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JP2004173264

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JP2004173264
PROBLEM TO BE SOLVED: To provide a compact and lightweight display device having a voice
output circuit. A display device of the present invention uses a speaker as a flat speaker, and an
audio signal processing device configured of thin film transistors on the display device. By
driving the speaker by BTL driving, the power supply voltage can be reduced and deterioration of
the thin film transistor can be prevented. As described above, by achieving the downsizing of the
speaker and the incorporation of the audio signal processing circuit in the display device, a
compact and lightweight portable information device capable of outputting audio can be realized.
[Selected figure] Figure 1
Display device
[0001]
The present invention relates to a display device which is formed of thin film semiconductor
elements and has an electrical signal processing circuit for driving an output device other than
visual, and more particularly to a display device in which an audio signal processing circuit for
driving a speaker is integrally formed on a substrate. In the present specification, the term
“speaker” refers to a general device that converts an electrical signal into sound, including a
vibrator that vibrates a member of a display device such as a glass substrate, a plastic substrate,
or a touch panel to output sound. To be.
[0002]
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2. Description of the Related Art In recent years, mobile phones have become widespread with
the progress of communication technology. In the future, more video transmissions and more
information transmissions are expected. On the other hand, personal computers are also
manufactured for mobile products due to their weight reduction. A large number of information
terminals called PDAs, which began as electronic notebooks, are also being produced and
disseminated. Also, with the development of display devices, most of these portable information
devices are equipped with flat panel displays.
[0003]
Among active matrix display devices, in recent years, production of display devices using lowtemperature polysilicon thin film transistors (hereinafter, thin film transistors are described as
TFTs) has been promoted. With low-temperature polysilicon TFTs, it is possible to integrally form
not only pixels but also signal line driver circuits around the pixel portion, so it is possible to
miniaturize the display device and achieve high definition, and further popularization will be in
the future. Expected.
[0004]
On the other hand, portable information devices are required not only visual display functions
but also other output functions, and in particular voice output functions. When an image is
displayed, if an audio is obtained, the image can be viewed more effectively, and the image can
be more enjoyed.
[0005]
However, a normal audio output device converts an electrical signal into audio using a cone
speaker or the like and outputs it. These cone speakers require a large area in portable
information devices, and have been an obstacle to reducing the size and weight of portable
information devices. FIG. 2 is an outline view of the periphery of a display device of a portable
information device having a conventional audio output function. An audio signal processing
circuit mounted on a cone speaker 207, an FPC 205, an opposing substrate 208, and a printed
substrate 206 in a display device in which a pixel portion 204, a source signal line drive circuit
202, and a gate signal line drive circuit 203 are integrally formed on a substrate 209. We put
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together 210 together. Here, the upper view shows a top view, and the lower view shows a side
view. Further, in the lower drawing, the source signal line drive circuit 202, the gate signal line
drive circuit 203, and the pixel portion 204 are omitted for simplification of the display.
[0006]
The cone speaker 207 has a large outer shape and is not suitable for reducing the size and
weight of portable devices. For this reason, a flat speaker as shown in FIG. 3 is being developed.
FIG. 3 is an outline view of the periphery of the display device of the portable information device
301 provided with a flat speaker. An audio signal mounted on the flat speaker 306, the FPCs 305
and 308, the counter substrate 310, and the printed substrate 311 in a display device in which
the pixel portion 304, the source signal line driver circuit 302, and the gate signal line driver
circuit 303 are integrally formed on the substrate 309. The processing circuit 307 is also
mounted. Here, the upper view shows a top view, and the lower view shows a side view. Further,
in the lower drawing, the source signal line drive circuit 302, the gate signal line drive circuit
303, and the pixel portion 304 are omitted for simplification of display.
[0007]
Although this speaker converts an electric signal into vibration and outputs sound as in a
conventional speaker, it is not a cone that is vibrated, but a glass substrate such as a display
device, a plastic substrate, a touch panel or the like. By using such a flat speaker, it is possible to
realize reduction in size and weight as compared with a portable information device using a
conventional cone speaker.
[0008]
FIG. 17 is an example of a flat speaker. In this example, the touch panel 1702, the lower
substrate 1705, the adhesive 1706, and the liquid crystal panel 1704 installed in the housing
1701 are vibrated by the speaker 1703 and sound is output. (See Non-Patent Document 1)
[0009]
Nikkei Electronics, August 26, 2002 p.52
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[0010]
Although the flat speaker as described above is a very effective means for reducing the size and
weight of the portable information device, the following problems remain.
As shown in FIG. 3, the audio signal processing circuit 307 for driving the speaker using the
planar speaker 306 arranges the printed circuit board 311 outside the display device as in the
conventional case, and mounts the LSI on it. Was. Therefore, in order to reduce the size and
weight of the portable information device, it was still incomplete.
