JPH06104659A - Voltage/current conversion circuit - Google Patents

Abstract

PURPOSE:To prevent the voltage/current conversion circuit from being oscillated even when an inductive load is connected to the circuit. CONSTITUTION:A state observing device 30 receiving an output current and an output voltage of the voltage/current conversion circuit 10 comprising operational amplifiers 2, 3 and outputting a differentiation proportional value of an output current is provided in the voltage/current conversion circuit and the input voltage to the voltage current conversion circuit 10 is corrected by the differentiation proportional value of the output current outputted from the state observing device 30 to suppress the oscillation by selecting an angle at which the frequency characteristic of the operational amplifiers 2, 3 and the frequency characteristic of the reciprocal of a feedback gain are crossed to be 20dB/dec. Furthermore, when the differentiation proportional value of the output current is fed back, no differentiation element is in use and an integration element is used to extract the differentiation value of the load current through the configuration of the state observing device 30 thereby avoiding the effect of noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage / current conversion circuit which makes a current flowing to a load correspond to an input voltage.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a conventional example of a voltage / current conversion circuit for converting a voltage into a current. As shown in FIG. 5, in the conventional voltage / current conversion circuit, the output resistance 4 is connected to the first operational amplifier 2 having a large gain, and the output signal of the output resistance 4 is supplied to the second operational amplifier having a large input impedance. 3 into the second operational amplifier 3
Of the first operational amplifier 2 is fed back to the non-inverting input terminal of the first operational amplifier 2.

Here, a load 5 is connected in series to the output resistor 4, and an input voltage e is applied to the inverting input terminal of the first operational amplifier 2.
_{When I} is given, its inverting input terminal voltage e ₋ and its non-inverting input terminal voltage e ₊ are as shown in the following equations 1 and 2. Further, the first operational amplifier output voltage e _O ^* becomes as shown in the following Expression 3. Here, e _O is the output voltage of the voltage-current conversion circuit 10, r is the resistance value of the output resistor 4, and R
₆ , R ₇ , R ₈ and R ₉ represent the resistance values of the resistor 6, the resistor 7, the resistor 8 and the resistor 9, respectively.

[0004]

[Equation 1]

[0005]

[Equation 2]

[0006]

[Equation 3]

Since the second operational amplifier 3 is an amplifier having a gain of 1 and an extremely large input impedance, the resistance values R ₈ and R ₉ of the resistors ₈ and ₉ can be ignored with respect to the load impedance Z. Here, it is assumed that the resistors 6 and 8 have the same resistance value (that is, R ₆ = R ₈ ) and the resistors 7 and 9 have the same resistance value (that is, R ₇ = R ₉ ), and the gain of the first operational amplifier 2 is If it is infinite, the following conditions are satisfied.

Inverted input terminal voltage e ₊ = non-inverted input terminal voltage e ₋ As a result, the following Equation 4 is obtained from the above Equations 1, 2 and 3, and from this Equation 4, the output current i _O and the input voltage are obtained. The relationship with e _I is as shown in Equation 5 below.

[0009]

[Equation 4]

[0010]

[Equation 5]

As is apparent from the equation (5), if the voltage / current conversion circuit circuit 10 shown in FIG. 5 is used, the output current i _O of this circuit is proportional to the input voltage e _I. That is, the input voltage e _{I of the} circuit can be converted into an output current i _O proportional to this.

[0012]

However, there is a time delay in the response of the first operational amplifier 2 which constitutes the voltage / current conversion circuit 10. Therefore, if the transfer function between the input and output of the first operational amplifier 2 is A ₀ / (1 + s · τ), the circuit shown in FIG. 5 can be rewritten into the block circuit shown in FIG.

FIG. 6 is a block circuit diagram showing the voltage / current conversion circuit shown in FIG. 5 in blocks. Further, FIG. 7 is an equivalent conversion block circuit diagram in which the block circuit shown in FIG. 6 is equivalently converted. Here, if the load 5 is an inductive load, the load impedance Z can be expressed as Z = s · L, and therefore the following expression 6 is established.

[0014]

[Equation 6]

By normalizing the above Equations 1, 2, and 3 and this Equation 6, the following Equations 7, 8, 9 and 10 are obtained.

