Audio transmission system

Abstract

To provide an audio transmission system capable of detecting disconnection while restraining complexity of wiring.SOLUTION: An audio transmission system includes: a master circuit; a slave circuit; one or more microphone modules including a differential output microphone; an input circuit; and an analog / digital converter outputting, to the slave circuit, an audio signal obtained by performing analog / digital conversion on a signal output from the input circuit. The input circuit includes: an operational amplifier having an input side to which a first output terminal and a second output terminal of the differential output microphone are connected and an output side to which an analog / digital converter is connected; a power supply connected to the input side of the operational amplifier and performing phantom power supply; and an output section connected between the input side of the operational amplifier and the slave circuit and outputting a first output voltage to the slave circuit when the differential output microphone is connected to the input circuit, and outputting a second output voltage different from the first output voltage to the slave circuit when the differential output microphone is not connected to the input circuit.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an audio transmission system. [Background technology]

[0002] 2. Description of the Related Art Conventionally, a two-wire communication system such as A2B (Automatic Audio Bus) (registered trademark) is known. This two-wire communication system can be applied to, for example, a vehicle.

[0003] For example, a known method for detecting a disconnection in a microphone module in a two-wire communication system is to provide a dedicated line for each microphone module and detect the disconnection in the microphone module depending on the state of the dedicated line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-150487 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the conventional technology requires the provision of a dedicated line for disconnection detection, which results in a problem of complex wiring.

[0006] An object of the present disclosure is to provide an audio transmission system capable of detecting disconnections while suppressing the complexity of wiring. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the audio transmission system of the present disclosure includes a master circuit, a slave circuit connected to the master circuit via one or more transmission lines, one or more microphone modules including a differential output microphone having a first output terminal and a second output terminal, an input circuit to which a signal from the differential output microphone is input, and an analog / digital converter that outputs an audio signal obtained by analog / digital conversion of the signal output from the input circuit to the slave circuit, wherein the input circuit includes an operational amplifier to whose input side the first output terminal and the second output terminal of the differential output microphone are connected and to whose output side the analog / digital converter is connected, a power supply that is connected to the input side of the operational amplifier and performs phantom power supply, and an output unit that is connected between the input side of the operational amplifier and the slave circuit, and that outputs a first output voltage to the slave circuit when the differential output microphone is connected to the input circuit, and outputs a second output voltage different from the first output voltage to the slave circuit when the differential output microphone is not connected to the input circuit. Effect of the Invention

[0008] According to the present disclosure, since it is not necessary to provide a dedicated line for disconnection detection and disconnection can be detected based on the voltage output from the output unit, it is possible to provide an audio transmission system capable of detecting disconnection while suppressing the complexity of wiring. Note that the effects described here are not necessarily limited to those described herein, and may be any of the effects described in this specification. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a voice transmission system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a state in which the voice transmission system of the first embodiment is mounted on a vehicle. [Diagram 3] FIG. 3 is a diagram for explaining the configuration of the slave board of the first embodiment. [Figure 4]FIG. 4 is a diagram illustrating an example of characteristics of the transistor according to the first embodiment. [Diagram 5] FIG. 5 is a diagram for explaining the configuration of a slave board according to a modified example of the first embodiment. [Figure 6] FIG. 6 is a diagram showing the voltage of the second terminal and the voltage of the collector in the second embodiment. [Figure 7] FIG. 7 is a diagram showing the voltage of the second terminal and the voltage of the collector in the second embodiment. [Figure 8] FIG. 8 is a diagram illustrating an example of the configuration of a DSP according to the second embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of the configuration of the microphone module according to the third embodiment. [Figure 10] FIG. 10 is a diagram illustrating an example of a configuration of an input circuit according to the third embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of a configuration of an input circuit according to the fourth embodiment. [Figure 12] FIG. 12 is a diagram showing a modified example of the output section. [Figure 13] FIG. 13 is a diagram showing a modified example of the output section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an audio transmission system according to an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings.

[0011] [1] First embodiment FIG. 1 is a diagram showing an example of the configuration of a voice transmission system 10 according to the first embodiment. As shown in FIG. 1, the audio transmission system 10 includes a plurality of microphone modules 1A to 1D (four in the example of FIG. 1), a slave board 2, and a master board 3. In the following, when the microphone modules 1A to 1D are not to be distinguished from one another, the final alphabetical letter will be omitted, such as "microphone module 1." The same notation will be used for each element included in the microphone module 1. Note that, although the number of microphone modules 1 is four in the example of FIG. 1, this is not limiting, and the number of microphone modules 1 can be changed as desired depending on the design concept, design conditions, etc.

