CN102525456A - Voltage control current source for electrical impedance tomography - Google Patents
Voltage control current source for electrical impedance tomography Download PDFInfo
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- CN102525456A CN102525456A CN2012100071794A CN201210007179A CN102525456A CN 102525456 A CN102525456 A CN 102525456A CN 2012100071794 A CN2012100071794 A CN 2012100071794A CN 201210007179 A CN201210007179 A CN 201210007179A CN 102525456 A CN102525456 A CN 102525456A
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Abstract
The invention provides a voltage control current source for electrical impedance tomography, which comprises a master control module, a signal generating module, a signal conditioning module, a current conversion module, an impedance conversion module and a programmed switch. The master control module outputs frequency and phase control signals to the signal generating module and outputs amplitude control signals to the signal conditioning module. The signal generating module outputs generated signals in modes of voltage with specific frequency and phase to the signal conditioning module, after the amplitude of the signals is adjusted by the signal conditioning module and the signals realize high-frequency harmonic suppression by the aid of the signal conditioning module, the signals are outputted to the current conversion module, and the current conversion module converts the inputted signals to current driven signals which are outputted to an EIT (electrical impedance tomography) system. When output frequency of the current source is higher than a set value, the programmed switch is switched on, and the impedance conversion module is communicated with the output of the current conversion module, so that output impedance of the current source is increased. The voltage control current source has wide operation bandwidth and a good dynamic performance.
Description
Technical field
The present invention can be applicable to thermometrically and technology for information acquisition field, relates to a kind of wideband low noise electric current generating apparatus that is used for electrical impedance tomography.
Background technology
Electrical impedance tomography (Electrical Impedance Tomography; EIT) technology is with the distribution of object under test internal electrical impedance and is changed to a kind of novel impedance detection and the imaging technique of imageable target; It is measured object under test surface induction voltage (or electric current) signal and comes the inner distribution of impedance of reconstruction of objects through object under test being added certain safe exciting current (or voltage).The energisation mode of current drives voltage measurement, because it is simple in structure, the precision height is widely used in the present EIT imaging system.
In order to reduce the influence of object under test impedance variation to current source output drive signal, the driving source that requires to use is a constant-current source, promptly requires current source to have high output impedance.Be applied as example with the electrical impedance tomography technology in the living body detection field; The bandwidth of operation of EIT acquisition system is generally at 1KHz～1MHz at present; Can obtain the organism distribution of impedance information below the 1MHz; But organism high-frequency resistance distribution character has equally also carried abundant physiology and pathological information, and this just needs excitation current source can export the pumping signal of higher frequency.But along with the rising of frequency, receive the restriction of the performance of integrated device own and the influence of parasitic capacitance and stray capacitance, the driving force of current source and output impedance all can decline to a great extent, and limit us and obtain impedance operator accurately.Simultaneously, the electrode potential information that is placed on subject surface according to subsides distributes to the test zone internal driving, and to carry out reconstruct be " morbid state " inverse problem, and any small disturbance all might cause the greatest differences of imaging results.So the current excitation source with broadband, low noise and good dynamic characteristics can guarantee imaging precision and stability.
Summary of the invention
The present invention is directed to existing current source limited bandwidth, or bandwidth is big but the bad problem of low frequency characteristic provides a kind of VCCS that is used for electrical impedance imaging, has the bandwidth of operation and the good dynamic characteristics of broad.
Technical scheme provided by the invention is:
A kind of VCCS that is used for electrical impedance tomography comprises main control module, signal generation module, signal condition module, current conversion module, impedance conversion module and grammed switch.It is characterized in that main control module receives frequency, phase place and the amplitude information of outside input, output frequency control signal and phase control signal are to the signal generation module, and the output amplitude control signal is to the signal condition module.The signal generation module outputs to the signal condition module with the signal of the voltage form of CF that produces and phase place; The signal condition module will carry out from the signal of signal generation module input outputing to current conversion module after amplitude adjustment and high-frequency harmonic suppress, and current conversion module becomes the signal of current drives to output to the EIT system conversion of signals of input.Main control module output grammed switch control signal makes the grammed switch conducting to grammed switch when the output frequency control signal is higher than setting value, the impedance conversion module is connected with the output of current conversion module, and the output impedance of current source is increased; When the output frequency control signal is lower than setting value, grammed switch is ended, the output of impedance conversion module and current conversion module is broken off.