[0011]
In order to solve the problems as described above, the present inventors considered driving thin
film semiconductor elements on a substrate of a display device, in particular, polysilicon TFTs to
drive output devices other than visual such as planar speakers. Unlike amorphous TFTs,
polysilicon TFTs have high driving capability, and thus can drive speakers and the like.
[0012]
The configuration of the present invention is shown below.
[0013]
The present invention relates to a display device having a thin film semiconductor element on a
substrate, wherein the display device comprises an electrical signal processing circuit for driving
an output device other than visual, and the electrical signal processing circuit is constituted by
the thin film semiconductor element. It is characterized by being
[0014]
Further, the present invention is characterized in that in the display device having the thin film
semiconductor element on the substrate, the display device has an audio signal processing
circuit, and the audio signal processing circuit is constituted by the thin film semiconductor
element.
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[0015]
Further, according to the present invention, in the display device having a thin film
semiconductor element on a substrate, the display device has an audio signal processing circuit,
the audio signal processing circuit is constituted by the thin film semiconductor element, and the
audio signal processing circuit It is characterized in that the speaker is driven by the output
signal.
[0016]
In the above configuration, the audio signal processing circuit includes a digital signal processing
circuit.
[0017]
Further, in the above configuration, the audio signal processing circuit includes a D / A
conversion circuit.
[0018]
Further, in the above configuration, the audio signal processing circuit includes an analog signal
processing circuit.
[0019]
Further, in the above configuration, the analog signal processing circuit is characterized by being
configured by an operational amplifier circuit.
[0020]
The present invention is characterized in that in the display device having a thin film
semiconductor element on a substrate, the thin film semiconductor element constitutes an analog
signal processing circuit, and a speaker is driven by an output signal of the analog signal
processing circuit.
[0021]
The present invention relates to a display device having a thin film semiconductor element on a
substrate, wherein the thin film semiconductor element constitutes an analog signal processing
circuit, and the analog signal processing circuit has a noninverting amplifier circuit and an
inverting amplifier circuit. The first terminal of the speaker is driven by the output signal of the
amplifier circuit, and the second terminal of the speaker is driven by the output signal of the
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inverting amplifier circuit.
[0022]
Further, in the display device having a thin film semiconductor element on a substrate, the thin
film semiconductor element constitutes an analog signal processing circuit, and the analog signal
processing circuit has a non-inversion amplifying circuit and an inverting amplification circuit.
The input terminal of the non-inversion amplification circuit and the input terminal of the
inversion amplification circuit are connected, and the output signal of the non-inversion
amplification circuit drives the first terminal of the speaker, and the output signal of the
inversion amplification circuit It is characterized in that the second terminal is driven.
[0023]
Further, the present invention provides a display device having a thin film semiconductor
element on a substrate, wherein the thin film semiconductor element constitutes an analog signal
processing circuit, and the analog signal processing circuit has a non-inversion amplifier circuit
and an inversion amplifier circuit. The output terminal of the non-inversion amplification circuit
is connected to the input terminal of the inversion amplification circuit, the first output of the
speaker is driven by the output signal of the non-inversion amplification circuit, and the speaker
is output by the output signal of the inversion amplification circuit. Driving the second terminal
of the
[0024]
Further, in the display device having a thin film semiconductor element on a substrate, the thin
film semiconductor element constitutes an analog signal processing circuit, and the analog signal
processing circuit is a first inverting amplifier circuit and a second inverting amplification circuit.
The output terminal of the first inverting amplifier circuit is connected to the input terminal of
the second inverting amplifier circuit, and the output signal of the first inverting amplifier circuit
drives the first terminal of the speaker And the second terminal of the speaker is driven by the
output signal of the second inverting amplification circuit.
[0025]
Further, in the display device having a thin film semiconductor element on a substrate, the thin
film semiconductor element constitutes an analog signal processing circuit, and the analog signal
processing circuit includes a preamplification circuit and a non-inversion amplification circuit. An
inverting amplifier circuit, wherein an output signal of the preamplifying circuit is input to the
noninverting amplifier circuit and the inverting amplifier circuit, and a first signal of the speaker
is driven by an output signal of the noninverting amplifier circuit; The second terminal of the
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speaker is driven by the output signal of the inverting amplification circuit.
[0026]
Further, in the display device having a thin film semiconductor element on a substrate, the thin
film semiconductor element constitutes an analog signal processing circuit, and the analog signal
processing circuit includes a preamplification circuit and a non-inversion amplification circuit.
