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JPH0630356

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DESCRIPTION JPH0630356
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
frequency characteristic variable circuit for variably processing the frequency characteristic of
reproduced sound in an audio reproduction apparatus such as a television apparatus, and a
television apparatus comprising the frequency characteristic variable circuit.
[0002]
2. Description of the Related Art Heretofore, various types of sound reproducing devices have
been proposed, such as television devices, which amplify a reproduced signal and reproduce it as
sound through a speaker device. In such an audio reproduction device, the reproduction signal is
supplied from a tuner device for receiving and demodulating broadcast radio waves, a video tape
recorder device, a video disk player device, and the like. In this sound reproduction device, the
reproduction signal is amplified by a sub amplifier circuit (preamplifier) that performs volume
control and tone control, and further amplified by a main amplifier circuit (main amplifier) and
sent to the speaker device, It is reproduced as sound.
[0003]
By the way, in such a sound reproducing apparatus, when electromagnetic noise from the outside
is mixed in the reproduction signal before being amplified by the main amplification circuit, the
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electromagnetic noise is also generated. It is amplified by the main amplifier circuit together with
the reproduction signal and reproduced as an audible sound. In particular, in a television
apparatus, a large current is consumed to drive the deflection yokes of a cathode ray tube
disposed in the vicinity of each of the amplification circuits, and the electromagnetic noise due to
the drive current of the deflection yokes is the reproduction signal There is a great risk of being
mixed into the The drive current of the deflection yoke is 15.734 KHz for horizontal deflection
current and 60 Hz for vertical deflection current in the case of NTSC system, and the horizontal
deflection current is 15.625 KHz for vertical deflection current in the case of PAL system. Is 50
Hz, and when it is reproduced as sound as electromagnetic noise, all become sound of audio
frequency. Such noise caused by the drive current of the magnetic yoke is reproduced as sound
as so-called buzz noise.
[0004]
Conventionally, in order to prevent electromagnetic noise from being reproduced as sound, a
filter is interposed between the sub-amplifying circuit and the main amplifying circuit. In this
case, a filtered reproduced signal is supplied to the main amplification means. This filter is a socalled low pass filter, high pass filter or the like, and reduces the component of a specific
frequency band for the reproduction signal and the electromagnetic noise mixed in the
reproduction signal. That is, by using a filter having a characteristic of reducing the frequency
component of the electromagnetic noise, it is possible to reduce the level of the acoustic noise
when the electromagnetic noise is reproduced as the acoustic.
[0005]
However, since the filter also passes the reproduced signal, if the cutoff characteristic of the
specific frequency is steep, the frequency characteristic of the reproduced signal will be greatly
changed. That is, if the cut-off frequency characteristic of the filter is steep, the sound in the
specific frequency band will not be reproduced, and the audibility of the reproduced sound will
be unnatural. Therefore, this filter can not sufficiently block the electromagnetic noise because
the filter needs to have a moderate characteristic for reducing the signal in the specific frequency
band.
[0006]
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Also, in order to prevent reproduction as the sound of the electromagnetic noise, electromagnetic
shielding of the path through which the reproduction signal is sent is performed. Such a shield is
performed by covering a circuit board or a cable with a shield plate made of a metal plate or the
like. However, applying such a shield leads to an increase in size and complexity of the
configuration of the above-described sound reproduction device and a complication of
manufacture.
[0007]
Therefore, the present invention has been proposed in view of the above-mentioned
circumstances, and does not increase the size and complexity of the structure of the sound
reproduction device or complicate the manufacturing, and can not hear the reproduced sound.
An object of the present invention is to provide a frequency characteristic variable circuit which
can suppress electromagnetic noise from being reproduced as sound without loss and a
television apparatus provided with the frequency characteristic variable circuit.
[0008]
In order to solve the above problems and achieve the above object, the frequency characteristic
variable circuit according to the present invention is supplied with the reproduction signal
amplified by the sub-amplifying means for performing volume control. And controlled by a
volume control signal for controlling an amplification factor in the sub amplification means,
variably processing the frequency characteristic of the reproduction signal according to the
volume control signal, and supplying the reproduction signal subjected to this processing to the
main amplification means It is
[0009]
Further, in the frequency characteristic variable circuit according to the present invention, the
reproduction signal amplified by the sub-amplifying means for performing volume control is
supplied, and is controlled by a noise detection signal obtained by detecting an ambient noise
level. The above-mentioned frequency characteristics are variably processed in accordance with
the noise detection signal, and the reproduced signal subjected to this processing is supplied to
the main amplification means.
[0010]
Further, the frequency characteristic variable circuit according to the present invention is
supplied with the reproduction signal amplified by the sub-amplifying means for performing
volume control, and is controlled according to the signal level of the reproduction signal to
control the frequency characteristic of the reproduction signal. The variable processing is
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performed according to the signal level of the reproduction signal, and the reproduction signal
subjected to this processing is supplied to the main amplification means.
