Sound output device

Abstract

To provide a sound output device having a function of normally correctly determining presence / absence of connection of a speaker.SOLUTION: A sound output device 100 includes a controller 110, a power amplifier 60, a low-pass filter 70, and a speaker 80. The controller 110 includes: first and second low-pass filters 120, 122 for removing a high frequency component of a sound input signal S2 and a sound output signal S3; a first peak detection section 130 for detecting a peak current SigInP of the sound input signal SigInL from which the high frequency component is removed; a second peak detection section 132 for detecting a peak current SigOutP of the sound output signal from which the high frequency component is removed; and a comparison section 140 for comparing the peak current SigInP with the peak current SigOutP when the peak current SigInP is equal to or more than a fixed current, and determining connection / non-connection of the speaker 80.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a sound output device that outputs sound from a speaker, and particularly relates to detection of connection / disconnection of a speaker.

Background Art

[0002] As a technique for detecting the presence or absence of a speaker connection in a sound output device, for example, in Patent Document 1, a speaker line is connected to a secondary winding of an output transformer, and a first voltage signal amplified by a voltage amplifier that negatively feeds back a voltage corresponding to the voltage induced in the secondary winding is compared with a second voltage signal corresponding to the voltage induced on the secondary winding side of the output transformer to detect the connection / disconnection of the speaker line. Further, the sound output device of Patent Document 2 includes a processing unit that processes an input signal, a speaker that outputs sound based on an output signal from the processing unit, and a determination unit that determines a failure of the processing unit from the difference between the level of the input signal and the level of the output signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional audio amplifiers have only checked the connection of the speaker at startup, but products related to safety such as proximity warning sound devices installed in electric vehicles etc. require constant checking of the speaker connection. To meet this requirement, an amplifier with an output current measurement function is used, the input current level and the output current level of the amplifier are compared, and when the output current level is sufficiently large, it is determined that the speaker is connected, and when the output current level is sufficiently small, it is determined that the speaker is not connected.

[0005] Figure 1 is a block diagram showing the configuration of a conventional sound output device (audio amplifier). The sound output device 10 includes a controller 20, a power amplifier 60, a low-pass filter 70, and a speaker 80. The controller 20 has a function to detect whether the speaker 80 is connected or not. The controller 20 includes a signal processing unit 30 and a comparison unit 40. The signal processing unit 30 receives an analog audio input signal S1 representing the original sound, performs processing such as noise reduction and amplification on the audio input signal S1, and provides the processed audio input signal S2 to the comparison unit 40 and the power amplifier 60.

[0006] The power amplifier 60 is a Class D amplifier and includes a PWM generator that generates a PWM (pulse width modulation) signal that changes the duty cycle of the pulses according to the input signal level of the input analog audio input signal S2, and a switching circuit that converts the PWM signal into a PWM output signal S3 which is amplified to a voltage level of +V / -V.

[0007] The low-pass filter 70 removes high-frequency components from the PWM output signal S3 output from the power amplifier 60 to generate an analog audio signal S4 in the audible range, and the speaker 80 outputs sound in response to the analog audio signal S4.

[0008] The power amplifier 60 further includes a function to measure the output current value of the PWM output signal S3 and provides the output current value (output current level) Iout to the comparison unit 40 of the controller 20. The comparison unit 40 compares the input current level Iin of the audio input signal S2 input to the power amplifier 60 with the output current level Iout of the power amplifier 60. If the output current level Iout is sufficiently larger than the input current level Iin, it determines that the speaker 80 is connected, and if the output current level Iout is sufficiently smaller than the input current level Iin, it determines that the speaker 80 is not connected. The controller 20 further outputs an alarm or the like to the display if it determines that the speaker 80 is not connected.

[0009] However, conventional methods for determining whether or not a speaker is connected have the following problems. In a Class D power amplifier 60 as shown in Figure 1, a low-pass filter 70 is connected to its output. Therefore, when the frequency of the PWM signal handled by the power amplifier 60 increases, the output current value Iout increases, making it difficult to distinguish whether or not the output current value Iout is high because a speaker 80 is connected. In other words, even if the speaker 80 is not connected, the output current level Iout may exceed the connection detection threshold, leading to a false determination that the speaker 80 is connected.

[0010] Furthermore, there is a delay between the input current level Iin of the audio input signal S2 input to the power amplifier 60 and the output current level Iout output from the power amplifier 60 due to the digital-to-analog conversion in the power amplifier 60, so the two cannot be simply compared. If they were compared directly, it could lead to misidentification of the speaker connection.

