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DESCRIPTION JP2002345071

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DESCRIPTION JP2002345071
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio signal reproduction apparatus suitable for use in reproduction of, for example, a super
audio CD.
[0002]
2. Description of the Related Art In recent years, as compared with analog power amplification
circuits, the audio signal reproduction apparatus has a power loss smaller and power conversion
efficiency better than analog power amplification circuits as power amplification circuits for
driving speakers. Power amplifier circuits are being used.
[0003]
As a conventional audio signal reproduction apparatus using this digital power amplification
circuit, for example, the one shown in FIG. 5 has been proposed.
Referring to the conventional audio signal reproduction apparatus as shown in FIG. 5, reference
numeral 1 in FIG. 5 denotes an audio signal input terminal to which an audio signal is supplied.
The voice signal is supplied to a pulse modulator 2 that modulates it into a pulse signal.
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[0004]
As the pulse modulator 2, for example, a pulse width modulator (PWM modulator) that pulse
width modulates this audio signal, a ΔΔ modulator that modulates this audio signal by ΔΣ
(digital-sigma), or the like is used. The output signal of this pulse modulator 2 is supplied to the
driver circuit 3. The driver circuit 3 amplifies the signal to an optimal signal for driving the pulse
amplification circuit 4 of the next stage.
[0005]
The output terminals 3a and 3b from which drive signals having different phases are obtained
from each other of the driver circuit 3 are respectively connected to switching elements
constituting the pulse amplification circuit 4, for example, control terminals or gates of power
MOS field effect transistors 4a and 4b. One controlled terminal, for example, a drain of the
switching element 4a is connected to the power supply terminal 4c to which the positive power
supply VD is supplied.
[0006]
The other controlled terminal of the switching element 4a, for example, the source is connected
to one controlled terminal of the switching element 4b, for example, the drain, and the other
controlled terminal of the switching element 4b, for example, the source is supplied with a
negative power supply VS. Connect to terminal 4d.
[0007]
The connection point of the other controlled terminal of switching element 4a and one controlled
terminal of switching element 4b, that is, the output terminal 4e is grounded via coil 5a and
speaker 6, and the connecting point of coil 5a and speaker 6 is a capacitor Ground via 5b.
The coil 5a and the capacitor 5b constitute a low pass filter, and constitute a demodulator 5 for
pulse signals.
[0008]
The anode of diode 7 and the cathode of diode 8 are provided such that the current (free
wheeling current) generated by the energy stored in coil 5a does not destroy switching elements
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4a and 4b. The cathode of the diode 7 is connected to the power supply terminal 4c, and the
anode of the diode 8 is connected to the power supply terminal 4d.
[0009]
In the conventional example of FIG. 5, the switching elements 4a and 4b of the pulse
amplification circuit (power amplification circuit) 4 are alternately turned on and off according to
the output drive signal from the driver circuit 3 as shown in FIGS. The pulse signal V0 as shown
in FIG. 6C is obtained at the output terminal 4e of the pulse amplification circuit 4 and the
current I0 as shown in FIG. 6D is obtained.
[0010]
The pulse signal V0 is demodulated into an analog audio signal by a demodulator 5 of a low pass
filter configuration consisting of a coil 5a and a capacitor 5b.
At this time, the freewheeling current generated due to the energy stored in the coil 5a flows to
the power supply terminals 4c and 4d via the diodes 7 and 8 and does not destroy the switching
elements 4a and 4b.
[0011]
By the way, in order to amplify the audio signal supplied to the audio signal input terminal 1
without distortion, the pulse signal V0 obtained at the output terminal 4e of the pulse
amplification circuit 4 is as shown in FIG. 2A. It should be an ideal rectangular wave, but in fact,
as shown in FIG. 2B, the pulse voltage V0 has noise voltage and surge voltage in the rise period
tr0 of the pulse signal V0 and the fall period tf0 of the pulse signal V0. The noise waveforms Vn0
and Vn1 are generated due to the cause.
[0012]
Here, the principle causes of the rising period tr0 and falling period tf0 of the pulse signal V0
and the noise waveforms Vn0 and Vn1 will be described.
