Patent Description:
Conventionally, a headset with a switch to mute an audio output from a microphone is known (see, for example, <CIT>). Microphones with a change-over switch are further known from <CIT> , <CIT>, and <CIT>.

A terminal capable of connecting an acoustic-electric transducer such as a microphone or a headset has a connection detection function for detecting that the acoustic-electric transducer is connected. This connection detection function is for detecting the connection of the acoustic-electric transducer by detecting a change in a voltage due to a current flowing through the acoustic-electric transducer when a plug of the acoustic-electric transducer is connected.

However, in a conventional circuit configuration, the current does not flow if the acoustic-electric transducer in the mute state is connected to the terminal, and the terminal cannot detect that the microphone is connected by using the connection detection function. Therefore, even if the microphone or the headset is connected to the terminal, the terminal does not detect them.

The present invention focuses on these points, and an object of the present invention is to provide an acoustic-electric transducer that allows the terminal to detect that the acoustic-electric transducer is connected even if the acoustic-electric transducer in the mute state is connected to the terminal.

The invention provides an acoustic-electric transducer according to claim <NUM>.

The current control circuit may include a capacitor that is charged by a current supplied from the terminal, and an electronic switch that sets a state between the first connection point and the second connection point to a conductive state until the capacitor is completely charged, and sets the state between the first connection point and the second connection point to a non-conductive state after the predetermined time passes.

The electronic switch is a field effect transistor, the capacitor is provided between the first connection point and a gate terminal of the field effect transistor, a drain terminal of the field effect transistor is electrically connected to the first connection point, and a source terminal of the field effect transistor is electrically connected to the second connection point. The current control circuit may further include a first resistor provided between (i) the changeover switch and the first connection point and (ii) the drain terminal of the field effect transistor.

A voltage of the gate terminal may increase until the capacitor is completely charged. A potential difference between the gate terminal and the source terminal may increase until the capacitor is completely charged, and a state between the drain terminal and the source terminal may become a conductive state. The voltage of the gate terminal may decrease after the capacitor is completely charged, and the state between the drain terminal and the source terminal may become a non-conductive state. The current control circuit may enter a high impedance state due to the state between the drain terminal and the source terminal becoming a non-conductive state.

The current control circuit may further include a second resistor provided between the second connection point and the capacitor. The second resistor may increase a potential of the gate terminal in accordance with the magnitude of the current flowing during a time from when the acoustic-electric transducer is connected to the terminal until the predetermined time passes.

The voltage of the first connection point may start decreasing from a power supply voltage of the terminal at the time when the acoustic-electric transducer is connected to the terminal, and may increase after the electronic switch enters a non-conductive state. The voltage of the first connection point may reach the power supply voltage of the terminal at the time when the current control circuit enters a high impedance state.

The predetermined time is longer than a minimum time required for the terminal to determine whether the acoustic-electric transducer is connected.

According to the present invention, the terminal can detect that the acoustic-electric transducer is connected even if the acoustic-electric transducer in the mute state is connected to the terminal.

<FIG> shows a configuration of an acoustic-electric transducer <NUM> according to the embodiment. The acoustic-electric transducer <NUM> is a device for transducing a sound into an electrical signal and is, for example, a microphone device. The acoustic-electric transducer <NUM> may be other devices such as a headset that is attached to a user's head. The acoustic-electric transducer <NUM> may further include a speaker for transducing an electrical signal generated by the terminal <NUM> into a sound.

The terminal <NUM> is, for example, a game device, an audio device, a communication device, a smart phone, or a computer. The acoustic-electric transducer <NUM> is attachable to / detachable from the terminal <NUM>, and outputs a transduced electrical signal to the terminal <NUM> while the acoustic-electric transducer <NUM> is connected to the terminal <NUM>. The terminal <NUM> processes an electrical signal inputted from the acoustic-electric transducer <NUM>. For example, the terminal <NUM> transduces the inputted electrical signal into a sound or transfers the inputted electrical signal to other devices.

