GB2307606A

GB2307606A - Muting in a microprocessor-controlled audio apparatus

Info

Publication number: GB2307606A
Application number: GB9523940A
Authority: GB
Inventors: Kok Seng Yeo; Tiew Chyuan Tan
Original assignee: Thomson Multimedia SA
Current assignee: Technicolor SA
Priority date: 1995-11-23
Filing date: 1995-11-23
Publication date: 1997-05-28
Also published as: GB9523940D0

Abstract

A mute control in a microprocessor controlled consumer device like a TV set is used to block the audio channels in certain operation modes. To achieve a muting even in undefined conditions of a microprocessor, a switch is provided in the audio channel, so that the audio signal is generally muted and amplified only when an applicable control signal is supplied by the microprocessor.

Description

Audio Mute Control The invention relates to an audio mute control, wherein the audio channel of devices, for example consumer devices, such as TV sets, can be blocked. Particularily the invention relates to a microprocessor-controlled consumer device wherein the microprocessor generates a mute signal.

It is generally known, e.g. from DE 42 33 475 Al to block the audio channels of a TV set in certain operation modes. Such a blocking is called muting, which is normally performed with the aid of a control signal which is delivered to an audio amplifier stage. In such known microprocessorcontrolled system this means that the muting function can only be performed, when such a control signal is present. In undefined operation modes of the microprocessor, for example during power-up and powerdown, the microprocessor may not generate an applicable mute control signal. In such cases the audio amplifiyer is not muted but powered so that any transient sound will be amplified and routed to the loudspeakers, because when the set is powered up, some time is needed for the microprocessor to initialize and gain control of the mute line. The other example is the power-down case.When the set is switched off, the microprocessor detects a power interrupt. After servicing the power interrupt routine, the microprocessor will be in the "halt" mode, which means that the mute output of the microprocessor has a high impedance, i.e. no mute signal of the microprocessor is generated. Therefore the audio amplifier will amplify any transient until the power present in the set collapses.

It is therefore an object of the present invention to securely mute audio signals of a microprocessor controlled audio channel of a consumer device even when the microprocessor is in an undefined state.

This object is solved by the subject matter of claim 1. Preferred embodiments are subject of the independent claims.

The invention comprises a mute circuit for muting a controlled audio channel, characterized in that the audio channel is generally blocked and that the audio channel processes audio signals only in defined operation modes or operation states, respectively.

Such a defined operation mode can be e.g. the normal operation mode of a device, where the mute circuit is used. That means that during switching-on and during switching-off said device, the audio channel is blocked. Also during all other operation modes, which may result e.g. by a failure of said device, the audio channel is blocked. Only during defined, e.g. normal, operation modes a control signal is generated, which makes the audio channel processing said audio signals.

The invention therefore shows the following two advantages: It allows an according control stage, which can be realised e.g. by a microprocessor, to have full control of the mute function of the audio amplifier, and the mute function is always in an "on" state unless it is unmuted by the control stage. Therefore the sound signal is generally muted and amplified only, when the microprocessor delivers an applicable control signal.

Means for switch of the mute circuit is closed when the microprocessor is in a defined state. Such a switch is preferably realized by a transistor. Further the power interrupt routine of the microprocessor comprises a mute instruction. The mute signal generated by the microprocessor is delivered to the transistor. Preferably the mute signal is applied to the base of the transistor. The voltages supplied to the base of the transistor are provided by a a voltage divider connected to the base of the transistor.

Further the transistor controls the mute control input of the audio amplifier, wherein the audio amplifier (i.e the audio channel) preferably comprises an integrated audio circuit.

A preferred embodiment of the invention will now be described with reference to the accompanying drawing, wherein Fig. 1 shows the basic principle of a first embodiment; Fig. 2 shows a schematics of the mute control circuit of an audio channel in a microprocessor controlled consumer device.

Fig. 1 shows a muting circuit having an audio source AS, which is connected to an amplifier AM through a switch S. This switch S is controlled by control means 1 and the output of the amplifier AM is led to a loudspeaker 3.

The switch S is provided for blocking the audio channel from the source AS to the amplifier AM, when an audio signal is to be muted. The switch S is controlled by the control means 1 such that it is closed only in defined operation modes. Such an operation mode may be e.g. the normal operation of a device, in which the muting circuit is used. In other modes than the defined modes, an according control signal from the control means 1 is missing and the switch S is open for blocking the audio signals.

Fig. 2 shows a second embodiment of a mute control circuit, which is for example provided in a TV set. The circuit mainly consists of the control means, which can be realised by a microprocessor, a voltage divider R1, R2, a transistor T, an audio IC 2 and a loudspeaker 3. In a preferred embodiment, the audio IC 2 is of type TDA 7253.

The microprocessor 1 has a mute pin 4, which is connected to the voltage divider R1, R2. The voltage divider R1, R2 is provided at the base terminal of transistor T. When the microprocessor 1 is in an undefined mode, the impedance at its mute pin 4 is high. In this case a positive voltage is provided by the voltage divider R1, R2 at the base of transistor T. Thereby transistor T is switched on and the mute signal is delivered to a mute pin (pin 3 of TDA 7253) of the audio IC 2. When a sound signal is to be amplified by the audio IC 2, which is input at the input 6 of the audio signal of the audio IC 2, the microprocessor is in low inpedance at its mute pin 4. Thereby the voltage at the base of the transistor T is low and the transistor T is switched off. In this case the audio IC 2 amplifies the audio signal provided at its input terminal 6.

With the mute control circuit added, said amplifier, i.e. the audio IC 2, is alway at the mute mode. It can only amplify when the microprocessor 1 unmutes the audio IC 2. Thus no transients are amplified during power up and power-down of the TV set.

Claims

1. Mute circuit for muting an audio channel, characterized in that means (1, T, 2) are provided to control said audio channel such that it processes audio signals only during given operation modes and that said audio channel is blocked in all other modes.

2. Mute circuit according to claim 1, wherein said means include a switch (S; T), which is closed in said given operation modes.

3. Mute circuit according to claim 1 or 2, wherein the switch (S) includes a transistor (T).

4. Mute circuit according to one of the preceding claims, characterized in that a microprocessor (1) is provided for controlling said audio channel and that a power interrupt routine of the microprocessor (1) comprises a mute instruction.

5. Mute circuit according to claim 4, wherein the mute signal generated by the microprocessor (1) controls the means (S; T).

6. Mute circuit according to claim 5, wherein the mute signal is applied to the base of the transistor (T).

7. Mute circuit according to claim 6, wherein the circuit comprises a voltage divider (R1, R2) connected to the base of the transistor (T).

8. Mute circuit according to claim 7, wherein the transistor (T) controls the mute control input (5) of an audio amplifier (2) of the audio channel.

9. Mute circuit according to claim 8, wherein the audio amplifier (2) comprises an integrated audio circuit.