The output signal of the preamplification circuit is input to the non-inversion amplification
circuit, the output signal of the non-inversion amplification circuit is input to the inversion
amplification circuit, and the output signal of the non-inversion amplification circuit is provided. ,
Thereby driving the first terminal of the speaker and driving the second terminal of the speaker
by the output signal of the inverting amplification circuit.
[0027]
Further, the present invention provides a display device having a thin film semiconductor
element on a substrate, wherein the thin film semiconductor element constitutes an analog signal
processing circuit, and the analog signal processing circuit comprises a preamplifier circuit and a
first inverting amplifier circuit. And a second inverting amplification circuit, and an output signal
of the preamplifying circuit is input to the first inverting amplification circuit, and an output
signal of the first inverting amplification circuit is the second inversion. The first terminal of the
speaker is driven by the output signal of the first inverting amplifier circuit, and the second
terminal of the speaker is driven by the output signal of the second inverting amplifier circuit. It
is characterized by
[0028]
In the above configuration, the non-inverted amplifier circuit or the inverted amplifier circuit is
characterized in that a speaker is driven through a buffer circuit.
[0029]
Further, in the above configuration, the analog signal processing circuit is characterized by being
driven by a power supply voltage less than 30V.
[0030]
Further, in the above configuration, the speaker is a flat speaker.
[0031]
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Further, in the above configuration, the flat speaker is characterized in that the display device
itself is used as a vibration medium.
[0032]
The present invention relates to a display device having thin film transistors on a substrate,
wherein the thin film transistors constitute an analog signal processing circuit, and the analog
signal processing circuit includes a differential circuit, a current mirror circuit, a constant current
source, and a source ground amplifier And the source follower, the constant current source is
electrically connected to the source electrode of the thin film transistor forming the differential
circuit, and the first output terminal of the differential circuit is the output terminal of the
current mirror circuit And the input terminal of the source-grounded amplifier, the second output
terminal of the differential circuit is electrically connected to the input terminal of the current
mirror circuit, and the output terminal of the source-grounded amplifier is the source The output
terminal of the source follower is electrically connected to the output terminal of the analog
signal processing circuit. It is characterized by being.
[0033]
Further, in the display device having a thin film transistor on a substrate, the thin film transistor
constitutes an analog signal processing circuit, and the analog signal processing circuit includes a
differential circuit, a first current mirror circuit, and a second A current mirror circuit, a third
current mirror circuit, and a constant current source, wherein the constant current source is
electrically connected to a source electrode of a thin film transistor forming the differential
circuit; One output terminal is electrically connected to the input terminal of the first current
mirror circuit, and the second output terminal of the differential circuit is electrically connected
to the input terminal of the second current mirror circuit. An output terminal of the first current
mirror circuit is electrically connected to an output terminal of the analog signal processing
circuit and an output terminal of a third current mirror circuit, and the second current mirror
circuit It is characterized by being electrically connected to the output terminal of the mirror
circuit input terminal of the third current mirror circuit.
[0034]
In the display device having a thin film transistor on a substrate, the present invention is
characterized in that the thin film transistor constitutes an analog signal processing circuit
having a differential circuit, and the differential circuit is constituted of a thin film transistor
having a multigate structure. And
[0035]
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In the display device having a thin film transistor on a substrate, the thin film transistor
constitutes an analog signal processing circuit having a differential circuit, and the differential
circuit connects a plurality of thin film transistors in parallel. .
[0036]
In the display device having a thin film transistor on a substrate, the present invention is
characterized in that the thin film transistor constitutes an analog signal processing circuit
having a differential circuit, and the differential circuit has a plurality of thin film transistors
arranged crosswise. And
[0037]
Further, the present invention is characterized in that, in a display device having thin film
transistors on a substrate, the thin film transistors constitute an analog signal processing circuit,
and output thin film transistors of the analog signal processing circuit are made of a plurality of
semiconductor thin films.
[0038]
Further, in the above configuration, the distance between the plurality of semiconductor thin
films is larger than the long side of the semiconductor thin film.
[0039]
The present invention relates to a display device in which thin film transistors are formed on a
substrate, wherein the thin film transistors constitute an analog signal processing circuit, and
output thin film transistors of the analog processing signal circuit have a plurality of channel
forming regions and source and drain regions respectively. It is characterized in that it is
composed of one semiconductor thin film.
[0040]
In the above configuration, the distance between the plurality of channel formation regions in the
semiconductor thin film is larger than the width of the channel formation region.
[0041]
The present invention relates to a display device having a thin film transistor on a substrate,
wherein the thin film transistor constitutes an analog signal processing circuit, and the thin film
transistor constituting an output stage of the analog signal processing circuit comprises a
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plurality of semiconductor thin films A conductive film is disposed between the semiconductor
thin films of
[0042]
Accordingly, the miniaturization of the speaker and the incorporation of the audio signal
processing circuit in the display device can be achieved, and a compact and lightweight portable
information device capable of outputting an audio can be realized.
