CN106226715A - Resonance digital receives system - Google Patents

Abstract

Resonance digital receives system, relates to resonance digital signal processing.It is provided with magnetic resonance reception coil, preamplifier, analog-digital converter, decimation filter, frequency mixer, frequency synthesizer, cic filter, FIR filter, compensating filter, FPGA, memorizer, host computer；Magnetic resonance reception coil successively with preamplifier, analog-digital converter, decimation filter is connected, the outfan of decimation filter is respectively with first, the input of the second frequency mixer is connected, the outfan of frequency synthesizer is respectively with first, the input of the second frequency mixer is connected, the outfan of the first frequency mixer successively with the first cic filter, first FIR filter is connected with the input of the first compensating filter, the outfan of the second frequency mixer successively with the second cic filter, second FIR filter is connected with the input of the second compensating filter, first, the outfan of the second compensating filter is connected with FPGA respectively.

Description

Resonance digital receives system

Technical field

The present invention relates to resonance digital signal processing, especially relate to a kind of resonance digital and receive system.

Background technology

Along with development and the maturation of software and radio technique, software and radio technique is being applied to resonance digital letter Number process field.Magnetic resonance digital receiver is frequently with digital if receiver based on software radio if digitization principle Structure, FID (free induction decay) radiofrequency signal is received by magnetic resonance reception coil, turns via after analog-digital converter resampling It is changed to digital signal, then carries out digital quadrature demodulation, and process through filtering extraction, finally give the FID numeral of relatively low rate Signal.

CIC (cascaded integrator-comb) wave filter has and realizes simple in construction, is suitable for the feature such as high magnification extraction, thus by extensively The general filtering extraction field being applied to magnetic resonance reception machine.But, in order to more efficiently apply resampling technique to reach to carry The purpose of high receiver signal to noise ratio, especially in the application scenario that static magnetic field strength is higher, now cic filter would operate in (may be up to hundreds of million Hz) under higher rate, arithmetic speed and the stability of device are had higher requirement by this；Simultaneously by Structure before the integrator in cic filter is in extraction, the operating rate of such two-forty will make integrator Computational burden increases, and the power consumption of receiver increases therewith.It addition, traditional reception system would commonly be used for the mixed of Digital Down Convert Frequently, after device is placed on analog-digital converter, apply resampling technique that frequency mixer will be made to be operated in resonance digital receives Under higher frequency, the hardware effort stability build-up of pressure to frequency mixer, the performance of frequency mixer is proposed higher requirement.

Chinese patent CN103135079A discloses the method for reseptance of a kind of magnetic resonance signal, by the line in receiving coil array Coil unit is divided into different coil unit groups；To each coil unit, set up carrier frequency and each coil list in this coil unit group Corresponding relation between unit's received signal；According to described corresponding relation, all coils unit in this coil unit group is received Signal carry out low noise amplification, filter and be mixed, obtain being carried on the intermediate-freuqncy signal on each corresponding carrier frequency of same channel；Right After described intermediate-freuqncy signal is amplified and filters, export and be digitized sampling to AD conversion unit, obtain digital domain signal.

Summary of the invention

The deficiency existed when resonance digital signal processing to improve cic filter to apply, the purpose of the present invention exists System is received in providing a kind of resonance digital.

The present invention is provided with magnetic resonance reception coil, preamplifier, analog-digital converter, the filtering extraction of poly phase improvement Device, the first frequency mixer, the second frequency mixer, Direct Digital Synthesizer, the first cic filter, the second cic filter, One FIR (having limit for length's unit impact response) wave filter, the second FIR filter, the first compensating filter, the second compensating filter, FPGA (field programmable gate array), memorizer, host computer；

The described outfan of magnetic resonance reception coil is connected with the input of preamplifier, the outfan of preamplifier It is connected with the input of analog-digital converter, the input of the decimation filter that the outfan of analog-digital converter improves with poly phase It is connected, the outfan of the decimation filter that poly phase improves defeated with the input of the first frequency mixer and the second frequency mixer respectively Enter end to be connected, the outfan of Direct Digital Synthesizer defeated with the input of the first frequency mixer and the second frequency mixer respectively Entering end to be connected, the outfan of the first frequency mixer and the input of the first cic filter are connected, the outfan of the first cic filter It is connected with the input of the first FIR filter, the outfan of the first FIR filter and the input phase of the first compensating filter Even, the outfan of the second frequency mixer and the input of the second cic filter are connected, the outfan of the second cic filter and second The input of FIR filter is connected, and the outfan of the second FIR filter and the input of the second compensating filter are connected, and first The outfan of compensating filter and the outfan of the second compensating filter are connected with the input of FPGA respectively, and FPGA is respectively with upper Position machine and memorizer are bi-directionally connected.

