CN105548654A - Circuit and method for weak current detection - Google Patents
Circuit and method for weak current detection Download PDFInfo
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- CN105548654A CN105548654A CN201510888507.XA CN201510888507A CN105548654A CN 105548654 A CN105548654 A CN 105548654A CN 201510888507 A CN201510888507 A CN 201510888507A CN 105548654 A CN105548654 A CN 105548654A
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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
Abstract
The invention discloses a circuit and a method for weak current detection and belongs to the current detection field. Geminate field effect transistors are employed by an input end to form a difference amplifier, and I-V conversion of a weak current is carried out; a voltage signal after conversion is sent to two sets of proportion operation circuits having symmetric in-phase input modes for proportion operation amplification; difference operation amplification of the voltage signal after proportion operation amplification is carried out, and a difference operation amplification voltage magnitude is measured. According to the method and the device, the junction type geminate field effect transistors are employed to form the difference amplifier as an input level, so input impedance is improved, and the relatively high common-mode inhibition ratio is acquired; the precise proportion operation circuit structures in the symmetric in-phase input modes are employed as the middle level, input impedance is further improved, and measurement precision is improved; the multiple operation amplifier difference amplification detection technology is employed, conflicts of useful-signal weakness and relatively high common-mode interference can be effectively solved, and high gain, high input resistance and the high common-mode inhibition ratio of the detection circuit are realized.
Description
Technical field
The invention belongs to current detecting field, be specifically related to a kind of weak current circuit and method.
Background technology
Existing weak current is generally adopt current sampling method, namely by special accurate sample resistance, current signal is transformed into voltage sampling signal, and voltage sampling signal and reference voltage compare computing, carry out FEEDBACK CONTROL by operational amplifier, thus reach current sense function.
Along with the reduction detecting electric current, the input impedance of operational amplifier will increase the impact of sensed current, has a strong impact on current detection accuracy.For highly sophisticated products such as semiconductor analysis instrument, current detection sensitivity requires often up to nA level, and even up to pA level, adopt traditional electric current detecting method, the precision not only detected is low, even cannot carry out current detecting.
Summary of the invention
For the above-mentioned technical matters existed in prior art, the present invention proposes a kind of weak current circuit and method, reasonable in design, overcome the deficiencies in the prior art, measuring accuracy is high.
To achieve these goals, the present invention adopts following technical scheme:
A kind of weak current circuit, comprises input stage amplifying circuit, intermediate amplifying circuit, output stage amplifier circuit, described input stage amplifying circuit comprise by technotron to pipe form to pipe differential amplifier circuit; Described intermediate amplifying circuit adopts two groups of scale operation amplifying circuits with homophase input form; Described output stage amplifier circuit adopts calculus of differences amplifying circuit;
Described input stage amplifying circuit carries out I-V conversion, converts low current signal to voltage signal; Voltage signal after conversion is carried out preliminary scale operation and amplifies by described intermediate amplifying circuit; Voltage signal after scale operation amplifies by described output stage amplifier circuit again carries out calculus of differences amplification, finally measures amplifying magnitude of voltage to calculus of differences.
The differential amplifier circuit that described input stage amplifying circuit mainly adopts technotron to form pipe, input impedance can be improved, obtain higher common-mode rejection ratio, reduce input bias current, thus effectively improve the sensitivity that operational amplification circuit detects low current signal;
Described intermediate amplifying circuit is homophase input mode scale operation amplifying circuit, adopts homophase input mode, and the signal realizing larger gain amplifies, and improves circuit input impedance further simultaneously;
Described output stage amplifier circuit is calculus of differences amplifying circuit, effectively can solve the faint and contradiction that common mode interference is relatively high of useful signal, realize the high-gain of testing circuit, high input resistance and high cmrr, improve measurement sensistivity, expansion measurement range, improves measurement result reliability.
