JP2003143687A - Detection circuit for microphone plug and line plug, common use circuit for jack, adaptor using the jack in common, and notebook pc provided with the common use jack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection circuit for microphone plug and line plug that can use a microphone jack and a line jack in common, a common use circuit for the jack, an adaptor using the jack in common, and a notebook PC provided with the common use jack. SOLUTION: While a plug of an external device to be connected is plugged into a jack and connected, a difference of impedance between a ring pin and a tip pin of the jack is obtained, whether the jack to which the external device is connected is a microphone or a line jack is detected on the basis of the difference of impedance to be obtained. In the case of the microphone jack, it is controlled so that a DC bias is applied to the ring pin or the tip pin of the jack, and in the case of the line jack, no DC bias is given to the ring pin and the tip pin of the jack, or in the case of a device using the line jack, the device is connected to the common use jack via an adaptor with a prescribed DC cut function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information terminal which requires the use of both a microphone jack and a line jack, and more particularly, to detect a microphone plug and a line plug, a common circuit for the jack, and a common jack. And a notebook PC equipped with a common jack.

[0002]

2. Description of the Related Art Information terminals, particularly jacks used for inputting / outputting audio for personal computer (PC) audio, require at least three jacks if the functions currently considered are inserted. The three are a microphone jack and a line jack as an input, and a headphone jack as an output. In recent years, the demand for notebook PCs with small housings such as B5 size is high,
In this notebook PC, it is becoming very difficult to arrange the three jacks in the housing. Therefore, various studies have been made in which the input-side microphone jack and the line jack are used as one common jack, and an output jack and eventually two jacks are used to assemble the system.

FIG. 7 is a block diagram showing an example of an input side line jack and a microphone jack in the conventional system and circuits around them. In FIG. 7, a line jack 111 and a microphone jack 131 are provided on the side surface of a system 101 such as a notebook PC.

The line jack 111 is a ring pin 11.
2, a tip pin 113, and a GND pin 114. The ring pin 112 is connected via a buffer 115 to a CODEC 116 which is a converter IC.
The tip pin 113 is CODE via the buffer 117.
It is connected to C116. The GND pin 114 is grounded. This line jack 111 has an external device 1
Eighteen plugs 119 are inserted. Line jack 11
With the plug 119 inserted in the plug 1, the ring portion 120 of the plug 119 and the ring pin 112 are connected to each other.
The tip portion 121 of the plug 19 and the tip pin 113 are connected, and the GND portion 122 of the plug 119 and the GND pin 114 are connected.
And are connected.

Similarly, the microphone jack 131 is provided with a ring pin 132, a tip pin 133 and a GND pin 134. The DC bias (Vcc) is supplied to the ring pin 132 via the resistor 141. The tip pin 133 is connected to the CODEC 11 via the preamplifier 142.
Connected to 6. The GND pin 134 is grounded. The plug 136 of the microphone 135 is inserted into the microphone jack 131. With the plug 136 inserted in the microphone jack 131, the ring portion 1 of the plug 136
37 and the ring pin 132 are connected, the tip portion 138 of the plug 136 and the tip pin 133 are connected, and the GND portion 139 of the plug 136 and the GND pin 134 are connected.

[0006]

In the example shown in FIG. 7, since the ring pin 132 of the microphone jack 131 needs a bias for the microphone 135, a DC bias (Vcc) of 3V to 5V is passed through the resistor 141. Need to add. The pin at the same position in the line jack 111 is used as an input signal for Rch (right channel) or Lch (left channel).

In order to reduce the mounting space, when one of the microphone jack 131 and the line jack 111 is eliminated,
When the line jack 111 is removed, the line plug 119
Even if is connected, unnecessary power is supplied to the line plug 11
9 is supplied to external equipment. On the other hand, if the microphone jack 131 is abolished, power is not supplied to the microphone 135.

The object of the present invention is to solve the above problems,
Allows common use of microphone jack and line jack,
Microphone and line plug detection circuit, jack shared circuit, jack shared adapter, and
It is intended to provide a notebook PC having a shared jack.

[0009]

A microphone plug and line plug detecting circuit of the present invention relates to a circuit for detecting whether a plug of an external device connected to a jack is a microphone plug or a line plug. In this circuit, with the plug of the external device to be connected inserted in the jack and connected, based on the comparison circuit that finds the impedance difference between the ring pin and the tip pin of the jack, and the impedance difference found by the comparison circuit , Detects whether the plug of the external device connected to the jack is a microphone plug or a line plug.

