JPH10256838A - Current feedback circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the stability of an open loop and then to attain a prescribed frequency band by amplifying the input signal according to the output of a conversion means which converts the output current of a current feedback circuit into voltage and performing the feedback to the amplifier means via a phase compensation element. SOLUTION: An error amplifier part 2 performs the compensation of phase via a resistance 23 and a capacitor 24 and amplifies again the input signal amplified at an amplifier part 1 in response to the output of an output current/ voltage conversion part 4. The part 4 converts the output current flowing to a coil 5 that is connected to the corresponding current feedback circuit as a load into voltage and amplifies this voltage. The circuit constants of the parts 2 and 4 are properly set according to the numerical value of the coil 5 connected as a load. Thus, the phase characteristic of the output current is controlled to the input and a prescribed frequency band is attained. Then the phase margin is increased for the frequency characteristic of a relevant open loop to secure the stability of this loop.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a CD, a CD-RO
The present invention relates to a current feedback circuit used as a circuit for supplying a current to a coil, such as a DISC device such as M, DVD, or MD, or a device having a motor.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional BTL type coil drive circuit. In the figure, 101 is a first operational amplifier, 102 is a second operational amplifier, 103, 104,
105 and 106 are resistors, 5 is a coil, 6 is an external load, 7
Is a servo circuit. The coil driving circuit includes a first operational amplifier 101, a second operational amplifier 102, resistors 103 and 104,
105, 106, the first operational amplifier 101
A reference voltage is applied to the non-inverting input terminal (+) of the current feedback circuit, while an input signal to the current feedback circuit is applied to the inverting input terminal (−) via the resistor 103 and the resistor 1
The output of the first operational amplifier 101 is fed back via the signal line 04.

A reference voltage is applied to the non-inverting input terminal (+) of the second operational amplifier 102, while the output of the first operational amplifier 101 is connected to the inverting input terminal (−) of the resistor 105.
Through the resistor 106 and the second through the resistor 106.
The output of the operational amplifier 102 is fed back. Then, a difference voltage between the output of the first operational amplifier 101 and the output of the second operational amplifier 102 is extracted as an output.

The coil drive circuit having the above-described configuration outputs a voltage in response to a control signal given from a servo circuit 7 for controlling the operation state of an external load 6, for example, and a coil connected to the output as a load. 5 is used to drive an external load 6 by passing a current through it.

[0005]

Here, in the coil driving circuit having the above configuration, assuming that the frequency bands of the first operational amplifier 101 and the second operational amplifier 102 are sufficiently higher than those of the input signal, No phase shift occurs between the input voltage and the output voltage. However, due to the inductance component of the coil 5, a phase shift occurs between the output voltage and the output current (current flowing through the coil 5) in a high frequency band. When this phase shift occurs, there is a possibility that the phase margin of the servo loop is deteriorated, so that the frequency band of the signal to be handled is limited.

Looking at how much the frequency band is limited, in the current feedback circuit having the above configuration, the output voltage is V _OUT , the output current is I _O , the inductance component and the resistance component of the coil 5 are L, respectively. , R _L and the angular frequency is ω
Then, I _O = V _OUT / (jωL + _RL ) {I _O / V _OUT = 1 / (jωL + _RL ) = (1 / L) ｛1 / (jω + ( _RL / L)} The frequency f _C is f _C = R _L / 2
πL, and the phase delay at this time is 45 °. In order not to affect the phase margin of the servo loop, it is ideal that the phase shift is zero within a necessary frequency band. Therefore, the frequency band does not become higher than the cutoff frequency f _C.

Then, the numerical value of the coil 5 whose load is the cutoff frequency f _C (inductance component and resistance component)
Since the frequency band is determined only by the coil, depending on the coil connected as the load, the frequency band cannot be sufficiently widened, and the standard cannot be satisfied. In other words,
The coils that can be connected as loads are limited.

Accordingly, the present invention provides a current feedback circuit capable of realizing a predetermined frequency band while ensuring stability in an open loop (prevention of oscillation) regardless of the numerical value of a connected load. The purpose is to:

[0009]

In order to achieve the above object, in a current feedback circuit according to the present invention, an output current flowing through a load of the current feedback circuit is provided in a current feedback circuit for outputting a voltage according to an input signal. Output current converted to voltage /
It has voltage converting means and amplifying means for amplifying an input signal in accordance with the output of the current / voltage converting means. In the amplifying means, feedback is provided via a phase compensation element.

