JP2011101183A - Sound output device and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce unwanted radiation that is generated by a sampling clock when amplifying sound data on the basis of PWM modulation. <P>SOLUTION: This sound output device for amplifying sound data and for output of the sound data as sound includes: a PWM modulating unit for modulating and amplifying the sound data on the basis of a sampling clock; a sampling clock generation unit for generating the sampling clock and varying the frequency of the sampling clock in accordance with a ground state of an external terminal; a control signal generation unit for generating a rectangular wave for controlling the sound output device; and a switching circuit connected between the external terminal and the control signal generation unit to switch the ground state in accordance with a waveform change in the rectangular wave. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an audio output device that outputs audio, and more particularly to an audio output device that amplifies audio data based on PWM modulation, and a display device.

  Conventionally, an audio output device that amplifies audio data with an amplifier and outputs the amplified audio data is known. The audio output device amplifies audio data using a class D amplifier. Here, the class D amplifier compares the internally generated sampling clock with the input audio data, and amplifies the audio data according to the comparison result.

  The class D amplifier outputs the comparison result as a PWM signal, and performs amplification by doubling the amplitude of the PWM signal. In addition, a triangular wave is mainly used as a sampling clock used in the class D amplifier, and the higher the sampling clock frequency, the higher the sampling interval, and it is possible to optimally amplify input audio data (for example, (See Patent Documents 1-4).

JP 2007-074442 A JP-A-2005-204217 JP 2005-136717 A JP-A-2005-051303

  As described above, the class D amplifier uses a sampling clock to perform PWM modulation, but when the frequency of the sampling clock is high, unnecessary radiation generated by this sampling clock becomes a problem.

  The present invention has been made in view of the above problems, and provides an audio output device or a display device capable of reducing unnecessary radiation generated by a sampling clock when audio data is amplified based on PWM modulation. To do.

  In order to solve the above problems, in the present invention, in an audio output device that amplifies audio data and outputs it as audio, a PWM modulator for modulating and amplifying the audio data based on a sampling clock; A sampling clock generating unit that generates a sampling clock and varies a frequency of the sampling clock according to a ground state of an external terminal; a control signal generating unit that generates a rectangular wave for controlling the audio output device; A switching circuit is connected between the external terminal and the control signal generator, and switches the ground state in accordance with a change in the waveform of the rectangular wave.

  In the invention configured as described above, the switching circuit is connected between the external terminal for changing the frequency of the sampling clock generated by the sampling clock generation unit and the control signal generation unit that outputs a rectangular wave. In response to the change in the waveform of the rectangular wave, the ground state of the external terminal is switched. Therefore, since the frequency of the sampling clock is changed according to the on / off state of the rectangular wave, the peak of a specific high frequency band fluctuates, and as a result, unnecessary radiation can be reduced.

Various configurations of the switching circuit can be assumed. As an example, the switching circuit connects the external terminal and the ground between the collector / emitter, and connects the control signal generator and the base. It is good also as a structure provided with the switch element connected by.
In the invention configured as described above, since the switching circuit is configured using the switch elements, the present invention can be realized with a simple configuration.

As an example of the sampling clock, the sampling clock may be a triangular wave.
In the invention configured as described above, the present invention can be applied to a PWM modulation unit using a triangular wave as a sampling clock.

Further, the PWM modulator and the sampling clock generator may be mounted on a one-chip IC.
In the invention configured as described above, the configuration of the amplifying unit can be made compact.

  As another example of the present invention, in a display device including an audio output unit that amplifies audio data and outputs it as audio, and a video output unit that outputs video based on the video data, based on a triangular wave A PWM modulator for modulating and amplifying the audio data, a sampling clock generator for generating the triangular wave and varying the frequency of the triangular wave according to the ground state of the external terminal, and the audio output device A control signal generating unit for generating a rectangular wave to connect, a collector / emitter connected between the external terminal and the ground, and a switch element connected to the control signal generating unit at a base, the pulse wave And a switching circuit for switching the ground state in accordance with the waveform change.

As described above, according to the present invention, it is possible to reduce unnecessary radiation generated by a sampling clock when amplifying audio data based on PWM modulation.
According to the invention of claim 2, the present invention can be realized with a simple configuration.
According to the third aspect of the present invention, the present invention can also be applied to a PWM modulation unit using a triangular wave as a sampling clock.
Furthermore, according to the invention concerning Claim 4, it becomes possible to make the structure of an amplification part compact.

3 is a block configuration diagram for explaining a configuration of a display device 100. FIG. FIG. 4 is a diagram for explaining a configuration of a sound amplifying unit 60. It is a wave form diagram for demonstrating the relationship between a sampling clock, input audio | voice data, and a PWM signal. It is a wave form diagram showing a waveform when class D amplifier 61 is measured with a spectrum analyzer. It is a figure for demonstrating the time change in a high frequency band.

