Impedance adjusting device for audio system

Abstract

To realize a device which can transmit an audio signal output from an audio signal output device and can set an output destination of the audio signal output device in a low impedance state, while suppressing power consumption.SOLUTION: An impedance adjustment device 1 includes: an adjustment unit 10 for adjusting an impedance between a first signal line 121 and a second signal line 122; and a transmission unit 40 for transmitting an audio signal input via the first signal line 121 and the second signal line 122. The adjustment unit 10 sets the impedance between the first signal line 121 and the second signal line 122 to be low during an initial period after an amplifier unit 112 starts operating, and changes the impedance between the first signal line 121 and the second signal line 122 to a high impedance, which is higher than the low impedance, after the initial period has elapsed. The transmission unit 40 is capable of transmitting the audio signal in a state where the impedance between the first signal line 121 and the second signal line 122 is being set to be high after the initial period has elapsed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an impedance adjustment device for an audio system. [Background technology]

[0002] The audio system disclosed in Patent Document 1 includes a sound source unit and a BTL amplifier in a head unit. In this audio system, an audio signal generated by the sound source unit is amplified by the BTL amplifier and output, and the signal is input to a speaker, from which sound is output. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-12370 A Summary of the Invention [Problem to be solved by the invention]

[0004] A configuration as shown in Fig. 5 is widely known as a typical audio system. The audio system in Fig. 5 is configured to provide an audio signal from an audio signal output device such as an in-vehicle deck or an in-vehicle navigation system to a speaker, and to emit audio corresponding to the audio signal from the speaker. In such a system, it is assumed that an audio signal is provided to a speaker having an impedance of, for example, about 2Ω to 8Ω, and therefore audio output from the amplifier is performed on the premise that the output destination has low impedance.

[0005] On the other hand, in some cases, it is desirable to provide an external amplifier in addition to the audio signal output device in the audio system. In order to meet such a requirement, an intermediate device having an amplifier function is provided between the audio signal output device and the speaker, as shown in FIG. 6. The audio system in FIG. 6 includes a converter and an amplifier (external amplifier) ​​as intermediate devices, and the converter converts the audio signal output from the audio signal output device to reduce its level, and provides the converted signal to the amplifier. The amplifier amplifies the converted audio signal provided by the converter and outputs it to the speaker. Note that the example in FIG. 6 is merely an example, and there may be other situations in which an audio system is constructed by combining an audio signal output device and an external amplifier. As an example, there may be a case in which an audio system is constructed by combining a non-genuine audio signal output device with a vehicle equipped with a genuine external amplifier.

[0006] However, when an audio system is constructed by combining an audio signal output device with an external amplifier device, some audio signal output devices do not properly output audio signals from their amplifier units if the output destination from the amplifier unit is in a high impedance state. If the audio signal output device is such a device, even if an audio system is constructed with a new combination, the audio signal output device will not properly output audio signals due to the output destination from the amplifier unit being in a high impedance state, and sound will not be output normally from the speakers.

[0007] The inventors of the present application have envisaged a method of always keeping the output path from the amplifier section low impedance as a method of solving such problems. The configuration of FIG. 7 is one example of such a method, and is an application of the above-mentioned solution to the example of FIG. 6. In the configuration of FIG. 7, a low-impedance component (e.g., a resistive element with a low resistance value) is always connected to the output path from the amplifier section, and the presence of such a low-impedance component allows the audio signal output device to recognize that the output destination of the amplifier section is low impedance. However, the configuration of FIG. 7 has a problem in that the resistive element with a low resistance value is always in a conductive state during the operation of the amplifier section, which makes it impossible to avoid an increase in current consumption and makes it easy for heat to be generated.

