JP2002297195A - Voice output system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voice output system which controls a class-D amplifier amplifying a digital signal outputted by a voice reproducing device with a pulse width modulated signal by converting the digital signal not into an analog signal, but directly into the pulse width modulated signal. SOLUTION: The digital signal outputted from a compact disk reproducing device 110 is outputted as latch data from a latch circuit 210. A counter 230 generates a count with clock pulses. A latch signal and the count are inputted to a comparator respective and compared with each other. The comparator outputs a high level when the count is less than the value of the latch signal and outputs a low level when the count exceeds the value of the latch signal. Consequently, the digital signal is converted directly into the pulse width modulated signal without being converted into an analog signal, and then inputted to the class-D amplifier 130.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio output system and, more particularly, to a digital signal output from an audio reproducing apparatus, which is not directly converted into an analog signal but directly converted into a pulse width modulated signal. Controlling a class D amplifier that amplifies the digital signal by the pulse width modulation signal;
It relates to an audio output system.

[0002]

2. Description of the Related Art A class D amplifier controlled by a digital method called a switching operation is disadvantageous to a sound reproducing apparatus in terms of frequency characteristics, crossover distortion, radiation noise, and the like. Have been. But,
Recently, the development of devices to cover these disadvantages, the ability to perform amplification more efficiently than Class B amplifiers, and the lower power consumption and heat generation have led to a focus on in-vehicle audio playback devices. The use of class D amplifiers instead of amplifiers utilizing linear amplification operations such as transistors is increasing.

In a class D amplifier, a switching element is turned on when a pulse of a pulse width modulation signal to be inputted is at a first level to supply maximum power, and is turned off when a pulse is at a second level. And no power is supplied. Therefore, when the ON / OFF of the switching element is repeated at the same interval, an average output of half the maximum power is obtained. If the ON time is longer, the output is larger than the average output, and if shorter, the output is smaller than the average output. As described above, the class D amplifier is an amplifier that amplifies an input signal using a change in an average output obtained by an on / off ratio of a switching element.

[0004] According to the magnitude of the output signal of the audio reproducing apparatus,
In order to control the on / off ratio of the switching of the class D amplifier, the output signal is pulse width modulated (PWM: Pulse).
Width Modulation). This modulation includes a ΔΣ method and the like, and converts a signal into a pulse width modulation signal having a pulse width corresponding to the magnitude of the value. The power output by the switching controlled by the pulse width modulation signal is supplied to a low-pass filter (Low Pass Fi).
, and is demodulated as an analog signal.

As described above, a pulse width modulation signal is obtained by performing pulse width modulation on an analog signal as in the ΔΣ method. On the other hand, at present, audio information processing is generally performed by digital signals. For example, in a compact disc reproducing device,
A digital signal is output. When such a digital signal is amplified by a D-class amplifier and reproduced as audio,
There is a problem that these digital signals must be converted into analog signals, and then the analog signals must be further modulated into pulse width modulation signals.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. A digital signal output from a sound reproducing apparatus is directly converted into a pulse width modulation signal without converting it into an analog signal. An object of the present invention is to propose an audio output system that controls a class D amplifier that amplifies the digital signal using the pulse width modulation signal.

[0007]

According to a first aspect of the present invention, a digital signal output from an audio reproducing apparatus has a pulse having a width corresponding to the value of the digital signal. A pulse width modulation device that converts the pulse width modulation signal into a pulse width modulation signal and outputs the pulse width modulation signal; and a pulse width modulation device that is turned on when the pulse of the pulse width modulation signal is at a first level and is at a second level. And a class D amplifier that amplifies the digital signal by outputting power when the switching element is turned on.

The pulse width modulation device compares a counter counted in accordance with a clock signal with a value of the counter and a value of the digital signal, and when the value of the counter is equal to or smaller than the value of the digital signal, Is high, and a comparator that generates the pulse width modulated signal having the pulse that goes low when the value of the digital signal is exceeded;
May be provided.

As described above, according to the first aspect of the present invention,
A pulse width modulation device converts a digital signal output from the audio playback device into a pulse width modulation signal having a pulse having a width corresponding to the value of the digital signal, and a switching element of a class D amplifier for amplifying the digital signal is provided. Turned on when the pulse of the pulse width modulated signal is at a first level;
And by turning off at the second level and outputting power when the switching element is turned on,
The class D amplifier amplifies the digital signal. Thus, the digital signal output from the audio reproduction device is not directly converted into an analog signal, but is directly converted into a pulse width modulation signal, and a D-class amplifier that amplifies the digital signal with the pulse width modulation signal is controlled. Therefore, a device for digital / analog signal conversion can be omitted, and data loss due to digital / analog signal conversion and analog / pulse width modulation signal conversion can be prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an audio output system 100 to which a pulse width modulation device, which is a conversion device for directly converting a digital signal into a pulse width modulation signal according to the present invention, is applied.

In order to convert the output digital signal of the compact disk reproducing device 110, which is an audio reproducing device, into a pulse width modulated signal by the pulse width modulating device 120, the output of the compact disk reproducing device 110 and the pulse width modulating device 120 are converted. Is connected to the input. The output of the pulse width modulator 120 and the input of the class D amplifier 130 are connected such that the output pulse width modulation signal of the pulse width modulator 120 controls the operation of the switching element of the class D amplifier 130. The output of the D-class amplifier 130 is connected to a speaker 150 via a low-pass filter 140 so that the output power of the D-class amplifier is removed as high-frequency components and output as voice.

