JP2767389B2 - Equalizer and audio device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equalizer and an audio device using the same, and more particularly, to an equalizer in a portable audio device such as a portable magnetic tape reproducing device and the like, which has a circuit configuration with a small number of elements and has continuous sound quality. The present invention relates to an equalizer that can be adjusted and is suitable for IC.

[0002]

2. Description of the Related Art FIG. 4 shows a equalizer used in a conventional audio apparatus and capable of continuously adjusting sound quality.
As shown in the figure, usually, a large number of variable Gm amplifiers are provided,
An equalizer is constructed by equivalently simulating a resistor and a capacitor by a gyrator circuit. Note that a control circuit for controlling the current of the variable Gm amplifier is omitted. Since one variable Gm amplifier uses a large number of transistors as shown in FIG. 5, as a result, this type of equalizer must have a large circuit scale when integrated.

[0003]

When such an equalizer is used in a portable audio device, it is difficult to form an IC at the same time as other circuits, and noise is generated due to the large number of circuit paths. Easy to do. The increase in the number of ICs not only reduces the cost, but also hinders miniaturization and thinning. Therefore, in a portable audio device, a combination circuit of a filter circuit using a capacitor and an amplifier is usually used as an equalizer. However, this type of device selects the sound quality stepwise by switching a switch, and has a disadvantage that the continuous sound quality adjustment as described above cannot be performed. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to provide an equalizer capable of continuously adjusting sound quality with a circuit configuration having a small number of elements. Another object of the present invention is to provide an audio device including an audio amplifier in which the equalizer is integrated with other circuits in an IC.

[0004]

SUMMARY OF THE INVENTION In order to achieve this object, an equalizer according to the present invention is characterized by a first and a second differential amplifier having a common output and a current source respectively.
A first negative feedback circuit for negatively feeding back a voltage signal extracted from this output to the first differential amplifier, a second negative feedback circuit for negatively feeding back the voltage signal to the second differential amplifier, A filter circuit provided in any one of the second negative feedback circuits; and a controller for controlling a current value of each current source in accordance with the sound quality adjustment signal, wherein the first and second differential amplifiers An amplifier having different frequency characteristics, wherein a characteristic between different frequency characteristics is selected by setting a current value of each current source by a controller.

[0005]

As described above, the outputs of the two differential amplifiers are made common, and at least one of the amplifiers has a frequency characteristic different from that of the other amplifier, and the output is fed back to each amplifier. Furthermore, the feedback amount of either amplifier is increased or decreased by increasing or decreasing the operating current of each current source, and the feedback amount of one of the amplifiers is made larger than the other, so that the characteristics of the amplifier with the larger feedback amount appear preferentially. Set by the controller. Thus, a frequency characteristic between different frequency characteristics can be selected according to the setting of the current value of each current source. As a result, the circuit of the equalizer body can be realized basically with the element configuration of the feedback circuit having two differential amplifiers and filters, the number of elements is reduced compared to the conventional one, and the operating current of each current source is adjusted. By doing so, the frequency characteristics of the entire amplifier can be continuously selected.

[0006]

FIG. 1 is a circuit diagram of an embodiment to which the equalizer of the present invention is applied, FIG. 2 is an explanatory diagram of a frequency characteristic to be adjusted, and FIG. 3 is another embodiment of the present invention. FIG. Numeral 1 denotes an equalizer, which is used to connect the first and second differential amplifiers 3 and 4 having the active load of the current mirror circuit 2 in common, the amplifier 5 for extracting an output from the common load, and the output of the amplifier 5 respectively. Differential amplifier 3,
Negative feedback circuits 6 and 7 having different feedback ratios for negative feedback to 4
It is composed of The bases of the transistors Q1 and Q3 of the first and second differential amplifiers 3 and 4 are commonly connected to an input terminal 8, and the output of the amplifier 5 is connected to an output terminal 9 for external sound quality operation. The frequency characteristic of the circuit of the equalizer 1 constituted by the amplifier is adjusted by the control circuit 10 that generates a control signal in response.