As further improvement of the present invention, the signal condition module comprises placed in-line successively programme-controlled gain transport and placing device and low pass filter, and the amplitude control signal outputs to the programme-controlled gain transport and placing device.
Further again, the signal generation module is a Direct Digital Frequency Synthesizers, the signal of the CF of generation and the voltage form of phase place.
Further again, the electric current generation module is the Howland current source, and it converts the voltage signal of signal condition module output to the pumping signal of current forms.
The invention has the beneficial effects as follows:
1) owing to adds impedance conversion module and grammed switch; Parasitic capacitance is to the influence of current source in the time of can compensating high frequency; The output impedance of current source when the output high-frequency signal is increased; Thereby reduced the influence of load variations, the distribution of impedance characteristic when helping to obtain the object under test high frequency to output current.
2) through adding the Howland current source, adopt operational amplifier, can obtain bigger output impedance with higher open-loop gain.
Description of drawings
Fig. 1 is the theory structure sketch map of the embodiment of the invention 1;
Fig. 2 is the theory structure sketch map of the embodiment of the invention 2;
Fig. 3 is a certain specific embodiment of impedance conversion module of the present invention;
Fig. 4 is the principle process sketch map of main control module in a certain embodiment of the present invention.
The specific embodiment
Below in conjunction with accompanying drawing the present invention is further specified.
Fig. 1 is the theory structure sketch map of the embodiment of the invention 1.As shown in the figure, a kind of VCCS that is used for electrical impedance tomography comprises main control module, signal generation module, signal condition module, current conversion module, impedance conversion module and grammed switch.Main control module receives frequency, phase place and the amplitude information of outside input.Main control module output frequency control signal and phase control signal are to the signal generation module, and the output amplitude control signal is to the signal condition module.The signal generation module outputs to the signal condition module with the signal of the voltage form of CF that produces and phase place; The signal condition module will carry out from the signal of signal generation module input outputing to current conversion module after amplitude adjustment and high-frequency harmonic suppress, and current conversion module becomes the signal of current drives to output to the EIT system conversion of signals of input.Main control module output grammed switch control signal arrives grammed switch, program control switch conduction when the output frequency control signal is higher than setting value, and the impedance conversion module is connected with the output of current conversion module, and the output impedance of current source is increased; Grammed switch ends when the output frequency control signal is lower than setting value, and the output of impedance conversion module and current conversion module is broken off.
Fig. 2 is the theory structure sketch map of the embodiment of the invention 2.As shown in the figure, comprise central controller, Direct Digital Frequency Synthesizers, programme-controlled gain transport and placing device, low pass filter, Howland current source, general impedance converter.Central controller adopts PLD to make.Central controller receives frequency, phase place and the amplitude information of outside input, and output frequency control signal and phase control signal are to Direct Digital Frequency Synthesizers.Usually, central controller receives frequency, phase place and the amplitude information that the user sets from host computer, forms frequency control signal, phase control signal and amplitude control signal.Comprise frequency control word, phase control words and amplitude control word in above-mentioned three kinds of control signals, the signal of the CF that Direct Digital Frequency Synthesizers then produces according to frequency control signal and phase control signal and the voltage form of phase place outputs to the programme-controlled gain transport and placing device.This process is a common practise to those skilled in the art.The programme-controlled gain transport and placing device receives the amplitude control signal of central controller output will carry out from the signal of Direct Digital Frequency Synthesizers input outputing to low pass filter after the amplitude adjustment.Low pass filter will carry out from the signal of Direct Digital Frequency Synthesizers input outputing to the Howland current source after high-frequency harmonic suppresses, and the Howland current source becomes the signal of current drives to output to the EIT system conversion of signals of input.Central controller links to each other with grammed switch; Central controller is judged the output frequency of current conversion module according to frequency control signal; When frequency control signal is that the grammed switch control signal of the frequency control word time output conducting that is higher than setting value makes the grammed switch conducting; General impedance converter is connected with the output of Howland current source, and the output impedance of whole device is increased; When frequency control signal is that the frequency control word grammed switch control signal that central controller output ends when being lower than setting value is ended grammed switch, the output disconnection of general impedance converter and Howland current source.
