JPS6138266Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a muting control signal generation circuit for a receiver such as a car radio, and in order to suppress the pop sound that occurs when the power is turned on, the present invention generates a muting control signal before the pop sound is generated. It is an object of the present invention to provide a muting control signal generation circuit that performs the following steps.

The present invention will be explained below with reference to examples.

FIG. 1 is a block diagram of a muting control signal generation circuit according to an embodiment of the present invention, which is applied to an in-vehicle stereo system.

In FIG. 1, reference numeral 1 denotes a muting control signal generating circuit of this embodiment which will be explained later, and the remaining parts except for the muting control signal generating circuit 1 constitute a power supply switching circuit used in an in-vehicle stereo system.

+B is the car's storage battery, and its output voltage is V ₁
It is. 2 is the ignition switch, ACC is the accessory terminal, 3 is the tuner on/off switch, AA is the terminal for the automatic antenna lifting device, 4
5 is a switch for giving priority to the tape recorder, and 5 is a stable output voltage V ₂ using the voltage V ₁ from the storage battery +B as input.
It is a stabilized power supply circuit that outputs voltage V ₁ > V ₂
It is.

On the other hand, 6 is a main amplifier circuit, which is shown by an equivalent resistance VR ₁ and a decoupling capacitor C ₁ .
At 7, the voltage _V1 of the power supply +B is applied through a resistor 9 for polarity detection, and a voltage lower than the voltage _V1 by the voltage drop caused by the resistor 9 is applied. It is a filter circuit such as a low-pass filter, and is shown by an equivalent resistance VR ₂ and an equivalent capacitor C ₂ . 8 is a tuner which operates when the output voltage of the stabilized power supply circuit 5 is applied and outputs the audio signal output to signal output circuits such as the main amplifier circuit 6 and the filter circuit 7, and has an equivalent resistance.
It is shown as VR ₃ and decoupling capacitor C ₃ . Further, M is a tape drive motor of the tape recorder, De is a tape deck, and Pe is a preamplifier circuit of the tape recorder, and these are operated by the voltage V ₁ of the power supply +B by switching the switch 4.

On the other hand, numeral 10 is a transistor whose base is connected to one end of the resistor 9 at point F and whose emitter is connected to the other end of the resistor 9 at point E, for detecting the reversal of the polarity of the current flowing through the resistor 9. That is, the resistor 9 and the transistor 10 constitute a muting control signal generation circuit, and when a current flows from the other end of the resistor 9 at point E to the one end of the resistor 9 at point F, it turns on and outputs a muting control signal from the collector.

The circuits other than the muting control signal generating circuit 1 have been conventionally used as a power supply switching circuit, and their operation is well known. The operation of this power supply switching circuit will be briefly explained.

First, by turning on switch 2 and turning on switch 3, a voltage _V1 is applied to terminal AA, and when the antenna is lowered, it rises, causing the antenna to protrude. On the other hand, voltage V ₁ is applied to main amplifier circuit 6 and filter circuit 7 via switches 2 and 3, and main amplifier circuit 6 and filter circuit 7 operate. At the same time, when switch 4 is set to the position shown in the figure, voltage V ₁ is stabilized by stabilized power supply circuit 5 and applied to tuner 8 as voltage V ₂ , tuner 8 operates, and main amplifier The output of the tuner 8 is amplified by the circuit 6, and broadcast reception is performed.

In this state, for example, when a cassette tape is loaded into the tape deck, the switch 4 is switched, voltage _V1 is supplied to the tape deck, and the contents of the tape are reproduced.

In particular, the present invention is intended to mute the pop sound of tuner 8 which occurs when switches 2 and 3 are turned off.

Therefore, in this embodiment, the above-described muting control signal generating circuit 1 is configured as follows. That is, the discharge time constant T ₁ of the main amplifier circuit 6
(=C ₁ ×VR ₁ ) and discharge time constant T ₂ of filter circuit 7
(=C ₂ × VR ₂ ), select T ₂ > T ₁ , and switch 2 or 3 between the discharge time constants T ₁ and T ₂ .
The point at which the power supply voltage of the filter circuit 7 becomes higher than the power supply voltage of the main amplifier circuit 6 when turning from on to off is the point at which the power supply voltage of the main amplifier circuit 6, that is, the input voltage of the stabilized power supply circuit 5, becomes higher than the power supply voltage of the stabilized power supply circuit 5. 5
The voltage is set to be before the lowest voltage _V4 that can output the stable output voltage _V2 . The resistance value of the resistor 9 is such that the power supply voltage of the filter circuit 7 is set to the stabilized power supply circuit 5 while the switches 2 and 3 are on.
The value is set to be higher than the minimum input voltage _V4 .

Next, the operation of this embodiment will be explained.

