KR101725021B1 - single power supply stereo headphone driving method using PWM - Google Patents

Abstract

The present invention relates to a method for driving a single-powered stereo headphone using a pulse wave modulation (PWM), and more specifically, to a method, in a stereo headphone which reproduces left (L) and right (R) audio information, comprising the following steps: supplying a PWM signal having a pulse width proportional to the amplitude of an L-R signal to a left channel signal terminal of a headphone; supplying a PWM signal having a pulse width proportional to the amplitude of an R-L signal to a right channel signal terminal of the headphone; and supplying a PWM signal having a pulse width proportional to the amplitude of a -(L+R) signal to a common signal terminal of the headphone, to operate the headphone. According to the present invention, a difference component (2L) between a left channel audio PWM and a common signal channel PWM is transferred to a left headphone and a difference component (2R) between a right channel audio PWM, and the common signal channel PWM is transferred to the right headphone. Since voltage offset between a signal channel and a common channel can be fundamentally prevented when such manner is used, a sophisticated intermediate voltage generation device for the common signal channel is not additionally required and a serial coupling condenser to a signal line is not separately required as well.

Description

Single-supply stereo headphone driving with PWM signal. {single power supply stereo headphone driving method using PWM}

The present invention relates to a headphone driving method using a PWM (Pulse Width Modulation) signal, which is a digital signal having only two levels of a supply voltage and a ground voltage.

A speaker driving method using a PWM (Pulse Width Modulation) signal, which is a digital signal, has recently been widely used because of its superior power efficiency over a conventional speaker driving method using an analog signal. Generally, two PWM signals are combined to drive one speaker. Therefore, in the case of a stereo speaker configuration having two channels, a total of four PWM signals are used. However, stereo headphones should be driven with only three signals: the left signal, the right signal, and the common signal. Therefore, it is not possible to use four PWM driving methods such as stereo speakers for headphones. In a single power supply system using only one supply voltage, conventional PWM headphone drivers have difficulties in providing a half voltage of the supply voltage precisely to supply to the common channel of the headphone. If a half voltage of the supply voltage is not precisely generated and supplied to the common channel, there is a DC offset in the audio signal, so pop noise occurs on and off, and power efficiency due to leakage current during operation Can also bring about degradation. Coupling capacitors can also be used in series with the audio signal lines of the headphones to avoid these side effects when the common channel voltage is not exactly one-half the supply voltage. The need for a precise common-signal channel voltage generator and the need for series coupling capacitors are key factors that make the design of PWM headphone drivers difficult.

Stereo headphones receive a total of three signals and output stereo audio. The conventional analog headphone driver transmits three signals to the headphone: a left analog audio signal, a right analog audio signal, and a common signal that maintains a fixed center voltage. The voltage of the common signal channel is the middle voltage of the audio signal range of the left and right channels. When the conventional headphone driving circuits are made of a single power source using only one supply voltage VDD, the audio signals of the left and right channels have a minimum ground level of 0 V and a maximum value of the supply voltage VDD level. Therefore, since the common signal channel should be the middle voltage of the audio signal range, one half of the supply voltage VDD must be output. Therefore, in a single power supply system using only one supply voltage (VDD), a voltage divider or the like must be built in to generate a voltage of 1/2 level of the supply voltage (VDD) accurately and output it to the common signal channel. Since the voltage of the common signal channel becomes the reference voltage of the audio output, if a voltage error occurs in the common signal channel, a voltage offset occurs in the audio signal. The voltage offset of the signal channel can cause a drop in efficiency due to a pop noise during on and off or leakage current during audio reproduction. To avoid this voltage offset, it is necessary to generate a voltage that is very accurate and low fluctuating supply voltage (VDD) 1/2 level. The embedding of such a sophisticated voltage divider increases the system cost. If it is not possible to precisely generate a half of the supply voltage (VDD), the series coupling capacitors must be placed on the left and right signal lines to prevent voltage offset. However, in the case of a single-power headphone amplifier using a series coupling capacitor, a series coupling capacitor is charged and discharged at the time of power-on / off, and a shock wave may be generated and pop noise may be generated. The use of series coupling capacitors also increases the cost of the system. Even when a stereo headphone is driven by a PWM signal of a single power supply, the problem of generating the intermediate voltage of the common channel described above is still present. An analog signal using a range from a 0V ground level to a supply voltage (VDD) level can be replaced by a PWM signal having two levels of a 0V ground level and a supply voltage (VDD) level. However, since the voltage of the common signal channel must also be exactly 1/2 of the supply voltage (VDD) in this case, a sophisticated intermediate voltage generator must be built in. The error of the intermediate voltage causes a drop in efficiency due to the pop noise at the time of turning on and off and the leakage current during the audio reproduction even in the PWM type headphone amplifier. Therefore, a reference signal having a half level of the supply voltage (VDD) There is a problem to give.