[0013]
(1) The rising period tr0 and the falling period tf0 of the pulse signal V0 are caused by the delay
of the response speed of the switching elements 4a and 4b and the parasitic capacitance of the
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switching elements 4a and 4b.
[0014]
(2) A freewheel current flows through the diodes 7 and 8 due to the energy stored in the coil 5a,
and immediately after the freewheel current flows in the forward direction of the diodes 7 and 8,
the diodes of the switching elements 4a and 4b are switched. When a reverse voltage is applied
to 7 and 8, a large current (reverse recovery current) flows in the reverse direction due to the
nature of the diode.
The reverse recovery current is superimposed on the load current I0 to generate a surge voltage.
[0015]
(3) When the speed of the current i changes when there is an inductor component in the wiring
or printed circuit board pattern, a noise voltage of Vn = -LXdi / dt is generated.
Since the freewheeling current flowing through the diodes 7 and 8 contains many high frequency
components and this di / dt is also large, a noise voltage is generated.
[0016]
In the conventional audio signal reproduction apparatus as shown in FIG. 5, as described in (1) to
(3) above, much noise and distortion occur in the pulse signal V0 obtained at the output terminal
4e of the pulse amplifier circuit 4. Do.
The noise and distortion are essentially inevitable in the configuration of the conventional audio
signal reproduction apparatus.
Accordingly, the voice signal demodulated by the demodulator 5 also includes noise and
distortion in the pulse signal V0 and is not an ideal rectangular wave, so that noise and distortion
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occur.
[0017]
In recent years, development of power devices such as high-speed power MOS field effect
transistors has progressed, and it has become possible to increase the switching speed of
switching elements.
If the switching speed of this pulse amplification circuit is increased, the resolution on the
frequency axis can be made finer, and the sound quality can also be improved.
[0018]
However, as a result of the increase in switching speed, the high frequency components of the
reverse recovery current and freewheel current described above also increase, so the noise
voltage and surge voltage also increase, and the result of the sound quality improvement due to
the increase in switching speed is reduced. I am doing it.
[0019]
An object of the present invention is to reduce sound quality deterioration caused by noise and
distortion of an output pulse signal generated by a pulse amplification circuit.
[0020]
The audio signal reproducing apparatus according to the present invention is suitable for pulse
modulation means for modulating an audio signal in the form of a pulse, and for driving the
output signal of this pulse modulation means for the pulse amplification means of the next stage.
Audio signal reproduction apparatus comprising: driver means for amplifying into a stable signal;
pulse amplification means for generating a pulse signal according to the output signal of the
driver means; demodulation means for demodulating an audio signal from the output signal of
the pulse amplification means A diode is connected between the output side of the pulse
amplifying means and the power supply, and a high frequency current suppressing means for
suppressing a high frequency current is connected in series to the diode.
[0021]
According to the present invention, since the high-frequency current suppression means for
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suppressing the high-frequency current is connected in series to the diode that flows the
freewheel current, the high-frequency component of the current (reverse recovery current or
freewheel current) flowing through this diode can be suppressed. The voltage and the surge
voltage can be reduced, noise and distortion of the pulse signal obtained on the output side of the
pulse amplification means can be reduced, and the sound quality of the audio signal obtained on
the output side of the demodulation means can be improved.
[0022]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the
audio signal reproducing apparatus according to the present invention will be described below
with reference to FIGS. 1 and 2. FIG.
In FIG. 1, parts corresponding to FIG. 5 are given the same reference numerals.
[0023]
In FIG. 1, reference numeral 1 denotes an audio signal input terminal to which an audio signal is
supplied, and the audio signal supplied to the audio input terminal 1 is supplied to a pulse
modulator 2 which modulates the audio signal into a pulse signal.
[0024]
As the pulse modulator 2, for example, a pulse width modulator that pulse-width modulates the
voice signal, a delta-sigma modulator that delta-sigma modulates the voice signal, or the like is
used.
The output signal of this pulse modulator 2 is supplied to the driver circuit 3.
The driver circuit 3 amplifies the signal to an optimum signal for driving the pulse amplification
circuit (power amplification circuit) 4 of the next stage.