[0016]

[Equation 7]

[0017]

[Equation 8]

[0018]

[Equation 9]

[0019]

[Equation 10]

However, in each of the above equations, E _N = Rated voltage of the circuit, I _N = Rated current of the circuit, and e _O , e _I , e
_{+ And} e ₋ are represented by the following formula 11, and K _R and T _L
Is expressed by the following formula 12.

[0021]

[Equation 11]

[0022]

[Equation 12]

Further, when the replacement by the value expressed by the following equation 13 is performed, the block circuit shown in FIG. 8 is obtained by performing the equivalent conversion of the block circuit after the equivalent conversion shown in FIG.

[0024]

[Equation 13]

FIG. 8 is a re-equivalent conversion block circuit diagram in which the equivalent conversion block circuit shown in FIG. 7 is equivalently converted again.
In the re-equivalent conversion block circuit shown in FIG. 8, the loop gain of the closed loop is A ^* .β. Here, A ^* is as shown in Expression 14, and β is as shown in Expression 15.

[0026]

[Equation 14]

[0027]

[Equation 15]

This loop gain A ^* .beta.
It can be rewritten as shown in.

[0029]

[Equation 16]

That is, since the difference between A ^* and 1 / β is A ^* · β, in order for this loop to be stable, the slope when this loop gain A ^* · β falls below 0 decibel is −20 dB / de
Must be c. This is equivalent to the angle at which A ^* and 1 / β intersect being −20 dB / dec.
FIG. 9 is a frequency characteristic diagram showing the frequency characteristic of the conventional voltage-current conversion circuit shown in FIG. 5, and FIG. 10 is also a frequency characteristic showing the frequency characteristic of the conventional voltage-current conversion circuit shown in FIG. In each of the figures, the horizontal axis indicates the angular frequency ω in rad.
/ S, and the vertical axis represents the gain in dB. As shown in FIGS. 9 and 10, when the load 5 is an inductive load, the above-described crossing angle θ is −40 dB / de.
Since it is c, the conventional voltage-current conversion circuit has a major drawback that it oscillates.

This will be described in more detail. That is, the output voltage e _O ^* of the first operational amplifier 2 and the voltage / current conversion circuit 1
The ratio of 0 to the output voltage e _O is 0. When A ^* is sufficiently larger than 1 / β (that is, A ^* >> 1 / β), the above ratio e _O ^* / e _O is Can be approximated.

[0032]

[Equation 17]

[0033] On the contrary, A ^* is 1 / beta sufficiently smaller than (i.e. A ^* «1 / β) ratio of the above-mentioned case e _O ^* / e
_O can be approximated by Equation 18.

[0034]

[Equation 18]

That is, the ratio e _O ^* / e _O is as shown in FIG. 9 or FIG.
It becomes a line approximation drawn with a thick line. However, actually, as shown by a dotted line, the resonance characteristic has a peak at an angular frequency value of ω ₁ . That is, as described above, the conventional circuit oscillates. Therefore, the purpose of this invention is to
The purpose is to prevent oscillation even when an inductive load is connected to the current conversion circuit.

[0036]

In order to achieve the above object, the voltage-current conversion circuit of the present invention has a series circuit of an output resistance and a load connected to the output side of a first operational amplifier having a large gain. , The output side voltage of this output resistor is input to the second operational amplifier having a large input impedance,
The output voltage of the second operational amplifier is input to the non-inverting input terminal of the first operational amplifier, and the output current corresponding to the input voltage applied to the inverting input terminal of the first operational amplifier is supplied to the load. In a voltage / current conversion circuit, current detection means for detecting an output current flowing to the load, and the output current and the output voltage of the first operational amplifier are input to output an amount proportional to a differential value of the output current. And a correction means for correcting the input voltage to the first operational amplifier by the differential proportional amount of the output current output by the state observer. Is an integral calculation means for outputting a simulated value of the output current,
A first gain that multiplies the output current simulation value by a predetermined number, a second gain that multiplies the deviation between the output current input to the state observer and the output current simulation value by a predetermined number, and the integral calculation means. And a third gain for multiplying the input signal by a predetermined number,
A value obtained by adding the output voltage of the first operational amplifier, the output signal of the first gain, and the output signal of the second gain, which are input to the state observing device, is used as an input signal to the integration calculating means, It is assumed that the output signal of the gain is a differential value proportional amount of the output current output by the state observer.