Preferably, described input stage amplifying circuit also comprises drain current adjustment circuit and working point arranges circuit, described drain current adjustment circuit is for adjusting the drain current to pipe differential amplifier circuit, and described working point arranges circuit for determining the working point in pipe differential amplifier circuit; Described drain current adjustment circuit and working point arrange circuit and are connected with to pipe differential amplifier circuit respectively by circuit.
Preferably, described drain current adjustment circuit adopts high precision matching resistor, is convenient to adjust the consistance to the drain current of pipe differential amplifier circuit.
Preferably, the circuit structure of described intermediate amplifying circuit adopts symmetric form, and peripheral resistance adopts high-accuracy resistance, drift, noise, offset voltage and offset current etc. is cancelled each other, can improve the measuring accuracy of circuit;
Preferably, this weak current circuit also comprises gain control feedback circuit, and this partial circuit, for controlling feedback factor and the phase compensation of weak current circuit, extends current measuring range, and further increases measuring accuracy.
Preferably, described drain current adjustment circuit comprises the first adjustable resistance and drain resistance, and drain resistance adopts matching resistor; One of them exit of first adjustable resistance is connected with the supply voltage of VCC, and two exits that the first adjustable resistance is relative are connected to one end of matching resistor in drain resistance respectively;
Described working point arranges circuit and comprises the 3rd technotron, the 4th resistance, the 5th resistance and the 6th resistance; One end ground connection of the 4th resistance, the other end of the 4th resistance and one end composition common port of the 5th resistance are connected to the grid of the 3rd technotron, the other end of the 5th resistance and one end composition common port of the 6th resistance are connected to the supply voltage of Vee, and the other end of the 6th resistance is connected to the source electrode of the 3rd technotron.
Preferably, described first technotron, the second technotron, the second resistance, the 3rd resistance and the second adjustable resistance are comprised to pipe differential amplifier circuit; One end of second resistance is connected to the grid of the first technotron, one end of 3rd resistance is connected to the grid of the second technotron, the other end ground connection of the 3rd resistance, two exits that second adjustable resistance is relative are connected between the source electrode of the first technotron and the source electrode of the second technotron, the drain electrode of the first technotron and the drain electrode of the second technotron are connected to the other end of matching resistor in drain resistance respectively, and another exit of the second adjustable resistance is connected to the drain electrode of the 3rd technotron.
Preferably, described intermediate amplifying circuit comprises the first operational amplifier, the second operational amplifier, the 12 resistance, the 13 resistance and the 3rd adjustable resistance, the in-phase input end of the first operational amplifier and the in-phase input end of the second operational amplifier are connected to the drain electrode of the first technotron and the drain electrode of the second technotron respectively, 12 resistance is connected between the inverting input of the first operational amplifier and its output terminal, 13 resistance is connected between the inverting input of the second operational amplifier and its output terminal, two exits that 3rd adjustable resistance is relative are connected between the inverting input of the first operational amplifier and the inverting input of the second operational amplifier, another exit of 3rd adjustable resistance is connected to the inverting input of the second operational amplifier.
Preferably, calculus of differences amplifying circuit comprises the 3rd operational amplifier, the 14 resistance, the 15 resistance, the 16 resistance and the 17 resistance; One end of 14 resistance is connected to the output terminal of the first operational amplifier, the other end of the 14 resistance and one end composition common port of the 16 resistance are connected to the inverting input of the 3rd operational amplifier, the other end of the 16 resistance is connected to the output terminal of the 3rd operational amplifier, one end of 15 resistance is connected to the output terminal of the second operational amplifier, the other end of the 15 resistance and one end composition common port of the 17 resistance are connected to the in-phase input end of the 3rd operational amplifier, the other end ground connection of the 17 resistance.
Preferably, described gain control feedback circuit comprises the 7th resistance, the 8th resistance and relay, and one end of the 7th resistance and the other end of the second resistance are connected to I
sone end of current source, I
sthe other end ground connection of current source, the other end of the 7th resistance and the 8th resistance are connected to one end of relay, and the other end of the 8th resistance and the other end composition common port of relay are connected to the output terminal of the 3rd operational amplifier.
The principle of weak current circuit of the present invention is:
When weak current is measured, low noise is the key of input stage Design of Amplification Circuit, the noise size of this one-level directly determines the noisiness of whole amplifier, the noise ratio bipolar transistor of field effect transistor is little, technotron noise figure is lower, therefore input stage adopts technotron as differential input structure, and meanwhile, technotron has very high direct current input resistance R
gS, so the open loop difference-mode input resistance of whole circuit is up to 10
11~ 10
14Ω, improves input resistance effectively.In addition, adopt and can also obtain higher common-mode rejection ratio to pipe, during technotron work, what its PN junction added is reverse voltage, and grid current is substantially zero, so the input bias current of circuit can be little of 10
-11~ 10
-12a.High input impedance makes tested weak current almost completely by feedback resistance, and almost nil by the electric current of amplifier internal resistance, makes measurement more accurate.
Because the noise requirements of input stage amplifying circuit is strict, very high gain can not be taken into account, therefore adopt integrated transporting discharging to be connected into scale operation structure to improve the gain of whole circuit in interstage amplifier section, thus amplify tested low current signal as far as possible.Meanwhile, adopt homophase input mode, circuit input impedance is improved further.Circuit structure adopts symmetric form, and peripheral resistance adopts high-accuracy resistance, and drift, noise, offset voltage and offset current etc. are cancelled each other, and improves the measuring accuracy of circuit, otherwise the enlargement factor of circuit, common-mode rejection ratio and precision etc. can obviously reduce.
Output stage amplifier circuit takes amplifier differential amplification detection technique, efficiently solves the faint and contradiction that common mode interference is relatively high of useful signal, realizes the high-gain of testing circuit, high input resistance and high cmrr.
In addition, the present invention also mentions a kind of weak current method, and the method adopts above-mentioned a kind of weak current circuit, carries out in accordance with the following steps:
Step 1: carry out I-V conversion by input stage amplifying circuit, convert low current signal to voltage signal;
Step 2: by intermediate amplifying circuit, the voltage signal after conversion is carried out preliminary scale operation and amplify;
Step 3: carry out calculus of differences amplification by the voltage signal after scale operation amplifies by output stage amplifier circuit, obtain calculus of differences and amplify magnitude of voltage;
Step 4: magnitude of voltage is amplified to calculus of differences and measures.
The Advantageous Effects that the present invention brings:
The present invention proposes a kind of weak current circuit and method, compared with prior art, a kind of weak current circuit and method, adopt and form differential amplifier as input stage by technotron to pipe, improve input impedance, obtain higher common-mode rejection ratio; Take the accurate scaling circuit structure of symmetrical homophase input form, circuit input impedance improves further, and drift, noise, offset voltage and offset current etc. are cancelled each other, and improves the measuring accuracy of circuit; Take many amplifiers differential amplification detection technique, efficiently solve the faint and contradiction that common mode interference is relatively high of useful signal, achieve the high-gain of testing circuit, high input resistance and high cmrr; Adopt gain control feedback circuit, not only extend current measuring range, further increase measuring accuracy.
Accompanying drawing explanation
Fig. 1 is the circuit structure block diagram of a kind of weak current circuit of the present invention.
Fig. 2 is the circuit diagram of a kind of weak current circuit of the present invention.
Fig. 3 is the FB(flow block) of a kind of weak current method of the present invention.
Wherein, 1-input stage amplifying circuit; 101-drain current adjustment circuit; 102-is to pipe differential amplifier circuit; 103-working point arranges circuit; 2-middle rank amplifying circuit; 3-output stage amplifier circuit; 4-gain control feedback circuit.
Embodiment
Below in conjunction with accompanying drawing and embodiment, the present invention is described in further detail:
Embodiment 1:
As shown in Figure 1, comprise input stage amplifying circuit 1, intermediate amplifying circuit 2, output stage amplifier circuit 3, described input stage amplifying circuit 1 comprise by technotron to pipe form to pipe differential amplifier circuit 102; Described intermediate amplifying circuit 2 adopts two groups of scale operation amplifying circuits with homophase input form; Described output stage amplifier circuit 3 adopts calculus of differences amplifying circuit.