With the above arrangement, the phase characteristics of the output current with respect to the input can be adjusted by appropriately setting the circuit constants of the phase element and the current / voltage conversion means, so that a predetermined frequency band can be satisfied. In addition, stability (prevention of oscillation) can be ensured in the open-loop frequency characteristics by using a phase margin.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a current feedback circuit according to an embodiment of the present invention, wherein 1 is a preamplifier unit, 2 is an error amplifier unit, 3 is an amplifier unit having the same configuration as the coil drive circuit shown in the related art, 4 is an output current / voltage converter, and 5 is a coil connected as a load to the current feedback circuit.

First, the preamplifier 1 includes an operational amplifier 11,
The reference voltage is applied to the non-inverting input terminal (+) of the operational amplifier 11, and the input signal to the current feedback circuit is connected to the inverting input terminal (-) of the operational amplifier 11. 12, and the output of the operational amplifier 11 is fed back via a resistor 13.
With such a configuration, the preamplifier 1 functions to amplify an input signal and take an interface.

The error amplifier 2 comprises an operational amplifier 21 having a very large DC gain, resistors 22 and 23, and a capacitor 24. The non-inverting input terminal (+) of the operational amplifier 21 has the preamplifier 1 An output is given. On the other hand, the output of the output current / voltage converter 4 is connected to the inverting input terminal (−) via the resistor 22, and the output of the operational amplifier 21 is connected in series to the resistor 23. , Through the capacitor 24. With such a configuration, the error amplifier unit 2 performs the phase compensation (phase lead compensation) for preventing oscillation by the resistor 23 and the capacitor 24 and outputs the input signal amplified by the preamplifier unit 1 to the output current /
Amplification is performed according to the output of the voltage circuit 4.

Next, the output current / voltage converter 4 includes a resistor 4
1, 43, 44, 45, 46, and an operational amplifier 42. The resistor 41 is connected in series with the coil 5 as a load to the output of the amplifier unit 3, and the non-inverting input terminal (+ ) Is connected to a connection point between resistors 43 and 44 connected in series between one end of the resistor 41 and the reference potential, while the other end of the resistor 41 is connected to the inverting input terminal (−) by a resistor 45. And the operational amplifier 4
2 is fed back via the resistor 46. With such a configuration, the output current / voltage converter 4 converts the output current flowing through the coil 5 into a voltage, and amplifies the voltage.

Since the amplifier section 3 has the same configuration as the current feedback circuit shown in the prior art, a description thereof will be omitted.

Here, in the current feedback circuit shown in FIG.
Assuming that the closed-loop gain of the error amplifier unit 2 is A and the feedback amount is B, the closed-loop gain G _C is as follows: G _C = V _OUT / V _IN = A / (1 + AB) On the other hand, L the inductance component of the coil 5, a resistive component, respectively, and R _L, the output current / voltage conversion circuit 4
Assuming that the resistance value of the resistor 41 is R _d , V _OUT = I _O (Ls + _RL + R _d ) (where s = jω), so that the preamplifier unit 1, the amplifier unit 3, and the output current / voltage circuit 4 Is 1, the DC gain G _m of the current feedback circuit shown in FIG.
_m = _IO / _VIN = {1 / (Ls + _RL + _Rd )}. multidot.A
/ (1 + AB)}.

The resistance values of the resistors 22 and 23 are R ₁ and R ₂ ,
When the capacitance of the capacitor 24 is C and the closed-loop gain of the error amplifier unit 2 is A and the feedback amount B is obtained and substituted into the above equation, G _m = K (s + Z) / ｛s ² + (ω ₀ / Q) s + ω ₀ ² ｝ where K = R ₂ / (LR ₁ ), Z = 1 / CR ₂ ω ₀ = ｛R _d / (CLR ₁ )｝ ^1/2 Q = L ｛R _d / (CLR ₁ )｝ ^{1 _{/ 2 / (R L + R}} d + R 2 R
_d / R ₁ ), which is a second-order pole (pole frequency f _P = ω _0).
/ (2π)) and a filter having a first-order zero point (zero point frequency f _Z = Z / (2π)).

The pole frequency f _P and the zero point frequency f _Z are determined not only by the coil 5 which is a load,
R _1, R _2, C, because it also depends on the constants of R _d, depending on the value of the coil 5 (inductance component), R _1,
If the constants of R ₂ , C and R _d are set appropriately, the DC gain G
The Bode diagram of _m is as shown in FIG. 2, and the phase characteristic of the output current with respect to the input can be adjusted to satisfy a predetermined frequency band.

