JP2004173264A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and lightweight display device in the display device having a voice output circuit. <P>SOLUTION: A speaker of the display device is defined as a flat speaker and a voice signal processor is constituted of a thin film transistor on the display device. Power supply voltage is reduced and degradation of the thin film transistor is prevented by defining drive of the speaker as BTL drive. Thus, small, lightweight portable information equipment capable of outputting voice is realized by achieving miniaturization of the speaker, built-in state of a voice signal processing circuit in the display device. <P>COPYRIGHT: (C)2004,JPO

Description

 The present invention relates to a display device including a thin-film semiconductor element and having an electric signal processing circuit for driving an output device other than a visual device, and particularly to a display device in which an audio signal processing circuit for driving a speaker is integrally formed on a substrate. Note that, in this specification, a speaker includes a vibrator that outputs sound by vibrating a member of a display device such as a glass substrate, a plastic substrate, or a touch panel, and generally refers to a device that converts an electric signal into sound. It shall be.

 2. Description of the Related Art In recent years, with the progress of communication technology, mobile phones have become widespread. In the future, transmission of moving images and more information transmission are expected. On the other hand, as for personal computers, mobile-friendly products have been produced due to their light weight. A large number of information terminals called PDA, which began with electronic notebooks, are also being produced and are becoming popular. Also, due to the development of display devices, most of these portable information devices are equipped with flat panel displays.

  Further, among active matrix display devices, in recent years, a display device using a low-temperature polysilicon thin film transistor (hereinafter, a thin film transistor is referred to as a TFT) has been commercialized. In a low-temperature polysilicon TFT, not only pixels but also a signal line driving circuit can be integrally formed around a pixel portion, so that a display device can be miniaturized and a high definition can be achieved. Expected.

  On the other hand, information portable devices are required to have not only a visual display function but also other output functions, and particularly a voice output function. When a video is displayed, if the audio is obtained, the video can be more effectively viewed and the video can be enjoyed more.

However, a normal audio output device converts an electric signal into a sound using a cone speaker or the like and outputs the sound. These cone speakers require a large area in portable information devices, and have hindered the miniaturization of portable information devices.
FIG. 2 is an external view of the periphery of a display device of a conventional portable information device having an audio output function. An audio signal processing circuit mounted on a cone speaker 207, an FPC 205, a counter substrate 208, and a printed board 206 in a display device in which a pixel portion 204, a source signal line driving circuit 202, and a gate signal line driving circuit 203 are integrally formed on a substrate 209. 210 together. Here, the upper figure shows a top view, and the lower figure shows a side view. Further, in the lower diagram, the source signal line driver circuit 202, the gate signal line driver circuit 203, and the pixel portion 204 are omitted for simplification of display.

  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 external view of the periphery of the display device of the portable information device 301 having a flat speaker. A display device in which a pixel portion 304, a source signal line driver circuit 302, and a gate signal line driver circuit 303 are integrally formed on a substrate 309, and an audio signal mounted on a planar speaker 306, FPCs 305 and 308, a counter substrate 310, and a printed substrate 311. The processing circuit 307 is mounted together. Here, the upper figure shows a top view, and the lower figure shows a side view. Further, in the lower diagram, a source signal line driver circuit 302, a gate signal line driver circuit 303, and a pixel portion 304 are omitted for simplification of display.

  This speaker converts an electric signal into vibration and outputs sound in the same manner as a conventional speaker, but vibrates not a cone but a glass substrate such as a display device, a plastic substrate, a touch panel, and the like. By using such a planar speaker, it is possible to realize a smaller and lighter weight than a portable information device using a conventional cone speaker.

  FIG. 17 shows an example of a planar speaker. In this example, sound is output by vibrating a touch panel 1702, a lower substrate 1705, an adhesive 1706, and a liquid crystal panel 1704 provided on a housing 1701 with a speaker 1703. (See Non-Patent Document 1)

Nikkei Electronics, August 26, 2002 p. 52

As described above, a planar speaker is a very effective means for reducing the size and weight of a portable information device, but the following problems remain.
As shown in FIG. 3, an audio signal processing circuit 307 for driving a speaker using a planar speaker 306 has a printed circuit board 311 arranged outside the display device and an LSI mounted thereon as in the conventional case. Was. Therefore, in order to reduce the size and weight of the portable information device, it is still incomplete.

In order to solve the above problems, the present inventors considered driving a non-visual output device such as a planar speaker using a thin film semiconductor element on a display device substrate, particularly, a polysilicon TFT. The polysilicon TFT has a high driving capability, unlike an amorphous TFT, and thus can drive a speaker or the like.