Weak current is input to the input end to pipe differential amplifier circuit 102, carries out preposition differential amplification, increases input impedance, current signal is transformed into voltage signal simultaneously, is convenient to back-end circuit signal transacting; The differential voltage signal exported the output terminal of pipe differential amplifier circuit 102 is input to the intermediate amplifying circuit 2 of two scale operation amplifying circuits compositions respectively, carries out the amplification of secondary scale operation, and further increases input impedance; Middle rank amplifying circuit 2 outputs signal output stage amplifier circuit 3, carries out calculus of differences and amplifies output, and again increase input impedance, carry out input-output impedance transformation simultaneously, reduce output impedance, avoid back-end circuit on the impact of testing circuit of the present invention; Drain current adjustment circuit 101 is for adjusting the drain current to pipe differential amplifier circuit 102, working point arranges circuit 103 for determining the working point in pipe differential amplifier circuit 102, and gain control feedback circuit 4 is for controlling feedback factor and the phase compensation of weak current circuit.
As shown in Figure 2, when measuring weak current, adopt at the input end of amplifier and be made up of to pipe differential amplifier circuit 102 as input stage pipe technotron, improve input resistance, technotron has very high direct current input resistance R
gS, so the open loop difference-mode input resistance of whole circuit is up to 10
11~ 10
14Ω; Meanwhile, adopt to pipe also can obtain higher common-mode rejection ratio; During technotron work, what its PN junction added is reverse voltage, and grid current is substantially zero, so the input bias current of circuit can be little of 10
-11~ 10
-12a; High input impedance makes tested weak current almost completely by feedback resistance, and almost nil by the electric current of amplifier internal resistance, makes measurement more accurate.
Described drain current adjustment circuit 101 comprises the first adjustable resistance R9 and drain resistance R1, and drain resistance R1 adopts high precision matching resistor, is convenient to adjust the consistance to the drain current of pipe differential amplifier circuit 102; One of them exit of first adjustable resistance R9 is connected with the supply voltage of VCC, and two exits that the first adjustable resistance R9 is relative are connected to one end of matching resistor in drain resistance R1 respectively.
Described working point arranges circuit 103 and comprises the 3rd technotron V3, the 4th resistance R4, the 5th resistance R5 and the 6th resistance R6; One end ground connection of the 4th resistance R4, the other end of the 4th resistance R4 and one end composition common port of the 5th resistance R5 are connected to the grid of the 3rd technotron V3, the other end of the 5th resistance R5 and one end composition common port of the 6th resistance R6 are connected to the supply voltage of Vee, and the other end of the 6th resistance R6 is connected to the source electrode of the 3rd technotron V3.
Described first technotron V1, the second technotron V2, the second resistance R2, the 3rd resistance R3 and the second adjustable resistance R10 are comprised to pipe differential amplifier circuit 102, one end of second resistance R2 is connected to the grid of the first technotron V1, one end of 3rd resistance R3 is connected to the grid of the second technotron V2, the other end ground connection of the 3rd resistance R3, two exits that second adjustable resistance R10 is relative are connected between the source electrode of the first technotron V1 and the source electrode of the second technotron V2, the drain electrode of the first technotron V1 and the drain electrode of the second technotron V2 are connected to the other end of matching resistor in drain resistance respectively, another exit of second adjustable resistance R10 is connected to the drain electrode of the 3rd technotron V3.
Described intermediate amplifying circuit comprises the first operational amplifier N1, the second operational amplifier N2, the 12 resistance R12, the 13 resistance R13 and the 3rd adjustable resistance R11, the in-phase input end of the first operational amplifier N1 and the in-phase input end of the second operational amplifier N2 are connected to the drain electrode of the first technotron V1 and the drain electrode of the second technotron V2 respectively, between the inverting input that 12 resistance R12 is connected to the first operational amplifier N1 and its output terminal, between the inverting input that 13 resistance R13 is connected to the second operational amplifier N2 and its output terminal, two exits that 3rd adjustable resistance R11 is relative are connected between the inverting input of the first operational amplifier N1 and the inverting input of the second operational amplifier N2, another exit of 3rd adjustable resistance R11 is connected to the inverting input of the second operational amplifier N2.