First, switches 2 and 3 are on, and switch 4 is in the position shown in FIG. Therefore, the power supply voltage V ₁ is applied to the main amplifier circuit 6.
A voltage V ₃ is applied to the filter circuit 7.
This voltage V ₃ has a relationship with voltages V ₁ and V ₄ such that V ₁ >
The relationship is V ₃ > V ₄ . Therefore, a current flows through the resistor 9 from the point F to the point E, and the voltage drop is in the opposite direction to the transistor 10, and the transistor 10 as a switching element is in an off state, and the transistor 10 receives the muting control signal. The broadcast is being received and played normally without any sound being emitted.

This period is shown in FIG. 2 as a period from time 0 to t _1- .

When the switch 2 or 3 is turned off at time t ₁ , the voltage at point F, that is, the voltage at the input terminal C of the stabilized power supply circuit 5 , decreases by the discharge time constant T ₁ of the main amplifier circuit 6 . At the same time, the voltage at point E also decreases due to the discharge time constant _T2 of the filter circuit 7.

However, between the discharge time constants T ₁ and T ₂ , T ₁ < T ₂
Since it is set in the relationship, F at time t ₂
The voltage VF at point and the voltage VE at point E become equal, and after time _t2 , the relationship between voltage VF and VE reverses,
VE＞VF.

Therefore, a current flows through the resistor 9 from point E to point F. The voltage drop that occurs across the resistor 9 due to this current is in the forward direction with respect to the base-emitter junction of the transistor 10, the transistor 10 is turned on, a muting control signal is generated from the collector of the transistor 10, and a muting circuit (not shown) generates a muting control signal. It takes.

At the time when this muting control signal is generated, the voltage VC at point C is higher than the voltage _V4 at which the stabilized power supply circuit 5 can output the stabilized voltage _V2 as described above, and the tuner 8 operates normally. are doing.

Next, when time _t3 is reached, the voltage VC becomes lower than the voltage _V4 , and the output voltage of the stabilized power supply circuit 5 cannot maintain the stabilized voltage _V2 . When the voltage VC decreases below the voltage _V4 at which the stabilized power supply voltage V cannot be maintained, the output of the tuner ₈ will be shaken and a pop sound will be generated _. A control signal is generated, and muting has already been applied at time _t3 , and the pop sound is completely suppressed, so no pop sound is generated.

In other words, the conventional pop sound generation process is that when the voltage VC at point C drops below the voltage _V4 , the tuner 8
The stabilizing voltage _V2 applied to point D decreased, and at this time the output of tuner 8 was changed, causing a popping sound. Muting is applied in between, completely suppressing popping sounds.

Next, other embodiments of the present invention will be described.

FIG. 3 is a block diagram of another embodiment of the present invention, which is an example in which the present invention is applied to an in-vehicle stereo system.

In FIG. 3, the same components as those of the embodiment of the present invention shown in FIG. 2 are given the same reference numerals.

In this embodiment, the input voltage of the stabilized power supply 5 that supplies the power supply voltage to the tuner 8 is taken from the terminal AA, and the base of the transistor 10 constituting the muting control signal generation circuit 1 is connected to the terminal AA instead of the point F at one end of the resistor 9. and the collector of the transistor 10 is connected to the muting control start side (Mt _{1 input terminal) of the second muting control circuit 12 which controls the on/off of the muting control signal by the signal from the tape deck De through the Zener diode 11} . do.

In addition, the discharge time constant of the resistor 9 and the main amplifier circuit 6
T ₁ and the discharge time constant T ₂ of the filter circuit 7 are set in the same manner as in the embodiment of the present invention.

Further, the second muting control circuit 12 is made up of transistors 13, 14 and 15.

The circuit of this embodiment excluding the muting control circuit 1 and the second muting control circuit 12 constitutes a power supply switching circuit used in a car stereo system, and the difference from FIG. The switch 3 can be turned on and off independently.

With switch 4 now in the position shown in Figure 3,
When switches 2 and 3 are turned on, the tuner 8, main amplifier circuit 6, and filter circuit 7 are powered on.
B voltage is applied and broadcast reception can be performed. Further, by turning off the switch 3, the tuner 8 can be independently turned off. Furthermore, if the cassette tape is loaded into the tape deck in this state, the switch 4 will switch and the tape deck will be loaded.
Power is applied to De, the main amplifier circuit 6, and the filter circuit 7, bypassing the switch 3, so that it can function as a tape recorder.

The operation of this embodiment configured as described above will now be explained.

Now, when switches 2 and 3 are on and tuner 8, main amplifier circuit 6 and filter circuit 7 are operating, if switch 2 is turned off, switch 3 will turn on the input terminal of stabilized power supply circuit 5. Since the connection points H and F are at the same potential, the operation of the embodiment shown in FIG. 3 is exactly the same as that of the embodiment shown in FIG. In this case, there is no difference whether the base of the transistor 10 is connected to the H point or the F point.

Next, suppose that the base of the transistor 10 is connected to point F, and if only the switch 3 is turned off, the power supply of the main amplifier circuit 6 and the power supply line of the stabilizing power supply circuit 5, that is, the tuner 8, will be disconnected. Since the potential at point H is disconnected from capacitor _C1 , it drops rapidly at the same time as switch 3 is turned off, and the muting control signal is delayed, causing tuner 8 to swing first and before the pop sound occurs. In some cases, the muting control signal is not generated and the popping sound cannot be completely suppressed.

