JP2009159043A - Mute circuit, audio signal amplification circuit using the same and control method of mute transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mute circuit expanding an amplitude range of an audio signal. <P>SOLUTION: In the mute circuit for audio signals, a mute transistor M10 is provided between a signal line 112, on which an audio signal S2 to be muted is propagated, and a ground terminal 108. A mute control circuit 12 changes a gate voltage Vg of a mute transistor M10 in a non-mute state in accordance with a voltage level V2 of the audio signal S2. The mute control circuit 12 supplies a ground voltage to a gate of the mute transistor M10 when the voltage level V2 of the audio signal S2 is higher than a predetermined threshold voltage Vt. When the voltage level V2 of the audio signal S2 is lower than the threshold voltage Vt, a negative voltage is supplied to the gate of the mute transistor M10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an audio signal mute technique.

  Various audio devices generate noise called pop sound or pop-up noise when the power is turned on / off, for example, when the device is activated. This pop sound is generated when the level of the electric signal input to the speaker changes suddenly with the power on. In order to suppress such pop noise, a mute circuit as described in Patent Document 2 is used. Or a mute circuit is utilized also in order to implement | achieve the silence state according to a user's instruction | indication.

  As described in FIG. 5 of Patent Document 2, in the conventional mute circuit, a mute transistor is provided between a signal line through which an audio signal propagates and a fixed voltage terminal such as a ground terminal. The mute transistor is composed of a MOSFET, the source is grounded, the drain is connected to the signal line, and a control signal for controlling mute is input to the gate. The back gate of the mute transistor is connected to the source and grounded as shown in FIG. According to this configuration, in the mute state, when the control signal becomes high level, the mute transistor is turned on, and the potential of the signal line is fixed to the ground potential.

  When the mute state is released and normal operation, ie, reproduction of an audio signal, is performed, the control signal becomes low level and the mute transistor is turned off. When reproducing an audio signal, the potential of the signal line swings to a positive and negative voltage with the ground potential of 0 V as the center. Here, when the mute transistor is constituted by a MOSFET, a body diode having an anode facing the back gate and a cathode facing the drain exists between the back gate and the drain. When the potential of the signal line swings in the negative direction and becomes lower than the forward voltage −Vf of the body diode, the potential of the signal line is clamped by −Vf, and there is a problem that sufficient amplitude cannot be obtained. When the potential of the signal line is clamped, waveform distortion occurs and reproduction at a large volume becomes difficult.

In order to solve this problem, as shown in FIG. 6 of Patent Document 2, the mute transistor is composed of two vertically stacked MOSFETs, and the back gate of each MOSFET is reversed by the body diode of the two MOSFETs. In some cases, wiring is performed in the direction.
JP 2001-223537 A JP 2005-303554 A Japanese Patent Laid-Open No. 7-240632 JP 2001-2444749 A

  Generally, when the mute transistor is turned off, a ground voltage is supplied to the gate of the mute transistor. In this state, when the potential of the signal line swings negatively and the potential difference between the gate of the mute transistor and the signal line exceeds the threshold voltage Vt of the transistor, the mute transistor is turned on and the audio signal amplitude range is limited. There is a problem of being.

  The present invention has been made in view of these problems, and an object thereof is to provide a mute circuit having an expanded amplitude range.

  One embodiment of the present invention relates to an audio signal mute circuit. The mute circuit generates a mute transistor provided between a signal line through which an audio signal to be muted propagates and a predetermined fixed voltage terminal, and a gate voltage of the mute transistor. A mute control circuit for turning off the mute transistor in a non-mute state. The mute control circuit changes the gate voltage of the mute transistor in the non-mute state according to the voltage level of the audio signal.

  According to this aspect, by changing the gate voltage according to the voltage level of the audio signal, it is possible to prevent the mute transistor from being turned on in the non-muted state, and the amplitude range can be expanded.

  The mute control circuit supplies a ground voltage to the gate of the mute transistor when the voltage level of the audio signal is higher than a predetermined threshold voltage, and the gate of the mute transistor when the voltage level of the audio signal is lower than the threshold voltage. A negative voltage may be supplied to.

The mute control circuit may supply a voltage of the same level as the audio signal to the gate of the mute transistor when the voltage level of the audio signal is lower than the threshold voltage.
In this case, since the audio signal mute transistor is supplied, a negative power source is not necessary.

  The mute control circuit supplies a power supply voltage to a driver circuit whose input terminal is instructed to mute and non-mute, an output terminal connected to the gate of the mute transistor, and a power supply terminal below the driver circuit. And a switch circuit. The switch circuit may change the power supply voltage according to the voltage level of the audio signal.

