JP2001244749A - Mute circuit and audio amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mute circuit, that is suitable for an audio circuit where malfunctions hardly takes place, even if an output voltage of a preamplifier is increased in the case of adopting an IC for a mute switching transistor(TR) and high dynamic range can be adopted and to provide an audio amplifier circuit. SOLUTION: The mute circuit is provided with an integrated circuit, where an amplifier and a mute switch circuit inserted between an output line of the amplifier and a reference voltage line are integrated, and a mute signal generating circuit that generates a mute signal. The mute switch circuit has 1st and 2nd NPN transistors(TRs), the emitter of the 1st TR is connected to the output line, the collectors of the 1st and 2nd TRs are connected, the emitter of the 2nd TR is connected to the reference voltage line and a mute signal turns on the 1st and 2nd TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mute circuit and an audio amplifier circuit. In this case, even if the output voltage of the preamplifier becomes large, a malfunction does not easily occur, a large dynamic range can be obtained, and a boss sound is hardly generated when the mute switch is turned ON / OFF. About.

[0002]

2. Description of the Related Art An audio signal processing circuit using a transistor or the like is accompanied by an unpleasant abnormal sound such as a so-called pop sound when a power switch is turned on, and in the worst case, a speaker is damaged via a power amplifier. There is also. Therefore, generally, a mute circuit is inserted to forcibly cut off or ground the audio signal path until the power amplifier or the like reaches a steady state. Alternatively, when a silent state is selected during operation of the device, the mute circuit is operated.

FIG. 4 shows an analog amplifying audio amplifier circuit 1 having a mute circuit of this kind. Reference numeral 2 denotes a preamplifier IC unit, which is formed as an IC, and includes a preamplifier 3, a mute signal generation circuit 7, Mute switch circuits SW1 and SW2 are provided. Reference numeral 6 denotes a magnetic head for reading an audio signal recorded on a tape, 4 denotes a power amplifier, and 5 denotes a speaker. Although the mute circuit may refer to the mute signal generation circuit 7 itself, in this specification, it is assumed that the mute circuit includes the mute signal generation circuit 7 and the mute switch circuits SW1 and SW2. The switch circuit SW1 is inserted between an output line between the preamplifier 3 and the power amplifier 4 and the ground GND, and the switch circuit SW2 is inserted in series with the input line. The configuration of the preamplifier IC unit 2 in this example operates with both positive and negative power supplies, and uses the ground potential as a signal reference. Also, the switch circuit SW1 is I
C, two mute signals M1 and M2 are generated, and the mute signal M1 is a switch circuit SW1 for muting.
, And the mute signal M2 is supplied to the switch circuit S
It is used for controlling W2.

[0004]

In an audio amplifier circuit, a bootstrap circuit is used to prevent saturation of a drive stage and generate a high output voltage, or a power supply voltage is boosted. In a digital audio amplifier circuit for a game machine, a CD player, or the like, an analog signal after digital-to-analog conversion of a digital value is amplified by a preamplifier. In this case, the output of the preamplifier is increased to obtain a large dynamic range. In many cases, the voltage is higher than the output of the analog audio signal and becomes a voltage of both positive and negative polarities. In a circuit that generates an output having such a high signal level, when muting is performed before the input of the main amplifier at the output stage, a high-withstand-voltage mute switch circuit that does not perform an ON operation except during the mute period is required. The switch circuit SW1 in the case of FIG.
Is an NPN and PNP transistor connected in parallel back-to-back, but in an audio amplifier circuit that adopts a large dynamic range, such as a digital audio amplifier circuit, the output voltage of the preamplifier becomes large. When the voltage of the output signal is shifted more than the negative power supply voltage, which is the reference voltage of the substrate, in the switch circuit SW1 in which the transistors are connected in parallel, the parasitic transistor whose collector is the substrate is connected to the negative voltage of the preamplifier. Since it is turned on by the output signal, a malfunction in which the switch circuit SW1 is turned on easily occurs. In the case where only the power supply on the positive side is operated and Vcc / 2 is used as a reference, the reference voltage of the substrate is usually set to the ground GND, but the output signal of the preamplifier must be maintained on the positive side. However, there is a disadvantage that a large dynamic range cannot be obtained.

Further, as described above, when the switch circuit SW1 is connected between the ground GND and the output of the amplifier, the ON / O of the switch circuit SW1 is muted.
There is a disadvantage that a pop sound is likely to be generated during the FF operation. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art. When an IC is used as a mute switching transistor, a malfunction does not easily occur even if the output voltage of a preamplifier becomes large, and the dynamic range is reduced. An object of the present invention is to provide a mute circuit and an audio amplifier circuit which can be widely adopted. Another object of the present invention is to provide a mute circuit and an audio amplifier circuit which can take a large dynamic range and hardly generate a pop sound when a mute switch is turned ON / OFF.

