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JP2007019716

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DESCRIPTION JP2007019716
To solve the problem, the conventional solution has a problem that an output becomes small
because an extra resistance intervenes when connecting four-terminal headphones, and because
an impedance of the headphones is not pure resistance when connecting three-terminal
headphones, cancellation is performed. There is a problem that the part where the effect does not
appear is generated or cross talk occurs, the separation of both channels is deteriorated, and
these problems are caused when connecting headphones with impedance different from the
resistance in the circuit. Had the problem of getting worse. A three-pole plug detection means is
provided, and when the three-pole plug is detected by the detection means, the negative side
output of both channels is direct current that matches the center voltage of the positive side
output. A differential non-differential circuit in a stereo digital amplifier characterized by
comprising a 50% duty pulse changeover switch 7 for switching an input to the drive circuit 2 to
a 50% duty pulse signal. [Selected figure] Figure 2
Differential non-differential conversion circuit
[0001]
The invention relates in particular to differential non-differential conversion circuits.
[0002]
In a full bridge stereo digital amplifier, a total of four output terminals, two positive and two
negative, are required for both channels.
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Therefore, it is desirable to use four-terminal headphones having four terminals as headphones
connected to such stereo digital amplifiers. However, in the market, three-terminal headphones
having three terminals are the majority. For this reason, in order to make it possible to use threeterminal headphones in a stereo digital amplifier which originally requires four terminals, for
example, an invention as disclosed in Patent Document 1 has been devised. JP 2003-87064 A
[0003]
However, in the method of using the negative electrode as the common ground, which is the
conventional solution method, there is a problem that the output becomes small because an extra
resistance intervenes when the 4-terminal headphone is connected. In addition, when connecting
the 3-terminal headphone, since the impedance of the headphone is not pure resistance, there is
a problem that a part where the cancellation effect does not appear is generated, or crosstalk
occurs, which causes the separation of both channels to deteriorate. These problems are further
exacerbated when headphones having a different impedance from the resistors in the circuit are
connected. (See Figure 1)
[0004]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide a differential non-differential conversion circuit that can solve the
above problems.
[0005]
The present invention has the following constitution in order to solve the above-mentioned
problems.
The gist of the invention according to claim 1 is a direct current having three-pole plug detection
means, in which the negative side outputs of both channels coincide with the center voltage of
the positive side output when the three-pole plug is detected by the detection means. A
differential non-differential circuit in a stereo digital amplifier is characterized by having a 50%
duty pulse changeover switch for switching an input to the negative side drive circuit to a 50%
duty pulse signal. According to a second aspect of the present invention, the three-pole plug
detection means detects connection of the three-pole plug by adding a three-pole plug detection
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2
signal from one of the two channels and detecting the signal from the other. The differential nondifferential circuit in the stereo digital amplifier according to claim 1. The subject matter of the
invention according to claim 3 resides in a differential non-differential circuit in a stereo digital
amplifier according to claim 1 or 2, wherein the central voltage is a voltage which is 1/2 of a
power supply voltage. The subject matter of the invention according to claim 4 is that in the
stereo digital amplifier according to any one of claims 1 to 3, the input to the differential nondifferential circuit is a 1-bit digital signal. It exists in a differential circuit. The gist of the
invention according to claim 5 is a direct current having a three-pole plug detection step, in
which the negative side outputs of both channels coincide with the center voltage of the positive
side output when the three-pole plug is detected by the detection step. The differential nondifferential switching method in a stereo digital amplifier is characterized in that the input to the
negative side drive circuit is switched to a 50% duty pulse signal. The gist of the invention
according to claim 6 is that the three-pole plug detection step detects a connection of the threepole plug by adding a clock outside the audible band from one of the two channels and detecting
the clock from the other. A differential non-differential switching method in a stereo digital
amplifier according to claim 5 characterized by the feature. The gist of the invention according to
claim 7 resides in the differential non-differential switching method in stereo digital amplifier
according to claim 5 or 6, characterized in that the central voltage is a voltage which is 1/2 the
power supply voltage. .
[0006]
The differential non-differential conversion circuit of the present invention is driven without any
extra resistance when connecting four-terminal headphones, and when connecting three-terminal
headphones, it is detected by the three-pole plug detection circuit and the negative side output is
50% duty Since it switches to a pulse signal, only the voltage for the signal is transmitted to the
load, and there is an advantage that an ideal signal can be output with either three terminals or
four terminals.
[0007]
Hereinafter, embodiments of the present invention will be described in detail.