Hereinafter, the configuration of the present invention will be described.

  According to the present invention, in a display device having a thin film semiconductor element on a substrate, the display device has an electric signal processing circuit for driving an output device other than a visual device, and the electric signal processing circuit is constituted by the thin film semiconductor element. It is characterized by being done.

  Further, in the present invention, in a display device having a thin film semiconductor element on a substrate, the display device has an audio signal processing circuit, and the audio signal processing circuit is constituted by the thin film semiconductor element.

  Further, according to the present invention, in a display device having a thin film semiconductor element over a substrate, the display device has an audio signal processing circuit, and the audio signal processing circuit is configured by the thin film semiconductor element. A speaker is driven by an output signal.

  Further, in the above configuration, the audio signal processing circuit includes a digital signal processing circuit.

  Further, in the above configuration, the audio signal processing circuit includes a D / A conversion circuit.

  Further, in the above configuration, the audio signal processing circuit includes an analog signal processing circuit.

  Further, in the above configuration, the analog signal processing circuit is configured by an operational amplifier circuit.

  According to the present invention, in a display device having a thin film semiconductor element on a substrate, the thin film semiconductor element forms an analog signal processing circuit, and a speaker is driven by an output signal of the analog signal processing circuit.

  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, the analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit, A first terminal of the speaker is driven by an output signal of the amplifier circuit, and a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit.

  The present invention also provides a display device having a thin film semiconductor element on a substrate, wherein the thin film semiconductor element forms an analog signal processing circuit, wherein the analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit, An input terminal of the non-inverting amplifier circuit and an input terminal of the inverting amplifier circuit are connected, and a first terminal of the speaker is driven by an output signal of the non-inverting amplifier circuit. It is characterized in that the second terminal is driven.

  Further, according to the present invention, in a display device having a thin film semiconductor element over a substrate, the thin film semiconductor element constitutes an analog signal processing circuit, and the analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit. An output terminal of the non-inverting amplifier circuit is connected to an input terminal of the inverting amplifier circuit, and drives a first terminal of a speaker by an output signal of the non-inverting amplifier circuit. The second terminal is driven.

  The present invention also 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, wherein the analog signal processing circuit has a first inverting amplifier circuit and a second inverting amplifier circuit. Circuit, an output terminal of the first inverting amplifier circuit is connected to an input terminal of the second inverting amplifier circuit, and a first terminal of the speaker is driven by an output signal of the first inverting amplifier circuit. The second terminal of the speaker is driven by an output signal of the second inverting amplifier circuit.

  Further, according to the present invention, in a display device having a thin film semiconductor element on a substrate, the thin film semiconductor element forms an analog signal processing circuit, and the analog signal processing circuit includes a preamplifier circuit, a non-inverting amplifier circuit, Having an inverting amplifier circuit, inputting the output signal of the preamplifier circuit to the non-inverting amplifier circuit and the inverting amplifier circuit, and driving the first terminal of the speaker by the output signal of the non-inverting amplifier circuit. And a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit.

  Further, according to the present invention, in a display device having a thin film semiconductor element on a substrate, the thin film semiconductor element forms an analog signal processing circuit, and the analog signal processing circuit includes a preamplifier circuit, a non-inverting amplifier circuit, An inverting amplifier circuit, an output signal of the preamplifier circuit is input to the non-inverting amplifier circuit, an output signal of the non-inverting amplifier circuit is input to the inverting amplifier circuit, and an output signal of the non-inverting amplifier circuit is output. Thus, the first terminal of the speaker is driven, and the second terminal of the speaker is driven by the output signal of the inverting amplifier circuit.

  According to the present invention, in a display device having a thin film semiconductor element on a substrate, the thin film semiconductor element constitutes an analog signal processing circuit, wherein the analog signal processing circuit includes a preamplifier circuit and a first inverting amplifier circuit. Having a second inverting amplifier circuit, the output signal of the preamplifier circuit is input to the first inverting amplifier circuit, the output signal of the first inverting amplifier circuit, the second inverting circuit Input to an amplifier circuit, driving a first terminal of the speaker by an output signal of the first inverting amplifier circuit, and driving a second terminal of the speaker by an output signal of the second inverting amplifier circuit. It is characterized by.

  In the above configuration, the non-inverting amplifier circuit or the inverting amplifier circuit drives a speaker via a buffer circuit.

  Further, in the above structure, the analog signal processing circuit is driven by a power supply voltage of less than 30V.