Fig. 3 is a certain specific embodiment of impedance conversion module of the present invention.The impedance conversion module is made up of general impedance converter; Be responsible for that equivalence is a ground connection inductance in circuit, as shown in the figure, comprise two operational amplifier OP1 and OP2; Fixed resistance R1, R3, R41, R42, fixed capacity C2, adjustable resistance R5 and single-pole double-throw switch (SPDT) S1.Wherein adjustable resistance R5 one end links to each other with ground, and the other end links to each other with a point.One end of resistance R 41 links to each other with a point, and the K2 point of the other end and single-pole double-throw switch (SPDT) S1 links to each other.One end of resistance R 42 links to each other with a point, and the K3 point of the other end and single-pole double-throw switch (SPDT) S1 links to each other.The K1 of single-pole double-throw switch (SPDT), K2 and K3 are connected resistance R 3, R41 and R42 respectively, are used for being connected with resistance R 3 with R42 gating one tunnel at R41.One end of resistance R 3 links to each other with K3, and the other end links to each other with the b point.One end of capacitor C 2 links to each other with the b point, and the other end links to each other with the c point.One end of resistance R 1 links to each other with the c point, and the other end links to each other with the d point.The input in the same way of operational amplifier OP1 links to each other with the d point, and reverse input end links to each other with the b point, and outfan links to each other with K3.The input in the same way of operational amplifier OP2 links to each other with a point, and reverse input end links to each other with the b point, and outfan links to each other with the c point.
When the output current frequency of whole device is higher, receive the influence of parasitic capacitance and stray capacitance, the output impedance meeting significantly reduces, and the output amplitude of constant-current source also can be affected.Introduce impedance conversion module and parasitic capacitance resonance, the output impedance when improving Current-Source Mode High Frequency.Add single-pole double-throw switch (SPDT) S2 and be used for the switching between controlling resistance R41 and the R42, the output equivalent inductance value is carried out coarse adjustment.Variable resistance R5 adopts adjustable resistance, is used for outputting inductance is carried out accurate adjustment.
The equiva lent impedance Z that sees into from the outfan d point of Fig. 3 can be represented by formula (1):
The equivalent inductance of general impedance converter can be calculated by formula (2):
In above-mentioned two formula, resistance R 4 is represented resistance R 41 or R42, and operational amplifier OP1 and operational amplifier OP2 select JFET operational amplifier OPA653 for use, and it has high input impedance, and the electric current that flows into the amplifier input is minimum.
In the specific embodiment of the present invention; Main control module is at first according to signal frequency, phase place and amplitude information; Form frequency control word, phase control words and amplitude control word; Main control module outputs to Direct Digital Frequency Synthesizers through output frequency control signal and phase control signal with frequency control word, phase control words then, through the output amplitude control signal amplitude control word is outputed to the programme-controlled gain transport and placing device.Wherein main control module is through comparison frequency control word and setting value; Whether the power frequency of judging whole device output is too high; When frequency control word is higher than setting value, when promptly power frequency is too high, export the control signal of closed grammed switch; Make the grammed switch conducting, general impedance converter is connected with the output of Howland current source; When frequency control word is lower than setting value, when promptly power frequency is not too high, export control signal by grammed switch, grammed switch is ended, at this moment, the output of general impedance converter and Howland current source is broken off.
In the specific embodiment of the present invention, can adopt broadband, low noise voltage feedback operational amplifier OPA843 to constitute the Howland current source, its open-loop gain has good dynamic property simultaneously up to 110dB.Direct Digital Frequency Synthesizers adopts AD9951 to realize, frequency that its basis obtains and phase information form the digital signal of CF and phase place, and converts digital signal to analog voltage signal output.