[0008] One of the objectives of the present disclosure is to realize an apparatus that can transmit an audio signal output from an audio signal output device and can put the output destination of the audio signal into a low impedance state in a manner that can reduce current consumption. [Means for solving the problem]

[0009] An impedance adjusting device for an audio system according to the present disclosure includes: The present invention is used in an audio system in which an audio signal is transmitted from an audio signal output device having an amplifier section through a signal transmission path having a first signal line and a second signal line, an adjustment unit that adjusts the impedance between the first signal line and the second signal line; a transmission unit that transmits the audio signal input via the first signal line and the second signal line; having the adjustment unit sets a predetermined low impedance between the first signal line and the second signal line during an initial period after the amplifier unit starts operating, and changes the impedance between the first signal line and the second signal line to a high impedance higher than the low impedance after the initial period has elapsed; The transmission section may transmit the audio signal in a state in which the first signal line and the second signal line are in the high impedance state after the initial period has elapsed. Effect of the Invention

[0010] According to the technology disclosed herein, it is possible to realize a device that can transmit an audio signal output from an audio signal output device and can put the output destination of the audio signal into a low impedance state in a manner that can suppress current consumption. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is an explanatory diagram conceptually illustrating an audio system in which an impedance adjustment device according to a first embodiment is used. [Diagram 2] FIG. 2 is a circuit diagram illustrating an internal configuration of the impedance adjustment device according to the first embodiment. [Diagram 3] FIG. 3 is a circuit diagram illustrating an internal configuration of an adjustment unit in the impedance adjustment device of FIG. [Figure 4] FIG. 4 is an explanatory diagram showing an example in which the impedance adjustment device according to the first embodiment is used in an audio system different from that in FIG. [Diagram 5] FIG. 5 is an explanatory diagram illustrating a simplified example of a conventional audio system. [Figure 6] FIG. 6 is an explanatory diagram showing a simplified example in which the audio system of FIG. 5 is modified to include an external amplifier. [Figure 7] FIG. 7 is an explanatory diagram showing a simplified example in which the audio system of FIG. 6 is modified to include a resistive element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Each of the following [1] to [4] is an example of a characteristic technique included in this disclosure.

[0013] [1] An audio system in which an audio signal is transmitted from an audio signal output device having an amplifier section through a signal transmission path having a first signal line and a second signal line, an adjustment unit that adjusts the impedance between the first signal line and the second signal line; a transmission unit that transmits the audio signal input via the first signal line and the second signal line; having the adjustment unit sets a predetermined low impedance between the first signal line and the second signal line during an initial period after the amplifier unit starts operating, and changes the impedance between the first signal line and the second signal line to a high impedance higher than the low impedance after the initial period has elapsed; The transmission unit may transmit the audio signal in a state in which the first signal line and the second signal line are in the high impedance state after the initial period has elapsed. Impedance adjustment device for audio systems.

[0014] The impedance adjustment device of [1] above can transmit an audio signal output from an audio signal output device, and can set the output destination of the audio signal to a low impedance state during the initial period.The impedance adjustment device of [1] above can change the output destination of the audio signal to a high impedance state after the initial period has elapsed, and therefore can suppress current consumption after the initial period has elapsed.

[0015] The impedance adjustment device of [1] above is particularly effective in the following cases, for example. Among currently available audio signal output devices, there are devices in which an audio signal is not properly output from the amplifier when the output destination from the amplifier is in a high impedance state. The inventor of the present application analyzed and verified this type of audio signal output device and confirmed that there are some devices in which an audio signal is properly output even if the output destination is changed to a high impedance after the initial period has elapsed, as long as the output destination is set to a low impedance in the initial period after the amplifier starts operating. The impedance adjustment device of [1] above is useful when used as the output destination of such an audio signal output device. In other words, when the output source of an audio signal is such an audio signal output device, the impedance adjustment device of [1] above can set the impedance between the first signal line and the second signal line to a low impedance in the initial period after the amplifier starts operating, so that the audio signal can be normally output from the amplifier. Then, after the initial period has elapsed, the impedance between the first signal line and the second signal line changes to a high impedance, so that the current consumption is suppressed, and the audio signal can be transmitted by the transmission unit in that state.

[0016] [2] The audio signal output device sets the first signal line and the second signal line to a first potential state during a period in which the operation of the amplifier unit is stopped, and changes the first signal line and the second signal line to a second potential state in response to the start of operation of the amplifier unit; The adjustment unit changes the state between the first signal line and the second signal line to the high impedance a predetermined time after the first signal line and the second signal line are changed to the second potential state. An impedance adjustment device for an audio system as described in [1].

[0017] The impedance adjustment device of [2] above can change the impedance between the first signal line and the second signal line to high impedance at an accurate timing a predetermined time after the amplifier unit starts operating. Therefore, the period (initial period) during which the impedance between the first signal line and the second signal line is low can be accurately determined within a certain period from the amplifier unit starts operating.

[0018] [3] The adjustment unit maintains the low impedance between the first signal line and the second signal line during a power-off period when the audio signal output device is not powered on, and when the audio signal output device is powered on, maintains the low impedance between the first signal line and the second signal line and then switches to the high impedance after the initial period has elapsed. An impedance adjusting device for an audio system according to [1] or [2].

[0019] The impedance adjustment device of [3] above can maintain a low impedance between the first signal line and the second signal line before and after power is applied to the audio signal output device, so there is no need to change the impedance before and after power is applied to the audio signal output device or after the amplifier section starts operating, which makes it possible to reduce the complexity of control.

[0020] [4] During a power-off period in which the audio signal output device is not powered on, the adjustment unit sets an impedance between the first signal line and the second signal line to be higher than the low impedance, and when the audio signal output device is powered on, the adjustment unit maintains the low impedance between the first signal line and the second signal line and then switches to the high impedance after the initial period has elapsed. An impedance adjusting device for an audio system according to [1] or [2].

[0021] The impedance adjustment device of [4] above can maintain a high impedance between the first signal line and the second signal line during the power-off period of the audio signal output device, thereby suppressing a large current from flowing between the first signal line and the second signal line for some reason during the power-off period. On the other hand, when the audio signal output device is powered on, the impedance between the first signal line and the second signal line can be changed to a low impedance, thereby making it possible to bring the signal line into a low impedance state at an appropriate time to match the initial period.

[0022] First Embodiment The following description relates to the first embodiment. 1. Overview of Audio System 100 1 illustrates an in-vehicle audio system 100 as an example of an audio system in which the impedance adjusting device 1 according to the first embodiment is used. The in-vehicle audio system 100 is also simply referred to as the audio system 100.

[0023] The audio system 100 shown in FIG. 1 includes an audio signal output device 110, a signal transmission path 120, a conversion device 50, an amplifier device 60, and a speaker 70. The audio signal output device 110 is, for example, an in-vehicle audio deck or an in-vehicle navigation system, and is a device that can generate and output an audio signal. The audio signal output device 110 includes a sound source unit 111 that generates an audio signal, and an amplifier unit 112 that amplifies the audio signal generated by the sound source unit 111. The audio signal output device 110 amplifies the audio signal generated by the sound source unit 111 using the amplifier unit 112, and outputs the amplified signal amplified by the amplifier unit 112 to the signal transmission path 120. In the following description, the audio signal generated by the sound source unit 111 is referred to as a first audio signal, and the amplified signal output from the amplifier unit 112 is referred to as a second audio signal. In other words, the second audio signal is a signal obtained by amplifying the first audio signal.

[0024] The sound source unit 111 includes, for example, a playback device such as a television, a radio, or a DVD player, a navigation device, or other audio signal generating device, and emits an audio signal generated based on at least any of the functions as a first audio signal.

[0025] The amplifier unit 112 outputs a second audio signal obtained by amplifying the first audio signal generated by the sound source unit 111. The second audio signal output from the amplifier unit 112 is, for example, a known balanced audio signal. For example, the amplifier unit 112 outputs a positive-phase audio signal to the first signal line 121, and outputs a reverse-phase audio signal obtained by inverting the audio signal of the first signal line 121 to the second signal line 122. Both signals output to the first signal line 121 and the second signal line 122 are the second audio signal. In a representative example, the balanced second audio signal is transmitted by the first signal line 121 and the second signal line 122, and input to the impedance adjustment device 1.

[0026] The impedance adjusting device 1 has a function of transmitting the second audio signal transmitted by the first signal line 121 and the second signal line 122 to the signal lines 71, 72, and a function of adjusting the impedance between the first signal line 121 and the second signal line 122. The impedance adjusting device 1 will be described in detail later.

[0027] The conversion device 50 attenuates the audio signals transmitted to the signal lines 71 and 72 by the impedance adjustment device 1, converts them into low-level signals, and provides the low-level signals to the amplifier device 60. The conversion device 50 has a first terminal connected to the signal line 71 and a second terminal connected to the signal line 72, and the first terminal and the second terminal are set to high impedance in the conversion device 50. In the case of such a conversion device 50, if the first terminal is directly connected to the first signal line 121 and the second terminal is directly connected to the second signal line 122 without connecting the impedance adjustment device 1 as shown in FIG. 1, the impedance between the first signal line 121 and the second signal line 122 will always be high impedance. In the configuration of FIG. 1, the impedance adjustment device 1 is used to avoid such a problem.

[0028] The amplifier device 60 is configured as a known amplifier. In a representative example, the amplifier device 60 amplifies the balanced audio signal (the above-mentioned low-level signal) generated by the conversion device 50 in a known configuration, and outputs the amplified balanced audio signal. The speaker 70 is a known speaker. The speaker 70 produces sound in response to the audio signal output from the amplifier device 60.

[0029] The audio signal output device 110 is powered on when a predetermined operation is performed in a vehicle equipped with the audio signal output device 110, and power is supplied from an on-board power source (not shown). The power supplied from the on-board power source to the audio signal output device 110 when the predetermined operation is performed is power that is essential for generating an audio signal in the sound source unit 111 and the amplifier unit 112. While the power is not supplied from the on-board power source to the audio signal output device 110, the audio signal output device 110 is in a power-off state, and when the power is supplied, the audio signal output device 110 is in a power-on state. A period during which the power is not supplied from the on-board power source to the audio signal output device 110 is a power-off period, and a period during which the power is supplied from the on-board power source to the audio signal output device 110 is a power-on period.

[0030] Specifically, when the above-mentioned predetermined operation is performed in the vehicle, the audio signal output device 110 is started in response to the supply of power from the in-vehicle power source, and the operation of the amplifier unit 112 starts simultaneously with the start of the audio signal output device 110 or after a predetermined short time has elapsed since the start of the audio signal output device 110. While the operation of the amplifier unit 112 is stopped, the first signal line 121 and the second signal line 122 are set to a predetermined low potential (for example, 0 V). For example, when the above-mentioned power is not supplied from the in-vehicle power source to the audio signal output device 110, the first signal line 121 and the second signal line 122 are set to the above-mentioned low potential (for example, 0 V). The potential state of the first signal line 121 and the second signal line 122 during the period when the operation of the amplifier unit 112 is stopped is the first potential state, and in a representative example, the first potential state is a state in which the potentials of the first signal line 121 and the second signal line 122 are both low potentials of about 0 V.

[0031] When the amplifier unit 112 starts operating in response to the activation of the audio signal output device 110, it raises the potentials of the first signal line 121 and the second signal line 122 to a reference potential (for example, 6V) higher than the low potential. The state of the potentials of the first signal line 121 and the second signal line 122 switched immediately after the amplifier unit 112 starts operating is the second potential state. In a representative example, the second potential state is a state in which the potentials of the first signal line 121 and the second signal line 122 are both about the reference potential (for example, 6V). The amplifier unit 112 sets the potentials of the first signal line 121 and the second signal line 122 to the reference potential in response to the start of its own operation, and then generates an amplified signal based on the reference potential in response to the audio signal provided from the sound source unit 111, and outputs the amplified signal to the signal transmission path 120. Specifically, the amplifier unit 112 outputs a positive-phase audio signal (voltage signal) based on the above-mentioned reference potential to the first signal line 121, and outputs a negative-phase audio signal (voltage signal) based on the above-mentioned reference potential to the second signal line 122.

