JPH0653746A - Amplifier circuit and sound volume controller - Google Patents

Abstract

PURPOSE:To prevent leakage of sound by providing a gain control means suppressing a signal level and a mute circuit muting its output to the amplifier circuit and selecting the mute mode for the mute circuit thereby suppressing an undesired output in the mute mode. CONSTITUTION:A mute circuit 90 passing/interrupting an output of a gain control means (VCA) 50 is placed to the output of the means 50. Differential amplifier pairs 92, 94 well matched with each other are provided on the circuit 90 and a constant current source 97 is connected to the pairs through a switch 96. With the switch 96 thrown to the position (a), the differential pair 92 is in operation selectively and an output of the VCA 50 applied to the pair 92 is extracted from an output terminal 100. Furthermore, with the switch 96 thrown to the position (b), the differential pair 94 is in operation selectively and a prescribed DC voltage, that is, a neutral voltage at signal output is extracted from the output terminal 100. Thus, the switch 96 is in the interlocking relation with the current source 70, and when the VCA 50 is set in the maximum attenuation, the switch 96 is forcibly set to the mute state (that is, thrown to the position (b)) thereby activating the differential pair 94.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifier circuit used for controlling a signal level, such as an electronic volume circuit, and a volume control device.

[0002]

2. Description of the Related Art Conventionally, as an amplifier circuit for controlling an audio level, there is, for example, Japanese Utility Model Laid-Open No. 41508/1990 "Audio Device". FIG. 6 shows an outline of this audio device. In this audio device, an electronic volume circuit 2 is provided on the front side and a mute circuit 4 is provided on the rear side, and an audio signal passing through the electronic volume circuit 2 and the mute circuit 4 is reproduced from a speaker 8 via an amplifier 6. A volume control signal Vc is applied from the mute control circuit 10 to the electronic volume circuit 2, and a mute control signal V _M is applied to the mute circuit 4. Volume control signal Vc
Is an analog signal that continuously changes from a high (H) level to a low (L) level, and is also a mute control signal V
_M is a high / low (H / L) 2-level switching signal. Therefore, when the mute control signal V _M is L, the mute is released, and when it is H, the mute is executed. That is, when the mute control signal V _M is L, the transistors 12 and 14 are both non-conductive, so that when the volume control signal Vc is applied to the electronic volume circuit 2, the volume control according to the level is performed. . On the other hand, when the mute control signal V _M is H, the transistor 12 becomes conductive due to the increase of the base potential, and as a result, the electronic volume circuit 2
As a result of the volume control signal Vc to be released and the transistor 14 becoming conductive, the output of the electronic volume circuit 2 is grounded and the audio signal to the amplifier 6 is released.

By the way, in this amplifier circuit, when the volume control signal Vc is set to L level, the attenuation amount of the electronic volume circuit 2 becomes maximum, but the operation of the mute circuit 4 is independently switched by the mute control signal V _M. Therefore, an attenuation difference occurs between the maximum attenuation amount of the electronic volume circuit 2 and the mute control of the mute circuit 4. A sound signal is obtained in the electronic volume circuit 2 even if the amount of attenuation is maximum, and this sound signal is reproduced from the speaker 8 through the amplifier 6.

Further, in such an audio device, since the mute control depends on the on-resistance of the transistor 14, it is difficult to eliminate the audio output and the noise output, and there is a variation in products in manufacturing. Prone to occur,
Moreover, the number of parts is large, which is disadvantageous in downsizing the device.

On the other hand, as shown in FIG. 7, in the amplifier circuit which performs the mute control by using the current control amplifier, I
It is excellent in that it can be easily converted to C and contributes to downsizing of the circuit. This amplifier circuit includes a current control amplifier (VCA) 1
6, a bias circuit 18, a variable current source 20 and a buffer circuit 22. A reference voltage V _reg is applied to the bias input terminal 24 as a constant bias voltage, VCA1.
An audio signal to be amplified from a signal source 32 is applied to the transistor differential pair 26 of 6 through input terminals 28 and 30. Then, each transistor differential pair 3 of the VCA 16
A constant bias voltage is applied from the bias circuit 18 and a control current is applied from the variable current source 20 to the base input sides of Nos. 4 and 36. That is, this amplifier circuit has the emitter voltage of the transistors 38 and 40, that is,
The gain is controlled by causing the base-emitter voltage V _BE difference in the transistor differential pair 34, 36 by the emitter voltage ratio of the transistors 38, 40.