[0043]
In the portable information device having the conventional audio output function, it is difficult to
reduce the size of the cone speaker and the drive circuit for driving the same, and the size of the
portable information device can not be reduced.
[0044]
The present invention realizes a display device having an audio output function with a small
volume by integrally forming a speaker as a flat speaker and a drive circuit for driving the
speaker on a substrate using a thin film semiconductor element, in particular, a TFT. .
The present invention makes it possible to reduce the size and weight of a portable information
device having an audio output function.
[0045]
FIG. 1 shows an outline view of a display device of the present invention.
As shown in FIG. 1, the display device 101 according to the present invention integrally forms a
pixel portion 104, a source signal line drive circuit 102, a gate signal line drive circuit 103, and
an audio signal processing circuit 105 on a substrate 109 by TFTs. The counter substrate 110 is
placed thereon.
Here, the upper view of FIG. 1 shows a top view, and the lower view shows a side view.
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Further, in the lower diagram, the source signal line drive circuit 102, the gate signal line drive
circuit 103, the pixel portion 104, and the audio signal processing circuit 105 are omitted for
simplification of the display.
Further, on the substrate 109, a flat speaker 106 is mounted.
The flat speaker 106 may be one that vibrates a substrate or the like to output sound, even if it
does not itself output sound.
The flat speaker 106 is electrically connected to the audio signal processing circuit 105 through
the FPC 108.
An external audio signal is input to the audio signal processing circuit 105 through the FPC 107
and is output to the flat speaker 106 through the FPC 108.
Here, as the substrate, a glass substrate, a plastic substrate, a stainless steel substrate, a silicon
substrate, or the like can be used.
[0046]
As described above, in the conventional portable information device, the electric signal
processing circuit, particularly the audio signal processing circuit, is integrally formed on the
display device using thin film semiconductor elements such as thin film transistors, thin film
resistors, and thin film capacitors. It becomes possible to solve the problem of reducing the size
and weight of the portable information device when the output function other than the visual
function, which is the problem, in particular the audio output function, is attached.
[0047]
FIG. 6 shows a block diagram of the audio signal processing circuit.
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The audio signal processing circuit shown in FIG. 6 is composed of three blocks.
The digital signal input to the digital signal input terminal 601 is arithmetically processed by the
digital signal processing circuit 603.
The processing here is decoding of a compressed digital signal or the like, but not limited to
decoding, other arithmetic processing such as filtering may be performed.
Next, the processed digital signal is input to the D / A conversion circuit 604, where the digital
signal is converted to an analog signal.
Then, the converted analog signal or an analog signal input from the outside directly to the
analog signal input terminal 602 is amplified by the analog signal processing circuit 605, output
from the output terminal 606, and sound output by the speaker.
The analog signal processing circuit comprises a non-inverting amplifier circuit, an inverting
amplifier circuit and the like using an operational amplifier circuit, but is not limited to the
operational amplifier circuit and may be another circuit.
Alternatively, the digital signal processing circuit 603 and the D / A conversion circuit 604 may
be mounted with an LSI chip, and the analog signal processing circuit may be formed on a
substrate by thin film semiconductor elements.
[0048]
As described above, in the analog signal processing circuit, amplification of the analog audio
signal is often performed by the operational amplifier circuit.
FIG. 4 is an equivalent circuit diagram when an operational amplifier circuit is manufactured
using a thin film semiconductor element, in particular a TFT.
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The operational amplifier includes a differential circuit composed of a TFT 401 and a TFT 402, a
current mirror circuit composed of a TFT 403 and a TFT 404, a constant current source
composed of a TFT 405 and a TFT 409, a source grounded circuit composed of a TFT 406, a TFT
407 and a TFT 408 The idling circuit configured, the source follower circuit configured with the
TFT 410 and the TFT 411, and the phase compensation capacitor 412 are included.
[0049]
The operation of the operational amplifier circuit of FIG. 4 will be described below.
When a positive signal is input to the non-inversion terminal, the drain current of the TFT 401
becomes larger than the drain current of the TFT 402 because the constant current source
configured of the TFT 405 is connected to the source of the TFT configuring the differential
circuit. The drain current of the TFT 403 is equal to the drain current of the TFT 402 because the
TFT 404 and the TFT 403 constitute a current mirror circuit, and the gate potential of the TFT
406 is lowered by the difference current of the drain current of the TFT 403 and the drain
current of the TFT 401 Change to
Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 is lowered, the TFT
406 operates to turn on more, and the drain current increases.
Thus, the gate potential of the TFT 410 rises, and accordingly, the source potential of the TFT
410, that is, the output terminal also rises.
[0050]
In addition, when a negative signal is input to the non-inversion input terminal, the drain current
of the TFT 401 becomes smaller than the drain current of the TFT 402, and the drain current of
the TFT 403 is the same as the drain current of the TFT 402. The gate potential of the TFT 406
changes in the rising direction by the difference current of
Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 rises, the TFT 406
operates in the direction to turn off and the drain current decreases.
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Thus, the gate potential of the TFT 410 is lowered, and accordingly, the source potential of the
TFT 410, that is, the output terminal is also lowered.
Thus, a signal in phase with the signal of the non-inverted input terminal is output from the
output terminal.
[0051]
When a positive signal is input to the inverting input terminal, the drain current of the TFT 401
becomes smaller than the drain current of the TFT 402, and the drain current of the TFT 403 is
the same as the drain current of the TFT 402. Thus, the gate potential of the TFT 406 changes in
the rising direction.
Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 rises, the TFT 406
operates in the direction to turn off and the drain current decreases.
Thus, the gate potential of the TFT 410 is lowered, and accordingly, the source potential of the
TFT 410, that is, the output terminal is also lowered.
[0052]
Further, when a-signal is input to the inverting input terminal, the drain current of the TFT 401
becomes larger than the drain current of the TFT 402, and the drain current of the TFT 403 is
the same as the drain current of the TFT 402. The gate current of the TFT 406 changes in the
decreasing direction by the difference current of the drain current.
Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 is lowered, the TFT
406 operates to turn on more, and the drain current increases.
Thus, the gate potential of the TFT 410 rises, and accordingly, the source potential of the TFT
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410, that is, the output terminal also rises.
Thus, a signal in reverse phase to the signal of the inverting input terminal is output from the
output terminal.
[0053]
In this example, the differential circuit is made of an Nch TFT and the current mirror circuit is
made of a Pch TFT, but the present invention is not limited to this and may be reversed.
Further, the circuit form is not limited to such circuit connection, and any circuit that can satisfy
the function as an operational amplifier circuit can be used.
In addition, this embodiment can be used in combination with the above-described first
embodiment.
[0054]
FIG. 5 shows an example in which the operational amplifier circuit is realized with a
configuration different from that of FIG.
In this example, the operational amplifier circuit includes a differential circuit formed of TFT 501
and TFT 502, a first current mirror circuit formed of TFT 503 and TFT 504, a second current
mirror circuit formed of TFT 505 and TFT 506, TFT 507, and TFT 508. The third current mirror
circuit configured, the constant current source configured by the TFT 509, and the phase
compensation capacitor 510 are included as components.
[0055]
The operation will be described below.
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When a positive signal is input to the non-inverting input terminal, the drain current of the TFT
501 becomes larger than the drain current of the TFT 502 because a constant current source
configured of the TFT 509 is connected to the common source of the differential circuit. Since
the drain of the TFT 501 is connected to the first current mirror circuit, a current proportional to
the TFT 501 flows through the TFT 504, and when the drain current of the TFT 501 increases,
the drain current of the TFT 504 also increases. In addition, when the current of the TFT 502
decreases, the drain current of the TFT 506 also decreases because the drain of the TFT 502 is
connected to the second current mirror circuit. Since the drain of the TFT 506 is connected to
the third current mirror circuit, if the drain current of the TFT 506 decreases, the drain current
of the TFT 508 also decreases. Thus, the potential of the output terminal rises.
[0056]
When a positive signal is input to the inverting input terminal, the drain current of the TFT 501
becomes smaller than the drain current of the TFT 502. Since the drain of the TFT 501 is
connected to the first current mirror circuit, a current proportional to the TFT 501 flows through
the TFT 504, and if the drain current of the TFT 501 decreases, the drain current of the TFT 504
also decreases. In addition, when the current of the TFT 502 is increased, the drain current of the
TFT 506 is also increased because the drain of the TFT 502 is connected to the second current
mirror circuit. Since the drain of the TFT 506 is connected to the third current mirror circuit, if
the drain current of the TFT 506 increases, the drain current of the TFT 508 also increases. By
the above, the potential of the output terminal is lowered.
[0057]
In this way, an output signal in phase with the signal input at the non-inversion terminal is
output to the output terminal, and an output signal in opposite phase to the signal input at the
inversion input terminal. This example has the advantage that the output signal amplitude can be
made larger than that of the operational amplifier circuit shown in the second embodiment
described above. The polarity of the TFTs may be reversed. In addition, this embodiment can be
used in combination with the above-described first embodiment.