<FIG> shows a configuration of the acoustic-electric transducer <NUM> and the terminal <NUM>. The acoustic-electric transducer <NUM> includes a sound input part <NUM>, a changeover switch <NUM>, a cable <NUM>, a connection part <NUM>, and a current control circuit <NUM>.

The sound input part <NUM> has a microphone <NUM> which is an acoustic-electric transducing part that transduces the sound inputted from the outside into the electrical signal. The microphone <NUM> is, for example, an electret condenser microphone.

The changeover switch <NUM> switches between a non-mute state where a sound-transduced electrical signal is outputted to the terminal <NUM> and a mute state where the sound-transduced electrical signal is not outputted to the terminal <NUM>. The changeover switch <NUM> conducts in the non-mute state and the acoustic-electric transducer <NUM> can receive power from the terminal <NUM>. In the non-mute state, the electrical signal generated by the microphone <NUM> is inputted to the terminal <NUM> via the changeover switch <NUM>, the cable <NUM>, and the connection part <NUM>. The changeover switch <NUM> is non-conductive in the mute state and the power from the terminal <NUM> is not supplied to the acoustic-electric transducer <NUM>. Therefore, in the mute state, the microphone <NUM> does not transduce the electrical signal even if the sound from an external source is received.

The cable <NUM> connects the acoustic-electric transducer <NUM> and the terminal <NUM>. The cable <NUM> transmits, to the terminal <NUM>, the electric signal transduced from the sound by the microphone <NUM>.

The connection part <NUM> is, for example, a connector plug provided at a tip end of the cable <NUM>. The connection part <NUM> has a first connection point <NUM> and a second connection point <NUM>. The first connection point <NUM> contacts a first contact A of a connector jack provided to the terminal <NUM>, and the second connection point <NUM> contacts a second contact B. The connection part <NUM> complies with, for example, the plug-in power standard and receives the power from the terminal <NUM>. The first contact A is, for example, a metal terminal connected to a power supply (Vcc) of the terminal <NUM>. The second contact B is, for example, a metal terminal connected to a ground of the terminal <NUM>. Therefore, a potential of the first contact A is higher than the potential of the second contact B.

The current control circuit <NUM> is a circuit that makes a current flow between the first contact A and the second contact B until a predetermined time passes from the time when the acoustic-electric transducer <NUM> is connected to the terminal <NUM>. The predetermined time is a time that is longer than the minimum time required for the terminal <NUM> to determine whether the acoustic-electric transducer <NUM> is connected, and is a time determined by the time constant of the current control circuit <NUM>. The current control circuit <NUM> is provided between the changeover switch <NUM> and the connection part <NUM>. The current control circuit <NUM> has a capacitor <NUM>, an electronic switch <NUM>, a resistor <NUM> (corresponding to a first resistor), and a resistor <NUM> (corresponding to a second resistor).

The capacitor <NUM> is arranged between the first connection point <NUM> and a gate terminal G of the electronic switch <NUM>. The capacitor <NUM> is charged by the power supplied from terminal <NUM>.

The electronic switch <NUM> is, for example, a field effect transistor. A drain terminal D of the electronic switch <NUM> is electrically connected to the first connection point <NUM> via the resistor <NUM>. Further, a source terminal S of the electronic switch <NUM> is electrically connected to the second connection point <NUM>. A voltage of the gate terminal G of the electronic switch <NUM> increases until the capacitor <NUM> is completely charged. As a result, a potential difference between the gate terminal G and the source terminal S increases, and a state between the drain terminal D and the source terminal S of the electronic switch <NUM> becomes a conductive state.

