JPH0451606A - Graphic equalizer circuit - Google Patents

Abstract

PURPOSE:To obtain the setting degree of the freedom of input bias and the like, to secure a dynamic range, to make a circuit into IC and to improve an SN ratio by constituting the circuit in such a way that an input-side is composed of a V/I conversion circuit and a resistance is inserted in serial to the input of an amplifier. CONSTITUTION:The V/I conversion circuit 11 is provided for the inputside and an input signal is received. A current corresponding to the voltage level of the input signal is caused to flow in a load resistance and a voltage is generated. The voltage is added to the amplifier of an operand amplifier. The current of the V/I conversion circuit 11 is received in an active filter 12a for attenuating and emphasizing the signal in accordance with a frequency and the voltage corresponding to the frequency is generated. The voltage is converted into the current in V/I conversion circuits 13a and 14a which are provided in correspondence with an attenuation-side and an emphasis-side. Furthermore, the circuit is constituted so that the current conversion output is added(or subtracted) by the load resistance. Thus, the degree of freedom can be obtained in the setting of an input bias, the dynamic range can sufficiently be secured, the circuit is made into IC and the SN ratio can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a graphic equalizer circuit, and more specifically, it has a large degree of freedom in setting the bias of an input signal, and can improve the S/N ratio. This invention relates to a graphic equalizer circuit suitable for IC implementation.

[Prior Art] FIGS. 3(a) and 3(b) are explanatory diagrams of a conventional graphic equalizer circuit.

As shown in figure (a), this circuit consists of an operational amplifier (O
P) Connect a variable resistor (volume, VR
) 2 are connected, and the variable terminal side thereof is grounded via a series resonant circuit 3 of LCr. The output signal (voltage) Vo of the operational amplifier 1 is fed back to the inverting input terminal via a resistor R, and the input signal (voltage) Vi is supplied via a resistor R1.

Here, if the open loop gain of operational amplifier 1 is A, then
A〉〉1, and let Ri and RQ be R1=Ro:R,
The following relationship holds true. (2) The input/output relationship at the resonant frequency f of the series resonant circuit 3 when the variable terminal of the volume 2 is at point A is expressed by the following equation. Note that at this time, no current flows through the volume 2. Therefore, the operational amplifier 1 becomes a buffer amplifier.

(2) The input/output relationship at the resonant frequency f of the series resonant circuit 3 when the variable terminal of the volume 2 is at point B is expressed by the following equation. Note that at this time, no current flows through the volume 2. Therefore, the operational amplifier 1 operates as a normal amplifier.

r ■The input/output relationship at the resonant frequency fO of the series resonant circuit 3 when the variable terminal of the volume 2 is at the midpoint is Vo=
It is Vj.

As can be understood from the above relational expression, this circuit has a graphic equalizer function. Note that r is the resistance value of the resistor r of the resonant circuit 3.

The above is a case where the number of series resonant circuits 3 is one.

Typically, a graphic equalizer circuit divides an audio band into about 5 to 7 parts, and attenuates or emphasizes a certain band around a specific center frequency. For this purpose, 5 to 7 series resonant circuits 3 having different center frequencies f and 5 to 7 corresponding volumes 2 are connected in parallel to the non-inverting input terminal and the inverting input terminal of the operational amplifier 1, respectively. Become.

Such a circuit has the drawback that it is difficult to integrate it into an IC because the volume 2 is connected to the input terminal of the operational amplifier 1.

Therefore, JP-A-63-276312 can be cited as an L tarn J path that can be more easily integrated into an IC. This circuit is constructed by pulling out the volume 2 to the outside, as shown in FIG.
A configuration is adopted in which the current values of I conversion circuits 3 and 4 are controlled. These V/I conversion circuits 3 and 4 receive an input signal via an active filter 5, and convert a voltage according to the frequency into a current value. The current values changed here are applied to the non-inverting input terminal and the inverting input terminal of the operational amplifier 1, respectively. As a result, a signal in the band set by the active filter 5 is obtained. In addition, V/I conversion circuit 3.4
are designed to operate differentially with respect to each other depending on the operation of the volumes.