  Further, in the above configuration, the speaker is a flat speaker.

  Further, in the above configuration, the flat speaker uses the display device itself as a vibration medium.

  According to the present invention, in a display device having a thin film transistor on a substrate, the thin film transistor forms 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 grounded amplifier. And a source follower, wherein the constant current source is electrically connected to a source electrode of a thin film transistor forming the differential circuit, and a first output terminal of the differential circuit is an output terminal of the current mirror circuit. And a second output terminal of the differential circuit is electrically connected to an input terminal of the current mirror circuit, and an output terminal of the common source amplifier is connected to the source terminal. An output terminal of the source follower is electrically connected to an input terminal of the follower, and an output terminal of the source follower is electrically connected to an output terminal of the analog signal processing circuit. It is characterized by being.

  Further, according to the present invention, in a display device having a thin film transistor over a substrate, the thin film transistor forms an analog signal processing circuit, and the analog signal processing circuit includes a differential circuit, a first current mirror circuit, and a second current mirror circuit. 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 an input terminal of the first current mirror circuit, a second output terminal of the differential circuit is electrically connected to an 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 calendar It is characterized by being electrically connected to the output terminal of the mirror circuit input terminal of the third current mirror circuit.

  In addition, the present invention provides a display device having a thin film transistor over a substrate, wherein the thin film transistor forms an analog signal processing circuit having a differential circuit, and the differential circuit is formed by a multi-gate thin film transistor. And

  Further, the present invention is a display device having a thin film transistor over a substrate, wherein the thin film transistor forms an analog signal processing circuit having a differential circuit, and the differential circuit connects a plurality of thin film transistors in parallel. .

  In addition, the present invention provides a display device having a thin film transistor over a substrate, wherein the thin film transistor constitutes an analog signal processing circuit having a differential circuit, and the differential circuit is provided with a plurality of thin film transistors. And

  Further, the present invention is characterized in that, in a display device having a thin film transistor on a substrate, the thin film transistor constitutes an analog signal processing circuit, and the output thin film transistor of the analog signal processing circuit comprises a plurality of semiconductor thin films.

  In the above structure, a distance between the plurality of semiconductor thin films is larger than a long side of the semiconductor thin film.

  According to the present invention, in a display device in which a thin film transistor is formed over a substrate, the thin film transistor forms an analog signal processing circuit, an output thin film transistor of the analog processing signal circuit has a plurality of channel formation regions, and has a source / drain region. It is characterized by being composed of one semiconductor thin film.

  In the above structure, a distance between the plurality of channel formation regions in the semiconductor thin film is larger than a width of the channel formation region.

  According to the present invention, in a display device having a thin film transistor on a substrate, the thin film transistor forms an analog signal processing circuit, and the thin film transistor forming an output stage of the analog signal processing circuit includes a plurality of semiconductor thin films. Characterized in that a conductive film is disposed between the semiconductor thin films.

  As described above, the miniaturization of the speaker and the incorporation of the audio signal processing circuit in the display device can be achieved, and a small and lightweight portable information device capable of outputting audio can be realized.

  In a conventional portable information device having an audio output function, it is difficult to reduce the size of a cone speaker and a driving circuit for driving the cone speaker, and it has not been possible to reduce the size of the portable information device.

  The present invention has realized a display device having a small volume audio output function by forming a speaker as a planar speaker and integrally forming a driving circuit for driving the speaker on a substrate using a thin film semiconductor element, particularly a TFT. . According to the present invention, a portable information device having an audio output function can be reduced in size and weight.

FIG. 1 shows an external view of the display device of the present invention. As shown in FIG. 1, a display device 101 of the present invention has a pixel portion 104, a source signal line driver circuit 102, a gate signal line driver circuit 103, and an audio signal processing circuit 105 formed integrally on a substrate 109 by using TFTs. The counter substrate 110 is provided thereon. Here, the upper view of FIG. 1 shows a top view, and the lower view shows a side view. In the lower diagram, a source signal line driver circuit 102, a gate signal line driver circuit 103, a pixel portion 104, and an audio signal processing circuit 105 are omitted for simplification of display. A flat speaker 106 is mounted on the substrate 109. The planar speaker 106 may output a sound by vibrating a substrate or the like without outputting the sound itself. The planar speaker 106 is electrically connected to the audio signal processing circuit 105 via the FPC 108. The external audio signal is input to the audio signal processing circuit 105 via the FPC 107, and is output to the flat speaker 106 via the FPC. Here, a glass substrate, a plastic substrate, a stainless steel substrate, a silicon substrate, or the like can be used as the substrate.

  As described above, by using a thin film semiconductor element such as a thin film transistor, a thin film resistor, and a thin film capacitor on a display device to integrally form an electric signal processing circuit, particularly an audio signal processing circuit, in a conventional portable information device, It is 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, particularly the sound output function, is attached.

FIG. 6 shows a block diagram of the audio signal processing circuit. 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 processed by the digital signal processing circuit 603. The processing here is decoding of a compressed digital signal, but is not limited to decoding, and 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 into an analog signal. Then, the converted analog signal or the analog signal directly input from the outside to the analog signal input terminal 602 is amplified by the analog signal processing circuit 605, output from the output terminal 606, and output as sound by a speaker. The analog signal processing circuit includes 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 formed by mounting an LSI chip, and the analog signal processing circuit may be formed on a substrate using a thin film semiconductor element.

  As described above, in an analog signal processing circuit, an operational amplifier circuit often amplifies an analog audio signal. FIG. 4 is an equivalent circuit diagram in the case where an operational amplifier circuit is manufactured using a thin film semiconductor element, particularly, a TFT. This operational amplifier includes a differential circuit composed of TFTs 401 and 402, a current mirror circuit composed of TFTs 403 and 404, a constant current source composed of TFTs 405 and 409, a grounded source circuit composed of TFT 406, a TFT 407 and a TFT 408. It comprises an idling circuit, a source follower circuit composed of TFTs 410 and 411, and a phase compensation capacitor 412.

  Hereinafter, the operation of the operational amplifier circuit of FIG. 4 will be described. When a + signal is input to the non-inverting terminal, the drain current of the TFT 401 becomes larger than the drain current of the TFT 402 because the constant current source constituted by the TFT 405 is connected to the source of the TFT constituting the differential circuit. The drain current of the TFT 403 becomes the same as the drain current of the TFT 402 because the TFT 404 and the TFT 403 form a current mirror circuit, and the gate potential of the TFT 406 decreases due to the difference current between the drain current of the TFT 403 and the drain current of the TFT 401. Changes to Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 decreases, the TFT 406 operates in a direction to turn on more, and the drain current increases. Accordingly, the gate potential of the TFT 410 increases, and accordingly, the source potential of the TFT 410, that is, the output terminal also increases.

  When a negative signal is input to the non-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. , The gate potential of the TFT 406 changes in a rising direction. Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 increases, the TFT 406 operates in a direction to turn off, and the drain current decreases. Therefore, the gate potential of the TFT 410 decreases, and accordingly, the source potential of the TFT 410, that is, the output terminal also decreases. Thus, a signal in phase with the signal at the non-inverting input terminal is output from the output terminal.

  When a + 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. Accordingly, the gate potential of the TFT 406 changes in a rising direction. Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 increases, the TFT 406 operates in a direction to turn off, and the drain current decreases. Therefore, the gate potential of the TFT 410 decreases, and accordingly, the source potential of the TFT 410, that is, the output terminal also decreases.

  When a negative 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 potential of the TFT 406 changes in a decreasing direction due to the difference current between the drain currents. Since the TFT 406 is a P-type TFT, when the gate potential of the TFT 406 decreases, the TFT 406 operates in a direction to turn on more, and the drain current increases. Accordingly, the gate potential of the TFT 410 increases, and accordingly, the source potential of the TFT 410, that is, the output terminal also increases. In this manner, a signal having a phase opposite to that of the signal at the inverting input terminal is output from the output terminal.

In this example, the differential circuit is made of an NchTFT and the current mirror circuit is made of a PchTFT. However, the present invention is not limited to this, and may be reversed. Further, the circuit type is not limited to such a circuit connection, and any circuit that satisfies the function as an operational amplifier circuit can be used.
This embodiment can be used in combination with the first embodiment.

FIG. 5 shows an example in which an operational amplifier circuit is realized with a configuration different from that of FIG. In this example, the operational amplifier circuit includes a differential circuit including TFTs 501 and 502, a first current mirror circuit including TFTs 503 and 504, a second current mirror circuit including TFTs 505 and 506, and TFTs 507 and 508. It has a third current mirror circuit configured, a constant current source configured by a TFT 509, and a phase compensation capacitor 510 as constituent elements.

  The operation will be described below. When a + 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 the constant current source including 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. If the drain current of the TFT 501 increases, the drain current of the TFT 504 also increases. 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 increases.

