WO2007148879A1

WO2007148879A1 - Headphone driver and method for driving the same

Info

Publication number: WO2007148879A1
Application number: PCT/KR2007/002636
Authority: WO
Inventors: Yong Hun Cho; Sang Jin Park
Original assignee: Ubi Sound Co., Ltd
Priority date: 2006-06-19
Filing date: 2007-05-31
Publication date: 2007-12-27
Also published as: KR100626987B1

Abstract

A headphone driver without use of an inductor or a capacitor and a method of driving the headphone driver are provided. The headphone driver includes three drivers, wherein signals applied to input ports of the drivers have the same duty cycle, so that the headphone driver can drive a headphone without use of an inductor or a capacitor. In the method of driving a headphone driver, two modulated signals obtained by performing pulse width modulation on a modulation reference signal and a to-be-reproduced signal are driven, the two modulated signals and the modulation reference signal have the same duty cycle, and the phases of the two modulated signals and modulation reference signal are not equal to each other. Accordingly, it is possible to reduce a noise that may be generated during the operation of the headphone driver.

Description

HEADPHONE DRIVER AND METHOD FOR DRIVING THE

SAME

Technical Field

[1] The present invention relates to a three-port headphone driver and, more particularly, to a headphone driver without use of an inductor or a capacitor so as not to generate a "pop" noise and a method of driving the headphone driver. Background Art

[2] A stereo sound generated from a sound source can be heard with various effects in comparison with a mono sound generated from the sound source. Therefore, in general, a music signal is reproduced in a stereo type by using two reproducing units. The to-be-reproduced signal is modulated by using various modulation methods. As an example of the modulation method, a width of the to-be-reproduced signal is modulated according to a pulse width modulation (PWM) method, and after that, the signal is amplified according to a switching amplification method.

[3] In a case where the stereo sound source is amplified and reproduced according to the

PWM method, stereo input signals are firstly modulated, so that two different pulse- width modulated signals are generated. The two modulated signals are individually amplified, and harmonics noise is removed from the amplified signals. Next, direct current (DC) coupling is performed, so that stereo signals are generated. The generated stereo signals can be directly reproduced through a speaker, a headphone, or an earphone.

[4] FlG. 1 illustrates an embodiment of a headphone driver using a single power provided to a conventional three-port stereo headphone.

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

[6] The drivers 101 and 111 amplify two modulated signals PWMl and PWM2 obtained by performing pulse width modulation on a to-be-reproduced sound source (not shown), respectively. In general, inverters having a high driving performance are used for the drivers 101 and 111. The LC filters 102 and 112 remove harmonics noise from the amplified modulated signals PWMl and PWM2, respectively. The RC filters 103 and 113 remove DC components from the modulated signals PWMl and PWM2 of which harmonics noise is removed, respectively.

[7] In general, a pulse-width modulated square wave signal has harmonics components corresponding to multiples of a frequency of the modulated signal. The harmonics components function as noise in terms of signal processing. Therefore, the harmonics noise needs to be removed from the modulated square waveform signal by using a low pass filter or a band pass filter. Particularly, an RC filter constructed with a resistor R and a capacitor C or an LC filter constructed with an inductor L and a capacitor C are used to remove the harmonics noise.

[8] In summary, the headphone driver 100 amplifies two modulated signals PWMl and

PWM2, and after that, transmits to a three-port stereo headphone jack 120 the signals from which the harmonics noise and the DC components are removed. At this time, a reference voltage GND as well as the two modulated signals PWMl and PWM2 is applied to the three-port stereo headphone jack 120.

[9] FTG. 3 is an internal circuit diagram of the LC filter 102 or 112 illustrated in HG. 1.

[ 10] FlG. 4 is an internal circuit diagram of the RC filter 103 or 113 illustrated in FlG. 1.

[11] Constructions and operations of the filters illustrated in FIGS. 3 and 4 are well known to circuit designers, and thus, detailed description thereof is omitted.

[12] FlG. 7 is a waveform diagram at internal nodes of the headphone driver illustrated in

FlG. 1 when two modulated signals, that is, square wave signals having a 50% duty (half duty) cycle are applied in a case where a stereo input signal is a non-sound signal.