[0011]
The television apparatus according to the present invention is provided with at least one of the
above-described frequency characteristic variable circuits.
[0012]
The frequency characteristic variable circuit according to the present invention is supplied with
the reproduction signal amplified by the secondary amplification means for volume control, and
detects the volume control signal for controlling the amplification factor in the secondary
amplification means and the ambient noise level. Controlled by the signal level of the noise
detection signal obtained or the reproduction signal, and the frequency characteristic of the
reproduction signal is variable according to the signal level of the volume control signal, the
noise detection signal, or the reproduction signal Since the processed reproduction signal is
supplied to the main amplification means, the electromagnetic noise is acoustic such as when the
volume is suppressed, when the ambient noise level is low, or when the signal level of the
reproduction signal is low. When the sound is easy to be clearly heard when being reproduced as
When the sound the electromagnetic noise is reproduced hardly be clearly listened does not
perform a variable processing of the frequency characteristics for the reproduction signal,
formed as providing a natural auditory frequency characteristic of the reproduced signal.
[0013]
Further, since the television apparatus according to the present invention includes at least one of
the above-described frequency characteristic variable circuits, noise in reproduced sound due to
the drive current of the deflection yoke is reduced.
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A specific embodiment of the
present invention will be described below with reference to the drawings.
The television apparatus according to the present invention configured to have the frequency
characteristic variable circuit according to the present invention is, as shown in FIG. 1, a
preamplifier comprising a tone controller 5 and a volume controller 6 serving as a sub-
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amplifying means; And a main amplifier 7 as a means.
[0015]
A reproduction signal received by the tuner device 2 through the antenna 1 and demodulated by
the demodulator 3 is supplied to the preamplifier through the input selector 4.
The tuner device 2 is configured to select and receive various broadcast radio waves such as
television broadcasting such as so-called VHF and UHF and satellite broadcasting such as socalled BS and CS.
The demodulator 3 is configured to perform demodulation according to various broadcast radio
waves, and when the broadcast radio waves are scrambled (encrypted), perform decryption and
decoding according to the scramble. .
[0016]
Reproduction signals V1 and V2 are supplied to the input selector 4 from a video tape recorder
device, a video disk player device or the like.
The input selector 4 selects one reproduction signal from the reproduction signals according to
the manual operation of the input selection switch of the input selector 4 and supplies it to the
preamplifier.
[0017]
The tone controller 5 which constitutes the above-mentioned preamplifier adjusts the frequency
characteristic of the above-mentioned reproduction signal based on a manual operation or a tone
control signal.
Then, a volume controller 6 constituting this preamplifier is supplied with a volume control
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signal (VOL CONT), and amplifies the reproduction signal by an amplification factor according to
the volume control signal.
[0018]
The reproduction signal amplified by the volume controller 6 is supplied to the main amplifier 7
as the main amplification means through the filter 9, which is the frequency characteristic
variable circuit according to the present invention, as shown in FIGS.
The main amplifier 7 amplifies the supplied reproduction signal with a constant amplification
factor and sends it to the speaker device 8.
The speaker device 8 reproduces the sent reproduction signal as sound.
[0019]
For example, as shown in FIG. 5, the filter 9 is a band pass filter that cuts off the frequency
characteristic of the reproduction signal by blocking about 16 kHz or more and about 50 Hz or
less, and operates controlled by the volume control signal. Do. The control by the volume control
signal for the filter 9 is performed when the volume control signal indicated by the arrow A in
FIG. 4 makes the amplification factor in the volume controller 6 less than a predetermined value,
as shown in FIG. When the volume control signal causes the amplification factor of the volume
controller 6 to be equal to or higher than a predetermined value, the device is in the nonoperation state.
[0020]
That is, in this television device, when the volume level of the reproduction sound in the speaker
device 8 is less than a predetermined level, the sound in the high frequency band of 16 KHz or
more and the low frequency band of 50 Hz or less is blocked. When the volume level of the
reproduction sound in the speaker device 8 is equal to or higher than a predetermined level, the
filter 9 does not operate, and the reproduction signal is reproduced as sound without changing
the frequency characteristic.
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[0021]
In this television apparatus, when electromagnetic noise caused by the drive current of the
deflection yoke of the cathode ray tube and the like is mixed into the reproduction signal, the
volume level of the reproduction sound in the speaker device 8 is higher than a predetermined
level. Noise in which electromagnetic noise is reproduced as sound is buried in the sound in
which the reproduction signal is reproduced and is hardly heard. At this time, since the filter 9
does not operate, the frequency characteristic of the reproduction signal gives a natural sense of
hearing when reproduced as sound.