[0011] Furthermore, in the Class D power amplifier 60, even when the input level of the audio input signal S2 is extremely low, current flows through the switching circuit (even if the input level is zero, current flows because the duty cycle of the PWM signal is 50%), which may lead to a misinterpretation that speaker 80 is connected when it is not.

[0012] The present invention aims to solve these conventional problems and to provide a sound output device that has a function to more accurately determine whether or not a speaker is connected during operation. [Means for solving the problem]

[0013] The sound output device according to the present invention is equipped with a function for detecting whether a speaker is connected or not, and comprises a Class D amplifier that receives an audio input signal and generates an amplified audio output signal from the audio input signal, a speaker that outputs sound in response to the audio output signal, and a detection means for detecting whether the speaker is connected or not, wherein the detection means comprises a first filter for removing high-frequency components from the audio input signal, a second filter for removing high-frequency components from the audio output signal, and a comparison unit that compares the audio input signal from which high-frequency components have been removed by the first filter with the audio output signal from which high-frequency components have been removed by the second filter, and determines whether the speaker is connected or not based on the comparison result.

[0014] In one embodiment, the sound output device further includes a first detection unit that detects a first peak current over a certain period of time of the audio input signal from which high-frequency components have been removed by the first filter, and a second detection unit that detects a second peak current over a certain period of time of the audio output signal from which high-frequency components have been removed by the second filter, wherein the comparison unit compares the first peak current and the second peak current and determines whether the speaker is connected or not based on the comparison result. In one embodiment, the detection means further includes a level check unit that checks the level of the first peak current, wherein the comparison unit determines whether the speaker is connected or not based on the level checked by the level check unit. In one embodiment, the comparison unit does not determine whether the speaker is connected or not if the level of the first peak current is below a certain level, and determines whether the speaker is connected or not if the level of the first peak current is above a certain level. In one embodiment, the comparison unit determines that the speaker is connected when the ratio or difference between the first peak current and the second peak current is greater than a first threshold. In one embodiment, the comparison unit determines that a speaker is not connected when the ratio or difference between the first peak current and the second peak current is less than a second threshold. In another embodiment, the sound output device further includes a low-pass filter between the amplifier and the speaker, the low-pass filter converts the PWM signal output from the amplifier into an audible analog audio signal. [Effects of the Invention]

[0015] According to the present invention, high-frequency components of the audio input signal and audio output signal are removed, and the audio input signal and audio output signal from which the high-frequency components have been removed are compared, thereby preventing misjudgment of speaker connection due to the high frequency of the amplifier's audio output signal. Furthermore, by comparing the peak current of the audio input signal and the peak current of the audio output signal, mismatches due to delays between the audio input signal and the audio output signal can be canceled, thereby preventing misjudgment of speaker connection. In addition, if the input level of the audio input signal is extremely low, misjudgment of speaker connection can be prevented by stopping the comparison between the audio input signal and the audio output signal. [Brief explanation of the drawing]

[0016] [Figure 1] This is a block diagram showing the configuration of a conventional sound output device. [Figure 2] This is a block diagram showing the configuration of a sound output device according to an embodiment of the present invention. [Figure 3] This table shows examples of speaker connection / disconnection determination according to embodiments of the present invention. [Figure 4] This is a block diagram showing the configuration of a sound output device according to another embodiment of the present invention. [Modes for carrying out the invention]

[0017] The sound output device according to the present invention has a function to detect whether or not a speaker is connected, not only at startup but also continuously (during the period of sound output). The sound output device according to the present invention is not particularly limited, but can be used, for example, as a proximity warning sound device or audio device that emits a warning sound from a speaker to nearby pedestrians in electric vehicles, etc. [Examples]

[0018] FIG. 2 is a block diagram showing the configuration of the sound output device according to an embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals. The sound output device 100 of the present embodiment includes a controller 110, a power amplifier 60, a low-pass filter 70, and a speaker 80.

[0019] The controller 110 has a function of detecting the connection or disconnection of the speaker in the sound output device 100. In addition to the signal processing unit 30 shown in FIG. 1, the controller 110 includes a first low-pass filter 120 that removes high-frequency components of the analog audio input signal S2 output from the signal processing unit 30, a first peak detection unit 130 that receives the audio input signal SigInL from the first low-pass filter 120 and detects the peak value (maximum value) of the input current level of the audio input signal SigInL over a certain period, a second low-pass filter 130 that removes high-frequency components of the output current level Iout output from the power amplifier 60, a second peak detection unit 132 that receives the audio output signal SigOutL from the second low-pass filter 122 and detects the peak value (maximum value) of the output current over a certain period of the audio output signal SigOutL, a comparison unit 140 that receives the detection signal SigInP detected by the first peak detection unit 130 and the detection signal SigOutP detected by the second peak detection unit 132 and determines the connection or disconnection of the speaker 80 based on the ratio or difference between the two, and a level check unit 150 that provides a control signal CNT to the comparison unit 150 based on the detection signal SigInP of the first peak detection unit 130.