In the above-described microphone jack and line jack detection method of the present invention, when the external device uses the microphone jack, the ring pin and the tip pin of the jack have the same level signal, that is, the same impedance, while the external device is the line jack. When using a jack, the jack ring pin and the tip pin usually have different levels of signals, that is, different impedances.Therefore, find the impedance difference between the jack ring pin and the tip pin, and connect based on the obtained impedance difference. The detected external device plug can detect whether it is a microphone plug or a line plug.

As a preferred concrete example of the detection circuit of the microphone plug and the line plug of the present invention, the judgment circuit judges that the plug to be detected is a microphone jack when the impedance difference is smaller than a predetermined value, and the impedance When the difference is larger than a predetermined value, it may be determined that the plug to be detected is the line plug. If the ring signal or tip pin of the jack is applied with DC bias at a level that does not affect the operation of external equipment, the left and right signal levels happen to be the same during line input. However, since the difference in impedance does not fall below a predetermined value and the plug is not erroneously detected, more accurate detection can be realized.

The jack common circuit of the present invention relates to a circuit in which a microphone jack and a line jack are shared by one jack. In this circuit, a detection circuit for detecting the microphone plug and the line plug of the present invention for detecting whether the plug of the external device connected to the jack is the microphone plug or the line plug, and the detection circuit connected to the jack. When the plug of the external device is determined to be the microphone plug, DC bias is applied to the ring pin or tip pin of the jack, and when the plug of the external device connected to the jack is determined to be the line plug,
And a switch circuit for controlling DC bias not to be applied to the ring pin and the tip pin of the jack.

In the above-described jack common circuit of the present invention, the jack is controlled by controlling whether or not the DC bias is applied depending on whether the plug of the external device connected to the jack is the microphone plug or the line plug. Regardless of whether the plug of the connected external device uses the microphone plug or the line plug, the operation of the external device is not always affected.

A preferred specific example of the jack common circuit of the present invention includes a differential amplifier as a comparison circuit and a determination circuit of a detection circuit, and a DC circuit as a switch circuit.
A transistor switch is provided between the bias and the ring pin or tip pin of the jack, and the output from the ring pin of the jack and the output from the tip pin are input to the differential amplifier. When the differential amplifier is LOW output, The transistor switch is opened and the differential amplifier is HIGH.
For output, close the transistor switch,
In addition, when it is determined that the plug of the external device connected to the jack with the LOW output of the differential amplifier is the microphone plug, the mute function of the microphone is turned off, the mute function of the line is turned on, and the differential amplifier is set to HIGH. When it is determined that the plug of the external device connected to the jack at the output is a line plug, control may be performed to turn on the mute function of the microphone and turn off the mute function of the line. In any case, the jack common circuit of the present invention can be more preferably implemented. The mute function can be switched manually or automatically.

An adapter for sharing a jack of the present invention relates to an adapter for also sharing a microphone jack having a DC bias applied to a ring pin or a tip pin as a line jack. In this adapter, a plug on the system side and a jack on the external device side are provided, and a ring line between the ring portion of the plug on the system side and the ring pin of the jack on the external device side,
Alternatively, of the tip lines between the tip portion of the plug on the system side and the tip pin of the jack on the external device side, a ring line or tip line to which DC bias is applied has a mechanism for preventing DC bias.

In the adapter for sharing a jack of the present invention, it is detected whether the external device to be connected by the user is a device using the microphone jack or a device using the line jack, and the device using the microphone jack is detected. In the case of, the plug of the external device is directly connected to the jack, and in the case of the device that uses the line jack, the plug of the external device is connected to the jack through the specified adapter, which affects the operation of the external device. It is possible to share the microphone jack and the line jack instead.

As a preferred concrete example of the adapter for sharing the jack of the present invention, regardless of whether the side to which the DC bias is applied is the ring pin side or the tip pin side, both the ring line and the tip line,
Sometimes using an adapter with a mechanism to prevent DC bias and the mechanism to prevent DC bias is a capacitor. In any case, the adapter for sharing the jack of the present invention can be implemented more preferably.

The notebook PC of the present invention is equipped with the above-described shared circuit for the jack of the present invention, and has one shared jack as a microphone jack and a line jack. Therefore, it is possible to construct a system with two jacks, an input jack and an output jack. As a result, not only the area of the parts on the main card of the PC can be reduced but also the volume of the case or the like can be reduced, and the cost can be reduced.

