CN101226207B - Active variable impedance synthesizer - Google Patents

Abstract

The invention relates to an active variable impedance synthesizer, which can standard impedances as standard capacitor or inductor for correcting LCR measuring instrument. The invention uses one basic capacitor or inductance circuit that forms a variable capacitor or inductance and uses one companion circuit connected with the basic capacitor or inductance circuit to form high-frequency high-precision impendence with variable range. The invention can be combined with equal potential track circuit to improve the accuracy of active variable impedance synthesizer.

Description

Active variable impedance synthesizer

Technical field

The present invention relates to the method that a kind of operation amplifier circuit is applied to three terminal impedance converter techniques, be particularly related to a kind of employing companion slowdown monitoring circuit, equipotential tracking circuit and determine to improve under the frequency operational amplifier stability circuit, to form high precision, wideband, the variable synthesizer of active impedance.

Background technology

The LCR measuring instrument is a kind of measurement instrument, and regularly application standard metering measurer (as capacitor, inductor) is used for measuring instrument is tested or calibrated, to keep its measuring accuracy.In the high precision LCR measuring instrument of accurate impedance metrology and measurement or debugging wideband, it is the metering measurers that lack high precision, high frequency that distinct issues are arranged.

Make 100kHz, low inductance, electric capacity and the AC resistance etalon of the loss 1MHz precision, stable is very difficult.The 16380A type 1pF, 10pF, 100pF and 1000pF four ends that U.S. Agilent company are arranged at present as the etalon of single body have CO-120-1 type 100pF, 200pF, 500pF and the coaxial air dielectric capacitor of 1000pF of 1406 type 100pF, the coaxial air dielectric capacitor of 1000pF and 20 manufacturings of the Xi'an ministry of electronics industry of U.S. QuadTech company to air dielectric capacitor.But the etalon capacitance value scope of these single bodies is not wide, and variable is confined to several points, the high-frequency inductor etalon that does not also have 100kHz, a 1MHz with exchange the measuring resistance measurer.Also have, the etalon of single body needs to be connected with measuring instrument respectively in metrology and measurement, measures a kind of measurer and will connect once, be very much trouble, and can not meet and spread over a whole area from one point, by monodrome to many-valued calibrating.At present, both at home and abroad (the LCR measuring instrument product as 20Hz～1MHz), high precision (0.05% and more than) is more and more for wideband, be widely used in the measurement to LCR element and parameter of metrological service, research unit, enterprises and institutions, the etalon of existing single body can not satisfy far away the metering demand of LCR measuring instrument both domestic and external and debugging demand.

The simulation of impedance and conversion are important application aspects of operational amplifier, high precision, wideband, variable active impedance synthesizer have very big development prospect, " Impedancesynthesizer " (US 5485115) patented technology has been applied in a kind of product that is called fecund product prover as U.S. Fluke company, the frequency of operation of its active standard capacitor can reach 50kHz, and uncertainty reaches 2 * 10 ^-3Grade, multiple capacitance is obtained with the gain of regulating operational amplifier by program control D/A converter.This standard capacitor can satisfy the needs of the hand-held capacitance meter of verification two end formulas, but can not satisfy the LCR measuring instrument demand of verification high precision (0.05% and more than).

Therefore, do not have also at present that the frequency of operation that is applicable to high precision LCR measuring instrument reaches 1MHz, the uncertainty grade reaches 10 ^-4The variable active capacitor device of the order of magnitude and variable active inductor product.

Summary of the invention

Technical matters to be solved by this invention provides a kind of adaptation higher frequency and has more high-precision active variable impedance synthesizer, can combination inductance or electric capacity.

The present invention solves the problems of the technologies described above the technical scheme that adopts to provide a kind of active variable impedance synthesizer, is suitable for the electric capacity of synthetic certain limit, and it comprises active condenser network and companion's slowdown monitoring circuit.

The active capacitor circuit has first end, second end and the 3rd end, it comprises first operational amplifier, first resistance, first electric capacity, first inductance, second electric capacity, second resistance and first variohm, first operational amplifier has first input end, second input end and output terminal, wherein first resistance, second electric capacity, first inductance are connected between first end of the first input end of first operational amplifier and active capacitor circuit, second input end of first operational amplifier connects the 3rd end of active condenser network, and the 3rd end is a cold end; The output terminal of first operational amplifier connects an end of first variohm, and the other end of first variohm connects second end of active condenser network; First electric capacity and second resistance are in parallel and be connected across between the first input end and output terminal of first operational amplifier.

Companion's slowdown monitoring circuit comprises second operational amplifier, first impedance, second impedance, the 3rd impedance and the second adjustable resistance device, second operational amplifier has first input end, second input end and output terminal, the first input end of second operational amplifier connects an end of first impedance, the other end of first impedance connects first end of described active capacitor circuit, second input end of second operational amplifier connects a cold end, and second impedance is connected across between the output terminal of the first input end of second operational amplifier and second operational amplifier; The 3rd impedance one end connects the first input end of second operational amplifier, and the other end connects the output terminal of first operational amplifier; The second adjustable resistance device one end connects the output terminal of second operational amplifier, and the other end connects second end of active condenser network.

In above-mentioned impedance compositor, the capacitance C of the resistance R of first resistance and first electric capacity satisfies: RC=1/ ω, wherein ω is the frequency of operation of active capacitor circuit.

In above-mentioned impedance compositor, the 3rd impedance of companion's slowdown monitoring circuit equates with the value of second impedance.