  The switch circuit supplies a ground voltage to the lower power supply terminal of the driver circuit when the voltage level of the audio signal is higher than the threshold voltage, and when the voltage level of the audio signal is lower than the threshold voltage, the switch circuit A voltage at the same level as the audio signal may be supplied to the lower power supply terminal.

  The switch circuit has one end connected to the signal line, the other end connected to the lower power supply terminal of the driver circuit, the potential of the control terminal fixed, one end grounded, and the other end the driver circuit And a second transistor connected to the lower power supply terminal and having an audio signal input to the control terminal.

Another aspect of the present invention also relates to an audio signal mute circuit. This mute circuit generates a mute transistor provided between a signal line through which an audio signal to be muted propagates and a fixed voltage terminal, and a gate voltage of the mute transistor. And a mute control circuit for turning off the mute transistor. The mute control circuit generates the gate voltage of the mute transistor using the audio signal in at least a certain period in which the voltage level of the audio signal is negative during the non-mute state.
According to this aspect, when the voltage level of the audio signal is negative, the gate voltage of the mute transistor can be made to follow the audio signal, so that the mute transistor can be prevented from being turned on in the non-mute state. Furthermore, according to this aspect, a negative power supply is not necessary, and the circuit area can be reduced.

  Another aspect of the present invention also relates to an audio signal mute circuit. This mute circuit generates a mute transistor provided between the signal line through which the audio signal to be muted propagates and the fixed voltage terminal, and the gate voltage of the mute transistor. And a mute control circuit for turning off the mute transistor. The mute control circuit has a driver circuit whose output terminal is connected to the gate of the mute transistor, one end connected to the signal line, the other end connected to the power supply terminal below the driver circuit, and the potential of the control terminal is fixed. And a second transistor having one end grounded, the other end connected to the lower power supply terminal of the driver circuit, and an audio signal input to the control terminal.

  Yet another embodiment of the present invention is an audio signal amplifier circuit. The audio signal amplifier circuit includes an amplifier that amplifies the audio signal, and a mute circuit that mutes the audio signal from which a DC component has been removed by a DC blocking capacitor provided at a stage subsequent to the output of the amplifier.

  Still another embodiment of the present invention relates to a method for controlling a mute transistor provided between a signal line through which an audio signal to be muted propagates and a ground terminal. The method includes a step of supplying a voltage for turning on the mute transistor to the gate of the mute transistor in the mute state, and a mute transistor when the voltage level of the audio signal is higher than a predetermined threshold voltage in the non-mute state. And supplying a negative voltage to the gate of the mute transistor when the voltage level of the audio signal is lower than the threshold voltage in the non-muted state.

  When the voltage level of the audio signal is lower than the threshold voltage in the non-mute state, a voltage having the same level as that of the audio signal may be supplied to the gate of the mute transistor.

  It should be noted that any combination of the above-described constituent elements and a representation obtained by converting the expression of the present invention between methods, apparatuses, and the like are also effective as an aspect of the present invention.

  With the mute circuit according to the present invention, the amplitude range can be expanded.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

  FIG. 1 is a circuit diagram showing a configuration of an audio signal amplifier circuit 100 according to an embodiment of the present invention. The audio signal amplifier circuit 100 is mounted on electronic devices such as a portable music player, a television, a mobile phone terminal with a music playback function, a digital still camera, and a digital video camera. The electronic device outputs an amplified audio signal to a connected speaker or earphone or to an external electronic device.

  The sound source 110 reads a digital audio signal recorded in a predetermined format on an optical disk, a hard disk, a flash memory, or the like, decodes it, and outputs it as a digital value signal. The digital audio signal S1 is input to the input terminal 102 of the audio signal amplifier circuit 100.

  The audio signal amplifier circuit 100 converts the audio signal S1 input to the input terminal 102 into an analog audio signal and amplifies it, and then outputs it from the output terminal 104. The audio signal amplifier circuit 100 includes a digital-analog converter (DAC) 20, an amplifier 22, a mute circuit 10, and a first resistor R1, and is a functional IC integrated on one semiconductor substrate.

  The DAC 20 converts the digital audio signal S1 into an analog audio signal S2. The amplifier 22 amplifies the analog audio signal S2 and outputs it from the output terminal 104 via the first resistor R1. The capacitor C <b> 1 is provided for DC blocking, and one end is connected to the output terminal 104 and the other end is connected to the output terminal 202 of the electronic device via the signal line 112. The second resistor R2 forms a low-pass filter together with the capacitor C1.