[0008]
The differential non-differential conversion circuit of the present invention is, as shown in FIG. 2,
a positive side drive circuit 1, a negative side drive circuit 2, a MOSFET 3, a coil 4, a capacitor 5,
a three pole plug detection circuit 6, 50% duty pulse The configuration includes the changeover
switch 7 and the like.
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The circuit diagram shown in FIG. 2 shows only the L side of both channels, and the actual
configuration is composed of two channels of differential non-differential conversion circuits.
[0009]
When a plug is inserted into the jack, a three-pole plug detection signal is transmitted from one
of the three pole plug detection circuits 6 of the LR both channels via the minus terminal.
The 3-pole plug detection signal is preferably a signal that does not affect listening, such as a
clock outside the audible band. If the 3-pole plug detection circuit 6 in the other channel can
receive the 3-pole plug detection signal from the channel that transmitted the 3-pole plug
detection signal, that is, the plug inserted in the jack is the 3-pole plug. Is detected. If the 3-pole
plug detection signal can not be received, it is determined to be a 4-pole plug.
[0010]
When the plug inserted into the jack is a four-pole plug, a normal digital signal is transmitted to
the negative side drive circuit 2. At this time, it becomes possible to drive the headphones
without intervening extra resistance.
[0011]
When the plug inserted into the jack is a three-pole plug, the 50% duty pulse switch 7 switches
the signal input to the negative side drive circuit 2 to a 50% duty pulse signal. The 50% duty
pulse signal means that the negative side drive is performed so that the negative side output of
both channels is a direct current that matches the center voltage of the positive side output, that
is, so that crosstalk does not occur between positive and negative electrodes in each channel. It is
a signal that is input to the circuit. By switching the signal input to the negative side drive circuit
2 to the 50% duty pulse signal, crosstalk between the positive electrode and the negative
electrode is prevented, and only the signal is transmitted to the headphone load.
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[0012]
FIG. 3 is an operation conceptual diagram of the differential non-differential circuit of the present
invention at the time of connecting the three-pole plug described above. For example, when the
center voltage of the positive electrode output is 1/2 of the power supply voltage, the output of
the positive electrode is obtained by adding an audio signal to 1/2 VCC which is the center
voltage. At this time, since the output of the negative electrode resulting from the input of the
50% duty pulse signal is 1/2 VCC, substantially no crosstalk occurs between the positive
electrode and the negative electrode, and only the audio signal is added to the headphone load .
[0013]
The 50% duty pulse switching switch 7 described above may be incorporated in a DSP (Digital
Signal Processor) for digital signal generation at the previous stage input to the positive side
drive circuit 1 and the negative side drive circuit 2. The differential non-differential circuit of the
present invention is adaptable to any type of stereo digital amplifier, and is also applicable to, for
example, a 1-bit digital amplifier.
[0014]
EXAMPLES The present invention will be specifically described below with reference to examples
of the present embodiment and comparative examples, but the present invention is not limited to
the following examples.
[0015]
A differential non-differential circuit was configured in accordance with the embodiment of the
present invention.
That is, a circuit having a positive side drive circuit 1, a negative side drive circuit 2, a MOSFET 3,
a coil 4, a capacitor 5, a three pole plug detection circuit 6, and a 50% duty pulse changeover
switch 7 is constructed. Connected. When a 4-pole plug headphone was connected, the 50% duty
pulse changeover switch 7 did not operate, and a normal output was sent to the drive circuit. The
output signal from the headphones did not drop in output as compared with the conventional
method when connecting three terminals. When headphones of a three-pole plug were
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connected, the 50% duty pulse changeover switch 7 was actuated, and a 50% duty pulse signal
was output to the drive circuit. The output audio signal was also well separated.
[0016]
The differential non-differential circuit of the present invention is driven without an extra
resistance when connecting four-terminal headphones, and when connecting three-terminal
headphones, it is detected by the three-pole plug detection circuit and the negative side output is
50% duty pulse Since the signal is switched to the signal, only the voltage for the signal is
transmitted to the load, and there is an advantage that it becomes possible to manufacture an
audio device capable of outputting an ideal signal with either three terminals or four terminals.
[0017]
Explanatory drawing of prior art The block diagram of this invention, and the explanatory
drawing of Example 1. Operation | movement conceptual diagram at the time of 3 pole plug
connection of this invention
Explanation of sign
[0018]
Reference Signs List 1 positive side drive circuit 2 negative side drive circuit 3 MOSFET 4 coil 5
capacitor 6 3 pole plug detection circuit 7 50% duty pulse changeover switch
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