In above-mentioned impedance compositor, the resistance of the second adjustable resistance device is adjusted in concert according to the resistance of first variohm.

In above-mentioned impedance compositor, the impedance compositor has a screening can, and it is connected to the cold end that second input end of first, second operational amplifier is connected by voltage follower, follows the tracks of to carry out equipotential; When connecting, the impedance compositor has a BNC connector at four ends, and its shell also is connected to the cold end that second input end of first, second operational amplifier is connected by voltage follower, follows the tracks of to carry out equipotential.The casing of LCR measuring instrument can be connected the shell or the BNC connector of impedance compositor with BNC web member (if the words that have) when measuring, so also connects described cold end indirectly.

The present invention also provides a kind of active variable impedance synthesizer, is suitable for the inductance of synthetic certain limit, and it comprises active inductive circuit and companion's slowdown monitoring circuit.

The active inductance circuit has first end, second end and the 3rd end, it comprises first phase inverter, first operational amplifier, first resistance, first electric capacity, first inductance, second electric capacity, second resistance and first variohm, and wherein the input end of first phase inverter connects first end of active inductive circuit; First operational amplifier has first input end, second input end and output terminal, wherein first resistance, second electric capacity, first inductance are connected between the output terminal of the first input end and first phase inverter, second input end of first operational amplifier connects the 3rd end of active inductive circuit, and the 3rd end is a cold end, the output terminal of first operational amplifier connects an end of first variohm, and the other end of first variohm connects second end of active inductive circuit; First electric capacity and described second resistance are connected across between the first input end and output terminal of first operational amplifier.

Companion's slowdown monitoring circuit comprises second phase inverter, second operational amplifier, first impedance, second impedance, the 3rd impedance and the second adjustable resistance device, and wherein the input end of second phase inverter connects first end of active inductive circuit; Second operational amplifier has first input end, second input end and output terminal, the first input end of second operational amplifier connects an end of first impedance, the other end of first impedance connects the output terminal of second phase inverter, second input end of second operational amplifier connects a cold end, and second impedance is connected across between the first input end and second operational amplifier output terminal of second operational amplifier; The 3rd impedance one end connects the first input end of second operational amplifier, and the other end connects the output terminal of first operational amplifier; The second adjustable resistance device one end connects the output terminal of second operational amplifier, and the other end connects second end of active inductive circuit.

In above-mentioned impedance compositor, the capacitance C of the resistance R of first resistance and first electric capacity satisfies: RC=1/ ω, wherein ω is the frequency of operation of active inductance circuit.

In above-mentioned impedance compositor, first phase inverter comprises the 3rd operational amplifier, the 3rd resistance, the 3rd electric capacity, the 4th resistance, the 4th electric capacity, the 3rd operational amplifier has first input end, second input end and output terminal, described the 3rd resistance and the 3rd capacitances in series are between first end of the first input end of the 3rd operational amplifier and active inductance circuit, the 4th resistance and the 4th electric capacity are in parallel and be connected across between the output terminal of the first input end of the 3rd operational amplifier and the 3rd operational amplifier, second input end of the 3rd operational amplifier is a cold end, the structural symmetry of second phase inverter and first phase inverter, the 3rd impedance of companion's slowdown monitoring circuit equates with second impedance.

In above-mentioned impedance compositor, the resistance of the second adjustable resistance device is adjusted in concert according to the resistance of first variohm.

In above-mentioned impedance compositor, the impedance compositor has a screening can, and it is connected to the cold end that second input end of described first, second operational amplifier is connected by voltage follower; And the LCR measuring instrument of impedance compositor has a casing, and it is connected to the cold end that second input end of first, second operational amplifier is connected by voltage follower, follows the tracks of to carry out equipotential.

The impedance compositor that active capacitor/inductance of the present invention is variable is owing to adopt above technical scheme, make it compared with prior art, utilize companion's slowdown monitoring circuit to improve precision and eliminate load effect, and combine the equipotential tracking technique, can reach very high precision, uncertainty reaches 1 * 10 when 10kHz ^-4, uncertainty reaches 2 * 10 when 100kHz ^-4, uncertainty reaches 5 * 10 when 1MHz ^-4Can satisfy the user substantially to 0.05 grade～0.1 grade the wideband LCR element and the measurement and the metering demand of parameter.

Description of drawings

For above-mentioned purpose of the present invention, feature and advantage can be become apparent, below in conjunction with accompanying drawing the specific embodiment of the present invention is elaborated, wherein:

Fig. 1 is the basic circuit according to the impedance compositor of the variable active capacitor of conduct of the embodiment of the invention.

Fig. 2 is the impedance compositor basic circuit according to the variable active inductance of conduct of the embodiment of the invention.

Fig. 3 is the companion's slowdown monitoring circuit fundamental diagram according to the embodiment of the invention.

Fig. 4 has the impedance compositor of companion's slowdown monitoring circuit and the synoptic diagram that the LCR measuring instrument is formed metering circuit.

Fig. 5 is the impedance condensating synthesizering circuit figure of synthetic variable active standard capacitance of the present invention.

Fig. 6 is the impedance condensating synthesizering circuit figure of synthetic variable active standard inductance of the present invention.

Fig. 7 A and Fig. 7 B are the equipotential tracking circuits according to the embodiment of the invention.

Fig. 8 is the structural drawing of active variable impedance synthesizer.