Calculus of differences amplifying circuit comprises the 3rd operational amplifier N3, the 14 resistance R14, the 15 resistance R15, the 16 resistance R16 and the 17 resistance R17, one end of 14 resistance R14 is connected to the output terminal of the first operational amplifier N1, the other end of the 14 resistance R14 and one end composition common port of the 16 resistance R16 are connected to the inverting input of the 3rd operational amplifier N3, the other end of the 16 resistance R16 is connected to the output terminal of the 3rd operational amplifier N3, one end of 15 resistance R15 is connected to the output terminal of the second operational amplifier N2, the other end of the 15 resistance R15 and one end composition common port of the 17 resistance R17 are connected to the in-phase input end of the 3rd operational amplifier N3, the other end ground connection of the 17 resistance R17.
The other end of one end and the second resistance R2 that described gain control feedback circuit 4 comprises the 7th resistance R7, the 8th resistance R8 and relay K the 1, seven resistance R7 is connected to I
sone end of current source, I
sthe other end ground connection of current source, the other end of the 7th resistance R7 and the 8th resistance R8 are connected to one end of relay K 1, and the other end of the 8th resistance R8 and the other end composition common port of relay K 1 are connected to the output terminal of the 3rd operational amplifier N3.
V1, V2 in Fig. 2 adopt technotron to pipe, to improve the common-mode rejection ratio to pipe differential amplifier circuit 102; R1 is drain resistance, adopts high precision matching resistor, is convenient to the consistance adjusting differential pair tube drain current; R2, R3 form symmetrical damping current-limiting resistance, for the protection of junction field to pipe V1, V2, and for eliminating grid oscillator signal; Determined the working point of V3 by R4, R5, ensure that it is operated in the quiescent operation state required for circuit; R9, R10 adopt accurate multiturn potentiometer, for adjusting the drain current of junction field to pipe V1, V2, thus reduce offset voltage and the offset current of circuit.R9 adopts low-noise accurate potentiometer, adjustable intermediate amplifying circuit 2 gain.Junction field is selected pipe V1, V2's, should according to resistance R
gSwith grid current I
gSmagnitude relationship carry out corresponding type selecting, by the input end serial connection field effect transistor at amplifier to pipe V1, V2, improve the input impedance of amplifier.
N1, N2 in Fig. 2 adopt the high-accuracy amplifier AD706 of the low input current of two-way, and input current is within 50pA; N3 adopts the high-accuracy amplifier OPA27 of ultra-low noise; Both be connected into scaling circuit form, and all adopt homophase input mode, make circuit input impedance high.Three-stage amplifier can ensure that circuit has good amplifying power, and circuit equivalent gain is more than 100dB.Circuit structure adopts symmetric form, peripheral resistance adopts high-accuracy resistance, drift, noise, offset voltage and offset current etc. are cancelled each other, and to improve the measuring accuracy of circuit, otherwise the enlargement factor of circuit, common-mode rejection ratio and precision etc. will obviously reduce.Disconnected and the short principle of void according to the void of integrated transporting discharging, can export and input pass is: Vo=-Is × R, and in formula, R is the series equivalent resistance value of R7 and R8.
R7, R8 in Fig. 2 adopt the ultrahigh precision resistor of ACC company, have high precision, high stability.K1 adopts the high insulated electro resistance type relay of 3U company, and have good electromagnetic shielding characteristic, the gear shift gain for tested electric current controls.When tested electric current is in 10pA ~ 100pA scope, control signal control K1 disconnects, and R equals R7 and R8 series connection resistance; When tested electric current is in 100pA ~ 1000pA scope, control signal control K1 closes, and R equals R7 resistance.So just the gain of realizing circuit can control conversion, its beneficial effect is can not only extend current measurement range, and can further increase measuring accuracy.
