JPS6036914Y2 - Television receiver audio muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an audio muting circuit that temporarily stops audio when switching channels or turning on the power of a television receiver.

As shown in FIG. 1a, a conventional sterilization muting circuit passes a negative polarity square wave signal A generated in connection with a channel switching operation or power-on operation of a television receiver through a current limiting resistor 1. The voltage is applied to the switching transistor 2 through the switching transistor and the resistors 3 and 4.
A circuit consisting of a charging/discharging capacitor 5 inverts the polarity of the signal A and slows its rise to convert it into a positive pulse voltage. It is applied to pin 4 of the frequency and audio amplification IC 7.

At this time, the DC voltage introduced into the 6th pin of the IC 7 is divided by the resistors 8 and 9.10, and a voltage corresponding to the voltage division ratio is applied to the 4th pin via the resistor 11. As a result, the volume is adjusted by controlling the gain of the audio amplifier circuit inside this IC, and in this case, when the DC voltage applied to pin 4, that is, the control voltage, is high, the gain becomes small. Therefore, if the peak value of the pulse voltage port is selected to an appropriate value, the audio output can be stopped.

By the way, in such a conventional example, the reason why the charging/discharging capacitor 5 is provided to make the rise of the pulse voltage applied to the IC 7 gradual is that the polarity of the square wave signal A is simply inverted and the pulse voltage applied to the IC 7 is inverted. If the voltage is applied, that IC
This is because the operating state of the internal audio amplification circuit changes rapidly, and noise due to transient phenomena is generated in the speaker.

Therefore, in order to completely eliminate the noise caused by transient phenomena that occur immediately after channel switching operations and power-on, it is sufficient to make the pulse voltage rise sufficiently slowly immediately after the arrival of the square wave signal A. However, if the charging time constant determined by resistor 3 and capacitor 5 is increased in order to make the rise characteristics of this pulse voltage port sufficiently gradual, this pulse voltage port will settle to a constant value as shown by the broken line in Figure 1. Since it takes a relatively long time to complete the process, the muting operation cannot be performed reliably during the channel switching period.

Conversely, if you want to ensure muting operation during the channel switching period, the charging time constant cannot be made too large, so the rise characteristic of the pulse voltage port should be made too slow as shown by the solid line in Figure 1. Therefore,
The generation of noise due to the aforementioned transient phenomenon could not be sufficiently prevented.

Note that the resistor 4 is for discharging the capacitor 5.

Therefore, the present invention proposes an audio muting circuit that solves these drawbacks.

That is, the audio muting circuit of the present invention, as shown in FIG. It is characterized by being connected to the ground point, as shown in Figure 1a.
Figures with the same number are constructed in the same way.

In the circuit of the present invention, when the rectangular wave signal A does not arrive and the base of the switching transistor 2 is at a positive potential, the charging/discharging capacitor 12 is
is charged, and the switching transistor 2 is turned off.

When a square wave signal A of negative polarity arrives in this state, the charge in the capacitor 12 is discharged through the resistor 1 and the signal source of the square wave signal A, so that the base potential of the switching transistor 2 gradually decreases. As a result, the charging current to the charging/discharging capacitor 5 flows through the resistor 3 and the switching transistor 2.

At this time, the magnitude of the charging current is determined by the rise characteristics of the switching transistor 2 when it is in the active state, the discharging time constant of the capacitor 12 and the resistor 1, and the charging time constant of the capacitor 5 and the resistor 3. , when transistor 2 is completely saturated (on), it is determined only by the charging time constant of capacitor 5 and resistor 3, so if each of the above time constants is selected appropriately, it will increase gradually in the initial stage and then increase in the middle stage. Since a charging current that increases relatively rapidly from to to late stage can be passed through capacitor 5, the voltage change that appears at the connection point of capacitor 5 and resistor 4 is as shown in Figure 2, and is applied to C7. This makes it possible to improve the rise characteristics of the output pulse voltage.

As described above, the audio muting circuit of the present invention converts the rectangular wave signal generated when switching channels or turning on the power into a pulse voltage that rises slowly at the beginning of the rise and rises relatively quickly from the middle to the late stages. Since the muting operation is performed using this pulse voltage,
It has the advantage of being able to completely prevent noise from occurring due to transient phenomena immediately after channel switching or power-on, and also being able to perform muting operations reliably during the channel switching period.In addition, it has a simple configuration and is therefore inexpensive. It is possible to achieve this and is practical.

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing a conventional audio muting circuit and its control voltage rise characteristics, respectively; Figures 2a and b
2A and 2B are diagrams respectively showing the muting circuit of the present invention and the rise characteristics of its control voltage. 2...Switching transistor, 12...
...First charge/discharge capacitor, 5...Second
Capacitor for charging and discharging.

Claims (1)

[Scope of utility model registration request] A rectangular wave signal generated at power-on or channel switching is applied to the input electrode of the switching transistor, and a first charging/discharging circuit is connected between the input electrode of the switching transistor and the ground point, and the first charging/discharging circuit is connected between the output electrode and the ground point. A second charging/discharging circuit is connected between the output electrodes, and a pulse voltage that slowly rises immediately after the arrival of the rectangular wave signal and then rises relatively quickly is extracted from the output electrode, and this pulse voltage is used to amplify the sound. An audio muting circuit for television receivers that stops circuit operation.