Fig. 9 be active variable impedance synthesizer and four ends to or the measurement wiring diagram of five-terminal measurement method LCR measuring instrument.

Figure 10 is the measurement wiring diagram of active variable impedance synthesizer and three-terminal p-n-p-n switch method LCR measuring instrument.

Embodiment

Following elder generation illustrates principle of the present invention with the basic circuit of the impedance compositor of combined capacity and inductance.

Fig. 1 is a kind of impedance compositor basic circuit of combined capacity, and this circuit comprises operational amplifier N1, resistance R 1, capacitor C 1 and variohm Z2, and they connect in the mode shown in scheming.Hypothesis Fig. 1 operational amplifier N1 is desirable earlier, the first end U _sThe signal source and the measurement input that connect the LCR measuring instrument are high-end, the second end U ₀₂Connect the signal source of LCR measuring instrument and measure input low side (being the measurement virtual earth end of LCR measuring instrument), the 3rd end V_GND is the virtual earth end of operational amplifier, can obtain following equation according to the operational formula of ratio amplifier:

U ₀₁/U _s＝-(1/jωC ₁)/R ₁

U ₀₁＝-U _s·(1/jωR ₁C ₁)

Because U ₀₂Be the virtual earth end, the variohm Z that then flows through as load ₂Electric current is:

I _O＝(U ₀₁-U ₀₂)/Z ₂＝-U _s·(1/jωR ₁C ₁)/Z ₂

Obtain active impedance U _s/ I _O=-j ω R ₁C ₁Z ₂

The active induction reactance X of equivalence _L=-j ω R ₁C ₁Z ₂=-j ω L

Because negative induction reactance promptly is positive capacitive reactance, then has-j ω L=1/j ω C

So, active capacitor C=1/ ω ²L=1/ (ω ²R ₁C ₁Z ₂)

Under definite frequency condition of 10kHz or 100kHz or 1MHz, can be designed to R ₁=1/ ω C ₁, be designed to Z ₂Be pure resistance.

Finally obtain: active capacitor C=1/ ω Z ₂

Formula C=1/ ω Z ₂The active capacitor amount of capacity that shows Fig. 1 under the steady job frequency only with the load Z of operational amplifier N1 ₂Relevant, the two is inversely proportional to, and that is to say to change pure resistance Z ₂Resistance can change the active capacitor capability value.Z ₂The big more then active capacitor of resistance capacity is more little, otherwise then the active capacitor capacity is big more.

Fig. 2 is a kind of impedance compositor basic circuit of combination inductance, this circuit is to add inverter circuit before the input end of circuit shown in Figure 1, wherein, first phase inverter is made up of amplifier N1, resistance R 1 and R2, the active capacitor circuit comprises resistance R 3, operational amplifier N2, capacitor C 1 and variohm Z4, and they connect in the mode shown in scheming.Suppose that operational amplifier N1 and N2 are desirable, the first end U _sThe signal source and the measurement input that connect the LCR measuring instrument are high-end, the second end U ₀₃Connect the signal source of LCR measuring instrument and measure input low side (being the virtual earth end), the 3rd end V_GND is the virtual earth end (cold end) of active capacitor amplifier, can obtain following equation according to the operational formula of ratio amplifier:

U ₀₁/U _s＝-R ₂/R ₁

U ₀₁＝-U _s·R ₂/R ₁

U ₀₂/U ₀₁＝-(1/jωC ₁)/R ₃

U ₀₂＝-U ₀₁·(1/jωC ₁·R ₃)＝-(-U _s·R ₂/R ₁)·(1/jωC ₁R ₃)＝(U _s·R ₂/R ₁)·(1/jωC ₁R ₃)

Because U ₀₃Be the virtual earth end, the first variohm Z that then flows through as load ₄Electric current is:

I _O＝(U ₀₂-U ₀₃)/Z ₄＝(-U ₀₁·(1/jωC ₁R ₃)/Z ₄＝-U ₀₁/(jωC ₁R ₃·Z ₄)

＝-(-U _s·R ₂/R ₁)/(jωC ₁R ₃·Z ₄)＝(U _s·R ₂)/(jωR ₁R ₃C ₁·Z ₄)

Work as R ₁=R ₂The time, the load Z that flows through ₄Electric current I=U _s/ (j ω R ₃C ₁Z ₄)

Obtain active impedance U _s/ I _O=j ω R ₃C ₁Z ₄

Be that equivalent active induction reactance is X _L=j ω R ₃C ₁Z ₄=j ω L

So active inductance L=R ₃C ₁Z ₄

Under definite frequency condition of 10kHz or 100kHz or 1MHz, can be designed to R ₃=1/ ω C ₁, i.e. L=(1/ ω C ₁) C ₁Z ₄, be designed to Z ₄Be pure resistance.

Finally obtain: active inductance L=Z ₄/ ω

Formula L=Z ₄The size of active inductance amount that/ω shows Fig. 2 under the steady job frequency only with the load Z of operational amplifier N2 ₄Relevant, the two is directly proportional, and that is to say to change pure resistance Z ₄Resistance can change the value of active inductance amount.Z ₄The big more then active inductance of resistance amount is big more, otherwise then the active inductance amount is more little.

In the present invention, every have an input end U _sWith output terminal U _oAnd and U _oThe impedance Z that is connected, and the other end of Z is connected to virtual earth end ∑ (being the input addition node of the nulling point exclusive disjunction device of electric bridge), then as long as at U _sAnd additional companion's slowdown monitoring circuit that is made of operational amplifier just can improve the accuracy that this section circuit signal transmits greatly between the ∑ point.