[0012] FIG. 2 is a diagram showing an example in which the voice transmission system 10 of the present embodiment is mounted on a vehicle 200. As shown in FIG. 2, microphone modules 1A and 1C are disposed on the left side of vehicle 200, and microphone modules 1B and 1D are disposed on the right side of vehicle 100. However, the arrangement of microphone module 1 is not limited to this and can be changed as desired depending on design concepts, design conditions, etc. Furthermore, the device in which audio transmission system 10 of the present embodiment is mounted is not limited to vehicle 200, and the system can be mounted in various devices.

[0013] Continuing the explanation by returning to Fig. 1, each microphone module 1 includes a differential output microphone 103 having a first output terminal 101 and a second output terminal 102. In this embodiment, the voltage supplied to the first output terminal 101 is higher than the voltage supplied to the second output terminal 102. The first output terminal 101 and the second output terminal 102 are connected to an input circuit 201 in the slave board 2, which will be described later.

[0014] Next, the configuration of the slave board 2 will be described. 1, the slave board 2 includes an input circuit 201, an analog / digital converter 202A, an analog / digital converter 202B, and a slave circuit 203. In the following description, when there is no need to distinguish between the analog / digital converter 202A and the analog / digital converter 202B, they will be referred to as the "analog / digital converter 202."

[0015] A signal from the differential output microphone 103 is input to the input circuit 201. More specifically, the input circuit 201 of this embodiment receives signals from each of the differential output microphone 103A included in the microphone module 1A, the differential output microphone 103B included in the microphone module 1B, the differential output microphone 103C included in the microphone module 1C, and the differential output microphone 103D included in the microphone module 1D.

[0016] 3 is a diagram illustrating only a circuit portion of the slave board 2 that corresponds to one microphone module 1 (microphone module 1B in the example of FIG. 3), but the circuit portions corresponding to the other three microphone modules 1 each have a similar configuration. Hereinafter, a specific configuration of the input circuit 201 will be described with reference to FIG. 3.

[0017] The circuit portion of the input circuit 201 that corresponds to the microphone module 1B includes an operational amplifier 204B, a power supply 205, and a transistor 206B. The first output terminal 101B and the second output terminal 102B of the differential output microphone 103B are connected to the input side of the operational amplifier 204B. In this embodiment, the first output terminal 101B is connected to the positive input side of the operational amplifier 204B, and the second output terminal 102B, which is at a lower potential than the first output terminal 101B, is connected to the negative input side of the operational amplifier 204B.

[0018] Furthermore, the analog / digital converter 202A is connected to the output side of the operational amplifier 204B. More specifically, the R channel terminal of the analog / digital converter 202A is connected to the output side of the operational amplifier 204B. With this configuration, the operational amplifier 204B outputs a signal obtained by differentially amplifying the analog audio signals input from the first output terminal 101B and the second output terminal 102B of the corresponding differential output microphone 103B as an analog audio signal of the microphone module 1B to the R channel input terminal of the analog / digital converter 202A.

[0019] In the first embodiment, analog / digital converter 202A is provided corresponding to microphone module 1A and microphone module 1B. More specifically, the output side of operational amplifier 204A included in the circuit portion of input circuit 201 corresponding to microphone module 1A is connected to the L channel terminal of analog / digital converter 202A, and the output side of operational amplifier 204B included in the circuit portion of input circuit 201 corresponding to microphone module 1B is connected to the R channel terminal of analog / digital converter 202A. That is, the analog audio signal of the microphone module 1A is input to the L channel terminal of the analog / digital converter 202A, and the analog audio signal of the microphone module 1B is input to the R channel terminal.

[0020] Similarly, an analog / digital converter 202B (not shown in FIG. 3) is provided corresponding to the microphone module 1C and the microphone module 1D. More specifically, the output side of operational amplifier 204C included in the circuit portion of input circuit 201 corresponding to microphone module 1C is connected to the L channel terminal of analog / digital converter 202B, and the output side of operational amplifier 204D included in the circuit portion of input circuit 201 corresponding to microphone module 1D is connected to the R channel terminal of analog / digital converter 202B.

[0021] That is, the analog audio signal of the microphone module 1C is input to the L channel terminal of the analog / digital converter 202B, and the analog audio signal of the microphone module 1D is input to the R channel terminal.

[0022] In the above configuration, the analog / digital converter 202A and the analog / digital converter 202B are serially connected to a data transmission line. Furthermore, a frame synchronization signal Frame and a bit clock signal Bit_Clock are input from a slave circuit 203 to the analog / digital converter 202A and the analog / digital converter 202B for time division multiplexing.

[0023] Then, the analog / digital converter 202A performs frame synchronization based on the frame synchronization signal Frame and the bit clock signal Bit_Clock and writes data into the frame data one bit at a time, thereby assigning the R channel digital audio signal and the L channel digital audio signal to the multiple time slots assigned to the analog / digital converter 202A and sending it to the analog / digital converter 202B as frame data.