FIG. 2 shows details of the pulse width modulation device 120. The input of a latch circuit 210 for latching the value of the output digital signal of the compact disk playback device 110 is
The compact disk player 11 is input so that a digital signal output from the compact disk player 110 and a clock pulse serving as a latch timing are input.
The output of 0 and the clock pulse are connected. The counter 230 counted by an n-times clock (n is an arbitrary integer) of the clock pulse includes a clock pulse multiplied by n through the n-times circuit 240 and the clock pulse for resetting the counter 230. The clock pulse is connected to the n-times circuit 240 having the clock pulse connected to the input so that the pulse is input.

In order to compare the value of the latched digital signal with the count by the n-times clock, a comparison is made so that the output of the latch circuit 210 and the output of the counter 230 are input to the comparison circuit 220. The latch circuit 210 and the counter 230 are connected to the circuit 220. The output of the comparator 220 is connected to the class D amplifier 130 in order to control the class D amplifier by the pulse width modulation signal generated by comparing the latched digital signal value with the count by the n-times clock.

The operation of the pulse width modulator 120 shown in FIGS. 1 and 2 will be described with reference to FIG.

A digital signal output from the compact disk reproducing device 110 is input to the latch circuit 210 shown in FIG. This digital signal is latched by a latch signal generated by a clock pulse and output from the latch circuit 210 as latch data. On the other hand, the counter 230 is reset by a reset signal generated at the same timing as the latch signal by the clock pulse, and generates a count by the clock pulse multiplied by n by the n-times circuit 240. That is, the count is started at the same time when the latch signal is generated.

Each of the latch signal and the count is input to a comparator and compared. The comparator outputs a first level signal, ie, high, when the count is less than or equal to the value of the latch signal, and outputs a second signal when the count exceeds the value of the latch signal.
, Ie, low. This allows
The latch signal, that is, the digital signal is directly converted into a pulse width modulation signal having a pulse having a width corresponding to the value of the digital signal without being converted into an analog signal.

The generated pulse width modulation signal is input to the class D amplifier 130, the switching element of the class D amplifier 130 is turned on when the pulse of the pulse width modulation signal is at the first level, and Turned off when level. The class D amplifier 130 amplifies the digital signal by outputting power when the switching element is turned on.

As described above, the pulse width modulation device converts the digital signal output from the audio reproducing device into a pulse width modulation signal having a pulse having a width corresponding to the value of the digital signal, and amplifies the digital signal. A switching element of a class amplifier is turned on when the pulse of the pulse width modulation signal is at a first level, and is turned off when the pulse is at a second level, and the switching element is turned on when the switching element is turned on. The class D amplifier amplifies the digital signal by outputting power. Thus, the digital signal output from the audio reproduction device is not directly converted into an analog signal, but is directly converted into a pulse width modulation signal, and a D-class amplifier that amplifies the digital signal with the pulse width modulation signal is controlled. Therefore, a device for digital / analog signal conversion can be omitted, and data loss due to digital / analog signal conversion and analog / pulse width modulation signal conversion can be prevented.

In the above-described embodiment, a compact disc reproducing device is used as an audio reproducing device for outputting a digital signal. However, the present invention is not limited to this, and any audio reproducing device having a digital output may be used. . Further, the configuration of the audio output system is not limited to the devices and circuits, and devices and circuits having equivalent functions may be used.

Further, the configuration of the pulse width modulation device is not limited to the configuration of the latch circuit, the counter, and the comparator.
Any configuration that can directly convert a digital signal into a pulse width modulation signal may be used. The first level of the pulse for turning on the switching element of the class D amplifier is set to high, and the second level of the pulse for turning off the switch is set to low. However, the present invention is not limited to this. The level may be low and the second level may be high. further,
Although the class D amplifier outputs power when the switching element is turned on, for example, it may be configured to output power when the switching element is turned off.

[0021]

According to the first aspect of the present invention, the pulse width modulation device converts a digital signal output from the audio reproduction device into a pulse width modulation signal having a pulse having a width corresponding to the value of the digital signal, A switching element of a class D amplifier that amplifies the digital signal is turned on when the pulse of the pulse width modulation signal is at a first level, and is turned off when the pulse of the pulse width modulation signal is at a second level; When turned on, the class D amplifier outputs power to amplify the digital signal. As a result, the digital signal output from the audio playback device is directly converted into a pulse width modulation signal without being converted into an analog signal,
D which amplifies the digital signal by the pulse width modulation signal
Since the class amplifier can be controlled, a device for digital / analog signal conversion can be omitted, and data loss due to digital / analog signal conversion and analog / pulse width modulation signal conversion can be prevented.

[Brief description of the drawings]

FIG. 1 shows a configuration block diagram of the present invention.

FIG. 2 shows a configuration diagram of a pulse width modulation device of the present invention.

FIG. 3 is a time chart showing a processing result of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 audio output system 110 compact disc reproducing device 120 pulse width modulator 130 class D amplifier 220 comparator 230 counter

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D020 AC07 5D045 DA20 5J091 AA02 AA27 AA41 AA66 CA21 CA36 CA92 FA04 FA18 KA17 KA35 KA42 KA62 SA05 TA06 UW02

Claims (2)

[Claims] 1. A pulse width modulation device for converting a digital signal output from an audio reproduction device into a pulse width modulation signal having a pulse having a width corresponding to the value of the digital signal, and outputting the pulse width modulation signal. A switching element that is turned on when the pulse of the pulse width modulation signal is at a first level, and is turned off when the pulse is at a second level, and when the switching element is turned on, An audio output system comprising: a class D amplifier that amplifies the digital signal by outputting power. 2. The pulse width modulation device, comprising: a counter that is counted according to a clock signal; and comparing a value of the counter with a value of the digital signal.
The pulse width modulation signal having the pulse, which has a first level when the value of the counter is equal to or less than the value of the digital signal, and has a second level when the value of the counter exceeds the value of the digital signal; The audio output system according to claim 1, further comprising: a comparator that generates: