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DESCRIPTION JP2010171590

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DESCRIPTION JP2010171590
A signal switching circuit which can be realized entirely by semiconductor elements without
using mechanical relays. An R audio amplifier 10 and an L audio amplifier 20 are supplied with a
negative voltage Vss as a power supply on the low voltage side, and when an audio signal is
selected by a switching signal select, the R audio amplifier 10 and the L audio amplifier 20
operates and the USB amplifier 30 sets the output end to the high impedance state, the negative
voltage Vss is input as the low voltage side power supply, and the digital signal is selected by the
switching signal select. The L audio amplifier 20 puts the output end in a high impedance state,
and the negative voltage generation circuit 40 stops its operation to stop the output of the
negative voltage, and the USB amplifier 30 operates to supply the ground voltage GND as a low
voltage side power supply. Was input. [Selected figure] Figure 1
Signal switching circuit
[0001]
The present invention relates to an audio device provided with a USB connector, and more
particularly to a signal switching circuit for using the data terminal of the USB connector as an
audio signal terminal.
[0002]
2. Description of the Related Art In recent years, with the progress of downsizing and
multifunctionalization of portable devices, it has become necessary to dispose many switches and
connectors in a small main body.
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For this reason, although the connector is being miniaturized, it has not been sufficient yet, and a
method has been conceived in which different signals are shared by one connector. A portable
digital audio device generally comprises a USB connector for downloading music data and the
like from a personal computer or the like to the device, and a headphone connector for listening
to voice. From such a thing, there existed a technique which enabled it to use a headphone
(earphone) connector by a USB connector (for example, refer patent document 1).
[0003]
FIG. 2 is a view showing an example of an internal circuit of a mechanical relay G6K-2G-Y
(hereinafter simply referred to as a relay) used in such a technique. The Vbus signal of the USB
signal is connected to the 1 pin of the relay 101 and the Vbus terminal of the USB connector 102
through the resistor R, the D + signal of the USB signal is 5 pins of the relay 101, and the D−
signal of the USB signal is the relay 101 Each is connected to 4 pins. The GND signal of the USB
signal is connected to the 8 pin of the relay 101 and the GND terminal of the USB connector 102,
respectively. The R signal of the audio signal is connected to pin 7 of the relay 101, the L signal
of the audio signal is connected to pin 2 of the relay 101, and the GND signal of the audio signal
is connected to the GND signal of the USB signal.
[0004]
The 6 pins of the relay 101 are connected to the D + terminal of the USB connector 102, the 3
pins of the relay 101 are connected to the D− terminal of the USB connector 102, and the diode
D is connected between the 1 pin and the 8 pin of the relay 101 . A coil L and two changeover
switches S1 and S2 are incorporated in the relay 101, the coil L is connected between pins 1 and
8 and the common terminal of the changeover switch S1 is connected to pin 3. The normal
contact terminal is connected to pin 2 and the normal open terminal is connected to pin 4. The
common terminal of changeover switch S2 is connected to pin 6, the normal contact terminal is
connected to pin 7 and the normal open terminal is connected to pin 5. ing.
[0005]
When the USB connector 102 is connected to a USB connector such as a personal computer or
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the like, a voltage of 5 V is applied between the GND terminal and the Vbus terminal of the USB
connector 102. A current flows, and the connection between the common terminals 3 and 6 of
the changeover switches S1 and S2 is switched to the 4 and 5 pins on the normally open terminal
side. As a result, the D + terminal of the USB connector 102 is connected to the D + signal of the
USB signal, and the D− terminal of the USB connector 102 is connected to the D− signal of the
USB signal. Data communication can be performed.
[0006]
When headphones are connected to the USB connector 102, no voltage is applied to the Vbus
terminal of the USB connector 102, so no power is supplied to the coil L and the connection
between the common pins 3 and 6 of the changeover switches S1 and S2 is , 2 pins and 7 pins on
the normal contact terminal side. Therefore, the R signal of the audio signal is input to the D +
terminal of the USB connector 102, and the L signal of the audio signal is input to the D- terminal
of the USB connector 102, and an audio signal is sent to the headphones from the device side.
Can.
[0007]
However, in FIG. 2, since mechanical relays are used, there is a problem that the number of parts
is increased, the shape is large, and the cost is high. In this case, the headphone connector is
omitted. It offsets the effects of the miniaturization. Therefore, it is conceivable to simply replace
the mechanical relay with a semiconductor analog switch, but in such a case, problems as
described below occur.