[0037]

When the load connected to the voltage / current conversion circuit is inductive, the feedback gain 1 / β increases in proportion to the frequency with respect to the constant current. In the present invention, this feedback gain 1 / β increases.
Is flattened in the high frequency region, and the angle θ at which the frequency characteristic A ^{* of the} amplifier and 1 / β intersect is set to −20 dB / dec.

In the present invention, assuming that the amount proportional to the differential value of the output current i _O is e _F ^* , this e _F ^* is expressed by the following equation 19. However, F is a feedback gain.

[0039]

[Formula 19]

When the differential value proportional amount e _F ^* of the output current i _O is fed back, the following formula 20 is established.

[0041]

[Equation 20]

Therefore, as shown in FIG. 7, the input voltages e _I and β
・ Equation 21 is obtained by adding e _O ^* .

[0043]

[Equation 21]

This e _F is fed back. At this time E
_I ^* = E _I -E _F ^* is input voltage e _I of FIG. Here, from the above expression 21 to β becomes β ^* shown in the following expression 22. However, although ω ₀ described in Expression 22 is shown in Expression 23,
If the value of ω ₀ is selected so that ω ₀ > (K _R / T _R ), the frequency characteristics of β and 1 / β are flat in the region of ω ≧ ω ₀ as shown in FIG. 4 described later. become.

[0045]

[Equation 22]

[0046]

[Equation 23]

[0047]

1 is a circuit diagram showing a first embodiment of the present invention, in which a load 5 and a voltage / current conversion circuit 1 are described.
0 and the first of the voltage / current conversion circuit 10
The operational amplifier 2, the second operational amplifier 3, the output resistance 4, the resistance 6, the resistance 7, the resistance 8 and the resistance 9 have the same names, uses and functions as those of the conventional circuit described in FIG. Is omitted.

In the present invention, the output current i _O supplied to the load 5 is detected by the current detector 20, and this output current i _O is input to the state observer 30 together with the first operational amplifier output voltage e _O ^*. There is. Since the state observer 30 outputs the differential value proportional amount e _F ^* of the output current, the voltage / current conversion circuit 1
The input voltage e _I input to 0 is corrected by this e _F ^* , and the correction result e _I ^* is input to the voltage-current conversion circuit 10 to obtain the frequency characteristics of β and 1 / β as described above. It is made flat so that the voltage / current conversion circuit 10 is prevented from oscillating.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention, showing the configuration of the state observer 30 shown in FIG. 1, which state observer differentiates the output current i _O. The value proportional amount is output. This state observing device is intended for the portion from the first operational amplifier 2 to the load 5 in the voltage / current conversion circuit 10, that is, the part represented by the formula 24, and its configuration is as shown in the formula 25.

[0050]

[Equation 24]

[0051]

[Equation 25]

However, the values of −25 above i _o , T _L , and K _R described in _Equation 25 are simulated values of i _o , T _L , and K _R , respectively, and g is the gain of the state observer. Yes, at this time, the following Expression 26 is established.

[0053]

[Equation 26]

Here, even if T _L and K _R are not equal to their respective simulated values, if the gain g is selected to be large, i _o will be equal to the simulated value thereof. Therefore, the value shown in the following Expression 27 is obtained from the input signal of the integration calculator 31.

[0055]

[Equation 27]

The value expressed by the equation (27) is proportional to the differential value di _O / dt of the output current i _O. By multiplying the differential proportional amount of the output current i _O detected in this way by the gain F in the third gain 34, F · s · T _L · i _O
Is defined as the output value e _F ^* of the state observer 30, and this e _F
^* _{Is used} to correct the input voltage e _I to the voltage / current conversion circuit 10.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention and shows the configuration of the current detector 20 shown in FIG. The current detector 20 is not constituted by a third operational amplifier 21 and the differential amplifier 22, the output current i _O detects a voltage drop r · i _O that occurs when flowing through the output resistor 4. FIG. 4 is a graph showing the frequency characteristics of the embodiment circuit shown in FIGS. 1 and 2, in which the horizontal axis represents the angular frequency ω in units of rad / s and the vertical axis represents the gain in units of dB. It represents. If a _value of ω ₀ > (K _R / T _R ) is selected as ω ₀ , the frequency characteristics of β and 1 / β become flat in the region of ω ≧ ω ₀ as shown in FIG. Become.