[0032] 2. Details of impedance adjustment device 1 1, the impedance adjustment device 1 is electrically connected to a first signal line 121 and a second signal line 122 through which an audio signal is transmitted from an audio signal output device 110. As shown in FIG. 2, the impedance adjustment device 1 includes a transmission unit 40 and an adjustment unit 10.

[0033] The transmission unit 40 transmits the second audio signal input via the first signal line 121 and the second signal line 122. The transmission unit 40 includes a first transmission unit 41 and a second transmission unit 42. The first transmission unit 41 has a metal wire capable of transmitting a voltage signal, one end of which is electrically connected to the first signal line 121 in a configuration in which it is shorted to the first signal line 121, and the other end of which is electrically connected to the signal line 71 in a configuration in which it is shorted to the signal line 71. The first transmission unit 41 transmits the positive-phase audio signal transmitted by the first signal line 121 to the signal line 71. The second transmission unit 42 has a metal wire capable of transmitting a voltage signal, one end of which is electrically connected to the second signal line 122 in a configuration in which it is shorted to the second signal line 122, and the other end of which is electrically connected to the signal line 72 in a configuration in which it is shorted to the signal line 72. The second transmission unit 42 transmits the negative-phase audio signal transmitted by the second signal line 122 to the signal line 72.

[0034] The adjustment unit 10 has a function of adjusting the impedance between the first signal line 121 and the second signal line 122. The adjustment unit 10 includes a delay unit 20, a switching unit 30, a switch 46, and a resistor 48. The adjustment unit 10 has a function of switching between a low impedance state in which the first signal line 121 and the second signal line 122 are conductive via the resistor 48 by turning the switch 46 on, and a high impedance state in which the path of the resistor 48 is not conductive by turning the switch 46 off.

[0035] 3, the delay unit 20 includes resistors 22 and 26 and a capacitor 24. The switching unit 30 includes a relay unit 34 and a FET 32. One end of the resistor 22 is electrically connected to the second transmission unit 42 in a configuration in which it is shorted to the second transmission unit 42. The other end of the resistor 22 is electrically connected to the FET 32 in a configuration in which it is shorted to the gate of the FET 32. One electrode of the capacitor 24 and one end of the resistor 26 are electrically connected to the other end of the resistor 22 and the gate, and the other electrode of the capacitor 24 and the other end of the resistor 26 are electrically connected to the ground.

[0036] When the amplifier unit 112 is not operating and the potentials of the second signal line 122 and the second transmission unit 42 are at a low level of about 0 V, the delay unit 20 maintains the gate potential of the FET 32 at a low level and maintains the FET 32 in an off state. When the amplifier unit 112 switches from a non-operating state to an operating state and the potentials of the second signal line 122 and the second transmission unit 42 switch from the low level to a high level of about a reference potential (for example, 6 V), the capacitor 24 is charged, and the gate potential of the FET 32 becomes equal to or higher than the threshold potential after a certain time from when the potentials of the second signal line 122 and the second transmission unit 42 switch from the low level to the high level. The threshold potential is a potential at which the FET 32 switches to an on state. In other words, the FET 32 turns to an on state after the certain time from when the amplifier unit 112 starts operating. During the period when the amplifier section 112 is not operating and until the above-mentioned certain time period has elapsed since the amplifier section 112 started operating, the gate potential of the FET 32 is less than the threshold potential, and therefore the FET 32 is maintained in the off state.

[0037] The switching unit 30 is configured such that when the FET 32 is in an off state, no current flows through the relay unit 34, and when the FET 32 is in an on state, a current flows from the power source V1 to the relay unit 34 and the FET 32. The relay unit 34 is a device that turns a switch 46 (FIG. 2) off when it is in a conducting state, and turns the switch 46 (FIG. 2) on when it is in a non-conducting state.

