JPH0119646B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention integrates an audio amplifier and a circuit that generates a control signal to reduce transient sounds that occur when the amplifier is turned on or when switching modes such as recording/playback. It relates to semiconductor integrated circuits.

In audio amplifiers used in tape recorders and the like, mode switching as described above is performed by a mechanical switch, and the electrical characteristics required for each mode are obtained. However, when switching modes or turning on the power, unpleasant transient sounds are generated. Conventionally, in order to reduce this transient noise, countermeasures had to be taken by changing the rise characteristics of the amplifier concerned or connecting a muting transistor, which required a lot of effort to create a control circuit. There was a problem.

The present invention has been made in view of the above points, and is a method that integrates a control signal generation circuit that can supply a control signal that can easily suppress transient noise generated from an amplifier when turning on the power or switching modes, and an amplifier. The purpose of the present invention is to provide a semiconductor integrated circuit constructed using the following methods.

FIG. 1 is a circuit diagram showing a transient sound control signal generation circuit used in an embodiment of the present invention, where V _cc is a DC power supply,
V _s is a stabilized power supply made from this power supply V _cc . _S1 is a changeover switch that works with the mode changeover switch of the amplifier to be controlled (not shown).The changeover contact is grounded through resistor _R1 and capacitor _C1 , and during recording, it is switched to contact A and connected to the power supply _Vcc.
During playback, the contact is switched to contact RO and connected to the ground point. A is the connection point between resistor _R1 and capacitor _C1 . On the other hand, a resistor R ₂ and _a capacitor _{C 2} are connected in series between the power supply V _cc and the ground point to obtain a time constant signal when the power is turned on. It is a connection point. Diodes D ₁ , D ₂ , D ₃ , D ₄ and D ₅ are connected in series in the forward direction between the connection point A and the ground point. From the stabilized power supply V _s , diodes D ₆ and D ₇ are connected via resistor R ₃ .
and D ₈ are connected in series in the forward direction, and the cathode of diode D ₈ is connected to the collector of transistor Q ₁ .
base and commonly connected transistor Q ₂ ,
It is connected to the base of _Q3 , and the emitters of transistors _Q1 and _Q2 are grounded. Transistors Q ₃ , Q ₄
The emitters of are commonly connected to the collector of transistor Q ₂ , the collector of transistor Q ₃ is connected to the regulated power supply V _s , the collector of transistor Q ₄ is connected to the base-collector of transistor Q ₅ and the base of transistor Q ₆ , The base of transistor _Q4 is connected to node A. Also, the emitters of transistors Q ₅ and Q ₆ are both stabilized power supplies.
Connected to V _s . The collector of transistor _Q6 is connected to the collector/base of transistor _Q7 and the base of transistor _Q8 , and the emitters of transistors _Q7 and _Q8 are both grounded.
The emitters of transistors Q ₉ and Q ₁₀ are commonly connected to the collector of transistor Q ₈ .
The base of _Q9 is connected to connection point A, and the collector is connected to the stabilized power supply _Vs. The base of the transistor Q ₁₀ is connected to the connection point between the resistor R ₃ and the diode D ₆ , and the collector is connected to the collector-base of the transistor Q ₁₁ and the base of the transistor Q ₁₂ .
The emitters of transistors Q ₁₁ and Q ₁₂ are both connected to the stabilized power supply V _s , the collector of transistor Q ₁₂ is connected to the base of transistor Q ₁₃ , and the bases of transistors Q ₁₁ and Q ₁₂ are connected to the collector of transistor Q ₁₄ . It is connected. The collector of the transistor _Q13 is connected to the stabilized power supply _Vs , and the control signal output terminal CONT is drawn out from the emitter. The base of transistor Q ₁₄ is connected to the base of transistor Q ₁₀ and the emitter of transistor Q ₁₆ along with the emitter of transistor Q ₁₅
connected to the collector. transistor Q ₁₅
The collector of is connected to the power supply V _cc and the base to connection point B. The emitter of transistor _Q16 is grounded and the base of the transistors connected in common
Connected to the bases of Q ₁ , Q ₂ , and Q ₃ . Transistors Q ₃ and Q ₄ connect the first comparator 1, transistors Q ₉ and Q ₁₀ connect the second comparator 2, and transistors
Q ₁₄ and Q ₁₅ constitute the third comparator 3.