[0008]
FIG. 3 is a diagram showing a circuit example when the mechanical switch of FIG. 2 is replaced
with a semiconductor analog switch. In FIG. 3, the audio signal is shown only on the R signal side
in order to simplify the description. The D + signal of the USB signal is connected to the D +
terminal of the USB connector 102 through the analog switch AS1. The R signal of the audio
signal is connected to the D + terminal of the USB connector 102 through the capacitor C and the
analog switch AS2. The inversion control terminal of the analog switch AS1 and the control
terminal of the analog switch AS2 are connected to the output terminal of the inverter circuit
INV, and the control terminal of the analog switch AS1 and the inversion control terminal of the
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analog switch AS2 are the input terminal of the inverter circuit INV and the USB connector 102
Respectively connected to the Vbus terminals of The Vbus terminal of the USB connector 102 is
pulled down to the ground voltage GND by a resistor R.
[0009]
The audio signal is input to the analog switch AS2 via the coupling capacitor C because it is
necessary to cut the DC component to be output to the headphones. As a result, a voltage is
applied to the analog switch AS2 in which the peak-to-peak voltage spans the positive voltage
and the negative voltage. When the power supply of the analog switch AS2 is a single power
supply of positive voltage and a negative voltage signal is input, a large leak current is generated
from the ground voltage GND toward the negative voltage signal, and in some cases, latch-up
Cause the problem. For this reason, it has not been possible to simply replace the mechanical
relay with a semiconductor switch.
[0010]
In addition, when the on resistance of the analog switch AS2 is large, not only the power sent to
the headphone is lost but also a problem that the damping factor is deteriorated occurs. In order
to reduce the on resistance of the analog switch AS2, it is necessary to increase the area of the
switch element on the chip, which causes a problem of an increase in the chip area and an
increase in cost.
[0011]
The present invention has been made to solve such a problem, and a signal switching circuit that
can be realized entirely by semiconductor elements without using mechanical relays and can
suppress an increase in semiconductor chips. The aim is to get
[0012]
A signal switching circuit according to the present invention switches between a digital signal
and an audio signal whose peak-to-peak voltage spans a positive voltage and a negative voltage
according to a switching signal input from the outside, and outputs it to a data terminal of a USB
connector. An audio amplifier unit that generates and outputs the audio signal from an external
audio signal input from the outside; and a tristate that generates and outputs the digital signal
from an external digital signal input from the outside. And a negative voltage generation circuit
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unit that generates and outputs a voltage smaller than a negative peak voltage of the audio
signal, and the audio amplifier unit has a low voltage side. The negative voltage from the negative
voltage generation circuit unit is supplied as a power supply, and the USB amplifier unit As a
power supply, either the negative voltage or the ground voltage from the negative voltage
generation circuit unit is supplied according to the switching signal, and the audio amplifier unit
operates when the audio signal is selected by the switching signal. At the same time, with the
output terminal in a high impedance state, the USB amplifier unit receives a negative voltage
from the negative voltage generation circuit unit as a low voltage side power supply, and the
digital signal is selected by the switching signal. When the audio amplifier unit sets the output
end to a high impedance state, the negative voltage generation circuit unit stops its operation to
stop the output of the negative voltage, the USB amplifier unit operates, and the low voltage A
ground voltage is input as the power supply on the side.
[0013]
Specifically, the switch unit is configured to switch the power supply on the low voltage side to
the USB amplifier unit according to the switch signal, and the USB amplifier unit is configured to
select the audio signal by the switch signal. When there is a negative voltage from the negative
voltage generation circuit unit as the low voltage side power supply from the changeover switch
unit, and when the digital signal is selected by the switching signal, as the low voltage side power
supply The ground voltage is input from the changeover switch unit.
[0014]
The USB amplifier unit may stop operation to reduce power consumption when the audio signal
is selected by the switching signal.
[0015]
Further, the audio amplifier unit may stop operation to reduce power consumption when the
digital signal is selected by the switching signal.
[0016]
The audio amplifier unit, the USB amplifier unit, and the negative voltage generation circuit unit
may be integrated in a semiconductor integrated circuit of one chip.
[0017]
The audio amplifier unit, the USB amplifier unit, the negative voltage generation circuit unit, and
the changeover switch unit may be integrated in a semiconductor integrated circuit of one chip.