[0038] In the adjustment unit 10 configured as described above, while the amplifier unit 112 is not operating, that is, when the potentials of the second signal line 122 and the second transmission unit 42 are at the above-mentioned low level, the FET 32 is maintained in the off state and the switch 46 is maintained in the on state, so that a low impedance is provided between the first signal line 121 and the second signal line 122. Then, after a certain time has elapsed since the amplifier unit 112 started operating, the FET 32 is switched to the on state, so that the switch 46 is switched to the off state, and thereafter, the switch 46 is maintained in the off state until the amplifier unit 112 stops operating. While the switch 46 is maintained in the off state, the impedance between the first signal line 121 and the second signal line 122 becomes a predetermined high impedance that is higher than the above-mentioned low impedance.

[0039] In the representative example described above, the period from when the amplifier unit 112 starts operating until the FET 32 switches to the on state is the "initial period". That is, the adjustment unit 10 operates to set the first signal line 121 and the second signal line 122 to the above-mentioned low impedance at least during the initial period after the amplifier unit 112 starts operating. Then, after the initial period has elapsed, specifically, after a predetermined time has elapsed after the first signal line 121 and the second signal line 122 have changed to the above-mentioned second potential state, the adjustment unit 10 operates to change the first signal line 121 and the second signal line 122 to a predetermined high impedance higher than the above-mentioned low impedance. Then, after the initial period has elapsed, the transmission unit 40 can transmit an audio signal in a state in which the first signal line 121 and the second signal line 122 are set to the above-mentioned high impedance.

[0040] The end timing of the initial period is preferably a timing later than an evaluation time when the audio signal output device 110 is affected by the impedance between the first signal line 121 and the second signal line 122. The evaluation time is a time when the amplifier unit 112 does not output an audio signal appropriately if the impedance between the first signal line 121 and the second signal line 122 is not equal to or less than a predetermined value at the evaluation time, and when the impedance between the first signal line 121 and the second signal line 122 is equal to or less than a predetermined value at the evaluation time, the amplifier unit 112 outputs an audio signal appropriately. The above-mentioned "low impedance" maintained in the initial period is a value smaller than the predetermined value. The evaluation time is a predetermined time immediately after the amplifier unit 112 starts operating. The end timing of the initial period is preferably a timing after the amplifier unit 112 starts operating and before the output of the second audio signal obtained by amplifying the first audio signal generated by the sound source unit 111 starts.

[0041] 3.Examples of effects The impedance adjustment device 1 can transmit the audio signal output from the audio signal output device 110, and can set the output destination of the audio signal to a low impedance state during the initial period. After the initial period has elapsed, the impedance adjustment device 1 can change the output destination of the audio signal to a high impedance state, and therefore can suppress current consumption after the initial period has elapsed.

[0042] The impedance adjustment device 1 is particularly effective in the following cases, for example. Some currently available audio signal output devices do not properly output audio signals from the amplifier when the output destination from the amplifier is in a high impedance state. The inventor of the present application analyzed and verified this type of audio signal output device and confirmed that some devices properly output audio signals if the output destination is set to low impedance in the initial period after the amplifier starts operating, even if the output destination is changed to high impedance after the initial period has elapsed. The impedance adjustment device 1 is useful when used as the output destination of such an audio signal output device. In other words, when the output source of the audio signal is such an audio signal output device, the impedance adjustment device 1 can set the impedance between the first signal line 121 and the second signal line 122 to low impedance in the initial period after the amplifier 112 starts operating, so that the audio signal can be normally output from the amplifier 112. Then, after the initial period has elapsed, the impedance between the first signal line 121 and the second signal line 122 changes to high impedance, so that the current consumption is suppressed after the initial period has elapsed, and the audio signal can be transmitted by the transmission unit 40 in that state.

[0043] The impedance adjusting device 1 can change the impedance between the first signal line 121 and the second signal line 122 to high impedance at an accurate timing a predetermined time after the operation start time of the amplifier section 112. Therefore, the period (initial period) during which the impedance between the first signal line 121 and the second signal line 122 is low can be easily determined accurately within a certain period from the operation start time of the amplifier section 112.