Fig. 3 is the companion's slowdown monitoring circuit fundamental diagram according to the embodiment of the invention.This companion's slowdown monitoring circuit comprises the second operational amplifier N2, first impedance Z 1, second impedance Z 2 ", the 3rd impedance Z 2 and the second adjustable resistance device Z ', they connect in the mode shown in scheming.This companion's slowdown monitoring circuit connects described second operational amplifier by first impedance Z 1 and has first input end, second input end and output terminal, described first input end connects the first end Us of main discharge circuit (for example being the above-mentioned formation electric capacity or the impedance compositor of inductance), connect main discharge circuit output terminal by the 3rd impedance Z 2, in addition, also by the second adjustable resistance device Z ' connection virtual earth end ∑.The load of main discharge circuit (the first variohm Z) connects Uo and virtual earth end ∑.

In Fig. 3, the transport function-H of main discharge circuit (j ω)=U _o/ U _sBe the voltage ratio function, showing that with dashed lines connects might not be the Direct Transform relation.The form of the general available impedance ratio of H (j ω) is expressed, and its ideal value can be expressed as Z ₂/ Z ₁

If actual value H (j ω) and ideal value Z ₂/ Z ₁Between the pass be:

$H\left(\mathrm{j\ω}\right)=\frac{Z_2}{Z_1}(1+{\mathrm{\Δ}}_1)$

And: Z ₂'=Z ₂(1+ Δ ₂), Z ₁'=Z ₁(1+ Δ ₃)

And the loop gain of establishing operational amplifier is a _fA _f, then the single order trace is by cancellation, and remaining error all is a Δ ₁, Δ ₂, Δ ₃With

The above trace (can be left in the basket) of second order.

With LCR measuring instrument circuit is example, input end U _sExtend to the interior metering circuit of LCR measuring instrument to this section of virtual earth end ∑ circuit, and, adopt admittance to represent, wherein Y for the ease of deriving _sBe the range admittance (sample resistance) in the LCR measuring instrument, see shown in Figure 4:

If actual value H (j ω) and ideal value Z ₂/ Z ₁=Y ₁/ Y ₂Between the pass be:

$H\left(\mathrm{j\ω}\right)=\frac{Y_1}{Y_2}(1+{{\mathrm{\δ}}_1}^{,})$

And: Y '=Y (1+ δ '), Y ₂"=Y ₂(1+ δ ₂")

And the open-loop gain of establishing operational amplifier is A, feedback factor:

$a_f=\frac{{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2^{\&prime;\&prime;}}{{\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00061.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2+{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2^{\&prime;\&prime;}}$

$\stackrel{\&CenterDot;}{{u_0}^{\&prime;}}=[-\frac{Y_1}{{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2^{\&prime;\&prime;}}{u}_0+\frac{Y_1}{{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2^{\&prime;\&prime;}}(1+{\mathrm{\&delta;}}_1^{\&prime;})\stackrel{\&CenterDot;}{u_s}][1-\frac{1}{1+a_f{A}_2}]$

The current potential of ∑ summing junction $\stackrel{\&CenterDot;}{e_{\mathrm{\&Sigma;}}}=\frac{Y{u}_0+Y^{\&prime;}\stackrel{\&CenterDot;}{{u_0}^{\&prime;}}+Y_s\stackrel{\&CenterDot;}{u_s}}{Y+Y^{\&prime;}+Y_s}$

$\frac{\stackrel{\&CenterDot;}{e_{\mathrm{\&Sigma;}}}}{\stackrel{\&CenterDot;}{u_s}}(Y+Y^{\&prime;}+Y_s)=-\frac{Y_{1}Y}{Y_2}(1+{\mathrm{\&delta;}}_1^{\&prime;})+\frac{Y_1{Y}^{\&prime;}}{{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2^{\&prime;\&prime;}}{\mathrm{\&delta;}}_1^{\&prime;}(1-\frac{1}{1+a_f{A}_2})+Y_s$

$=Y_s-\frac{Y_{1}Y}{Y_2}(1+{\mathrm{\&delta;}}_1^{\&prime;})+\frac{Y_{1}Y(1+{\mathrm{\&delta;}}^{\&prime;})}{Y_2(1+{\mathrm{\&delta;}}_2^{\&prime;\&prime;})}{\mathrm{\&delta;}}_1^{\&prime;}(1-\frac{1}{1+a_f{A}_2})$

$=Y_s-\frac{Y_{1}Y}{Y_2}[1+{\mathrm{\&delta;}}_1^{\&prime;}-{\mathrm{\&delta;}}_1^{\&prime;}(1+{\mathrm{\&delta;}}^{\&prime;}-{\mathrm{\&delta;}}_2^{\&prime;\&prime;}-\frac{1}{1+a_f{A}_2})]$

$\&ap;Y_s-\frac{Y_1\mathrm{<figure-callout\; id="2"\; label="Y\; Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}{Y_{}}$

If virtual earth terminal potential $\stackrel{\&CenterDot;}{e_{\mathrm{\&Sigma;}}}=0,$ Then $\frac{Y_s}{Y}=\frac{Y_1}{{\mathrm{<figure-callout\; id="2"\; label="Y"\; filenames="S2007101735999E00041.png,S2007101735999E00051.png"\; state="\{\{state\}\}">Y</figure-callout>}}_2}.$

Be Y _s/ Y equates with the selected ideal value of H (j ω), clearly, if do not add companion's slowdown monitoring circuit, then can only equate with the actual value of H (j ω).The supposition of having used the above trace of second order to omit above, as each trace all 2 * 10 ^-4About, then can reach 10 at least from error analysis ^-7The circuit accuracy this shows the accuracy that companion's slowdown monitoring circuit can largely improve circuit.At this, variohm Z ' (Y ' inverse) has played Z (inverse of Y) companion survey effect, in order accurately to measure variable Z, a Z ' close with its value just need be arranged simultaneously.

