JP2017118311A - Class-d amplifier circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a class-D amplifier circuit capable of improving a noise suppression effect in a switching frequency domain while suppressing capacitance increase in a capacitor of a low-pass filter.SOLUTION: A first low-pass filter and a second low-pass filter are inserted into a first signal line and a second signal line in which signal currents in differential modes flow. A first shunt circuit formed from a series circuit of a first inductor and a first capacitor is inserted between the first signal line and a ground. A second shunt circuit formed from a series circuit of a second inductor and a second capacitor is inserted between the second signal line and the ground. The first inductor and the second inductor are coupled in such a manner that magnetic fluxes caused by common-mode components of the currents are weakened by each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a class D amplifier circuit applied to an output stage of a class D amplifier.

  Patent Document 1 below discloses a low-pass filter applied to the output stage of a class D amplifier of a bridged transformerless (BTL) output system. In a BTL output class D amplifier, a low pass filter is inserted for each of a positive output and a negative output. This low-pass filter extracts an audio signal by removing a switching frequency component of pulse width modulation from the pulse width modulation signal.

JP 2003-1224029 A

  In the conventional low-pass filter, a sufficient noise suppression effect cannot be obtained in a low frequency range that is about the switching frequency of the class D amplifier. In order to increase the noise suppression effect in the low frequency range of the switching frequency, the capacitance of the low-pass filter capacitor must be increased. However, when the capacity of the capacitor is increased, the class D amplifier is easily damaged by overcurrent.

  An object of the present invention is to provide a class D amplifier circuit capable of enhancing a noise suppression effect in a switching frequency region while suppressing an increase in capacitance of a capacitor of a low-pass filter.

A class D amplifier circuit according to the first aspect of the present invention provides:
A first signal line and a second signal line through which a differential mode signal current flows;
A first low-pass filter inserted in the first signal line;
A second low-pass filter inserted in the second signal line;
A first shunt circuit comprising a series circuit of a first inductor and a first capacitor, and inserted between the first signal line and ground;
A series circuit of a second inductor and a second capacitor, and a second shunt circuit inserted between the second signal line and the ground,
The first inductor and the second inductor are coupled so that the magnetic flux due to the common mode component of the current is weakened.

  Since the first inductor and the second inductor are coupled so that the magnetic flux due to the common mode component of the current is weakened, the combination of the first shunt circuit and the second shunt circuit for the current of the common mode component The impedance is smaller than the combined impedance with respect to the current of the differential mode component. For this reason, it is possible to suppress the differential mode signal current from flowing into the ground, and to allow common mode noise to flow into the ground. Thereby, the suppression effect of common mode noise can be enhanced in a low frequency range of about the switching frequency.

In the class D amplifier circuit according to the second aspect of the present invention, in addition to the configuration of the class D amplifier circuit according to the first aspect,
The differential mode signal current input to one end of the first signal line and the second signal line is pulse-width modulated,
The average value of the resonance frequency and the antiresonance frequency for the current of the common mode component of the first low-pass filter, the second low-pass filter, the first shunt circuit, and the second shunt circuit is the pulse width. More than the switching frequency of the modulated signal current.

  In particular, the common mode noise suppression effect in the switching frequency region can be enhanced.

In the class D amplifier circuit according to the third aspect of the present invention, in addition to the configuration of the class D amplifier circuit according to the first to third aspects,
The self-inductance of the first inductor and the self-inductance of the second inductor are the same.

  The common mode noise suppression effect can be further enhanced.

In the class D amplifier circuit according to the fourth aspect of the present invention, in addition to the configuration of the class D amplifier circuit according to the first to third aspects,
The first inductor and the second inductor are composed of coils wound around a common winding core in opposite directions, and a common current flowing through the first signal line and the second signal line. When the mode component flows through the first inductor coil and the second inductor coil, magnetic fields opposite to each other are generated.

In the class D amplifier circuit according to the fifth aspect of the present invention, in addition to the configuration of the class D amplifier circuit according to the first to third aspects,
The first inductor and the second inductor are composed of coils wound around a common winding core in the same direction, and currents flowing through the first signal line and the second signal line The common mode component flows through the first inductor coil and the second inductor coil, thereby generating magnetic fields in opposite directions.