[0058]
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A speaker driving method in the analog signal processing circuit will be described with reference
to FIG. In the conventional connection, as shown in FIG. 7A, in many cases, one of the two
terminals of the planar speaker 703 is connected to the non-inverting amplifier circuit 702, and
the other terminal is grounded for driving. The When outputting sound using a conventional
cone speaker, although it was possible to drive even using such a driving method, the one using a
piezoelectric element that is often used for a flat speaker is used. Unlike the cone speaker, the
element configuration has a problem that a high voltage is required. That is, although the sound
pressure required for a portable information device was obtained with an amplitude of 1 Vrms
with a cone speaker, a voltage amplitude of about 10 Vrms was required with a flat speaker.
[0059]
Therefore, in the driving method of FIG. 7A, the power supply voltage of the analog signal
processing circuit 702 needs a voltage of 30 V or more. However, in the case of using a
polysilicon TFT as a drive device, there has been a major problem in driving a circuit with such a
voltage. It is a problem that when the drain voltage is set high in a polysilicon TFT, particularly
an Nch TFT, the generation of hot carriers degrades the characteristics, particularly the gm
(transconductance) in the linear region. Therefore, although the device is devised in terms of the
structure of the TFT, the voltage which can be driven without deteriorating the TFT is about 15 V
when using the LDD structure, and about 25 V even when using GOLD (gate overlap LDD). It is.
Because of these problems, assuming that the driving method as shown in FIG. 7A is used,
driving at 30 V or more is required, and therefore, it has been impossible to realize an analog
signal processing circuit with polysilicon TFTs.
[0060]
Therefore, the inventors considered driving a flat speaker using Bridged Tranceformer Less (BTL)
driving as shown in FIG. 7 (B). In the BTL drive shown in FIG. 7B, the analog signal processing
circuit is constituted by two circuits of a non-inversion amplification circuit 705 and an inversion
amplification circuit 706, and one terminal of the planar speaker 707 is an output of the noninversion amplification circuit The other terminal is connected to the output of the inverting
amplifier circuit 706. With such driving, substantially double the amplitude can be obtained, so
that the driving amplitude of the flat speaker can be driven at 5 Vrms in one circuit.
[0061]
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Therefore, in the case of FIG. 7B, the power supply voltage of 30 V is not necessary, the circuit
can be driven with a voltage of 20 V or less, and an analog signal processing circuit can be
configured using polysilicon TFTs. . Further, this embodiment can be used in combination with
the above-described first to third embodiments.
[0062]
Although the BTL driving is realized using the non-inversion amplification circuit 802 and the
inversion amplification circuit 803 in FIG. 8A, the connection method is different from that of the
fourth embodiment. The input signal is not input to both the non-inverted amplifier circuit 802
and the inverted amplifier circuit 803, but is input only to the non-inverted amplifier circuit 802.
The input of the inverting amplifier circuit 803 is connected to the output of the non-inverting
amplifier circuit 802. The noninverting amplifier circuit 802 drives a first terminal of the speaker
804 and the input of the inverting amplifier circuit 803, and the output of the inverting amplifier
circuit 803 drives a second terminal of the speaker 804.
[0063]
Although the BTL driving is realized using the inverting amplifier circuit 806 and the inverting
amplifier circuit 807 in FIG. 8B, the connection method is different from that in FIGS. 7B and 8A.
The input signal is input to the inverting amplifier circuit 806, and the input of the inverting
amplifier circuit 807 is connected to the output of the inverting amplifier circuit 806. The output
of the inverting amplifier 806 drives the first terminal of the speaker 808 and the input of the
inverting amplifier circuit 807, and the inverting amplifier circuit 807 drives the second terminal
of the speaker 808. Further, this embodiment can be used in combination with the abovedescribed first to third embodiments.
[0064]
In FIG. 9, buffer circuits 904 and 905 are added after the non-inversion amplification circuit 902
and the inversion amplification circuit 903 respectively, and the output of the buffer circuit 904
drives the first terminal of the speaker 906, and the output of the buffer circuit 905 is a speaker
The second terminal of 906 is being driven. Thus, the speaker may be driven through the buffer
circuit. Although a buffer circuit is added to the example shown in FIG. 7B in FIG. 9, a buffer
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circuit may be added to the circuits shown in FIGS. 8A and 8B. Further, this embodiment can be
used in combination with the above-described first to third embodiments.
