CN103383404B - Current measurement circuit - Google Patents

Current measurement circuit Download PDF

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Publication number
CN103383404B
CN103383404B CN201310277996.6A CN201310277996A CN103383404B CN 103383404 B CN103383404 B CN 103383404B CN 201310277996 A CN201310277996 A CN 201310277996A CN 103383404 B CN103383404 B CN 103383404B
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circuit
feedback
switch
current
current measurement
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CN103383404A (en
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宫辉
李荐民
邵贝贝
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Tsinghua University
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Tsinghua University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0023—Measuring currents or voltages from sources with high internal resistance by means of measuring circuits with high input impedance, e.g. OP-amplifiers

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

The present invention relates to a kind of current measurement circuit, comprise integrating circuit, analog to digital conversion circuit, processor unit and ON-OFF control circuit, input current signal to be measured is converted into voltage signal by described integrating circuit, described voltage signal is converted to digital signal by analog-digital conversion circuit as described, and described processor unit is for controlling this current measurement circuit and calculating the value of current signal of input according to the data of analog-digital conversion circuit as described transmission; Described integrating circuit comprises an operational amplifier and a feedback network, described operational amplifier has an inverting input, a normal phase input end and an output terminal, inverting input described in described feedback network one termination, output terminal described in another termination, described positive input end grounding; Described feedback network comprises the first feedback circuit and second feedback circuit in parallel with this first feedback circuit, and described ON-OFF control circuit controls to switch described first feedback circuit and the second feedback circuit by described processor unit.

