KR100626987B1 - A headphone driver and the method for driving the driver - Google Patents

Abstract

The present invention discloses a headphone driver and a headphone driver driving method that do not use an inductor or a capacitor. The headphone driver is composed of only three drivers, and by equalizing the duty cycle of the signals applied to the input terminal of each driver, the headphone driver functions to drive the headphones without using an inductor or a capacitor. In the headphone driver driving method, a headphone driver is driven using two modulation signals obtained by performing pulse width modulation on a modulation reference signal and a reproduction signal, and the duty cycles of the two modulation signals and the modulation reference signal are the same. The phases of the two modulation signals and the modulation reference signal do not coincide with each other to suppress noise that may occur during operation of the headphone driver.

3-terminal stereo headphones, pulse width modulation, phase difference, pop noise

Description

A headphone driver and the method for driving the driver}

1 is an embodiment of a headphone driver using a single power source applied to a conventional three-terminal stereo headphones.

2 is an embodiment of a headphone driver that additionally uses a half power applied to conventional three-terminal stereo headphones.

FIG. 3 is an internal circuit diagram of the LC filter shown in FIG. 1.

4 is an internal circuit diagram of the RC filter shown in FIG. 1.

FIG. 5 is an internal circuit diagram of the LC filter shown in FIG. 2.

6 is a circuit diagram of a headphone driver according to the present invention.

FIG. 7 is a waveform diagram of internal nodes of FIG. 1 when a stereo input signal is silent and a square wave signal having a 50% duty is applied to two modulation signals.

FIG. 8 is a waveform diagram of internal nodes of a headphone driver according to the present invention shown in FIG. 6 when no sound source is reproduced.

9 is a waveform diagram of internal nodes of a headphone driver according to the present invention shown in FIG. 6 when there is a sound source to be reproduced.

FIG. 10 is a waveform diagram of the internal nodes of FIG. 6 when two modulated signals PWM1 and PWM2 having a constant phase difference compared to the waveform of the reference signal PWM_REF are input.

The present invention relates to a three-terminal headphone driver, and more particularly, to a headphone driver and a method of driving a headphone driver that do not use an inductor or a capacitor and do not generate pop noise. .

Since sound is more abundant when played in stereo than when playing a sound source in mono, it is common to play a music signal in stereo form using two playback devices when playing music signals with headphones. . The signal to be reproduced is converted into various modulation methods, for example, PWM (Pulse Width Modulation), which modulates the width of the reproduction signal, and then switched and amplified and output.

In order to amplify and reproduce a stereo sound source using a PWM method, first, a stereo input signal is modulated to generate two different pulse width modulated signals. After amplifying the two generated modulation signals, removing the high frequency noise included in the amplified signal, and performing a DC coupling (Direct Current Coupling) to generate a stereo signal. Stereo signals generated through the above process can be directly reproduced through a speaker, headphones or earphones.

1 is an embodiment of a headphone driver using a single power source applied to a conventional three-terminal stereo headphones.

Referring to FIG. 1, the headphone driver 100 includes drivers 101 and 111, LC filters 102 and 112, and RC filters 103 and 113.

The drivers 101 and 111 amplify each of the two modulation signals PWM1 and PWM2 which are pulse-width modulated with each sound source (not shown) to be reproduced. The drivers 101 and 111 generally use an inverter having a high driving capability. The LC filters 102 and 112 remove high frequency noise included in each of the amplified modulation signals PWM1 and PWM2. The RC filters 103 and 113 remove direct current (DC) components included in the modulated signals PWM1 and PWM2 from which high frequency noise is removed.

In general, a pulse width modulated square wave signal has harmonics components corresponding to multiples of the frequency of the modulated signal. In terms of signal processing, these high frequency components act as noise. Therefore, the modulated square wave signal should be removed with a high frequency noise using a low pass filter or a band pass filter, and an RC filter implemented using a resistor (R) and a capacitor (C). An LC filter implemented using an inductor (L) and a capacitor (C) performs this function.

In summary, the headphone driver 100 amplifies two modulation signals PWM1 and PWM2, and then transmits a signal obtained by removing high frequency noise and DC components to the stereo headphone jack 120. At this time, the three-terminal stereo headphone jack 120 is provided with a reference voltage GND in addition to the two modulated signals PWM1 and PWM2.