  When a + 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. If the drain current of the TFT 501 decreases, the drain current of the TFT 504 also decreases. When the current of the TFT 502 increases, the drain current of the TFT 506 also increases 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. Thus, the potential of the output terminal decreases.

In this manner, an in-phase output signal is output to the output terminal with respect to the signal input of the non-inverting terminal, and an in-phase output signal is output to the signal input of the inverting input terminal. This example has an advantage that the output signal amplitude can be larger than that of the operational amplifier circuit described in the second embodiment. The polarity of the TFT may be reversed.
This embodiment can be used in combination with the first embodiment.

  FIG. 7 illustrates a method of driving a speaker in an analog signal processing circuit. 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 to drive. Was. In the case of outputting sound using a conventional cone speaker, it was possible to drive even with such a driving method, but the one using a piezoelectric element often used for a flat speaker is not There was a problem that the element configuration was different from the cone speaker and required a high voltage. That is, a cone speaker can obtain a sound pressure required for a portable information device even with an amplitude of 1 Vrms, but a flat speaker needs a voltage amplitude of about 10 Vrms.

  Therefore, in the driving method in FIG. 7A, the power supply voltage of the analog signal processing circuit 702 needs to be 30 V or more. However, when a polysilicon TFT is used as a driving device, there is a large problem in driving a circuit with such a voltage. This is a problem in that when a drain voltage is set high in a polysilicon TFT, particularly in an Nch TFT, the generation of hot carriers causes deterioration of characteristics, and particularly, gm (mutual conductance) in a linear region is remarkably deteriorated. For this reason, the structure of the TFT has been devised, but the voltage that can be driven without deteriorating the TFT is about 15 V when the LDD structure is used, and about 25 V even when the GOLD (gate overlap LDD) is used. It is. Due to such a problem, when a driving method as shown in FIG. 7A is premised, a driving of 30 V or more is required, so that an analog signal processing circuit cannot be realized with a polysilicon TFT.

  Therefore, the inventors considered driving a planar speaker by using a BTL (Bridged Transformer Less) drive as shown in FIG. 7B. In the BTL drive shown in FIG. 7B, the analog signal processing circuit is constituted by two circuits, a non-inverting amplifier circuit 705 and an inverting amplifier circuit 706, and one terminal of the planar speaker 707 is connected to the output of the non-inverting amplifier circuit 705. The other terminal is connected to the output of the inverting amplifier circuit 706. By performing such driving, a substantially double amplitude can be obtained, so that the driving amplitude of the flat speaker can be driven at 5 Vrms by one circuit.

Therefore, in the case of FIG. 7B, a power supply voltage of 30 V is not required, and the circuit can be driven by a voltage of 20 V or less, and an analog signal processing circuit can be formed using a polysilicon TFT. .
This embodiment can be used in combination with the first to third embodiments.

  In FIG. 8A, BTL driving is realized using a non-inverting amplifier circuit 802 and an inverting amplifier circuit 803, but the connection method is different from that of the fourth embodiment. The input signal is not input to both the non-inverting amplifier circuit 802 and the inverting amplifier circuit 803, but is input only to the non-inverting amplifier circuit 802. The input of the inverting amplifier 803 is connected to the output of the non-inverting amplifier 802. The non-inverting amplifier circuit 802 drives the 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 the second terminal of the speaker 804.

FIG. 8B illustrates a case where BTL driving is realized by using an inverting amplifier circuit 806 and an inverting amplifier circuit 807, but the connection method is different from those 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 807, which drives the second terminal of the speaker 808.
This embodiment can be used in combination with the first to third embodiments.

In FIG. 9, buffer circuits 904 and 905 are added after the non-inverting amplifier circuit 902 and the inverting amplifier circuit 903, respectively, and the first terminal of the speaker 906 is driven by the output of the buffer circuit 904. The second terminal 906 is being driven. As described above, the speaker may be driven via the buffer circuit. In FIG. 9, a buffer circuit is added to the example shown in FIG. 7B, but a buffer circuit may be added to the circuits shown in FIGS. 8A and 8B.
This embodiment can be used in combination with the first to third embodiments.

FIG. 10 shows an example of an analog signal processing circuit. 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 signal is first amplified by a factor of 5 in the preamplifier circuit 1001. The output signal is input to a non-inverting amplifier circuit 1002 and an inverting amplifier circuit 1003, each of which is amplified 10 times, and a speaker 1004 is connected between the output terminals.
A 50-fold signal is generated at both ends of the speaker 1004, and the signals are out of phase. As a result, the signal becomes 100-fold. The use of the two-stage amplifier circuit enables stable amplification. Here, the operational amplifier circuit described in the second embodiment is used for each amplifier circuit. However, the circuit configuration is not limited to this, and another circuit configuration may be used. Further, the amplification factor and the distribution of the amplification factor are not limited to the above numerical values, and may be other values.

