JPH0353801B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier output characteristic control circuit that can arbitrarily set the output impedance of the amplifier.

For example, when a speaker is connected as a load to an amplifier, if the speaker cord connecting the load connection terminal of the amplifier and the speaker is long, the damping factor of the amplifier will be relatively reduced due to the line impedance, and as a result, the damping factor of the speaker will be reduced. There is a problem in that the characteristics cannot be maximized. On the other hand, there is a demand for being able to arbitrarily set the damping factor of the amplifier in order to optimize the timbre of the sound generated from the speaker.

In order to solve such problems, the present applicant previously set the output impedance of the amplifier to a negative value by current feedback in Japanese Patent Laid-Open No. 54-65461, and thereby the load connection terminal of the amplifier A method of canceling the line impedance between the line and the load is shown. Figure 1 is a circuit diagram showing the configuration of an amplifier output characteristic control circuit using this method. 2 and 3, the current supplied to the load 6 is amplified by an amplifier 4 (shown as an operational amplifier) and supplied to the load 6 inserted between the load connection terminals 5a and 5b. and the ground point, and the detection output is fed back to the inverting input terminal of the amplifier 4 via a feedback control circuit consisting of an amplifier 8 and a resistor 9. Amplifier 4 between load connection terminals 5a and 5b
The output impedance of the line 10 connected to the load 6 is set to a negative value in order to cancel out the line impedance of the line 10 to which the load 6 is connected.

By the way, changes in the output impedance of an amplifier, for example, if the load is a speaker, will affect the load only especially in the low frequency band. Therefore, if the load is a speaker,
If the output impedance (ie, damping factor) is improved only in the low frequency band, the influence of the output impedance can be removed more efficiently. It would be more advantageous if the output impedance could be controlled only in the frequency band of interest, depending on the type of load. Further, it is desirable that the gain of the amplifier is not affected by the impedance of the load or the frequency of the signal, even if an output characteristic control circuit is provided.

The present invention has been made in view of the above circumstances, and the first aspect of the present invention is to provide an amplifier output characteristic control circuit in which the gain of the amplifier does not depend on the impedance of the load ZL. , a current detection circuit that is inserted in series with a load ZL connected to the load connection terminal of the amplifier and detects the current supplied to the load ZL, and a detection output of this current detection circuit is fed back to the input side of the amplifier. a feedback control circuit; a first transfer characteristic portion Gv ₁ that does not depend on the value of the load ZL; The transfer characteristic setting circuit includes an equivalent impedance of the load ZL so as to have a transfer characteristic of 1/Gv ₂ when expressed as a product of a second transfer characteristic portion Gv ₂ that depends on the value of the load ZL. a first correction circuit disposed in front of the amplifier; The output impedance to ZL is controlled, and the voltage gain GT, which is expressed by the ratio of the signal voltage input to the first correction circuit and the voltage applied across the load ZL, does not depend on the value of the load ZL. It is characterized by what it did.

In addition to the object of the first invention, the second invention aims to provide an output characteristic control circuit for an amplifier in which the gain of the amplifier does not depend on the transfer characteristic of the feedback control circuit, and In addition, the detection output of this current detection circuit is determined by the transfer characteristic Ts
a feedback control circuit that feeds back the signal voltage input to the amplifier to the input side of the amplifier, and a signal voltage input to the amplifier and the load.
The voltage gain Gv expressed as the ratio to the voltage applied across ZL depends on the first transfer characteristic portion Gv ₁ that does not depend on the value of the transfer characteristic Ts of the feedback control circuit and the value of the transfer characteristic Ts of the feedback control circuit. a second correction circuit disposed in front of the amplifier and set to have a transfer characteristic of 1/Gv ₂ when expressed as a product of a second transfer characteristic portion Gv ₂ ;
The output impedance to the load ZL is controlled according to the feedback amount of the detection output of the current detection circuit that is fed back to the input side of the amplifier via the feedback control circuit, and is input to the second correction circuit. The present invention is characterized in that the voltage gain GT expressed by the ratio of the signal voltage to the voltage applied across the load ZL does not depend on the transfer characteristic Ts of the feedback control circuit.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a circuit diagram showing the configuration of a first embodiment of the present invention, and in this figure, parts corresponding to those in FIG. 1 are given the same reference numerals. In addition, this figure 2 is illustrated as an example of the configuration of an amplifier that can arbitrarily change the output impedance in the following explanation of the embodiment, and the difference from the one described above in figure 1 is as follows. , the load can be grounded on one side. It goes without saying that the present invention is not particularly applicable to the one shown in FIG. 2, but can also be applied to the one shown in FIG. In FIG. 2, signal input terminal 1 is connected to a non-inverting input terminal 4a of an amplifier (shown as an operational amplifier) 4. In FIG. amplifier 4
A feedback dividing resistor 2 (value R 1 ) is inserted between the inverting input terminal 4b of the amplifier 4 and the ground point, and a feedback dividing resistor 2 (value R ₁ ) is inserted between the inverting input terminal 4b and the output terminal 4c of the amplifier 4. A resistor 3 (value R ₂ ) is inserted.
A resistor 7 (current detection circuit, value Rs) is inserted between the output terminal 4c of the amplifier 4 and the load connection terminal 5. One end of the resistor 7 on the output terminal 4c side is connected to an inverting input terminal of a control amplifier (feedback control circuit) 8, and the other end of the resistor 7 is connected to a non-inverting input terminal of the control amplifier 8. This control amplifier 8 outputs a differential voltage applied between its non-inverting input terminal and its inverting input terminal from its output terminal in accordance with its transfer characteristic Ts. The output terminal of the control amplifier 8 and the inverting input terminal 4 of the amplifier 4
A resistor 9 (value R ₃ ) is inserted between the resistor 9 and b.
Further, a load (impedance Z _L ) 6 is connected via a line 10 between the load connection terminal 5 and the ground point.

