CN1327303A - Method for improving stability of operation amplifier circuit under determined frequency - Google Patents

Abstract

The method of improving the stability of operation amplifier comprises adding serial RC branch to the positive feedback loop, changing the negative feedback loop into parallel RC branch, connecting parallel RC circuit between the positive input and earth and between the negative input and earth in case of virtual earth as reference, and changing the parallel RC circuit between the positive input and the virtual earth into serial equal RC circuit. The circuits of the present inventino are simple and reliable, and the present invention can ensure the stability of the operation amplifier circuit while raising the precision of the operational amplifier and raising the working frequency greatly.

Description

Determine to improve under the frequency method of stability of operation amplifier circuit

The present invention relates to a kind of method that is used for operation amplifier circuit, particularly a kind of in the method for determining to improve under the frequency situation stability of operation amplifier circuit.

As everyone knows, operational amplifier has been widely used in various fields, amplify voltage phase shift and value conversion as electromagnetic detection, electric weight, integration and differential circuit, active instrument transformer, the active compensation circuit, mock standard device sensor circuit and high accuracy admittance case and formation high accuracy electric bridge active parts etc. wherein have pair computing circuit accuracy and stability requirement all very high certainly first-elected defense sector and metrological service.

But some amplifier really demonstrates high open-loop gain when direct current or low frequency use, when frequency of utilization raise, its effective open-loop gain can significantly descend and bring phase drift, usually can not satisfy desirability.

In fact, the stability of amplifier and the amplifying stage number that its open-loop gain is closely related, amplifier is interior are many more, and the chance of phase shift is just many more, and stability will be poor more.

In order to improve the accuracy of operational amplifier, on the basis of the operational amplifier basic circuit of being everlasting, additional more operation amplifier circuit makes the circuit complexity.But, facts have proved that complicated just easy vibration the (vibration of inoperative frequency) more of operation amplifier circuit brought the problem of more stability of operation amplifier circuit.

The objective of the invention is in order to solve the problem of existing stability of operation amplifier circuit, and proposition is a kind of under the frequency of utilization of determining, by on the operation amplifier circuit regenerative circuit, adding or change over the resistance capacitance series arm, on negative feedback loop and connect or change over the resistance capacitance parallel branch, or be that the resistance capacitance parallel connection that will be connected with the virtual earth end under the virtual earth end situation changes series connection at reference voltage, thereby make the operational amplifier closed loop of determining under the frequency, avoid taking place improving under definite frequency of vibration of inoperative frequency the method for stability of operation amplifier circuit.

The technical scheme that realizes the object of the invention is: the method for determining to improve under the frequency stability of operation amplifier circuit, comprise operation amplifier circuit, be characterized in, additional or the equivalence of former resistance element legs changed over a resistance capacitance series arm on described operational amplifier positive feedback loop; On described operational amplifier negative feedback loop additional or with the loop in the equivalence of former impedance component branch road change over a resistance capacitance parallel branch.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, under the situation that keeps operation amplifier circuit basic operation relation, the equivalent admittance value of the resistance capacitance parallel branch of adding on the equivalent admittance value of additional resistance capacitance series arm and the negative feedback loop on its positive feedback loop equates or becomes to determine ratio.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, described one-tenth determines that ratio is meant in the prototype circuit that amplifier positive input terminal node resultant admittance value and the resultant admittance of negative input end node are worth when unequal, exist certainty ratio really between the resultant admittance value.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, comprise that also reference point is under the situation of virtual earth end, at operational amplifier just, negative input end respectively is being connected a resistance capacitance parallel branch with earth terminal.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, in reference point the two resistance capacitance parallel branches that the positive and negative input of the operational amplifier of virtual earth end is connected with earth terminal, under the situation that keeps operation amplifier circuit basic operation relation, its capacitance equates with capacitance or is in direct ratio, its resistance value and the inverse proportion that resistance value equates or one-tenth is corresponding.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, the described amplifier positive input terminal node resultant admittance value and the resultant admittance of negative input end node of being meant in the prototype circuit in direct ratio or inversely proportional is worth when unequal, has certainty ratio really between the resultant admittance value.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, comprise that also reference point is under the situation of virtual earth end, hold with ground at the positive and negative input of operational amplifier respectively to be connected the resistance capacitance parallel branch.The resistance capacitance parallel branch that will be connected simultaneously between operational amplifier positive input terminal and virtual earth end is transformed into equivalent resistance capacitance series arm; Capacitance in this resistance capacitance series arm equals the twice of capacitance in the parallel branch and series impedance in the resistance capacitance series arm equates with the capacitive reactance mould value of series capacitance under operating frequency.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, described resistance capacitance series arm also can be again and between amplifier positive input terminal and the virtual earth end rest parts electricity lead and be in parallel.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, when operational amplifier is used for the current compensation circuit of last trading day/capacitive load, resistance on described operational amplifier positive feedback loop is transformed into a resistance value and the equal resistance capacitance series arm of capacitive reactance mould value, positive input terminal at amplifier is the end that original load connects simultaneously, under the situation that keeps operation amplifier circuit basic operation relation, additional corresponding ground capacity/resistance.