[0044] In the representative example described above, the adjustment unit 10 maintains a low impedance between the first signal line 121 and the second signal line 122 during the power-off period in which the audio signal output device 110 is not powered on. When the audio signal output device 110 is powered on, the adjustment unit 10 maintains the low impedance between the first signal line 121 and the second signal line 122, and then switches to a high impedance after the initial period has elapsed. Specifically, the adjustment unit 10 switches the switch 46 to an off state after the initial period has elapsed, and then maintains the switch 46 in an off state while the amplifier unit 112 is operating, thereby maintaining a high impedance between the first signal line 121 and the second signal line 122. Then, when the amplifier section 112 switches from an operating state to an operating stop state, the adjustment section 10 switches the switch 46 to an on state in response to the potentials of the second signal line 122 and the second transmission section 42 dropping to the above-mentioned low potential (for example, 0 V), and thereafter keeps the switch 46 on again until the above-mentioned initial period has elapsed, thereby maintaining a low impedance between the first signal line 121 and the second signal line 122. In this way, the impedance adjustment device 1 can continuously maintain a low impedance between the first signal line 121 and the second signal line 122 before and after the audio signal output device 110 is powered on, so there is no need to change the impedance before and after the audio signal output device 110 is powered on and after the amplifier section 112 starts operating, and this makes it possible to suppress complication of control.

[0045] <Other embodiments> The present invention is not limited to the embodiments described above and in the drawings. For example, the features of the above or later described embodiments can be combined in any combination within a range that does not contradict. Furthermore, any feature of the above or later described embodiments can be omitted unless it is clearly stated as essential. Furthermore, the above described embodiments may be modified as follows.

[0046] In the embodiment described above, the adjustment unit 10 continuously maintains a low impedance between the first signal line 121 and the second signal line 122 before and after the power supply is turned on for the audio signal output device 110, but is not limited to this example. For example, the adjustment unit 10 may set an impedance between the first signal line 121 and the second signal line 122 higher than the low impedance during a power-off period when the power supply is not turned on for the audio signal output device 110, and when the power supply is turned on for the audio signal output device 110, may maintain a low impedance between the first signal line 121 and the second signal line 122 and then switch to the high impedance after the initial period has elapsed. Specifically, the adjustment unit 10 determines whether the audio signal output device 110 is powered on by monitoring the above-mentioned predetermined operation (for example, an operation to turn on an accessory switch) or the power supply to the audio signal output device 110, and maintains the switch 46 in the off state from when the switch 46 is switched to the off state after the initial period has elapsed until the audio signal output device 110 is next switched from the power off state to the power on state. Then, the switch 46 is maintained in the on state from when the audio signal output device 110 is switched from the power off state to the power on state until the next initial period has elapsed. In this example, the first signal line 121 and the second signal line 122 are maintained at the above-mentioned high impedance from the time when the initial period has elapsed until the audio signal output device 110 is next switched from the power off state to the power on state. Then, the first signal line 121 and the second signal line 122 are maintained at the above-mentioned low impedance from when the audio signal output device 110 is switched from the power off state to the power on state until the next initial period has elapsed. This impedance adjustment device can maintain a high impedance between the first signal line 121 and the second signal line 122 during the power-off period of the audio signal output device 110, and can therefore suppress a large current from flowing between the first signal line 121 and the second signal line 122 for some reason during the power-off period. On the other hand, when the audio signal output device 110 is powered on, the impedance between the first signal line 121 and the second signal line 122 can be changed to a low impedance, and therefore a low impedance state can be achieved at an appropriate time to match the initial period.

[0047] In the above-described embodiment, a circuit as shown in FIG. 3 is used as an example of the delay unit 20, but the configuration is not limited to this. The delay unit 20 may be, for example, a timer circuit that counts a certain time after any signal line of the signal transmission path 120 changes to a reference potential and outputs a predetermined signal after the certain time. In this case, the switching unit 30 may operate to keep the switch 46 in an OFF state from when the timer circuit outputs the predetermined signal until a predetermined end timing (for example, the timing when the amplifier unit 112 stops operating), and to keep the switch 46 in an ON state for at least the certain time.

