Patent Description:
<CIT> discloses a telephone headset click-free muting circuit. In a click-free muting circuit for a headset condenser microphone <NUM> connected to a telephone <NUM>, actuation of mute switch <NUM> feeds base current to bipolar transistors Q1 and Q2, which gradually turn on and short-circuit the microphone <NUM>. The gradual switching of the transistors, caused by capacitors C1 and C2, eliminates muting clicks. When Q1 and Q2 are on, series transistor Q3 no longer receives base current and turns off to provide hard muting. Resistor R23 ensures that the output of the headset detection circuit <NUM> has approximately the same duration as the actuation of switch <NUM> (figure <NUM>), which may be located at the headset or at a headset interface box between the headset <NUM> and telephone set <NUM>. Q1 and the diodes D1 may be eliminated.

<CIT> discloses a speech interrupt circuit in telephone set. A transistor(TR) Q turning on/off a bias voltage applied to a transmitter T, and a base voltage of the TR Q is switched by a mute changeover switch S. The base voltage of the TR Q is slowly changed by a time constant comprising a C1 and a R1 to turn on/off the TR Q. Thus, the bias voltage applied to the transmitter T is slowly changed and a click noise due to changeover of the mute changeover switch S is not generated.

Conventionally, a microphone provided with a switch for muting is known (refer to <CIT>, for example).

When a switch for muting is switched while sound is input to a microphone, there is a problem that noise is generated.

This invention focuses on this point, and an object of the invention is to reduce the noise generated when the microphone is switched to a mute state.

A headset according to the present invention is defined by claim <NUM>.

The voltage generator may include a delay circuit that makes a time required for a transition of a level of the control voltage longer than a time required for switching of the operation switch.

The voltage generator may generate the control voltage on the basis of power supplied from the external device via the first transmission line, for example.

One end of the operation switch may be connected to a ground, and the other end of the operation switch may be connected to the voltage generator, the voltage generator may generate the control voltage at a high level when the operation switch is not conducting, and may generate the control voltage at a low level when the operation switch is conducting, and the electronic switch may be in a conductive state when the control voltage is at a high level, and may be in a non-conductive state when the control voltage is at a low level.

The electronic switch is a field effect transistor, and the voltage generator includes : a capacitor provided between a gate terminal of the electronic switch and a ground, a first resistor provided between the gate terminal and a drain terminal of the electronic switch, and a second resistor provided between the gate terminal and the operation switch, with one end of the second resistor which is opposite to the gate terminal side entering into an open state in the non-mute state and the one end of the second resistor being connected to a ground in the mute state.

A resistance value of the second resistor may be smaller than a resistance value of the first resistor.

The headset may further comprise: a capacitor provided in series with the operation switch, between the first transmission line and a ground, wherein the operation switch may be provided between the first transmission line and one end of the capacitor, and the other end of the capacitor may be connected to the ground.

The headset may further comprise: a speaker that outputs a sound based on a second electrical signal output by the external device; and a second transmission line that transmits the second electrical signal from the external device to the speaker, the second transmission line being accommodated in a cable in which the first transmission line is accommodated.

According to the present invention, it is possible to reduce noise which is generated when a microphone is switched to a mute state.

<FIG> shows a configuration of a headset <NUM> according to the embodiment The headset <NUM> is equipment that is used by being connected to an external device <NUM>, and is capable of (i) inputting a first electrical signal based on a sound collected in the headset <NUM> to the external device <NUM>, and (ii) emitting a sound, based on a second electrical signal output from the external device <NUM>, from a speaker.

The external device <NUM> is, for example, a gaming device, an audio device, a communication device, a smartphone, or a computer. The external device <NUM> can emit the sound based on the first electrical signal input from the headset <NUM>, and output the second electrical signal via the headset <NUM> by converting sound data read from a medium, in which the sound data is stored, into the second electrical signal. The external device <NUM> may transmit the first electrical signal received from the headset <NUM> to another device via a network, or may output the second electrical signal received from another device to the headset <NUM>.

The headset <NUM> includes a headset body <NUM>, a mute operation part <NUM>, a cable <NUM>, and a connection terminal <NUM>. The headset body <NUM> is a device which is mounted on a human head, collects ambient sounds, and emits the sound based on the second electrical signal received from the external device <NUM>.

The headset body <NUM> includes a microphone <NUM>, a right speaker <NUM>, a left speaker <NUM>, a headband <NUM>, and an arm <NUM>. The microphone <NUM> converts a sound into the first electrical signal. The microphone <NUM> is, for example, an electret condenser microphone. The right speaker <NUM> and the left speaker <NUM> output the sound based on the second electrical signal received from the external device <NUM>.