[0058]

According to the present invention, there is provided a state observing device for inputting the output current and output voltage of the voltage-current conversion circuit composed of the operational amplifier and outputting the differential value proportional amount of the output current, The input voltage to the voltage / current conversion circuit is corrected by the amount proportional to the differential value of the output current output by the state observer. Therefore, since the frequency characteristic of the inductance is apparently constant in the high frequency region,
The angle at which the frequency characteristic of the operational amplifier and the reciprocal of the feedback gain, that is, the frequency characteristic of 1 / β intersect is −
It becomes 20 dB / dec, and the effect of preventing resonance and suppressing oscillation can be obtained. Further, when feeding back the differential value proportional amount of the output current described above, the circuit of the state observer is configured to extract the differential value of the load current using the integral element without using the differential element, The effect of avoiding the risk of being affected by noise is also obtained. Also, by making the feedback amount of this output current differential value variable,
Since the frequency characteristic of the inductance can be apparently changed at a predetermined angular frequency value, a voltage / current conversion circuit having stable dynamic characteristics can be obtained according to the inductor chair.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a graph showing frequency characteristics of the embodiment circuit shown in FIGS. 1 and 2;

FIG. 5 is a circuit diagram showing a conventional example of a voltage / current conversion circuit for converting a voltage into a current.

6 is a block circuit diagram showing the voltage / current conversion circuit shown in FIG. 5 in blocks.

7 is an equivalent conversion block circuit diagram in which the block circuit illustrated in FIG. 6 is equivalently converted.

FIG. 8 is a re-equivalent conversion block circuit diagram obtained by re-equivalently converting the equivalent conversion block circuit shown in FIG.

9 is a frequency characteristic diagram showing frequency characteristics of the conventional voltage-current conversion circuit shown in FIG.

FIG. 10 is a frequency characteristic diagram showing frequency characteristics of the conventional voltage-current conversion circuit shown in FIG.

[Explanation of symbols]

2 1st operational amplifier 3 2nd operational amplifier 4 Output resistance 5 Load 10 Voltage / current conversion circuit 20 Current detector 21 3rd operational amplifier 22 Differential amplifier 30 State observer 31 Integral calculator 32 1st gain 33 2nd gain 34 3rd gain e _I Input voltage e _O Output voltage e _O ^* First operational amplifier output voltage i _O Output current

Claims (3)

[Claims] 1. A series circuit of an output resistance and a load is connected to the output side of a first operational amplifier having a large gain, and the output side voltage of this output resistance is input to a second operational amplifier having a large input impedance. The output voltage of the second operational amplifier is input to the non-inverting input terminal of the first operational amplifier, and the output current corresponding to the input voltage applied to the inverting input terminal of the first operational amplifier is supplied to the load. Voltage·
In the current conversion circuit, current detection means for detecting the output current flowing to the load,
A state observer which inputs the output current and the output voltage of the first operational amplifier and outputs an amount proportional to the differential value of the output current, and a differential value proportional amount of the output current output by the state observer. And a correction means for correcting the input voltage to the first operational amplifier. 2. The voltage / current conversion circuit according to claim 1, wherein the state observer outputs integral simulation means for outputting a simulated value of the output current, and a first multiple for multiplying the simulated output current value by a predetermined number. A gain, a second gain that multiplies a deviation between the output current input to the state observer and the simulated output current by a predetermined number, and a third gain that multiplies an input signal to the integration calculation unit by a predetermined number. A value obtained by adding the output voltage of the first operational amplifier, the output signal of the first gain, and the output signal of the second gain, which are input to the state observing device, as an input signal to the integration calculation means, A voltage-current conversion circuit, wherein the output signal of the third gain is a differential value proportional amount of the output current output by the state observer. 3. The voltage / current conversion circuit according to claim 1, wherein the current detecting means for detecting the output current flowing to the load has a difference between the input voltage of the output resistor and the output voltage. A voltage-current conversion circuit characterized by using dynamic amplification means as a constituent element.