[0065]
An example of the analog signal processing circuit is shown in FIG. In this circuit, the voltage
amplification factor is set to 100 times. As an input signal, a signal of about 100 mVrms is input,
and the preamplifying circuit 1001 first amplifies the signal five times. The output signal is input
to the non-inverted amplifier circuit 1002 and the inverted amplifier circuit 1003, amplified by
10 times each, and the speaker 1004 is connected between the output terminals thereof. A 50fold signal is generated at both ends of the speaker 1004, and since they are in opposite phase,
the result is 100-fold. As described above, stable amplification is possible by using the two-stage
amplifier circuit. Here, each amplifier circuit uses the operational amplifier circuit described in
the second embodiment. However, the circuit configuration is not limited thereto, and other
circuit configurations may be used. Also, the amplification factor and the distribution of
amplification factors may be other values as well as the above-mentioned values.
[0066]
In the example of FIG. 10, although the output signal of the preamplification circuit is input to
the non-inversion amplification circuit and the inversion amplification circuit, the output signal of
the pre-amplification circuit is input to the non-inversion amplification circuit. The output signal
may be input to the inverting amplification circuit, and a speaker may be connected between the
output terminal of the non-inverting amplification circuit and the output terminal of the inverting
amplification circuit.
[0067]
Alternatively, the output signal of the preamplification circuit is input to the first inverting
amplification circuit, the output signal of the first inverting amplification circuit is input to the
second inverting amplification circuit, and the output terminal of the first inverting amplification
circuit , And a speaker may be connected between the output terminal of the second inverting
amplifier circuit.
Further, this embodiment can be used in combination with the above-described embodiment.
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[0068]
18 and 19 show the measurement results of the characteristics of the prototyped amplifier. The
result is non-inverted, 50 times that of the amplifier. Here, the distortion rate is represented as
THD (total harmonic distortion rate) in FIG. FIG. 18 shows the relationship between the input
voltage and the output voltage of the amplifier and the distortion rate. Here, the slope of the
graph of the voltage characteristics of the input voltage and the output voltage represents the
gain (amplification) of the measuring instrument, and if the relationship between the input and
output deviates from a straight line, distortion occurs in the output. Here, the distortion rate rises
as the input voltage increases, but the distortion rate becomes 1% when the input voltage is 0.07
Vrms, and when the output voltage becomes approximately 3.5 Vrms, that is, 10 Vpp. is there.
This can obtain a practical amplitude in driving a flat speaker. Further, FIG. 19 shows the
relationship between the input frequency and the output voltage. The vertical axis represents the
ratio (gain) of the voltage of the output to the voltage of the input of the amplifier. Here, the gain
is approximately 34 dB, that is, the amplification is 50 times in the frequency region where there
is no distortion, but the output voltage drops from 10 KHz, and the output voltage drops 30% at
about 15 KHz . This indicates that the frequency band of the audio signal is a sufficient band.
[0069]
FIG. 11 is a plan view of a TFT constituting a differential circuit of an analog signal processing
circuit using an operational amplifier circuit. FIG. 11A shows the arrangement of a normal
differential circuit. The TFTs 1101 and the TFTs 1102 are disposed adjacent to each other, and
the common source electrode 1107, the drain electrodes 1105 and 1106, and the gate
electrodes 1103 and 1104 are drawn out.
[0070]
In an analog signal processing circuit using an operational amplifier circuit, the balance of TFTs
constituting a differential circuit is important. In particular, since a TFT using polysilicon has a
larger variation than a single crystal transistor, the countermeasure is important. In FIG. 11B,
TFTs constituting a differential circuit are configured in parallel as a countermeasure against
variations. In FIG. 11B, channel formation regions 1111 and 1118 are disposed adjacent to each
other and used as one TFT. In addition, channel formation regions 1112 and 1119 are disposed
adjacent to each other and used as one TFT. The source electrodes have channel formation
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regions 1111 and 1118 in common, channel formation regions 1112 and 1119 in common, and
are drawn out by common source 1117. Further, the drain electrode 1115 and the gate electrode
1113 corresponding to the channel formation regions 1111 and 1118 are drawn out. The drain
electrode 1116 and the gate electrode 1114 corresponding to the channel formation regions
1112 and 1119 are drawn out. With such a parallel configuration, the TFT characteristics are
averaged and the variation is reduced.
[0071]
What is shown in FIG. 12A is one in which the TFT constituting the differential circuit is a double
gate TFT. In the double gate TFT, the drain electrodes 1205 and 1206 and the source electrode
1207 are the same as in FIG. 11A, but the gate electrodes 1203 and 1204 each have two channel
formation regions. By using such a double gate TFT, it is possible to reduce the averaging effect
of the TFT characteristics and the drain voltage applied to one TFT, and to reduce the current
deviation due to the drain voltage modulation. Although a double gate is shown here, it may be a
triple or more gate.