The voltage of the gate terminal G decreases after the capacitor <NUM> is completely charged, and the state between the drain terminal D and the source terminal S of the electronic switch <NUM> becomes a non-conductive state. As a result, the electronic switch <NUM> reduces the current flowing between the first contact A and the second contact B after the predetermined time passes from the time when the connection part <NUM> is connected to the terminal <NUM>. Since the time required for the state between the drain terminal D and the source terminal S to change from the conductive state to the non-conductive state depends on capacitance of the capacitor <NUM>, the predetermined time is determined by the capacitance of the capacitor <NUM>.

Due to the state between the drain terminal D and the source terminal S of the electronic switch <NUM> becoming the non-conductive state, the current control circuit <NUM> enters a high impedance state and does not affect other circuits. The current based on the sound inputted to the microphone <NUM> flows between the first contact A and the second contact B in this state.

The resistor <NUM> is arranged between (i) the first connection point <NUM> and the changeover switch <NUM> and (ii) the drain terminal D of the electronic switch <NUM>. The resistor <NUM> prevents a short circuit from occurring between the first contact A and the second contact B when the state between the drain terminal D and the source terminal S of the electronic switch <NUM> is conductive. The resistor <NUM> is provided between the second connection point <NUM> and the capacitor <NUM>. The resistor <NUM> increases the potential of the gate terminal G in accordance with the magnitude of the current flowing during a time from when the acoustic-electric transducer <NUM> is connected to the terminal <NUM> until the predetermined time passes. As a result, the potential of the gate terminal G changes in accordance with the amount of charge of the capacitor <NUM>.

Next, a configuration of the terminal <NUM> will be described with reference to <FIG>. The terminal <NUM> includes a resistor <NUM>, an amplifier <NUM>, a voltage detection circuit <NUM>, an audio processing circuit <NUM>, and a control part <NUM>.

The voltage detection circuit <NUM> detects the voltage of the first contact A. The voltage detection circuit <NUM> provides notification about the detected voltage of the first contact A to the control part <NUM>. The amplifier <NUM> amplifies the electrical signal transduced from the sound by the microphone <NUM>. The audio processing circuit <NUM>, for example, executes a process of outputting the sound based on the electrical signal inputted from the amplifier <NUM> to a speaker or executes a process of transmitting the electrical signal through a communication line.

The control part <NUM> is, for example, a Central Processing Unit (CPU) and controls respective parts of the terminal <NUM>. If the voltage detected by the voltage detection circuit <NUM> is equal to or greater than a threshold, the control part <NUM> determines that the acoustic-electric transducer <NUM> is not connected to the terminal <NUM>, and if the voltage detected by the voltage detection circuit <NUM> is less than the threshold, the control part <NUM> determines that the acoustic-electric transducer <NUM> is connected to the terminal <NUM>. The threshold is set below the maximum value assumed as the voltage of the first contact A within the predetermined time from the time when the acoustic-electric transducer <NUM> is connected to the terminal <NUM>. For example, the control part <NUM> switches between an on state and an off state of a microphone (not shown) built in the terminal <NUM> on the basis of the voltage of the first contact A detected by the voltage detection circuit <NUM>.

<FIG> shows a change in voltage when the acoustic-electric transducer <NUM> is connected to the terminal <NUM>. Vcc in <FIG> is a power supply voltage of the terminal <NUM>. <FIG> shows a voltage between the gate terminal G and the source terminal S of the electronic switch <NUM>. <FIG> shows the voltage of the first contact A detected by the voltage detection circuit <NUM>. A time T1 in <FIG> indicates a time at which the acoustic-electric transducer <NUM> is connected to the terminal <NUM>.

As shown in <FIG>, the voltage between the gate terminal G and the source terminal S of the electronic switch <NUM> increases due to the power supply from the terminal <NUM> starting at the time T1. As a result, the state between the drain terminal D and the source terminal S becomes conductive, and so the current flows between the first contact A and the second contact B. As the capacitor <NUM> accumulates the charge due to the current flowing in, an inter-terminal voltage of the capacitor <NUM> gradually increases. Therefore, the potential appearing on the gate terminal G side gradually lowers, the voltage between the gate terminal G and the source terminal S gradually decreases, and the electronic switch <NUM> at a time T2 enters the non-conductive state.