[0019]

1 is a flowchart for explaining an example of a detection circuit for a microphone plug and a line plug according to the present invention. The detection circuit of the microphone plug and the line plug of the present invention will be described according to the example shown in FIG. 1. First, the plug of the external device to be connected is inserted into the jack to be detected and connected. Next, the difference in impedance between the jack and the ring focus tip pin is obtained. afterwards,
It is determined whether the obtained impedance difference is 0. If the result of determination is that the impedance difference is 0, it is determined that the plug to be detected is the microphone plug. If the result of determination is that the impedance difference does not match 0, the plug to be detected is determined to be a line plug. Even in the case of a preferred example in which a DC bias of a level that does not affect the operation of an external device is added to the ring pin or the tip pin of the jack, in the case of the microphone plug, the ring pin and the tip pin are connected inside the microphone and have the same level. Therefore, the difference in impedance is zero. Therefore, the same detection method can be adopted.

In the above description of FIG. 1, the determination circuit that constitutes the detection circuit determines whether or not the impedance difference is zero. This is because, theoretically, when the difference in impedance is 0Ω, it is determined to be a microphone jack. However, in an actual circuit, even if a plug is connected to a microphone jack, an impedance difference of several Ω, typically 0.5 Ω to 3 Ω usually remains due to contact resistance and signal line resistance. is there. Therefore, the impedance difference when the external device is a microphone is calculated, and when the impedance difference less than that value is detected, it is determined that the plug of the external device connected to the jack is the microphone plug, and the value of the impedance difference is more than that value. It is preferable that the plug of the external device connected to the jack is determined to be the line plug when the impedance difference is detected. In addition, in the present invention, when the description "when the impedance difference is 0" is meant to include the value of the small impedance difference (about several Ω at most) within a certain range as described above.

FIG. 2 is a block diagram showing the configuration of an example of a jack common circuit of the present invention using the detection circuit shown in FIG. In the example shown in FIG. 2, a notebook type P
One common jack 11 having a microphone jack function and a line jack function is provided on the side surface of the system 1 such as C.

The shared jack 11 is provided with a ring pin 12, a tip pin 13 and a GND pin 14. The ring pin 12 is connected via a buffer 15 to a CODEC 16 which is a converter IC. Tip pin 13
Is a CODEC via the buffer 17 and the preamplifier 18.
It is connected to 16. The GND pin 14 is grounded. The plug 22 of the external device 21 or the plug 32 of the microphone 31 is inserted into the shared jack 11. When the plug 22 of the external device 21 is inserted, the ring portion 23 of the plug 22 and the ring pin 12 are connected and the plug 22
The tip portion 24 and the tip pin 13 are connected, and the GND portion 25 of the plug 22 and the GND pin 14 are connected. When the plug 32 of the microphone 31 is inserted, the ring portion 33 and the ring pin 12 of the plug 32 are connected, the tip portion 34 and the tip pin 13 of the plug 32 are connected, and the GND portion 35 and the GND pin of the plug 32 are connected. 14 is connected.

The above construction is the same as the conventional example shown in FIG. In the example shown in FIG. 2, the common circuit of the jack of the present invention is characterized in that the output from the ring pin 12 and the output from the tip pin 13 of the common jack 11 are supplied to the differential amplifier 41. DC to supply to 12
The transistor switch 42 is provided between the resistor 43 and the ring pin 12 in the bias (Vcc: 3.3V to 5V as an example) line, and the LOW from the differential amplifier 41 is provided.
The point is that the opening and closing of the transistor switch 42 is controlled by the output and the HIGH output. In a specific example of controlling the opening / closing of the transistor switch 42, first, the difference in impedance between the ring pin 12 and the tip pin 13 is calculated by the differential amplifier 41.
As the output of. The output of the differential amplifier 41 is obtained as a LOW output when the obtained impedance difference is 0, and as a HIGH output when the impedance difference is other than 0. When the output of the differential amplifier 41 is LOW level, the jack is determined to be a microphone jack, the transistor switch 42 receiving the LOW level output is opened, and the DC bias (Vcc) is supplied to the ring pin 12. . On the other hand, when the output of the differential amplifier 41 is at the HIGH level, the jack is determined to be the line jack, and the HIGH
The transistor switch 42 receiving the level output is closed, and the DC bias (Vcc) is not supplied to the ring pin 12.