Improve the method for stability of operation amplifier circuit under above-mentioned definite frequency, wherein, described corresponding ground capacity/resistance be instigate the amplifier positive input terminal to earth terminal and amplifier positive input terminal to the total impedance of electronegative potential point in the parallel connection value of all resistance equate with the capacitive reactance mould value in parallel of all electric capacity.

Because the present invention has adopted above technical scheme, can guarantee stability of operation amplifier circuit, and the computing accuracy is improved greatly, and the operating frequency of using also improves greatly.

Concrete structure of the present invention and performance are further provided by following embodiment and accompanying drawing thereof.

See also accompanying drawing.

Fig. 1 a is that the voltage reference points of its input of operational amplifier is the prototype circuit figure of earth terminal.

Fig. 1 b, Fig. 1 c are that the voltage reference points corresponding to its input of the utility model operation amplifier circuit of Fig. 1 a is two kinds of embodiment schematic diagrames of earth terminal.

Fig. 2 a is that the voltage reference points of its input of operation amplifier circuit is the prototype figure that connects the virtual earth end;

Fig. 2 b, Fig. 2 c, Fig. 2 d, Fig. 2 e are respectively that the voltage reference points of its input of the utility model operation amplifier circuit is several situation embodiment schematic diagrames that connect the virtual earth end.

Fig. 3 a is the prototype figure that operation amplifier circuit is used for the current compensation circuit of last trading day load.

Fig. 3 b, Fig. 3 c, Fig. 3 d, Fig. 3 e, Fig. 3 f, Fig. 3 g are respectively the schematic diagrames of several embodiment of the utility model operation amplifier circuit current compensation circuit of being used for the last trading day load.

Fig. 4 a is the circuit prototype figure that the positive and negative input node of operation amplifier circuit resultant admittance value equates.

Fig. 4 b is at the positive feedback loop additional resistance capacitances in series branch road of operational amplifier with at the circuit diagram of negative feedback loop additional resistance electric capacity parallel branch.

Do detailed explanation below in conjunction with each embodiment.

The present invention uses and the object of enforcement is divided into three major types:

The first kind, at operation amplifier circuit, the voltage reference points of its prototype circuit amplifier in is the situation of earth terminal.

Second class, at operation amplifier circuit, the voltage reference points of its prototype circuit amplifier in is not earth terminal but the situation of virtual earth end.

The 3rd class at operation amplifier circuit, is used for the current compensation circuit of last trading day capacitive load electric current.

For ease of statement, earlier relevant components and parts sign is made the following description:

R ₁And C ₁Be illustrated in the resistance capacitance of negative feedback loop;

R ₁' and C ₁' be illustrated in the resistance capacitance of positive feedback loop;

R _dAnd C _dBe meant negative input end resistance to earth electric capacity;

R _d' and C _d' make a comment or criticism input resistance to earth and electric capacity;

R _p' and C _p' resistance capacitance between input and the virtual earth end of making a comment or criticism. $R_p^{\′}=\frac{1}{C_p^{\′}\mathrm{\ω}}$

See also Fig. 1 a, this is that the voltage reference points at its input of operation amplifier circuit is the prototype figure of the operational amplifier of earth terminal (reducing the first kind).

Fig. 1 b is that the voltage reference points that the present invention is directed to its input of operation amplifier circuit is the embodiment schematic diagram of the situation of earth terminal (reducing the first kind).The situation of the present invention after adding series and parallel resistance capacitance branch road on the positive-negative feedback loop of this operational amplifier.In this embodiment, under the various circuit conditions that the embodiment of the invention sets, all to satisfy condition $R_{}$ ${}_1\&ap;\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">c</figure-callout>}}_1\mathrm{\&omega;}}(R_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\mathrm{\&omega;}\&ap;1),$ ω=2 π f wherein, ω is an angular frequency, and f is a frequency, and its unit is Hz, and C also will satisfy condition ₁≈ C ₁' R ₁≈ R ₁'.

Simultaneously, resistance and electric capacity are got following value approx in the branch road:

${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1\&ap;\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">c</figure-callout>}}_1\mathrm{\&omega;}}$ Be R ₁c ₁ω ≈ 1

c ₁≈c ₁′R ₁≈R ₁′

Among the figure with Y _A1', Y _A2', Y _A3', Y _b' respectively with Y _A1, Y _A2, Y _A3, Y _bApproximately equal is example (this is common way).But, if the former is the latter's n ₁Doubly, the fundamental relation formula of operational amplifier is still constant, in this case, implements the 2C in the illustration ₁' must correspondingly change into 2n ₁C ₁', and among the figure Must correspondingly change into

In addition, in this case, existing really between the resultant admittance value of the resultant admittance value of amplifier positive input terminal node and amplifier negative input end node, certainty ratio is n ₁

See Fig. 1 c embodiment, its action principle and Fig. 1 b embodiment are basic identical, difference is that its positive feedback loop is that to connect one " 1 " operational amplifier by the output of prototype operational amplifier be phase inverter, because phase inverter has been arranged, a termination phase inverter output of resistance capacitance series arm in this positive feedback loop, the other end of resistor-capacitor series circuit then is connected with the negative input end of prototype operational amplifier.This embodiment circuit is compared with Fig. 1 b embodiment, and its advantage is the influence that positive feedback branch will not be subjected to prototype operational amplifier positive input terminal node resultant admittance value, promptly is not subjected to the influence of ratio between the resultant admittance of prototype amplifier positive-negative input end node.If replace this phase inverter with paraphase double voltage amplifier, can make series impedance in the positive feedback branch and series capacitance value respectively with negative feedback loop in additional parallel resistance and shunt capacitance equivalence.

