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DESCRIPTION JP2017092841

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DESCRIPTION JP2017092841
Abstract: [Problem] To provide an amplification device capable of always measuring the
temperature of a speaker normally. An amplification device (1) includes an adder (13) that adds a
pilot signal SP to an input audio signal Sa, an amplifier (15) that amplifies the signal Se output
from the adder and supplies the signal to a speaker (2). The temperature detection circuit 18
which extracts the signal component of the pilot signal SP from the current detection signal V1
that detects the current flowing through the speaker 2 and detects the temperature of the
speaker 2 based on the signal component; And a limit circuit 11 for limiting the maximum
amplitude of the audio signal Sa such that a margin corresponding to the pilot signal SP is
generated with respect to the maximum allowable input of the amplifier 15. [Selected figure]
Figure 1
Amplifier
[0001]
The present invention relates to an amplifier that measures the temperature of a speaker and
drives the speaker.
[0002]
When the speaker is driven based on the audio signal, current flows in a coil provided in the
speaker, and the temperature of the speaker rises.
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Therefore, from the viewpoint of protecting the speaker, temperature measurement of the
speaker has been conventionally performed.
[0003]
For example, in Patent Document 1, a DC voltage of a voltage value determined in advance on the
input side of the speaker is applied to the coil of the speaker, and a signal representing the DC
current value flowing through the coil and the voltage value applied to the coil A temperature
measuring device is described which derives the temperature of the coil.
[0004]
JP, 2014-20976, A
[0005]
However, in the above-described conventional temperature measurement device, when the
amplitude of the audio signal is large and exceeds the maximum allowable input of the amplifier
for driving the speaker, the audio signal output from the amplifier is clipped. Even if a voltage is
applied to the coil of the speaker, the DC voltage is buried in the clip signal, and there is a
problem that the temperature of the coil or the speaker can not be measured properly.
[0006]
Then, this invention is made in view of the said subject, and it aims at providing the amplifier
which enabled it to measure the temperature of a speaker normally always.
[0007]
In order to achieve the above object, first of all, the present invention is an amplifying device,
which is an adder for adding a pilot signal to an input audio signal, and a speaker for amplifying
a signal output from the adder. And a temperature detection circuit for extracting a signal
component of the pilot signal from a current detection signal obtained by detecting the current
flowing through the speaker, and detecting the temperature of the speaker based on the signal
component; And a limit circuit for limiting the maximum amplitude of the audio signal so that a
margin corresponding to the pilot signal is generated with respect to the maximum allowable
input of the amplifier on the front stage side.
[0008]
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According to the present invention, after the audio signal is subjected to amplitude limitation
corresponding to the pilot signal by the limit circuit, the pilot signal is added to the audio signal.
Therefore, it is possible to prevent the signal from being clipped when the signal output from the
adder is amplified in the amplifier, and to transmit the pilot signal to the speaker normally.
[0009]
Secondly, in the amplification apparatus having the first configuration, the present invention is
characterized in that the pilot signal is a signal of a predetermined frequency in an inaudible
range.
[0010]
According to the present invention, a pilot signal of a predetermined frequency can be normally
transmitted to the speaker, and the temperature of the speaker can be measured without
affecting the sound quality output from the speaker.
[0011]
Third, in the amplifying apparatus having the second configuration, the present invention further
includes a high pass filter for removing a signal of a band including the predetermined frequency
from the audio signal on the front side of the adder, the temperature The detection circuit is
configured to extract a signal component of the predetermined frequency from the current
detection signal.
[0012]
According to the present invention, the signal component different from the pilot signal can be
prevented from being mixed into the pilot signal, and the temperature of the speaker can be
accurately detected.
[0013]
Fourth, according to the present invention, in the amplifying device having the second or third
configuration, the temperature detection circuit may be configured to delay the pilot signal with
respect to the signal component of the pilot signal extracted from the current detection signal. ,
And integrating the one period of the pilot signal to detect the temperature of the speaker.
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[0014]
According to the present invention, the temperature of the speaker can be detected with high
accuracy.
[0015]
Fifth, according to the present invention, in the amplifying device having any one of the first to
fourth configurations, the audio signal is provided at the front stage of the limit circuit based on
the temperature of the speaker detected by the temperature detection circuit. The configuration
further includes a volume control circuit that amplifies or attenuates.