[0048] In the embodiment described above, the impedance adjustment device 1 is configured to switch the impedance between the first signal line 121 and the second signal line 122 to high impedance a certain time after the amplifier unit 112 is started, but is not limited to this configuration. The impedance adjustment device 1 may be configured to switch the impedance between the first signal line 121 and the second signal line 122 to high impedance a certain time after the power supply to the audio signal output device 110 is turned on, or may be configured to switch the impedance between the first signal line 121 and the second signal line 122 to high impedance a certain time after the accessory switch is switched from the off state to the on state.

[0049] The above-described embodiment is an example applied to the audio system 100 as shown in FIG. 1, but may be applied to an audio system 200 as shown in FIG. 4. The audio system 200 in FIG. 4 uses an amplifier device 250 having a voice conversion function and a digital signal processor (DSP) function like the converter device 50, instead of the converter device 50 and the amplifier device 60 in FIG. 1. In the amplifier device 250, the impedance between the first terminal connected to the signal line 71 and the second terminal connected to the signal line 72 is higher than the low impedance described above. In this example, the impedance adjustment device 1 can operate in the same way as in the first embodiment.

[0050] In the embodiment described above, the audio signal is output from the amplifier unit 112 to the signal transmission path 120 in a balanced manner, but the impedance adjustment device may be applied to an audio system in which the audio signal is output from the amplifier unit 112 to the signal transmission path in an unbalanced manner. In this case, the delay unit 20 may be connected to a positive phase signal line.

[0051] It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments disclosed herein, and is intended to include all modifications within the scope indicated by the claims or within the scope equivalent to the claims. [Explanation of symbols]

[0052] 1: Impedance adjustment device 10: Adjustment section 40: Transmission section 41: First transmission section 42: Second transmission section 100: Audio system 110: Audio signal output device 112: Amplifier section 120: Signal transmission line 121: First signal line 122: Second signal line

Claims

1. The present invention is used in an audio system in which an audio signal is transmitted from an audio signal output device having an amplifier section through a signal transmission path having a first signal line and a second signal line, an adjustment unit that adjusts the impedance between the first signal line and the second signal line; a transmission unit that transmits the audio signal input via the first signal line and the second signal line; having the adjustment unit sets a predetermined low impedance between the first signal line and the second signal line during an initial period after the amplifier unit starts operating, and changes the impedance between the first signal line and the second signal line to a high impedance higher than the low impedance after the initial period has elapsed; The transmission unit may transmit the audio signal in a state in which the first signal line and the second signal line are in the high impedance state after the initial period has elapsed. Impedance adjustment device for audio systems.

2. the audio signal output device sets the first signal line and the second signal line to a first potential state during a period in which the operation of the amplifier unit is stopped, and changes the first signal line and the second signal line to a second potential state in response to the start of operation of the amplifier unit; The adjustment unit changes the impedance between the first signal line and the second signal line to the high impedance a predetermined time after the first signal line and the second signal line are changed to the second potential state.

2. An impedance adjustment device for an audio system according to claim 1.

3. The adjustment unit maintains the low impedance between the first signal line and the second signal line during a power-off period in which the audio signal output device is not powered on, and when the audio signal output device is powered on, maintains the low impedance between the first signal line and the second signal line and then switches to the high impedance after the initial period has elapsed.

3. The impedance adjusting device for an audio system according to claim 1 or 2.

4. The adjustment unit sets an impedance between the first signal line and the second signal line to be higher than the low impedance during a power-off period in which the audio signal output device is not powered on, and when the audio signal output device is powered on, maintains the low impedance between the first signal line and the second signal line and then switches to the high impedance after the initial period has elapsed.

3. The impedance adjusting device for an audio system according to claim 1 or 2.

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