By model machine circuit test data result in table 1:
Table 1 test data
As can be seen from Table 1, model machine circuit of the present invention all has the good linearity within the scope of 10pA ~ 100pA and 100pA ~ 1000pA, and circuit has higher weak current measurement sensitivity and degree of accuracy.For the weak current being low to moderate 10pA, its maximum error of measuring is only 1.128%, and for the weak current of electric current 1000pA, its measuring error is more merely 0.021%.Owing to have employed gain control feedback circuit, not only extend current measuring range, further increase measuring accuracy in high-grade range ability.
Embodiment 2:
On the basis of above-described embodiment, the invention provides a kind of weak current method (as shown in Figure 3), for detecting weak current, wherein, carrying out in accordance with the following steps:
Step 1: carry out I-V conversion by input stage amplifying circuit, convert low current signal to voltage signal;
Step 2: by intermediate amplifying circuit, the voltage signal after conversion is carried out preliminary scale operation and amplify;
Step 3: carry out calculus of differences amplification by the voltage signal after scale operation amplifies by output stage amplifier circuit, obtain calculus of differences and amplify magnitude of voltage;
Step 4: magnitude of voltage is amplified to calculus of differences and measures.
A kind of weak current circuit of the present invention and method, adopt and form differential amplifier as input stage by technotron to pipe, improve input impedance, obtain higher common-mode rejection ratio; Take the accurate scaling circuit structure of symmetrical homophase input form, circuit input impedance improves further, and drift, noise, offset voltage and offset current etc. are cancelled each other, and improves the measuring accuracy of circuit; Take many amplifiers differential amplification detection technique, efficiently solve the faint and contradiction that common mode interference is relatively high of useful signal, achieve the high-gain of testing circuit, high input resistance and high cmrr; Adopt gain control feedback circuit, not only extend current measuring range, further increase measuring accuracy.Circuit of the present invention has higher measurement sensitivity and good measuring accuracy, the linearity, reaches the design object of patent of the present invention.
Certainly, above-mentioned explanation is not limitation of the present invention, and the present invention is also not limited in above-mentioned citing, and the change that those skilled in the art make in essential scope of the present invention, remodeling, interpolation or replacement also should belong to protection scope of the present invention.
Claims (10)
1. a weak current circuit, comprises input stage amplifying circuit, intermediate amplifying circuit, output stage amplifier circuit, it is characterized in that: described input stage amplifying circuit comprise by technotron to pipe form to pipe differential amplifier circuit; Described intermediate amplifying circuit adopts two groups of scale operation amplifying circuits with homophase input form; Described output stage amplifier circuit adopts calculus of differences amplifying circuit;
Described input stage amplifying circuit carries out I-V conversion, converts low current signal to voltage signal; Voltage signal after conversion is carried out preliminary scale operation and amplifies by described intermediate amplifying circuit; Voltage signal after scale operation amplifies by described output stage amplifier circuit again carries out calculus of differences amplification, finally measures amplifying magnitude of voltage to calculus of differences.
2. weak current circuit according to claim 1, it is characterized in that: described input stage amplifying circuit also comprises drain current adjustment circuit and working point arranges circuit, described drain current adjustment circuit is for adjusting the drain current to pipe differential amplifier circuit, and described working point arranges circuit for determining the working point in pipe differential amplifier circuit; Described drain current adjustment circuit and working point arrange circuit and are connected with to pipe differential amplifier circuit respectively by circuit.
3. weak current circuit according to claim 1, is characterized in that: the circuit structure of described intermediate amplifying circuit adopts symmetric form.
4. weak current circuit according to claim 1, is characterized in that: this weak current circuit also comprises gain control feedback circuit, and described gain control feedback circuit is for controlling feedback factor and the phase compensation of weak current circuit.