[0006]

The first aspect of the present invention for achieving the above object is a mute circuit and an audio amplifier circuit, which are characterized in that an amplifier is inserted between an output line of the amplifier and a reference voltage line. And a mute signal generation circuit for generating a mute signal, wherein the mute switch circuit has first and second NPN transistors and a first mute switch circuit. Are connected to the output line, the collectors of the first and second transistors are connected to each other, the emitter of the second transistor is connected to the reference voltage line, and the first and second transistors are connected according to the mute signal. The transistor is turned on. Further, a feature of the mute circuit and the audio amplifier circuit of the second invention for achieving the other object is that an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line, and , An mute signal generation circuit for generating a mute signal, and a mute control circuit for receiving the mute signal and turning on the mute switch circuit.
A first and a second transistor of the type
Are connected to the output line, the collectors of the first and second transistors are connected to each other, the emitter of the second transistor is connected to the reference voltage line, and the mute signal generation circuit receives the mute signal. A control signal for turning on the transistor after turning on the second transistor and for turning off the transistor after turning off the second transistor when the mute signal is stopped is applied to the bases of the first and second transistors.

Further, a third aspect of the present invention for achieving the other object is that an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line, and a mute signal are provided. The generated mute signal generation circuit and the mute switch circuit
A mute control circuit for N / OFF, wherein the mute switch circuit includes an output side (for example, a collector-emitter) connected in series between the output line and the reference line.
The first and second transistors are sequentially connected such that the first transistor is the upstream side and the second transistor is the downstream side, and after the mute signal generation circuit receives the mute signal and turns on the second transistor, When the first transistor is turned on, and when the mute signal is stopped, the first and second control signals for turning off the first transistor after turning off the second transistor are transmitted.
To the base of the transistor.

[0008]

As described above, in the first invention, the mute switch circuit has the first and second NPN transistors, and the emitter of the first transistor is connected to the output line; The collectors of the first and second transistors are connected to each other, and the emitter of the second transistor is connected to a reference voltage line. Thereby, when the mute switch circuit is not in the mute operation state and the mute switch circuit is in the OFF state, the second transistor on the downstream side is turned off even if the output line of the amplifier is swung to the negative side.
In this state, the collector of the upstream first transistor whose emitter is connected to the output line is in a floating state, so that this transistor and the parasitic transistor hardly turn on, and a large dynamic range is taken. be able to. Further, in the second and third inventions, the ON / OFF operation of the first transistor and the second transistor is not performed simultaneously, so that the ON / OFF transition at the time of the mute operation of the mute switch circuit is performed. Since the impedance seen from the output line of the amplifier in the state becomes high, the transient current value flowing at the time of the mute operation of the mute switch circuit becomes very small, thereby suppressing occurrence of hop-on. As a result, when the switching transistor for mute is formed into an IC, an audio amplifier circuit which does not easily malfunction even when the output voltage of the preamplifier becomes large or swings to the negative side and which can take a large dynamic range is realized. be able to.

[0009]

FIG. 1 is a block diagram of an embodiment to which a mute circuit according to the present invention is applied, FIG. 2 is a timing chart for explaining the operation of a mute switch, and FIG. FIG. The difference between FIG. 1 and FIG. 4 is that the audio amplifier circuit 10 of FIG.
Is a digital audio amplifying circuit, which converts a digital input signal reproduced from a digital signal reproducing circuit 8 such as a game machine or a CD reproducing circuit into a D
A / A conversion circuit (D / A) 12 receives the converted analog signal, and converts the converted analog signal to a preamplifier 13. The mute switch circuit is a switch circuit SW shown in FIG.
1 in that a switch circuit SW is provided, the switch circuit SW is provided before the power amplifier 4, and the mute signal control circuit 14 is provided between the mute signal generation circuit 7 and FIG. . The mute signal M2 generated by the mute signal generation circuit 7 is unnecessary in the circuit of this embodiment and will not be described. Here, the preamplifier 13
Is a circuit that operates with a positive power supply, generates an output signal based on the ground GND level, and takes a large dynamic range. To this end, an amplifier operating on the basis of + Vcc / 2 is connected to the power amplifier 4 by AC coupling via a series circuit of a capacitor C1, a resistor R, and a capacitor C2, as shown in the figure.