The method of the connection in series-parallel branch road of additional or transformation resistance and electric capacity on the operational amplifier feedback loop has significant effect:

1, when circuit is derivative-type, the electric capacity of the parallel connection in the negative feedback loop works, and has suppressed high-frequency harmonic (to input voltage U ₁In high-frequency harmonic) high power amplify, thereby suppressed output voltage U ₀The wave distortion and the higher-order of oscillation;

2, when circuit is integral form, characteristics by the what integral form exist imbalance and disturbed inherent shortcoming to direct current and low frequency, added after the branch road, parallel resistor works, make in original closed loop the negative feedback of direct current and low frequency very weak, become the strong negative feedback close, thereby avoided DC maladjustment and low-frequency disturbance with operating frequency.

3, when circuit is the resistance ratio, because the shunt capacitance in the additional branches, can avoid the contingent higher-order of oscillation of circuit, in order not destroy the basic operation relational expression of prototype circuit operational amplifier, must be in the series arm of positive feedback loop while additional resistance electric capacity.

4, when frequency higher (relatively operating frequency), electric capacity is equivalent to short circuit, but the series resistance in the positive feedback loop works, guarantee that positive feedback is more than negative feedback a little less than.

5, when frequency was low, electric capacity was equivalent to high impedance even open circuit, positive feedback intensity very a little less than, can not compare with the negative feedback intensity of negative feedback loop far away, guarantee the effect of stability.

Fig. 2 a is the prototype figure of input reference point when being virtual earth, between the positive input terminal of amplifier and virtual earth end admittance Y is arranged _b' connect.

When the present invention is the virtual earth end in operational amplification circuit input reference point, at the Y that is connected with virtual earth end (VG) of amplifier positive input terminal _b' in contained resistance, the different situations of electric capacity provide four embodiment, as Fig. 2 (b), shown in Fig. 2 (c), Fig. 2 (d) and Fig. 2 (e).Virtual earth end of the present invention similarly is earth terminal in circuit, is not in fact again earth terminal, and it is the output of virtual earth follower, and the input of follower is connected with virtual earth, and this kind follower plays a part repetition virtual earth voltage.When earth terminal D replaces with virtual earth end VG, only adopt the method for previous embodiment 1 additional branches can't guarantee the stable of circuit.Thereby this is to bring the circuit shakiness because in fact the virtual earth end constitutes the new feedback path that is difficult for being perceiveed by people to operation amplifier circuit, and the virtual earth end is the output of follower simultaneously, should be regarded as new interference source.It should be noted: the virtual earth end of representing with VG should come electronegative potential point LV (also the claiming virtual earth sometimes) difference of mentioning with the back.

Fig. 2 b is the same with the first kind, respectively connects a string, parallel resistor capacitive branch on its positive negative feedback loop, and in addition, the present invention also is connected resistance and electric capacity parallel branch respectively between the positive-negative input end of amplifier and ground.

Virtual earth end VG is that new feedback element is again an interference source as previously mentioned, additional Rd and Kd and R over the ground _d', C _d' after make and disturb signal from the earth terminal bypass, and weakening feedback effect, though the voltage reference points of circuit is virtual earth (VG), behind the additional equivalent branch road of the positive-negative input end of pair amplifier, do not change the character of reference point, and should be the input of the common mode of the earth terminal D voltage that a common mode is arranged concerning virtual earth VG, well-known, the common mode input is not change the basic operation relational expression of operation amplifier circuit.

To additional resistance to earth electric capacity, Rd, Cd, R _d', C _d', and do not require R _dWith Equate,, can make as long as can satisfy stability requirement $R_d\&NotEqual;\frac{1}{C_d\mathrm{\&omega;}},$ $R_d^{\&prime;}\&NotEqual;\frac{1}{C_d^{\&prime;}\mathrm{\&omega;}},$ But the C value is got smaller value, and the R value is got more greatly and is advisable.Certainly make the also gang mould value of Rd and Cd close with impedance or admittance value in the negative feedback loop, but the Cd value is unsuitable excessive, the R value is unsuitable too small.