[0025]
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One and the other output terminals 3a and 3b of this driver circuit 3 can obtain driving signals
different in phase from each other as switching elements constituting pulse amplifier circuit 4,
for example, control terminals or gates of power MOS field effect transistors 4a and 4b. The
respective controlled terminals of the switching element 4a, for example, the drain thereof are
connected to the power supply terminal 4c to which the positive power supply VD is supplied.
[0026]
The other controlled terminal of the switching element 4a, for example, the source is connected
to one controlled terminal of the switching element 4b, for example, the drain, and the other
controlled terminal of the switching element 4b, for example, the source is supplied with a
negative power supply VS. Connect to terminal 4d.
[0027]
The connection point of the other controlled terminal of switching element 4a and one controlled
terminal of switching element 4b, that is, the output terminal 4e is grounded via coil 5a and
speaker 6, and the connecting point of coil 5a and speaker 6 is a capacitor Ground via 5b.
The coil 5a and the capacitor 5b constitute a low pass filter, and constitute a demodulator 5 for
pulse signals.
[0028]
In this example, current (free wheeling (Free Wheeling) is generated due to the energy stored in
coil 5a through high frequency current suppression element 9 made of an inductor such as a
ferrite bead, for example, which suppresses high frequency current at output terminal 4e. ) Is
connected to the anode of a diode 7 provided so as not to destroy the switching element 4a, and
the cathode of the diode 7 is connected to the power supply terminal 4c.
[0029]
Further, in this example, the output terminal 4e is connected to the cathode of a diode 8 provided
so that the current (free wheeling current) generated by the energy stored in the coil 5a does not
destroy the switching element 4b. The anode of the diode 8 is connected to the power supply
terminal 4d via the high frequency current suppression element 10 formed of an inductor such
as a ferrite bead for suppressing high frequency current.
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[0030]
In this example, switching elements 4a and 4b of pulse amplification circuit (power amplification
circuit) 4 are alternately repeated on and off according to the output drive signal from driver
circuit 3 as shown in FIGS. 6A and 6B. An output pulse signal as shown in FIG. 6C is obtained at
the output terminal 4e of the pulse amplification circuit 4 and an output current as shown in FIG.
6D is obtained.
[0031]
This output pulse signal is demodulated into an analog audio signal by the demodulator 5 of the
low pass filter configuration consisting of the coil 5a and the capacitor 5b.
At this time, the freewheeling current generated due to the energy stored in the coil 5a flows to
the power supply terminals 4c and 4d via the diodes 7 and 8 and does not destroy the switching
elements 4a and 4b.
[0032]
Further, according to the present embodiment, since the high frequency current suppression
elements 9 and 10 including inductors such as ferrite beads for suppressing high frequency
current are connected in series to the diodes 7 and 8 for flowing the freewheel current, Can
suppress the high frequency components of the current (reverse recovery current and free wheel
current) flowing in the noise, and can reduce the noise voltage and the surge voltage, and the
noise of the pulse signal V1 obtained at the output terminal 4e of the pulse amplification circuit
4 Distortion can be reduced, and the sound quality of the audio signal obtained on the output
side of the demodulator 5 can be improved.
[0033]
In this case, the ferrite bead is characterized in that it is a saturable inductor having a large
inductance in the band of high frequency current causing this noise and distortion, and magnetic
saturation and a small inductance in the band below this high frequency current. Most of the
freewheeling current flows through the diodes 7 and 8 and the switching elements 4a and 4b are
not destroyed, and the ferrite beads do not impair the effects of the diodes 7 and 8.
[0034]
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3 and 4 each show another example of the embodiment of the present invention.
In FIG. 3 and FIG. 4, portions corresponding to FIG. 1 are given the same reference numerals, and
the detailed description thereof is omitted.
[0035]
In the example of FIG. 3, the driver circuit 3 of FIG. 1 is a driver circuit 20 of the BTL system, and
one and the other output terminals 20 a and other output terminals 20 a can be obtained with
drive signals different in phase from each other. 20b are respectively connected to control
terminals of switching elements constituting the pulse amplification circuit 21, for example,
power MOS field effect transistors 21a and 21b, and one controlled terminal of the switching
element 21a is supplied with positive power VD (DC power supply Connected to the power
supply terminal 21c).