[0022]
When the volume level of the reproduction sound in the speaker device 8 is less than the
predetermined level, the electromagnetic noise mixed in the reproduction signal is amplified by
the main amplifier 7 and reproduced as sound regardless of the volume level. Ru. Therefore,
noise in which the electromagnetic noise is reproduced as sound can be heard without being
buried in the reproduced sound. However, at this time, since the filter 9 operates, the
electromagnetic noise is blocked before being supplied to the main amplifier 7, and the
reproduction as sound is suppressed. When the volume level of the reproduction sound in the
speaker device 8 is less than a predetermined level, even if the frequency characteristic of the
sound in which the reproduction signal is reproduced is subjected to variable processing, the
influence of the variable processing is Because the playback volume is low, it is hardly audible.
[0023]
As the filter 9, one configured as a so-called digital filter can be used, but as shown in FIG. 3, one
configured as an analog filter may be used.
[0024]
When the filter 9 is configured as an analog filter, in the filter 9, as shown in FIG. 3, the
reproduction signal is transmitted via the first resistor R1 and the second capacitor C2. The
signal is supplied to the main amplifier 7.
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The filter 9 has first and fourth transistors Tr1 and Tr4 whose volume control signal is supplied
to the base terminal via the limiting resistor. The base terminal of the first transistor Tr1 is
grounded via a limiting resistor. The emitter terminal of the first transistor Tr1 is grounded. A
power supply VCC is supplied to the collector terminal of the first transistor Tr1 via a limiting
resistor. The collector terminal of the first transistor Tr1 is connected to the base terminal of the
second transistor Tr2. The emitter terminal of the second transistor Tr2 is grounded. The
collector terminal of the second transistor Tr2 is connected between the first resistor R1 and the
second capacitor C2 via a first capacitor C1. On the other hand, the base terminal of the fourth
transistor Tr4 is grounded via a limiting resistor. The emitter terminal of the fourth transistor
Tr4 is grounded. The collector terminal of the fourth transistor Tr4 is supplied with a power
supply V CC via a limiting resistor. The collector terminal of the fourth transistor Tr4 is
connected to the base terminal of the third transistor Tr3. The emitter terminal of the third
transistor Tr3 is grounded. The collector terminal of the third transistor Tr3 is connected
between the second capacitor C2 and the main amplifier 7 via a second resistor R2.
[0025]
When the level of the volume control signal is equal to or higher than a predetermined level and
the amplification factor of the volume controller is equal to or higher than a predetermined
value, the filter 9 includes the first and fourth transistors Tr1 and Tr4. The second and third
transistors Tr2 and Tr3 are turned off to be in a non-operational state. When the level of the
volume control signal is less than a predetermined level and the amplification factor of the
volume controller is less than a predetermined value, the filter 9 causes the first and fourth
transistors Tr1,. The transistor Tr4 is turned off, and the second and third transistors Tr2 and
Tr3 are turned on to be in an operating state.
[0026]
Further, as shown in FIG. 7, the filter 9 may have a characteristic having a so-called trap band
which blocks only a signal of a specific frequency band. In this case, in the filter 9, as shown in
FIG. 6, the reproduction signal is supplied to the main amplifier 7 via the first resistor R1 and the
second resistor R2. The filter 9 has a first transistor Tr1 whose volume control signal is supplied
to the base terminal via a limiting resistor. The base terminal of the first transistor Tr1 is
grounded via a limiting resistor. The emitter terminal of the first transistor Tr1 is grounded. The
power supply VCC is supplied to the collector terminal of the first transistor Tr1 via a limiting
resistor. The collector terminal of the first transistor Tr1 is connected to the base terminal of the
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second transistor Tr2. The emitter terminal of the second transistor Tr2 is grounded. The
collector terminal of the second transistor Tr2 is connected between the first resistor R1 and the
second resistor R2 via a first inductor L1 and a first capacitor C1. The collector terminal of the
second transistor Tr2 is connected between the second resistor R2 and the main amplifier 7 via
the first inductor L1 and the second capacitor C2.
[0027]
In the filter 9, when the level of the volume control signal is equal to or higher than a
predetermined level and the amplification factor of the volume controller is equal to or higher
than a predetermined value, the first transistor Tr1 is turned on. The second transistor Tr2 is
turned off to be in a non-operating state. When the level of the volume control signal is less than
a predetermined level and the amplification factor of the volume controller is less than a
predetermined value, the first transistor Tr1 is turned off. The second transistor Tr2 is turned on
to be in an operating state.