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[0018]
According to the signal switching circuit of the present invention, since the audio signal for
headphones etc. can be output from the USB terminal only with the semiconductor circuit
without using the mechanical relay, a large circuit component occupying a space can be
obtained. It becomes unnecessary, the equipment and the circuit can be miniaturized, and the
cost can be reduced.
[0019]
In addition, since the coupling capacitor, which occupies a large mounting area, is not necessary,
the connection pad for connecting the coupling capacitor is not necessary. As a result, significant
downsizing and cost reduction can be achieved.
Furthermore, since no analog switch is used, the output impedance of the audio signal can be
reduced without increasing the chip area.
Furthermore, since the semiconductor integrated circuit is integrated into one chip, further
miniaturization and cost reduction can be achieved.
[0020]
FIG. 3 is a diagram showing an example of a signal switching circuit according to the first
embodiment of the present invention.
It is the figure which showed the example of a circuit of the conventional signal switching circuit.
FIG. 7 is a diagram showing another circuit example of the conventional signal switching circuit.
[0021]
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Next, the present invention will be described in detail based on the embodiments shown in the
drawings.
First Embodiment
FIG. 1 is a diagram showing an example of a signal switching circuit according to a first
embodiment of the present invention.
In FIG. 1, the signal switching circuit 1 includes an R audio amplifier 10, an L audio amplifier 20,
a USB amplifier 30, a negative voltage generation circuit 40, an inverter circuit 50, a changeover
switch SW1, and a USB connector 60.
The R audio amplifier 10 and the L audio amplifier 20 form an audio amplifier, the USB amplifier
30 forms a USB amplifier, the negative voltage generation circuit 40 forms a negative voltage
generation circuit, and the changeover switch SW1 makes a changeover switch.
[0022]
The R audio amplifier 10 is an amplification circuit that amplifies the right signal ARi of the audio
stereo signal, amplifies the input audio signal ARi, and generates and outputs a headphone
driving audio signal ARo. Further, the R audio amplifier 10 has a control input terminal, and a
switching signal select is inputted to the control input terminal. The R audio amplifier 10
operates when the switching signal select is at a high level, and stops operating when the
switching signal select is at a low level, the power consumption becomes almost zero and the
output end is in a high impedance state.
[0023]
Similarly, the L audio amplifier 20 is an amplification circuit that amplifies the left signal ALi of
the audio stereo signal, amplifies the input audio signal ALi, and generates and outputs an audio
signal ALo for headphone driving. Further, the L audio amplifier 20 also has a control input
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terminal, and a switching signal select is input to the control input terminal. The L audio
amplifier 20 operates when the switching signal select is at a high level, and stops operating
when the switching signal select is at a low level, the power consumption becomes almost zero
and the output end is in a high impedance state.
[0024]
The USB amplifier 30 is an interface circuit that inputs and outputs digital signals. When a digital
signal Digital output from an internal circuit of a device (not shown) is input, the USB amplifier
30 converts the digital signal into digital signals Digital + and Digital-, and transmits the digital
signals via corresponding data terminals D + and D- of the USB connector 60. Output to the
outside. Also, the USB amplifier 30 outputs the digital signals Digital + and Digital− input from
the data terminals D + and D− of the USB connector 60 as digital signals Digital to a circuit (not
shown) inside the device.
[0025]
The USB amplifier 30 also has a control input terminal, and an inverted switching signal selectB
obtained by inverting the switching signal select by the inverter circuit 50 is input to the control
input terminal. Furthermore, the output on the USB connector 60 side of the USB amplifier 30 is
in a tri-state configuration, and the state of the output end of the USB amplifier 30 is controlled
by the inversion switching signal selectB. That is, when the inversion switching signal selectB is
at the low level, the output end of the USB amplifier 30 is in the high impedance state and the
operation is stopped, and the power consumption becomes almost zero. When the inversion
switching signal selectB is high level, the USB amplifier 30 operates to generate and output a
high or low level signal according to the signal level of the input digital signal Digital.