In the above configuration, the voltage applied between the signal input terminal 1 and the ground point is v ₁ , the voltage between the output terminal 4c of the amplifier 4 and the ground point is v ₂ , and the voltage between the load connection terminal 5 and the ground point is v 1 . _v0 is the voltage between the output terminal of the control amplifier 8 and the ground point, _vX is the voltage between the output terminal of the control amplifier 8 and the ground point, _i1 is the current flowing into the ground point through the resistor 2, and the output of the control amplifier 8 When the current flowing into the terminal is i ₂ and the current flowing into the load 6 via the load connection terminal 5 is i _L , the voltage v ₂ at the output terminal 4c of the amplifier 4 is v ₂ = v ₁ + R ₂ (i ₁ + i ₂ )... Or, it can be expressed as v ₂ = v ₀ + Rs・i _L = v ₀ + Rs・v ₀ /Z _L = v ₀ (1+Rs/Z _L ...) Therefore, these formulas and From this, the following formula is obtained: v ₁ +R ₂ (i ₁ +i ₂ )=v ₀ (1+Rs/Z _L )...

On the other hand, the currents i ₁ and i ₂ are respectively i ₁ = v ₁ /R ₁ ... i ₂ = v ₁ −v _X /R ₃ ..., and the voltage v _X at the output terminal of the control amplifier 8
is _vX =Ts( _v0 − _v2 )... By substituting _the above formula _{into this formula} , _{we obtain v}・v ₀ /R ₃ ... is obtained. Then, by substituting this equation and the above equation into the above equation, v ₁ (1+R ₂ /R ₁ +R ₂ /R ₃ ) =v ₀ {1+Rs/Z _L (1-R ₂ /R ₃ Ts)}... From this equation, the voltage gain Gv between the signal input terminal 1 and the load connection terminal 5 in this embodiment, that is, Gv=v ₀ /v ₁ =1+R ₂ /R ₁ +R ₂ /R ₃ / 1+R _S /Z _L (1-
_R2 / _R3 )Ts)... is obtained. In addition, _Gv1 =1+ _R2 / _R1 + _R2 / _R3 , and _Gv2 =1+Rs/ZL(1- _R2 / _R3Ts ). When the resistance values of resistor 3 and resistor 9 are equal, that is, when R ₂ = R ₃ , this voltage gain Gv is G _v = 2 + R ₂ /R ₁ /1 + R _S /Z _L (1-Ts)...' becomes. In addition, in this embodiment, the output impedance of the amplifier 4 side at the load connection terminal 5 (this output impedance is Z ₀ ) is the voltage v ₀ in the no-load state, that is, when the impedance Z _L is infinite, is v ₀ ' In this case, Z ₀ = Z _L (v ₀ ′/v ₀ −1) ..., and this formula is expressed as follows: If the voltage gain G _v when the impedance Z _L is infinite is G _v ′, then Z ₀ = Z _L (G _v ′/G _v −1) .... Here, G′v can be expressed as Gv′=1+R ₂ /R ₁ +R ₂ /R ₃ ... from the above formula. , by substituting this equation and the above equation into the equation, the output impedance Z ₀ is: Z ₀ = Z _L {1+R ₂ /R ₁ +R ₂ /R ₃ /1+R ₂ /R ₁ +R ₂ /R ₃ /1
+R ₃ /Z _L (1-R ₂ /R ₃ Ts)-1} =Rs (1-R ₂ /R ₃ Ts)... Also, the output impedance shown in this formula
In particular, Z ₀ becomes Z ₀ =Rs(1-Ts)...' when R ₂ =R ₃ . Therefore, from this equation, it is understood that the output impedance Z ₀ can be arbitrarily set to a positive value by setting the transfer characteristic Ts to Ts≦1, and to a negative value by setting Ts>1. In particular, if the line impedance of the line 10 in FIG. By setting Ts, line impedance r can be completely canceled out.

In this way, according to the first embodiment, it is possible to set the output impedance Z ₀ to any positive or negative value, thereby canceling out the impedance of the line 10 for connecting the load. can.

Next, a second embodiment of the invention will be described.

In the second embodiment, the damping factor is improved more in the low frequency band for the case where a load is connected, such as a speaker, which requires a large damping factor especially in the low frequency band. This is how it was done. Figure 3 shows
2 is a circuit diagram showing the configuration of this second embodiment, and in this figure, parts corresponding to those in FIG. 2 are given the same reference numerals. Further, this second embodiment is a modification of the first embodiment shown in FIG. 2, and the control amplifier 8 in the first embodiment has a larger amount of feedback in the low frequency band. The control amplifier 8 is replaced with the control amplifier 8 shown in FIG. In FIG. 3, the control amplifier 8 includes operational amplifiers 80 and 81. In this control amplifier 8, a resistor 82 (value
r ₁ ) is inserted, and a resistor 83 (value r ₂ ) is inserted between the non-inverting input terminal 80a and the ground point. A resistor 84 (value r ₁ ) is inserted between the inverting input terminal 80b of the operational amplifier 80 and the load connection terminal 5, and a resistor 85 is inserted between the inverting input terminal 80b and the output terminal 80c of the operational amplifier 80. (value r ₂ ) is inserted. Further, a resistor 86 is connected between the output terminal 80c and the inverting input terminal 81b of the operational amplifier 81.
(value r ₂ ) is inserted. The non-inverting input terminal 81a of the operational amplifier 81 is grounded, and the operational amplifier 81
A resistor 87 (value r 1 ), a variable resistor 88 (value R ₀ ) and a variable capacitor 89 (value C ₀ ) connected in parallel to each other are connected between the inverting input terminal 81b of No. ₁ and the output terminal 81c.
are inserted in series. The output terminal 81c of this operational amplifier 81 is connected to the resistor 9 (this second
In the embodiment, it is connected to one end of the value R ₂ ).

In the above configuration, the transfer characteristic Ts of the control amplifier 8 in this second embodiment is as follows.
First, if the voltage between the output terminal 80c of the operational amplifier 80 and the ground point is _vy , then in this control amplifier 8, the transfer characteristic Ts ₁ determined by the operational amplifier 80 and the resistors 82 to 85 is as follows: Ts ₁ = v _y /v ₀ −v ₂ =−r ₂ /r ₁ ..., and the transfer characteristic Ts ₂ determined by the operational amplifier 81, resistors 86, 87, variable resistor 88, and variable capacitor 89 is Ts ₂ = v _x / v _y = -1/r ₂ (r ₁ +1/s・C ₀ R ₀ )...
However, s=jω. Therefore, the transfer characteristic Ts is determined from the equations as follows: Ts=Ts ₁ .Ts ₂ =1+1/r ₁ /R ₀ +s.C ₀ r ₁ . . .

Therefore, the voltage gain Gv between the signal input terminal 1 and the load connection terminal 5 in this second embodiment is
By substituting the formula into the above formula, we get Gv=2+R ₂ /R ₁ /1−R _S /Z _L・1/r ₁ /R ₀ +s・c ₀・r ₁
......, and the output impedance Z ₀ in this second embodiment can be obtained by substituting the formula into the above formula, Z ₀ = -Rs/r ₁ /R ₀ +s・C ₀・r ₁ = -Rs/ r ₁ (1/R ₀ +s
・_C0 )
... It becomes.

The solid line y shown in A of FIG. 4 shows the frequency characteristic of the output impedance Z ₀ in this second embodiment.
Z ₀ approaches the value "-Rs·R ₀ /r ₁ " in the low frequency band, while it approaches the value "0" in the high frequency band. Therefore, if the line impedance of the line 10 for connecting the load 6 is r, then by setting Rs・R ₀ /r ₁ = r..., the line impedance r can be completely canceled out in the low frequency band. I can do it. Note that the solid line g shown in FIG. 4B shows the frequency characteristic of the voltage gain Gv in this second embodiment.

Next, a third embodiment of the invention will be described. In the third embodiment, the voltage gain Gv does not depend on the impedance Z _L of the load 6 in the first embodiment.

FIG. 5 is a circuit diagram showing the configuration of this third embodiment. The third embodiment shown in this figure differs from the first embodiment in that a signal input terminal 1 and a load connection terminal 5 are connected between the signal input terminal 1 and the non-inverting input terminal 4a of the amplifier 4. voltage gain between
Gv (transfer characteristic Ts may be changed), but a correction circuit 90a (first correction circuit) having a transfer characteristic Ts _L is inserted to cancel the dependence on the impedance Z _L of the load 6. be.

In this correction circuit 90a, the signal input terminal 1
is connected to the non-inverting input terminal 4a of the amplifier 4 via a resistor 91 (value R ₄ ), and is connected to an impedance circuit 93 (impedance is −K·Z _L ) via an impedance circuit 92 (impedance is K·Z L ).
Rs(1-Ts)) and an inverting input terminal 94b of the operational amplifier 94. operational amplifier 9
The non-inverting input terminal 94a of the operational amplifier 94 is grounded, and the output terminal 94c of the operational amplifier 94 is connected to the other end of the impedance circuit 93 and connected to the resistor 95.
(value R ₄ ) of the amplifier 4 via the non-inverting input terminal 4a
It is connected to the.

In the above configuration, the transfer characteristic Ts _L of the correction circuit 90a can be expressed as a voltage gain between the signal input terminal 1 and the non-inverting input terminal 4a of the amplifier 4 (this voltage gain is designated as Gs _L ). , when the voltage between the non-inverting input terminal 4a and the ground point is _v3 , Ts _L = Gs _L = v ₃ /v ₁ = 1 + R _S /Z _L (1-Ts) / 2...〓
〓 becomes. Further, since the voltage gain Gv between the non-inverting input terminal 4a and the load connection terminal 5 is as shown in the above equation, the total voltage gain G _T between the signal input terminal 1 and the load connection terminal 5 is: G _T =Gs _L ·G _v =1+R ₂ /2R ₁ ... From this equation, it can be seen that the total gain G _T in this third embodiment is independent of the impedance Z _L of the load 6.

Next, a fourth embodiment of the invention will be described.

FIG. 6 is a circuit diagram showing the configuration of this fourth embodiment, and this fourth embodiment differs from the transfer characteristic of the correction circuit 90a in the third embodiment shown in FIG.
Even when the control amplifier 8 in the second embodiment shown in FIG. 3 is used as the control amplifier 8, the voltage gain Gv (including the transfer characteristic Ts) is constant regardless of the signal frequency _. The transfer characteristic Ts _L ′
It is set to . Note that in this fourth embodiment, the load is
Constant voltage gain independent of ZL impedance
It is clear that Gv can be obtained.

In FIG. 6, an impedance circuit 93 in a correction circuit 90b (second correction circuit) is composed of a parallel circuit of a resistor 93a and a capacitor 94b. The impedance Z ₉₃ of this impedance circuit 93 must be Z ₉₃ =-K.Rs (1-Ts) as described in the third embodiment. By substituting the transfer characteristic Ts of the control amplifier 8 shown in the above equation into this equation, the impedance Z ₉₃ is calculated as follows: Z ₉₃ =K・Rs/r ₁ (1/R ₀ +S・C ₀ )=(r
₁ (1/R ₀ + S・C ₀ )/K・Rs) ^-1 = (1/K・R _S・R ₀
/r ₁ +1/K・R _S /r ₁・s・C ₀ ) ^-1 = (
K・Rs・R ₀ /r ₁ K・Rs/r ₁・S・C ₀ )...〓〓 becomes. From this formula, impedance circuit 93
_{This fourth _ _} The voltage gain Gv between the signal input terminal 1 and the load connection terminal 5 in the embodiment is constant regardless of the frequency of the signal to be amplified.