FIG. 3 is a block diagram showing the configuration of another example of the jack common circuit of the present invention using the detection circuit shown in FIG. In the example shown in FIG. 3, the same members as those in the example shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. The difference between the example shown in FIG. 3 and the example shown in FIG.
A DC bias (Vb: 1.5 or less as an example) of a level that does not affect the operation of the external device 21 is connected to the ring pin 12 of the shared jack 11 via the resistor 44 even when the external device 21 is connected to the shared jack 11. Is the point that is added. In this example, the DC bias is applied to the ring pin 12, but the same applies to the tip pin 13.

As shown in FIG. 3, when a DC bias of a level that does not affect the operation of the external device 21 is applied, the output of the differential amplifier 31 is the ring pin 12 and the tip pin 1.
The value corresponding to this DC bias is added to the difference in impedance from 3 However, shared jack 11
When using as a microphone jack, since the ring portion 33 and the tip portion 34 are connected in the microphone 31, both the ring pin 12 and the tip pin 13 have the same value as the DC bias. Therefore, the output of the differential amplifier 41 becomes 0, and the microphone jack and line jack detection method shown in FIG. 1 can be used as in FIG. In this example, when the common jack 11 is used as a line jack, even if the output of the ring section 23 and the output of the tip section 24 happen to be at the same level, the output of the differential amplifier 41 corresponds to this DC bias. It takes a value and does not become 0. Therefore, the detection accuracy of the microphone jack and the line jack can be increased.

FIG. 4 is a block diagram showing still another structure of the jack common circuit of the present invention using the detection circuit shown in FIG. In the example shown in FIG. 4, the same members as those in the example shown in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted. The example shown in FIG. 4 differs from the example shown in FIG. 2 in that the output of the differential amplifier 41 is configured to be added to the CODEC 16.

In the example shown in FIG. 4, a differential amplifier 41 indicating whether the shared jack 11 is a microphone jack or a line jack.
According to the LOW level output and the HIGH level output, the microphone-related device and the line-related device of the system are muted to adjust the entire system. That is, the LOW output of the differential amplifier 41 indicating that the shared jack 11 is a microphone jack is the GP of the CODEC 16.
Upon entering IO-IN, the input selector of the CODEC 16 automatically turns off the cute function of the microphone in the system and turns on the mute function of the line. On the other hand, the HIGH output of the differential amplifier 41 indicating that the shared jack 11 is a line jack is CODEC.
When entering 16 GPIO-IN, the input selector of the CODEC 16 automatically turns on the mute function of the microphone in the system and turns off the mute function of the line.

In the above-described example, the microphone-related device and the line-related device are automatically muted according to the output of the differential amplifier 41 input to the CODEC 16, but the differential amplifier input to the CODEC 16 is configured. The output of 41 may be transmitted to the user by some means, and the user may manually check the mute box of the volume control panel on the display device. In this example, when the common jack 11 is used as a microphone jack, mute related to the microphone is turned on.
Even if it is, the mute can be canceled and the entire system can be adjusted.

With the jack common circuit of the present invention shown in FIGS. 2 to 4, the following effects can be obtained. (1) It is possible to reduce the space for one connector while maintaining the line function and the microphone function. (2) Compared to the conventional product having three jacks for line, microphone, and earphone, the user does not need to check the input jack when using the line / microphone, which improves usability. (3) The possibility of damaging the external output device can be eliminated.

FIG. 5 is a diagram for explaining the configuration of an example of an adapter for sharing the jack of the present invention. Figure 5
In the example shown in FIG. 2, the same members as those in the example shown in FIGS. 2 to 4 are designated by the same reference numerals, and the description thereof will be omitted. In the adapter for sharing the jack of the present invention shown in FIG. 5, the ring pin 12 or the tip pin 1 of the common jack 11 is used.
3, a DC bias (Vcc) is always applied. Then, it is necessary to identify in advance whether the device to be connected to the common jack 11 by the user is the microphone 31 requiring the DC bias from the external device 21 which is damaged when the DC bias is applied. When the device to be connected to the shared jack 11 is the microphone 31, the plug 32 of the microphone 31 is directly inserted into the shared jack 11 for connection. On the other hand, when the device to be connected to the shared jack 11 is the external device 21, the external device 2 is connected to the shared jack 11 via the adapter 51 having the function of cutting the DC component, which will be described in detail below.
1 plug 22 is connected. This makes it possible to use both the microphone jack and the line jack.