[0024] More specifically, in this first embodiment, the digital audio signal of microphone module 1A (digital audio signal of the L channel) and the digital audio signal of microphone module 1B (digital audio signal of the R channel) are assigned to two time slots of frame data corresponding to the L channel digital audio signal and the R channel digital audio signal assigned to analog / digital converter 202A.

[0025] Then, the analog / digital converter 202B, which receives the frame data from the analog / digital converter 202A, assigns the R channel digital audio signal and the L channel digital audio signal to the multiple time slots assigned to the analog / digital converter 202B that make up the frame data input from the analog / digital converter 202A based on the frame synchronization signal Frame and the bit clock signal Bit_Clock, and sends the completed frame data to the slave circuit 203.

[0026] More specifically, in this first embodiment, the digital audio signal of microphone module 1C (digital audio signal of the L channel) and the digital audio signal of microphone module 1D (digital audio signal of the R channel) are assigned to two time slots of frame data corresponding to the L channel digital audio signal and the R channel digital audio signal assigned to analog / digital converter 202B, and are sent to slave circuit 203 as completed frame data. As a result, the slave circuit 203 outputs a multiplexed digital audio signal to the master board 3.

[0027] Continuing with the explanation of the input circuit 201, in the example of Fig. 3, the power supply 205 is connected to the input side of the operational amplifier 204B and performs phantom power supply. In the example of FIG. 3, the non-inverting input terminal of operational amplifier 204B is connected to power supply 205 via phantom resistor R1031, while the inverting input terminal of operational amplifier 204B is grounded via phantom resistor R1032.

[0028] The transistor 206B is connected between the input side of the operational amplifier 204 and the slave circuit 203. The transistor 206B is an example of an "output section" that outputs a first output voltage to the slave circuit 203 when the differential output microphone 103 is connected to the input circuit 201, and outputs a second output voltage different from the first output voltage to the slave circuit 203 when the differential output microphone 103 is not connected to the input circuit 201.

[0029] In this case, when the differential output microphone 103 is not connected to the input circuit 201, this includes cases where the differential output microphone 103 cannot output an audio analog signal normally, such as when the output terminal of the differential output microphone 103 is not physically connected to the input circuit 201, or when it is not electrically connected due to a broken wire, etc.

[0030] Depending on the type of transistor 206, one of the first output terminal 101B and the second output terminal 102B is connected to the base or gate of a transistor 206B, and the collector or drain serving as an output terminal of the transistor 206B is connected to the slave circuit 203. Here, the types of transistors refer to NPN bipolar transistors, PNP bipolar transistors, N-channel MOS transistors, P-channel MOS transistors, and the like.

[0031] In the first embodiment, the transistor 206B is an NPN type bipolar transistor. Therefore, in the example of FIG. 3, of the first output terminal 101B and the second output terminal 102B, the second output terminal 102B which is on the lower potential side is connected to the base of the transistor 206B.

[0032] Furthermore, when the differential output microphone 103 is connected to the input circuit 201, the voltage of the second output terminal 102B is set to be greater than the threshold (voltage) of the transistor 206B. That is, the transistor 206B is set to be in an on state, and a connection detection signal of the differential output microphone 103 is output.

[0033] In this embodiment, when the differential output microphone 103 and the input circuit 201 are connected, i.e., when the first output terminal 101B and the second output terminal 102B are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 204B, respectively, the values ​​of the voltage of the second output terminal 102B, the voltage of the power supply 205, the resistor R1031 and the resistor R1032 are set so that the voltage of the second output terminal 102B is greater than the threshold of the transistor 206B.

[0034] FIG. 4 is a diagram showing an example of the characteristics of the transistor 206B of the present embodiment. In the example of FIG. 4, the voltage of the base as a control input terminal is represented on the horizontal axis as an input voltage, and the voltage of the collector as an output terminal is represented on the vertical axis as an output voltage.

[0035] In the example of FIG. 4, the threshold voltage of the transistor 206B is about 0.7 V. When the base voltage (input voltage) is less than 0.7 V, the transistor 206B is turned off and the collector voltage (output voltage) becomes the same potential as the power supply voltage Vdd.

[0036] In the example of Fig. 3, the collector voltage as the output terminal at this time is about 3.3V. On the other hand, when the base voltage is 0.7V or more, the transistor 206B is turned on, and the collector is grounded and has the same potential as the ground potential GND (0V in this example). In the example of Fig. 3, the collector voltage at this time is 0V.

[0037] Continuing with the explanation of Fig. 3. In this embodiment, the voltage of the power supply 205 is, for example, 8V, and when the differential output microphone 103B is connected to the input circuit 201 (when the first output terminal 101B and the second output terminal 102B are operatively connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 204B via smoothing capacitors, respectively), the voltage of the second output terminal 102B is set to 2V. In this case, the voltage of the second output terminal 102B input to the gate of the transistor 206B exceeds the threshold value (0.7V), so that the transistor 206B is turned on.