Embodiments of the present invention will be described below in the following order with reference to the drawings.
(1) First embodiment:
(2) Other embodiments:

(1) First embodiment:
Hereinafter, a first embodiment in which an audio output device according to the present invention is embodied will be described with reference to the drawings. In the first embodiment, the description will be made based on a display device having the function of an audio output device, but the audio output device is not limited to a display device as long as audio data is amplified and output. .

  FIG. 1 is a block configuration diagram for explaining the configuration of the display device 100. The main part of the display apparatus 100 is shown below. Reference numeral 90 denotes a front end unit that demodulates broadcast signals received by various antennas (not shown). Reference numeral 80 denotes a back-end unit which performs descrambling of demodulated data and decoding processing of compressed video / audio data. Reference numeral 70 denotes a display, which displays a video based on the decoded video data. Reference numeral 60 denotes an audio amplifying unit that amplifies the decoded audio data. Reference numeral 50 denotes a speaker, which outputs amplified sound. Reference numeral 30 denotes a main controller that controls driving of the display device 100.

  When various antennas receive a carrier wave, the front end unit 90 modulates and extracts a broadcast signal superimposed on the carrier wave. The front end unit 90 includes a switching circuit that operates in response to a channel selection signal from the remote control device, and outputs a broadcast signal corresponding to a desired channel to the back end unit 80 by the switching circuit.

  The back-end unit 80 includes a demultiplexing unit that de-scrambles the data demodulated by the front-end unit 90 and decodes video / audio data compressed by the MPEG method. Further, the back end unit 80 includes a video signal processing unit that performs signal processing on the decoded video data.

  The display 70 displays a video based on the video data decoded by the back end unit 80. In the present embodiment, the display 70 is a liquid crystal display, and outputs light from a backlight (not shown).

  The main controller (control signal generator) 30 includes a CPU, a ROM, and a RAM, and controls the driving of the display device 100 by various programs stored in the ROM. The main controller 30 also supplies the display 70 with a rectangular BL-ADJ signal for dimming control of the backlight constituting the display device 100 and a rectangular VCOM-PWM signal that is a common voltage signal.

With the above configuration, the display device 100 demodulates and decodes video data and audio data from a broadcast signal received by an antenna (not shown), outputs video on the display 70, and outputs audio on the speaker 50.
The audio amplifying unit 60 internally generates a sampling clock and amplifies input audio data based on the sampling clock. However, since the frequency of the sampling clock is high, unnecessary radiation becomes a problem. Therefore, in the present embodiment, the audio amplifying unit 60 has a configuration that reduces unnecessary radiation by changing the frequency of the sampling clock.

FIG. 2 is a diagram for explaining the configuration of the audio amplifying unit 60. FIG. 3 is a waveform diagram for explaining the relationship among a sampling clock, input audio data, and a PWM signal.
The audio amplifying unit 60 includes a class D amplifier 61 that amplifies the audio data decoded by the back-end unit 80, and a switching circuit 62 that changes the frequency of the sampling clock that is internally generated by the class D amplifier 61. Has been. Here, the class D amplifier 61 is a one-chip IC, and is connected to the back-end unit 80 via the input terminal 61a, and is connected to the speaker 50 via the output terminals 61b, 61c, 61d, and 61e. The class D amplifier 61 is connected to the switching circuit 62 through a frequency adjustment terminal 61f. Further, the class D amplifier 61 is connected to the external clock 63 by a clock terminal 61g, and generates a sampling clock from a clock signal of a predetermined cycle supplied from the external clock 63.

  The class D amplifier 61 includes a PWM signal generation unit 40, drivers 41 and 42, class D output stages 43 and 44, and a triangular wave generation unit 45 therein. With the above configuration, when audio data is supplied to the class D amplifier 61 through the input terminal 61a, the PWM signal generator 40 compares the input audio data with the sampling clock supplied from the triangular wave generator 45, and based on the audio data. PWM signal is generated (FIG. 3). The drivers 41 and 42 amplify the PWM signal by switching the class D output stages 43 and 44 based on the generated PWM signal. Thereafter, the amplified PWM signal is output from the output terminals 61b, 61c, 61d, and 61e, converted into an analog signal by a filter circuit (not shown) of the speaker 50, and then output as sound. The PWM signal generator 40, the drivers 41 and 42, and the class D output stages 43 and 44 constitute the PWM modulator of the present invention.

  The class D amplifier according to the present embodiment is configured as a full bridge type including class D output stages 43 and 44 including two or more switch elements, but is not limited thereto. That is, the class D amplifier 61 may be a half bridge type. Further, the class D amplifier 61 can be made compact by making the class D amplifier 61 into one chip.

  Further, the switching circuit 62 includes a switching element 62a that is collector-connected via the frequency adjusting terminal 61f and the resistor R1, and whose emitter is grounded. The base of the switching element 62a is connected to the main controller 30 via the resistor R2. In the present embodiment, the base of the switching element 62a is connected in parallel to the output line from which the main controller 30 outputs the BL-ADJ signal, and the switching element 62a when the rectangular-wave BL-ADJ signal is at a high level. A base current is supplied to the base of 62a.