Companion's slowdown monitoring circuit is except having this function, and it also has a vital role can eliminate load effect exactly.The active impedance compositor of Fig. 1, Fig. 2 circuit can along with pull-up resistor case or admittance case (as the Z among Fig. 1 ₂With the Z among Fig. 2 ₄) magnitude variations and produce load effect.And application companion slowdown monitoring circuit technology, connect on the termination another close ten in companion's slowdown monitoring circuit load and advance relevant resistance box or the additive property admittance case value that reaches multivalue dependency of value with the main circuit load, just can eliminate the load effect of different values, improve the accuracy that additive property is transmitted in the measuring process greatly.As, be equipped with two ten of major-minors and advance the relevant resistance box (describing) that reaches multivalue dependency of value in the back, reached by indivedual high-precision wides frequently standard values be increased to and comprise that ten advance the standard value that value and non-ten is advanced the relevant multivalue dependency of value, make the big increase of wide coverage of tested LCR measuring instrument measurement point.

Below just explanation add the circuit of the active impedance compositor of companion's slowdown monitoring circuit.

The variable active standard capacitance circuit of three ends of Fig. 5 is to add companion's slowdown monitoring circuit composition on the circuit base of Fig. 1.Wherein operational amplifier N501 is as first operational amplifier, and resistance R 501 (i.e. first resistance) is as input resistance, and establishing its resistance is R1, capacitor C 502 (first electric capacity) is as feedback capacity, if its resistance is C1, R1=1/ ω C1 then, wherein ω is the frequency of operation of circuit.Terminal H is as first end of impedance compositor, and terminal L is as second end of impedance compositor, and terminal V_GND all connects the measurement terminal of LCR measuring instrument as the virtual earth end.

Because the variable active standard capacitance frequency of operation of three ends of the present invention can reach 1MHz, and the frequency of operation of precision operational-amplifier is not very high, and bigger arithmetic eror is arranged when being operated in high frequency, and self-excitation takes place circuit easily.For example, selecting the open-loop voltage gain representative value of OP37 type ultra-low noise precision operational-amplifier is 124dB (DC), the gain bandwidth product representative value is 63MHz, when this OP37 is operated in 1MHz, the open loop frequency individual features curve of consulting this operational amplifier obtains its open-loop voltage gain and will reduce to below the 40dB (1MHz), that is to say, the open-loop voltage gain that is operated in OP37 under the frequency 1MHz only is 100 times, can extrapolate arithmetic eror from the analysis of discharge circuit closed loop gain and can reach-1%, this arithmetic eror can not satisfy the designing requirement of precision operational-amplifier circuit.

For the higher-order of oscillation may take place in the first and second operational amplifier N501 that avoid Fig. 5 and the circuit of N502, the present invention adopts the method for determining to improve under the frequency operation amplifier circuit job stability, on main circuit input resistor R501, connected a capacitor C501 and an inductor L501, resistor R 502 in parallel on feedback condenser C502.Here, notice that the component values that increases selects to guarantee that the impedance conversion calculation function of operation amplifier circuit and operational precision can not become, be that modulus of impedance value after modulus of impedance value and capacitor C502, resistor R 502 parallel connections after inductor L501, resistor R 501, the capacitor C501 series connection should equate, wherein the inductor L501 that is cascaded with capacitor C501 can play the effect of finely tuning phase place.The detail with reference patent " determines to improve under the frequency method of stability of operation amplifier circuit " (ZL01105505.7) more specifically.In addition, all connected RC Hi-pass filter (as R503, C503 and R506, C507) at the output terminal of all operational amplifiers and connect filtering ground (F_GND),, improved the job stability of circuit to prevent the circuit generation higher-order of oscillation.

The companion's slowdown monitoring circuit of Fig. 5 and the circuit parameter of main circuit are approaching, and specifically, the output signal of main circuit is coupled to the input end of the second operational amplifier N502 of companion's slowdown monitoring circuit by the capacitor C507 as the 3rd impedance.According to the analysis to companion's slowdown monitoring circuit of above-mentioned Fig. 4, the coupling capacitance C507 that is designed to conduct the 3rd impedance of Fig. 5 equates with the feedback capacity C505 capacity of conduct second impedance of the second operational amplifier N502 of companion's slowdown monitoring circuit; The pull-up resistor case or the admittance case (Z of companion's slowdown monitoring circuit ₂) resistance of (the second adjustable resistance device) and the pull-up resistor case of main circuit or admittance case (Z ₁) resistance of (first variohm) equates, wherein, Z ₁When changing different resistances, Z ₂Be to need to switch synchronously.