See Fig. 2 c, when the operational amplifier circuit, in the prototype circuit, the Y that the amplifier positive input terminal is connected with the virtual earth end _b' parallel connection of resistance and electric capacity appears, and parallel resistance R _p' and shunt capacitance C _p' just under operating frequency, meet $R_p^{\&prime;}\&ap;\frac{1}{C_p^{\&prime;}\mathrm{\&omega;}}$ 。In this case, the addition thereto that present embodiment adopted is on the basis of Fig. 2 b, be R _p' and C _p' change into the series connection of equivalence (determine under the frequency equivalent) from the state of parallel connection.As long as satisfy condition: when $R_p^{\&prime;}\&ap;\frac{1}{C_p^{\&prime;}\mathrm{\&omega;}}$ Just can be with the R of prototype _p' with C _p' state in parallel change into 2C _p' with

Series connection.

High frequency from virtual earth end VG or low-frequency disturbance signal are not only from R like this _p' and C _p' bypass, and to high frequency, the suitable what short circuit of the electric capacity in the series connection and series resistance is being undertaken the input intensity that suppresses the high frequency input signal, to low frequency, the electric capacity in the series connection is being undertaken the input intensity that suppresses the low frequency input signal.

See Fig. 2 d, embodiment 4, work as operation amplifier circuit, in the prototype circuit, and amplifier positive input terminal and the parallel connection that occurs resistance and electric capacity during the virtual earth end is connected, and the pass of its parallel resistance R and shunt capacitance C is $R<R_p^{\&prime;}\&ap;\frac{1}{\mathrm{C\&omega;}}$ , at this C _p' be C, order $\frac{1}{R}=\frac{1}{R^{\&prime;}}+\frac{1}{R_p^{\&prime;}},$ $R_p^{\&prime;}=\frac{1}{\mathrm{C\&omega;}}$ 。

The present invention is with R _p' change into 2C with the parallel branch of C _p' and

Series arm after again and R _k' parallel connection.

See Fig. 2 e, work as operation amplifier circuit, amplifying in the prototype circuit is the Y that positive input terminal is connected with the virtual earth end _b' in the parallel connection of resistance and electric capacity appears, and the pass of its parallel resistance R and shunt capacitance C is $R>R_p^{\&prime;}\&ap;\frac{1}{C_p^{\&prime;}\mathrm{\&omega;}}$ The time (C=C wherein _p'), then get R _kMake $\frac{1}{R_p^{\&prime;}}=\frac{1}{R}+\frac{1}{R_k}$ Promptly $\frac{1}{R_k}=\frac{1}{R_p^{\&prime;}}-\frac{1}{R}$ , in this case, must be with R _kBe converted to the negative input end of amplifier, simultaneously the Rk other end be connected with virtual earth end VG, only in this way could keep the basic operation relational expression of prototype operation amplifier circuit not to be destroyed.

Fig. 2 d and the measure that Fig. 2 e embodiment is adopted can improve the reason of stability of operation amplifier circuit with described in Fig. 2 c embodiment mutually roughly the same.

Under various situations, the amplifier negative input end can change into the series connection form of resistance and electric capacity to Rd and the Cd of ground D, or after the resistance capacitance series connection again with resistance parallel connection or resistance capacitance series connection after again with the electric capacity parallel connection.

Ask for an interview Fig. 3 a, Fig. 3 b, Fig. 3 c, Fig. 3 d, Fig. 3 e, Fig. 3 f, Fig. 3 g.

Wherein: Fig. 3 a is the prototype figure that general operation amplifier circuit is used for the current compensation circuit of last trading day, capacitive load electric current; Fig. 3 b, Fig. 3 c, Fig. 3 d, Fig. 3 e, Fig. 3 f, Fig. 3 g are respectively that the utility model operation amplifier circuit is used for last trading day, several situation embodiment schematic diagrames (reducing the 3rd class) of the current compensation circuit of capacitive load electric current.

Ask for an interview Fig. 3 a, this is the current compensation electrical equipment prototype circuit figure commonly used of general last trading day load.Prototype circuit is under the normal situation of closed loop, and the voltage of amplifier negative input end also should be approximately equal to U _B, the electric current on the two equivalent series resistance R that flow through like this equates that because of the high input impedance of amplifier negative input end clearly the output voltage of operational amplifier closed loop is necessary for 2U _BLoad resistance R from load end B to electronegative potential point LV _LOn electric current equal U _B/ R _LIf output voltage 2U from operational amplifier output terminal _BThe voltage U of ordering to load end B _BBetween compensating resistance R _L' be approximately equal to R _L, then pass through R _L' electric current be $\frac{2U_B-U_B}{R_L^{\&prime;}}$ Promptly , this electric current and load current The current value approximately equal opposite for B point direction, therefore just play compensating action.This is the basic functional principle of common current compensation circuit.So-called electronegative potential point LV, it is not the output of operational amplifier usually, and generally passes through impedance Z _CWith certain voltage U _CBe connected.During big the or impedance Z c complex structure of the Δ Z impedance that is connected as load end B, unsettled situation will occur, as everyone knows, the important feature of current compensation circuit is that the amplifier anode is connected with load end B, and the anode of amplifier to be the positive feedback end be extremely responsive is easy to form positive feedback, thereby produce vibration and imbalance, make the operational amplifier closed loop be in abnormal state, can not reach the purpose of current compensation, also relevant circuit be made troubles.One of purpose of the present invention is the stability problem that solves sort circuit.