[0016]
According to the present invention, the speaker can be protected based on the temperature of the
speaker detected by the temperature detection circuit.
[0017]
According to the present invention, when driving a speaker with an audio signal obtained by
adding a pilot signal, it is possible to suppress clipping of the signal output from the amplifier, so
the temperature of the speaker is determined based on the signal component of the pilot signal.
It will always be able to measure normally.
[0018]
It is a block diagram showing an example of 1 composition of an amplification device.
It is a figure which shows the concept of the signal in each part of an amplifier.
It is a figure which shows the structural example of a temperature detection circuit.
[0019]
Hereinafter, preferred embodiments of the present invention will be described in detail with
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reference to the drawings.
In the embodiment described below, members which are common to each other are denoted by
the same reference numerals, and redundant description thereof will be omitted.
[0020]
FIG. 1 is a block diagram showing one configuration example of the amplification device 1 in the
present invention.
The amplification device 1 includes a drive circuit for driving the speaker 2 and drives the
speaker 2 based on the input audio signal Sa.
The amplification device 1 is configured to constantly measure the temperature of the speaker 2
while driving the speaker 2 by the audio signal Sa, and to control the driving state of the speaker
2 based on the measured temperature.
[0021]
The amplification device 1 includes a volume adjustment circuit 10, a DA converter 14, and an
amplifier 15 as a configuration for driving the speaker 2.
In addition, as a configuration for measuring the temperature of the speaker 2 and controlling
the driving state of the speaker 2, the amplification device 1 has a limit circuit 11, a high pass
filter 12, an adder 13, an IV conversion circuit 16, and AD conversion. And a temperature control
circuit 18, a volume control circuit 19, and a pilot signal output circuit 20.
[0022]
The pilot signal output circuit 20 is a circuit that outputs a pilot signal SP to be added to the
input audio signal Sa in order to measure the temperature of the speaker 2.
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For example, the pilot signal output circuit 20 in the present embodiment generates an AC signal
of 4 Hz which is an inaudible area as a pilot signal SP, and outputs the pilot signal SP to the
adder 13.
[0023]
The volume adjustment circuit 10 is a circuit that amplifies the audio signal Sa input as a digital
signal at an adjustable amplification factor.
The amplification factor in the volume adjustment circuit 10 is controlled by a volume control
circuit 19 described later.
The audio signal Sb amplified by the volume adjustment circuit 10 is output to the limit circuit
11.
[0024]
The limit circuit 11 is a circuit that limits the amplitude of the audio signal Sb.
That is, since the pilot signal SP is added to the audio signal Sb in the adder 13 at the subsequent
stage, the limit circuit 11 limits the maximum amplitude of the audio signal Sb to a
predetermined value in the previous stage of the adder 13 in advance.
Then, the audio signal Sc whose maximum amplitude is limited in the limit circuit 11 is output to
the high pass filter 12.
[0025]
The high pass filter 12 is a filter that removes signal components in the inaudible range from the
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audio signal Sc, and is formed of, for example, an IIR filter with a small delay.
That is, since the audio signal Sa to be input may include a low frequency signal component in
the inaudible range, the high pass filter 12 may receive such a low frequency signal component
on the front stage side of the adder 13. It is removed from the audio signal Sc.
The cutoff frequency of the high pass filter 12 in this embodiment is a frequency higher than the
frequency of the pilot signal SP, and is set to, for example, 50 Hz. As a result, the signal
component of 50 Hz or less included in the audio signal Sc is removed by the high-pass filter 12,
and the audio signal Sd having no signal component in the frequency range of the pilot signal SP
is obtained. The audio signal Sd from which the low frequency signal component has been
removed by the high pass filter 12 is output to the adder 13.
[0026]
The adder 13 adds the pilot signal SP output from the pilot signal output circuit 20 to the audio
signal Sd output from the high pass filter 12, and sends the audio signal Se on which the pilot
signal SP is superimposed to the DA converter 14. Output.
[0027]
The DA converter 14 is, for example, a ΔΣ type DA converter, and performs high-speed DA
conversion on the audio signal Se output from the adder 13 and outputs it to the amplifier 15.