Next, the open loop frequency characteristics of the current feedback circuit shown in FIG. 1 will be examined. In the circuit of FIG. 3 equivalently representing the current feedback circuit shown in FIG. 1, the frequency characteristic when the feedback loop from the output is cut at the point shown in FIG. 3 is the open loop frequency characteristic. Since coming affecting open-loop gain and first pole of the operational amplifier 21 in the error amplifier section 2 negligible when considering the closed loop, and these A _O, the resistance value R _0, the capacitance C ₀
Are equivalently shown by an RC low-pass filter having.

[0020] In FIG. 3, considered by dividing the V _IN and the first stage to the output of the buffer BF _1, in two stages eyes from the output of the buffer BF ₁ to V _OUT. First, the transfer function T ₁ in the first stage is T ₁ = (R _d / L) {1 / (s + P ₁ )} where P ₁ = ( _RL + R _d ) / L and has one pole.

Next, the second stage of the transfer function T _{2 are, T 2 = -K 2 (s} + Z 2) / {(s + P A) (s +
P _B )｝ where K ₂ = A _O P ₀ R ₂ / (R ₁ + R ₂ ), Z ₂ = 1 /
(CR ₂ ) P ₀ = 1 / (R ₀ C ₀ ) (P ₀ is the first pole angular frequency of the operational amplifier 21) P _A and P _B are transfer functions 1 / (s ² +
pole angular frequency .beta.s + gamma) _{Incidentally, β = (P 0 R 1} + A O P 0 R 1 + P 0 R 2 + Z 2 R 2) /
(R ₁ + R ₂ ) γ = P ₀ Z ₂ R ₂ / (R ₁ + R ₂ ), and has one zero point and two poles.

From the above, the open-loop transfer function T _OL is given by T _OL = − (K ₂ R _d / L) (s + Z ₂ ) / ｛(s + P _A )
_{(S + P B) (s} + P 1)} , and the this zero point one (zero-point frequency: Z _2/2
π) and three poles (pole frequency: P _A / 2π, P _B /
2π, P ₁ / 2π).

Therefore, the zero point frequency (Z ₂ / 2π)
And the pole frequency _{(P A / 2π, P B} / 2π, P 1/2
π) indicates not only the coil 5 as a load but also R ₁ , R ₂ ,
C, because it also depends on the constants of R _d, depending on the value of the coil 5 (inductance _{component), R 1, R 2,} C, R
If the constants of _d are set appropriately, the frequency characteristics of the open loop are as shown in FIG. 4, and the stability (prevention of oscillation) can be secured by increasing the phase margin (phase lead compensation).

As described above, in the current feedback circuit of the present embodiment, the circuit constants of the error amplifier 2 and the current / voltage converter 4 depend on the values (inductance and resistance) of the coil 5 connected as a load. By appropriately setting the phase characteristics of the output current with respect to the input,
In addition to satisfying the predetermined frequency band, the phase margin is also used in the open loop frequency characteristics,
Stability (prevention of oscillation) can be ensured.

In the above description, only the embodiment of the BTL system has been described. However, a single-phase (OTL) coil drive in which the output is connected to only one side of the load can be similarly configured.

[0026]

As described above, according to the current feedback circuit of the present invention, by setting the circuit constant appropriately in accordance with the connected load, the phase margin in the open-loop frequency characteristic can be increased, and the stability can be improved. Since the frequency characteristics of the phase of the output current with respect to the input can be adjusted while ensuring the performance (oscillation prevention), a predetermined frequency band can be realized, so that the load that can be connected is not limited.

[Brief description of the drawings]

FIG. 1 is a block diagram of a current feedback circuit according to an embodiment of the present invention.

FIG. 2 is a diagram (Board diagram) showing a frequency characteristic of an output current with respect to an input in the current feedback circuit of FIG. 1;

FIG. 3 is an equivalent circuit diagram used for obtaining an open-loop frequency characteristic in the current feedback circuit of FIG. 1;

FIG. 4 is a diagram (Board diagram) showing an open loop frequency characteristic in the current feedback circuit of FIG. 1;

FIG. 5 is a block diagram of a conventional BTL-type coil drive circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Preamplifier part 2 Error amplifier part 3 Amplifier part 4 Output current / voltage conversion part 5 Coil 6 External load 7 Servo circuit 11 Operational amplifier 12, 13 Resistance 21 Operational amplifier 22, 23 24 Capacitor 41 Resistance 42 Operational amplifier 43, 44, 45 , 46 resistance 101 first operational amplifier 102 second operational amplifier 103, 104, 105, 106 resistance

Claims (1)

[Claims] A current / voltage conversion means for converting an output current flowing through a load of the current feedback circuit into a voltage, and outputting the voltage;
A current amplifying means for amplifying an input signal in accordance with an output of the current / voltage converting means, wherein the amplifying means performs feedback via a phase compensation element.