic range of a signal, which is applied to the technical field of electronic information and aims at solving the problems of signal distortion and unsatisfactory dynamic range in the prior art; and performing gain compensation, phase compensation and direct current bias compensation on the digital signal output by the ADC in a digital domain of the receiving device; the technical effects of carrying out larger receiving gain on the signal with smaller amplitude and carrying out smaller receiving gain on the signal with larger amplitude are achieved, and the dynamic range of the magnetic resonance receiving signal is improved.)

1. A magnetic resonance receiving method for improving the dynamic range of signals is characterized in that the structure of a magnetic resonance signal receiving device based on the magnetic resonance signal receiving device comprises the following steps: an amplifier, an ADC, and a receiving device digital domain;

the amplifier adopts a signal amplification circuit with receiving gain and input signal amplitude in a smooth curve relationship;

the first analog signal received by the magnetic resonance signal receiving device is amplified by an amplifier and then converted into a first digital signal by an ADC (analog to digital converter), and the first digital signal converted by the ADC is subjected to gain, phase and direct current offset compensation in a digital domain of the receiving device to obtain a second digital signal.

2. The magnetic resonance receiving method for improving the dynamic range of the signal as claimed in claim 1, wherein the process of compensating the gain, the phase and the dc offset of the first digital signal in the digital domain of the receiving device to obtain the second digital signal comprises: and inputting a known second analog signal into the magnetic resonance signal receiving device, and testing to obtain a gain compensation value, a phase compensation value and a direct current bias direct compensation value, so that the gain compensation, the phase compensation and the direct current bias direct compensation are carried out on the first digital signal, and the compensated second digital signal is finally obtained.

3. The magnetic resonance receiving method for improving the dynamic range of the signal according to claim 2, is characterized by comprising the following steps:

s1, inputting a known second analog signal to the magnetic resonance signal receiving device, wherein the power intensity value Pin of the analog signal gradually rises from-70 dBm to +10dBm and is adjusted by taking +1dB as a step;

s2, testing and recording the output power strength value of each power strength value of the analog signal after signal amplification of the amplifier, and then fitting the power curve function values Pout of all the output signals processed by the signal amplifier to obtain a gain curve G (Pin) of Pout-Pin;

testing and recording the phase value of the output signal of the amplifier, and fitting a curve function of the phase values of all the output signals of the signal amplifier, wherein the function of the curve function and the power intensity value Pin of the analog signal of the input amplifier is as follows: p (Pin);

testing and recording the direct current bias value of the output signal of the amplifier, and then fitting a direct current bias curve function of all the output signals of the signal amplifier, wherein the function of the curve function and the power intensity value Pin of the analog signal of the input amplifier is defined as DC _ offset (Pin);

s3, recording the analog signal obtained in the step S1, amplifying the analog signal by an amplifier, converting the analog signal into a digital signal B through an ADC, and performing benchmarking on the digital signal B and Pout to obtain a mapping formula;

s4, obtaining a first analog signal power strength value according to the first digital signal and the mapping formula of the step S3;

s5, obtaining a gain compensation value according to the gain curve of the step S2 and the first analog signal power strength value;

s6, searching for P (Pin) according to the power intensity value of the first analog signal to obtain a phase compensation value;

s7, searching DC _ offset (Pin) according to the first analog signal power strength value to obtain a DC offset compensation value;

and S8, compensating the first digital signal according to the gain compensation value in the step S5, the phase compensation value in the step S6 and the DC offset compensation value in the step S7 to obtain a second digital signal.

4. A method as claimed in claim 3, wherein the first analog signal has a power level in the range of-70 dBm to +10 dBm.

5. A method as claimed in claim 3, wherein the mapping formula of step S3 is:

Pin＝10-G(Pin)-20*lg[(2^(N-1)-1)/B]

wherein, N is the ADC conversion bit width.

Technical Field

The invention belongs to the technical field of electronic information, and particularly relates to a magnetic resonance receiving technology for improving a signal dynamic range.