The amplifier 15 amplifies the audio signal Sf converted to an analog signal in the DA converter
14 by a predetermined gain A to generate a drive signal Vo, and outputs the drive signal Vo to
the speaker 2 to drive the speaker 2 Do. Such an amplifier 15 operates with positive and negative
power supply voltages, generates a drive signal Vo within the possible output range determined
by the positive and negative power supply voltages, and outputs the drive signal Vo to the
speaker 2. Therefore, when the amplifier 15 adds the gain A to the audio signal Sf and outputs it
while exceeding the output possible range, the drive signal Vo is clipped at the upper limit value
or the lower limit value of the output possible range. That is, the amplifier 15 has a maximum
allowable input capable of outputting the drive signal Vo without clipping, and when the
amplitude of the audio signal Sf input to the amplifier 15 does not exceed the maximum
allowable input, the drive signal Vo is clipped. It is output to the speaker 2 without being output.
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[0028]
FIG. 2 is a diagram showing the concept of signals in each of the above-mentioned parts. First,
FIG. 2A shows an example of the pilot signal SP output from the pilot signal output circuit 20. As
shown in FIG. The pilot signal SP is an AC signal of 4 Hz as described above, and its amplitude is
Vp. The pilot signal output circuit 20 always outputs a pilot signal SP as shown in FIG. 2A to the
adder 13.
[0029]
FIG. 2 (b) shows an example of the audio signal Sa input to the volume adjustment circuit 10.
After such an audio signal Sa is amplified in the volume adjustment circuit 10, when amplitude
limitation is applied in the limit circuit 11, the audio signal Sc output from the limit circuit 11 is a
signal as shown in FIG. 2 (c). It becomes. That is, the audio signal Sc output from the limit circuit
11 is a signal whose maximum amplitude is limited to the predetermined value Ath. Here, in the
limit circuit 11, in order to limit the maximum amplitude of the audio signal Sc, the
predetermined value Ath has a margin corresponding to the amplitude Vp of the pilot signal SP
with respect to the maximum allowable input Amax of the amplifier 15. It is preset. The limit
circuit 11 outputs the audio signal Sb as it is when the amplitude of the input audio signal Sb is
less than or equal to the predetermined value Ath, whereas it exceeds the predetermined value
Ath when the amplitude of the audio signal Sb exceeds the predetermined value Ath. The signal is
removed, and the amplitude is limited to a predetermined value Ath and output. As a result, the
maximum amplitude of the audio signal Sc output from the limit circuit 11 becomes a
predetermined value Ath as shown in FIG. 2C, and for the maximum allowable input Amax of the
amplifier 15, the amplitude Vp equivalent of the pilot signal SP Room for
[0030]
Then, after the low frequency signal component is removed by the high pass filter 12, when the
audio signal Sd and the pilot signal SP are added in the adder 13, the audio signal Se output from
the adder 13 is shown in FIG. It becomes a signal as shown in). That is, since the maximum
amplitude of the audio signal Sc is limited to the predetermined value Ath in the limit circuit 11,
the maximum amplitude of the audio signal Se is the amplifier 15 even if the pilot signal SP is
added to the audio signal Sd in the adder 13. Not exceed the maximum allowable input Amax.
Therefore, since the drive signal Vo is not clipped in the amplifier 15, the pilot signal SP for
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measuring the temperature of the speaker 2 is transmitted to the speaker 2 in a state of being
superimposed on the drive signal Vo.
[0031]
On the other hand, the speaker 2 includes the voice coil 3, and when the current according to the
drive signal Vo flows to the voice coil 3, the diaphragm vibrates to perform sound output. The
voice coil 3 is made of copper or the like, and has a resistance of 8Ω under a temperature
environment of 0 degrees, for example. When current flows in such a voice coil 3, the
temperature of the voice coil 3 rises, and the resistance value of the voice coil 3 changes. In the
present embodiment, the temperature of the speaker 2 is measured by measuring the fluctuation
of the resistance value of the voice coil 3. That is, the temperature of the voice coil 3 itself is
measured as the temperature of the speaker 2.
[0032]
One end of the voice coil 3 is connected to the amplifier 15, and the other end is connected to
the ground point via the resistor Rc. Therefore, when the current IR flows to the voice coil 3 by
the drive signal Vo, the current IR also flows to the resistor Rc, and a potential difference
corresponding to the current IR is generated at both ends of the resistor Rc. The IV conversion
circuit 16 is a circuit connected between the voice coil 3 and the resistor Rc to convert the
current IR flowing through the resistor Rc into a voltage, and converts the current detection
signal V1 appearing as a voltage according to the current IR into an AD converter Output to 17.