The operation of this embodiment circuit will be explained below. Two comparators 1 and 2 are connected between the connection point A and the control signal output terminal CONT, and the voltage generated at the connection point A performs a window comparator operation to turn on/off the control signal output. Off is performed.

Now, if we consider that the changeover switch _S1 changes from contact RO to contact A, that is, from playback mode to recording mode, the potential at connection point A changes from ground potential to the time constant of resistor _R1 and capacitor _C1 . It increases towards the power supply voltage _Vcc . The base potential of the transistor Q ₃ of the first comparator 1 is always maintained at the forward voltage V _BE of the diode-connected transistor Q ₁ ≈0.7V, and when the base potential of the transistor Q ₄ becomes higher than this, the transistor Q ₄ becomes conductive, and current flows through the mirror circuit consisting of transistors Q ₅ , Q ₆ , Q ₇ , and Q ₈ . At the same time, the base potential of the transistor _Q10 of the second comparator 2 is always
Forward voltage of D ₆ , D ₇ , D ₈ and transistor Q ₁
The current is set to 4V _BE , and until the base potential of transistor _Q9 exceeds 4V _BE , current flows to transistor _Q10 , current flows to the mirror circuit consisting of transistors _Q11 and _Q12 , and this flows to transistor _Q13.
During this period, drive the control signal output terminal CONT.
A control signal is output from. In this state, when the potential at the connection point becomes higher than 4V _BE , transistor Q ₉ of the second comparator 2 becomes conductive, transistor Q ₁₀ is immediately turned off, and current flows through the mirror circuit consisting of transistors Q ₁₁ and Q ₁₂ . The current stops, the base of transistor _Q13 is not driven, the control signal from the control signal output terminal CONT disappears, and the control signal generation operation when switching from playback mode to recording mode is completed.

Conversely, when the changeover switch S ₁ switches from contact A to contact B, i.e. from recording mode to playback mode, 5V _BE is generated due to diodes D ₁ to _{D 5} .
The potential at the connection point A, which has been maintained at , is reduced by the time constant of the capacitor C ₁ and the resistor R ₁ by switching the changeover switch S ₁ . And this potential is 4V _BE
When the transistor of the second comparator 2 becomes
Q ₁₀ becomes conductive and transistors Q ₁₁ ,
Current flows through the mirror circuit consisting of _Q12 , which drives transistor _Q13 and outputs the control signal output terminal.
A control signal is output to CONT. When the potential at the connection point A further decreases to below V _BE , the transistor Q ₃ of the first comparator 1 becomes conductive and the transistor Q ₄ is soon turned off, and the transistors Q ₅ , Q ₆ and Q ₇ , Q ₈ The current in the mirror circuit is now cut off, the current no longer flows to the second comparator 2, the transistor _Q13 is not driven, the control signal from the control signal output terminal CONT disappears, and the switching from recording mode to playback mode occurs. The control signal generation operation at the time is completed.

Next, the control signal generation operation when the power is turned on will be explained. At the same time as the power is turned on, a potential of 4V _BE is supplied to the base of one transistor _Q14 constituting the third comparator 3, but the potential of the connection point B connected to the base of the other transistor _Q15 is There is a time delay as the rise occurs due to the time constant of resistor R ₂ and capacitor C ₂ , transistor Q ₁₄ becomes conductive, current flows through the mirror circuit consisting of transistors Q ₁₁ and Q ₁₂ , and drives transistor Q ₁₃ for control. Signal output terminal
A control signal is output to CONT. When the potential at connection point B rises and exceeds 4V _BE , transistor Q ₁₅ becomes conductive, and transistor Q ₁₄ quickly turns off.
_Q13 is no longer driven and the control signal output terminal
The control signal from CONT disappears, and the control signal generation operation at power-on is completed.

As mentioned above, when switching modes, the potential at connection point A reaches from V _BE to 4V _BE , or from 4V _BE to
It outputs a control signal while it reaches V _BE , and when the power is turned on, it outputs a control signal until the potential at connection point B reaches 4V _BE , and the generation period of the control signal is
It can be adjusted by controlling the time constants of R ₁ C ₁ and R ₂ C ₂ .