  In the example of FIG. 10, the output signal of the preamplifier is input to the non-inverting amplifier and the inverting amplifier. However, the output signal of the preamplifier is input to the non-inverting amplifier, and The output signal may be input to the inverting amplifier circuit, and a speaker may be connected between the output terminal of the non-inverting amplifier circuit and the output terminal of the inverting amplifier circuit.

Alternatively, the output signal of the preamplifier is input to the first inverting amplifier, the output signal of the first inverting amplifier is input to the second inverting amplifier, and the output terminal of the first inverting amplifier is Alternatively, a speaker may be connected to the output terminal of the second inverting amplifier circuit.
This embodiment can be used in combination with the above-described embodiment.

18 and 19 show the results of measuring the characteristics of the prototyped amplifier. This result shows a non-inverted one, that of a 50-fold 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 factor. Here, the slope of the graph of the voltage characteristics of the input voltage and the output voltage represents the gain (amplification degree) of the measuring instrument. If the relationship between the input and output deviates from a straight line, the output will be distorted. Here, the distortion rate increases with an increase in the input voltage, but the distortion rate becomes 1% when the input voltage is 0.07 Vrms, and when the output voltage becomes about 3.5 Vrms, that is, 10 Vpp. is there. As a result, a practically usable amplitude can be obtained in driving a planar speaker.
FIG. 19 shows the relationship between the input frequency and the output voltage. The vertical axis represents the ratio (gain) of the output voltage to the input voltage of the amplifier. Here, the gain is about 34 dB in the frequency region where there is no distortion, that is, the amplification degree is 50 times, but the output voltage decreases from 10 kHz and the output voltage decreases by 30% at about 15 kHz. . This indicates that the band is sufficient for the frequency band of the audio signal.

  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 an arrangement of a normal differential circuit. The TFT 1101 and the TFT 1102 are arranged adjacent to each other, and lead out a common source electrode 1107, drain electrodes 1105 and 1106, and gate electrodes 1103 and 1104.

  In an analog signal processing circuit using an operational amplifier circuit, it is important to balance TFTs forming a differential circuit. In particular, a TFT using polysilicon has a larger variation than a single crystal transistor, and therefore, a countermeasure is important. FIG. 11B shows a configuration in which TFTs constituting a differential circuit are arranged in parallel as a measure against variation. In FIG. 11B, channel formation regions 1111 and 1118 are arranged adjacent to each other and used as one TFT. Further, channel forming regions 1112 and 1119 are arranged adjacent to each other and used as one TFT. The source electrode has common channel forming regions 1111 and 1118, has common channel forming regions 1112 and 1119, and is drawn out by a common source 1117. In addition, a drain electrode 1115 and a gate electrode 1113 corresponding to the channel formation regions 1111 and 1118 are drawn out. A drain electrode 1116 and a gate electrode 1114 corresponding to the channel formation regions 1112 and 1119 are drawn out. By adopting such a parallel configuration, TFT characteristics are averaged, and variations are reduced.

  FIG. 12A shows an example in which a TFT constituting a 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 those in FIG. 11A, but each of the gate electrodes 1203 and 1204 has two channel formation regions. With such a double-gate TFT, the averaging effect of the TFT characteristics, the drain voltage applied to one TFT can be reduced, and the current deviation due to the drain voltage modulation can be reduced. Although a double gate is shown here, a triple or more gate may be provided.

FIG. 12B illustrates a TFT in which a differential circuit is formed in a crossing arrangement. As shown in FIG. 12B, the channel formation regions 1211 and 1219 are arranged obliquely and connected by a gate wiring 1214, a source wiring 1217, and a drain wiring 1215 to use as one TFT. ing. Further, the channel formation regions 1212 and 1218 are arranged obliquely and connected by a gate wiring 1213, a source wiring 1217, and a drain wiring 1216, and used as one TFT. Furthermore, a straight line connecting the channel formation region 1211 and the channel formation region 1219 and a straight line connecting the channel formation region 1212 and the channel formation region 1218 are arranged so as to cross each other. With such an arrangement, it is possible to reduce variations due to positions such as gradient of impurity doping and laser crystallization. These dispersion measures can be used in combination.
This embodiment can be used in combination with the above-described embodiment.