The headset body <NUM> is connected to the external device <NUM> via the cable <NUM>. The headset body <NUM> can transmit the first electrical signal to the external device <NUM> and receive the second electrical signal from the external device <NUM> while the connection terminal <NUM> provided at one end of the cable <NUM> is connected to the external device <NUM>.

The mute operation part <NUM> is an operation part for switching between (i) a mute state in which the first electrical signal based on the sound collected in the microphone <NUM> is not input to the external device <NUM> and (ii) a non-mute state in which the first electrical signal is input to the external device <NUM>. A user of the headset <NUM> can switch between the mute state and the non-mute state by operating an operation switch <NUM>, which will be described later, provided in the mute operation part <NUM>.

The connection terminal <NUM> is, for example, a connector plug provided at a tip of the cable <NUM> for connecting the cable <NUM> to the external device <NUM>. The connection terminal <NUM> conforms to plug-in power standards, for example, and is capable of transmitting the first electrical signal from the headset body <NUM> to the external device <NUM>, transmitting the second electrical signal from the external device <NUM> to the headset body <NUM>, and providing power supplied from the external device <NUM> to the mute operation part <NUM>.

<FIG> schematically shows internal structures of the headset <NUM> and the external device <NUM>. As shown in <FIG>, the cable <NUM> accommodates a first transmission line <NUM>, a ground wire <NUM>, a second transmission line <NUM>, a third transmission line <NUM>, and a ground wire <NUM>, and the respective transmission lines are connected to the external device <NUM> via the connection terminal <NUM>.

The first transmission line <NUM> is a transmission line for transmitting the first electrical signal generated by the microphone <NUM> to the external device <NUM>, and is connected to an input circuit of the external device <NUM> via the connection terminal <NUM>. The input circuit of the external device <NUM> includes a resistor <NUM>, a capacitor <NUM>, and an amplifier <NUM>. Power is supplied to the first transmission line <NUM> from a power source (VCC) connected via the resistor <NUM>. The first electrical signal transmitted through the first transmission line <NUM> is input to the amplifier <NUM> via the capacitor <NUM>.

The ground wire <NUM> is a ground wire connected to a ground of the external device <NUM>. The ground wire <NUM> is connected to one of a plurality of terminals of the microphone <NUM>.

The second transmission line <NUM> and the third transmission line <NUM> are accommodated in the cable <NUM> together with the first transmission line <NUM>, and transmit the second electrical signal from the external device <NUM> to the right speaker <NUM> and the left speaker <NUM>. The second transmission line <NUM> is connected to an amplifier <NUM> included in an output circuit of the external device <NUM> and to the right speaker <NUM>. The second transmission line <NUM> transmits the second electrical signal corresponding to a sound emitted from the right speaker <NUM>. The third transmission line <NUM> is connected to an amplifier <NUM> included in the output circuit of the external device <NUM> and to the left speaker <NUM>. The third transmission line <NUM> transmits the second electrical signal corresponding to a sound emitted from the left speaker <NUM>.

The ground wire <NUM> is a ground wire connected to the ground of the external device <NUM>. The ground wire <NUM> is connected to one of a plurality of terminals of the right speaker <NUM> and the left speaker <NUM>.

Hereinafter, the configuration of the mute operation part <NUM> will be described in detail while referring to <FIG>. The mute operation part <NUM> includes an operation switch <NUM>, an electronic switch <NUM>, and a voltage generator <NUM>. The voltage generator <NUM> includes a capacitor <NUM>, a resistor <NUM>, and a resistor <NUM>.

The operation switch <NUM> is a device for receiving a switching operation between (i) a non-mute state in which the first electrical signal is transmitted to the external device <NUM> and (ii) a mute state in which the first electrical signal is not transmitted to the external device <NUM>. The operation switch <NUM> may be any device as long as it can switch between conductive and non-conductive states, and is, for example, a slide switch, a tact switch, or a push switch. One end of the operation switch <NUM> is connected to the ground, and the other end of the operation switch <NUM> is connected to the voltage generator <NUM>. <FIG> shows the non-mute state in which the operation switch <NUM> is not conducting.