Band filter can be provided with between outfan and the analog-digital converter input of described preamplifier.

Present invention employs the decimation filter that poly phase improves, the operating rate of overall decimation filter is reduced. Again in order to improve the shortcomings such as Polyphase filter extraction multiplying power is relatively low, filter factor amendment is dumb, give full play to CIC simultaneously Wave filter realizes simple in construction, extraction multiplying power relatively advantages of higher, present invention employs the decimation filter improved at poly phase The structure combined with cic filter.The frequency mixer being used for Digital Down Convert is placed on modulus turns to improve traditional method The deficiency existed after parallel operation, the present invention uses after frequency mixer is positioned over the decimation filter that poly phase improves, makes Frequency mixer away from analog-digital converter, thus alleviate frequency mixer pressure, reduce frequency mixer operating frequency.The present invention is substantially reduced Resonance digital receives the operating frequency of some key modules of system, improves processing capability in real time, more effectively meets In high magnetostatic field environment and high magnification resampling technique.

Accompanying drawing explanation

Fig. 1 is the composition frame chart of the embodiment of the present invention.

Fig. 2 is the theory diagram of the decimation filter that poly phase improves.

Detailed description of the invention

Seeing Fig. 1, the present invention is provided with magnetic resonance reception coil 1, preamplifier 2, analog-digital converter 4, poly phase change Decimation filter the 5, first frequency mixer the 6, second frequency mixer 7 of entering, Direct Digital Synthesizer the 8, first cic filter 9, Second cic filter the 10, the oneth FIR (having limit for length's unit impact response) wave filter the 11, second FIR filter 12, first compensates Wave filter the 13, second compensating filter 14, FPGA (field programmable gate array) 15, memorizer 16, host computer 17；

Described magnetic resonance reception coil 1 receives the input of magnetic resonance radio frequency signal, and the outfan of magnetic resonance reception coil 1 is with front The input putting amplifier 2 is connected, and the outfan of preamplifier 2 is connected with the input of analog-digital converter 4, analog-digital converter The input of the decimation filter 5 that the outfan of 4 improves with poly phase is connected, the decimation filter 5 that poly phase improves Outfan is connected with the input of the first frequency mixer 6 and the input of the second frequency mixer 7 respectively, Direct Digital Synthesizer The outfan of 8 is connected with the input of the first frequency mixer 6 and the input of the second frequency mixer 7 respectively, the output of the first frequency mixer 6 End is connected with the input of the first cic filter 9, the outfan of the first cic filter 9 and the input of the first FIR filter 11 End is connected, and the outfan of the first FIR filter 11 and the input of the first compensating filter 13 are connected, the second frequency mixer 7 defeated Go out end to be connected with the input of the second cic filter 10, the outfan of the second cic filter 10 and the second FIR filter 12 Input is connected, and the outfan of the second FIR filter 12 and the input of the second compensating filter 14 are connected, the first compensation filter The outfan of device 13 and the outfan of the second compensating filter 14 input with FPGA 15 respectively is connected, FPGA 15 respectively with Host computer 16 and memorizer 17 are bi-directionally connected.

Band filter 3 can be provided with between outfan and analog-digital converter 4 input of described preamplifier 2.

In FIG, labelling s_sinN () is the digital local oscillator signal of the first frequency mixer 6, labelling s_cosN () is the second frequency mixer 7 Digital local oscillator signal；I (n) is the FID digital baseband signal of homophase, and Q (n) is orthogonal FID digital baseband signal.