In order to implement a headphone amplifier driven by a single power source, in the present invention, all three terminals of the headphone are driven by using three PWM signals having two voltage levels of a 0V ground level and a supply voltage (VDD). The first PWM signal is made to have a pulse width proportional to a signal (L-R) obtained by subtracting the right channel audio signal (R) from the left channel audio (L). The second PWM signal is made to have a pulse width proportional to the signal (R-L) obtained by subtracting the left channel audio (L) from the right channel audio (R). The third PWM signal is commonly used for both channels and is made to have a pulse width that is inversely proportional to the signal (L + R) plus the audio of both channels. The difference component 2L between the PWM signal (L-R) of the left channel and the PWM signal (-L-R) of the common channel is outputted through the left headphone. The difference component 2R between the PWM signal R-L of the right channel and the PWM signal -L-R of the common channel is outputted through the right speaker or the headphone. This method eliminates the need to add a separate intermediate voltage generating circuit to generate the common channel signal. A PWM signal having a duty ratio of 50% is output to both the left and right audio signal channels and the common signal channel in the absence of the power on / off state or the audio signal absence state, so that there is no difference component between the audio signal channel and the common signal channel, Since the output is in the '0' state, it is possible to avoid the pop noise or the leakage current.

The present invention not only transmits an audio signal in the form of a PWM signal using only two states of a 0V ground level and a supply voltage (VDD) level, but also an intermediate voltage required for a common signal terminal of a headphone is also 0V ground level and a supply voltage VDD. Level PWM signal using only two states. Therefore, there is no need to additionally provide a sophisticated voltage generating circuit for generating a half of the supply voltage (VDD) for the common signal terminal. Since only a PWM signal, which is a kind of digital signal, is used, it is possible to implement a headphone driving circuit by using a general digital I / O pin operated by a single power supply or a digital buffer. Since all three outputs can be implemented with only digital I / O or digital buffers, it is possible to embed and embed a headphone driver in an IC using only a digital circuit. Since a PWM signal having a 50% duty ratio (duty ratio) is output for both the left channel signal, the right channel signal and the common channel signal while the power is turned on and off or the audio signal is held at '0' The energy of the component becomes '0' and the same effect as that of the audio signal versus the voltage reference of the common reference signal is '0'. That is, the drop in efficiency due to the pop noise or the leakage current, which occurs when the voltage offset of the audio signal to the common reference signal exists, can be fundamentally avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically shows the entire configuration of a headphone driving system according to the present invention; FIG.
FIG. 2 illustrates each PWM waveform and a left headphone output waveform produced using a simple audio signal having only five steps in order to explain the principle of the present invention. FIG.
FIG. 3 is a diagram showing each PWM waveform and a left headphone output waveform generated when a phase difference is given to a PWM of a common channel and a PWM of an audio channel using a simple audio signal having only five steps in order to explain the principle of the present invention.
DESCRIPTION OF THE EMBODIMENTS
110: An adder that creates an L + R signal to be used for the common signal channel of the headphones.
130: A subtractor that produces an LR signal to be used for the headphone left channel.
140: Reversal that inverts the L + R signal to create an - (L + R) signal to be used for the common signal channel of the headphones.
150: A subtractor that produces an RL signal to be used on the right channel of the headphone.
190: A digital buffer that amplifies the current so that the left channel PWM signal can drive the headphones.
200: A digital buffer that amplifies the current so that a common channel PWM signal can drive the headphones.
210: A digital buffer that amplifies the current so that the right channel PWM signal can drive the headphones.
S100: Left channel output PWM signal.
S200: Right channel output PWM signal.
S300: Common channel output PWM signal.