[13] Referring to FIGS. 7 and 1, the first modulated signal PWMl is amplified by the first driver 101 at the node Nl. The harmonics noise is removed from the amplified signal by the first LC filter 102 at the node N2, and subsequently, the DC voltage component is removed by the first RC filter 103 at the node N3. The second modulated signal PWM2 is amplified by the second driver 111 at the node N4. The harmonics noise is removed from the amplified signal by the second LC filter 112 at the node N5, and subsequently, the DC voltage component is removed by the second RC filter 113 at the node N6.

[14] FlG. 2 illustrates an embodiment of a headphone driver using a half power additionally provided to a conventional three-port stereo headphone.

[15] Referring to FlG. 2, the headphone driver 200 includes drivers 201 and 211 and LC filters 202 and 212.

[16] There are two differences between the headphone driver 100 using the single power

VDD illustrated in FlG. 1 and the headphone driver 200 using an additional half power VDD/2 illustrated in HG. 2.

[17] In the headphone driver 100 using the single power VDD illustrated in FlG. 1, the two LC filters 102 and 112 and the two RC filters 103 and 113 which are connected in series are used. However, in the headphone driver 200 using an additional half power VDD/2 illustrated in HG. 2, the two LC filters 202 and 212 are used, but an RC filter is not used. In addition, the headphone driver 200 applies a bias voltage which is the half power voltage VDD/2, that is, a half of the power voltage VDD to the three-port stereo headphone jack 220. Since the bias voltage which is the half power voltage is applied to the three-port stereo headphone jack 220, DC voltage levels of the stereo signals output from the two LC filters 202 and 212 are equal to that of the bias voltage. Therefore, any RC filter for performing DC coupling is not additionally required.

[ 18] FTG. 5 is an internal circuit diagram of the LC filter 202 or 212 illustrated in HG. 2.

[19] Constructions and operations of the filters illustrated in FlG. 5 are well known to circuit designers, and thus, detailed description thereof is omitted.

[20] The headphone driver 100 illustrated in FlG. 1 requires two LC and RC filters. Since coils used for the LC filters 102 and 112 are expensive and large-sized, there is a disadvantage in the headphone driver 100. In addition, in case of a three-port stereo headphone having an impedance of 32Ω, the RC filters 103 and 113 need to be constructed with a capacitance having capacitance of about 220μF. If the coil or the capacitor is used for a mobile device, there is a disadvantage in terms of costs and size.

[21] In order to solve the disadvantages, there has been proposed such a headphone driver

200. However, the headphone driver needs to be provided with an additional circuit for generating the half power. In general, an analog amplifier is used for the additional circuit for generating the half power. However, the analog amplifier results in reduction in efficiency of the headphone driver. Moreover, due to an offset voltage and nonlinearity of the analog amplifier, a "pop" noise may be generated at the time of driving the amplifier. Disclosure of Invention Technical Problem

[22] The present invention provides a headphone driver without use of an inductor or a capacitor. [23] The present invention also provides a method of driving a headphone driver without generation of a "pop" noise at the time of operating the headphone driver.

Technical Solution [24] According to an aspect of the present invention, there is provided a headphone driver having three drivers to which signals having the same duty cycle are input. [25] According to another aspect of the present invention, there is provided a method of driving a headphone driver, wherein two modulated signals obtained by performing pulse width modulation on a modulation reference signal and a to-be-reproduced signal are driven, wherein the two modulated signals and the modulation reference signal have the same duty cycle, and wherein phases of the two modulated signals and modulation reference signal are not equal to each other.

Brief Description of the Drawings [26] FlG. 1 illustrates an embodiment of a headphone driver using a single power provided to a conventional three-port stereo headphone. [27] FlG. 2 illustrates an embodiment of a headphone driver using a half power additionally provided to a conventional three-port stereo headphone.

[28] FlG. 3 is an internal circuit diagram of an LC filter illustrated in FlG. 1.

[29] FlG. 4 is an internal circuit diagram of an RC filter illustrated in FlG. 1.

[30] FlG. 5 is an internal circuit diagram of an LC filter illustrated in FlG. 2.

[31] FlG. 6 is a circuit diagram of a headphone driver according to the present invention.

[32] FlG. 7 is a waveform diagram at internal nodes of the headphone driver illustrated in

[33] FlG. 8 is a waveform diagram at internal nodes of the headphone driver illustrated in

FlG. 6 according to the present invention in a case where there is no reproduced sound source.

[34] FlG. 9 is a waveform diagram at the internal nodes of the headphone driver illustrated in FlG. 6 according to the present invention in a case where there is a to- be-reproduced sound source.