As shown in <FIG>, the voltage of the first contact A (i.e., the voltage of the first connection point) starts decreasing from Vcc at the time T1 when the acoustic-electric transducer <NUM> is connected to the terminal <NUM>, and increases after the electronic switch <NUM> enters the non-conductive state at the time T2. Thereafter, the voltage of the first contact A reaches Vcc at the time when the current control circuit <NUM> enters the high-impedance state.

Although the above description has exemplified a case where the electronic switch <NUM> is the field effect transistor, the electronic switch <NUM> may be an NPN bipolar transistor. In this case, the gate terminal, the source terminal, and the drain terminal of the field-effect transistor in <FIG> correspond to a base terminal, a collector terminal, and an emitter terminal of the NPN bipolar transistor.

Further, the above description has exemplified the configuration in which the current control circuit <NUM> controls the current flowing between the first contact A and the second contact B with the electronic switch <NUM>, but the configuration of the current control circuit <NUM> is not limited thereto. The current control circuit <NUM> may include a processor that operates by executing software, for example. In this case, the processor, activated by the current supplied from the terminal <NUM>, may reduce the impedance of the circuit provided between the first contact A and the second contact B to make the current flow between the first contact A and the second contact B. The processor increases the impedance of the circuit provided between the first contact A and the second contact B to interrupt the current after the predetermined time passes.

According to the acoustic-electric transducer <NUM> according to the present embodiment, the current control circuit <NUM> makes the current flow between the first contact A and the second contact B until the predetermined time passes from the time when the connection part <NUM> is connected to the terminal <NUM>. Therefore, the control part <NUM> of the terminal <NUM> can determine, on the basis of the voltage detected by the voltage detection circuit <NUM>, whether the acoustic-electric transducer <NUM> is connected. Further, the current control circuit <NUM> reduces the current flowing between the first contact A and the second contact B after the predetermined time passes, and enters the high-impedance state. Therefore, the current control circuit <NUM> does not affect characteristics of the electrical signal generated by the microphone <NUM>.

Claim 1:
An acoustic-electric transducer (<NUM>) for transducing a sound into an electrical signal, comprising:
a connection part (<NUM>) that has a first connection point (<NUM>) configured to contact a first contact (A) in a terminal (<NUM>) for processing the electrical signal, and a second connection point (<NUM>) configured to contact a second contact (B) having a potential lower than the potential of the first contact (A);
an acoustic-electric transducing part configured to transduce a sound inputted from an external source into an electrical signal;
a changeover switch (<NUM>) that is provided on a first transmission line (<NUM>) that is included in a cable (<NUM>) connecting the connection part (<NUM>) and the acoustic-electric transducing part and is connected to the first connection point (<NUM>), and the changeover switch (<NUM>) being configured to switch between a non-mute state where the electrical signal is outputted to the terminal (<NUM>) and a mute state where the electrical signal is not outputted to the terminal (<NUM>); and
a current control circuit (<NUM>) configured to make a current flow between the first connection point (<NUM>) and the second connection point (<NUM>) until a predetermined time passes from the time when the connection part (<NUM>) is connected to the terminal (<NUM>) and configured to reduce the current flowing between the first connection point (<NUM>) and the second connection point (<NUM>) after the predetermined time passes, wherein the predetermined time is longer than the minimum time required for the terminal (<NUM>) to determine whether the acoustic-electric transducer (<NUM>) is connected, and the predetermined time is determined by the time constant of the current control circuit (<NUM>), the current control circuit (<NUM>) being provided between the first transmission line (<NUM>) and a second transmission line (<NUM>) that is included in the cable (<NUM>) and connected to the second connection point (<NUM>).