[0036]
The other controlled terminal of the switching element 21a is connected to one controlled
terminal of the switching element 21b, and the other controlled terminal of the switching
element 21b is grounded (negative electrode of DC power supply).
[0037]
A connection point of the other controlled terminal of the switching element 21a and one
controlled terminal of the switching element 21b, that is, the output terminal 21d is connected to
one input terminal of the speaker 6 via the coil 22a. The connection point of one of the input
terminals is grounded via the capacitor 22b.
The coil 22a and the capacitor 22b constitute a low pass filter, and constitute a pulse signal
demodulator 22.
[0038]
In this example, current (free wheeling (Free Wheeling) is generated due to the energy stored in
the coil 22a via the high frequency current suppression element 23 composed of an inductor
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such as a ferrite bead, for example, which suppresses the high frequency current at the output
terminal 21d. ) Is connected to the anode of a diode 24 provided so as not to destroy the
switching element 21a, and the cathode of this diode 24 is connected to the power supply
terminal 21c.
[0039]
Further, the output terminal 21d is connected to the cathode of a diode 25 provided so that the
current (free wheel current) generated by the energy stored in the coil 22a does not destroy the
switching element 21b, and the anode of the diode 25 is It grounds via the high frequency
current suppression element 26 which consists of inductors, such as a ferrite bead, for example
which suppresses a high frequency current.
[0040]
Also, switching elements such as power MOS field effect transistors 28a and 28b, which
respectively constitute one pulse amplifying circuit 28, output terminals 20c and 20d on one side
and the other side where drive signals having different phases from each other can be obtained.
The control terminal is connected, and one controlled terminal of the switching element 28a is
connected to the power terminal 28c to which the positive power source VD is supplied (the
positive terminal of the DC power source is connected).
[0041]
The other controlled terminal of the switching element 28a is connected to one controlled
terminal of the switching element 28b, and the other controlled terminal of the switching
element 28b is grounded (negative electrode of DC power supply).
[0042]
A connection point of the other controlled terminal of the switching element 28a and one
controlled terminal of the switching element 28b, that is, the output terminal 28d is connected to
the other input terminal of the speaker 6 via the coil 29a. The connection point of the other input
terminal is grounded via a capacitor 29b.
The coil 29 a and the capacitor 29 b constitute a low pass filter and constitute a pulse signal
demodulator 29.
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[0043]
In this example, current (free wheeling (Free Wheeling) is generated due to the energy stored in
the coil 29a via the high frequency current suppression element 30 made of an inductor such as
a ferrite bead or the like for suppressing the high frequency current, for example. ) Is connected
to the anode of a diode 31 provided so as not to destroy the switching element 28a, and the
cathode of this diode 31 is connected to a power supply terminal 28c.
[0044]
Further, the output terminal 28d is connected to the cathode of a diode 32 provided so that the
current (freewheel current) generated by the energy stored in the coil 29a does not destroy the
switching element 28b, and the anode of the diode 32 is It grounds via the high frequency
current suppression element 33 which consists of inductors, such as a ferrite bead, for example
which suppresses a high frequency current.
[0045]
In the example of FIG. 3, the switching elements 21a and 21b and the switching elements 28a
and 28b of the pulse amplification circuit 21 and the pulse amplification circuit 28 are opposite
to each other in phase opposite to each other according to the output drive signal from the BTL
driver circuit 20. As shown in FIG. 6B, ON and OFF are alternately repeated, and output pulse
signals as shown in FIG. 6C having opposite phases are obtained at the output terminals 21d and
28d of the pulse amplification circuits 21 and 28 and outputs as shown in FIG. A current is
obtained.
[0046]
The output pulse signal is demodulated into an analog audio signal by the low pass filter type
demodulator 22 consisting of a coil 22a and a capacitor 22b and the low pass filter type
demodulator 29 consisting of a coil 29a and a capacitor 29b.
At this time, freewheel current generated due to energy stored in the coil 22a and the coil 29a
flows to the power terminal 21c, the ground, the power terminal 28c and the ground through the
diodes 24 and 25 and the diodes 31 and 32, and switching The elements 21a and 21b and the
switching elements 28a and 28b are not destroyed.