See Fig. 3 (b) embodiment, this is the basic measures of taking for the raising circuit stability at the current compensation circuit of prototype circuit Fig. 3 (a) last trading day load.Under the prerequisite that keeps operation amplifier circuit basic operation relation, be prototype in the positive feedback loop compensating resistance R _L' branch road changes over the resistance capacitance series arm, for making this change equivalence and effective, must the while be load end at the positive input terminal of amplifier, additional corresponding ground capacity C '.When negative feedback one side is the bleeder circuit that is made of two substitutional resistance R, capacitor C ' value be by its capacitive reactance mould value and load resistance R _LValue equates to decide.Equivalence and effective conversion should be electric capacity 2C ' and resistance in positive feedback loop like this

The branch road that is in series.In fact determining that its condition is under the frequency $R_L^{\&prime;}\&ap;\frac{1}{C^{\&prime;}\mathrm{\&omega;}}$ 。So just can under the stable situation of holding circuit, realize the target of the current compensation of prototype circuit under the operating frequency.Owing to change over the resistance capacitance series arm at positive feedback loop, and be the bypass channel that load end has a ground connection at the amplifier positive input terminal simultaneously, therefore under the high frequency or low frequency situation beyond operating frequency, make circuit can not form strong positive feedback, and make the negative feedback of operational amplifier when high and low frequency always be better than positive feedback, thereby avoid vibration and imbalance.

See Fig. 3 (c) embodiment, this is to be further to improve addition thereto that its stability is taked at the current compensation circuit of prototype circuit Fig. 3 (a) last trading day load.Here it is keeps identical with Fig. 3 (b) embodiment in positive feedback one side, and the circuit that negative feedback one side two substitutional resistance R constitute is changed over the circuit that resistance capacitance is in parallel and series connection constitutes.This is the parallel branch that typically former resistive element branch road equivalence in the negative feedback loop is changed over a resistance capacitance, in order to make in the negative feedback loop this change effective, just realize the change of equivalence, must make corresponding changes at amplifier negative input end original R branch road over the ground.Owing to changed over the parallel connection of resistance capacitance at negative feedback loop, so made operation amplifier circuit prevent that the ability of the higher-order of oscillation is stronger.But Fig. 3 (c) embodiment not right and wrong adopt can not, this depends primarily on the Z that is connected with load end _CWith the formation of Δ Z how.If the measure that Fig. 3 (b) is adopted is enough to make circuit stable, then adopt the measure meeting among Fig. 3 (c) to bring unnecessary trouble.Because select two substitutional resistance R for use, make things convenient for manyly than the element of selecting 4 equivalences in resistance capacitance connection in series-parallel two branch roads for use.Yet be not enough to satisfy under the situation that circuit stability requires at Fig. 3 (b), except that Fig. 3 (c), also have a kind of preferable selection, Here it is Fig. 3 (d) embodiment.

See Fig. 3 (d) embodiment, this is the circuit that is combined by Fig. 3 (b) Fig. 3 (c), and this is a kind ofly also to be not enough to satisfy the circuit stability requirement at Fig. 3 (b) embodiment, and adopts the preferable selection under the situation that Fig. 3 (c) embodiment there is no need.Reason is to select for use the resistance nominal value, and two substitutional resistances are very convenient arbitrarily, and trouble is the resistance capacitance element of 4 non-equivalences, the high more trouble more of its accuracy requirement.Allow to be attached to the other resistance capacitance connection in series-parallel branch road of R in Fig. 3 (d) embodiment, its equivalent admittance value (mould value) is quantitatively than the electric conductivity value of substitutional resistance

For little, just the equiva lent impedance mould value of resistance capacitance branch road is big far beyond substitutional resistance R, people know the branch road that is connected in parallel on the R side, its modulus of impedance value is big more, influence is just more little, also just low more to the relative accuracy requirement of resistance value in the additional branch road and capacitance like this, be easily and select the not high resistance capacitance element of accuracy requirement for use, price is also low.Facts have proved, usually the less capacity cell of a capacity just can make the higher-order of oscillation stop in parallel connection on the negative feedback loop, this just illustrates is influencing under the stability requirement condition with higher, measure among Fig. 3 (d) embodiment is that practicality is arranged very much, and this embodiment circuit also is one of example of additional resistance electric capacity parallel branch on the operational amplifier negative feedback loop.

See Fig. 3 (e) embodiment, this is identical in essence with Fig. 3 (b) embodiment, but it is in the prototype current compensation circuit, and negative feedback one side is not to be made of and the circuit that is made of the resistance of two non-equivalences the measure of the raising circuit stability of being taked substitutional resistance R.Shown in Fig. 3 (e), the resistance m of negative feedback loop ₁R.Like this, electric capacity that is in series in the positive feedback loop and resistance value will make corresponding changes; Be the series capacitance value by 2C ' change into by , and series impedance

Change into

Negative feedback one side bleeder circuit all adopts substitutional resistance in the common current compensation circuit, only in special occasion, for example works as the voltage U of load end _BHigher, and the maximum output voltage that operational amplifier allowed is not enough to provide 2U _BThe time, get less m ₁Value (m ₁＜1) just seems necessary.Must be pointed out, in this case, not only can carry out but also can adopt the measure that is similar among Fig. 3 (c) and Fig. 3 (d) embodiment according to the embodiment of Fig. 3 (e).M on certain principle ₁Can also get value greater than 1.