[0038] On the other hand, when the differential output microphone 103B is not connected to the input circuit 201 and is disconnected (when the second output terminal 102B is not connected to the non-inverting input terminal of the operational amplifier 204B), the base of the transistor 206B is grounded via the resistor R1032 and has the same potential as the ground potential GND. As a result, the voltage of the gate of the transistor 206B becomes approximately 0 V and falls below the threshold, so that the transistor 206B is turned off.

[0039] 3, the collector (an example of an "output terminal") of transistor 206B is connected to slave circuit 203. As described above, when differential output microphone 103B and input circuit 201 are connected, transistor 206B is turned on, so that the collector is grounded and has the same potential as ground potential GND, and ground potential GND is output to slave circuit 203 as the first output voltage.

[0040] Furthermore, as described above, when the differential output microphone 103B and the input circuit 201 are not connected and are disconnected, the transistor 206B is turned off. As a result, a voltage dropped from the power supply voltage Vdd by the amount of the resistor R1 interposed between the power supply and the collector of the transistor 206B is output as the second output voltage from the collector of the transistor 206B to the slave circuit 203. In the following description, the voltage (first output voltage or second output voltage) output from the collector to the slave circuit 203 may be referred to as a GPIO signal (GPIO0 to GPIO3 in FIG. 1).

[0041] The slave circuit 203 outputs, in addition to the above-mentioned digital audio signal, a GPIO signal output from the collector of the transistor 206 provided for each microphone module 1 to the master board 3. This concludes the description of the configuration of the slave board 2.

[0042] Returning to Fig. 1, the following describes the configuration of the master board 3. As shown in Fig. 1, the master board 3 includes a master circuit 301, a signal processing circuit (hereinafter referred to as "DSP") 302, an output circuit 303, and a communication circuit 304.

[0043] The master circuit 301 outputs the digital audio signal and the GPIO signal received from the slave circuit 203 to the DSP 302. The DSP 302 has a function (determination unit) of determining, based on the GPIO signal for each microphone module 1, whether or not the microphone module 1 (differential output microphone 103) and the input circuit 201 are connected.

[0044] More specifically, when the GPIO signal input from the master circuit 301 indicates a first output voltage, the judgment unit judges that the differential output microphone 103 and the input circuit 201 are connected, and when the GPIO signal indicates a second output voltage, the judgment unit judges that the differential output microphone 103 is not connected to the input circuit 201.

[0045] In this embodiment, the judgment unit is provided in DSP 302, but this is not limited thereto. For example, the judgment unit may be provided in master circuit 301, or may be provided on the slave board 2 side (for example, slave circuit 203, etc.).

[0046] The DSP 302 connected to the master circuit 301 performs processing such as filtering on the digital audio signal input from the master circuit 301 , generates data according to the output format, and passes it to the output circuit 303 .

[0047] The output circuit 303 outputs the data input from the DSP 302 to devices such as the speaker 4. The output circuit 303 can also output the data input from the DSP 302 to the outside via the communication circuit 304.

[0048] [1.1] Modification of the first embodiment FIG. 5 is a diagram for explaining the configuration of a slave board according to a modified example of the first embodiment. In FIG. 5, the same parts as those in FIG. 3 are denoted by the same reference numerals. 5, like FIG. 3, illustrates only a circuit portion of the slave board 2X that corresponds to one microphone module 1 (microphone module 1B in the example of FIG. 5). The circuit portions corresponding to the other three microphone modules 1 each have a similar configuration. Hereinafter, a specific configuration of the input circuit 201X will be described with reference to FIG. 5.

[0049] The circuit portion of the input circuit 201X that corresponds to the microphone module 1B includes an operational amplifier 204B, a power supply 205, and a transistor 206B. The first output terminal 101B and the second output terminal 102B of the differential output microphone 103B are connected to the input side of the operational amplifier 204B. In this embodiment, the first output terminal 101B is connected to the positive input side of the operational amplifier 204B, and the second output terminal 102B, which is at a lower potential than the first output terminal 101B, is connected to the negative input side of the operational amplifier 204B.

[0050] Furthermore, the analog / digital converter 202A is connected to the output side of the operational amplifier 204B. More specifically, the R channel terminal of the analog / digital converter 202A is connected to the output side of the operational amplifier 204B. With this configuration, the operational amplifier 204B outputs a signal obtained by differentially amplifying the analog audio signals input from the first output terminal 101B and the second output terminal 102B of the corresponding differential output microphone 103B as an analog audio signal of the microphone module 1B to the R channel input terminal of the analog / digital converter 202A.