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[0047]
Further, according to the present embodiment, the high frequency current suppression elements
23 and 26 and the high frequency current suppression, each of which comprises an inductor
such as a ferrite bead for suppressing the high frequency current in series with the diodes 24
and 25 flowing the freewheel current and the diodes 31 and 32, respectively. Since the elements
30 and 33 are connected, high frequency components of the current (reverse recovery current
and free wheel current) flowing through the diodes 24 and 25 and the diodes 31 and 32 can be
suppressed, and noise voltage and surge voltage can be reduced. As shown in FIG. 2C, noise and
distortion of the mutually opposite phase pulse signal V1 obtained at the output terminals 21d
and 28d of the pulse amplification circuits 21 and 28 can be reduced, and an audio signal
obtained at the output side of the demodulators 22 and 29 It is possible to improve the sound
quality of
[0048]
In the example of FIG. 4, in the example of FIG. 1, the diodes 7 and 8 for flowing the freewheel
current are respectively constituted by a parallel circuit of a plurality of diodes 7a, 7b... 7n and a
parallel circuit of a plurality of diodes 8a, 8b. As shown in FIG. 2D, the rising period tr and the
falling period tf of the output pulse signal V2 are shortened.
Others are configured in the same manner as in FIG.
[0049]
The rise period tr and fall period tf of the output pulse signal of the pulse amplification circuit 4
are caused by the delay of the response speed of the switching elements 4a and 4b, the parasitic
capacitance of the switching elements 4a and 4b, etc. When the current flowing to the parasitic
capacitance increases, this period tr, tf becomes longer.
As the rising period tr and falling period tf are shorter, distortion of the output pulse signal is
reduced to be closer to the ideal waveform of FIG. 2A, distortion of the demodulated voice signal
is also reduced and sound quality is improved.
[0050]
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As shown in FIG. 4, when the diodes for flowing the freewheeling current are formed by a
parallel connection circuit of a plurality of diodes, the current of each diode can be reduced, and
the parasitic capacitances of the switching elements 4a and 4b are cancelled. Since there are
effects as well, the rising period tr and falling period tf of this output pulse signal can be
shortened as shown in FIG. 2D.
[0051]
Thus, in the example of FIG. 4, the same operation and effect as in the example of FIG. 1 can be
obtained, and furthermore, the rising period tr and falling period tf of the output pulse signal V2
can be shortened as shown in FIG. Distortion of the signal is also reduced, and the sound quality
can be further improved.
[0052]
In the above example, a high frequency current suppression element comprising an inductor
such as a ferrite bead is provided in series with both the diodes 7 and 8, both the diodes 24 and
25, and both the diodes 31 and 32, It can be easily understood that the same function and effect
as described above can be obtained by providing this high frequency current suppression
element in series with the diode.
[0053]
Further, it goes without saying that the present invention is not limited to the above-described
example and that various other configurations can be adopted without departing from the scope
of the present invention.
[0054]
According to the present invention, since the high frequency current suppression element for
suppressing the high frequency current is connected in series to the diode for passing the free
wheel current, the high frequency component of the current (reverse recovery current or free
wheel current) flowing through this diode Noise and surge voltage can be reduced, noise and
distortion of the pulse signal obtained on the output side of the pulse amplification circuit can be
reduced, and the sound quality of the audio signal obtained on the output side of the
demodulator can be improved. it can.
[0055]
Brief description of the drawings
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[0056]
1 is a block diagram showing an example of an embodiment of the audio signal reproduction
apparatus of the present invention.
[0057]
2 is a diagram for explaining the present invention.
[0058]
3 is a configuration diagram showing another example of the embodiment of the present
invention.
[0059]
4 is a configuration diagram showing another example of the embodiment of the present
invention.
[0060]
5 is a block diagram showing an example of a conventional audio signal reproduction apparatus.
[0061]
6 is a diagram for explaining the audio signal reproduction device.
[0062]
Explanation of sign
[0063]
1. Audio signal input terminal 2. Pulse modulator 3. Driver circuit 4. Pulse amplification circuit
4a, 4b Switching element 5. Demodulator 6. Speaker 7, 8 .... Diodes 9, 10 .... High frequency
current suppression elements
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