[0006]

By the way, in this amplifier circuit, even when the current Ic of the variable current source 20 and the current I of the transistor 42 are equal, the transistors 44, 4
The base current flows through the transistor 6, and the emitter current of the transistor 40 cannot be completely eliminated. For example, the collector current I _C of the transistor 44, the current of the variable current source 20, the emitter current I _E of the transistor 38 are equal, the base current I _B of the transistor 44 is equal to the base current of the transistor 46, and the base current is I. If it is _B , the maximum attenuation amount ATT _max in this amplifier circuit is

[0007]

[Equation 1]

[0008] Where I _E = 100 μA, I _B
.. = 100/120 .mu.A (where .beta. = 120), the maximum attenuation amount ATT _max = -29.7 dB is large, and the signal cannot be narrowed down.

Therefore, in the amplification gain control using such an amplification circuit, it is theoretically impossible to eliminate the passing signal, as in the audio device shown in FIG.
Even if the gain is made as small as possible, a minute level signal output V _O is generated at the output terminal 48 through the buffer circuit 22, and this is reproduced as an audio output, that is, a noise output.

Therefore, an object of the present invention is to provide an amplifier circuit and a volume control device which suppresses such unnecessary output during mute and prevents sound leakage during mute.

[0011]

That is, in the amplifier circuit of the present invention, the gain control means (current variable amplifier 50) for suppressing the signal level by the gain control based on the control input and the output on the output side are suppressed. And a switching means (switch 96) for switching the mute circuit side to the mute state according to the control level of the gain control means.

Further, in the volume control device of the present invention, the output signals of the plurality of electronic devices are selected by the signal selecting means (the output switching circuit 11).
5) a volume control device for selectively controlling the volume to be taken out from the speaker (123) via the speaker (123),
The output signals of the plurality of electronic devices are amplified by the signal control means (electronic volume control 116) (power amplifier 12).
When the volume output from the speaker is cut down when outputting to 2), the mute means (mute circuit 11)
It is characterized in that sound leakage is suppressed by interlocking with 8).

[0013]

The amplifier circuit of the present invention is characterized in that the operation switching of the mute circuit installed on the output side of the gain control means is linked to the control on the gain control means side. When the attenuation control on the gain control means side reaches the maximum level, that is,
By shifting the mute circuit to the mute state, the mute state is shifted to the maximum mute state. At the time of muting, only the switching means of the buffer circuit operates, no unnecessary output is generated on the output side, and the conventional sound leakage can be reliably prevented.

In the volume control device of the present invention,
The output signals of a plurality of electronic devices are selectively applied through the signal selection means to control the volume to be taken out from the speaker, but the output signals of the plurality of electronic devices are transmitted to the amplification means through the volume and sound quality control circuits. In this case, when the volume of the sound taken out from the speaker is cut down, the mute means is interlocked, so that sound leakage from the speaker can be reliably prevented.

[0015]

The present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 shows an embodiment of the amplifier circuit of the present invention. In this amplification circuit, a bias circuit 60 and a variable current source 70 are installed on the front side as a gain control means together with a current variable amplifier (VCA) 50. VCA5
0 is a differential pair 52, 5 composed of a pair of transistors.
4, 56 are installed and a double balanced differential amplifier is used. The differential pair 52 includes transistors 522 and 524, the differential pair 54 includes transistors 542 and 544, and a differential pair 56.
Is composed of transistors 562 and 564. A constant current source 526 for flowing an operating current is connected to the emitter sides of the transistors 522, 524, and the operating current of the VCA 50 is determined by this constant current source 526. Also,
The input terminal 52 is provided at the bases of the transistors 522 and 524.
The input signal to be amplified is applied from the signal source 80 through 8,530.

A base current compensating circuit 58 is installed in the VCA 50. That is, the transistor 5
Transistors 582 and 5 are provided on the collector side of 44 and 562.
84 is installed, a transistor 586 is installed, a transistor 586 having a common base with the transistors 544 and 562 is connected in series to the collector side of the transistor 586, and the emitter of the transistor 586 is connected to the power supply line 74. Connected and the collector of transistor 588 is grounded.