The first differential amplifier 3 includes a transistor Q1
, Q2 and their current sources 3a, and have transistors Q5 and Q6 of the current mirror 2 as loads on their respective collector sides. The second differential amplifier 4 includes transistors Q3 and Q4 and its current source 4a, and has the transistors Q5 and Q6 of the current mirror circuit 2 as loads on the respective collector sides. The negative feedback circuit 6 is a circuit composed of series-connected resistors R1 and R2 for dividing the voltage of the output terminal 9, and the voltage at the voltage dividing point is fed back to the base of the transistor Q2. Negative feedback circuit 7
Is a series circuit composed of a resistor R3 for dividing the voltage of the output terminal 9 and a CR filter circuit 7a, a CR filter 7b connected in parallel to the CR filter circuit 7a, and a CR circuit connected in parallel to the resistor R3. A filter 7c is connected to a voltage dividing point by the resistor R3 and the CR filter circuit 7a, and is connected to the base of the transistor Q4.
The divided voltage is fed back. Here, each resistance value and the capacitance of the capacitor are selected so that the feedback rate of the negative feedback circuit 7 is lower than the feedback rate of the negative feedback circuit 6.

CR filter circuit 7a and CR filter 7
c is a filter for setting a low-frequency gain, and the CR filter circuit 7a is composed of a series circuit of a resistor R4 and an electrolytic capacitor C1. Also, the CR filter circuit 7c
Consisting of a series circuit of a resistor R6 and a capacitor C3, CR
The filter 7b is a filter for setting a high-frequency gain, and comprises a series circuit of a resistor R5 and a capacitor C2.
The current sources 3a and 4a have their current values controlled in accordance with the current values of the DC current signals A and B from the control circuit 10, respectively, and the current values of the DC current signals A and B increase or decrease. The control circuit 10 includes two voltage / current conversion circuits each having an inverting amplifier and a current converted from the two voltage / voltage conversion circuits in a relationship in which the adjustment voltage signal of the variable resistor 11 is in the opposite direction. And two current mirrors respectively receiving DC current signals, and generate DC current signals A and B at the output side of each current mirror. As a result, current signals A and B at predetermined levels corresponding to the DC voltage generated according to the operation of the variable resistor 11 for sound quality adjustment are obtained.

In an equalizer circuit having an amplifier having a common load, when voltage is fed back to the respective differential amplifiers 3 and 4 from the same output terminal 9 side,
The amount of feedback to the first differential amplifier 3 is determined by the ratio of the resistance values of the resistors R1 and R2 to the output voltage, and the gain of the differential amplifier 3 and the amplifier 5 depends on the open loop gain. A
Then, the gain G = A / (1−Aβ) ≒ (R1 / R
2) +1, where β = R1 / (R1 + R2).
The amount of feedback to the second differential amplifier 3 depends on the output voltage and the impedance according to the parallel circuit impedance Z1 of the resistor R3 and each CR filter 7c and the frequency of the parallel circuit of the CR filter circuits 7a and 7b. The amplification factor of the differential amplifiers 4 and 5 is determined by the ratio of Z2, and the gain G = A1 / (1−A
β) ≒ {R3‖ (R6 + 1 / ωC3)} / R4 + 1, where β = Z1 / (Z1 + Z2) and R3‖ (R6
+ 1 / ωC3) is a resistance R3, a resistance R6 and a capacitor
With the parallel resistance value by the impedance of the series circuit of C3
is there.

Considering first the amplification characteristics of the amplifier composed of the differential amplifier 3 and the amplifier 5 with respect to the input signal, the feedback circuit 6 is a feedback by the resistors R1 and R2. G ≒ (R1 / R
2) Flat characteristics due to +1. As a result, the characteristic do of FIG. 2 is obtained by this amplifier. Next, considering the amplification characteristic of the amplifier composed of the differential amplifier 4 and the amplifier 5 with respect to the input signal, the feedback circuit 7 has a frequency characteristic and the electrolytic capacitor C of the low frequency component of the input signal.
In a frequency band in which the resistance value of 1 is negligible, the resistance R
3 and the lowest feedback ratio determined by the resistor R4, the gain of this amplifier becomes the maximum gain G ≒ (R3 / R
4) It becomes +1. As the frequency component becomes higher in frequency, the resistance value of the electrolytic capacitor C1 increases, the feedback voltage increases due to the resistance value of the series circuit of the resistor R4 and the electrolytic capacitor C1, and the gain G of this amplifier decreases. . When the frequency of the frequency component of the input signal is in the middle range, the resistance of the electrolytic capacitor C1 increases.
In addition, the resistance value of the series circuit of the resistor R6 and the capacitor C3 of the CR filter 7c decreases, and the feedback voltage increases.
I do. Therefore, the gain of this amplifier is represented by a gain G ≒ (R
6 / R4) +1. However, it is assumed that R6 <R3. On the other hand, for the frequency of the high-frequency component of the input signal, the series circuit of the resistor R5 and the capacitor C2 or the resistor R4
, The feedback voltage value is restricted to some extent, and the gain in the high frequency range is also suppressed low. The gain of this amplifier becomes the gain G ≒ (R6 / R4‖R5) +1. Therefore, when the current value of the current source 4a is set near the maximum current value, the characteristic dm of FIG. 2 is obtained.