The present invention proposes a kind of resonance digital and receives system.N rank cic filter design poly phase is utilized to improve Decimation filter.Traditional N rank cic filter transmission function is:

H (z)=[(1-z^-R)/(1-z^-1)]^N,

Wherein R is decimation factor.Assume

R=2^KM,

Wherein K and M is positive integer, then transfer function H (z) can be analyzed to non-recursive part

$H_1\left(z\right)={\[(1-z^{-2^K})/(1-z^{-1})\]}^N={\[\underset{i=0}{\overset{2^K-1}{\Σ}}{z}^{-i}\]}^N=\underset{i=0}{\overset{K-1}{\Π}}{(1+z^{-2^i})}^N,$

And recursive component

$H_2\left(z^{2^K}\right)={\[(1-z^{-2^{K}M})/(1-z^{-2^K})\]}^N.$

From expression formula it can easily be seen that, H₁(z) be decimation factor be 2^KWave filter,For decimation factor Wave filter for M.First to recursive componentDoing identical transformation, its structure is equivalent to H₂Z the upper decimation factor of () cascade is M's Withdrawal device, wherein

H₂(z)=[(1-z^-M)/(1-z^-1)]^N。

Again to non-recursive part H₁Z () is done poly phase and is obtained

$H_1\left(z\right)=\underset{i=0}{\overset{2^K-1}{\Σ}}{z}^{-i}{E}_i\left(z^{2^K}\right),$

Wherein E_i(z) be i-th (i=0,1 ..., 2^K-1) multi-phase components of the heterogeneous branch road of bar, expression formula is

E_i(z)=(a_i0+a_i1z^-1+...+a_i(N-1)z^1-N),

Wherein coefficient a_ij(j=0 ..., N-1) together decided on by N and K.Thus obtain 2^KBar poly phase branch road, i-th One delay unit z of heterogeneous route^-iCascade multi-phase componentsThe upper decimation factor of cascade is 2 again^KWithdrawal device.Again to often The heterogeneous branch road of bar carries out Nobel identical transformation, obtains the structure of i-th heterogeneous branch road for by a delay unit zⁱTake out in cascade Taking the factor is 2^KWithdrawal device cascade multi-phase components E again_i(z)；And wherein delay unit zⁱCan use again at the i-th-1 branch road The upper unit delay unit z of cascade on the basis of time delay^-1Structure, therefore delay unit zⁱCan be by unit delay unit z^-1Deng Valency is replaced.The result of the heterogeneous branch road on each road being added up by an accumulator, its result is equivalent to after poly phase Non-recursive part H₁(z).Thus, the non-recursive part after poly phase is cascaded upper H₂Z () cascades decimation factor again is M Withdrawal device, just can obtain poly phase improve decimation filter structure, as shown in Figure 2.

The workflow that reception system is complete described below:

FID radiofrequency signal is received by magnetic resonance reception coil and obtains FID analog if signal, amplifies through preamplifier To the amplitude being suitable for analog-digital converter sampling.Filter out-of-band noise by band filter afterwards, recycle analog-digital converter pair FID analog if signal carries out L times of resampling (usual L is more than 2) and obtains FID digital medium-frequency signal, it is assumed that its sampling rate F_s。 Afterwards FID digital medium-frequency signal being sent into the decimation filter that poly phase improves, extracting multiple is

R=2^KM,

Wherein K and M is positive integer, 2^KExtraction is completed by the non-recursive part after its poly phase again, and M times is extracted by recurrence It is partially completed.

Because this resonance digital receives system and uses digital quadrature demodulation technology, it is therefore desirable to obtain homophase and orthogonal two Road FID digital baseband signal.FID digital medium-frequency signal after being extracted by the decimation filter improved through poly phase is divided into two Road, is separately input to the first frequency mixer and the second frequency mixer, and wherein the first frequency mixer obtains homophase FID number for Digital Down Convert Word baseband signal, the second frequency mixer obtains orthogonal FID digital baseband signal for Digital Down Convert.First frequency mixer and second mixes Frequently the digital local oscillator signal of device is generated by Direct Digital Synthesizer.From principle, input the numeral of the first frequency mixer Local oscillation signal s_sinN () should be with the digital local oscillator signal s of resonance digital emission system_tN () is with frequency homophase, and input second The digital local oscillator signal s of frequency mixer_cosN () should be with s_sinN () is with frequency, phase 90 degree.In this reception system, due to After one frequency mixer and the second frequency mixer are positioned at the decimation filter that poly phase improves, it is assumed herein that the mould needed for certain transmitting The frequency intending carrier signal is f_c, then the digital local oscillator signal that Direct Digital Synthesizer generates is