Claims (4)
1. VCCS that is used for electrical impedance tomography; Comprise main control module, signal generation module, signal condition module, current conversion module, impedance conversion module and grammed switch; It is characterized in that; Main control module receives frequency, phase place and the amplitude information of outside input, and output frequency control signal and phase control signal are to the signal generation module, and the output amplitude control signal is to the signal condition module; The signal generation module outputs to the signal condition module with the signal of the voltage form of CF that produces and phase place; The signal condition module will carry out from the signal of signal generation module input outputing to current conversion module after amplitude adjustment and high-frequency harmonic suppress, and current conversion module becomes the conversion of signals of input the signal output of current drives; Main control module output grammed switch control signal makes the grammed switch conducting to grammed switch when the output frequency control signal is higher than setting value, the impedance conversion module is connected with the output of current conversion module, and the output impedance of current source is increased; When the output frequency control signal is lower than setting value, grammed switch is ended, the output of impedance conversion module and current conversion module is broken off.
2. the VCCS that is used for electrical impedance tomography according to claim 1 is characterized in that, the signal condition module comprises placed in-line successively programme-controlled gain transport and placing device and low pass filter, and the amplitude control signal outputs to the programme-controlled gain transport and placing device.
3. the VCCS that is used for electrical impedance tomography according to claim 2 is characterized in that the signal generation module is a Direct Digital Frequency Synthesizers.
4. according to claim 2 or the 3 described VCCSs that are used for electrical impedance tomography, it is characterized in that the electric current generation module is the Howland current source.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105656489A (en) * | 2016-03-08 | 2016-06-08 | 天津大学 | Exciting current source for bioelectrical impedance imaging |
| CN109709428A (en) * | 2019-01-04 | 2019-05-03 | 广东电网有限责任公司 | A kind of source of high frequency current of waveform amplitude-frequency separation real-time control |
| CN113796848A (en) * | 2020-05-29 | 2021-12-17 | 芯海科技（深圳）股份有限公司 | Human body impedance measuring method, device and computer readable storage medium |
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| US5544662A (en) * | 1991-07-09 | 1996-08-13 | Rensselaer Polytechnic Institute | High-speed electric tomography |
| CN102048537A (en) * | 2010-10-08 | 2011-05-11 | 西安理工大学 | Multifrequency synchronous excitation current source used in bio-electrical impedance frequency spectrum measurement |
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2012
- 2012-01-11 CN CN2012100071794A patent/CN102525456A/en active Pending
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5544662A (en) * | 1991-07-09 | 1996-08-13 | Rensselaer Polytechnic Institute | High-speed electric tomography |
| CN102048537A (en) * | 2010-10-08 | 2011-05-11 | 西安理工大学 | Multifrequency synchronous excitation current source used in bio-electrical impedance frequency spectrum measurement |
Non-Patent Citations (3)
| Title |
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| TONG等: "Calibration methods for a multi-channel multi-frequency EIT system", 《PHYSIOL. MEAS.》, vol. 28, 31 December 2007 (2007-12-31) * |
| 周兴龙等: "电阻抗断层成像(EIT)的多频信号源设计", 《生物医学工程学进展》, vol. 29, no. 2, 31 December 2008 (2008-12-31) * |
| 鞠康等: "基于直接数字频率合成的混合频率恒流源设计", 《仪器仪表学报》, vol. 31, no. 9, 31 December 2010 (2010-12-31) * |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105656489A (en) * | 2016-03-08 | 2016-06-08 | 天津大学 | Exciting current source for bioelectrical impedance imaging |
| CN105656489B (en) * | 2016-03-08 | 2018-10-30 | 天津大学 | A kind of excitation current source for bio-electrical impedance imaging |
| CN109709428A (en) * | 2019-01-04 | 2019-05-03 | 广东电网有限责任公司 | A kind of source of high frequency current of waveform amplitude-frequency separation real-time control |
| CN113796848A (en) * | 2020-05-29 | 2021-12-17 | 芯海科技（深圳）股份有限公司 | Human body impedance measuring method, device and computer readable storage medium |
| CN113796848B (en) * | 2020-05-29 | 2024-02-06 | 芯海科技（深圳）股份有限公司 | Human body impedance measurement method, device and computer readable storage medium |
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Application publication date: 20120704 |