Here, the amplifier 5 is configured such that the differential amplifiers 3 and 4 amplify the input signal with the common amplifier 5 via the load of the common current mirror 2 and the sum of the respective outputs is output. Voltage. In such a state, when the operating currents are the same, the operation of the amplifier of the circuit having the larger feedback amount among the feedback circuits connected to the output is prioritized. The reason is that, in the case of the wired OR output, the larger the feedback amount is for the same output voltage, the larger the effect of reducing the amplification factor is obtained from the above equation. As the amplification factor of the amplifier decreases, the feedback circuit with a larger amount of feedback acts on the lowered output voltage more than the feedback of other amplifiers, and the feedback is performed again. The amplification characteristic appears preferentially by an amount corresponding to the ratio of the amplifier to the feedback amount of the other amplifier set in the circuit. Therefore, by controlling the feedback amounts of the two amplifiers, it is possible to obtain characteristics obtained by combining the respective characteristics with each other at a predetermined ratio.

Here, the frequency characteristics of the differential amplifier 3 and the differential amplifier 4 are different due to the difference in the frequency characteristics of the negative feedback circuits 6 and 7, one is a flat characteristic and the other is a low-frequency characteristic. And the high frequency gain has a high frequency characteristic. As a result, it is possible to obtain, as the frequency characteristics of the entire amplifier, characteristics obtained by combining the characteristics of the differential amplifier 3 and the differential amplifier 4 in accordance with the respective feedback amounts. Negative feedback circuit 7
Is set in advance to be lower than the feedback ratio of the negative feedback circuit 6, so that the characteristic in the middle range is made to be the flat characteristic of the differential amplifier 3 having a large feedback amount. This expands the range of the mid-range flat characteristic with little sound quality emphasis. The actual feedback amount is determined by the operating current of each of the differential amplifiers 3 and 4.

The operating current of each amplifier can be controlled by the current sources 3a and 4a by the control current values of the DC current signals A and B from the control circuit 10, and these current sources 3a and 4a are set to the same operating current. In some cases, the characteristics of the differential amplifier 3 take precedence, and the characteristics of the equalizer 1 gradually decrease as the frequency emphasis increases, as shown in FIG. Further, when only the current source 3a operates and the current of the current source 4a is cut off, complete flat characteristics as shown by do in FIG. 2 are obtained. Conversely, the current source 3
The current of the current source 4a becomes larger than the current of the differential amplifier 4a.
When the feedback voltage of the differential amplifier 4 becomes higher than the feedback voltage of the differential amplifier 3, the characteristics of the differential amplifier 4 take precedence. At that time, the frequency characteristics as determined by the CR filters 7a, 7b, 7c are exhibited. In such a case,
According to the operating current set in the current source 4a, d1 in FIG.
A continuously changing frequency characteristic up to d2,..., dm is obtained.

Therefore, when the variable resistor 11 is not in the operation state of bass and treble enhancement, for example, when the variable terminal of the variable resistor 11 is at the lower limit,
The control current signal A that maximizes the current value of the current source 3a is generated, and the operating current of the current source 4a is zero. At this time, the amplifier of the equalizer 1 has a gain G ≒
The amplifier has a flat frequency characteristic of (R1 / R2) +1. Then, when the variable terminal of the variable resistor 11 is operated upward and in the operation state of bass and treble enhancement, the operating current of the current source 3a is reduced and the operating current of the current source 4a is increased according to the amount of operation. Current signals A and B
Generate. Further, when the operation of the variable resistor 11 reaches the upper limit, the operating current of the current source 3a is set to zero,
The operating current of the current source 4a is maximized. At this time, the low-frequency gain is G ≒ (R3 / R4) +1, the middle-frequency gain is gain G ≒ (R6 / R4) +1, and the high-frequency gain is gain G ≒ (R6 / R4‖R5). ) +1.

FIG. 3 shows a configuration in which the differential amplifier 3 is replaced with a differential amplifier 4b having a configuration similar to that of the differential amplifier 4. Each of the amplifiers is provided with a current mirror 2 independently. Are commonly connected to the output terminal 9. This greatly changes the frequency characteristics of the entire amplifier according to the frequency characteristics of the amplifiers 4 and 4b. The CR filters 7a ', 7a of the differential amplifier 4b
b 'and 7c' have different frequency characteristics from those of the CR filters 7a, 7b and 7c. These differential amplifiers 4
When the operating currents of the current sources 4a and 40a of the differential amplifier 4b are set to be substantially equal ,
A frequency characteristic obtained by combining the frequency characteristics is obtained. Increasing the operating current of the differential amplifier 4, emphasis lever, the frequency characteristics of the differential amplifier 4 is reduced the operating current of the differential amplifier 40
can do. Further, to reduce the operating current of the differential amplifier 4, lever increases the operating current of the differential amplifier 4b, the difference
The frequency characteristics of the dynamic amplifier 4b can be emphasized. In the embodiment shown in FIG. 3, the amplifier 5 is not provided because the loads in the differential amplifiers are not common. This fruit
In the embodiment, the load connected to the output terminal 9 is common.
become.

As described above, when the equalizer of this embodiment is integrated into an IC, a series circuit of the capacitor C1 or the resistor R4 and the capacitor C1 constituting the low-pass filter is externally provided. Other capacitors or resistors are capacitances that can be made into ICs.

[0017]

As can be understood from the above description, according to the present invention, two differential amplifiers have a common output, and at least one amplifier has a frequency characteristic different from that of the other amplifier. The output is fed back to each amplifier, and the amount of feedback of one of the amplifiers is increased or decreased by increasing or decreasing the operating current of each current source. Since the control circuit is set so that the characteristics of the amplifier appear preferentially, a frequency characteristic between different frequency characteristics can be selected according to the setting of the current value of each current source. As a result, the circuit of the equalizer body can be realized basically with the element configuration of the feedback circuit having two differential amplifiers and filters, the number of elements is reduced compared to the conventional one, and the operating current of each current source is adjusted. By doing so, the frequency characteristics of the whole amplifier can be continuously selected, and the equalizer suitable for IC integration can be obtained. In particular, in a portable audio device, it contributes to downsizing and thinning.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment to which an equalizer of the present invention is applied.

FIG. 2 is an explanatory diagram of a frequency characteristic to be adjusted.

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

FIG. 4 is a block diagram of an equalizer of a conventional audio device.

FIG. 5 is an example of a circuit of a variable Gm amplifier in the equalizer of FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Equalizer, 2 ... Current mirror circuit, 3,4 ... Differential amplifier, 5 ... Amplifier, 6,7 ... Negative feedback circuit, 8 ... Input terminal, 9 ... Output terminal, 10 ... Control circuit, 11 ...
Variable resistor.

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H03G 5/02 H03G 5/12 H03G 5/14 H04R 3/04 101

Claims (3)

(57) [Claims] 1. A first and a second differential amplifier having a common output and a current source respectively, and a first negative feedback for negatively feeding back a voltage signal extracted from the output to the first differential amplifier. Circuit; a second negative feedback circuit that negatively feeds back the voltage signal to the second differential amplifier; a filter circuit provided in any of the first and second negative feedback circuits; And a controller for controlling the current value of each of the current sources in accordance with the first and second differential amplifiers. The first and second differential amplifiers are amplifiers having different frequency characteristics. An equalizer in which a characteristic between the different frequency characteristics is selected by setting. 2. The equalizer according to claim 1, wherein a negative feedback rate of said first negative feedback circuit is larger than a negative feedback rate of said second negative feedback circuit. 3. A first and a second differential amplifier having a common output and a current source respectively, and a first negative feedback for negatively feeding back a voltage signal extracted from the output to the first differential amplifier. Circuit; a second negative feedback circuit that negatively feeds back the voltage signal to the second differential amplifier; a filter circuit provided in any of the first and second negative feedback circuits; A controller for controlling the current value of each of the current sources according to the following: an adjusting unit for generating the sound quality adjustment signal; and an output stage amplifier for receiving and amplifying the voltage signal, An audio device in which a differential amplifier is an amplifier having different frequency characteristics, and a characteristic between the different frequency characteristics is selected by setting a current value of each of the current sources by the controller. .