[35] FlG. 10 is a waveform diagram at the internal nodes of the headphone driver illustrated in FlG. 6 according to the present invention in a case where two modulated signals PWMl and PWM2 which have predetermined phase differences with respect to a waveform of a reference signal PWM-REF are input. Best Mode for Carrying Out the Invention

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

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

[38] Referring to FlG. 6, the headphone driver 600 includes three drivers 601 to 603.

According to the present invention, since a pulse width modulation reference signal PWM-REF is applied to a three-port stereo headphone jack 620 by via of the headphone driver 600, the headphone driver 600 has a simple construction in comparison with the conventional headphone drivers 100 and 200 illustrated in FIGS. 1 and 2.

[39] In the headphone driver according to the present invention, a square waveform signal having the same period and phase as those of two pulse- width modulated signals PWMl and PWM2 and a 50% duty cycle is used as the pulse width modulation reference signal PWM-REF.

[40] FlG. 8 is a waveform diagram at internal nodes of the headphone driver illustrated in

FlG. 6 according to the present invention in a case where there is no reproduced sound source. [41] Referring to FlG. 8, stereo signals, that is, the two modulated signals PWMl and

PWM2 have the same period and phase as those of the pulse width modulation reference signal PWM-REF. The waveforms N61 to N63 of the signals obtained by amplifying the three signals in the respective drivers 601 to 603 have the same amplitude with the same period and phase. According to the present invention, it should be noted that amplitudes of the signals output from the three drivers are equal to each other irrespective of the amplitudes of the three signals PWMl, PWM2, and PWM_REF.

[42] Since the amplitudes and phases of the two modulated signals PWMl and PWM2 and the modulation reference signal PWM-REF, difference signals N61-N63 and N62-N63 become 0 (zero). Since these waveforms are equal to each other, there are no AC and DC potential differences. Therefore, any LC filter for removing harmonics noise and any RC filter for removing DC components are not needed. As described above, these filters are necessarily used for a conventional headphone driver.

[43] FlG. 9 is a waveform diagram at the internal nodes of the headphone driver illustrated in FlG. 6 according to the present invention in a case where there is a to- be-reproduced sound source.

[44] Referring to FlG. 9, in a case where there is a to-be-reproduced sound source, when the two modulated signals PWMl and PWM2 having difference pulse widths for the sound source are input, the pulse widths of the two modulated signals PWMl and PWM2 are increased or decreased. Therefore, the difference components PWM1-PWM_REF and PWM2-PWM_REF between the modulated signals PWMl and PWM2 and the pulse width modulation reference signal PWM-REF, that is, a common port signal becomes a positive or negative pulse. The frequency of the difference component is two times those of the two modulated signals PWMl and PWM2. Namely, the frequency is increased by two times.

[45] In general, a moving-coil sound pressure generating device is used for a headphone or earphone. The moving-coil sound pressure generating device has a characteristic of an inductor, so that inductance thereof is increased as the frequency increases. In this manner, since the electric characteristics of the device and loads result in effects of an embedded LC filter, the headphone driver 200 illustrated in FlG. 6 according to the present invention has an advantage in that an additional LC filter needs not to be used.

[46] Particularly, as illustrated in FlG. 9, since the difference components

PWM1-PWM_REF and PWM2-PWM_REF having a frequency characteristic that the frequencies thereof is two times higher than those of the two modulated signals PWMl and PWM2 are applied to the load, the high frequency signals can be easily blocked by only the self inductance of the headphone or the earphone.

[47] In the headphone driver according to the above-described embodiment of the present invention, if an amount of modulation for the two modulated signals PWMl and PWM2 is small, noise may be generated in the headphone or the earphone. Namely, in a case where the drivers are operated so as to reproduce a small sound volume, since the three signals PWMl, PWM2, and PWM-REF having substantially the same phases applied to the respective drivers 601 to 603, edges of the three signals cause interference therebetween.

[48] In general, waveforms of the signals are maintained by a current applied from one power VDD. In any system, a current which can be applied from the same power at the same time is limited to a constant amount. Since the waveforms of the signals of the drivers are maintained by using the same power VDD, if the signals are driven approximately at the same time, the amounts of current applied to the drivers are changed. In addition to the decrease in current, the amounts of current applied to the drivers are varied in time. In this case, distortion in output waveforms of the drivers may occur due to arrangement of the three drivers 601 to 603 or gaps between the input ports and the drivers. The distortion in output waveforms results in noise of the headphone or the earphone. The noise is reproduced as an acoustic sound "shaa" in the headphone or the earphone.