See Fig. 3 (f) embodiment, this be the measure taked of the current compensation circuit when being electric capacity at load to improve the stability of circuit, basic identical described in its reason and Fig. 3 (b) embodiment.Slightly different is to be that the load resistance among Fig. 3 (b) is connected with electronegative potential point (LV), and load capacitance is connected with electronegative potential point (LV) among Fig. 3 (f), as long as electronegative potential point (LV) and virtual earth are connected consideration, just the situation of latter's appearance often under cover more makes the circuit factors of instability than the former complexity because electric capacity is connected with virtual earth as can be known; Addition thereto among Fig. 3 (g) embodiment helps the further solution of stability problem.

See Fig. 3 (g) embodiment, this is to be connected with electronegative potential point (LV) for overcoming load capacitance, the High-frequency Interference of bringing to circuit and the measure taked.Fig. 3 (g) embodiment is actually on the basis of Fig. 3 (f) embodiment, additional stronger resistance capacitance series arm on the operational amplifier positive feedback loop.Be load end at the amplifier positive input terminal simultaneously, on the basis of Fig. 3 (f), add the parallel branch of corresponding resistance to earth electric capacity again.Concerning positive feedback loop, the resistance capacitance series arm next door resistance capacitances in series branch road of going up in parallel again, its synthesis result still is the resistance capacitance series arm; Yet the pair amplifier positive input terminal is a load end, and other has added capacitance resistance parallel branch over the ground, so just for the high frequency waves signal provides better the passage of bypass over the ground, thereby suppresses the higher-order of oscillation.

In addition, parsing to Fig. 3 (g) embodiment circuit can directly not resolved promptly from the current compensation circuit of prototype counteracting capacitive load by Fig. 3 (f) embodiment circuit: when operational amplifier is used to offset the current compensation circuit of capacitive load, electric capacity on the operational amplifier positive feedback loop is transformed into a resistance value and the equal resistance capacitance series arm of capacitive reactance mould value, positive input terminal at amplifier is the end that original load connects simultaneously, under the situation that keeps operation amplifier circuit basic operation relation, additional corresponding earth resistance and electric capacity; At this, corresponding ground capacity/resistance be instigate the amplifier positive input terminal to earth terminal and amplifier positive input terminal to the total impedance of electronegative potential point in the parallel connection value of all resistance equate with the capacitor value in parallel of all electric capacity.

About adopting patent measure of the present invention to improve under the situation of circuit stability, operation amplifier circuit still can keep the demonstration of prototype circuit basic operation relation, will be example with general operational amplifier below, makes mathematical derivation.

To the prototype operation amplifier circuit, get amplifier positive input terminal node resultant admittance value and equate to be example, its circuit diagram such as Fig. 4 (a) with amplifier negative input end node resultant admittance value.

Adopt one of the technology of the present invention, in operational amplifier negative feedback loop additional resistance electric capacity parallel branch, circuit diagram such as Fig. 4 (b) after operational amplifier positive feedback loop additional resistance capacitances in series branch road.

Mathematic(al) argument is as follows:

(1) prototype circuit is discussed earlier.U _iBe input voltage, U _oBe output voltage, and e is the residual difference threshold voltage between operational amplifier negative input end and the positive input terminal.According to linear superposition theorem, final (stack result) voltage of node is the stack that each input is folded to the voltage of this node respectively, promptly $e=\frac{Y_a{U}_i}{(Y_a+Y_b)}+\frac{Y_b{U}_o}{(Y_a+Y_b)}-----\left(1\right)$ If the open loop multiplication factor of amplifier is K, consider negative feedback, following equation should be arranged:

-k _e＝U _o(2)

(1) formula substitution (2) formula gets

$-k(\frac{Y_a{U}_i}{Y_a+Y_b}+\frac{Y_b{U}_o}{Y_a+Y_b})=U_O$ Promptly $-k\frac{Y_a{U}_i}{(Y_a+Y_b)}=U_O(1+\frac{k{Y}_b}{Y_a+Y_b})----\left(3\right)$ ∴ $U_O=\frac{-k{Y}_a{U}_i}{(Y_a+Y_b)(1+\frac{k{Y}_b}{Y_a+Y_b})}=\frac{-Y_a{U}_i}{\frac{(Y_a+Y_b)}{k}+Y_b}=\frac{-Y_a{U}_i}{Y_b\&lsqb;1+\frac{Y_a+Y_b}{K{Y}_b}\&rsqb;}---\left(4\right)$

From (4) formula as can be known, when K → ∞, $U_o\&ap;\frac{-Y_a}{Y_b}{U}_i$ , the basic operation relational expression of Here it is operational amplifier.

(2) before proving additional resistance electric capacity connection in series-parallel branch road, parallel branch and series arm are being determined that the admittance value under the frequency compares.