The electronic switch <NUM> is provided between the microphone <NUM> and the external device <NUM>, and switches between (i) the conductive state in which the first electrical signal is transmitted and (ii) the non-conductive state in which the first electrical signal is not transmitted. The electronic switch <NUM> is, for example, an N-channel metal oxide semiconductor field effect transistor (MOSFET). A source terminal of the electronic switch <NUM> is connected to the microphone <NUM>, a gate terminal of the electronic switch <NUM> is connected to the voltage generator <NUM>, and a drain terminal of the electronic switch <NUM> is connected to the external device <NUM> via the first transmission line <NUM> and the connection terminal <NUM>. The electronic switch <NUM> switches between the conductive state and the non-conductive state on the basis of a control voltage input from the voltage generator <NUM> to the gate terminal.

The electronic switch <NUM> is in the conductive state when the control voltage is at a high level, and is in the non-conductive state when the control voltage is at a low level. The high-level voltage is, for example, a voltage equal to or greater than the maximum voltage of the first electrical signal input from the microphone <NUM>. The low-level voltage is, for example, a voltage less than the minimum voltage of the first electrical signal input from the microphone <NUM>.

When the control voltage input to the gate terminal is at the high level, the gate voltage becomes higher than the source voltage, and therefore the electronic switch <NUM> enters into the conductive state. When the control voltage is at the low level, the gate voltage becomes lower than the source voltage, and therefore the electronic switch <NUM> enters into the non-conductive state. In the conductive state of the electronic switch <NUM>, the electronic switch <NUM> outputs the first electrical signal, which is input to the source terminal from the microphone <NUM>, from the drain terminal with almost no attenuation of the first electrical signal, and therefore the headset <NUM> enters into the non-mute state. On the other hand, in the non-conductive state of the electronic switch <NUM>, the electronic switch <NUM> does not transmit the first electrical signal, which is input to the source terminal from the microphone <NUM>, to the drain terminal, and therefore the headset <NUM> enters into the mute state.

The voltage generator <NUM> generates a control voltage for controlling the electronic switch <NUM> to switch between the conductive state and the non-conductive state of the electronic switch <NUM>. The voltage generator <NUM> generates the control voltage corresponding with the state of the operation switch <NUM>. If the electronic switch <NUM> is the N-channel MOSFET, the voltage generator <NUM> generates a low-level control voltage when the operation switch <NUM> is conducting, and generates a high-level control voltage when the operation switch <NUM> is not conducting. The voltage generator <NUM> generates the control voltage on the basis of the power supplied from the external device <NUM> via the first transmission line <NUM>.

The capacitor <NUM> is provided between the gate terminal of the electronic switch <NUM> and the ground. The resistor <NUM> is provided between the gate terminal and the drain terminal of the electronic switch <NUM>. The resistor <NUM> is provided between the gate terminal of the electronic switch <NUM> and the operation switch <NUM>. One end of the resistor <NUM>, which is opposite to the gate terminal side, enters into an open state when the operation switch <NUM> is in the non-mute state (the state shown in <FIG>). One end of the resistor <NUM>, which is opposite to the gate terminal side, enters into a state connected to the ground when the operation switch <NUM> is in the mute state (the operation switch <NUM> is in a closed state).

Since one end of the resistor <NUM> is open in the non-mute state shown in <FIG>, power is supplied from the external device <NUM> via the resistor <NUM>, and therefore the high-level control voltage is input to the gate terminal of the electronic switch <NUM>. As a result, the electronic switch <NUM> enters into the conductive state, and the first electrical signal, which is input to the source terminal from the microphone <NUM>, is output from the drain terminal.

On the other hand, when the operation switch <NUM> is switched to the mute state by the user's operation, one end of the resistor <NUM> is connected to the ground, and therefore the voltage of the control voltage input to the gate terminal of the electronic switch <NUM> changes to the low level. As a result, the electronic switch <NUM> enters into the non-conductive state, and the first electrical signal, which is input to the source terminal from the microphone <NUM>, is not output from the drain terminal. It is preferable that a resistance value of the resistor <NUM> is sufficiently smaller than a resistance value of the resistor <NUM> so that the voltage of the gate terminal of the electronic switch <NUM> in the mute state becomes sufficiently low. The resistance value of the resistor <NUM> is, for example, equal to or more than <NUM>/<NUM> and equal to or less than <NUM>/<NUM> of the resistance value of the resistor <NUM>.

When the operation switch <NUM> enters into the conductive state, a bypass connecting the first transmission line <NUM>, the resistor <NUM>, the resistor <NUM>, the operation switch <NUM>, and the ground wire <NUM>, in this order, is formed. As a result, the level of the first electrical signal input to the amplifier <NUM> of the external device <NUM> becomes smaller because a part of the first electrical signal flows to the ground via the bypass. In the mute operation part <NUM>, the electronic switch <NUM> is switched to the non-conductive state after the level of the first electrical signal input to the external device <NUM> is decreased in this manner, and therefore the level of noise input to the external device <NUM> can be reduced.