  The triangular wave generator (sampling clock generator) 45 of the class D amplifier 61 has a function that can change the frequency of the sampling clock in accordance with the resistance value connected to the frequency adjustment terminal 61f. For example, when the frequency adjustment terminal 61f is in an open state, the frequency of the sampling clock to be generated is around 283 Hz. On the other hand, when the frequency adjustment terminal 61f is grounded, the frequency of the sampling clock to be generated is around 370 Hz. Therefore, in this embodiment, by inputting a rectangular wave BL-ADJ signal to the base of the switching element 62a, the switching element 62a is switched on / off at a predetermined cycle, and the connection state of the frequency adjustment terminal 61f is set at a predetermined interval. Switch to ground or open. As a result, the frequency of the sampling clock does not become a constant value and changes, for example, from 283 Hz to 370 Hz.

  FIG. 4 is a waveform diagram showing waveforms when the class D amplifier 61 is measured with a spectrum analyzer. FIG. 5 is a diagram for explaining a time change in the high frequency band. As shown in FIG. 4, the radiation from the class D amplifier 61 has a peak in the high frequency band near 103 Hz. That is, the D-class amplifier 61 becomes unnecessary radiation in this high frequency band. On the other hand, when the time change of the high frequency band is observed in the class D amplifier according to the present embodiment, the frequency of the sampling clock fluctuates within a predetermined width, so that the high frequency peak fluctuates up and down with time (FIG. 5). Therefore, when the high-frequency peak value is averaged, the average value is lower than the conventional high-frequency peak value. As a result, unnecessary radiation having a specific high frequency is reduced and unnecessary radiation is reduced.

  As described above, according to the present embodiment, unnecessary radiation from the sound amplifying unit 60 can be reduced by the simple configuration using the switching element 62a and the rectangular wave conventionally provided in the display device 100.

(2) Other embodiments:
There are various modifications of the present invention. For example, a product in which an audio output device is realized is not limited to a display device. That is, any product may be used as long as the product has the function of the audio output device according to the present invention.

  In addition, the use of a triangular wave as the sampling clock is an example, and other waveforms may be used as the sampling clock.

  Furthermore, the signal supplied to the switching circuit is not limited to the BL-ADJ signal, and may be any signal other than the VCOM-PWM signal described above as long as it is a rectangular wave.

Needless to say, the present invention is not limited to the above embodiments. It goes without saying for those skilled in the art,
・ Applying mutually interchangeable members and configurations disclosed in the above embodiments by appropriately changing the combination thereof.− Although not disclosed in the above embodiments, it is a publicly known technique and the above embodiments. The members and configurations that can be mutually replaced with the members and configurations disclosed in the above are appropriately replaced, and the combination is changed and applied. It is an embodiment of the present invention that a person skilled in the art can appropriately replace the members and configurations that can be assumed as substitutes for the members and configurations disclosed in the above-described embodiments, and change the combinations and apply them. It is disclosed as.

  DESCRIPTION OF SYMBOLS 30 ... Main controller, 40 ... PWM signal generation part, 41, 42 ... Driver, 43, 44 ... Class D output stage, 45 ... Triangular wave generation part, 50 ... Speaker, 60 ... Sound amplification part, 61 ... Class D amplifier, 61a ... Input terminal 61b, 61c, 61d, 61e ... Output terminal, 61f ... Frequency adjustment terminal, 61g ... Clock terminal, 62 ... Switching circuit, 62a ... Switching element, 63 ... External clock, 70 ... Display, 80 ... Back end unit , 90 ... Front end part, 100 ... Display device

Claims (5)

In an audio output device that amplifies audio data and outputs it as audio,
A PWM modulator for modulating and amplifying the audio data based on a sampling clock;
A sampling clock generator for generating the sampling clock and varying the frequency of the sampling clock according to the ground state of the external terminal;
A control signal generator for generating a rectangular wave for controlling the audio output device;
An audio output device comprising: a switching circuit that is connected between the external terminal and the control signal generator and switches the ground state in accordance with a change in the waveform of the rectangular wave.   2. The audio output according to claim 1, wherein the switching circuit includes a switch element that connects the external terminal and the ground between a collector and an emitter, and connects the control signal generator with a base. 3. apparatus.   The audio output device according to claim 1, wherein the sampling clock is a triangular wave.   The audio output device according to any one of claims 1 to 3, wherein the PWM modulation unit and the sampling clock generation unit are mounted on a one-chip IC. In a display device comprising: an audio output unit that amplifies audio data and outputs it as audio; and a video output unit that outputs video based on the video data.
A PWM modulator for modulating and amplifying the audio data based on a triangular wave;
A sampling clock generator that generates the triangular wave and varies the frequency of the triangular wave according to the ground state of the external terminal;
A control signal generator for generating a rectangular wave for controlling the audio output device;
A switching circuit that connects a collector / emitter between the external terminal and the ground and includes a switch element that is connected to the control signal generator at the base, and switches the ground state in accordance with a change in the waveform of the pulse wave. And a display device.

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