[0020] The signal processing unit 30 receives an analog audio input signal S1 representing an original sound, performs filtering processing, amplification processing, etc., and provides the processed analog audio input signal S2 to the first low-pass filter 120 and the power amplifier 60.

[0021] The power amplifier 60 is composed of a class-D amplifier, and includes a PWM (pulse width modulation) generator that generates a PWM signal for changing the duty ratio of a pulse according to the input signal level of the analog audio input signal S2, and a switching circuit that converts the PWM output signal into a PWM output signal S3 amplified to a voltage level of +V / -V. The switching circuit includes, for example, transistors performing a push-pull operation connected in series between a voltage source of +V and a voltage source of -V, and generates a PWM output signal S3 at a level of +V by turning on one transistor and turning off the other transistor in response to the PWM signal, and generates a PWM output signal S3 at a level of -V by turning off one transistor and turning on the other transistor.

[0022] The low-pass filter 70 is designed with a cut-off frequency according to the impedance of the speaker 80 and the characteristics of the power amplifier 60, removes high-frequency components from the PWM output signal S3 from the power amplifier 60 to generate an analog audio signal S4 in the audible band, and the speaker 80 outputs sound in response to the analog audio signal S4.

[0023] The power amplifier 60 further measures an output current value based on the PWM output signal S3, and provides an analog signal representing the measured output current value Iout to a second low-pass filter 122.

[0024] The first low-pass filter 120 receives the analog audio input signal S2, removes high-frequency components of the analog audio input signal S2 above a predetermined cut-off frequency f1, and provides the removed signal SigInL to the first peak detection unit 130.

[0025] The second low-pass filter 122 has the same configuration as the first low-pass filter 120, removes high-frequency signals above a predetermined cut-off frequency f2 (f1 = f2) from the analog signal representing the output current value Iout, and provides the removed signal SigOutL to the second peak detection unit 132.

[0026] The first and second low-pass filters 120 and 122 pre-remove high-frequency components from the input current level of the audio input signal S2 and the output current level S3 of the PWM output signal S3, thereby preventing the comparison unit 140 from comparing the input current levels and output current levels of the high-frequency components of the audio input signal S2 and the audio output signal S5. When the frequency of the PWM signal handled by the power amplifier 60 increases, the current consumed by the low-pass filter 70 increases, and the output current level increases even when the speaker is not connected, which may cause misjudgment of whether the speaker is connected or not, so this situation is avoided.

[0027] The first peak detection unit 130 receives the signal SinInL from the first low-pass filter 120, detects the highest peak value (maximum value) of the signal SinInL during a predetermined period T1 (for example, a period of 5ms), and provides a detection signal SinInP indicating that peak value to the comparison unit 140 and the level check unit 150. The second peak detection unit 132 is configured identically to the first peak detection unit 130, receives the signal SigOutL from the second low-pass filter 122, detects the highest peak (maximum value) of the signal SigOutL during a predetermined period T2 (T1=T2), and provides a detection signal SigOutP indicating that peak value to the comparison unit 140. By detecting peak values ​​over a certain period using the first and second peak detection units 130 and 132, the comparison between the input current level and the output current level by the comparison unit 140 compensates for the delay associated with measuring the output current value Iout in the power amplifier 60. In other words, the effect of delay between the audio input signal S2 and the PWM output signal S3 can be ignored.

[0028] The level check unit 150 provides the comparison unit 140 with a control signal CNT to enable / disable the comparison unit 140 based on the detection signal SinInP from the first peak detection unit 130. For example, if the peak value of the input current level of the audio input signal is extremely small (i.e., smaller than the threshold), the level check unit 150 outputs a control signal CNT (e.g., an L-level signal) to prevent the comparison unit 140 from performing a comparison, and if the peak value of the input current level is greater than or equal to the threshold, it outputs a control signal CNT (e.g., an H-level signal) to enable the comparison unit 140 from performing a comparison. This prevents misjudgment of speaker connection / disconnection by preventing the comparison unit 140 from performing a comparison when the input signal level of the audio input signal S2 is small.