  The DAC 20 and the amplifier 22 may be configured by ΔΣ modulation and a class D amplifier. In this case, the audio signal amplifier circuit 100 performs ΔΣ modulation on the audio signal S1 input to the input terminal 102, converts it into a bit stream, amplifies it, and outputs it from the output terminal 104. The bit stream audio signal output from the output terminal 104 is input to the filter. The filter removes high frequency components of the bit stream.

  The audio signal amplifying circuit 100 according to the present embodiment has a mute function in order to suppress a pop sound generated from a speaker at the time of activation or the like. Hereinafter, the mute function will be described.

  The mute function is realized by the mute circuit 10 including the mute transistor M10 and the mute control circuit 12.

  The mute terminal 106 of the audio signal amplifier circuit 100 is connected to the signal line 112 subsequent to the DC decoupling capacitor C1. The potential of the signal line 112 swings positively and negatively around the ground voltage of 0 V when reproducing the audio signal. The mute circuit 10 realizes a mute state by fixing the potential of the signal line 112 according to the control signal Scont.

  The mute transistor M10 is provided between the signal line 112 through which the audio signal to be muted propagates and a predetermined fixed voltage terminal, that is, the ground terminal 108. The mute transistor M10 includes a first mute transistor M11 and a second mute transistor M12 which are N-channel MOSFETs provided in series between the signal line 112 and the ground terminal 108. In the following description, it will be understood by those skilled in the art that the drain and the source of the MOSFET are only distinguished for convenience of explanation and may be read in reverse.

  The drain of the first mute transistor M11 is connected to the signal line 112 via the mute terminal 106. The source and gate of the second transistor M2 are connected in common with the source and gate of the first mute transistor M11, respectively, and the drain thereof is grounded.

  The back gates of the first mute transistor M11 and the second mute transistor M12 are connected so that the body diodes are arranged in opposite directions. That is, the back gates of the first mute transistor M11 and the second mute transistor M12 are connected to the respective sources.

  The first mute transistor M11 and the second mute transistor M12 function together as one MOSFET. That is, the commonly connected gates of the first mute transistor M11 and the second mute transistor M12 correspond to the gate of the mute transistor M10, the drain of the first mute transistor M11 is connected to the drain of the mute transistor M10, and the second mute transistor M12 is connected. The drain corresponds to the source of the mute transistor M10.

  The mute control circuit 12 generates the gate voltage Vg of the mute transistor M10, turns on the mute transistor M10 in the mute state, and turns off the mute transistor M10 in the non-mute state.

  The mute control circuit 12 controls the voltage level V2 of the audio signal S2 (that is, the mute transistor M10) so that the gate-drain voltage Vgd and the gate-source voltage Vgs of the mute transistor M10 do not exceed the MOSFET threshold voltage Vt. The gate voltage Vg of the mute transistor M10 in the non-mute state is changed according to the drain voltage. That is, the lower the voltage level V2 of the audio signal S2, the lower the gate voltage Vg of the mute transistor M10 is set.

  According to this configuration, even when the audio signal S2 swings in the non-mute state, the mute transistor M10 can be kept off, so that the transmission of the audio signal S2 is not hindered by the mute transistor M10 and the amplitude range is expanded. Can do.

Hereinafter, a specific configuration example of the mute control circuit 12 will be described. The mute control circuit 12 supplies the ground voltage (0 V) to the gate of the mute transistor M10 when the voltage level V2 of the audio signal S2 is higher than a predetermined threshold voltage Vth in the non-mute state. When the voltage level V2 of the audio signal S2 is lower than the threshold voltage Vth, a negative voltage is supplied to the gate of the mute transistor M10. The threshold voltage Vth is desirably a ground voltage of 0 V or less.
In this case, in the non-muted state, the mute transistor M10 can be suitably maintained in the off state.

  When the voltage level V2 of the audio signal S2 is lower than the threshold voltage Vth, the mute control circuit 12 supplies a negative voltage having the same level as that of the audio signal S2 to the gate of the mute transistor M10. That is, the mute control circuit 12 generates the gate voltage Vg of the mute transistor M10 using the audio signal S2 during at least a certain period in which the voltage level V2 of the audio signal S2 is negative during the non-mute state. In this case, since a negative power supply is not necessary, an increase in circuit scale can be suppressed.

The mute control circuit 12 includes a driver circuit 14 and a switch circuit 16.
The driver circuit 14 has a control signal Scont instructing a mute state and a non-mute state input to its input terminal, and its output terminal connected to the gate of the mute transistor M10. The driver circuit 14 can be configured by an inverter or a buffer. The driver circuit 14 outputs either the state of outputting the power supply voltage Vdd applied to the upper power supply terminal or the power supply voltage Vss applied to the lower power supply terminal according to the level of the control signal Scont.

  As a result, when the driver circuit 14 outputs the upper power supply voltage Vdd, the mute transistor M10 is turned on. In other words, the power supply voltage Vdd is set to a level at which the mute transistor M10 can be turned on, that is, larger than the threshold voltage between the gate and drain of the second mute transistor M12.

  The power supply voltage Vss at the lower power supply terminal of the driver circuit 14 is supplied by the switch circuit 16. The switch circuit 16 changes the lower power supply voltage Vss according to the voltage level V2 of the audio signal S2.

  When the voltage level V2 of the audio signal S2 is higher than the threshold voltage Vth, the switch circuit 16 supplies the ground voltage (0 V) to the lower power supply terminal of the driver circuit 14, and the voltage level V2 of the audio signal S2 is the threshold. When the voltage is lower than the value voltage Vth, a voltage having the same level as that of the audio signal S2 is supplied to the lower power supply terminal of the driver circuit 14.

  In the non-muted state, the driver circuit 14 outputs the lower power supply voltage Vss. Therefore, according to this configuration, the level of the gate voltage of the mute transistor M10 can be suitably changed in the non-mute state.

In order to realize the above function, the switch circuit 16 is specifically configured as follows.
The switch circuit 16 includes a first transistor M1 and a second transistor M2. The first transistor M1 has one end (drain) connected to the signal line 112 and the other end (source) connected to the lower power supply terminal of the driver circuit 14, so that the potential of the control terminal (gate) is fixed. The second transistor M2 has one end (source) grounded, the other end (drain) connected to the lower power supply terminal of the driver circuit, and the audio signal S2 input to the control terminal (gate).

  The above is the specific configuration of the switch circuit 16. Next, the operation of the switch circuit 16 will be described. FIG. 2 is an operation waveform diagram of the mute circuit 10 of FIG.

  The first transistor M1 and the second transistor M2 are complementarily turned on according to the voltage level V2 of the audio signal S2. When the voltage level V2 of the audio signal S2 exceeds the threshold voltage Vt of the MOSFET, the gate-source voltage Vgs of the second transistor M2 exceeds the threshold voltage Vt, so that the second transistor M2 is completely turned on to supply power. The voltage Vss becomes the ground voltage 0V. In this state, the gate voltage Vg of the mute transistor M10 is equal to the ground voltage 0V.

  When the voltage level V2 of the audio signal S2 becomes lower than -Vt, the gate-drain voltage Vgs of the first transistor M1 exceeds the threshold voltage Vt, so that the first transistor M1 is completely turned on and the power supply voltage Vss is the audio signal. It becomes the same level as S2. In this state, the gate voltage Vg of the mute transistor M10 is the same level as that of the audio signal S2.

  When the audio signal S2 has a voltage level V2 near the ground voltage (-Vt <V2 <Vt), the first transistor M1 and the second transistor M2 are not completely turned on, but are close to the on state. Since only a very small current flows through the channel and the body diode of the first transistor M1 and the second transistor M2, their voltage drop is very small. Therefore, the power supply voltage Vss becomes the ground voltage 0V in the range of V2> 0V, and the power supply voltage Vss follows the voltage level V2 of the audio signal S2 in the range of V2 <0V.

  As described above, according to the switch circuit 16 of FIG. 1, the gate voltage Vg of the mute transistor M10 in the non-muted state is set to the ground voltage 0V when V2> 0V, and to the voltage level V2 corresponding to the audio signal S2 when V2 <0V. Can be set.

  In this case, when the audio signal S2 swings in the negative direction, the gate voltage Vg of the mute transistor M10 follows the audio signal S2, and the gate-drain voltage Vgd of the mute transistor M10 does not exceed the threshold voltage Vt of the MOSFET. Therefore, the audio signal S2 can be prevented from being clamped, and the amplitude range of the audio signal S2 can be expanded.

  This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the embodiment, the case where the mute transistor M10 is configured using two N-channel MOSFETs has been described, but a combination of an N-channel and a P-channel may be used, or a single MOSFET may be configured.

  Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments are merely illustrative of the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangements can be made without departing from the spirit of the present invention.