The VCA 50 is also provided with an output section 59 for taking out the amplified output of the VCA 50. That is, a constant current source 590 as an active load is installed between the collector of the transistor 542 and the power supply line 74, and a constant current source 592 that is current-coupled to the constant current source 590 is installed. A constant current source 594 is connected in series to the current source 592. Further, a constant current source 596 as an active load is installed between the collector of the transistor 564 and the power supply line 74. A transistor 598 current-coupled to the constant current source 596.
A constant current source 5 is installed in the transistor 598.
A transistor 599, which is current-coupled with 94, is connected in series. That is, the differential outputs taken out from the differential pairs 54 and 56 of the VCA 50 are the transistors 598 and 59.
9 and is taken out from both collector sides.

A constant current source 62 is installed in the bias circuit 60 for setting a constant bias with respect to the VCA 50, and a current mirror circuit 64 is installed as a means for shunting the constant current of the constant current source 62. There is. The current mirror circuit 64 includes a diode 642, transistors 644 and 646, and resistors 647, 648 and 649. A transistor 652 is installed between the collector of the transistor 644 and the power supply line 74, a transistor 654 is installed between the collector of the transistor 646 and the power supply line 74, and a base of each of the transistors 652 and 654 is installed. A reference voltage Vref is applied from a reference voltage source through the input terminal 66. A diode 656 is connected in the opposite direction between the base and the emitter of the transistor 654. This diode 656 constitutes a voltage source. The bias output obtained on the emitter side of the transistor 652 is
The bias output applied to the bases of the transistors 542 and 564 of the VCA 50 and obtained on the emitter side of the transistor 654 is the transistors 544, 562 and 5
Added to 88 bases.

On the output side of the VCA 50, a mute circuit 90 for passing or blocking the output is installed. This mute circuit 90 has 2
Two differential pairs 92 and 94 are provided side by side, and each differential pair 9
A constant current source 97 is connected to the switches 2, 94 via a switch 96 as a switching means. The differential pair 92 is one in which the emitters of the transistors 922 and 924 are connected in common, and the differential pair 94 is the transistors 942 and 944.
The emitters of are commonly connected. A current mirror circuit 98 is connected to each differential pair 92, 94 as a common active load, and the current mirror circuit 98 is composed of transistors 982, 984. Also,
The base and emitter of the transistor 950 are connected between the bases and collectors of the transistors 924 and 944, and the constant current source 95 is connected between each base and the ground point.
2 are connected, and each differential pair 92, 94 constitutes an all-feedback differential amplifier in which a common load and operating current are set. A constant bias voltage V _{B is} applied to the base of the transistor 922 of the differential pair 92 via the resistor 954.
Is added and the output of the VCA 50 is supplied. Further, only a constant bias voltage V _B is set to the base of the transistor 942 of the differential pair 94 by a bias circuit different from that on the differential pair 92 side. Therefore, when the virtual contact of the switch 96 is switched to the side a, the differential pair 92 is selectively operated and the differential pair 9
The output of VCA50 added to 2 is output terminal 100
When the virtual contact of the switch 96 is switched to the side b, the differential pair 94 is selectively activated and the output terminal 100 receives a constant DC voltage, that is,
The midpoint voltage at the time of signal output is taken out.

In this case, the switch 96 is the variable current source 7
When the VCA 50 is shifted to the maximum attenuation state, the switch 96 is forcibly muted, that is, the contact b side and the differential pair 94 are set to the operating state.

Next, referring to FIG. 2, constant current sources 590, 592,
The specific circuit configuration example showing the current coupling relationship in 594, 596 and transistors 598, 599 is shown. That is, the constant current sources 590 and 592 are composed of the current mirror circuit shown in FIG. 2A, and the constant current source 596 and the transistor 598 are composed of the current mirror circuit shown in FIG. 2B. The constant current source 594 and the transistor 599 are configured by the current mirror circuit shown in FIG. That is, regarding these current coupling relationships, the bases of both transistors are made common, and the current ratio can be set to a desired relationship by the emitter area.