  By adopting the configuration according to the fourth aspect or the fifth aspect, it is possible to realize the first inductor and the second inductor that are coupled so that the magnetic flux due to the common mode component of the current is weakened.

  Since the first inductor and the second inductor are coupled so that the magnetic flux due to the common mode component of the current is weakened, the combination of the first shunt circuit and the second shunt circuit for the current of the common mode component The impedance is smaller than the combined impedance with respect to the current of the differential mode component. For this reason, it is possible to suppress the differential mode signal current from flowing into the ground, and to allow common mode noise to flow into the ground. Thereby, the suppression effect of common mode noise can be heightened in a low frequency region about the switching frequency.

FIG. 1 is an equivalent circuit diagram of the BTL output class D amplifier circuit according to the first embodiment. FIG. 2 is a perspective view of a circuit component in which the first inductor and the second inductor used in the class D amplifier circuit according to the first embodiment are housed in one package. FIG. 3A is a graph showing a simulation result of a transmission spectrum of common mode noise in a class D amplifier circuit, and FIGS. 3B and 3C are equivalent circuit diagrams of a class D amplifier circuit according to a comparative example to be simulated, FIG. 3D is an equivalent circuit diagram of the class D amplifier circuit according to the first embodiment to be simulated. FIG. 4A is a graph showing a simulation result of a transmission spectrum of common mode noise in a class D amplifier circuit, and FIGS. 4B and 4C are equivalent circuit diagrams of the class D amplifier circuit according to Example 1 to be simulated. . FIG. 5 is an equivalent circuit diagram of the class D amplifier circuit according to the second embodiment. FIG. 6 is a perspective view of a circuit component in which the first inductor and the second inductor used in the class D amplifier circuit according to the second embodiment are housed in one package.

  FIG. 1 shows an equivalent circuit diagram of a BTL output class D amplifier circuit according to the first embodiment. The audio signal Sa is input to the pulse width modulation circuit 10. The pulse width modulation circuit 10 outputs two pulse width modulation signals (PWM signals) PWM1 and PWM2 having a pulse width corresponding to the level of the audio signal Sa. The two PWM signals PWM1 and PWM2 have waveforms that complement each other.

  The PWM signals PWM1 and PWM2 are input to the control terminals of the first switching circuit 13 and the second switching circuit 14 via the first gate driver 11 and the second gate driver 12, respectively. Each of the first switching circuit 13 and the second switching circuit 14 includes a series circuit of a p-channel MOSFET and an n-channel MOSFET. The power supply voltage VDD is applied to one end of the series circuit, and the other end is connected to the ground GND. The interconnection points between the p-channel MOSFET and the n-channel MOSFET of the first switching circuit 13 and the second switching circuit 14 are referred to as a first terminal T1 and a second terminal T2, respectively.

  The first terminal T1 is connected to the first output terminal TO1 via the first signal line 20, and the second terminal T2 is connected to the second output terminal TO2 via the second signal line 30. It is connected to the. A load 50 is connected between the first output terminal TO1 and the second output terminal TO2. The load 50 is, for example, a speaker that converts an electric signal into a sound wave.

  The electrical signal output from the first terminal T 1 passes through the first signal line 20, the first output terminal TO 1, the load 50, the second output terminal TO 2, and the second signal line 30. Return to terminal T2. A differential mode signal current Id flows through the first signal line 20 and the second signal line 30.

  A first low-pass filter 21 is inserted in the first signal line 20, and a second low-pass filter 31 is inserted in the second signal line 30. The first low-pass filter 21 includes, for example, an inductor L3 inserted in series with the first signal line 20, and a capacitor C3 inserted between the first signal line 20 and the ground GND. The second low-pass filter 31 includes, for example, an inductor L4 inserted in series with the second signal line 30 and a capacitor C4 inserted between the second signal line 30 and the ground GND.

  The first shunt circuit 22 is connected between the first signal line 20 and the ground GND. The second shunt circuit 32 is connected between the second signal line 30 and the ground GND. As an example, the first shunt circuit 22 is connected to the first signal line 20 between the first low-pass filter 21 and the load 50. As an example, the second shunt circuit 32 is connected to the second signal line 30 between the second low-pass filter 31 and the load 50.