The present invention is a method of driving a stereo headphone using a single power supply using three PWM signals. The PWM signal is a digital signal having two states of '0' and '1'. The PWM signal is a signal in which pulses having the same magnitude as the supply voltage (VDD) have a constant periodicity and are continuous. The width of each PWM pulse S120 may be varied each time. As the audio information S110 to be transmitted in the PWM signal has a large value, the pulse width S120 increases in proportion to the audio size. As the audio information S110 to be transmitted becomes smaller, the pulse width S120 becomes larger It becomes smaller proportionally. In the present invention, three PWM signals are used to transmit stereo audio information composed of left channel (L) audio data (100) and right channel (R) audio data to a stereo headphone. The first PWM signal S100 is a PWM signal having a pulse width proportional to the L-R signal, and the second PWM signal S200 is a PWM signal having a pulse width proportional to the R-L signal. The third PWM signal 300 is a PWM signal commonly used for both channels and having a pulse width proportional to the - (L + R) signal. The difference component 2L between the PWM signal S100 of the left channel containing the L-R component and the PWM signal S300 of the common channel containing the - (L + R) component is outputted through the left headphone 220. The difference component 2R between the PWM signal S200 of the right channel containing the R-L component and the PWM signal S300 of the common channel containing the - (L + R) component is outputted through the right headphone 230. The PWM signal S120 of the left channel and the PWM signal S321 of the common channel may have an artificial phase difference to improve audio characteristics. The PWM signal of the right channel and the PWM signal S321 of the common channel may have an artificial phase difference in order to improve audio characteristics. The left channel PWM generator 160 may employ oversampling and delta sigma modulation techniques to improve signal resolution. The common channel PWM generator 170 may be applied with oversampling and delta sigma modulation techniques to improve signal resolution. The right channel PWM generator 180 may be applied with oversampling and delta sigma modulation techniques to improve signal resolution.

110: An adder that creates an L + R signal to be used for the common signal channel of the headphones.
130: A subtractor that produces an LR signal to be used for the headphone left channel.
140: Reversal that inverts the L + R signal to create an - (L + R) signal to be used for the common signal channel of the headphones.
150: A subtractor that produces an RL signal to be used on the right channel of the headphone.
190: A digital buffer that amplifies the current so that the left channel PWM signal can drive the headphones.
200: A digital buffer that amplifies the current so that a common channel PWM signal can drive the headphones.
210: A digital buffer that amplifies the current so that the right channel PWM signal can drive the headphones.
S100: Left channel output PWM signal.
S200: Right channel output PWM signal.
S300: Common channel output PWM signal.

Claims (4)

A stereo headphone driving method for reproducing left audio information (L) and right audio information (R), comprising the steps of: supplying a left channel signal terminal of a headphone with a PWM signal having a pulse width proportional to the size of the LR signal; A PWM signal having a pulse width proportional to the magnitude of the RL signal is supplied to the channel signal terminal and a PWM signal having a pulse width proportional to the magnitude of the - (L + R) signal is supplied to the common signal terminal of the headphone Wherein the stereo headphone is a stereo headphone.
The method according to claim 1, wherein the three PWM signals supplied to the stereo headphones are respectively amplified by a digital buffer, and then transmitted to the headphones.
The method according to claim 1, wherein the PWM is generated so that there is an artificial phase difference between the PWM signals transmitted to the stereo headphones.
The method as claimed in claim 1, wherein a PWM signal proportional to an audio signal whose resolution is increased by oversampling and delta sigma modulation is generated at each signal terminal of the stereo headphone and transmitted to a headphone.

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