The capacitor <NUM> and the resistor <NUM> function as a delay circuit that makes a time required for a transition of the level of the control voltage longer than a time required for switching of the operation switch <NUM>. Specifically, due to the capacitor <NUM> provided between the gate terminal of the electronic switch <NUM> and the ground, the rate of voltage change at the time of transition of the voltage of the gate terminal of the electronic switch <NUM> from the high level to the low level is reduced. Specifically, a time required for the voltage of the gate terminal of the electronic switch <NUM> to change from the high level to the low level is longer than a time required for the operation switch <NUM> to change from the non-conducting state (non-mute state) to the conducting state (mute state).

Since the control voltage gradually changes from the high level to the low level, an impedance between the source terminal and the drain terminal of the electronic switch <NUM> gradually changes. As a result, noise due to a change in impedance that would occur when the operation switch <NUM> is switched to the mute state is hardly generated even if some components of the first electrical signal are input to the external device <NUM>.

It should be noted that when a plurality of transmission lines are accommodated in the same cable, an electrostatic coupling due to induction by mutual capacitances between the transmission lines or a magnetic coupling due to induction by mutual inductances between the transmission lines rarely occurs. <FIG> shows frequency characteristics of a level of sound transmitted between the transmission lines by the electrostatic coupling and the magnetic coupling. As shown in <FIG>, the level of sound induced between the transmission lines by magnetic coupling is approximately constant regardless of the frequency of sound. On the other hand, the level of sound induced between the transmission lines by the electrostatic coupling is less than the level of sound induced between the transmission lines by the magnetic coupling in an audible frequency region. In particular, the lower the frequency, the lower the level of sound induced between the transmission lines by capacitive coupling.

In the configuration shown in <FIG>, since the resistor <NUM> and the resistor <NUM> are provided in series with the operation switch <NUM>, the current flowing from the first transmission line <NUM> to the ground wire <NUM> becomes sufficiently small in the mute state. As a result, in the headset <NUM> having the configuration shown in <FIG>, the magnetic coupling among the first transmission line <NUM>, the second transmission line <NUM>, and the third transmission line <NUM> is less likely to occur, and the problem of the sound based on the second electrical signal, which is transmitted via the second transmission line <NUM> and the third transmission line <NUM>, being input to the external device <NUM> via the first transmission line <NUM> can be prevented. As such, the magnetic coupling hardly occurs according to the configuration of the headset <NUM>, and therefore even if the first transmission line <NUM>, the ground wire <NUM>, the second transmission line <NUM>, the third transmission line <NUM>, and the ground wire <NUM> are in close contact with each other, sound leakage hardly occurs, which is preferable when the cable <NUM> needs to be thinned.

In the above explanation, the voltage generator <NUM> configured with analog elements was illustrated as an example, but the voltage generator <NUM> may be configured with digital circuits. For example, the voltage generator <NUM> may include a central processing unit (CPU) and a DA converter, wherein the voltage generator <NUM> may generate a digital value according to the state of the operation switch <NUM> by executing programs with the CPU, and may generate a control voltage by converting the digital value into an analog signal with the DA converter.

In the above explanation, the headset <NUM> including the right speaker <NUM> and the left speaker <NUM> was illustrated as an example, but the headset <NUM> does not need to include the right speaker <NUM> and the left speaker <NUM>. That is, the headset <NUM> may have a function of inputting sound, and does not need to have a function of outputting sound. Also, the headset <NUM> may have one speaker.

In the above explanation, an N-channel MOSFET was illustrated as an example of the electronic switch <NUM>, but the electronic switch <NUM> may be another device. For example, the electronic switch <NUM> may include a P-channel MOSFET and may include a bipolar transistor.

In the above explanation, an electret condenser microphone was illustrated as an example of the microphone <NUM>, but the microphone <NUM> may be another microphone. However, the configuration of the headset <NUM> is suitable for an electret condenser microphone that requires a large capacity of power.