  The first shunt circuit 22 includes a series circuit of a first inductor L1 and a first capacitor C1. The second shunt circuit 32 includes a series circuit of a second inductor L2 and a second capacitor C2. The first inductor L1 and the second inductor L2 are coupled so that magnetic fluxes due to the common mode component of the current weaken each other. Such a bond is called a “negative bond”. The first inductor L1, the first capacitor C1, and the resonance frequency for the common mode component of the current flowing through the first shunt circuit 22 and the second shunt circuit 32 are substantially equal to the switching frequency of the class D amplifier. The element constants of the second inductor L2, the second capacitor C2, and the mutual inductance between the first inductor L1 and the second inductor L2 are set.

Here, the common mode component of the current means a component flowing in the same direction among the currents flowing through the first shunt circuit 22 and the second shunt circuit 32. For example, the current flowing from the first signal line 20 toward the ground GND in the first shunt circuit 22 is represented as I1, and the current flowing from the second signal line 30 toward the ground GND in the second shunt circuit 32 is represented as I1. This is expressed as I2. When the common mode component of the current flowing through the first shunt circuit 22 and the second shunt circuit 32 is expressed as Ic and the differential mode component is expressed as Id, the following relational expression is established.
I1 = Id + (1/2) Ic
I2 = −Id + (1/2) Ic

From the above relational expression, the common mode component Ic of the current flowing through the first shunt circuit 22 and the second shunt circuit 32 is expressed by the following formula.
Ic = I1 + I2

  FIG. 2 is a perspective view of a circuit component in which the first inductor L1 and the second inductor L2 are housed in one package. Two coils 41 and 42 are formed by two wires wound around the core 35. In FIG. 2, one coil 41 is represented by a solid line and the other coil 42 is represented by a broken line. One coil 41 corresponds to the first inductor L1, and the other coil 42 corresponds to the second inductor L2. The two coils 41 and 42 are wound in opposite directions. In other words, one coil 41 is right-handed and the other coil 42 is left-handed. The flange portions 36 are attached to both ends of the winding core 35, respectively. External electrodes 37 and 38 are formed on each of the flange portions 36.

  One external electrode 37 becomes a terminal of the first inductor L1, and the other external electrode 38 becomes a terminal of the second inductor L2. In FIG. 2, the winding type is shown as the first inductor L1 and the second inductor L2, but it is also possible to use a laminated type or a thin film type.

  Next, the excellent effect of Example 1 will be described. If there is a variation in inductance between the inductor L3 of the first low-pass filter 21 and the inductor L3 of the second low-pass filter 31, the first signal line 20 and the second signal line 20 are converted by mode conversion between the differential mode and the common mode. The common mode component of the current flowing through the signal line 30 increases. In particular, the common mode component of the switching frequency of the class D amplifier and the frequency range of its harmonics increases. This common mode component is called “common mode noise”. When the common mode noise flows into the load 50, electromagnetic radiation noise is generated due to the common mode noise flowing through the wiring to the load 50.

  In the first embodiment, since the coupling between the first inductor L1 and the second inductor L2 is a negative coupling, the impedance to the common mode component of the current flowing through the first shunt circuit 22 and the second shunt circuit 32 is , Smaller than the impedance for the differential mode component. For this reason, the common mode noise current flowing through the first signal line 20 and the second signal line 30 easily flows to the ground GND via the first shunt circuit 22 and the second shunt circuit 32. As a result, the generation of electromagnetic radiation noise can be suppressed by reducing the common mode noise current flowing into the load 50.

  In order to enhance the effect of reducing common mode noise, the self-inductance of the first inductor L1 and the self-inductance of the second inductor L2 are made equal, and the capacitance of the first capacitor C1 and the capacitance of the second capacitor C2 are Are preferably equal.

  Furthermore, since the resonance frequency for the common mode component of the current flowing through the first shunt circuit 22 and the second shunt circuit 32 is substantially equal to the switching frequency of the class D amplifier, the impedance to the common mode noise current in the switching frequency region is particularly high. Get smaller. For this reason, a particularly high noise suppression effect is obtained in the switching frequency region.

  The first inductor L1 and the second inductor L2 are omitted, the first shunt circuit 22 is configured by only the first capacitor C1, and the second shunt circuit 32 is configured by only the second capacitor C2. In addition, an effect of reducing common mode noise flowing into the load 50 can be obtained. However, in the configuration in which the first inductor L1 and the second inductor L2 are omitted, the differential mode audio signal also easily flows to the ground GND via the first shunt circuit 22 and the second shunt circuit 32. .

  If the first inductor L1 and the second inductor L2 are arranged in the first shunt circuit 22 and the second shunt circuit 32, respectively, but the two are not coupled, the first shunt circuit 22 and The impedance of the second shunt circuit 32 with respect to the differential mode audio signal is not sufficiently high. Therefore, the differential mode audio signal is likely to flow to the ground GND via the first shunt circuit 22 and the second shunt circuit 32.

  In the first embodiment, the first inductor L1 and the second inductor L2 have mutual inductances that are positively coupled to the differential mode component of the current flowing through the first shunt circuit 22 and the second shunt circuit 32. For this reason, the first inductor L1 and the second inductor L2 exhibit high impedance with respect to the differential mode component. Due to the high impedance, the differential mode audio signal flowing through the first signal line 20 and the second signal line 30 is unlikely to flow through the first shunt circuit 22 and the second shunt circuit 32 to the ground GND.

  When the audio signal flows to the ground GND, there is an increased concern that the class D amplifier may be damaged due to overcurrent. In the first embodiment, since the first shunt circuit 22 and the second shunt circuit 32 exhibit high impedance with respect to the differential mode audio signal, damage to the class D amplifier due to overcurrent is suppressed.

  Next, with reference to the drawings from FIG. 3A to FIG. 3D, the simulation results of the common mode noise suppression effect of the class D amplifier circuit according to the first embodiment and the class D amplifier circuit according to the comparative example will be described.

  FIG. 3A shows the simulation result of the transmittance of the common mode noise in the class D amplifier circuit. The horizontal axis represents the frequency in the unit “MHz”, and the vertical axis represents the transmittance in the unit “dB”. The broken line 3B, the solid line 3C, and the solid line 3D in FIG. 3A indicate the transmittance of the class D amplifier circuit according to the comparative example illustrated in FIG. 3B, the comparative example illustrated in FIG. 3C, and the first embodiment illustrated in FIG. .

  In the comparative example shown in FIGS. 3B and 3C, the first shunt circuit 22 and the second shunt circuit 32 (FIG. 1) of the class D amplifier circuit according to the first embodiment are not provided. Other circuit configurations are the same as those of the class D amplifier circuit according to the first embodiment. In the comparative example shown in FIG. 3B, the inductances of the inductors L3 and L4 are 10 μH, and the capacitances of the capacitors C3 and C4 are 1 μF. In the comparative example shown in FIG. 3C, the inductances of the inductors L3 and L4 are 2.7 μH, and the capacitances of the capacitors C3 and C4 are 0.22 μF.

  In Example 1 shown in FIG. 3D, the inductances of the inductors L3 and L4 and the capacitances of the capacitors C3 and C4 are the same as the inductances of the inductors L3 and L4 and the capacitances of the capacitors C3 and C4 of the comparative example shown in FIG. 3C, respectively. Is the same. The combined inductance Ld for the differential mode component of the first inductor L1 and the second inductor L2 is 10 μH, and the combined inductance Lc for the common mode component is 0.25 μH. The capacitances of the first capacitor C1 and the second capacitor C2 are 0.22 μF. At this time, the resonance frequency at which the impedance of the first shunt circuit 22 and the second shunt circuit 32 has a minimum value with respect to the common mode component is about 480 kHz.

  In the first embodiment, as shown in FIG. 1, the capacitor C3 of the first low-pass filter 21 and the capacitor C4 of the second low-pass filter 31 are in parallel with the first shunt circuit 22 and the second shunt circuit 32. It is connected to the. The antiresonance frequency at which the impedance of the parallel connection circuit of the capacitors C3 and C4, the first shunt circuit 22 and the second shunt circuit 32 has a maximum value is about 679 kHz.