Can calculate the capacity C=1/ ω Z that obtains the active standard capacitor of Fig. 5 ₁, show that active standard capacitance amount of capacity is at the load Z that only determines under the frequency of operation with impedance inverter circuit ₁Relevant, the two is inversely proportional to.That is to say, change pure resistance Z ₁Resistance (synchronous change pure resistance Z ₂Resistance) can change active capacitor capability value, Z ₁The big more then active capacitor of resistance capacity is more little, otherwise then the active capacitor capacity is big more.

The variable active standard inductance circuit of three ends of Fig. 6 is to add companion's slowdown monitoring circuit composition on the circuit base of Fig. 2.Wherein, companion's slowdown monitoring circuit has the inverter circuit identical with inductive circuit.Operational amplifier N602 is as first operational amplifier, and resistance R 604 (i.e. first resistance) is as input resistance, and establishing its resistance is R1, capacitor C 605 (first electric capacity) is as feedback capacity, if its resistance is C1, R1=1/ ω C1 then, wherein ω is the frequency of operation of circuit.Terminal H is as first end of impedance compositor, and terminal L is as second end of impedance compositor, and terminal V_GND all connects the measurement terminal of LCR measuring instrument as the virtual earth end.

With top described, the open-loop voltage gain that is operated in amplifier OP37 under the frequency 1MHz is no more than 100 times, so the arithmetic eror when the variable active standard inductance of three ends is operated in high frequency also can not be ignored.Be operational amplifier N601～contingent higher-order of oscillation of N604 circuit of avoiding Fig. 7, the same method of determining to improve under the frequency operation amplifier circuit job stability that adopts of the present invention.A capacitor C601 has connected on main circuit input resistor R601, capacitor C602 in parallel on feedback resistor R602, a capacitor C604 and inductor L601 have connected on input resistor R604, resistor R 605 in parallel on feedback condenser C605, wherein the inductor L601 that is cascaded with capacitor C604 plays the effect of fine setting phase place; A capacitor C608 has connected on companion's slowdown monitoring circuit input resistor R608, capacitor C609 in parallel on feedback resistor R609, the capacitor C613 that on input resistor R612, connected, resistor R 613 in parallel on feedback condenser C614; Output terminal at all operational amplifiers has all connected a RC Hi-pass filter (F_GND) with connecing filtering, has improved the job stability of circuit.The output signal of main circuit operational amplifier N601 is coupled to the input end of accompanying slowdown monitoring circuit operational amplifier N603 by the capacitor C504 of resistor R 607 and serial connection, and the output signal of main circuit operational amplifier N602 is coupled to the input end of companion's slowdown monitoring circuit operational amplifier N604 by capacitor C611.

Accompany the analysis of slowdown monitoring circuit according to above-mentioned Fig. 4, the coupling capacitance C611 of design drawing 6 (the 3rd impedance) equates with feedback capacity C614 (second impedance) capacity of second operational amplifier of companion's slowdown monitoring circuit; The pull-up resistor case or the admittance case (Z of companion's slowdown monitoring circuit ₂) (the second adjustable resistance device) resistance also with the pull-up resistor case or the admittance case (Z of main circuit ₁) (first variohm) resistance equates, wherein, Z ₁When changing different resistances, Z ₂Be to need to switch synchronously.

Can calculate the inductance value L=Z that obtains the active standard inductor of Fig. 6 ₄/ ω, the size that shows Fig. 6 active inductance amount is at the load Z that only determines under the frequency of operation with impedance inverter circuit ₁Relevant, the two is directly proportional.That is to say, change pure resistance Z ₁Resistance can change the value of active inductance amount, Z ₁The big more then active inductance of resistance amount is big more, otherwise then the active inductance amount is more little.

Adopted the self-equilibrating bridge circuit in the LCR measuring instrument of four ends to mensuration, measuring splicing ear is to adopt BNC type plugs and sockets to connect, and the shell of BNC connector is used to connect the screen layer of slotted line rather than connects casing ground or greatly.Four ends are that the conductor of BNC type plugs and sockets shell also is the loop of disequilibrium survey marking current to the mensuration design feature, flow through the electric current and the unequal measuring error that causes of electric current that flows through I-V operational amplifier feedback resistance of measured piece DUT when frequency is higher with compensation.Therefore, four ends can make stray capacitance and remaining inductance reduce to minimum when the sensing lead to method, to guarantee best measuring accuracy.

But, because the position of active impedance standard and LCR measuring instrument connecting line is unfixing, the distribution parameter influence that distribution parameter influence that active impedance standard internal connection line exists and active impedance standard PCB routing exist, making BNC type plugs and sockets shell and operational amplifier virtual earth (V_GND) at four ends when measuring is not same current potential, the casing ground (G_GND) of LCR measuring instrument is not same current potential with operational amplifier virtual earth (V_GND), slotted line screen layer that is connected with measuring instrument casing ground (G_GND) and operational amplifier virtual earth (V_GND) neither same current potentials, between the tie point of various places or screen layer have leakage current to flow through to each connecting line, influenced the accuracy of active impedance standard.In like manner, when three-terminal p-n-p-n switch or five-terminal measurement, the casing ground (G_GND) of LCR measuring instrument is not same current potential with operational amplifier virtual earth (V_GND), slotted line screen layer that is connected with measuring instrument casing ground (G_GND) and operational amplifier virtual earth (V_GND) neither same current potentials, between the tie point of various places or screen layer also have leakage current to flow through to each connecting line, influenced the accuracy of active impedance standard.