The AD converter 17 is, for example, a ΔΣ AD converter, and performs high-speed AD
conversion of the current detection signal V1 output from the IV conversion circuit 16. The
current detection signal Sv converted to a digital signal by the AD converter 17 is output to the
temperature detection circuit 18.
[0033]
FIG. 3 is a diagram showing a configuration example of the temperature detection circuit 18, and
FIGS. 3A and 3B show different configuration examples. First, the temperature detection circuit
18 shown in FIG. 3A includes the low pass filter 31, the absolute value circuit 32, and the
averaging circuit 33. The low pass filter 31 is a filter that removes high frequency components
from the current detection signal Sv output from the AD converter 17. The low pass filter 31 is
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formed of, for example, an IIR filter with a small delay. The cutoff frequency of the low pass filter
31 is set to a frequency higher than the frequency of the pilot signal SP and lower than the cutoff
frequency of the high pass filter 12 described above. In the present embodiment, the cutoff
frequency of the low pass filter 31 is set to, for example, 10 Hz. Therefore, the low pass filter 31
can extract only the signal component corresponding to the frequency (4 Hz) of the pilot signal
SP from the current detection signal Sv output from the AD converter 17, and transmits the
signal component to the absolute value circuit 32. Output. The absolute value circuit 32 is a
circuit that outputs the absolute value of the signal output from the low pass filter 31. The
averaging circuit 33 is a circuit that outputs the temperature detection signal St corresponding to
the amplitude of the signal component corresponding to the frequency of the pilot signal SP by
integrating and averaging the signals output from the absolute value circuit 32. . The
temperature detection signal St is a signal corresponding to the temperature of the speaker 2.
That is, when the temperature of the voice coil 3 rises and the resistance value of the voice coil 3
rises, the current IR flowing through the voice coil 3 decreases accordingly. At this time, the
current component corresponding to the pilot signal SP included in the current IR also decreases.
Therefore, the temperature detection signal St corresponding to the amplitude of the signal
component (the signal component corresponding to the frequency of the pilot signal SP)
extracted from the current detection signal Sv has a signal level gradually increased as the
temperature of the speaker 2 rises. It is a signal that becomes smaller and is a signal according to
the temperature of the speaker 2.
[0034]
Further, the temperature detection circuit 18 shown in FIG. 3B is configured to include a low
pass filter 31, a delay circuit 34, a multiplier 35, and an averaging circuit 33. In the temperature
detection circuit 18 shown in FIG. 3B, the pilot signal SP output from the pilot signal output
circuit 20 is supplied to the delay circuit 34. The low pass filter 31 is the same as that shown in
FIG. 3A, and the signal S1 obtained by extracting only the signal component corresponding to the
frequency (4 Hz) of the pilot signal SP from the signal Sv output from the AD converter 17 is
used. The signal S1 is generated and output to the multiplier 35. Here, when Vt is an amplitude
according to the temperature of the speaker 2 and ω is an angular velocity, the signal S1 can be
expressed as S1 = Vt · sin ωt (Expression 1).
[0035]
The delay circuit 34 delays the pilot signal SP output from the pilot signal output circuit 20 and
generates a signal S2 in which the phase of the pilot signal SP is synchronized with the phase of
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the signal S1 output from the low pass filter 31 The signal S2 is output to the multiplier 35. This
signal S2 can be expressed as S2 = Vpsin ωt (Expression 2).
[0036]
The multiplier 35 generates a multiplication signal S3 by multiplying the signal S1 and the signal
S2 and outputs the multiplication signal S3 to the averaging circuit 33. The multiplication signal
S3 can be expressed as S3 = S1 · S2 = Vtsin ωt · Vpsin ωt (Expression 3).
[0037]
The averaging circuit 33 outputs the temperature detection signal St by integrating and
averaging the multiplication signal S3 output from the multiplier 35 for one cycle of the pilot
signal SP. The processing by the averaging circuit 33 can be expressed by the following equation
4.
[0038]
[0039]
According to the formula 4, the temperature detection signal St output from the averaging circuit
33 does not include a frequency component, so that the amplitude Vt according to the
temperature of the speaker 2 can be detected with high accuracy.
Therefore, the temperature detection circuit 18 shown in FIG. 3B can detect the temperature of
the speaker 2 more accurately than the temperature detection circuit 18 shown in FIG. 3A.