[Problem to be solved] In the circuit shown in Figure 3(a), even if the resonant circuit is simulated by a coil, an external capacitor is required, and multiple volumes connected to the operational amplifier are provided. Therefore, noise is likely to be generated due to these routings, and there is also a drawback that the number of pins for wiring connections from the circuit to the outside is large.

On the other hand, in the circuit shown in Figure (b), although it is easier to integrate into an IC than the circuit shown in Figure (a), it requires a resistor R1 in series with the input terminal, and its value can be changed to the feedback resistance of operational amplifier 1. Since it has to be set to approximately the same value as , there are limitations in circuit design and limitations in the level of the input voltage Vi. Also, depending on the input bias level, the S/N
The disadvantage is that the ratio is reduced and a sufficient dynamic range cannot be obtained.

The present invention solves the problems of the prior art, and aims to provide a graphic equalizer circuit that is easy to integrate into an IC, is not limited by bias levels, etc., and has a large dynamic range. do.

[Means for Solving the Problems] The graphic equalizer circuit of the present invention has a feature that achieves the above object.
/I conversion circuit, an active filter receiving the output of the first V/I conversion circuit, and a load resistor receiving the output of the first V/I conversion circuit.
receiving the voltage generated across this load resistor at its first input;
an amplifier whose output side is fed back through a feedback resistor to its first second input having a phase opposite to that of the first input, and whose output side is connected to the first input or the voltage generating side of the load resistor;
a second V/I conversion circuit that receives the output of the active filter and whose gain is controlled according to the current value of the variable current source; the output side of the second V/I conversion circuit is connected to the second input side of the amplifier;
a third V/I conversion circuit that receives the output of the active filter and whose gain is controlled according to the current value of the variable current source;
The current value of each variable current source of the /1 conversion circuit is controlled externally.

[Function] In this way, a V/I conversion circuit is provided on the input side, receives a human input signal, causes a current corresponding to the voltage level of the input signal to flow through the load resistor, generates a voltage, and applies the voltage to an operational amplifier, etc. In order to apply the current to the amplifier and attenuate the signal according to the frequency, the current of the V/I conversion circuit is received by an active filter to generate a voltage corresponding to the frequency, and this is applied to the attenuation side. The V/I conversion circuits provided for the emphasis side and the emphasis side are used to convert the output into current, and these current conversion outputs are added (or subtracted) using the load resistor. , there is no need to insert a resistor in series on the input side.

Since the input side is a V/I conversion circuit and a resistor is inserted in series with the input of the amplifier, there is a degree of freedom in setting input bias, etc., and the dynamic range can be increased. We can secure enough. Furthermore, since it is not directly controlled by a volume control system, but is controlled by direct current, it is suitable for IC implementation, and the circuit can have a large S/N ratio.

[Embodiment] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a basic block diagram of a graphic equalizer circuit to which the present invention is applied, and FIG. 2 is a specific circuit diagram thereof. Note that the same components as in FIG. 3 are indicated by the same reference numerals.

Reference numeral 10 denotes a graphic equalizer circuit, which receives a human input signal Vi through a V/I conversion circuit 11 and outputs its current output to a load resistor RL. The terminal 11a of the load resistor RL is
This is a terminal at which a voltage is generated by the above-mentioned current, and this is connected to the non-inverting input terminal of the operational amplifier 1. Also,
The opposite terminal is connected to the reference bias line Vr.

The output current of the V/I conversion circuit 11 is further divided into a plurality of active filters 12a, l2b*...
, and the current output of the active filter 12a is V
/I conversion circuits 13a and 14a, respectively. The output current of the V/I conversion circuit 13a is applied to the terminal 11a connected to the non-inverting input terminal of the load resistor RL, and the output current of the V/I conversion circuit 14a is applied to the inverting input terminal of the operational amplifier 1. It is being Note that the V/I conversion circuits 13a and 14a normally operate in opposite phases.