  The inductances of the inductors L3 and L4 used in the comparative example shown in FIG. 3C and the first embodiment shown in FIG. 3D are smaller than the inductances of the inductors L3 and L4 used in the comparative example shown in FIG. 3B. Furthermore, the capacitances of the capacitors C3 and C4 used in the comparative example shown in FIG. 3C and the first embodiment shown in FIG. 3D are smaller than the capacitances of the capacitors C3 and C4 used in the comparative example shown in FIG. 3B.

  As shown by the broken line 3B in FIG. 3A, in the comparative example shown in FIG. 3B, the transmittance is −20 dB or less in the frequency range from 0.1 MHz to 1 GHz, and the effect of sufficiently reducing common mode noise is obtained. It turns out that it is obtained. However, in the comparative example shown in FIG. 3B, compared to the comparative example shown in FIG. 3C and the first embodiment shown in FIG. The mounting area of the first inductor L1 and the second inductor L2 becomes large.

  In the comparative example shown in FIG. 3C, coils having a low inductance are used as the inductors L3 and L4 compared to the comparative example of FIG. 3B. However, as shown by a solid line 3C in FIG. 3A, it can be seen that the transmittance is higher than that of the comparative example shown in FIG. 3B. That is, the effect of reducing common mode noise is low.

  In the first embodiment shown in FIG. 3D, as shown by a solid line 3D in FIG. 3A, the transmittance is a minimum value in the vicinity of the resonance frequency 480 kHz with respect to the common mode component of the first shunt circuit 22 and the second shunt circuit 32. (Insertion loss shows maximum value). This resonance frequency is set substantially equal to the switching frequency of the class D amplifier. For this reason, common mode noise in the switching frequency region can be effectively suppressed. The common mode noise suppression effect in the vicinity of the switching frequency is equal to or greater than that of the comparative example shown in FIG. 3B. Furthermore, even in the frequency range of 100 kHz or more and less than 480 kHz, the class D amplifier circuit according to the first embodiment shown in FIG. 3D may have a common mode noise suppressing effect substantially equivalent to that in the comparative example shown in FIG. 3B. Recognize.

  The average of the resonance frequency 480 kHz and the antiresonance frequency 679 kHz of the class D amplifier circuit according to the first embodiment shown in FIG. 3D is 579.5 kHz. In the frequency range below the average value of the resonance frequency and the anti-resonance frequency, the transmittance of the class D amplifier circuit according to the first embodiment shown in FIG. 3D is lower than the transmittance of the class D amplifier circuit shown in FIG. 3C. . This means that the common mode noise suppression effect is improved by inserting the first shunt circuit 22 and the second shunt circuit 32 (FIG. 1).

  In Example 1 shown in FIG. 3D, a common mode noise suppression effect equivalent to that of the comparative example of FIG. 3B is obtained in a frequency region below the switching frequency without using a high-inductance coil as in the comparative example of FIG. 3B. be able to. Since it is not necessary to use a high-inductance coil as the inductors L3 and L4, the mounting area of the inductors L3 and L4 can be reduced.

  In addition, as the first inductor L1 and the second inductor L2, circuit components housed in one package as shown in FIG. 2 are used. For this reason, the expansion of the mounting area by mounting the first inductor L1 and the second inductor L2 can be suppressed.

  Next, the transmittance when the resonance frequency and antiresonance frequency of the class D amplifier circuit according to the first embodiment are changed will be described with reference to FIGS. 4A to 4C.

  FIG. 4A shows the simulation result of the transmittance spectrum of common mode noise in the class D amplifier circuit as in FIG. 3A. The horizontal axis represents the frequency in the unit “MHz”, and the vertical axis represents the transmittance in the unit “dB”. A broken line 3B and a solid line 3C in FIG. 4A are the same as those shown in FIG. 3A. That is, the broken line 3B and the solid line 3C indicate the transmittance of the class D amplifier circuit according to the comparative example illustrated in FIGS. 3B and 3C, respectively.