In FIG. 2, the waveforms of the transient sound generated from the audio amplifier during recording/reproduction switching and the control signal output from this embodiment circuit are shown in a and b, respectively. As shown in the figure, a control signal is output when a transient sound occurs, and this control signal can be used to reduce the transient sound.

In FIG. 3, the rise characteristics of the audio amplifier when the power is turned on and the waveforms of the control signal output from this embodiment circuit are shown by broken lines and solid lines, respectively. A control signal is also output when the output rises, and this control signal can be used to suppress unpleasant output sound.

FIG. 4 is a block circuit diagram showing the configuration of an embodiment of the present invention, in which 11 is a recording input terminal, 12 is a playback input terminal, 13 is a recording amplifier, 14 is a playback amplifier, and 15 is a recording/playback switch. , 16 is an output capacitor, 17 is an output terminal, 18 is a first
The control signal generation circuit 19 shown in the figure is a transistor that opens and closes according to a control signal from its control signal output terminal CONT, and the control signal generation circuit 1
8 is configured to operate with the same power supply _Vcc as the power supply for both amplifiers 13 and 14, and the internal changeover switch _S1 is the recording/playback changeover switch 1.
5, so this circuit 1
It is clear from the above description that the control signal obtained from the transistor 8 makes the transistor 19 conductive, thereby suppressing the transient sound output at power-on and mode switching. Further, in the present invention, since the control signal generation circuit and the amplifier are integrated into one semiconductor substrate, it is possible to downsize the device.

FIG. 5 is a block configuration diagram showing another embodiment of the present invention, in which 20-1, . . . , 20-n are signal input terminals, 21-1, .
-1,...22-n is an output capacitor, 23-
1,...,23-n are output terminals, 19-1,...
..., 19-n are terminals from the control signal generation circuit 18.
The amplifier output terminals 23-1, . . . are conductive only during the period of the control signal supplied through CONT.
..., 23-n are grounded. In this embodiment, each amplifier 21-1, ..., 21-n
and control signal generating circuit 18 are formed within the same semiconductor chip. That is, as long as the power source is common to the control signal generation circuit 18 and the mode switching is performed in common for all amplifiers, it is possible to reduce transient noise for the plurality of amplifiers 21-1, . . . , 21-n.

As explained above, in the present invention, a control signal generation circuit that generates a control signal when switching the operating mode of an audio amplifier or when turning on the power, thereby suppressing transient noise, is integrated with the audio amplifier into a single semiconductor substrate. Since it is configured inside the body, the unpleasant sound output during the above transition is eliminated, comfortable sound output can be obtained, and the device can be made smaller.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a transient sound control signal generation circuit used in the present invention, Fig. 2 is a waveform diagram showing the transient sound output when switching the operation mode and the control signal obtained by the above circuit, and Fig. 3 4 is a waveform diagram showing the rise characteristics of the audio amplifier when the power is turned on and the control signal obtained by the above circuit, FIG. 4 is a block diagram showing the configuration of one embodiment of the present invention, and FIG. FIG. 2 is a block diagram showing the configuration of an embodiment. In the figure, 1, 2, 3 are voltage comparators, R ₁ ,
C ₁ , R ₂ , C ₂ are the resistors and capacitors that constitute the time constant circuit, CONT is the control signal output terminal, 13, 14, 21-1, ..., 21-n are the audio amplifiers, and 18 is the transient sound control This is a signal generation circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An audio amplifier, which generates a first variable DC voltage that changes with a predetermined time constant when the audio amplifier is powered on, outputs a control signal and operates while the value of the first variable DC voltage is within a predetermined range. Generates a second variable DC voltage that changes with a predetermined time constant when switching modes, and outputs a control signal while the second variable DC voltage is within a predetermined range using a window comparator method using two voltage comparators; A semiconductor integrated circuit characterized in that a transient output sound suppressing circuit for suppressing transient output sound generated when the power of the audio amplifier is turned on or the operating mode is switched by the control signal is built in the same semiconductor substrate.