[0051] Then, the analog / digital converter 202A performs frame synchronization based on the frame synchronization signal Frame and the bit clock signal Bit_Clock and writes data into the frame data one bit at a time, thereby assigning the R channel digital audio signal and the L channel digital audio signal to the multiple time slots assigned to the analog / digital converter 202A and sending it to the analog / digital converter 202B as frame data.

[0052] Then, the analog / digital converter 202B, which receives the frame data from the analog / digital converter 202A, assigns the R channel digital audio signal and the L channel digital audio signal to the multiple time slots assigned to the analog / digital converter 202B that make up the frame data input from the analog / digital converter 202A based on the frame synchronization signal Frame and the bit clock signal Bit_Clock, and sends the completed frame data to the slave circuit 203. As a result, the slave circuit 203 outputs a multiplexed digital audio signal to the master board 3.

[0053] The explanation of the input circuit 201X will continue. In the example of FIG. 5 as well, the power supply 205 is connected to the input side of the operational amplifier 204B and performs phantom power supply. Also in the example of FIG. 5, the non-inverting input terminal of operational amplifier 204B is connected to power supply 205 via phantom resistor R1031, and the inverting input terminal of operational amplifier 204B is grounded via phantom resistor R1032.

[0054] The transistor 206BX is connected between the input side of the operational amplifier 204 and the slave circuit 203. The transistor 206B is an example of an "output section" that outputs a first output voltage to the slave circuit 203 when the differential output microphone 103 is connected to the input circuit 201, and outputs a second output voltage different from the first output voltage to the slave circuit 203 when the differential output microphone 103 is not connected to the input circuit 201.

[0055] The first output terminal 101B is connected to the base serving as a control input terminal of the transistor 206BX, and the collector serving as an output terminal of the transistor 206BX is connected to the slave circuit 203 via the resistor R11 of the voltage dividing resistors R11 and R12.

[0056] In the modification of the first embodiment, the transistor 206BX is a PNP-type bipolar transistor. In the example of FIG. 5, of the first output terminal 101B and the second output terminal 102B, the first output terminal 101B on the higher potential side is connected to the base of the transistor 206BX as a control input terminal.

[0057] Furthermore, when the differential output microphone 103 is connected to the input circuit 201, the voltage of the first output terminal 101B is set to be smaller than the threshold of the transistor 206BX. In other words, the transistor 206BX is set to be in the on state.

[0058] In a modified example of the first embodiment, when the differential output microphone 103 is connected to the input circuit 201, i.e., when the first output terminal 101B and the second output terminal 102B are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 204B, respectively, the values ​​of the voltage of the first output terminal 101B, the voltage of the power supply 205, the resistor R1031 and the resistor R1032 are set so that the voltage of the first output terminal 101B is smaller than the threshold of the transistor 206B.

[0059] As described above, in the first embodiment or the modified example of the first embodiment, the slave board 2 is provided with the input circuit 201, and the input circuit 201 is provided with a transistor 206 for each differential output microphone 103. One of the first output terminal 101 and the second output terminal 102 of the differential output microphone 103 is connected to the base of the transistor 206 as a control input terminal, and the collector of the transistor 206 as an output terminal is connected to the slave circuit 203.

[0060] Then, the transistor 206 outputs a first output voltage to the slave circuit 203 when the differential output microphone 103 is connected to the input circuit 201, and outputs a second output voltage to the slave circuit 203 when the differential output microphone 103 is not connected to the input circuit 201. In other words, the output voltage of the transistor 206 differs depending on whether the differential output microphone 103 and the input circuit 201 are connected or not.

[0061] That is, by checking the output voltage, it is possible to determine whether or not the differential output microphone 103 is connected to the input circuit 201 . Therefore, according to this embodiment, there is no need to set up a dedicated line for disconnection detection, and disconnection can be detected based on the voltage output from transistor 206, so it is possible to provide an audio transmission system 1 that can detect disconnection while suppressing the complexity of wiring.

[0062] Also, in the above description, the transistor 206 (transistor 206X) is a bipolar transistor, but it is also possible to configure the transistor 206 to be an N-channel MOS transistor or a P-channel MOS transistor.

[0063] [2] Second embodiment Next, a second embodiment will be described. The second embodiment differs from the first embodiment in that the DSP 302 prohibits the determination unit from making a determination when the audio level of the audio signal (digital audio signal) input from the master circuit 301 is greater than the threshold value.

[0064] FIG. 6 is a diagram showing the voltage at the second output terminal 102 and the voltage at the transistor 206 (collector voltage) when the operating region of the microphone module 1 is in a linear region in which the sound level of the input sound and the output voltage of the microphone module 1 are proportional to each other.