s_t(n)=sin (2 π f_cN),

Then can obtain Direct Digital Synthesizer and be input to the digital local oscillator signal of the first frequency mixer and be

s_sin(n)=sin (2 π f_c2^KMn/F_s),

Direct Digital Synthesizer is input to the digital local oscillator signal of the second frequency mixer

s_cos(n)=cos (2 π f_c2^KMn/F_s)。

First frequency mixer output speed is F_s/(2^KM) homophase FID digital baseband signal I₁(n), the second frequency mixer output Speed is F_s/(2^KM) orthogonal FID digital baseband signal Q₁(n)。

By I₁N () input carries out second level extraction to the first cic filter, extracting multiple is D, and the signal after extraction is sent into First FIR filter eliminates unnecessary frequency content, is input to the first compensating filter the most again, to revise owing to front two-stage is taken out Take the amplitude distortion that filter passband unevenness produces；Final FID digital baseband signal I (n) exporting homophase, its speed is F_s/(2^KMD).By Q₁N () input carries out second level extraction to the second cic filter, extracting multiple is D, and the signal after extraction send Enter the second FIR filter and eliminate unnecessary frequency content, be input to the second compensating filter the most again, to revise due to front two-stage The amplitude distortion that decimation filter passband unevenness produces；FID digital baseband signal Q (n) of final output orthogonal, its speed is F_s/(2^KMD).I (n) and Q (n) signal parallel are inputted to FPGA, FPGA carries out third time filtering extraction, K Space Reconstruction, pressure Reduce the staff code and process to a series of signal such as host computer transmission FID data.FPGA is by the homophase FID number after compressed encoding simultaneously Word baseband signal and orthogonal FID digital baseband signal are stored in memorizer, in order to hereafter operator is repeated several times reading FID data message.

The present invention uses the decimation filter that poly phase improves to coordinate the structure of cic filter, by the position of extraction to Front movement, thus alleviate the pressure of integrator in cic filter, reduce the speed ability requirement of extraction hardware.Simultaneously will be mixed Frequently, after device is positioned over the multidirectional decimation filter decomposing and improving, the operating frequency of frequency mixer is reduced.The present invention is substantially reduced Resonance digital receives the operating frequency of some key modules of system, improves processing capability in real time, more effectively meets In high magnetostatic field environment and high magnification resampling technique.

Claims (2)

1. resonance digital receive system, it is characterised in that be provided with magnetic resonance reception coil, preamplifier, analog-digital converter, The decimation filter of poly phase improvement, the first frequency mixer, the second frequency mixer, Direct Digital Synthesizer, a CIC filter Ripple device, the second cic filter, the first FIR filter, the second FIR filter, the first compensating filter, the second compensating filter, FPGA, memorizer, host computer；

The described outfan of magnetic resonance reception coil is connected with the input of preamplifier, the outfan of preamplifier and mould The input of number converter is connected, the input phase of the decimation filter that the outfan of analog-digital converter improves with poly phase Even, the outfan of the decimation filter that poly phase improves respectively with input and the input of the second frequency mixer of the first frequency mixer End is connected, the outfan of Direct Digital Synthesizer respectively with input and the input of the second frequency mixer of the first frequency mixer End is connected, and the outfan of the first frequency mixer and the input of the first cic filter are connected, the outfan of the first cic filter with The input of the first FIR filter is connected, and the outfan of the first FIR filter and the input of the first compensating filter are connected, The outfan of the second frequency mixer and the input of the second cic filter are connected, the outfan of the second cic filter and the 2nd FIR The input of wave filter is connected, and the outfan of the second FIR filter and the input of the second compensating filter are connected, and first compensates The outfan of wave filter and the outfan of the second compensating filter are connected with the input of FPGA respectively, FPGA respectively with host computer It is bi-directionally connected with memorizer.

2. resonance digital receives system as claimed in claim 1, it is characterised in that the outfan of described preamplifier and mould It is provided with band filter between number converter input.