It is a circuit diagram which shows the structure of the audio signal amplifier circuit which concerns on embodiment of this invention. FIG. 2 is an operation waveform diagram of the mute circuit of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Mute circuit, M10 ... Mute transistor, M11 ... 1st mute transistor, M12 ... 2nd mute transistor, 12 ... Mute control circuit, 14 ... Driver circuit, 16 ... Switch circuit, M1 ... 1st transistor, M2 ... 2nd Transistor 20 ... DAC 22 ... Amplifier 100 ... Audio signal amplifier circuit 102 ... Input terminal 104 ... Output terminal 106 ... Mute terminal 110 ... Sound source R1 ... First resistor R2 ... Second resistor C1 ... Capacitor, 112, signal line, Scont, control signal, S2, audio signal.

Claims (11)

An audio signal mute circuit,
A mute transistor provided between a signal line through which an audio signal to be muted propagates and a predetermined fixed voltage terminal;
A mute control circuit for generating a gate voltage of the mute transistor, turning on the mute transistor in a mute state, and turning off the mute transistor in a non-mute state;
With
The mute control circuit changes a gate voltage of the mute transistor in a non-mute state according to a voltage level of the audio signal. The mute control circuit
When the voltage level of the audio signal is higher than a predetermined threshold voltage, a ground voltage is supplied to the gate of the mute transistor,
2. The mute circuit according to claim 1, wherein when the voltage level of the audio signal is lower than the threshold voltage, a negative voltage is supplied to the gate of the mute transistor. The mute control circuit
3. The mute circuit according to claim 2, wherein when the voltage level of the audio signal is lower than the threshold voltage, a voltage of the same level as that of the audio signal is supplied to the gate of the mute transistor. The mute control circuit
A driver circuit in which a signal indicating a mute state is input to an input terminal, and an output terminal is connected to the gate of the mute transistor;
A switch circuit for supplying a power supply voltage to a lower power supply terminal of the driver circuit;
Including
The mute circuit according to claim 1, wherein the switch circuit changes the power supply voltage in accordance with a voltage level of the audio signal. The switch circuit is
When the voltage level of the audio signal is higher than the threshold voltage, a ground voltage is supplied to the lower power supply terminal of the driver circuit,
5. The mute circuit according to claim 4, wherein when the voltage level of the audio signal is lower than the threshold voltage, a voltage of the same level as that of the audio signal is supplied to a lower power supply terminal of the driver circuit. . The switch circuit is
A first transistor having one end connected to the signal line, the other end connected to a lower power supply terminal of the driver circuit, and a fixed potential of the control terminal;
A second transistor having one end grounded, the other end connected to a lower power supply terminal of the driver circuit, and the audio signal input to a control terminal;
The mute circuit according to claim 5, comprising: An audio signal mute circuit,
A mute transistor provided between a signal line through which an audio signal to be muted propagates and a fixed voltage terminal;
A mute control circuit for generating a gate voltage of the mute transistor, turning on the mute transistor in a mute state, and turning off the mute transistor in a non-mute state;
With
The mute control circuit generates the gate voltage of the mute transistor using the audio signal in at least a certain period during which the voltage level of the audio signal is negative during the non-mute state. Mute circuit to be used. An audio signal mute circuit,
A mute transistor provided between a signal line through which an audio signal to be muted propagates and a fixed voltage terminal;
A mute control circuit for generating a gate voltage of the mute transistor, turning on the mute transistor in a mute state, and turning off the mute transistor in a non-mute state;
With
The mute control circuit
A driver circuit in which a signal indicating a mute state is input to an input terminal, and an output terminal is connected to the gate of the mute transistor;
A first transistor having one end connected to the signal line, the other end connected to a lower power supply terminal of the driver circuit, and a fixed potential of the control terminal;
A second transistor having one end grounded, the other end connected to a lower power supply terminal of the driver circuit, and the audio signal input to a control terminal;
A mute circuit comprising: An amplifier that amplifies the audio signal;
The mute circuit according to any one of claims 1 to 8, wherein an audio signal from which a DC component has been removed is muted by a DC blocking capacitor provided at a subsequent stage of the output of the amplifier;
An audio signal amplifying circuit comprising: A method for controlling a mute transistor provided between a signal line through which an audio signal to be muted propagates and a ground terminal,
Supplying a voltage for turning on the mute transistor to the gate of the mute transistor in a mute state;
Supplying a ground voltage to the gate of the mute transistor when the voltage level of the audio signal is higher than a predetermined threshold voltage in a non-mute state;
Supplying a negative voltage to the gate of the mute transistor when the voltage level of the audio signal is lower than the threshold voltage in a non-mute state;
A method comprising the steps of:   The voltage of the same level as that of the audio signal is supplied to the gate of the mute transistor when the voltage level of the audio signal is lower than the threshold voltage in a non-mute state. Method.

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