[0065] 6, since the voltage of the second output terminal 102 exceeds the threshold of the transistor 206, the transistor 206 is turned on, the collector is grounded, and the ground potential GND (approximately 0 V in this example) is output as the first output voltage. In this case, since the GPIO signal indicates the first output voltage, it is determined that the microphone module 1 is in a connected state, that is, the differential output microphone 103 is connected to the input circuit 201.

[0066] Figure 7 is a diagram showing the voltage at the second output terminal 102 and the voltage at the transistor 206 when the operating region of the microphone module 1 is in a saturation region where the sound level of the input sound and the output voltage of the microphone module 1 are not proportional to each other and the output voltage becomes constant above a certain sound level.

[0067] In the example of Figure 7, there is a period during which the minimum voltage of the second output terminal 102 is below the threshold of the transistor 206, and therefore there is a period during which the transistor 206 is in the off state, and the collector voltage becomes the second output voltage (>0V) that is dropped by the resistor R1 from the power supply voltage Vdd of the transistor 206B.

[0068] In this case, even if the microphone module 1 is in a connected state, the GPIO signal indicates the second output voltage during a period in which the minimum voltage of the second output terminal 102 is below the threshold of the transistor 206, and it is determined that the differential output microphone 103 and the input circuit 201 are not connected. In other words, when the microphone module 1 is in the saturation region, an erroneous determination occurs in determining whether or not the microphone module 1 is in a connected state (connection determination).

[0069] Therefore, in the second embodiment, when the microphone module 1 is in the saturation region, that is, when the audio signal level corresponding to the digital audio signal output from the slave circuit 203 (the digital audio signal input to the master circuit 301) is greater than a threshold value, the DSP 302 can prevent the above-mentioned erroneous detection by disabling the judgment by the judgment unit.

[0070] 8, the DSP 302 may include a buffer (gate) 2021 and a level detection unit 2022. When the GPIO signal is less than a predetermined reference value, the level detection unit 2022 outputs an enable signal that sets the buffer 2021 in an operable state (enabled state).

[0071] In this example, the second output voltage is set to a value greater than the reference value, so that when the second output voltage is input as a GPIO signal to the buffer 2021, the buffer 2021 outputs a high-level signal. In this example, the buffer 2021 outputting a high-level signal means that a non-connected state (disconnection) of the microphone module 1 has been detected.

[0072] The level detection unit 2022 receives a digital audio signal from the master circuit 301. When the audio signal level corresponding to the digital audio signal received from the master circuit 301 is greater than a threshold value, the level detection unit 2022 outputs an enable signal to the buffer 2021 to disable the output of the buffer 2021 (for example, to put the output terminal into a high impedance state), and stops the output operation of the buffer 2021.

[0073] As described above, according to the second embodiment, even if the operating region of the microphone module 1 is in the saturated region, the connection state of the microphone module 1 can be accurately determined, thereby preventing erroneous determination of the connection.

[0074] [3] Third embodiment Next, a third embodiment will be described. As shown in Figure 9 or Figure 10, the third embodiment further includes a Zener diode 501 connected between the first output terminal 101 and the second output terminal 102, and the Zener voltage of the Zener diode 501 is set so that the voltage of the first output terminal 101 or the second output terminal 102 connected to the gate of the transistor 206 is within a range that maintains the operating state of the transistor 206 when the differential output microphone 103 and the input circuit 201 are connected.

[0075] As in the first embodiment described above, when the transistor 206 is an NPN bipolar transistor, the second output terminal 102 which is on the lower potential side of the first output terminal 101 and the second output terminal 102 is connected to the base of the transistor 206.

[0076] The Zener voltage of the Zener diode 501 is set so that the minimum value of the voltage of the second output terminal 102, which is connected to the base of the transistor 206, of the first output terminal 101 and the second output terminal 102 exceeds the threshold value of the transistor 206. In this example, since the operating state of the transistor 206 when the differential output microphone 103 and the input circuit 201 are connected is the on state, the Zener voltage is set so that the minimum value of the voltage of the second output terminal 102 exceeds the threshold value of the transistor 206.

[0077] 3, the phantom resistors R1031 and R1032 of the power supply 205 that supplies phantom power are generally set to the same resistance value. Also, the base sink current of the transistor 206 is assumed to be negligibly small compared to the current flowing through the phantom resistor R1032.