The above-mentioned mute switch circuit SW comprises a series circuit of an NPN transistor Q1 and an NPN transistor Q2 connected between a connection point N between a resistor R and a capacitor C2 and a ground GND. The emitter of the transistor Q1 is connected to the connection point N, the collector is connected to the collector of the transistor Q2, and the emitter of the transistor Q2 is connected to the ground GND. Transistor Q
A capacitor C3 is connected to the base of the mute signal control circuit 14 between the base and the ground GND, and this base is connected to the collector of the output-side transistor Q5 connected to the current mirror of the mute signal control circuit 14 and connected thereto. The output current is turned on. Further, the base of the transistor Q2 is connected to the collector of the output-side transistor Q4 connected to the current mirror of the mute signal control circuit 14, and is turned on in response to the output current.

The mute signal control circuit 14 has a transistor Q3 on the input side, transistors Q4 and Q5 on the output side, and an NPN transistor connected to a current mirror PNP transistor whose emitter side is connected to the power supply line + Vcc. Transistor Q
6, and the above-mentioned capacitor C3. The NPN transistor Q6 has a resistor R1 connected to the emitter of the transistor Q3.
, The collector of which is connected, and the emitter of which is connected to ground GND. Then, the mute signal M1 is received at the base of the NPN transistor Q6. When the transistor Q6 receives the mute signal M1 (a signal of a predetermined voltage level for turning on the transistor Q6), the transistor Q6 is turned on, and the transistor Q3 is turned on. The output from Q5 is supplied to the base of transistor Q1 and the base of transistor Q2. At this time, the capacitor C3 is inserted between the base of the transistor Q1 and the ground GND.
2 is turned on first, and then the transistor Q1 is turned on. When the mute signal M1 turns off (ground level), the transistor Q6 turns off, and the transistor Q1 turns off with a slight delay after the transistor Q2 turns off. FIG. 2 shows this ON / OFF state.

FIG. 2 shows the operation timing of the mute signal M1, the transistor Q1, and the transistor Q2. The ON operation of the transistor Q1 and the transistor Q2 lags behind the transistor Q2 by Δt. In the OFF state, the transistor Q1 lags behind the transistor Q2 by Δd. As a result, the impedance of the switch circuit SW at the time of the mute operation as seen from the output of the preamplifier 13 has a higher value in a transient state than when each switch transistor is turned on / off. That is, when the switch circuit SW is in a transitional state operation in which the transition is made from OFF to ON or from ON to OFF, one of the transistors Q1 and Q2 connected in series by turning off one and turning on the other. The impedance becomes high. When the impedance of the switch circuit SW becomes a high value in the transient state, the waveform of the boss sound generated by the switch circuit SW during the mute operation can be suppressed to a very low level. To explain this further, here:
The base voltage of the transistor Q1 is set to VB, and the capacitor C
Assuming that the capacity of C is C and the drive current value is i, if VB = ∫idt / C Δt ≦ VB · C / i VB = 0.7, then Δt ≦ 0.7 × C / i. When the time Δt is equal to or lower than the audio frequency and equal to or lower than 20 Hz (or equal to or higher than the audio frequency and equal to or higher than 20 kHz), the boss sound is inaudible to humans. The drive current value i applied to the bases of the transistors Q1 and Q2 is 5 mA to 10 mA.
If the capacitance of the capacitor C3 is set to several tens pF to several hundred pF, the waveform of the boss sound generated by the switch circuit SW can be suppressed to a very low level and 20 Hz or less.

Next, the relationship between the ON malfunction and the dynamic range of the switch circuit SW during periods other than the mute period (when the mute is OFF) will be described. The preamplifier 13
An amplifier that operates on the basis of + Vcc / 2 in order to obtain a large dynamic range. By passing through the capacitor C1, it becomes an audio signal based on the ground GND level. Here, the output has a large positive and negative amplitude. Change. This signal is applied to the switch circuit SW. Even in such a circuit, the switch circuit SW rarely malfunctions with the negative output voltage of the preamplifier 13. It is a switch circuit S
W is composed of a series circuit of a transistor Q1 and a transistor Q2.
Is turned off, so long as this state is maintained, the collector side of the upstream transistor Q1 is in a floating state. In this state, the emitter side of the upstream transistor Q1 receives the output voltage of the preamplifier 13, and when the output voltage is a large negative voltage, the voltage between the base (ground potential) and the emitter of the transistor Q1 becomes 0.7 V or more, and the transistor Q1 is turned on. May be driven to state. Even in such a state, no current is supplied from the collector side of the transistor Q1 because the downstream transistor Q2 is OFF. Therefore, the switch circuit SW is not turned ON as a whole. Of course, the switch circuit SW is OF
When the emitter side of the upstream transistor Q1 receives a large positive voltage in the F state, the transistor Q1
Since there is a reverse bias between the base and the emitter of No. 1, it does not turn on.