Parallel branch: its admittance value $Y_{}$ ${}_1=\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\mathrm{<figure-callout\; id="1"\; label="j\; C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">j</figure-callout>}{C}_{}{}_1\mathrm{\&omega;}=\frac{1}{R_1}(1+j{R}_1{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1\mathrm{\&omega;})-----\left(5\right)$

Series arm: its admittance value $Y_{}^{}$ ${}_1^{\&prime;}=\frac{1}{(\frac{1}{2}{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}+\frac{1}{\mathrm{<figure-callout\; id="2C"\; label="j"\; filenames="A0110550500212.png"\; state="\{\{state\}\}">j</figure-callout>}2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}})}=\frac{2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}}{({\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}+\frac{1}{j})}=\frac{2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}}{({\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}-j)}---\left(6\right)$

Get R ₁C ₁ω ≈ 1, R ₁' C ₁' ω ≈ 1 just has ${\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}=\frac{1}{R^{\&prime;}}$

And get R ₁=R ₁'=R

Then (5) formula becomes ${\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1=\frac{1}{R}(1+j)---\left(7\right)$

(6) formula becomes ${\mathrm{<figure-callout\; id="1"\; label="Y"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">Y</figure-callout>}}_1^{\&prime;}=\frac{2{\mathrm{<figure-callout\; id="1"\; label="C"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">C</figure-callout>}}_1^{\&prime;}\mathrm{\&omega;}}{(1-j)}=\frac{2}{R^{\&prime;}}\left(\frac{1}{1-j}\right)=\frac{2}{R}\left(\frac{1+j}{1-j^2}\right)=\frac{2}{R}\left(\frac{1+\mathrm{<figure-callout\; id="1"\; label="j"\; filenames="A0110550500171.png"\; state="\{\{state\}\}">j</figure-callout>}}{1+1}\right)=\frac{1}{R}(1+j)----\left(8\right)$

As seen (8) formula and (7) formula equate, that is:

Y ₁＝Y ₁′＝Y(9)

(3) circuit below behind the additional paired branch road of discussion.Use e _nAnd e _pRepresent final (stack result) voltage of negative input end and positive input terminal respectively, behind the additional paired branch road $e_n=\frac{Y_a{U}_i}{(Y_a+Y_b+Y)}+\frac{(Y_b+Y)U_o}{(Y_a+Y_b+Y)}----\left(10\right)$ $e_p=\frac{Y{U}_o}{(Y_a+Y_b+Y)}-----\left(11\right)$

-k(e _n－e _p)＝U _o(12)

With (10) formula and (11) formula substitution (12) formula, $-k\&lsqb;\frac{Y_a{U}_i}{(Y_a+Y_b+Y)}+\frac{(Y_b+Y)U_o}{(Y_a+Y_b+Y)}\&rsqb;+k\frac{Y{U}_o}{(Y_a+Y_b+Y)}=U_o-----\left(13\right)$

(13) formula left side arrangement abbreviation is had $-k\frac{U_a{U}_i}{(Y_a+Y_b+Y)}-k\frac{Y_b{U}_o}{(Y_a+Y_b+Y)}=U_o$ Promptly $-k\frac{Y_a{U}_i}{(Y_a+Y_b+Y)}=U_o\&lsqb;1+\frac{k{Y}_b}{(Y_a+Y_b+Y)}\&rsqb;$ Just get following formula $U_o=\frac{-k{Y}_a{U}_i}{\&lsqb;1+\frac{k{Y}_b}{(Y_a+Y_b+Y)}\&rsqb;(Y_a+Y_b+Y)}=\frac{-Y_a{U}_i}{\&lsqb;\frac{(Y_a+Y_b+Y)}{k}+Y_b\&rsqb;}=\frac{-Y_a{U}_i}{Y_b\&lsqb;1+\frac{(Y_a+Y_b+Y)}{k{Y}_b}\&rsqb;}$

Compare (14) formula and (4) formula, as seen its difference only is the error term of denominator.(14) formula is than having increased in (4) formula error term If Y and Y _bClose at the order of magnitude, the additive error of bringing for the raising circuit stability is (if original error is 0.2%, after additional admittance value is approximately the paired branch road of Y, its error will become 0.3%) that can allow so.Usually, as long as can satisfy the requirement that improves circuit stability, additional branches admittance value Y should hang down unsuitable high, even compares Y on the order of magnitude _bLow.(9) formula Y in a word ₁=Y ' ₁=Y is a very important prerequisite, is putting before this, and the Y value is changeable, can with Y _bIrrelevant.

Advantage of the present invention is:

(1) it is out of control integrating circuit to be generally the direct current that prevents exchange status when work, generally adopts T-shaped net Network; And the present invention is superior far beyond additional T-shaped network, high efficiency and the sorrow of undamped time length.

(2) in the differential circuit, because differential circuit is very weak to the negative-feedback of high-frequency circuit, harmonic frequency more High just more big to the circuit interference. And employing the inventive method can make high frequency close loop negative feedback and operating frequency state Close, high-frequency harmonic there is not especially big effect.