[0078] This makes the currents flowing through the resistors R1031 and R1032 equal. When the Zener voltage Vz is set to an appropriate value equal to or less than the voltage Pоwer of the power supply 205, the maximum voltage of the first output terminal 101 and the minimum voltage of the second output terminal 102 can be expressed by the following Equations 1 and 2, respectively. Maximum voltage of the first output terminal 101 = (Power + Vz) / 2 (Equation 1) Minimum voltage of the second output terminal 102=(Power-Vz) / 2 (Equation 2)

[0079] In the third embodiment, by setting the Zener voltage Vz so that the minimum voltage of the second output terminal 102 expressed by the above formula 2 exceeds the threshold value of the transistor 206, the transistor 206 maintains the ON state even when the operating region of the microphone module 1 is in the saturation region. In other words, even if the operating region of the microphone module 1 is in the saturation region, the operating state of the transistor 206 maintains the ON state when the differential output microphone 103 and the input circuit 201 are connected, so that the collector is grounded and the ground potential GND (0 V in this example) is output as the first output voltage. In this case, since the GPIO signal indicates the first output voltage, it is determined that the microphone module 1 is connected to the input circuit 201.

[0080] That is, according to the third embodiment, similarly to the second embodiment, even if the operating region of the microphone module 1 is in the saturated region, the connection state of the microphone module 1 can be accurately determined, thereby preventing erroneous determination of the connection.

[0081] 9, the Zener diode 501 may be provided in the microphone module 1. Also, the Zener diode 501 may be provided in the input circuit 201, for example, as shown in FIG.

[0082] [4] Fourth embodiment Next, a fourth embodiment will be described. The fourth embodiment differs from the above-mentioned embodiments in that a resistor for adjusting the threshold of the transistor 206 is provided. As shown in FIG. 11, a first resistor R11 is connected to the gate of the transistor 206. This first resistor R11 is also provided in the above-mentioned embodiments. As shown in FIG. 11, this embodiment further includes a second resistor R1033 connected in series with the first resistor R11, and a third resistor R1034 having one end connected to the connection point between the first resistor R11 and the second resistor R1033 and the other end connected to the power supply Vdd.

[0083] As in the above-described embodiments, the transistor 206 is an NPN bipolar transistor. In the fourth embodiment, the resistance values ​​of the first resistor R11, the second resistor R1033, and the third resistor R1034 are set so that the threshold of the transistor 206 is lower than the minimum value of the voltage of the second output terminal 102 connected to the gate of the transistor 206.

[0084] As a result, even if the microphone module 1 is in the saturation region, the operating state of the transistor 206 when the differential output microphone 103 and the input circuit 201 are connected is maintained in the on state, so that the GPIO signal indicates the first output voltage in the same manner as above, and the microphone module 1 is determined to be in a connected state. In other words, even if the microphone module 1 is in the saturation region, erroneous determination of the connection can be prevented.

[0085] Although the embodiments of the present disclosure have been described above, the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These novel embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0086] Furthermore, the effects of the embodiments described in this specification are merely examples and are not limiting, and other effects may also be obtained.

[0087] [5] Other variations of the embodiment Other variations of the embodiment will be described below.

[0088] [5.1] First other variant In each of the above-described embodiments, the transistor 206 is used as an example of the “output unit”. However, the present invention is not limited to this. For example, as shown in FIG. 12, a comparator 207B may be used as the “output unit”. In the example of FIG. 12, a reference voltage is input to the inverting input terminal of the comparator 207B via a voltage dividing resistor, and the second output terminal 102B is connected to the non-inverting input terminal. The output side of the comparator 207 B is connected to the slave circuit 203 .

[0089] As a result, when the differential output microphone 103B is connected to the input circuit 201, the voltage at the non-inverting input terminal of the comparator 207B becomes lower than the reference voltage input to the inverting input terminal, so that the output of the comparator 207B becomes low level and a GPIO signal indicating a low level is output to the slave circuit 203.

[0090] On the other hand, when the differential output microphone 103B is not connected to the input circuit 201, the output of the comparator 207B becomes high level, and the voltage of the non-inverting input terminal of the comparator 207B becomes higher than the reference voltage input to the inverting input terminal, so that a GPIO signal indicating a high level is output to the slave circuit 203.

[0091] 12, the output voltage level (high level or low level) of comparator 207B differs depending on whether differential output microphone 103 is connected to input circuit 201, and therefore by checking this output voltage, it is possible to determine whether differential output microphone 103 is connected to input circuit 201. In other words, according to the configuration of Fig. 12, there is no need to provide a dedicated line for disconnection detection, and disconnection can be detected based on the voltage output from comparator 207B, making it possible to provide audio transmission system 1 that is capable of detecting disconnection while suppressing the complexity of wiring.

[0092] [5.2] Second other variant Also, for example, as shown in FIG. 13, a microcomputer 208B may be employed as the "output section." 13, the microcomputer 208B includes an analog / digital converter (referred to as "ADC") 2081 and an I / O port 2082. The voltage of the second output terminal 102B is input to the ADC 2081, and the ADC 2081 converts the input analog voltage signal into a digital voltage signal. The I / O port 2082 outputs the digital voltage signal input from the ADC 2081 to the slave circuit 203.