To this, the present invention adopts the equipotential tracking circuit solution shown in a kind of Fig. 7 A and Fig. 7 B: when promptly four ends are to measurement, shown in Fig. 7 A, BNC socket shell at the active impedance compositor inserts a voltage follower circuit that is made of operational amplifier N1, the output of follower N1 connects the virtual earth of other operational amplifiers, virtual earth end (V_GND) as the operational amplifier of Fig. 1～shown in Figure 3 carries out equipotential and follows the tracks of.So-called equipotential is followed the tracks of and is meant between each virtual earth end and the screening can equipotential, but they are not again direct connections.

Similarly, shown in Fig. 7 B, tie point on active impedance compositor and LCR measuring instrument casing ground (G_GND) also inserts a voltage follower circuit that is made of operational amplifier N2, and the output of follower N2 connects the virtual earth end (V_GND) of other operational amplifiers, carries out equipotential and follows the tracks of.

In like manner, when three-terminal p-n-p-n switch or five-terminal measurement, also can insert a voltage follower circuit that is made of operational amplifier at the tie point on active impedance compositor and LCR measuring instrument casing ground (G_GND), the output of follower connects the virtual earth end (V_GND) of operational amplifier, carries out equipotential and follows the tracks of.

The enforcement of equipotential tracking circuit solution, make and reach screen layer between the various ground tie point not having electric current or have only very little leakage current to flow through because current potential equates between each connection, eliminate the various spuious effects of distribution parameters of active impedance compositor to reach, improved the computing accuracy of active impedance compositor.

Fig. 8 illustrates the active normal impedance compositor structural drawing with above-mentioned active capacitor or inductance basic circuit, companion's slowdown monitoring circuit and equipotential tracking circuit.As shown in Figure 8, each indoor design of casing 101 with active normal impedance compositor 100 of function of shielding has active preferred circuit plate 110, the main circuit pull-up resistor case Z by Fig. 5 or circuit diagram made shown in Figure 6 ₁With companion's slowdown monitoring circuit pull-up resistor case Z ₂, and place inner three independently in the shielding box of active standard container, under determining frequency, each is made into a capacitive/inductive standard set-up.The upper left side is 5 connection terminals among Fig. 8, wherein Hc, Hp, Lp, Lc adopt the BNC web member, and the shell of BNC connector and GND link are connected with the operational amplifier input end of equipotential tracking circuit (with reference to Fig. 7 A with shown in Fig. 7 B) in the active preferred circuit plate 110 respectively.Main circuit load Z1 and the just signal of 4 resistance that companion's slowdown monitoring circuit load Z2 draws in Fig. 8 can increase or reduce resistance according to the needs of measurement point.When switch SW 1 and SW2 were closed, Z1 was connected with active preferred circuit plate 110 with Z2, and adjusted in concert Z1 and Z2 can change the electric capacity that the active impedance compositor synthesized or the value size of inductance.Switch SW 1 and SW2 are disconnected, then the main circuit load Z1 that is connected with active preferred circuit plate 110 respectively has two H terminals to be connected with the variable resistive load of L terminals with the outside with companion's slowdown monitoring circuit load Z2, and the Z1 of adjusted in concert outside and Z2 can change the value size of active standard equally.Tested LCR measuring instrument measurement point is many, stability is strong in order to make, and Z1 can dispose ten with Z2 and advance relevant resistance device or the additive property admittance case that reaches multivalue dependency of value.

Fig. 9 be active normal impedance compositor 100 and four ends to or the measurement wiring diagram of five-terminal measurement method LCR measuring instrument 200, above-mentioned five measurement terminal Hc, Hp, Lp, Lc and GND shown in the figure respectively with four ends to or corresponding five measurement terminal of five-terminal measurement method LCR measuring instrument 200 (as Agilent 4284ALCR measuring instrument) be connected, frequency of operation according to active standard, the test frequency of LCR measuring instrument is set, can measures.

Figure 10 is the measurement wiring diagram of active normal impedance compositor 100 and three-terminal p-n-p-n switch method LCR measuring instrument 300.Convert Hc, Hp, Lp, the Lc four measuring terminal of active normal impedance compositor 100 to two measurement terminal of H, L corresponding with the LCR measuring instrument 300 (as the AH2700 precision capacitance bridge) of three-terminal p-n-p-n switch method respectively H, L two measurement terminal connections by converter 400, the GND of active normal impedance compositor 100 directly is connected with the GND of this LCR measuring instrument.The inside of converter is with Hc, Hp end and H end short circuit, with Lp, Lc end and L end short circuit, realizes the translation function of four/two ends.According to the frequency of operation of active normal impedance compositor 100, the test frequency of LCR measuring instrument is set, can measure.

Through experiment and testing authentication, the variable impedance synthesizer of high precision wideband active capacitor/inductance of the present invention can reach very high precision, and uncertainty reaches 1 * 10 when 10kHz ^-4, uncertainty reaches 2 * 10 when 100kHz ^-4, uncertainty reaches 5 * 10 when 1MHz ^-4Can satisfy the user substantially to 0.05 grade～0.1 grade the wideband LCR element and the measurement and the metering demand of parameter.

Though the present invention discloses as above with preferred embodiment, so it is not in order to limit the present invention, can also be applied to make the variableimpedance synthesizer of high precision wideband active pull-up as the present invention.Any those skilled in the art, without departing from the spirit and scope of the present invention, when can doing a little modification and perfect, so protection scope of the present invention is when with being as the criterion that claims were defined.