However, as the present embodiment, the temperature detection circuit 18 shown in FIG. 3A may
be adopted, or the temperature detection circuit 18 shown in FIG. 3B may be adopted.
[0040]
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The temperature detection signal St obtained as described above is output to the volume control
circuit 19. The volume control circuit 19 is a circuit that outputs a control signal CNT that
controls the volume adjustment circuit 10 to the volume adjustment circuit 10 based on the
temperature detection signal St. When the temperature of the speaker 2 specified based on the
temperature detection signal St is equal to or lower than a predetermined temperature, the
volume control circuit 19 holds the control signal CNT for holding the amplification factor in the
volume adjustment circuit 10 at a predetermined value in a constant state. Output. Thus, the
speaker 2 can be driven in a state in which the output power of the speaker 2 is held in a
constant state. On the other hand, when the temperature of the speaker 2 specified based on the
temperature detection signal St exceeds the predetermined temperature, the volume control
circuit 19 switches the amplification factor in the volume adjustment circuit 10 to a value smaller
than the predetermined value. Output control signal CNT. As a result, the output power of the
speaker 2 is reduced, so that the temperature of the speaker 2 can be further prevented from
rising, and the speaker 2 can be protected. The volume control circuit 19 can also amplify the
input audio signal Sa by the control signal CNT.
[0041]
Further, a low pass filter may be inserted between the volume control circuit 19 and the volume
adjustment circuit 10. In this case, when the volume control circuit 19 switches the amplification
factor in the volume adjustment circuit 10 to a value smaller than a predetermined value, the low
pass filter delays the control signal CNT. As a result, the volume adjustment circuit 10 gradually
reduces the amplification factor without changing the amplification factor rapidly, so that the
sound quality output from the speaker 2 is prevented from being temporarily deteriorated. be
able to.
[0042]
As described above, the amplification apparatus 1 according to the present embodiment limits
the amplitude of the audio signal Sb by the amount equivalent to the pilot signal SP before the
adder 13 that adds the pilot signal SP to the input audio signal Sa. In the case where the pilot
signal SP is superimposed by the adder 13 in the subsequent stage, the limiter circuit 11 includes
the limit circuit 11 to be applied, and the limit circuit 11 limits the maximum amplitude of the
audio signal Sb to the predetermined value Ath in advance. However, the audio signal Sf input to
the amplifier 15 can be prevented in advance from exceeding the maximum allowable input of
the amplifier 15. Therefore, the drive signal Vo output from the amplifier 15 can be prevented
from clipping, and the pilot signal SP for measuring the temperature of the speaker 2 will not be
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buried in the clip signal. It will always be able to measure normally.
[0043]
In particular, since the limit circuit 11 limits the maximum amplitude of the audio signal Sb so
that a margin corresponding to the pilot signal SP is generated with respect to the maximum
allowable input of the amplifier 15 as described above, the drive signal Vo can be prevented from
clipping. The speaker 2 can be driven while maintaining the output power of the speaker 2 in the
range as much as possible. That is, the limit circuit 11 performs the amplitude limitation so as to
lower the maximum amplitude of the audio signal Sb by an amount corresponding to the
amplitude Vp of the pilot signal SP, so that the output power of the speaker 2 is significantly
reduced. It can be suppressed.
[0044]
As mentioned above, although one Embodiment of this invention was described, this invention is
not limited to what was mentioned above, A various deformation | transformation is applicable.
For example, in the above embodiment, the case where the limit circuit 11 is provided before the
high pass filter 12 is illustrated. However, the present invention is not limited to this, and the
limit circuit 11 may be provided downstream of the high pass filter 12.
[0045]
Moreover, in the said embodiment, the case where pilot signal SP was an AC signal of 4 Hz was
illustrated. However, the pilot signal SP is not necessarily limited to the AC signal, and may be a
DC signal. Further, even when the pilot signal SP is an AC signal, the frequency of the pilot signal
SP is not limited to 4 Hz, and may be a predetermined frequency in the inaudible range.
[0046]
DESCRIPTION OF SYMBOLS 1 ... Amplifier device, 2 ... Speaker 11: Limit circuit 12 12 High pass
filter 13 Adder 15 Amplifier 18 Temperature detection circuit 19 Volume control circuit 20 Pilot
signal output circuit SP Pilot Signals Sa, Sb, Sc, Sd, Se, Sf... Audio signals.
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