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 the output of the operational amplifier circuit drives a load such as a speaker, a large current flows, so that it is necessary to increase the gate width. In general, in a semiconductor integrated circuit, as shown in FIG. 13, when the gate width is increased, the transistor is reduced by overlapping the source regions 1301 and 1303 or the drain regions 1302 and 1304 to reduce the area. In this manner, the gate wiring 1305 does not change, but the source / drain regions can be reduced.
However, in an analog signal processing circuit, a current always flows in addition to rising and falling, as in a digital signal processing circuit. Therefore, the temperature of the TFT rises due to self-heating. In particular, a TFT formed on a glass substrate or the like having a low thermal conductivity has a remarkable temperature rise, and the reliability is deteriorated. For this reason, some heat radiation measures are required.

FIG. 15 shows an example in which a TFT constituting an output portion is divided into semiconductor thin films 1504, 1505, 1506, and 1507 having a small gate width, and a distance between the semiconductor thin films is set to prevent a temperature rise. 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 each semiconductor thin film. Here, it is preferable that the interval between the semiconductor thin films is larger than the long side of the semiconductor thin film because heat can be more effectively radiated. In FIG. 15, the interval X and the interval Y are larger than the long side a (a> b) of the semiconductor thin film.

  FIG. 14 shows the channel formation region in each semiconductor thin film finely separated. Four TFTs having 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 each semiconductor thin film. In each semiconductor thin film, the channel forming region is separated, but the source / drain region is one by one. By subdividing the channel forming region serving as a heat source in this way, it is also possible to suppress a rise in temperature. Here, it is preferable 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 more effective heat dissipation is possible.

FIG. 16 shows an example in which a conductive film 1604 is provided between each semiconductor thin film by a gate electrode 1602 in addition to the embodiment shown in FIG. In order to release 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. The shape is not limited to the shape shown in FIG.
In this way, by devising the shape of the TFT in the output stage, the heat radiation effect can be enhanced, and a circuit with large current consumption can be formed on the display device using the TFT.
This embodiment can be used in combination with the above-described embodiment.

1 is an external view of a display device of the present invention. FIG. 9 is an external view of a conventional display device. FIG. 9 is an external view of a conventional display device. FIG. 2 is an equivalent circuit diagram of the operational amplifier circuit of the present invention. FIG. 2 is an equivalent circuit diagram of the operational amplifier circuit of the present invention. Block diagram of the audio signal processing circuit of the present invention FIG. 3 is a diagram illustrating connection between an analog signal processing circuit of the present invention and a speaker. FIG. 3 is a diagram illustrating connection between an analog signal processing circuit of the present invention and a speaker. FIG. 3 is a diagram illustrating connection between an analog signal processing circuit of the present invention and a speaker. FIG. 2 is a diagram showing an embodiment of the analog signal processing circuit of the present invention. Diagram showing the arrangement of differential circuits Diagram showing the arrangement of differential circuits The figure which shows the output TFT of the operational amplifier circuit The figure which shows the output TFT of the operational amplifier circuit The figure which shows the output TFT of the operational amplifier circuit The figure which shows the output TFT of the operational amplifier circuit Example of flat speaker Diagram showing measurement results of amplifier characteristics Diagram showing measurement results of amplifier characteristics

Claims (29)