The other active filters 12b, . . . Φ also have two V
/I conversion circuits are respectively connected to their output sides, and these V/I conversion circuits are connected to the V/I conversion circuit 13 al 1
4A are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 1, respectively, but these are omitted in the figure.

Note that the feedback resistor RO to the inverting input terminal side of operational amplifier 1
Here, Ro=RL, and its resistance value is the same as the load resistance RL. In addition, the voltage-current conversion rate of each V/I conversion circuit is set to 1/RL (or KXI
/RL). K is the V/I conversion circuit 13a, 14a
The gain g- is controlled by externally controlling the current values of the current sources 13b and 14b of these emitter-coupled differential pairs. selectively controlled by the control circuit 15.

When the setting of the volume 16 is at the middle point, the control circuit 15 controls the currents of the current sources of the V/I conversion circuits 13a and 14a to be zero, so that neither of them operates. Further, in a signal attenuation state where the setting of the volume 16 is below the midpoint, only the V/I conversion circuit 13a is operated and the operation of the V/I conversion circuit 14a is stopped. Furthermore, in the signal emphasis state where the setting is above the midpoint, the V/I
Only the conversion circuit 14a is operated and the operation of the V/I conversion circuit 13a is stopped.

Next, I will explain this kind of control operation. Note that the voltage at the non-inverting input terminal of operational amplifier 1 (voltage at terminal 11a)
is VL, and for convenience of explanation, it is assumed that the pressure Vl is the ground level. In addition, the V/I conversion circuits 13a and 14a will be mainly explained, and other active filters 12b, . . .
Since the circuit is the same, its explanation will be omitted.

■ Signal attenuation state In this case, ■ Only the /I conversion circuit 13a operates according to the setting value of the volume 16 below the midpoint, and the V/I
The conversion circuit 14a is controlled to be inoperative. Therefore, the operational amplifier 1 becomes a Tsuk Sofa amplifier. The input/output relationship is Vo I Vl 1+ (however, the frequency fo is the active filter 12
center frequency of a).

As a result, the amount of attenuation for the input signal Vi can be controlled by selecting the value of K. And at maximum signal attenuation (
When the setting of the volume 16 corresponds to when the volume 2 of FIG. 3(a) is set to point A), the V/I conversion circuit 1
The gain K of 3a takes the largest value.

■Signal emphasis state In this case, only the V/I conversion circuit 14a operates according to the setting value of the volume 16 above the midpoint, and
The conversion circuit 13a is controlled to be inoperative. As a result, the relationship between the input signal Vi and the non-inverting input VL of the operational amplifier 1 is Vl=VL. Therefore, the input/output relationship is as follows (however, the frequency fo is the active filter 12
center frequency of a).

As a result, the amount of emphasis for the input signal v1 can be controlled by selecting the value of K. And when the signal is maximized (
When the setting of volume 16 corresponds to setting volume 2 to point B in FIG. 3(a), V/I conversion turn 1
4. The gain K of a takes the largest value.

■Flat state At this time, V/I conversion circuit 13a, V/I conversion circuit 1
4a are controlled so that they do not operate together.

Since the operational amplifier 1 simply functions as a buffer, VI=VD. This corresponds to the setting of the volume 16 when the volume 2 of FIG. 3(a) is set to the midpoint.

For this reason, this circuit can be provided with the function of a graphic equalizer, and the signal (voltage) can be
Since the circuit configuration is such that the input voltage is input, there is no need to insert a resistance value in series on the input side. Moreover, the input signal is V
Since the signal is received by the /I conversion circuit 11, the bias level on the input side can be set freely, and there is no possibility that the S/N ratio will decrease or that a sufficient dynamic range cannot be obtained due to the input bias level.

FIG. 2 shows a specific example of the circuit shown in FIG. 1, and 21 corresponds to the V/I conversion circuit 11 in FIG.

22 is an active filter circuit constituting a bandpass filter. This circuit 22 is a circuit in which a differentiating circuit 24 consisting of a variable 211 circuit 23 and a capacitor C1, and an integrating circuit 25 consisting of a variable 211 circuit 25 and a capacitor C2 are connected in series.

26 is a circuit corresponding to the V/I conversion circuit 13a,
27 is a circuit corresponding to the V/I conversion circuit 14a.

Further, 28 corresponds to the operational amplifier 1.

Here, the current value I of the current source 28a of the V/I conversion circuit 26 is
Attenuation control of the input signal can be performed by selectively setting the value of A, and the current value IB of the current source 27a of the V/I conversion circuit 27 can be controlled.
By selectively setting the value of , it is possible to control the emphasis of the input signal. Furthermore, if the current values IA and IB are set to zero, an output with flat characteristics can be obtained. Therefore, the input signal can be attenuated or emphasized by DC control.

As explained above, in the embodiment, the ■/■ conversion circuit 13
Although only one of V/I conversion circuits a and 14a is selectively operated, these V/I conversion circuits may be differentially controlled by the control circuit 15. For example, the conversion conductance of the V/I conversion circuit 13a may be controlled by ( 1-a) llgie, V/I
If (1+a)·gm, the conversion circuit 14a converts this a
may be controlled by the volume 16 so that 1≧a≧−1.

Note that in this case as well, when a is set to the midpoint of a=0, the operation of the V/I conversion circuits 13a and 14a can be stopped.

In the embodiment, the V/I conversion circuit 11. 13a, 14
The voltage-current conversion rate of a is the same or is set to XK,
These do not necessarily have to be the same.

Further, although the load resistance RL and the feedback resistance RO of the operational amplifier 1 have the same value, they do not need to take the same value. For example, if the value of K of the V/I conversion circuit 13a + 14a is doubled to 2K, the load resistance RL is changed to the feedback resistance R.
It is also possible to make it 1/2 of the value of O, that is, RL/2, or the V/I conversion circuit 13 a v 14 a
It is also possible to set the values of K to different values. Accordingly, the values of the V/I conversion circuit 11 and the load resistance RL can be set to various values.

[Effects of the Invention] As can be understood from the above explanation, in this invention, the input side is a V/I conversion circuit, and a resistor is not inserted in series with the input of the amplifier. Therefore, there is a degree of freedom in setting input bias, etc., and a sufficient dynamic range can be ensured. Furthermore, since it is not directly controlled by a volume control system, but is controlled by direct current, it is suitable for IC implementation, and the circuit can have a large S/N ratio. As a result, it is possible to realize a graphic equalizer circuit that has a small number of pins and is easy to downsize.

[Brief explanation of drawings]

Figure 1 is a basic block diagram of a graphic equalizer circuit to which the present invention is applied, Figure 2 is a specific circuit diagram thereof, and Figures 3 (a) and (b) are diagrams of a conventional graphic equalizer circuit. It is an explanatory diagram. 1.28... Operational amplifier, 2.16... Volume, 3... Series resonant circuit, 4.5t 11, 13a* 14a---V/I conversion circuit, 15... Control circuit, 22. ...Band filter. Patent applicant population - Company representative Patent attorney Kajiyama Kojiro

Claims (1)

[Claims] (1) a first voltage-current conversion circuit that receives an input signal;
An active filter receiving this output and a first voltage -
A load resistor receives the output of the current conversion circuit, and a first input receives the voltage generated in the load resistor, and the output side receives the voltage generated in the load resistor through a feedback resistor to a second input having a phase opposite to that of the first input. an amplifier whose output side is connected to the first input or the voltage generating side of the load resistor, receives the output of the active filter, and whose gain is controlled according to the current value of the variable current source. a second voltage-current conversion circuit, the output side of which is connected to the second input side of the amplifier;
a third voltage-current converter circuit that receives the output of the active filter and whose gain is controlled according to the current value of the variable current source, the second voltage-current converter circuit and the third voltage-current converter circuit; A graphic equalizer circuit characterized in that the current value of each variable current source of the current conversion circuit is externally controlled.