In addition, in this fourth embodiment and the third embodiment described above, when a speaker is connected as the load 6, the speaker impedance Z _L
can be expressed as an equivalent circuit in which a resistor Ra, a resistor Rb connected in parallel with each other, a capacitor C, and an inductor L are usually connected in series as shown in FIG. 7, and have frequency characteristics as shown in FIG. 8. Therefore, an impedance circuit corresponding to the equivalent circuit shown in FIG. 7 may be used as the impedance circuit 92 in the correction circuits 90a and 90b.

As explained above, according to the amplifier output characteristic control circuit according to the present invention, the first explanation is that the amplifier has a dependency relationship of voltage gain on load impedance between the input terminal and the load connection terminal of the amplifier. Since the first correction circuit having a transfer characteristic having an inverse functional relationship with the first correction circuit is provided in front of the first correction circuit, a constant voltage gain can always be obtained regardless of the impedance of the load, no matter what kind of load is connected.

Further, as a second invention, in addition to the configuration of the first invention, an amplifier is provided with a dependency relationship and an inverse functional relationship of a voltage gain between an input terminal of the amplifier and a load connection terminal on the transfer characteristic of the feedback control circuit. Since the second correction circuit with the transfer characteristic is pre-installed,
In addition to the effects of the first invention described above, it becomes possible to keep the voltage gain constant regardless of the frequency of the signal to be amplified, no matter what transfer characteristic is set as the transfer characteristic of the feedback control circuit.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a configuration example of a conventional output characteristic control circuit of an amplifier, FIG. 2 is a circuit diagram showing a configuration of a first embodiment of the present invention, and FIG. FIG. 4 is a frequency characteristic diagram for explaining the embodiment; FIG. 5 is a circuit diagram showing the structure of the third embodiment of the present invention; FIG.
The figure is a circuit diagram showing the configuration of a fourth embodiment of the invention, FIG. 7 is a circuit diagram showing an equivalent circuit of the impedance circuit 92 in the third and fourth embodiments of the invention, and FIG. 8 is an equivalent circuit diagram. It is a frequency characteristic diagram of a circuit. 1... Signal input terminal, 4... Amplifier, 5... Load connection terminal, 6... Load, 7... Current detection circuit (resistance), 8... Feedback control circuit (control amplifier), 9
0a...first correction circuit (correction circuit), 90b...
...Second correction circuit (correction circuit).

Claims (1)

[Claims] 1. Load ZL connected to the load connection terminal of the amplifier
a current detection circuit inserted in series to detect the current supplied to the load ZL, a feedback control circuit that feeds back the detection output of the current detection circuit to the input side of the amplifier, and a signal input to the amplifier. The voltage gain Gv expressed as the ratio between the voltage and the voltage applied across the load ZL is a first voltage gain Gv that does not depend on the value of the load ZL.
The load has a transfer characteristic of 1/Gv ₂ when expressed as the product of a transfer characteristic portion Gv ₁ and a second transfer characteristic portion Gv ₂ that depends on the value of the load ZL.
a first correction circuit configured with a transfer characteristic setting circuit including an equivalent impedance of ZL and disposed in front of the amplifier; The load ZL depends on the amount of feedback of the detection output of the current detection circuit.
In addition to controlling the output impedance for
The output of the amplifier is characterized in that the voltage gain GT expressed by the ratio of the signal voltage input to the first correction circuit and the voltage applied across the load ZL does not depend on the value of the load ZL. Characteristic control circuit. 2 Load ZL connected to the load connection terminal of the amplifier
a current detection circuit inserted in series to detect the current supplied to the load ZL; a feedback control circuit for feeding back the detection output of the current detection circuit to the input side of the amplifier with a transfer characteristic Ts; The voltage gain Gv expressed as the ratio of the input signal voltage to the voltage applied across the load ZL is determined by a first transfer characteristic portion Gv 1 that does not depend on the value of the transfer characteristic Ts of the feedback control circuit and the voltage gain _Gv of the feedback control circuit. a second correction circuit installed in front of the amplifier and set to have a transfer characteristic of 1/Gv _{2 when expressed as a product of a second transfer characteristic portion Gv 2 that} depends on the value of the transfer characteristic Ts; and controlling the output impedance to the load ZL according to the feedback amount of the detection output of the current detection circuit that is fed back to the input side of the amplifier via the feedback control circuit, and The output characteristic of the amplifier is characterized in that the voltage gain GT expressed by the ratio of the signal voltage input to the correction circuit and the voltage applied across the load ZL does not depend on the transfer characteristic Ts of the feedback control circuit. control circuit. 3. The output characteristic control circuit for an amplifier according to claim 2, wherein the transfer characteristic Ts of the feedback control circuit increases the amount of feedback in a low frequency band.