3 is an internal circuit diagram of the LC filter 102, 112 shown in FIG.

4 is an internal circuit diagram of the RC filters 103 and 113 shown in FIG.

The configuration and operation of the filter illustrated in FIGS. 3 and 4 are circuits generally known to a circuit designer, and thus description thereof will be omitted.

FIG. 7 is a waveform diagram of internal nodes of FIG. 1 when a stereo input signal is silent and a square wave signal having 50% duty is applied to two modulation signals.

Referring to FIGS. 7 and 1, the first modulated signal PWM1 is amplified while passing through the first driver 101 (N1). The amplified signal is removed with high frequency noise while passing through the first LC filter 102 (N2), and then DC voltage is removed by the first RC filter 103 (N3). The second modulated signal PWM2 is amplified while passing through the second driver 111 (N4). The amplified signal is removed with high frequency noise while passing through the second LC filter 112 (N5), and then the DC voltage is removed by the second RC filter 113 (N6).

2 is an embodiment of a headphone driver that additionally uses a half power applied to conventional three-terminal stereo headphones.

Referring to FIG. 2, the headphone driver 200 includes drivers 201 and 211 and LC filters 202 and 212.

The headphone driver 100 using only a single power supply VDD shown in FIG. 1 and the headphone driver 200 additionally using a half power supply VDD / 2 shown in FIG. 2 have two differences. The headphone driver 100 using only a single power supply shown in FIG. 1 uses two LC filters 102 and 112 and two RC filters 103 and 113 connected in series, and a reference power supply to the headphone jack 120. GND). On the other hand, the headphone driver 200 additionally using the half power shown in FIG. 2 uses two LC filters 202 and 212 and no RC filter, and the headphone driver 200 is a three-terminal stereo. A bias voltage having a half voltage level VDD / 2 of a power supply voltage is supplied to the headphone jack 220. Since the bias voltage having the half voltage level is supplied to the three-terminal stereo headphone jack 220, since the stereo signal output from the two LC filters 202 and 212 and the DC voltage level of the bias voltage are the same, DC coupling An RC filter to perform the need not be additionally used.

FIG. 5 is an internal circuit diagram of the LC filters 202 and 212 shown in FIG.

Since the configuration and operation of the filter illustrated in FIG. 5 are circuits generally known to a circuit designer, a description thereof will be omitted.

The headphone driver 100 shown in FIG. 1 should use two filters (LC filter and RC filter). Coils used in LC filters 102 and 112 have the disadvantage of being expensive and bulky. In addition, in the case of three-terminal stereo headphones having an impedance of 32 Ω (Ohm), the RC filters 103 and 113 must be configured using a capacitor C having a capacitance of about 220 μF (Micro Farad). . The use of coils or capacitors in mobile devices has significant disadvantages in terms of cost and volume.

In order to improve this, the headphone driver 200 which does not include an RC filter has also been proposed, but a new disadvantage arises in that a circuit for generating a half power supply must be added. In addition, an analog amplifier is generally used in a circuit added to generate a half power supply. The use of the analog amplifier not only reduces the efficiency of the headphone driver but also causes pop noise at startup due to the offset voltage and nonlinearity of the analog amplifier. May occur.

The technical problem to be achieved by the present invention is to provide a headphone driver (Headphone Driver) that does not use an inductor (Capacitor).

Another object of the present invention is to provide a headphone driver driving method in which pop noise does not occur when the headphone driver operates.

According to an aspect of the present invention, a headphone driver includes three drivers, and duty cycles of signals input to each driver are the same.

In addition, according to another aspect of the present invention, a headphone driver driving method includes driving two modulation signals obtained by performing pulse width modulation on a modulation reference signal and a reproduction signal, and the two modulation signals and the modulation reference signal. The duty cycle of is the same and the phase of the two modulation signals and the modulation reference signal is characterized in that they do not coincide with each other.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings.

6 is a circuit diagram of a headphone driver according to an embodiment of the present invention.