[0028]
Further, as shown in FIG. 9, the filter 9 may have a characteristic of blocking only the signal in
the low frequency band, and the blocking characteristic may be varied. In this case, in the filter 9,
as shown in FIG. 8, the reproduction signal is supplied to the main amplifier 7 via the first
resistor R1 and the second resistor R2. The portion between the first and second resistors R1 and
R2 is grounded via the first capacitor C1. The filter 9 has a first transistor Tr1 whose volume
control signal is supplied to the base terminal via a limiting resistor. The base terminal of the first
transistor Tr1 is grounded via a limiting resistor. The emitter terminal of the first transistor Tr1
is grounded. A power supply VCC is supplied to the collector terminal of the first transistor Tr1
via a limiting resistor. The collector terminal of the first transistor Tr1 is connected to the base
terminal of the second transistor Tr2. The emitter terminal of the second transistor Tr2 is
grounded. The collector terminal of the second transistor Tr2 is connected between the second
resistor R2 and the main amplifier 7 via a second capacitor C2.
[0029]
In the filter 9, when the level of the volume control signal is equal to or higher than a
predetermined level and the amplification factor of the volume controller is equal to or higher
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than a predetermined value, the first transistor Tr1 is turned on. The second transistor Tr2 is
turned off to be in a non-operating state. When the level of the volume control signal is less than
a predetermined level and the amplification factor of the volume controller is less than a
predetermined value, the first transistor Tr1 is turned off. The second transistor Tr2 is turned on
to be in the operating state, and the cutoff characteristic of the low frequency band of the
reproduction signal is increased.
[0030]
Further, in the frequency characteristic variable circuit according to the present invention, the
filter 9 is limited to the one in which the switching control between the operating state and the
non-operating state is performed by the volume control signal as shown in the above
embodiment. Alternatively, the switching control may be performed by a noise detection signal
obtained by detecting an ambient noise level. This noise detection signal can be easily detected
using a microphone device or the like and an amplification circuit. In this case, the filter 9 is
inactivated when the ambient noise level is high, and activated when the ambient noise level is
low and the sound in which the electromagnetic noise is reproduced is easy to be heard, the
frequency including the noise Cut off the band signal.
[0031]
Furthermore, in the frequency characteristic variable circuit according to the present invention,
the filter 9 may perform switching control between the operating state and the non-operating
state according to the signal level of the reproduction signal. In this case, the filter 9 is
inactivated when the level of the reproduction signal is high. Then, even when the volume control
signal has set the amplification factor of the volume controller 6 to a predetermined value or
more, the filter 9 has a low level of the reproduction signal and a small volume of reproduction
sound. In other words, the operation state is made, and the signal in the frequency band
including the electromagnetic noise is shut off, and the electromagnetic noise prevents the
reproduced noise from being heard.
[0032]
Note that the frequency characteristic variable circuit according to the present invention is not
limited to the television set as shown in the above-mentioned embodiment, but is applicable to
various sound reproducing devices.
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[0033]
The filter 9 in the frequency characteristic variable circuit as described above may be configured
to perform frequency variable processing on the reproduction signal amplified by the main
amplifier 7.
In this case, the filter 9 is used by being interposed between the main amplifier 7 and the
speaker device 8.
[0034]
As described above, in the frequency characteristic variable circuit according to the present
invention, the volume control for supplying the reproduction signal amplified by the secondary
amplification means for volume control and controlling the amplification factor in the secondary
amplification means. It is controlled by a signal, a noise detection signal obtained by detecting an
ambient noise level, or the signal level of the reproduction signal to control the frequency
characteristic of the reproduction signal, the volume control signal, the noise detection signal, or
the reproduction. The variable processing is performed according to the signal level of the signal,
and the reproduction signal subjected to this processing is supplied to the main amplification
means.
[0035]
Therefore, this frequency characteristic variable circuit makes the sound clear when
electromagnetic noise is reproduced as sound, such as when the volume is suppressed, the
ambient noise level is low, or the signal level of the reproduction signal is low. When it is easy to
listen to the audio signal, the variable characteristic of the reproduction signal is changed.
Conversely, when the sound reproduced by the electromagnetic noise is hard to be heard clearly,
the variable characteristic of the reproduction signal is not changed. In addition, the frequency
characteristics of the reproduction signal can be made to give a natural hearing sensation.
[0036]
Further, a television set according to the present invention includes at least one of the abovedescribed frequency characteristic variable circuits.
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Therefore, in this television set, it is possible to reduce noise in reproduced sound caused by the
drive current of the deflection yoke.
[0037]
That is, according to the present invention, it is possible to reproduce electromagnetic noise as
sound without increasing the size and complexity of the structure of the sound reproducing
device or complicating the manufacturing and without impairing the sense of hearing the
reproduced sound. It is possible to provide a frequency characteristic variable circuit which can
be suppressed and a television apparatus provided with the frequency characteristic variable
circuit.
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