In the example shown in FIG. 5, the adapter 51 is
The plug 61 on the system side and the jack 71 on the external device side are integrally formed. A ring line 81 between the ring portion 62 of the plug 61 on the system side and the ring pin 72 of the jack 71 on the external device side.
In addition, a capacitor 82 for preventing DC bias is provided. Further, a capacitor 84 for preventing DC bias is provided on a tip line 83 between the tip portion 63 of the plug 61 on the system side and the tip pin 73 of the jack 71 on the external device side. Furthermore, the GND portion 64 of the plug 61 and the GND pin 74 of the jack 71
And are connected by a GND line 85. Therefore, regardless of whether the DC bias is applied to the ring line 81 side or the tip line 83 side, the DC bias is cut only by transmitting the signal to the external device side.

In the above example, the ring line 81
Capacitors are installed on both the tip line 83 and
It goes without saying that the present invention can be achieved by providing a capacitor only on the line to which the DC bias is applied, in the example shown in FIG. 5, only on the ring line 81. Further, in the above-mentioned example, the capacitor is illustrated as the means for preventing the DC bias, but it goes without saying that any means other than the capacitor can be used as long as it can prevent the passage of the DC component.

FIG. 6 is a diagram showing the configuration of another example of the adapter 51 shown in FIG. In the example shown in FIG. 6, the same members as those in the example shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. In the example shown in FIG. 6, the adapter 51 is configured by connecting a plug 61 and a jack 71, which are separately configured, with a flexible cable 91. In this example as well, similar to the example shown in FIG. 5, the function of the adapter 51 can be fulfilled.

According to the second invention of the method for sharing a microphone jack and a line jack of the present invention shown in FIGS. 5 and 6, the following effects can be obtained. (1) It is possible to reduce the space for one audio jack in the system without impairing the microphone function and the line function. (2) It can be realized at a lower cost than the conventional method. (3) It is flexible to the needs of the user. For example, a user who does not need the line function does not need an adapter,
A lower cost system can be provided to the user.

Further, as a notebook PC, the first invention of the method for sharing a microphone jack and a line jack of the present invention described above can be mounted, and one shared jack can be used as a microphone jack and a line jack. In that case, the system can be assembled with two jacks, an input jack and an output jack. As a result, not only the area of the parts on the main card of the PC can be reduced but also the volume of the case or the like can be reduced, and the cost can be reduced.

In the above description, the case where the microphone jack and the line jack are shared is explained, but a jack requiring the supply of DC bias similar to the microphone jack and a DC bias similar to the line jack are supplied. It is needless to say that the present invention can be preferably applied to the case where the jack is used and the operation is affected.

Further, in the present invention, the jacks have been described as the line jack and the microphone jack in the above description, but the line jack and the microphone jack here have the following concept. In other words, the line jack is a device that does not require power supply from the PC body and the PC.
An interface for connecting to. For example, it refers to an interface for guiding signals output from electronic parts such as capacitors, resistors, and transistors in external equipment to a PC. Since these electronic parts are driven by the power supply of the external equipment, power is supplied from the PC. No need.
The microphone jack refers to an interface for connecting the PC to a device that needs to be supplied with power from the PC body. Typically, the microphone jack is a terminal for guiding the output from the electric condenser microphone to the PC. The electric condenser microphone generally includes a condenser for collecting sound and further an amplifier for amplifying an output from the condenser, for example, MOSFET.
Have. The output from the MOSFET is P as an audio signal.
Input to C. To drive this amplifier, P
Generally, power is supplied from C.

[0038]

As is apparent from the above description, according to the present invention, the microphone jack and the line jack can be shared without damaging the connected external equipment. Therefore, the space for one jack can be reduced.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining an example of a detection circuit for a microphone plug and a line plug according to the present invention.

FIG. 2 is a block diagram showing a configuration of an example of a jack common circuit of the present invention using the detection circuit shown in FIG.

FIG. 3 is a block diagram showing the configuration of another example of the jack common circuit of the present invention using the detection circuit shown in FIG.

FIG. 4 is a block diagram showing still another configuration of the jack common circuit of the present invention using the detection circuit shown in FIG.

FIG. 5 is a diagram showing a configuration of an example of an adapter for sharing a jack of the present invention.

FIG. 6 is a diagram showing the configuration of another example of the adapter shown in FIG.

FIG. 7 is a block diagram showing an example of a line jack and a microphone jack on the input side and a circuit around the input jack in the conventional system.