Referring to FIG. 6, the headphone driver 600 includes three drivers 601 to 603. The configuration of the headphone driver 600 according to the present invention is simpler than that of the conventional headphone drivers 100 and 200 illustrated in FIGS. 1 and 2, and the three-terminal stereo headphone jack 620 of the headphone driver 600 is illustrated. This is the result of supplying the pulse width modulation reference signal PWM_REF.

That is, according to the present invention, a square wave signal having the same period and phase as the pulse width modulation reference signals PWM_REF and the 50% duty with the two pulse width modulation signals PWM1 and PWM2 is used according to the present invention. The key idea of the headphone driver.

FIG. 8 is a waveform diagram of internal nodes of the headphone driver according to the present invention shown in FIG. 6 when no sound source is reproduced.

Referring to FIG. 8, the period and phase of a stereo signal, that is, two modulation signals PWM1 and PWM2 and a pulse width modulation reference signal PWM_REF are the same. The waveforms N61 to N63 of the signals amplified by the three signals using the drivers 601 to 603 are amplified to the same amplitude, but have the same period and phase. At this time, in order to accurately implement the technical idea of the present invention, the magnitude of the signal output from each driver should be the same regardless of the magnitude of the three signals PWM1, PWM2, and PWM_REF.

Since the two amplified modulation signals PWM1 and PWM2 and the modulation reference signal PWM_REF have the same magnitude and phase, the difference signals N61-N63 and N62-N63 between these two signals are zero. Becomes Since these waveforms are the same, there is no potential difference in AC and DC, and therefore, both the LC filter for removing high frequency noise and the RC filter for removing DC components, which have been inevitably used in the past, are not necessary at the same time.

9 is a waveform diagram of internal nodes of a headphone driver according to the present invention shown in FIG. 6 when there is a sound source to be reproduced.

Referring to FIG. 9, when two modulation signals PWM1 and PWM2 having a sound source to be reproduced and having different pulse widths are input to the sound source, the two modulation signals PWM1 and PWM2 of which the pulse width is modulated As the pulse width increases or decreases, the difference components (PWM1-PWM_REF, PWM2-PWM_REF) from the pulse width modulation reference signal PWM_REF, which are common terminal signals, become a positive pulse or a negative pulse. In addition, the pulse signals representing the difference components are twice as frequently as the two modulated signals PWM1 and PWM2. That is, the frequency doubles.

Most headphones and earphones use a moving coil type sound pressure generator. The moving coil type negative pressure generator has the property of an inductor, and the inductance increases with high frequency. Since the electrical characteristics of the device and the load as described above generates the effect as if the LC filter is built in the case of the headphone driver 600 according to the present invention shown in Figure 6 has the advantage that no separate LC filter is used have.

In particular, as shown in FIG. 9, the inductance of the headphones or the earphone itself is applied to the load because the difference components (PWM1-PWM_REF and PWM2-PWM_REF) having frequency characteristics twice as fast as the two modulated signals PWM1 and PWM2 modulated as shown in FIG. Only high frequency signals can be blocked better.

When the modulation amount of the two modulation signals PWM1 and PWM2 is small in the headphone driver according to the embodiment of the present invention, noise may occur in the headphones or earphones. That is, since the three signals PWM1, PWM2, and PWM_REF having substantially the same phase are applied to the corresponding drivers 601 to 603 when starting to operate the driver for reproducing at a low volume, the edges of the three signals. ) May interfere with each other.

The waveform of the signals is generally maintained by the current supplied from one power supply (VDD), which is limited to a certain amount of current that can be supplied from the power supply at the same time in any system. In addition, since the operation of the drivers uses the same power supply (VDD) as the power used to maintain the waveform of the signals, the amount of current supplied to the driver changes if the signals are driven at the same time. In addition to the current can be reduced at this time, the amount of current supplied will change over time. In this case, distortion may occur in the output waveform of the driver due to the arrangement of the three drivers 601 to 603 or an interval between the input signal and the corresponding driver. Waveforms distorted due to the above causes appear as noise generated from headphones or earphones. The noise is reproduced as a sound that "charges" in headphones or earphones.

The noise can be prevented through a method of forcibly allocating a constant phase difference between the reference signal PWM_REF and the two modulated signals PWM1 and PWM2.