[0072]
What is shown in FIG. 12 (B) is one in which the TFTs constituting the differential circuit are
arranged in a cross. As shown in FIG. 12B, in the cross-over layout, the channel forming regions
1211 and 1219 are disposed diagonally and connected by a gate wiring 1214, a source wiring
1217, and a drain wiring 1215, and used as one TFT. ing. Further, channel formation regions
1212 and 1218 are disposed diagonally and connected by a gate wiring 1213, a source wiring
1217, and a drain wiring 1216, and used as one TFT. Further, the straight line connecting the
channel formation region 1211 and the channel formation region 1219 crosses the straight line
connecting the channel formation region 1212 and the channel formation region 1218. Such an
arrangement makes it possible to reduce positional variations such as the gradient of impurity
doping and laser crystallization. These variation countermeasures can be used in combination.
Further, this embodiment can be used in combination with the above-described embodiment.
[0073]
FIG. 13 shows an example of a transistor used for an output portion of an analog signal
processing circuit using an operational amplifier circuit. When driving a load such as a speaker,
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an output portion of the operational amplifier circuit needs to have a large gate width in order to
pass a large current. Generally, in a semiconductor integrated circuit, as shown in FIG. 13, when
the gate width is increased, the source region 1301 or 1303 or the drain region 1302 or 1304 is
overlapped to reduce the size of the transistor in order to reduce the area. Thus, although the
gate wiring 1305 is not changed, the source / drain regions can be reduced. However, in the
analog signal processing circuit, as in the digital signal processing circuit, not only rising and
falling but also current flows constantly. Therefore, the temperature of the TFT rises due to selfheating. In particular, in the case of a TFT formed on a glass substrate or the like having a small
thermal conductivity, the temperature rise is remarkable and the reliability is deteriorated.
Therefore, some heat dissipation measures are required.
[0074]
The example shown in FIG. 15 is an example in which the TFT constituting the output part is
divided into semiconductor thin films 1504, 1505, 1506 and 1507 with small gate widths, and
temperature rise is prevented by taking the distance between the respective semiconductor thin
films. It is. Four TFTs having the size of the island 1504 are arranged at a distance. The gate
electrode 1502, the source electrode 1501, and the drain electrode 1503 connect the respective
semiconductor thin films. Here, it is desirable that the distance between the semiconductor thin
films be larger than the long side of the semiconductor thin film, because heat can be dissipated
more effectively. In FIG. 15, the interval X and the interval Y are set larger than the long side a
(a> b) of the semiconductor thin film.
[0075]
What is shown in FIG. 14 is one in which the channel formation regions in each semiconductor
thin film are finely divided. Four TFTs of the size of the semiconductor thin film 1404 are
arranged at a distance. The gate electrode 1402, the source electrode 1401, and the drain
electrode 1403 connect the respective semiconductor thin films. In each semiconductor thin film,
the channel formation regions are separated but the source and drain regions are one by one. It
is also possible to suppress the temperature rise by subdividing the channel formation region
which is a heat generation source in this manner. Here, it is desirable that the distance d to the
adjacent channel formation region is larger than the width W of the subdivided channel
formation region (for example, 1405) because heat can be dissipated more effectively.
[0076]
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FIG. 16 shows an example in which a conductive film 1604 is provided by a gate electrode 1602
between each semiconductor thin film in addition to the embodiment shown in FIG. In order to
dissipate the heat generated in the channel of each semiconductor thin film, a conductive film
1604 is provided. The conductive film is not limited to the gate electrode material, and may be a
source / drain electrode material or another material. Also, the shape is not limited to the shape
of FIG. Thus, by devising the shape of the TFT in the output stage, the heat radiation effect can be
enhanced, and a circuit with a large current consumption can be formed on the display device by
the TFT. Further, this embodiment can be used in combination with the above-described
embodiment.
[0077]
FIG. 1 is an outline view of a display device of the present invention. The outline drawing of the
conventional display apparatus. The outline drawing of the conventional display apparatus. The
equivalent circuit schematic of the operational amplifier circuit of this invention. The equivalent
circuit schematic of the operational amplifier circuit of this invention. The block diagram of the
audio signal processing circuit of this invention The figure which showed the connection of the
analog signal processing circuit of this invention, and a speaker. The figure which showed the
connection of the analog signal processing circuit of this invention, and a speaker. The figure
which showed the connection of the analog signal processing circuit of this invention, and a
speaker. The figure which showed the Example of the analog signal processing circuit of this
invention. Diagram showing the layout of differential circuits Diagram showing the layout of
differential circuits Diagram showing the output TFTs of op amp circuits Diagram showing the
output TFTs of op amp circuits Diagram showing the output TFTs of op amp circuits Diagram
showing the output TFTs of op amp circuits Example of measurement of the characteristic of the
amplifier Figure of measurement of the characteristic of the amplifier
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