In a display device having a thin film semiconductor element on a substrate,
The display device has an electrical signal processing circuit for driving an output device other than the visual,
The display device, wherein the electric signal processing circuit is configured by the thin film semiconductor element. In a display device having a thin film semiconductor element on a substrate,
The display device has an audio signal processing circuit,
The display device, wherein the audio signal processing circuit is configured by the thin film semiconductor element. In a 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 configured by the thin film semiconductor element,
A display device, wherein a speaker is driven by an output signal of the audio signal processing circuit. In claim 2 or claim 3,
The display device, wherein the audio signal processing circuit includes a digital signal processing circuit. In claim 2 or claim 3,
The display device, wherein the audio signal processing circuit includes a D / A conversion circuit. In claim 2 or claim 3,
The display device, wherein the audio signal processing circuit includes an analog signal processing circuit. In claim 6,
The display device, wherein the analog signal processing circuit is configured by an operational amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
A display device, wherein a speaker is driven by an output signal of the analog signal processing circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit,
The first terminal of the speaker is driven by the output signal of the non-inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit,
An input terminal of the non-inverting amplifier circuit and an input terminal of the inverting amplifier circuit are connected,
The first terminal of the speaker is driven by the output signal of the non-inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a non-inverting amplifier circuit and an inverting amplifier circuit,
An output terminal of the non-inverting amplifier circuit is connected to an input terminal of the inverting amplifier circuit,
Driving the first terminal of the speaker by the output signal of the non-inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a first inverting amplifier circuit and a second inverting amplifier circuit,
An output terminal of the first inverting amplifier circuit is connected to an input terminal of the second inverting amplifier circuit,
Driving a first terminal of the speaker by an output signal of the first inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the second inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a preamplifier, a non-inverting amplifier, and an inverting amplifier.
An output signal of the preamplifier circuit is input to the non-inverting amplifier circuit and the inverting amplifier circuit,
The first terminal of the speaker is driven by the output signal of the non-inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a preamplifier, a non-inverting amplifier, and an inverting amplifier.
An output signal of the preamplifier circuit is input to the non-inverting amplifier circuit,
An output signal of the non-inverting amplifier circuit is input to the inverting amplifier circuit,
The first terminal of the speaker is driven by the output signal of the non-inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the inverting amplifier circuit. In a display device having a thin film semiconductor element on a substrate,
The thin film semiconductor device forms an analog signal processing circuit,
The analog signal processing circuit has a preamplifier circuit, a first inverting amplifier circuit, and a second inverting amplifier circuit,
An output signal of the preamplifier circuit is input to the first inverting amplifier circuit,
An output signal of the first inverting amplifier circuit is input to the second inverting amplifier circuit,
A first terminal of a speaker is driven by an output signal of the first inverting amplifier circuit,
A display device, wherein a second terminal of the speaker is driven by an output signal of the second inverting amplifier circuit. In any one of claims 9 to 15,
A display device, wherein the non-inverting amplifier circuit or the inverting amplifier circuit drives a speaker via a buffer circuit. In any one of claims 6 to 16,
The display device, wherein the analog signal processing circuit is driven by a power supply voltage of less than 30V. In any one of claims 3 to 17,
The display device, wherein the speaker is a flat speaker.   19. The display device according to claim 18, wherein the planar speaker uses the display device itself as a vibration medium. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit,
The analog signal processing circuit has a differential circuit, a current mirror circuit, a constant current source, a source grounded amplifier, and a source follower,
The constant current source is electrically connected to a source electrode of a thin film transistor forming the differential circuit,
A first output terminal of the differential circuit is electrically connected to an output terminal of the current mirror circuit and an input terminal of the common source amplifier,
A second output terminal of the differential circuit is electrically connected to an input terminal of the current mirror circuit,
An output terminal of the source grounded amplifier is electrically connected to an input terminal of the source follower,
A display device, wherein an output terminal of the source follower is electrically connected to an output terminal of the analog signal processing circuit. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit,
The analog signal processing circuit has a differential circuit, a first current mirror circuit, a second current mirror circuit, a third current mirror circuit, and a constant current source,
The constant current source is electrically connected to a source electrode of a thin film transistor forming the differential circuit,
A first output terminal of the differential circuit is electrically connected to an input terminal of the first current mirror circuit,
A second output terminal of the differential circuit is electrically connected to an 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,
A display device, wherein an output terminal of the second current mirror circuit is electrically connected to an input terminal of the third current mirror circuit. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit having a differential circuit,
The display device, wherein the differential circuit is configured by a thin film transistor having a multi-gate structure. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit having a differential circuit,
The display device, wherein the differential circuit connects a plurality of thin film transistors in parallel. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit having a differential circuit,
The display device, wherein the differential circuit has a plurality of thin film transistors arranged in a crossing manner. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit,
A display device, wherein the output thin film transistor of the analog signal processing circuit comprises a plurality of semiconductor thin films.   26. The display device according to claim 25, wherein a distance between the plurality of semiconductor thin films is longer than a long side of the semiconductor thin film. In a display device in which a thin film transistor is formed on a substrate,
The thin film transistor constitutes an analog signal processing circuit,
A display device, wherein the output thin film transistor of the analog processing signal circuit is constituted by a semiconductor thin film having a plurality of channel formation regions and one source / drain region. 28. The display device according to claim 27, wherein a distance between the plurality of channel formation regions in the semiconductor thin film is larger than a width of the channel formation region. In a display device having a thin film transistor on a substrate,
The thin film transistor constitutes an analog signal processing circuit,
A display device, wherein a thin film transistor constituting an output stage of the analog signal processing circuit is formed of a plurality of semiconductor thin films, and a conductive film is arranged between the plurality of semiconductor thin films.

Images