Background

Although the development of ADC performance is very rapid in the last years, the dynamic range of ADC is still the bottleneck of high performance receiving link, so that the high speed ADC needs to be developed for several years to meet the requirement of the most advanced nmr system on the high dynamic range of the received signal. During a commercial magnetic resonance sequence scan, the receive gain of the magnetic resonance receive chain is generally kept constant, and the conventional implementation method has the following disadvantages: under the condition of ensuring that the part with larger amplitude of the received signal does not overflow, a fixed receiving gain parameter is set, so that the part with smaller amplitude of the received signal cannot fully utilize the full-scale range of the ADC in the ADC link, and the dynamic range of the part with smaller amplitude of the signal is reduced by the implementation mode. In recent years, some engineers in the magnetic resonance industry have proposed dynamically adjusting the receive gain during sequence operation so that both larger and smaller portions of the received signal amplitude achieve a high signal dynamic range.

ZL 201710348442.9 "receiver, signal reception processing method, and magnetic resonance imaging apparatus" propose an implementation manner in which the gain mode of the received signal gain circuit is rapidly switched during the process of receiving signals, so that signals with smaller amplitude achieve a larger reception gain, and signals with larger amplitude do not overflow, thereby increasing the dynamic range of the signals received by the receiver. However, in practical implementation, it is difficult to ensure that the switching time of the gain mode is shorter than the sampling period of the analog-to-digital conversion circuit, so that a certain sampling time point of the analog-to-digital conversion circuit may fall in the switching process of the gain mode. Meanwhile, the method proposed in the patent may cause signal distortion to some extent during the implementation process, because the switching process of the receiving gain mode may cause the fluctuation of the signal waveform.

ZL 201910356813.7 'a receiver, a signal receiving method and a magnetic resonance imaging device' invents a receiver, a signal receiving method and a magnetic resonance imaging device, which make full use of a linear working area and a nonlinear distortion area of an amplifier circuit in the receiver, when a received analog signal is smaller than a preset amplitude, the amplifier circuit is in the linear working area, when the analog signal is larger than the preset amplitude, the amplifier circuit is in the nonlinear distortion area, an analog-to-digital conversion circuit quantizes the analog signal amplified by the amplifier into a digital signal and corrects the digital signal, so that all the received signals obtain the linearly amplified digital signal. Because the nonlinear distortion region of the amplifier has the characteristic of gain compression, compared with the analog signal amplified in a normal linear mode, the analog signal amplified by utilizing the compression gain has smaller amplitude so as to reduce the requirement on the high dynamic range of the ADC, and simultaneously reduce the system cost and the power consumption. However, the patent uses the nonlinear distortion region of the amplifier circuit, because of the nonlinear characteristics of the amplifier device, the signal amplified by the nonlinear distortion region of the amplifier can generate unnecessary multiple harmonic components, the patent proposes that these multiple harmonic components are filtered out by the filter circuit, but the third harmonic component is very close to the useful signal frequency point, so it is not practical to completely filter out the third and other higher harmonic components, but if this problem cannot be completely solved, the method proposed by the patent cannot achieve the expected effect of improving the dynamic range of the signal received by the receiver.

Disclosure of Invention

In order to solve the technical problem, the invention provides a magnetic resonance receiving method for improving the dynamic range of signals, which can perform larger receiving gain on signals with smaller amplitude and perform smaller receiving gain on signals with larger amplitude, thereby improving the dynamic range of the magnetic resonance receiving signals.

The technical scheme adopted by the invention is as follows: a magnetic resonance receiving method for improving the dynamic range of signals is based on a magnetic resonance signal receiving device, and the structure of the magnetic resonance signal receiving device comprises the following steps: an amplifier, an ADC, and a receiving device digital domain;

the amplifier adopts a signal amplification circuit with receiving gain and input signal amplitude in a smooth curve relationship;

the first analog signal received by the magnetic resonance signal receiving device is amplified by an amplifier and then converted into a first digital signal by an ADC (analog to digital converter), and the first digital signal converted by the ADC is subjected to gain, phase and direct current offset compensation in a digital domain of the receiving device to obtain a second digital signal.