[49] The noise can be prevented by forcibly allocating predetermined phase differences between the modulation reference signal PWM-REF and the two modulated signals PWMl and PWM2.

[50] FIG. 10 is a waveform diagram at the internal nodes of the headphone driver illustrated in FIG. 6 according to the present invention in a case where two modulated signals PWMl and PWM2 which have predetermined phase differences with respect to the waveform of the reference signal PWM-REF are input.

[51] Referring to FIG. 10, the edges of the three signals are generated at different timings.

Therefore, the distortion in the outputs N61 to N63 of the drivers operating according to the three signals are not be generated. Since the first modulated signal PWMl is input with a phase by a predetermined offset preceding the phase of the reference signal PWM-REF, the waveforms N61 and N63 output from the drivers 601 and 603 in respect to these signals are not distorted in comparison with the input signals. Similarly, since the second modulated signal PWM2 is input with a phase by a predetermined offset lagging behind the phase of the reference signal PWM-REF, the waveforms N62 and N63 output from the drivers 602 and 603 in response to these signals are not distorted in comparison with the input signals. Therefore, the difference signals N61-N63 and N62-N63 between the signals output from the drivers 601 to 603 are generated in non-distorted waveforms.

[52] In FIG. 10, the phase of the first modulated signal PWMl precedes that of the reference signal PWM-REF, and the phase of the second modulated signal PWM2 lags behind the reference signal PWM-REF. Alternatively, opposite phases may be available.

[53] In this case, it should be noted that the phase differences need to be suitably adjusted so that the difference components PWM1-PWM_REF and PWM2-PWM_REF between the reference signal PWM-REF and the modulated signals PWMl and PWM2 must not be high frequency pulse signal. On the other hand, due to the phase differences, a noise at the initial driving time, that is, the "pop" noise may be generated. In order to reduce the noise at the initial driving time, the drivers may be initially driven without phase differences at the initial driving time, and after that, the phase differences may be gradually increased.

[54] The method of allocating predetermined phase differences between the reference signal PWM-REF and the modulated signals PWMl and PWM2 may be employed in the conventional headphone drivers 100 and 200 as well as the headphone driver according to the present invention.

[55] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. Industrial Applicability

[56] In a headphone driver according to the present invention, since various filters necessarily used for a conventional headphone driver needs not be used, it is possible to reduce a size of a system. Accordingly, the headphone driver is suitable for a compact system, and power consumption can be reduced. In addition, in a method of driving a headphone driver according to the present invention, it is possible to minimize a standby noise or a "pop" noise which may be generated when there is no to-be-reproduced sound source or just before the sound source is reduced.

Claims

[I] A headphone driver which drives two modulated signals and a modulation reference signal, comprising: a first driver which amplifies a first modulated signal; a second driver which amplifies a second modulated signal; and a third driver which amplifies the modulation reference signal.

[2] The headphone driver of Claim 1, wherein the two modulated signals and the modulation reference signal have the same duty cycle.

[3] The headphone driver of Claim 1, wherein signals output from the drivers have the same amplitude.

[4] The headphone driver of Claim 2, wherein the duty cycle is 50%.

[5] The headphone driver of Claim 2, wherein the two modulated signals are obtained by performing pulse width modulation of the to-be-reproduced signal.

[6] The headphone driver of Claim 2, wherein the modulation reference signal is used as a reference signal for comparing sizes of the two modulated signals in the reproduction of the two modulated signals.

[7] A method of driving a headphone driver which drives two modulated signals obtained by performing pulse width modulation on a modulation reference signal and a to-be-reproduced signal, wherein the two modulated signals and the modulation reference signal have the same duty cycle, and wherein phases of the two modulated signals and modulation reference signal are not equal to each other.

[8] The method of Claim 7, wherein the duty cycle is 50%.

[9] The method of Claim 7, wherein, in a case where one of the two modulated signals has a phase preceding that of the modulation reference signal, the other modulated signal has a phase lagging behind that of the modulation reference signal. [10] The method of Claim 7, wherein phases between the two modulated signals and the modulation reference signal are equal to each other at an initial driving time for the headphone driver, and the phase differences gradually increase in time.

[II] The method of Claim 7, wherein the two modulated signals and the modulation reference signal are amplified so as to have the same amplitude.