The operation of the parasitic transistor which causes a malfunction in this case will be described with reference to FIG. FIG.
FIG. 3 is a schematic sectional view of a semiconductor structure of a switch circuit SW part. As shown, P-sub (P-type substrate)
The NPN transistors Q1 and Q2 are integrated adjacent to each other on the surface of the transistor 15, the emitter of the transistor Q1 is connected to the output line 13A of the preamplifier 13, and the emitter of the transistor Q2 is connected to the ground GND. The collectors of the transistors Q1 and Q2 are connected to each other via a wiring line 16, and the bases of the transistors Q1 and Q2 are connected to the current source i of the transistors Q5 and Q4, respectively.
Driven by In this case, the emitter side is the preamplifier 13
The transistor Q1 receiving the output voltage of the
There is a PNP parasitic transistor Q7 shown by a dotted line. The parasitic transistor Q7 is connected to the transistor Q1.
The transistor has a base B as an emitter, a collector of the transistor Q1 as a base, and a P-sub 15 portion as a collector. The transistor Q2 has a P
There is a parasitic transistor Q8 of PNP indicated by a dotted line formed in -sub15. This is a transistor having the base B of the transistor Q2 as the emitter, the collector of the transistor Q2 as the base, and the P-sub 15 portion as the collector.

Here, when a large negative voltage is applied from the preamplifier 13 to the emitter E side of the transistor Q1, the potential between the base B and the emitter E of the transistor Q1 becomes forward, so that the parasitic transistors Q7 and Q8 are turned on. There is a problem of being driven. At this time, the parasitic transistor Q7
Is connected to the collector C side of the transistor Q2 and is in the OFF state, so that it becomes a floating bias connected to the ground GND with a high resistance value, and becomes a reverse bias between the collector C and the base B of the transistor Q1. The parasitic transistor Q7 is OF
The F state is maintained, and the base transistor and the emitter of the parasitic transistor Q7 do not operate with a reverse bias. The base of the parasitic transistor Q8 is connected to the collector C side of the transistor Q2, and is not turned on because the transistor Q2 is in the OFF state and the emitter E or the base B of the transistor Q2 is at the ground GND potential. . Here, when a large positive voltage is applied to the emitter E side of the transistor Q1, the direction between the base B and the emitter E of the transistor Q1 is reversed, so that the transistor Q1 is maintained in the OFF state, and the ON operation of the parasitic transistors Q7 and Q8 is not performed. No problem.

As described above, in the embodiment, an example of an output line of a preamplifier having both positive and negative polarities is given as a line to be dropped to the ground GND (or a reference potential) for a mute operation. Realizes a mute switch circuit which is hard to be turned on in a negative polarity. Even if the mute switch circuit is used by being connected to the line of the positive output signal, the mute switch circuit is driven when it is driven negative by noise or the like. Since the mute circuit having the switch circuit does not malfunction, the dynamic range can be extended to the vicinity of the ground GND. Therefore, it is needless to say that the present invention is not limited to the above-described embodiment.

[0017]

As can be understood from the above description, the first
In the first invention, in the first invention, the mute switch circuit has first and second transistors of NPN type, and the emitter of the first transistor is connected to the output line, and the first and second transistors are connected to the output line. The collectors of the two transistors are connected to each other, and the emitter of the second transistor is connected to the reference voltage line. Accordingly, when the mute switch circuit is not in the mute operation state and the mute switch circuit is in the OFF state, the emitter of the output transistor is turned off because the second transistor downstream is in the OFF state even if the output line of the amplifier is swung to the negative side. Since the collector of the upstream first transistor connected to the line is in a floating state, this transistor and the parasitic transistor are turned on.
And the dynamic range can be increased. In the second invention, the ON / OFF state of the first transistor and the second transistor is further increased.
Since the OFF operation is not performed at the same time, the impedance seen from the output line of the amplifier in the transient state of ON / OFF at the time of the mute operation of the mute switch circuit becomes high, so the transient current value flowing at the time of the mute operation of the mute switch circuit Is small, thereby suppressing the occurrence of hop-on. As a result, when the switching transistor for mute is formed into an IC, an audio amplifier circuit which does not easily malfunction even when the output voltage of the preamplifier becomes large or swings to the negative side and which can take a large dynamic range is realized. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment to which a mute circuit of the present invention is applied.

FIG. 2 is a timing diagram illustrating the operation of a mute switch.

FIG. 3 is a schematic sectional view of a semiconductor structure of a mute switch circuit part.