  A solid line 4B and a solid line 4C in FIG. 4A indicate the transmittance of the class D amplifier circuit according to the first embodiment illustrated in FIGS. 4B and 4C, respectively. In the class D amplifier circuit shown in FIG. 4B and FIG. 4C, the inductances of the inductors L3 and L4, the capacitances of the capacitors C3 and C4, and the combined inductance Lc for the common mode components of the first shunt circuit 22 and the second shunt circuit 32 Are identical to these values shown in FIG. 3D. In the class D amplifier circuit shown in FIG. 4B, the capacitances of the first capacitor C1 and the second capacitor C2 are both set to 0.6 μF. In the class D amplifier circuit shown in FIG. The capacitances of the first capacitor C1 and the second capacitor C2 are both set to 22000 pF.

  The resonance frequency of the class D amplifier circuit shown in FIG. 4B is about 291 kHz, and the anti-resonance frequency is about 561 kHz. The resonance frequency of the class D amplifier circuit shown in FIG. 4C is about 1.52 MHz, and the anti-resonance frequency is about 1.59 MHz.

  In the class D amplifier circuit shown in FIG. 4B, similarly to the class D amplifier circuit shown in FIG. 3D, the class D amplifier circuit shown in FIG. It can be seen that the common mode noise suppression effect is almost equivalent to

  From the simulation result of the class D amplifier circuit shown in FIG. 3D (solid line 3D in FIG. 3A) and the simulation result of the class D amplifier circuit shown in FIG. 4B (solid line 4B in FIG. 4A), the first low-pass filter 21, second By making the average value of the resonance frequency and antiresonance frequency of the low-pass filter 31, the first shunt circuit 22, and the second shunt circuit 32 with respect to the common mode component equal to or higher than the switching frequency of the class D amplifier circuit, It can be seen that a sufficient suppression effect of common mode noise in the switching frequency region and lower frequency regions can be obtained.

  In the class D amplifier circuit shown in FIG. 4C, as shown by the solid line 4C in FIG. 4A, the transmittance is the class D amplifier shown in FIG. 3B in the frequency region below the average value of the resonance frequency and the antiresonance frequency. Although not as low as the circuit transmittance (dashed line 3B), it is lower than the equivalent ratio (solid line 3C) of the class D amplifier circuit shown in FIG. 3C. That is, common mode noise is reduced compared to the comparative example shown in FIG. 3C. The class D amplifier circuit of FIG. 4C is obtained by adding a first shunt circuit 22 and a second shunt circuit 32 to the class D amplifier circuit of FIG. 3C, and therefore the first shunt circuit 22 and the second shunt circuit. By adding 32, it can be said that a certain common mode noise reduction effect is obtained.

  However, in the frequency range significantly lower than the resonance frequency of the class D amplifier, the difference between the transmittance of the class D amplifier circuit shown in FIG. 4C and the transmittance of the class D amplifier circuit shown in FIG. 3C becomes small. . In other words, if the resonance frequency of the class D amplifier circuit is too high compared to the switching frequency, the common mode noise reduction effect in the switching frequency region is reduced.

  In the simulation result shown in FIG. 4A, when the switching frequency is 480 kHz, a certain common mode noise reduction effect can be obtained by employing the class D amplifier circuit of FIG. 4C having a resonance frequency of about 1.52 MHz. Recognize. It can be said that when the resonance frequency for the common mode component of the class D amplifier circuit is three times or less the switching frequency, a constant common mode noise reduction effect can be obtained.

  Next, a class D amplifier circuit according to the second embodiment will be described with reference to FIGS. Hereinafter, differences from the first embodiment will be described, and description of common configurations will be omitted.

  FIG. 5 shows an equivalent circuit diagram of the class D amplifier circuit according to the second embodiment. In the first embodiment, the first inductor L1 (FIG. 1) of the first shunt circuit 22 and the second inductor L2 (FIG. 1) of the second shunt circuit 32 have a mutual inductance that is negatively coupled. It was. In the second embodiment, the first inductor L1 and the second inductor L2 have a mutual inductance that is positively coupled.