As described above, the headset <NUM> includes the operation switch <NUM> that receives the switching operation between the non-mute state and the mute state, the voltage generator <NUM> that generates the control voltage corresponding to the state of the operation switch <NUM>, and the electronic switch <NUM> that switches between (i) the conductive state in which the first electrical signal is transmitted and (ii) the non-conductive state in which the first electrical signal is not transmitted, on the basis of the control voltage. With this configuration of the headset <NUM>, the first transmission line <NUM> is disconnected by the electronic switch <NUM> after the potential of the first transmission line <NUM> is lowered to the level close to the ground potential, and therefore noise is hardly transmitted to the external device <NUM>.

Further, since the control voltage for changing the electronic switch <NUM> to the non-conductive state gradually changes, it is possible to reduce noise generated when the electronic switch <NUM> disconnects the first transmission line <NUM> even if some components of the first electrical signal are input to the external device <NUM>.

Furthermore, since the electronic switch <NUM> has the resistor <NUM> and the resistor <NUM>, the impedance of a loop formed by the first transmission line <NUM> and the ground wire <NUM> in the mute state is high, so that (i) the current flowing through the loop is small, and (ii) the magnetic coupling is less likely to occur among the first transmission line <NUM>, the second transmission line <NUM>, and the third transmission line <NUM>. As a result, the sound based on the second electrical signal transmitted on the second transmission line <NUM> and the third transmission line <NUM> can be prevented from being output from the external device <NUM> or being transmitted from the external device <NUM> to another device.

<FIG> shows an internal structure of a headset <NUM> according to an example not covered by the claims. The headset <NUM> is different from the headset <NUM> in that the headset <NUM> has a mute operation part 2a instead of the mute operation part <NUM> in the headset <NUM> shown in <FIG>, and is otherwise the same.

The mute operation part 2a includes an operation switch <NUM> and a capacitor <NUM>. One end of the operation switch <NUM> is connected to the first transmission line <NUM>, and the other end of the operation switch <NUM> is connected to the ground wire <NUM> via the capacitor <NUM>. When the user causes the operation switch <NUM> to enter the conductive state, a loop is formed from the power supply, via the resistor <NUM>, the connection terminal <NUM>, the first transmission line <NUM>, the operation switch <NUM>, the capacitor <NUM>, and the ground wire <NUM> to the ground, and therefore the first electrical signal based on the sound collected by the microphone <NUM> is not transmitted through the first transmission line <NUM>, and the headset <NUM> enters into the mute state. If the operation switch <NUM> is rendered to the conductive state in this manner, a line in which the first electrical signal is flowing would not be disconnected, and therefore noise is hardly generated when the headset <NUM> is switched from the non-mute state to the mute state.

Claim 1:
A headset (<NUM>) comprising:
a microphone (<NUM>) that converts a sound to a first electrical signal;
a first transmission line (<NUM>) that transmits the first electrical signal generated by the microphone (<NUM>) to an external device (<NUM>);
a connection terminal (<NUM>) that connects the first transmission line (<NUM>) to the external device (<NUM>);
an operation switch (<NUM>) that receives an operation for switching between (i) a non-mute state in which the first electrical signal is transmitted to the external device (<NUM>) and (ii) a mute state in which the first electrical signal is not transmitted to the external device (<NUM>);
an electronic switch (<NUM>) that switches between (i) a conductive state in which the first electrical signal is transmitted and (ii) a non-conductive state in which the first electrical signal is not transmitted, on the basis of a control voltage which changes according to the state of the operation switch (<NUM>), the electronic switch (<NUM>) being provided between the microphone (<NUM>) and the connection terminal (<NUM>); and
a voltage generator (<NUM>) that generates the control voltage on the basis of power supplied from the external device (<NUM>) via the first transmission line (<NUM>), and
wherein the electronic switch (<NUM>) is a field effect transistor, and the voltage generator (<NUM>) includes:
a capacitor (<NUM>) provided between a gate terminal of the electronic switch (<NUM>) and a ground,
a first resistor (<NUM>) provided between the gate terminal and a drain terminal of the electronic switch (<NUM>), and
a second resistor (<NUM>) provided between the gate terminal and the operation switch (<NUM>), with one end of the second resistor (<NUM>) which is opposite to the gate terminal side entering into an open state in the non-mute state and the one end of the second resistor (<NUM>) being connected to a ground in the mute state, wherein
one end of the first resistor (<NUM>) is connected to the external device (<NUM>) via the first transmission line (<NUM>) and to the drain terminal, and the other end of the first resistor (<NUM>) is connected to the second resistor (<NUM>) and the gate terminal, and
the voltage generator (<NUM>) generates the control voltage based on the power provided from the external device (<NUM>) in the non-mute state and the control voltage becomes a ground level when the second resistor (<NUM>) is connected to the ground in the mute state.