The process of compensating the gain, the phase and the direct current offset value of the first digital signal in the digital domain of the receiving device to obtain a second digital signal comprises the following steps: and inputting a known second analog signal into the magnetic resonance signal receiving device, and testing to obtain a gain compensation value, a phase compensation value and a direct current bias direct compensation value, so that the gain compensation, the phase compensation and the direct current bias direct compensation are carried out on the first digital signal, and the compensated second digital signal is finally obtained.

The method specifically comprises the following steps:

s1, inputting a known second analog signal to the magnetic resonance signal receiving device, wherein the power intensity value Pin of the analog signal gradually rises from-70 dBm to +10dBm and is adjusted by taking +1dB as a step;

s2, testing and recording the output power strength value of each power strength value of the analog signal after signal amplification of the amplifier, and then fitting the power curve function values Pout of all the output signals processed by the signal amplifier to obtain a gain curve G (Pin) of Pout-Pin;

testing and recording the phase value of the output signal of the amplifier, and fitting a curve function of the phase values of all the output signals of the signal amplifier, wherein the function of the curve function and the power intensity value Pin of the analog signal of the input amplifier is as follows: p (Pin);

testing and recording the direct current bias value of the output signal of the amplifier, and then fitting a direct current bias curve function of all the output signals of the signal amplifier, wherein the function of the curve function and the power intensity value Pin of the analog signal of the input amplifier is defined as DC _ offset (Pin);

s3, recording the analog signal obtained in the step S1, amplifying the analog signal by an amplifier, converting the analog signal into a digital signal B through an ADC, and performing benchmarking on the digital signal B and Pout to obtain a mapping formula;

s4, obtaining a first analog signal power strength value according to the first digital signal and the mapping formula of the step S3;

s5, obtaining a gain compensation value according to the gain curve of the step S2 and the first analog signal power strength value;

s6, searching for P (Pin) according to the power intensity value of the first analog signal to obtain a phase compensation value;

s7, searching DC _ offset (Pin) according to the first analog signal power strength value to obtain a DC offset compensation value;

and S8, compensating the first digital signal according to the gain compensation value in the step S5, the phase compensation value in the step S6 and the DC offset compensation value in the step S7 to obtain a second digital signal.

The power intensity value of the first analog signal ranges from-70 dBm to +10 dBm.

The mapping formula of step S3 is:

Pin＝10-G(Pin)-20*lg[(2^(N-1)-1)/B]

wherein, N is the ADC conversion bit width.

The invention has the beneficial effects that: the method of the invention removes the function of automatic gain control inside the receiving device, and simplifies the software control flow; the compensation method provided by the invention can carry out larger receiving gain on the signal with smaller amplitude and carry out smaller receiving gain on the signal with larger amplitude, thereby improving the dynamic range of the magnetic resonance receiving signal.

Drawings

Fig. 1 is a schematic diagram of a conventional magnetic resonance signal receiving apparatus;

FIG. 2 is a schematic diagram of an apparatus for receiving magnetic resonance signals according to the present invention;

FIG. 3 is a flow chart of a method of the present invention;

fig. 4 is a corresponding relationship between an input analog signal power value Pin and an output analog signal power value Pout of the amplifier according to the embodiment of the present invention;

fig. 5 is a corresponding relationship between an input analog signal power value Pin and a signal gain g (Pin) of the amplifier according to the embodiment of the present invention;

fig. 6 is a signal amplifying circuit according to an embodiment of the present invention, in which the receiving gain and the input signal amplitude have a smooth curve relationship.

Detailed Description

In order to facilitate the understanding of the technical contents of the present invention by those skilled in the art, the present invention will be further explained with reference to the accompanying drawings.

As shown in fig. 1, the conventional magnetic resonance signal receiving apparatus mainly includes: controllable amplifier, ADC and receiving device digital domain module. The receiving device is internally integrated with the automatic gain control function, software is required to issue a command to the digital domain module of the receiving device, and the receiving gain of the controllable amplifier is automatically controlled through the controllable gain parameter, so that the software control flow of the implementation mode is relatively complex.