FIG. 4 is a block diagram illustrating an example of a conventional mute circuit.

[Explanation of symbols]

 1, 10: audio amplifier circuit, 2, 11: preamplifier IC section, 3, 13: preamplifier, 4: power amplifier, 5: speaker, 6: magnetic head, 7: mute signal generation circuit, 8: digital signal reproduction circuit, 12: D / A conversion circuit (D / A), 14: Mute signal control circuit, 15: P-sub (P type substrate), 16: Wiring line, SW, SW1, SW2: Switch circuit, M1, M2 ... Mute signal, Q1 to Q7 ... transistors.

Continued on the front page F term (reference) 5D020 AA01 AC02 5J092 AA02 AA41 AA51 CA32 CA48 CA49 FA20 FR02 HA08 HA25 HA29 HA32 HA33 HA38 HA39 KA00 KA34 KA62 MA00 MA21 QA02 SA05 TA01 TA06

Claims (8)

[Claims] An integrated circuit in which an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line are integrated, and a mute signal generation circuit for generating a mute signal, The mute switch circuit has first and second NPN transistors, an emitter of the first transistor is connected to the output line, and collectors of the first and second transistors are connected to each other. The second
Wherein the emitter of the transistor is connected to the reference voltage line, and the first and second transistors are turned on in response to the mute signal. 2. An integrated circuit in which an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line are integrated, a mute signal generating circuit for generating a mute signal, and the mute A mute control circuit for turning on / off the mute switch circuit in response to a signal, wherein the mute switch circuit has first and second NPN-type transistors, and the emitter of the first transistor is an emitter. Connected to the output line, the collectors of the first and second transistors are connected to each other, and the second
The mute signal generation circuit receives the mute signal, turns on the second transistor, turns on the first transistor, and stops the mute signal. A mute circuit, wherein a control signal for turning off the first transistor after turning off the second transistor is applied to the bases of the first and second transistors. 3. The reference line is a ground line,
3. The mute circuit according to claim 2, wherein the amplifier is a preamplifier, and a capacitor is inserted in series with the output line, and an emitter of the first transistor is connected after the capacitor. 4. An integrated circuit in which an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line are integrated, and a mute signal generation circuit for generating a mute signal, The mute switch circuit has first and second NPN transistors, an emitter of the first transistor is connected to the output line, and collectors of the first and second transistors are connected to each other. The second
Wherein the emitter of the transistor is connected to the reference voltage line. 5. An integrated circuit in which an amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line are integrated, a mute signal generation circuit for generating a mute signal, and the mute A mute control circuit for turning on / off the mute switch circuit in response to a signal, wherein the mute switch circuit has first and second NPN-type transistors, and the emitter of the first transistor is an emitter. Connected to the output line, the collectors of the first and second transistors are connected to each other, and the second
The emitter of the transistor is connected to the reference voltage line, and the mute signal generation circuit receives the mute signal, turns on the second transistor, turns on the first transistor, and turns on the mute signal. An audio amplifier circuit, wherein when stopped, a control signal for turning off the first transistor after turning off the second transistor is applied to the bases of the first and second transistors. 6. The reference line is a ground line, the amplifier is a preamplifier, a capacitor is inserted in the output line, and an emitter of the first transistor is connected after the capacitor. 5
An audio amplifier circuit as described. 7. An amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line, a mute signal generation circuit for generating a mute signal, and the mute switch circuit receiving the mute signal And a mute control circuit for turning on / off the mute switch circuit, wherein the mute switch circuit sequentially includes an output side in series between the output line and the reference line, with a first transistor being an upstream side and a second transistor being a downstream side. A first transistor and a second transistor connected to the first transistor, wherein the mute signal generation circuit receives the mute signal, turns on the second transistor, turns on the first transistor, and turns on the mute signal. Is stopped, the first transistor is turned off after the second transistor is turned off. A mute circuit, wherein a control signal for setting to F is applied to bases of the first and second transistors. 8. An amplifier, a mute switch circuit inserted between an output line of the amplifier and a reference voltage line, a mute signal generation circuit for generating a mute signal, and the mute switch circuit receiving the mute signal And a mute control circuit for turning on / off the mute switch circuit, wherein the mute switch circuit sequentially includes an output side in series between the output line and the reference line, with a first transistor being an upstream side and a second transistor being a downstream side. A first transistor and a second transistor connected to the first transistor, wherein the mute signal generation circuit receives the mute signal, turns on the second transistor, turns on the first transistor, and turns on the mute signal. Is stopped, the first transistor is turned off after the second transistor is turned off. An audio amplifier circuit, wherein a control signal for setting to F is applied to the bases of the first and second transistors.