[Explanation of symbols]

1 system, 11 shared jacks, 12,72 ring pins, 13,73 tip pins, 14,74 GN
D pin, 15, 17 buffer, 16 CODEC, 1
8 preamplifier, 21 external equipment, 22, 32, 61
Plug, 23, 33, 62 Ring part, 24, 34, 6
3 Tips, 25, 35, 64 GND, 31
Microphone, 41 differential amplifier, 42 transistor switch, 43, 44 resistance, 51 adapter, 71 jack, 81 ring line, 82, 84 capacitor, 8
3 tip lines, 85 GND lines, 91 cables

Continued front page    (72) Inventor Kozo Nishino             1623 1423 Shimotsuruma, Yamato-shi, Kanagawa Japan             BM Co., Ltd. Daiwa Office (72) Inventor Takashi Sugawara             1623 1423 Shimotsuruma, Yamato-shi, Kanagawa Japan             BM Co., Ltd. Daiwa Office (72) Inventor ▲ Taka ▼ Toshiki Hashi             1623 1423 Shimotsuruma, Yamato-shi, Kanagawa Japan             BM Co., Ltd. Daiwa Office F-term (reference) 5D017 BD05                 5D020 BB00 BB03

Claims (10)

[Claims] 1. A circuit for detecting whether a plug of an external device connected to the jack is a microphone plug or a line plug, and the plug of the external device to be connected is inserted into the jack and connected to the ring of the jack. A comparison circuit that obtains the impedance difference between the pin and the tip pin, and a determination circuit that detects whether the plug of the external device connected to the jack is a microphone plug or a line plug, based on the impedance difference obtained by the comparison circuit. A detection circuit for a microphone plug and a line plug, which includes: 2. The judgment circuit judges that the plug to be detected is a microphone plug when the impedance difference is smaller than a predetermined value, and the line plug to be detected when the impedance difference is larger than a predetermined value. The detection circuit for the microphone plug and the line plug according to claim 1, which is determined to be 3. The ring pin or tip pin of the jack has a level of D that does not affect the operation of an external device.
The microphone and line plug detection circuit according to claim 2, wherein a C bias is applied. 4. A microphone jack and a line jack
The microphone plug and line plug according to any one of claims 1 to 3, which is a circuit shared by two jacks, for detecting whether a plug of an external device connected to the jack is a microphone plug or a line plug. When the detection circuit of and, and the detection circuit determines that the plug of the external device connected to the jack is the microphone plug, the DC bias is applied to the ring pin or the tip pin of the jack and the external device connected to the jack. And a switch circuit for controlling the DC bias not to be applied to the ring pin and the tip pin of the jack when the plug is determined to be the line plug. 5. A differential amplifier is provided as the comparison circuit and the decision circuit of the detection circuit, and a transistor switch provided between the DC bias and the ring pin or tip pin of the jack is provided as the switch circuit.
Input the output from the ring pin of the jack and the output from the tip pin to the differential amplifier, open the transistor switch when the differential amplifier is LOW output, and open the transistor switch when the differential amplifier is HIGH output. The shared circuit for a jack according to claim 4, wherein the shared circuit is controlled to be closed. 6. When it is determined that the plug of the external device connected to the jack with the LOW output of the differential amplifier is a microphone plug, the mute function of the microphone is turned off, the mute function of the line is turned on, and the differential Amplifier is HIGH
When the plug of the external device connected to the jack is judged to be the line plug at the output, the mute function of the microphone is turned on.
6. The jack common circuit according to claim 5, wherein the line mute function is turned off. 7. An adapter for sharing a microphone jack having a DC bias applied to a ring pin or a tip pin also as a line jack, comprising a system-side plug and an external device-side jack, Of the ring line between the ring part of the plug and the jack ring pin on the external device side, or the tip line between the tip part of the plug on the system side and the tip pin of the jack on the external device side,
An adapter characterized in that a ring line or a tip line to which a DC bias is applied has a mechanism for preventing the DC bias. 8. The adapter according to claim 7, wherein both the ring line and the tip line have a mechanism for preventing DC bias regardless of whether the side to which the DC bias is applied is the ring pin side or the tip pin side. 9. The adapter according to claim 7, wherein the mechanism for preventing the DC bias is a capacitor. 10. A notebook PC, comprising the jack common circuit according to claim 4 mounted therein and one common jack as a microphone jack and a line jack.