5. weak current circuit according to claim 2, is characterized in that: described drain current adjustment circuit comprises the first adjustable resistance and drain resistance, and drain resistance adopts matching resistor; One of them exit of first adjustable resistance is connected with the supply voltage of VCC, and two exits that the first adjustable resistance is relative are connected to one end of matching resistor in drain resistance respectively;
Described working point arranges circuit and comprises the 3rd technotron, the 4th resistance, the 5th resistance and the 6th resistance; One end ground connection of the 4th resistance, the other end of the 4th resistance and one end composition common port of the 5th resistance are connected to the grid of the 3rd technotron, the other end of the 5th resistance and one end composition common port of the 6th resistance are connected to the supply voltage of Vee, and the other end of the 6th resistance is connected to the source electrode of the 3rd technotron.
6. weak current circuit according to claim 1, is characterized in that: describedly comprise the first technotron, the second technotron, the second resistance, the 3rd resistance and the second adjustable resistance to pipe differential amplifier circuit; One end of second resistance is connected to the grid of the first technotron, one end of 3rd resistance is connected to the grid of the second technotron, the other end ground connection of the 3rd resistance, two exits that second adjustable resistance is relative are connected between the source electrode of the first technotron and the source electrode of the second technotron, the drain electrode of the first technotron and the drain electrode of the second technotron are connected to the other end of matching resistor in drain resistance respectively, and another exit of the second adjustable resistance is connected to the drain electrode of the 3rd technotron.
7. weak current circuit according to claim 1, is characterized in that: described intermediate amplifying circuit comprises the first operational amplifier, the second operational amplifier, the 12 resistance, the 13 resistance and the 3rd adjustable resistance, the in-phase input end of the first operational amplifier and the in-phase input end of the second operational amplifier are connected to the drain electrode of the first technotron and the drain electrode of the second technotron respectively, 12 resistance is connected between the inverting input of the first operational amplifier and its output terminal, 13 resistance is connected between the inverting input of the second operational amplifier and its output terminal, two exits that 3rd adjustable resistance is relative are connected between the inverting input of the first operational amplifier and the inverting input of the second operational amplifier, another exit of 3rd adjustable resistance is connected to the inverting input of the second operational amplifier.
8. weak current circuit according to claim 1, is characterized in that: calculus of differences amplifying circuit comprises the 3rd operational amplifier, the 14 resistance, the 15 resistance, the 16 resistance and the 17 resistance; One end of 14 resistance is connected to the output terminal of the first operational amplifier, the other end of the 14 resistance and one end composition common port of the 16 resistance are connected to the inverting input of the 3rd operational amplifier, the other end of the 16 resistance is connected to the output terminal of the 3rd operational amplifier, one end of 15 resistance is connected to the output terminal of the second operational amplifier, the other end of the 15 resistance and one end composition common port of the 17 resistance are connected to the in-phase input end of the 3rd operational amplifier, the other end ground connection of the 17 resistance.
9. weak current circuit according to claim 4, is characterized in that: described gain control feedback circuit comprises the 7th resistance, the 8th resistance and relay, and one end of the 7th resistance and the other end of the second resistance are connected to I
sone end of current source, I
sthe other end ground connection of current source, the other end of the 7th resistance and the 8th resistance are connected to one end of relay, and the other end of the 8th resistance and the other end composition common port of relay are connected to the output terminal of the 3rd operational amplifier.
10. a weak current method, is characterized in that: adopt a kind of weak current circuit as claimed in claim 1, carry out in accordance with the following steps:
Step 1: carry out I-V conversion by input stage amplifying circuit, convert low current signal to voltage signal;
Step 2: by intermediate amplifying circuit, the voltage signal after conversion is carried out preliminary scale operation and amplify;
Step 3: carry out calculus of differences amplification by the voltage signal after scale operation amplifies by output stage amplifier circuit, obtain calculus of differences and amplify magnitude of voltage;
Step 4: magnitude of voltage is amplified to calculus of differences and measures.
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Application publication date: 20160504 |