The magnetic resonance signal receiving device mainly comprises modules as shown in fig. 2, and the related technology mainly relates to an amplifier, an ADC and a digital domain module of the receiving device. The receiving device cuts the function of automatic gain control, and does not need fussy software control flow to automatically control the receiving gain.

The invention provides a method and a receiving device for receiving and acquiring magnetic resonance radio frequency signals. A signal amplitude compressor/expander technology is adopted in an amplifier link and a receiving device digital domain module of the receiving device, the dynamic range of a sampling signal is improved, the function of automatic gain control integrated in the traditional receiving device is eliminated, and the software control flow is simplified.

The invention introduces a signal amplification circuit with receiving gain and input signal amplitude in a smooth curve relationship as shown in fig. 6 into a magnetic resonance signal receiving device, namely, the amplification circuit is used as an amplifier in fig. 2, and the amplification circuit can carry out larger receiving gain on signals with smaller amplitude and carry out smaller receiving gain on signals with larger amplitude; however, the signal processed by the amplifying circuit needs to be subjected to gain compensation, phase compensation and direct current bias compensation, and the invention provides corresponding innovative solutions for the compensation methods.

As shown in fig. 3, which is a flow chart of the method of the present invention, the method of the present invention is based on a signal amplification circuit in which the signal amplification gain and the power intensity value of the input signal form a smooth curve, so that the part with larger amplitude of the received signal does not overflow, and the amplification circuit acts as a compressor on the input received signal; meanwhile, the part with smaller amplitude of the received signal is enabled to take on the function of the signal expander, so that the part with smaller amplitude of the received signal can more fully utilize the full-scale range of the ADC. The method specifically comprises the following steps:

s1, gradually increasing the input signal power Pin of the receiving device from-70 dBm to +10dBm, and adjusting by taking +1dB as a step;

s2, obtaining G (Pin), P (G), DC _ offset (Pin) function curves;

s3, inputting the analog signal power intensity value Pin and the digital signal value B to perform benchmarking to obtain a mapping formula;

s4, calculating to obtain an input analog signal power intensity value Pin according to the digital signal value B;

s5, calculating according to the input analog signal power intensity value Pin to obtain Bcomp;

s6, searching P (Pin) according to the Pin, and calculating to obtain Pcomp;

s7, searching DC _ offset (Pin) according to Pin, and calculating to obtain DC _ offset _ comp;

and S8, outputting the compensated digital signal.

The gain curve g (pin) acquisition process is:

the sine wave signal with a single frequency point is input into the amplifier, the power intensity value is defined as Pin, the value of Pin gradually rises from-70 dBm to +10dBm, the gain correction work is gradually carried out by taking +1dB as a step, the output power intensity value of each power intensity value of the input signal after the signal amplification of the amplifier is tested and recorded, and then the power intensity value curve function value Pout of all the output signals after the signal amplifier is processed is fitted, as shown in FIG. 4. The gain curve is g (Pin) ═ Pout-Pin, as shown in fig. 5; the maximum of the gain curve is found from g (pin), named Gmax, and the gain compensation curve function Gcomp-g (pin). The corresponding relationship between the power value Pin of the input analog signal of the amplifier and the power value Pout of the output analog signal is shown in fig. 4, and the corresponding relationship between the power value Pin of the input analog signal of the amplifier and the signal gain g (Pin) is shown in fig. 5.

The realization process of the analog signal power intensity value Pout and the digital signal value benchmarking is as follows:

and setting the amplitude power intensity value of the full bias signal of the ADC as Pmax, wherein the Pmax of most ADCs is generally +10dBm, and in order to visually express the idea of the invention, the Pmax is set as +10 dBm. Defining the signal input power of the ADC as Pout, and then the difference between the full bias signal amplitude intensity value of the ADC and the input power of the ADC is 10-Pout. Assuming that the ADC conversion bit width is N bits, the size of the quantized digital signal corresponding to +10dBm is 2^ (N-1) -1; because all gain, phase and dc offset value compensation work is performed in the digital domain module of the receiving device, the power intensity value of the analog signal input to the amplifier needs to be obtained through the digital signal value, and then the gain, phase and dc offset value to be compensated are obtained from the fitted gain, phase and dc offset value function curve according to the power intensity value of the analog signal input to the amplifier, so that it is necessary to perform calibration on the digital signal value and the power intensity value of the analog signal input to the amplifier.

As shown in fig. 2, the whole magnetic resonance receiving apparatus receives each analog power intensity value, the signal power intensity value amplified by the amplifier is Pout, and then the signal power intensity value is input to the ADC, the analog signal is quantized into a digital signal by the ADC, and the digital signal is expressed in a binary format; at the output of the digital domain of the receiver, the binary format of the digital signal B needs to be aligned with the power strength Pout of the signal input to the ADC, and the power difference can be converted into the logarithm of the ratio of the digital signals, as shown in equation 1:

10-Pout ═ 20 x lg [ (2^ (N-1) -1)/B ] (formula 1)

Substituting g (Pin) Pout-Pin into equation 1, equation 2 is obtained:

10-Pin-g (Pin) ═ 20 × lg [ (2^ (N-1) -1)/B ] (formula 2)

Further derivation of equation 2 yields equation 3:

10-g (Pin) -20 × lg [ (2^ (N-1) -1)/B ] (formula 3)

The gain compensation process is as follows:

defining the gain value to be compensated as Gcomp, the compensated digital signal value is Bcomp, and the functional relationship between Bcomp and Gcomp is shown in formula (4):

bcomp [10^ (Gcomp/20) ]. B (equation 4)

The relationship between the gain value Gcomp to be compensated and Gmax and G (Pin) is shown in equation (5):

gcomp ═ Gmax-g (pin) (equation 5)

Gmax, G (Pin) of formula (5) is obtained in step S2 by way of measurement and fitting, as can be seen from formula (3): the analog signal input power intensity value Pin can be obtained from the digital signal value B through a target calculation mode.

The gain-compensated digital signal value Bcomp can be obtained by combining the formulas (3), (4) and (5).

The phase correction and compensation process comprises the following steps:

inputting a sine wave signal with a single frequency point into an amplifier, gradually increasing the power intensity Pin from-70 dBm to +10dBm, gradually carrying out phase correction work by taking +1dB as a step, correspondingly testing and recording the phase value of the output signal of the amplifier, and then fitting a curve function of all phase values of the output signal of the signal amplifier, wherein the function of the curve function and the signal intensity Pin of the input amplifier is as follows: p (Pin). Defining that the maximum phase value of the output signal of Pin via the amplifier is P0, the phase compensation value Pcomp satisfies: pcomp ═ P0-P (pin).

The compensated phase value of the output signal of the digital domain of the receiving device is P0-Pcomp.

The process of DC offset correction and compensation is as follows:

inputting sine wave signal with single frequency point to the amplifier, the power intensity Pin is gradually increased from-70 dBm to +10dBm, gradually developing DC bias correction work by taking +1dB as step, correspondingly testing and recording the DC bias value of the output signal from the amplifier, and then fitting out all DC bias curve functions of the output signal of the signal amplifier, wherein the function of the curve function and the input amplifier signal intensity value Pin is defined as DC _ offset (Pin). Setting the DC offset of the amplifier output signal corresponding to an input signal power strength value of-70 dBm to DC _ offset0, the DC offset compensation value DC _ offset _ comp satisfies the functional relation: DC _ offset _ comp ═ DC _ offset0-DC _ offset (pin).

The compensated DC offset value of the output signal in the digital domain of the receiving device is DC _ offset0-DC _ offset _ comp.

It will be appreciated by those of ordinary skill in the art that the embodiments described herein are intended to assist the reader in understanding the principles of the invention and are to be construed as being without limitation to such specifically recited embodiments and examples. Various modifications and alterations to this invention will become apparent to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.