However, in this embodiment, the transistor 10
The base of the filter circuit 7 is connected to the H point where the voltage decreases with a time constant smaller than that of the filter circuit 7 (terminal AA is not shown).
The load does not include a large capacitor and is mostly grounded through a resistor. ), the potential at point H drops sharply from the potential at point E when switch 3 is turned off, and almost at the same time as switch 2 is turned off, transistor 10 is turned on and a muting control signal is generated from the collector of transistor 10. On the other hand, after switch 2 is turned off, the voltage at point H is
When the voltage drops below _V4 , the output of the tuner 8 swings and generates a pop sound, but since the transistor 10 turns on earlier, the pop sound is completely suppressed.

Further, according to the circuit shown in this embodiment, when the switch 3 is in the OFF state and a cassette tape is inserted and the device is operated as a tape recorder, the potential at the H point becomes zero through the load of the terminal AA, and the potential of the transistor 10 becomes zero. continues to be in the on state, and the muting control signal from the muting control circuit 1 continues to be output. However, the muting signal of the muting control circuit 1 is applied to the base of the transistor 14 and acts to turn on the transistors 14 and 15, but in this case, the voltage from the switch 4 is
Since V ₁ is applied to the base of transistor 13, transistor 13 is turned off, and the collector of transistor 15 does not output the second muting control signal.

On the other hand, when the switch 3 is turned off and the device is not operated as a tape recorder, that is, when no cassette tape is loaded, the base potential of the transistor 13 is zero, and the collector of the transistor 13 is connected to a capacitor _C1 or C. ₂ is applied, and the transistor 13 is turned on. Further, the mutating control signal from the mutating control signal generation circuit 1 turns on transistors 14 and 15, and the second mutating control circuit 12 generates a muting control signal.

Here, the action of the Zener diode 11 will be explained. The initial value of the muting control signal generated by the transistor 10 is a voltage slightly lower than the voltage _V1 of the power supply +B. Further, the voltage relationship for operating the second muting control signal circuit 12 requires that the voltage at the emitter of the transistor 13 be equal to or higher than the voltage at the base of the transistor 14. That is, when not operating as a tape recorder, the transistor 13
In order to turn on the transistor 15 even when the transistor 15 is on, the collector voltage of the transistor 14, that is, if the transistor 14 is on, the emitter voltage of the transistor 14 is approximately equal to the emitter voltage of the transistor 15, that is, approximately the emitter voltage of the transistor 13. It needs to be lower than the voltage by VBE. Further, when the base voltage of the transistor 14 is higher than the emitter voltage of the transistor 14 by VBE, the transistor 14 is turned on.
Therefore, the emitter voltage of transistor 13 needs to be equal to or higher than the base voltage of transistor 14.

On the other hand, if switch 2 or 3 is turned off,
As explained with reference to FIG. 2, the potential at point E and the potential at the emitter of transistor 13, that is, point F, are reversed, so without Zener diode 12,
At the time when the potential at point E and the potential at point F are reversed, no muting control signal is generated from the collector of transistor 15 for the above-mentioned reason. Therefore, the Zener diode 12 lowers the level of the muting control signal from the muting control signal generating circuit 1 to the minimum necessary level.
Therefore, the transistors 13 to 15 can be maintained in the on state for a sufficiently long period, and a sufficiently long muting control signal can be obtained from the second muting control circuit 12.

As explained above, according to the present invention, it is possible to completely suppress the pop sound from the tuner when the power is turned off, and the muting control signal generation circuit for suppressing the pop sound can be configured extremely easily. can.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention;
The figure is a diagram for explaining the operation of an embodiment of the present invention.
FIG. 3 is a block diagram of another embodiment of the present invention. 1... Muting control signal generation circuit, 2,
3 and 4...Switch, 5...Stabilized power supply circuit, 6...Main amplifier circuit, 7...Filter circuit, 8
...Chiyuna.

Claims (1)

[Scope of utility model registration request] It has a power supply, a switch, and a first terminal connected to the power supply via the switch, and tunes a stable voltage when the voltage supplied from the first terminal is equal to or higher than a first predetermined value. a stabilized power supply circuit that supplies power to the power supply; and a stabilized power supply circuit that is connected to the power supply via the switch;
An audio device comprising an output circuit for amplifying and outputting an audio signal from the tuner, wherein the output circuit is provided with a second terminal, and when the switch is turned on, the voltage value supplied to the first terminal is smaller than the voltage value supplied to the first terminal, and means for supplying a voltage greater than the first predetermined value to the second terminal, and when the switch is turned off, the voltage at the second terminal reaches the first predetermined value later than the voltage at the first terminal; a descending time constant means;
A switching element is provided between the first and second terminals, and before the voltage supplied to the first terminal drops to a first predetermined value at the time of the switch-off,
A muting control signal generation circuit characterized in that the switching element outputs a muting control signal.