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EP-4262237-B1 - SOUND OUTPUT DEVICE

EP4262237B1EP 4262237 B1EP4262237 B1EP 4262237B1EP-4262237-B1

Inventors

  • MATSUYAMA, MINORU

Dates

Publication Date
20260506
Application Date
20230329

Claims (7)

  1. A sound output device (100) having a function of detecting connection or disconnection of a speaker, the sound output device (100) comprising: a class D amplifier (60) configured to receive a sound input signal and generate a sound output signal obtained by amplifying the sound input signal; a speaker (80) configured to output a sound in response to the sound output signal; and a detection unit (110) configured to detect connection or disconnection of the speaker (80), characterized in that the detection unit (110) includes a first filter (120) configured to remove a high-frequency component of the sound input signal, a second filter (122) configured to remove a high-frequency component of the sound output signal, and a comparison unit (140) configured to compare the sound input signal from which the high-frequency component has been removed by the first filter (120) with the sound output signal from which the high-frequency component has been removed by the second filter (122), and determine connection or disconnection of the speaker (80) on the basis of a comparison result.
  2. The sound output device (100) according to claim 1, further comprising: a first detection unit (130) configured to detect a first peak current, in a certain period, of the sound input signal from which the high-frequency component has been removed by the first filter (120); and a second detection unit (132) configured to detect a second peak current, in a certain period, of the sound output signal from which the high-frequency component has been removed by the second filter (122), wherein the comparison unit (140) is configured to compare the first peak current with the second peak current, and to determine connection or disconnection of the speaker (80) on the basis of a comparison result.
  3. The sound output device (100) according to claim 2, wherein the detection unit (110) further includes a level check unit (150) configured to check a level of the first peak current, and the comparison unit (140) is configured to determine connection or disconnection of the speaker (80) on the basis of the level checked by the level check unit (150).
  4. The sound output device (100) according to claim 3, wherein the comparison unit (140) is configured to not determine connection or disconnection of the speaker (80) in a case where the level of the first peak current is less than a certain level, and to determine connection or disconnection of the speaker (80) in a case where the level of the first peak current is equal to or higher than the certain level.
  5. The sound output device (100) according to any one of claims 2 to 4, wherein the comparison unit (140) is configured to determine that the speaker (80) is connected when a ratio or a difference between the first peak current and the second peak current is more than a first threshold value.
  6. The sound output device (100) according to any one of claims 2 to 5, wherein the comparison unit (140) is configured to determine that the speaker (80) is not connected when a ratio or a difference between the first peak current and the second peak current is less than a second threshold value.
  7. The sound output device (100) according to any one of claims 1 to 6, further comprising a low-pass filter (70) between the amplifier (60) and the speaker (80), wherein the low-pass filter (70) is configured to convert a PWM signal output from the amplifier (60) into an analog sound signal in an audible band.

Description

The present invention relates to a sound output device that outputs a sound from a speaker, and particularly relates to detection of connection/disconnection of the speaker. As a technique for detecting the presence or absence of speaker connection of a sound output device, for example, in JP 3355065 B2, a speaker line is connected to a secondary winding of an output transformer, and connection/disconnection of the speaker line is detected by comparing a first voltage signal amplified by a voltage amplifier that negatively feeds back a voltage corresponding to a voltage induced in the secondary winding with a second voltage signal corresponding to a voltage induced on the secondary winding side of the output transformer. A sound output device in JP 2019-48528 A includes a processing unit that performs processing on an input signal, a speaker that outputs a sound on the basis of an output signal from the processing unit, and a determination unit that determines a failure of the processing unit from a difference between a level of the input signal and a level of the output signal. In a conventional audio amplifier, connection of a speaker is checked only at the time of starting, but a product related to safety such as a proximity warning sound device mounted on an electric vehicle or the like is required to constantly check connection of a speaker. In order to satisfy this requirement, an amplifier having an output current measurement function is used, and an input current level and an output current level of the amplifier are compared. In a case where the output current level is sufficiently high, it is determined that the speaker is connected, and in a case where the output current level is sufficiently low, it is determined that the speaker is not connected. Fig. 1 is a block diagram illustrating a configuration of a conventional sound output device (audio amplifier). A sound output device 10 includes a controller 20, a power amplifier 60, a low-pass filter 70, and a speaker 80, and the controller 20 has a function of detecting connection or disconnection of the speaker 80. The controller 20 includes a signal processing unit 30 and a comparison unit 40, and the signal processing unit 30 receives an analog sound input signal S1 indicating an original sound, performs processing such as noise removal or amplification on the sound input signal S1, and provides the processed sound input signal S2 to the comparison unit 40 and the power amplifier 60. The power amplifier 60 is a class D amplifier, and includes a PWM generator that generates a pulse width modulation (PWM) signal for changing a duty ratio of a pulse according to an input signal level of the analog sound input signal S2 that has been input, and a switching circuit that converts the PWM signal into a PWM output signal S3 amplified to a voltage level of +V/-V. The low-pass filter 70 removes a high-frequency component from the PWM output signal S3 output from the power amplifier 60 to generate an analog sound signal S4 in an audible band, and the speaker 80 outputs a sound in response to the analog sound signal S4. The power amplifier 60 further has a function of measuring an 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 an input current level Iin of the sound input signal S2 input to the power amplifier 60 with the output current level Iout of the power amplifier 60, determines that the speaker 80 is connected when the output current level Iout is sufficiently higher than the input current level Iin, and determines that the speaker 80 is not connected when the output current level Iout is sufficiently lower than the input current level Iin. The controller 20 further outputs an alarm or the like to a display in a case where it is determined that the speaker 80 is not connected. However, such a conventional method for determining the presence or absence of speaker connection has the following problems. In the class D power amplifier 60 as illustrated in Fig. 1, since the low-pass filter 70 is connected to the output thereof, in a case where a frequency of the PWM signal handled by the power amplifier 60 becomes high, the output current value Iout increases, and thus it is difficult to distinguish whether or not the output current value Iout is large because the speaker 80 is connected. That is, even in a case where the speaker 80 is not connected, the output current level Iout exceeds a threshold value for connection determination, and thus it is erroneously determined that the speaker 80 is connected. Since there is a delay associated with the digital-to-analog conversion in the power amplifier 60 between the input current level Iin of the sound input signal S2 input to the power amplifier 60 and the output current level Iout output from the power amplifier 60, the input current level Iin and the output c