FIG. 10 is a waveform diagram of the internal nodes of FIG. 6 when two modulated signals PWM1 and PWM2 having a constant phase difference compared to the waveform of the reference signal PWM_REF are input.

Referring to FIG. 10, since the edges of the three signals occur at different times, the phenomenon of distorting the outputs N61 to N63 of the driver operated by the three signals does not occur. That is, since the input first modulated signal PWM1 has a predetermined offset phase ahead of the reference signal PWM_REF, the waveforms N61 and 603 output from the drivers 601 and 603 in response to these signals are output. N63) is not distorted when compared with the input signals. Similarly, since the second modulated signal PWM2 input has a predetermined offset phase compared to the reference signal PWM_REF, waveforms N62 and N63 output from the drivers 602 and 603 in response to these signals. ) Is not distorted when compared with the input signals. Therefore, the shape of the difference signals N61-N63 and N62-N63 of the signals output from the drivers 601 to 603 can be generated quite clean.

In FIG. 10, the first modulated signal PWM1 is shown to be out of phase with respect to the reference signal PWM_REF and the second modulated signal PWMM is out of phase with respect to the reference signal PWM_REF, but has a reversed phase. It is also possible.

However, it is necessary to set the phase difference appropriately so that the difference components (PWM1-PWM_REF, PWM2-PWM_REF) of the reference signal PWM_REF and the two modulated signals PWM1 and PWM2 do not become pulse shapes having high frequency components. have. In addition, since the phase difference may generate some driving noise during the initial driving of the driver, the initial driving noise may be reduced by initially driving without phase difference and then slowly increasing the phase difference. You can.

The constant phase difference between the two modulation signals PWM1 and PWM2 and the reference signal PWM_REF is not only used in the headphone driver 600 according to the present invention, but also in the headphone drivers 100 and 200 that are conventionally used. ) Can be applied as is.

The technical spirit of the present invention has been described above with reference to the accompanying drawings. However, the present invention is illustrated by way of example and not by way of limitation. In addition, it is apparent that any person having ordinary knowledge in the technical field to which the present invention belongs may make various modifications and imitations without departing from the scope of the technical idea of the present invention.

As described above, the headphone driver according to an embodiment of the present invention can reduce the size of the system because it is not necessary to use various filters that have been conventionally used. Accordingly, there is an advantage that the system can be miniaturized, and the power consumption can be reduced. In addition, the headphone driver driving method according to another embodiment of the present invention has an advantage of minimizing standby noise or pop noise that may occur when there is no sound source to be played or just before playing the sound source.

Claims (11)

In the headphone driver for driving two modulation signals and a modulation reference signal, A first driver for amplifying the first modulated signal; A second driver for amplifying the second modulated signal; And And a third driver for amplifying the modulation reference signal. The headphone driver of claim 1, wherein duty cycles of the two modulation signals and the modulation reference signal are the same. The method of claim 1, The amplitude of the signals (Amplitude) output from the drivers are all the same, the headphone driver. The method of claim 2, wherein the duty cycle, Headphone driver characterized by being 50%. The method of claim 2, wherein the two modulated signals, And a signal obtained by performing pulse width modulation on the reproduction signal. The method of claim 2, wherein the modulation reference signal, The headphone driver according to claim 2, wherein the reproduction of the two modulated signals serves as a reference signal for comparing the magnitudes of the two modulated signals. A driving method of a headphone driver for driving two modulation signals obtained by performing pulse width modulation on a modulation reference signal and a reproduction signal, Duty cycles of the two modulation signals and the modulation reference signal are the same, And the phases of the two modulation signals and the modulation reference signal do not coincide with each other. The method of claim 7, wherein the duty cycle, The headphone driver driving method, characterized in that 50%. The method of claim 7, wherein And when the phase of one of the two modulation signals is faster than the phase of the modulation reference signal, the phase of the other modulation signal is slower than the phase of the modulation reference signal. The method of claim 7, wherein the phase between the two modulation signals and the modulation reference signal, The first method of driving the headphone driver, the headphone driver driving method, characterized in that the difference gradually increases with time. The method of claim 7, wherein the two modulation signals and the reference modulation signal are amplified and processed to the same magnitude.

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