Description

Current measurement circuit
Technical field
The present invention relates to a kind of current measurement circuit, particularly relate to a kind of metering circuit that can be used for measuring in real time great dynamic range weak current.
Background technology
When detecting radioactive ray (such as γ, β ray, neutron etc.) and other feeble signal (such as the low light level, micro-vibration etc.), being all generally first utilize suitable detector to be converted into faint electric current, then weak current being amplified and measures.When detecting feeble signal, the dynamic range of the weak current that detector exports is sometimes very large.Such as, when measuring gamma-rays with ionization chamber, the scope of the current signal that ionization chamber exports can reach 10 -14a ~ 10 -6a, belongs to the category of weak current.Weak current metering circuit is not only wanted to measure the weak current of great dynamic range like this, also need to have volume little, the feature such as can to measure in real time, thus can integrate with detector and form Weak absorption device.Common reometer cannot meet above-mentioned requirements, generally needs the special weak current metering circuit of design just may reach above-mentioned requirements.
At present, the measuring method of two kinds of weak currents is mainly contained: across resistance method and integrating capacitor method.Normally by the feedback resistance of the different resistances adopting one or more parallel connection, low current signal is converted to voltage signal across resistance method, then, by analog to digital conversion (ADC) circuit, voltage signal is converted into digital signal.But, higher across the requirement of resistance method to feedback resistance, amplifier and whole system antijamming capability, and the detection of weak current is by the restriction of feedback resistance self resistance, thus more difficult measurement 10 -15to 10 -13the atomic weak current of A.Integrating capacitor method can be used for detecting relative to across the fainter current signal of resistance method.Integrating capacitor method is by low current signal being converted into voltage signal in electric capacity upper integral, then carrys out calculating current value by the change in voltage in the adc circuit measuring unit time.Integrating capacitor method can measure atomic weak electric current by improving Measuring Time, but integrating capacitor method is by the restriction of capacitance, limited to the measurement range of weak current, and the response time is slow.
Summary of the invention
In view of this, necessaryly a kind of current measurement circuit can measuring great dynamic range weak current is provided.
A kind of current measurement circuit, comprise integrating circuit, analog to digital conversion circuit, processor unit and ON-OFF control circuit, input current signal to be measured is converted into voltage signal by described integrating circuit, described voltage signal is converted to digital signal by analog-digital conversion circuit as described, and described processor unit is for controlling this current measurement circuit and calculating the value of current signal of input according to the data of analog-digital conversion circuit as described transmission; Described integrating circuit comprises an operational amplifier and a feedback network, described operational amplifier has an inverting input, a normal phase input end and an output terminal, inverting input described in described feedback network one termination, output terminal described in another termination, described positive input end grounding; Described feedback network comprises the first feedback circuit and second feedback circuit in parallel with this first feedback circuit, the first switch that described first feedback circuit comprises a feedback resistance and connects with this feedback resistance; Described second feedback circuit comprises an integrating capacitor, second switch and one the 3rd switch, described integrating capacitor is connected with described second switch, described integrating capacitor connect with second switch after circuit and described 3rd switch in parallel, described ON-OFF control circuit controls to switch described first feedback circuit and the second feedback circuit by described processor unit.
Relative to prior art, the embodiment of the present invention by measuring the mode that described integrating capacitor and feedback resistance combine electric current in integrating circuit, because described integrating capacitor can carry out integration to fainter electric current, by measuring the rate of change of integral voltage, current signal value to be measured can be calculated.Utilize feedback resistance can measure larger weak current, thus achieve the real-time measurement of great dynamic range weak current, current measurement circuit of the present invention can measure the great dynamic range electric current of 1fA ~ 1 μ A in real time.
Accompanying drawing explanation
The theory diagram of the current measurement circuit that Fig. 1 provides for the embodiment of the present invention.
The circuit diagram of the current measurement circuit that Fig. 2 provides for the embodiment of the present invention.
Main element symbol description
Integrating circuit U1
Analog to digital conversion circuit U2
Processor unit U3
ON-OFF control circuit U4
Pre-integration circuit U5
Temperature sensor circuit U6
Digital interface circuit U7
Operational amplifier A
Feedback resistance R f
Transmission resistance R p
First switch S 1
Second switch S 2
3rd switch S 3
4th switch S 4
Integrating capacitor C i
Pre-integration electric capacity C p
Following embodiment will further illustrate the present invention in conjunction with above-mentioned accompanying drawing.
Embodiment
Below in conjunction with the accompanying drawings and the specific embodiments current measurement circuit provided by the invention is described in further detail.
Refer to Fig. 1, the embodiment of the present invention provides a kind of current measurement circuit, and this current measurement circuit can measure the great dynamic range electric current of 1fA ~ 1 μ A in real time.This current measurement circuit comprises an integrating circuit U1, analog to digital conversion (ADC) circuit U 2, processor unit U3 and ON-OFF control circuit U4.Described integrating circuit U1 is by the current signal I of input inbe converted into voltage signal, described voltage signal is converted into digital signal and imports described processor unit U3 into by described adc circuit U2, and described processor unit U3 receives described digital signal union and draws described current signal I insize.
See also Fig. 2, described integrating circuit U1 comprises an operational amplifier A and a feedback network further.
Described operational amplifier A has an inverting input (-), a normal phase input end (+) and an output terminal (Vo).Described current signal I to be detected ininput from described inverting input, described positive input end grounding.The inverting input of operational amplifier A described in one termination of described feedback network, the output terminal of operational amplifier A described in another termination.
Described operational amplifier A can choose the imported operational amplifier of the lower FET of leakage current, and described leakage current is less than 1 skin peace (pA).The model of operational amplifier A described in the invention process is AD549.
Described feedback network comprises one first feedback circuit and second feedback circuit in parallel with described first feedback circuit.Described first feedback circuit comprises a feedback resistance R fand with this feedback resistance R ffirst switch S of series connection 1.This feedback resistance R fresistance can be 100K to 100M.The R of feedback resistance described in the embodiment of the present invention fresistance be 10M.This first feedback circuit can be used to measure the larger weak current of current value.In embodiments of the present invention, this first feedback circuit can measure the electric current being greater than 1nA.In addition, described feedback network can comprise the first feedback circuit of multiple parallel connection, the feedback resistance R in the plurality of first feedback circuit fresistance value different, thus the measurement of different range ability current signal can be realized.
Described second feedback circuit comprises an integrating capacitor C i, second switch S 2, and the 3rd switch S 3.Described integrating capacitor C iwith described second switch S 2series connection, described integrating capacitor C iwith described second switch S 2with described 3rd switch S after series connection 3in parallel.Described second switch S 2for controlling the disconnection of this second feedback circuit with closed.Described 3rd switch S 3for controlling described integrating capacitor C ithe bleed off of the electric charge of upper accumulation.Preferably, this integrating capacitor C icapacitance scope be 1pF to 1000pF.Integrating capacitor C described in the embodiment of the present invention icapacitance be 50pF.This second feedback circuit can be used to measure the relatively little weak current of current value.In embodiments of the present invention, this second feedback circuit can measure the electric current being less than 10nA.
The voltage signal that described adc circuit U2 is used for described integrating circuit U1 exports is converted to digital signal.Particularly, this adc circuit U2 can to described integrating capacitor C ithe integral voltage of upper accumulation and feedback resistance R fon voltage carry out gathering and changing into digital signal.Described adc circuit realizes by an ADC chip.Adc circuit described in the embodiment of the present invention adopts 24 ∑s-Δ type ADC chip.
Described ON-OFF control circuit U4 can be used to switch described first feedback circuit and the second feedback circuit to realize the real-time detection of current signal in different range ability.Particularly, described ON-OFF control circuit U4 is used for controlling described first switch S 1, second switch S 2and the 3rd switch S 3closed and disconnected.Described first switch S 1, second switch S 2and the 3rd switch S 3be the switch of high-insulativity.Described first switch S 1, second switch S 2and the 3rd switch S 3insulation resistance be not less than 10 12.
Further, described current measurement circuit comprises a pre-integration circuit U 5, and this pre-integration circuit U 5 can at described integrating capacitor C ithe current signal I to input is carried out in the process of bleed off electric charge incarry out integration, thus the dead time that this current measurement circuit exists current detecting can be avoided, to reach the object of the electric current detecting described input in real time.
This pre-integration circuit U 5 comprises a pre-integration electric capacity C p, transmission resistance R pand the 4th switch S 4.Described pre-integration electric capacity C pone end ground connection, transmit resistance R described in another termination p.Described 4th switch S 4resistance R is transmitted described in one termination p, the other end is the output terminal of this pre-integration circuit U 5, connects the input end of described integrating circuit U1, particularly, connects the inverting input of described operational amplifier A.
Described pre-integration electric capacity C pcapacitance scope be 1pF to 10nF.Described 4th switch S 4for the switch of high-insulativity.Described 4th switch S 4insulation resistance be not less than 10 12.Described 4th switch S 4controlled by described ON-OFF control circuit U4.
Integrating capacitor C in described integrating circuit U1 iduring bleed off electric charge, described 4th switch S 4disconnect, the current signal I of input inat described pre-integration electric capacity C pupper integral.After described integrating circuit U1 completes electric charge bleed off, described 4th switch S 4closed, described pre-integration electric capacity C pthe electric charge of upper accumulation is through described transmission resistance R prelease, flows to integrating circuit U1, then gathers to calculate by described adc circuit U2 and processor unit U3 to obtain current signal size, thus can solve the problem that traditional integrating capacitor method exists the dead time.Be appreciated that when not considering the dead time that described integrating circuit U1 bleed off electric charge causes, described pre-integration circuit U 5 is an optional element in this current measurement circuit.When described current measurement circuit does not comprise described pre-integration circuit U 5, current signal I to be detected inbe directly inputted in described integrating circuit U1, in the embodiment of the present invention, described current signal I to be detected indirectly inputted by the inverting input of described operational amplifier A.
Described processor unit U3, for controlling described ON-OFF control circuit U4, reads the data of described adc circuit U2 output terminal and the current signal I of the input of process acquisition in real time inmeasurement result.Described processor unit U3 can be Programmadle logic device, as microcontroller, microprocessor or FPGA(FieldProgrammableGateArray).This programmable logic device (PLD) can complete the real-time process of the control and measurement result of measurement automatically, draws the final measurement of input current.The U3 of processor unit described in the embodiment of the present invention adopts described microcontroller implementation.
Described current measurement circuit can comprise a temperature sensor circuit U6 further, for gathering environment temperature, with to current signal I inmeasurement result correct, thus improve the measuring accuracy of this current measurement circuit.Described temperature sensor circuit U6 realizes by temperature sensor and the metering circuit that is connected with this temperature sensor.Described temperature sensor can be thermistor.In addition, described temperature sensor circuit U6 also can adopt temperature survey integrated chip to realize.The environment temperature that described temperature sensor circuit U6 gathers is transferred to described processor unit U3 and corrects.
Described current measurement circuit can comprise a digital interface circuit U7 further and be used for described current signal I inmeasurement result be transferred to other electronic equipments and carry out recording, analyze or showing in real time.Particularly, described digital interface circuit U7 is by the mode of Ethernet, usb communication or serial communication and other electronic equipment communications.This electronic equipment can be computing machine, liquid crystal display or charactron.
The course of work of this current measurement circuit is as follows: first, and described second feedback circuit is started working, i.e. described second switch S 2and the 4th switch S 4closed, described first switch S 1and the 3rd switch S 3 disconnect, described current signal I to be detected inat described integrating capacitor C iupper integral produces integral voltage, and described integral voltage is changed into digital data transmission and carries out process acquisition current signal I to described processor unit U3 by described adc circuit U2 inmeasurement result.When current signal I being detected invalue excessive (that is, the current signal value measured close to or exceed the higher limit of the current signal that described second feedback circuit can record itself) time, described second feedback circuit quits work, and described first feedback circuit is started working, i.e. described first switch S 1with the 4th switch S 4closed, described second switch S 2with the 3rd switch S 3disconnect, the current signal I of described input inby at described feedback resistance R fthe voltage of upper generation detects its current signal I insize.Similarly, when described processor unit U3 obtains current signal I intime less, namely, the current signal value measured close to or when being less than the lower limit of the range of current that described first feedback circuit can be measured, described processor unit U3 switches described first feedback circuit carries out current signal again detection to described second feedback circuit.Thus the current signal value that can detect accurately in real time in great dynamic range.
When described second feedback circuit work, the current signal I of input inat described integrating capacitor C iupper integral produces integral voltage, when this integral voltage exceedes this integrating capacitor C ithreshold value time, second switch S 2with S 3close, the 4th switch S simultaneously 4disconnect, make this integrating capacitor C icarry out electric charge bleed off.The current signal I now inputted inat described pre-integration electric capacity C pupper integral, as described integrating capacitor C iafter electric charge bleed off, described second feedback circuit normally works, i.e. the 3rd switch S 3disconnect, second switch closes S 1, the 4th switch S simultaneously 4closed, described pre-integration electric capacity C pthe electric charge of upper accumulation is by described transmission resistance R pbe transferred to described integrating capacitor C iupper integral, the integral voltage of generation obtains described integrating capacitor C by adc circuit U2 and processor unit U3 iwithin the time period of bleed off electric charge, the size of the current signal value of input, thus the existence avoiding this current measurement circuit dead time, achieve the real-time detection of great dynamic range electric current.
The embodiment of the present invention by measuring the mode that described integrating capacitor and feedback resistance combine electric current in integrating circuit, because described integrating capacitor can carry out integration to fainter electric current, by measuring the rate of change of integral voltage, current signal value to be measured can be calculated.Utilize feedback resistance can measure larger weak current, thus achieve the measurement of great dynamic range weak current, current measurement circuit of the present invention can measure the great dynamic range electric current of 1fA ~ 1 μ A in real time.In addition, because described feedback resistance is combined with integrating capacitor, therefore, feedback resistance chooses conventional low-temperature coefficient resistance, greatly can reduce the difficulty of circuit design and feedback resistance type selecting.In addition, the real-time switching between the first feedback circuit and the second feedback circuit can be realized by ON-OFF control circuit, i.e. the switching of different measuring range, thus the real-time measurement of great dynamic range weak current can be realized.Finally, the components and parts in current measurement circuit of the present invention are conventional components and parts, therefore, are easy to practical application, and this current measurement circuit have less volume can be embedded into need measure weak current equipment in use.
In addition, those skilled in the art also can do other changes in spirit of the present invention, and certainly, these changes done according to the present invention's spirit, all should be included within the present invention's scope required for protection.

Claims (6)

1. a current measurement circuit, comprise integrating circuit, analog to digital conversion circuit, processor unit and ON-OFF control circuit, input current signal to be measured is converted into voltage signal by described integrating circuit, described voltage signal is converted to digital signal by analog-digital conversion circuit as described, and described processor unit is for controlling this current measurement circuit and calculating the value of current signal of input according to the data of analog-digital conversion circuit as described transmission; It is characterized in that,
Described integrating circuit comprises an operational amplifier and a feedback network, described operational amplifier has an inverting input, a normal phase input end and an output terminal, inverting input described in described feedback network one termination, output terminal described in another termination, described positive input end grounding; Described feedback network comprises the first feedback circuit and second feedback circuit in parallel with this first feedback circuit, the first switch that described first feedback circuit comprises a feedback resistance and connects with this feedback resistance; Described second feedback circuit comprises an integrating capacitor, second switch and one the 3rd switch, described integrating capacitor is connected with described second switch, described integrating capacitor connect with second switch after circuit and described 3rd switch in parallel, described ON-OFF control circuit controls to switch described first feedback circuit and the second feedback circuit by described processor unit;
Described current measurement circuit comprises a pre-integration circuit further, described pre-integration circuit is used for carrying out integration to the current signal of input in the process of described integrating capacitor electric charge bleed off, described pre-integration circuit comprises a pre-integration electric capacity, transmission resistance and one the 4th switch, described pre-integration electric capacity one end ground connection, the other end is electrically connected with one end of described transmission resistance, described transmission resistance is connected with the 4th switch, resistance is transmitted, the inverting input of operational amplifier described in another termination described in one termination of described 4th switch.
2. current measurement circuit as claimed in claim 1, it is characterized in that, the resistance of described feedback resistance is 100K Ω to 100M Ω.
3. current measurement circuit as claimed in claim 1, it is characterized in that, the capacitance scope of described integrating capacitor is 1pF to 1000pF.
4. current measurement circuit as claimed in claim 1, is characterized in that, comprise one further for the temperature sensor circuit of testing environment temperature, the described environment temperature detected is input to described processor unit and corrects the current signal value detected.
5. current measurement circuit as claimed in claim 1, is characterized in that, comprise a digital interface circuit further, and this digital interface circuit is used for the current signal value detected to be transferred to an electronic equipment.
6. current measurement circuit as claimed in claim 1, it is characterized in that, the capacitance scope of described pre-integration electric capacity is 1pF to 10nF.
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