The operation of the above configuration will be described below.
In the VCA 50, when the current of the variable current source 70 becomes larger than the current of the transistor 646, the surplus current flows to the diode 656 side. At this time, the input terminals 71, 72
Potential difference between the base and emitter of the transistor V _F
Which is twice the value of 2V _F. At this time, theoretically VCA
The output of 50 is a signal output at a noise level, but in reality, the bias voltage fluctuates due to the output impedance of the bias circuit side set at the bases of the transistors 922 and 942 and the resistance value of the resistor 954. If the resistance value of the resistor 954 is 1 kΩ and the resistance value of the resistor 954 is 1 kΩ, the gain is 20 log (1000 / 0.1) = 80 dB (2), and by setting the bias circuit of the transistor 942 separately, mute The signal is set to be equal to or lower than the noise level of the differential pair 94 forming the buffer circuit.

In FIG. 3A, Ic is the variable current characteristic of the variable current source 70, and I _o is the transistor 65.
4 shows the constant current characteristics flowing in No. 4. Further, FIG. 3B shows the output V _O generated at the output terminal 100.

As is clear from these characteristics, in the section T in which the variable current Ic of the variable current source 70 exceeds the constant current I _o flowing through the transistor 654, the switch 96 switches to the b side as the variable current Ic increases. Output terminal 1
The output V _O generated at 00 is rapidly shifted to the noise level on the side of the differential pair 94 as the buffer circuit, and the audio output is switched to the noise level or lower. As a result, it is possible to reliably prevent the generation of unnecessary sound that is audible. Further, in this circuit, the mute circuit 90 is configured by a differential pair having good matching on the IC, and stable volume level control and mute control can be performed without being affected by temperature characteristics and variations in circuit elements. Can be done.

Next, FIG. 4 shows a concrete embodiment of a switching control circuit for simultaneously performing switching control of the constant current source 97 for the variable current source 70 and the differential pairs 92, 94 in the amplifier circuit shown in FIG. Shows.

A continuously changing control voltage Vc is applied to the input terminal 102. The control voltage Vc and the reference voltage V
A differential amplifier 200 is installed as a comparison means for comparing r and extracting a current according to the magnitude relation between the two. This differential amplifier 200 is provided with a pair of transistors 202 and 204 forming a differential pair. The emitters of the transistors 202 and 204 are commonly connected through resistors 206 and 208, and an intermediate connection point therebetween. Power line 209
A constant current source 210 for supplying an operating current to the differential pair is connected between and. A control voltage Vc is set to the base of the transistor 202 through the input terminal 102, and a reference voltage Vr is set to the base of the transistor 204 by the voltage source 212. The collector of the transistor 204 is provided with a ground line, and the collector side of the transistor 202 is provided with a current mirror circuit 214 for extracting a current as a comparison output. The current mirror circuit 214 is composed of transistors 216 and 218. The output current output through the transistor 218 is supplied to the collector side of the transistor 218 and the power supply line 20.
9 is extracted as a control current obtained in accordance with the comparison between the control voltage Vc and the reference voltage Vr through the current mirror circuit 220 provided between the control voltage Vc and the reference voltage Vr. The current mirror circuit 220 is composed of transistors 222 and 224. That is, the variable current extracted from the collector side of the transistor 224 is added to the variable current source 70 of FIG. 1 as a control current. In addition, the transistor 224
Can itself be used as a variable current source, and its output current may be directly input to the input terminal 72.

The switching control circuit shown in FIG. 1 corresponds to the level of the control voltage Vc applied to the input terminal 102.
A differential switch circuit 400 is installed as means for switching the operating current for the differential pair 92 and 94 shown in FIG. The differential switch circuit 400 is provided with transistors 402 and 404 that form a differential pair with common emitters. A control voltage Vc is applied to the base of the transistor 402 through the input terminal 102, and the transistor 4
The reference voltage Vp is applied from the voltage source 405 to the base of 04. The levels of the reference voltage Vp and the reference voltage Vr are set according to the variable current of the variable current source 70 and the operation switching conditions of the differential pairs 92 and 94. A constant current source 300 corresponding to the constant current source 97 is installed on the emitter side of the transistors 402 and 404.
The constant current due to 0 becomes the operating current of the differential pair 92, 94.
The transistor 40 is on the collector side of the transistor 402.
A current mirror circuit 406 for extracting a constant current when the transistor 2 is conductive, and a current mirror circuit 408 for extracting a constant current when the transistor 404 is conductive are provided on the collector side of the transistor 404. The current mirror circuit 406 is composed of transistors 410 and 412, and the current mirror circuit 408 is composed of current mirror circuits 414 and 416.