[0026]
The negative voltage generation circuit 40 is a DC-DC converter using a charge pump with a
capacitor, and the lowest voltage of the negative side of the peak-to-peak voltage in the audio
signals ARo and ALo output from the R audio amplifier 10 and L audio amplifier 20 It generates
and outputs a negative voltage Vss smaller than that. The negative voltage Vss output from the
negative voltage generation circuit 40 is supplied to the negative power supply terminals of the R
audio amplifier 10 and the L audio amplifier 20, respectively, and is further supplied to the
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terminal A of the changeover switch SW1. In addition, the negative voltage generation circuit 40
also has a control input terminal, and the switching signal select is input to the control input
terminal. The negative voltage generation circuit 40 outputs the negative voltage Vss when the
switching signal select is at a high level, and stops the operation when the switching signal select
is at a low level to stop the supply of the negative voltage Vss.
[0027]
The changeover switch SW1 is a changeover switch having a control terminal, and the common
terminal C of the changeover switch SW1 is connected to the low voltage side power supply
terminal of the USB amplifier 30. The terminal B of the changeover switch SW1 is connected to
the ground voltage GND, and the changeover signal select is input to the control terminal of the
changeover switch SW1. The switching switch SW1 connects the common terminal C to the
terminal A when the switching signal select is high level, and connects the common terminal C to
the terminal B when the switching signal select is low level.
[0028]
In such a configuration, when the switching signal select is at a high level, the USB connector 60
is connected to the audio signal. Since the switching signal select is at the high level, the negative
voltage generation circuit 40 generates and outputs the negative voltage Vss. The R audio
amplifier 10 and the L audio amplifier 20 are also respectively operated to amplify the
corresponding input audio signals ARi and ALi to generate and output audio output signals ARo
and ALo. The positive and negative power supply voltages Vdd and Vss are input to the R audio
amplifier 10 and the L audio amplifier 20 respectively, and the peak-to-peak of the output audio
output signals ARo and ALo is a voltage ranging from a positive voltage to a negative voltage. It
has become.
[0029]
Further, since the common terminal C of the changeover switch SW1 is connected to the terminal
A, the negative voltage Vss is input to the low voltage side power supply terminal of the USB
amplifier 30. Furthermore, since the output end of the USB amplifier 30 is in a high impedance
state and the negative voltage Vss is input to the low voltage side power source, even if negative
voltages appear on the data terminals D + and D− of the USB connector 60. The current does not
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flow into the USB amplifier 30.
[0030]
Next, when the switching signal select is at low level, the USB connector 60 is connected to the
digital signal. When the switching signal select becomes low level, the USB amplifier 30 starts its
operation, and conversely, the R audio amplifier 10 and the L audio amplifier 20 stop their
operations and put the respective output terminals in a high impedance state. The negative
voltage generation circuit 40 also stops its operation and the negative voltage Vss is not output.
Furthermore, the common terminal C of the changeover switch SW1 is connected to the terminal
B side, and the low voltage side power supply voltage of the USB amplifier 30 is connected to the
ground voltage GND.
[0031]
That is, digital signals Digital + and Digital− output from the USB amplifier 30 are output from
the data terminals D + and D− of the USB connector 60 correspondingly. At this time, since each
output terminal of the R audio amplifier 10 and the L audio amplifier 20 is in a high impedance
state, the digital signals Digital + and Digital− do not flow into the R audio amplifier 10 and the L
audio amplifier 20. Conversely, the output signals of the R audio amplifier 10 and the L audio
amplifier 20 do not affect the digital signals Digital + and Digital−.
[0032]
Further, since the ground voltage GND is connected to the power supply on the low voltage side
of the USB amplifier 30, it is possible to prevent the voltages of the digital signals Digital + and
Digital- output from the USB amplifier 30 from becoming negative voltages. . In the first
embodiment, the dedicated switching signal select is used as the switching signal. However, as
shown in the conventional example of FIG. 3, a signal obtained by inverting the Vbus voltage of
the USB connector is used as the switching signal select. You may
[0033]
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As described above, the signal switching circuit according to the first embodiment realizes the
switching circuit using only semiconductor elements, so that all these circuits can be mounted on
a semiconductor device of one chip, and in addition, conventionally The need for the coupling
capacitor which occupies the mounting area is eliminated, and the connection pad for connecting
the coupling capacitor is also eliminated. As a result, significant downsizing and cost reduction
can be achieved. Also, since the analog switch is prevented from entering the path for outputting
the audio signal, the output impedance can be reduced without increasing the chip area.
[0034]
1 signal switching circuit 10 R audio amplifier 20 L audio amplifier 30 USB amplifier 40 negative
voltage generation circuit 50 inverter circuit 60 USB connector SW1 switch
[0035]
JP 2006-519522 gazette
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