(3) in the phase inverter situation, if the tie point on ground is not directly but the virtual earth follower Output, feedback can appear like this, vibration also can appear, can avoid this kind after adopting the inventive method Oscillatory occurences takes place. Even reference point is not the virtual earth end, adopt the present invention also can bring benefit, because some is put Big device integrated package internal structure can be with the character of differential circuit. Facts have proved, can keep away after employing the inventive method Exempt from the appearance of higher-order of oscillation situation.

(4) to current compensation circuit, usually require the degree of compensation not high, for example the benefit of offset current Repay efficient 95% or high getting final product slightly, this coupling accuracy of just saying additional branches is not high. And hold in many situations Easily vibrate, adopt the inventive method just can avoid later this vibration situation to take place.

(5) circuit complexity in the composite admittance device adopts the inventive method very effectively simple.

(6) voltage transformation (comprising phase shift and value conversion) adopts the present invention that combinatorial operation is amplified Holding circuit was stable when the device circuit improved the accuracy of conversion.

(7) operating frequency range of the present invention's application is very wide, can stride across 100kHz to 1MHz.

(8) circuit of the present invention is simple and reliable, can guarantee stability of operation amplifier circuit, can make fortune again Calculate exactness accurately and greatly improve, and the operating frequency of using also improves greatly.

Claims (10)

1. determine to improve under the frequency method of stability of operation amplifier circuit, comprise operation amplifier circuit, it is characterized in that, additional or the equivalence of former resistance element legs changed over a resistance capacitance series arm on described operational amplifier positive feedback loop; On described operational amplifier negative feedback loop additional or with the loop in the equivalence of former impedance component branch road change over a resistance capacitance parallel branch.

2. improve the method for stability of operation amplifier circuit under definite frequency according to claim 1, it is characterized in that, under the situation that keeps operation amplifier circuit basic operation relation, the equivalent admittance value of the resistance capacitance parallel branch of adding on the equivalent admittance value of additional resistance capacitance series arm and the negative feedback loop on its positive feedback loop equates or becomes to determine ratio.

3. improve the method for stability of operation amplifier circuit under definite frequency according to claim 2, it is characterized in that, described one-tenth determines that ratio is meant in the prototype circuit that amplifier positive input terminal node resultant admittance value and the resultant admittance of negative input end node are worth when unequal, exist certainty ratio really between the resultant admittance value.

4. improve the method for stability of operation amplifier circuit under definite frequency according to claim 1, it is characterized in that, comprise that also reference point is under the situation of virtual earth end, at operational amplifier just, negative input end respectively is being connected a resistance capacitance parallel branch with earth terminal.

5. improve the method for stability of operation amplifier circuit under definite frequency according to claim 4, it is characterized in that, in reference point the two resistance capacitance parallel branches that the positive and negative input of the operational amplifier of virtual earth end is connected with earth terminal, under the situation that keeps operation amplifier circuit basic operation relation, its capacitance equates with capacitance or is in direct ratio, its resistance value and the inverse proportion that resistance value equates or one-tenth is corresponding.

6. improve the method for stability of operation amplifier circuit under definite frequency according to claim 5, it is characterized in that, the described amplifier positive input terminal node resultant admittance value and the resultant admittance of negative input end node of being meant in the prototype circuit in direct ratio or inversely proportional is worth when unequal, has certainty ratio really between the resultant admittance value.

7. improve the method for stability of operation amplifier circuit under definite frequency according to claim 1, it is characterized in that, comprise that also reference point is under the situation of virtual earth end, hold with ground at the positive and negative input of operational amplifier respectively to be connected the resistance capacitance parallel branch.To be connected the resistance capacitance parallel branch that operational amplifier positive input terminal and virtual earth end ask simultaneously and be transformed into equivalent resistance capacitance series arm; Capacitance in this resistance capacitance series arm equals the twice of capacitance in the parallel branch and series impedance in the resistance capacitance series arm equates with the capacitive reactance mould value of series capacitance under operating frequency.

8. improve the method for stability of operation amplifier circuit under definite frequency according to claim 7, it is characterized in that, described resistance capacitance series arm also can be again and between amplifier positive input terminal and the virtual earth end rest parts electricity lead and be in parallel.

9. improve the method for stability of operation amplifier circuit under definite frequency according to claim 1, it is characterized in that, when operational amplifier is used for the current compensation circuit of last trading day/capacitive load, resistance on described operational amplifier positive feedback loop is transformed into a resistance value and the equal resistance capacitance series arm of capacitive reactance mould value, positive input terminal at amplifier is the end that original load connects simultaneously, under the situation that keeps operation amplifier circuit basic operation relation, additional corresponding ground capacity/resistance.

10. improve the method for stability of operation amplifier circuit under definite frequency according to claim 9, it is characterized in that, described corresponding ground capacity/resistance be instigate the amplifier positive input terminal to earth terminal and amplifier positive input terminal to the total impedance of electronegative potential point in the parallel connection value of all resistance equate with the capacitive reactance mould value in parallel of all electric capacity.

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