  FIG. 6 is a perspective view of a circuit component in which the first inductor L1 and the second inductor L2 are housed in one package. Two coils 41 and 42 are formed by two wires wound around the core 35. In FIG. 6, one coil 41 is represented by a solid line, and the other coil 42 is represented by a broken line. One coil 41 corresponds to the first inductor L1, and the other coil 42 corresponds to the second inductor L2.

  In the first embodiment, as shown in FIG. 2, the two coils 41 and 42 are wound in opposite directions. In the second embodiment, the two coils 41 and 42 are wound in the same direction. In other words, if one coil 41 is right-handed, the other coil 42 is also right-handed, and if one coil 41 is left-handed, the other coil 42 is also left-handed. External electrodes 37 and 38 are formed on each of the flange portions 36 attached to both ends of the winding core 35.

  As shown in FIG. 5, the current I1 flowing from the first signal line 20 to the ground GND through the first inductor L1 is the first end of the winding core 35 (FIG. 6). The second end to the second end. On the other hand, the current I2 flowing from the second signal line 30 to the ground GND through the second inductor L2 is the second end of the winding core 35 (FIG. 6). From the end) to the first end.

  For this reason, the common mode component of the current flowing through the first signal line 20 and the second signal line 30 flows through the first inductor L1 and the second inductor L2, so as in the case of the first embodiment. Magnetic fields opposite to each other are generated. Therefore, as in the case of the first embodiment, an effect of reducing common mode noise flowing into the load 50 can be obtained.

  Each of the above-described embodiments is an exemplification, and needless to say, partial replacement or combination of the configurations shown in the different embodiments is possible. About the same effect by the same composition of a plurality of examples, it does not refer to every example one by one. Furthermore, the present invention is not limited to the embodiments described above. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

10 pulse width modulation circuit 11 first gate driver 12 second gate driver 13 first switching circuit 14 second switching circuit 20 first signal line 21 first low-pass filter 22 first shunt circuit 30 second Signal line 31 second low-pass filter 32 second shunt circuit 35 core 36 flange 37, 38 external electrodes 41, 42 coil 50 load C1 first capacitor C2 second capacitor C3, C4 capacitor GND of low-pass filter Ground I1, I2 Current Id Differential mode signal current L1 First inductor L2 Second inductor L3, L4 Low pass filter inductor Lc Inductance Ld for common mode component Sa Inductance Sa for differential mode component Audio signal T1 First terminal 2 a second terminal TO1 first output terminal TO2 second output terminal VDD supply voltage

Claims (5)

A first signal line and a second signal line through which a differential mode signal current flows;
A first low-pass filter inserted in the first signal line;
A second low-pass filter inserted in the second signal line;
A first shunt circuit comprising a series circuit of a first inductor and a first capacitor, and inserted between the first signal line and ground;
A series circuit of a second inductor and a second capacitor, and a second shunt circuit inserted between the second signal line and the ground,
A class D amplifier circuit in which the first inductor and the second inductor are coupled so that magnetic fluxes due to a common mode component of current are weakened. The differential mode signal current input to one end of the first signal line and the second signal line is pulse-width modulated,
The average value of the resonance frequency and the antiresonance frequency for the current of the common mode component of the first low-pass filter, the second low-pass filter, the first shunt circuit, and the second shunt circuit is the pulse width. The class D amplifier circuit according to claim 1, wherein the class D amplifier circuit is equal to or higher than a switching frequency of the modulated signal current.   The class D amplifier circuit according to claim 1 or 2, wherein a self-inductance of the first inductor and a self-inductance of the second inductor are the same.   The first inductor and the second inductor are composed of coils wound around a common winding core in opposite directions, and a common current flowing through the first signal line and the second signal line. 4. The class D amplifier circuit according to claim 1, wherein a magnetic field having a direction opposite to each other is generated when a mode component flows through the coil of the first inductor and the coil of the second inductor. 5. .   The first inductor and the second inductor are composed of coils wound around a common winding core in the same direction, and currents flowing through the first signal line and the second signal line 4. The class D amplifier according to claim 1, wherein a common mode component flows in the first inductor coil and the second inductor coil to generate magnetic fields in opposite directions. 5. circuit.

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