According to such a configuration, the input terminal 102
Is compared with the reference voltages Vr and Vp, the variable current source 70 is controlled through the differential amplifier 200, and the operation of the differential switch circuit 400 switches the operation of the differential pair 92 and 94. Since this is performed, stable volume level control and mute control can be performed without being affected by temperature characteristics and variations in circuit elements.

Next, FIG. 5 shows an embodiment of the volume control device of the present invention. This volume control device uses the amplifier circuit shown in FIG. 1, and an FM receiver 111, an AM receiver 112, a cassette deck 113, a CD player 114, and the like are installed on the front side as a plurality of electronic devices. Has been done. Each output signal of the plurality of electronic devices is arbitrarily selected in addition to the output switching circuit 115 which constitutes the signal selection means, and the FM to be taken out as an audio output at the output side thereof.
Receiver 111, AM receiver 112, cassette deck 11
3 or the output signal of the CD player 114 or the like is selectively taken out.

On the output side of the output switching circuit 115, an electronic volume control 116 comprising the variable current amplifier 50 in the above-mentioned embodiment is installed as signal control means, and on the output side thereof a mute circuit 118 is installed as mute means. ing. The mute circuit 118 corresponds to the mute circuit 90 of the above embodiment. These electronic volume 1
The 16 and mute circuit 118 are configured to be controlled by a control unit 120 which is a single control means, and the control is performed by a variable resistor 121 operated by an operation knob.

On the output side of the mute circuit 118, a power amplifier 122 is installed as an amplification means,
The amplified output is applied to the speaker 123, which converts it into an audio output.

With such a configuration, the output signals of the FM receiver 111, the AM receiver 112, the cassette deck 113, the CD player 114, etc., which are a plurality of electronic devices from which audio output should be selectively taken out from the speaker 123, are output. The electronic volume 11 is selected by the output switching circuit 115.
Added to 6. In the electronic volume 116, its level is adjusted by a variable resistor 121 which is an external operating means, and a voice output corresponding to the signal level is obtained from the speaker 123. Then, when the level, that is, the sound volume is cut down, the control unit 120 interlocks with the mute circuit 118 correspondingly and suppresses the level. As a result, complete mute from the speaker 123 is realized,
Sound leakage can be prevented.

[0034]

As described above, according to the amplifier circuit of the present invention, since the mute circuit shifts to the mute state at the maximum attenuation, the circuit element is different from the signal suppression by operating the circuit element. It is possible to reliably prevent extraction of an unnecessary signal, that is, so-called sound leakage without being affected by the temperature characteristics of No. 1 and without deteriorating the SN ratio during operation, and prevent discomfort due to unnecessary sound.

Further, according to the volume control device of the present invention, when the volume is fully reduced, the signal can be suppressed by the mute means, so that unpleasant sound leakage can be prevented and the muting state can be completed. it can.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a current mirror circuit in the amplifier circuit shown in FIG.

FIG. 3 is a diagram showing operating characteristics of the amplifier circuit shown in FIG.

FIG. 4 is a circuit diagram showing a specific example of a switching control circuit suitable for level control and mute control of the amplifier circuit shown in FIG.

FIG. 5 is a block diagram showing an embodiment of a volume control device of the present invention.

FIG. 6 is a circuit diagram showing a conventional audio device.

FIG. 7 is a circuit diagram showing a conventional amplifier circuit.

[Explanation of symbols]

 50 current variable amplifier (gain control means) 90 mute circuit 96 switch (switching means) 111 FM receiver (electronic equipment) 112 AM receiver (electronic equipment) 113 cassette deck (electronic equipment) 114 CD player (electronic equipment) 115 output Switching circuit (signal selection means) 116 Electronic volume (signal control means) 118 Mute circuit (mute means) 122 Power amplifier (amplification means) 123 Speaker

Claims (2)

[Claims] 1. An amplifier circuit comprising a gain control means for suppressing a signal level by gain control based on a control input, and a mute circuit for suppressing an output on the output side thereof, wherein the gain control means controls the gain control means. An amplifier circuit comprising switching means for switching the mute circuit side to a mute state according to a level. 2. A volume control device for controlling the volume to be taken out from a speaker by selectively applying output signals of a plurality of electronic devices via a signal selection means, wherein the output signals of the plurality of electronic devices are signaled. A volume control device, wherein when the volume output from the speaker is cut down when output to the amplification means through the control means, sound leakage is prevented by interlocking with the mute means.