Claims (10)

1. an active variable impedance synthesizer is suitable for synthesizing the electric capacity of certain limit, it is characterized in that, described impedance compositor comprises active condenser network and companion's slowdown monitoring circuit, wherein:

Described active capacitor circuit has first end, second end and the 3rd end, it comprises first operational amplifier, first resistance, first electric capacity, first inductance, second electric capacity, second resistance and first variohm, described first operational amplifier has first input end, second input end and output terminal, wherein said first resistance, second electric capacity, first inductance is connected between first end of the first input end of described first operational amplifier and described active capacitor circuit, second input end of described first operational amplifier connects the 3rd end of described active capacitor circuit, and described the 3rd end is a cold end; The output terminal of described first operational amplifier connects an end of described first variohm, and the other end of first variohm connects second end of described active capacitor circuit; Described first electric capacity and described second resistance are in parallel and be connected across between the output terminal of the first input end of described first operational amplifier and first operational amplifier;

Described companion's slowdown monitoring circuit comprises second operational amplifier, first impedance, second impedance, the 3rd impedance and the second adjustable resistance device, described second operational amplifier has first input end, second input end and output terminal, the first input end of described second operational amplifier connects an end of described first impedance, the other end of first impedance connects first end of described active capacitor circuit, second input end of described second operational amplifier connects a cold end, and described second impedance is connected across between the output terminal of the first input end of described second operational amplifier and second operational amplifier; Described the 3rd impedance one end connects the first input end of described second operational amplifier, and the other end connects the output terminal of described first operational amplifier; Described the second adjustable resistance device one end connects the output terminal of described second operational amplifier, and the other end connects second end of described active capacitor circuit.

2. impedance compositor as claimed in claim 1 is characterized in that, the capacitance C of the resistance R of described first resistance and described first electric capacity satisfies: RC=1/ ω, wherein ω is the frequency of operation of described active capacitor circuit.

3. impedance compositor as claimed in claim 1 is characterized in that, the 3rd impedance of described companion's slowdown monitoring circuit equates with the value of second impedance.

4. impedance compositor as claimed in claim 1 is characterized in that, the resistance of described the second adjustable resistance device is adjusted in concert according to the resistance of described first variohm.

5. impedance compositor as claimed in claim 1 is characterized in that, described impedance compositor has a screening can, and it is connected to the cold end that second input end of described first, second operational amplifier is connected by voltage follower.

6. an active variable impedance synthesizer is suitable for synthesizing the inductance of certain limit, it is characterized in that, described impedance compositor comprises active inductive circuit and companion's slowdown monitoring circuit, wherein:

Described active inductance circuit has first end, second end and the 3rd end, it comprises first phase inverter, first operational amplifier, first resistance, first electric capacity, first inductance, second electric capacity, second resistance and first variohm, and wherein the input end of first phase inverter connects first end of described active inductance circuit; Described first operational amplifier has first input end, second input end and output terminal, wherein said first resistance, second electric capacity, first inductance are connected between the output terminal of the first input end of described first operational amplifier and described first phase inverter, second input end of described first operational amplifier connects the 3rd end of described active inductance circuit, and described the 3rd end is a cold end, described first operational amplifier output terminal connects an end of described first variohm, and the other end of first variohm connects second end of described active inductance circuit; Described first electric capacity and described second resistance are connected across between the output terminal of the first input end of described first operational amplifier and first operational amplifier;

Described companion's slowdown monitoring circuit comprises second phase inverter, second operational amplifier, first impedance, second impedance, the 3rd impedance and the second adjustable resistance device, and wherein the input end of second phase inverter connects first end of described active inductance circuit; Described second operational amplifier has first input end, second input end and output terminal, the first input end of described second operational amplifier connects an end of described first impedance, the other end of first impedance connects the output terminal of described second phase inverter, second input end of described second operational amplifier connects a cold end, and described second impedance is connected across between the output terminal of the first input end of described second operational amplifier and second operational amplifier; Described the 3rd impedance one end connects the first input end of described second operational amplifier, and the other end connects the output terminal of described first operational amplifier; Described the second adjustable resistance device one end connects the output terminal of described second operational amplifier, and the other end connects second end of described active inductance circuit.

7. impedance compositor as claimed in claim 6 is characterized in that, the capacitance C of the resistance R of described first resistance and described first electric capacity satisfies: RC=1/ ω, wherein ω is the frequency of operation of described active inductance circuit.

8. impedance compositor as claimed in claim 6, it is characterized in that, described first phase inverter comprises the 3rd operational amplifier, the 3rd resistance, the 3rd electric capacity, the 4th resistance, the 4th electric capacity, described the 3rd operational amplifier has first input end, second input end and output terminal, described the 3rd resistance and the 3rd capacitances in series are between first end of the first input end of described the 3rd operational amplifier and described active inductance circuit, described the 4th resistance and the 4th electric capacity are in parallel and be connected across between the output terminal of the first input end of described the 3rd operational amplifier and the 3rd operational amplifier, second input end of described the 3rd operational amplifier is a cold end, the structural symmetry of described second phase inverter and described first phase inverter, the 3rd impedance of described companion's slowdown monitoring circuit equates with described second impedance.

9. impedance compositor as claimed in claim 6 is characterized in that, the resistance of described the second adjustable resistance device is adjusted in concert according to the resistance of described first variohm.

10. impedance compositor as claimed in claim 6 is characterized in that, described impedance compositor has a screening can, and it is connected to the cold end that second input end of described first, second operational amplifier is connected by voltage follower.

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