[0093] 13, the output voltage of I / O port 2082 differs depending on whether differential output microphone 103 is connected to input circuit 201, and by checking this output voltage, it is possible to determine whether differential output microphone 103 is connected to input circuit 201. In other words, according to the configuration of Fig. 13, there is no need to provide a dedicated line for disconnection detection, and disconnection can be detected based on the voltage output from comparator 207B, making it possible to provide audio transmission system 1 that is capable of detecting disconnection while suppressing the complexity of wiring.

[0094] In short, the "output unit" may be configured to be connected between the input side of the operational amplifier 204 and the slave circuit 203, and to output a first output voltage to the slave circuit 203 when the differential output microphone 103 and the input circuit 201 are connected, and to output a second output voltage different from the first output voltage to the slave circuit 203 when the differential output microphone 103 and the input circuit 201 are not connected. For example, as described above, the "output unit" may be the transistor 206, the comparator 207, or the microcomputer 208.

[0095] The above-described embodiment may be arbitrarily combined with the above-described modified examples, or the above-described modified examples may be arbitrarily combined with each other. Also, the above-described embodiments may be arbitrarily combined with each other. [Explanation of symbols]

[0096] 1. 1A~1D Microphone Module 2 Slave Board 3 Master Board 10. Audio Transmission System 101, 101A~101D 1st output terminal 102, 102A~102D 2nd output terminal 103, 103A~103D Differential output microphones 201 Input circuit 202 Analog / Digital Converter 203 Slave Circuit 204 Operational Amplifier 205 Power supply 206, 206B, 206BX transistors 207 Comparator 208 Microcomputer 301 Master Circuit 302 DSP 303 Output circuit 304 Communication Circuits R11 First Resistor R1033 Second Resistor R1034 The Third Resistance

Claims

1. A master circuit, a slave circuit connected to the master circuit via one or more transmission lines; one or more microphone modules including a differential output microphone having a first output terminal and a second output terminal; an input circuit to which a signal from the differential output microphone is input; an analog / digital converter that performs analog / digital conversion on a signal output from the input circuit and outputs an audio signal to the slave circuit; The input circuit includes: an operational amplifier having an input side connected to the first output terminal and the second output terminal of the differential output microphone and an output side connected to the analog / digital converter; a power supply connected to an input side of the operational amplifier and performing phantom power supply; an output section connected between an input side of the operational amplifier and the slave circuit, and which outputs a first output voltage to the slave circuit when the differential output microphone is connected to the input circuit, and outputs a second output voltage different from the first output voltage to the slave circuit when the differential output microphone is not connected to the input circuit; Audio transmission system.

2. a determination unit that determines that the differential output microphone is connected to the input circuit when the first output voltage is output from the output unit, and that the differential output microphone and the input circuit are not connected when the second output voltage is output from the output unit; 2. The audio transmission system according to claim 1.

3. the output section is a transistor, one of the first output terminal and the second output terminal is connected to a control input terminal of the transistor, and an output terminal of the transistor is connected to the slave circuit; 3. The audio transmission system according to claim 1 or 2.

4. The transistor constituting the output section is an NPN type transistor, a PNP type transistor, an N-channel MOS transistor, or a P-channel MOS transistor, Either the first output terminal or the second output terminal is connected to a control input terminal of the transistor, and a voltage of an output terminal connected to the control input terminal is set to a voltage that can maintain an on-state with respect to a threshold voltage of the transistor.

4. The audio transmission system according to claim 3.

5. A signal processing circuit connected to the master circuit is further provided. The signal processing circuit prohibits the determination unit from making a determination when the audio signal is greater than a threshold value.

3. The audio transmission system according to claim 2.

6. a Zener diode connected between the first output terminal and the second output terminal; a Zener voltage of the Zener diode is set so that a voltage of the output terminal connected to the control input terminal, out of the first output terminal and the second output terminal, is within a range that maintains the on-state of the transistor when the differential output microphone and the input circuit are connected.

4. The audio transmission system according to claim 3.

7. When the transistor is an NPN-type transistor, the output terminal on the low potential side of the first output terminal or the second output terminal is connected to a control input terminal of the transistor, a Zener voltage of the Zener diode is set so that a minimum value of a voltage of the output terminal connected to the control input terminal of the transistor, either the first output terminal or the second output terminal, exceeds a threshold value of the transistor.

7. The audio transmission system according to claim 6.

8. The Zener diode is provided in the input circuit.

7. The audio transmission system according to claim 6.

9. The Zener diode is provided in the microphone module.

7. The audio transmission system according to claim 6.

10. a first resistor connected to a control input terminal of the transistor; a second resistor connected in series with the first resistor; a third resistor having one end connected to the connection point between the first resistor and the second resistor and the other end connected to a power source; 8. The audio transmission system according to claim 7.

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