[0029] The comparison unit 140, in response to the control signal CNT from the level check unit 150, compares the peak value indicated by the detection signal SinInP with the peak value indicated by the detection signal SigOutP if the input level of the audio input signal S2 is above a certain level. If the ratio or difference between the two is greater than or equal to a threshold, it determines that the speaker 80 is connected. If the ratio or difference between the two is less than the threshold, it determines that the speaker 80 is not connected (open). For example, the comparison unit 140 determines that the speaker 80 is connected when (SigOutP / SigInP) > 1.0, and determines that the speaker 80 is not connected when (SigOutP / SigInP) < 0.5.

[0030] Figure 3 is a table showing examples of speaker connection / disconnection determination. In the conventional technology, the ratio of the peak values ​​of input / output currents for speaker connection / open is 2.93, whereas in this embodiment, the ratio is 4.23, making it possible to increase the difference (margin) from the threshold for determining speaker connection or disconnection. As a result, it is now possible to reliably confirm whether the speaker is connected or not (in this embodiment, the difference from the threshold is improved by 3 dB compared to the conventional method).

[0031] As described above, this embodiment removes high-frequency components from the audio input signal and audio output signal, and by comparing the peak currents of the removed audio input signal and audio output signal over a certain period, it is possible to prevent misjudgment of speaker connections due to the high frequency of the PWM signal handled by the power amplifier, and to cancel out mismatches caused by delays between the audio input signal and audio output signal, thereby preventing misjudgment of speaker connections. Furthermore, if the input level of the audio input signal is extremely low, misjudgment of speaker connections can be prevented by stopping the comparison between the audio input signal and the audio output signal.

[0032] Next, other embodiments of the present invention will be described. In the sound output device 100 shown in Figure 2 above, an example was shown in which the controller 110 detects speaker connection / disconnection using an analog circuit, but the equivalent processing of the analog circuit may be performed by a digital circuit.

[0033] Figure 4 is a block diagram showing the configuration of an audio output device according to another embodiment of the present invention. In the audio output device 100A, the controller 110 includes an AD converter 160 that digitally converts an audio input signal S2 and an AD converter 170 that digitally converts an analog signal indicating an output current value Iout. The first and second low-pass filters 120, 122, the first and second peak detection units 130, 132, the level check unit 150 and the comparison unit 140 are configured by digital circuits. In yet another embodiment, the controller 110 may be a circuit that mixes digital and analog circuits.

[0034] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of the invention as described in the claims. [Explanation of symbols]

[0035] 60: Power amplifier 70: Low-pass filter 80: Speaker 100, 100A: Sound output device 110: Controller 120, 122: Low-pass filter 130, 132: Peak detection circuit 140: Comparison Section 150: Level Check Section 160, 170: AD converter

Claims

1. A sound output device equipped with a function to detect whether a speaker is connected or disconnected, A Class D amplifier that receives an audio input signal and generates an amplified audio output signal from that audio input signal, A speaker that outputs sound in response to the aforementioned audio output signal, The system includes detection means for detecting whether the speaker is connected or disconnected, The detection means includes a first filter that removes high-frequency components from the input current level of the audio input signal, A second filter that removes high-frequency components from the output current level of the aforementioned audio output signal, A comparison unit compares the input current level of the audio input signal from which high-frequency components have been removed by the first filter with the output current level of the audio output signal from which high-frequency components have been removed by the second filter, and determines whether the speaker is connected or not based on the comparison result. A sound output device having a sound output function.

2. The sound output device further includes a first detection unit that detects a first peak current during a certain period of time of the audio input signal from which high-frequency components have been removed by the first filter, The system includes a second detection unit that detects a second peak current during a certain period of time in the audio output signal from which high-frequency components have been removed by the second filter, The sound output device according to claim 1, wherein the comparison unit compares the first peak current with the second peak current and determines whether the speaker is connected or not based on the comparison result.

3. The detection means further includes a level check unit for checking the level of the first peak current, The sound output device according to claim 2, wherein the comparison unit determines whether the speaker is connected or not based on the level checked by the level check unit.

4. The sound output device according to claim 3, wherein the comparison unit does not determine whether the speaker is connected or not when the level of the first peak current is below a certain level, and determines whether the speaker is connected or not when the level of the first peak current is above a certain level.

5. The sound output device according to claim 2, wherein the comparison unit determines that a speaker is connected when the ratio or difference between the first peak current and the second peak current is greater than a first threshold.

6. The sound output device according to claim 2, wherein the comparison unit determines that a speaker is not connected when the ratio or difference between the first peak current and the second peak current is smaller than a second threshold.

7. The sound output device according to claim 1, further including a low-pass filter between the amplifier and the speaker, wherein the low-pass filter converts the PWM signal output from the amplifier into an analog audio signal in the audible range.

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