Class D Amplifier

Abstract

To reduce electromagnetic radiation of a class-D amplifier.SOLUTION: A class-D amplifier 100 comprises an input amplification circuit 10, a modulation circuit 20, an output amplification circuit 40, and an output filter 50, all of which are mounted on a single printed circuit board 300. The input amplification circuit 10 amplifies an input signal using input ground G1 as a reference potential. The modulation circuit 20 outputs a pulse that has been modulated using the signal amplified by the input amplification circuit 10 and whose switching frequency is 1.7 MHz or higher. The output amplification circuit 40 amplifies the pulse using output ground G2 as a reference potential. The output filter 50 generates an output signal by allowing a low-frequency component of the amplified pulse to pass therethrough. On the printed circuit board 300, a solid pattern 302 of the output earth G2 is formed across the input amplification circuit 10, the modulation circuit 20, the output amplification circuit 40, and the output filter 50.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a class D amplifier that drives a load with pulses modulated based on an input signal. [Background technology]

[0002] Patent Document 1 discloses a class D amplifier that has an input amplifier circuit that amplifies an input signal, a modulation and amplification circuit that outputs a pulse that is pulse-width modulated by the output signal of the input amplifier circuit, and an output filter that passes low-frequency components of the pulse output by the modulation and amplification circuit and supplies it to a load, and negatively feeds back the output signal of the output filter to the input of the input amplifier circuit. This class D amplifier can amplify the input signal with low distortion and high efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 6,297,692 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the performance of the semiconductor switching elements that make up class-D amplifiers has improved, making it possible to increase the switching speed of class-D amplifiers by more than an order of magnitude compared to conventional methods. However, increasing the switching frequency of a class-D amplifier increases the amount of unwanted electromagnetic radiation from the amplifier.

[0005] The present invention has been made in consideration of the above-described circumstances, and has an object to suppress unwanted radiation in a class D amplifier. [Means for solving the problem]

[0006] The present invention provides a class D amplifier comprising an input amplifier circuit, a modulation circuit, an output amplifier circuit, and an output filter mounted on a single printed circuit board, wherein the input amplifier circuit amplifies an input signal using an input earth as a reference potential, the modulation circuit outputs a pulse having a switching frequency of 1.7 MHz or more modulated by the signal amplified by the input amplifier circuit, the output amplifier circuit amplifies the pulse using an output earth as a reference potential, and the output filter passes low-frequency components of the amplified pulse to generate an output signal, and wherein on the printed circuit board a solid pattern of the output earth is formed across the input amplifier circuit, the modulation circuit, the output amplifier circuit, and the output filter.

[0007] The present invention also provides a class D amplifier having an input amplifier circuit, a modulation circuit, an output amplifier circuit, and an output filter mounted on a single printed circuit board, wherein the input amplifier circuit amplifies an input signal using an input earth as a reference potential, the modulation circuit outputs a pulse modulated by the signal amplified by the input amplifier circuit, the output amplifier circuit amplifies the pulse using an output earth as a reference potential, and the output filter passes low-frequency components of the amplified pulse to generate an output signal, and on the printed circuit board, a solid pattern of the output earth is formed across the input amplifier circuit, the modulation circuit, the output amplifier circuit, and the output filter, and the class D amplifier further has a feedback circuit that negatively feeds back the voltage at a connection point of the output filter with one end of the load to the inverting input of the input amplifier circuit, and a feedback circuit that negatively feeds back the voltage between the connection point of the solid pattern with the other end of the load to the non-inverting input of the input amplifier circuit. [Brief description of the drawings]

[0008] [Figure 1] 1 is a circuit diagram showing a configuration of a class-D amplifier according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a layout diagram showing the configuration of the class D amplifier mounted on a printed circuit board. [Diagram 3]FIG. 1 is a layout diagram of a class-D amplifier as a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 is a circuit diagram showing the configuration of a class-D amplifier 100 according to an embodiment of the present invention. This class-D amplifier 100 includes an input amplifier circuit 10, a modulation circuit 20, a separation section 30, an output amplifier circuit 40, an output filter 50, and a feedback circuit 60. In this class-D amplifier 100, the input amplifier circuit 10 and the modulation circuit 20 operate with an input earth G1 as a reference potential, and the output amplifier circuit 40 operates with an output earth G2 as a reference potential.

[0010] The input amplifier circuit 10 is an amplifier that amplifies an input signal given as a difference voltage between input terminals 15p and 15n, and includes differential amplifiers 11 and 12 and a capacitor 13. The non-inverting input of the differential amplifier 11 is connected to the input terminal 15p via a resistor R1, and is also connected to an input earth G1 via a resistor R3. The inverting input of the differential amplifier 11 is also connected to the input terminal 15n via a resistor R2, and is also connected to the input earth G1 via a resistor R4. The differential amplifier 11 amplifies a voltage difference caused by a positive-phase input signal and a negative-phase input signal supplied from the input terminals 15p and 15n via resistors R1 and R2, respectively. The differential amplifier 12 operates as an integrator by connecting a capacitor 13 between its output and inverting input. This integrator integrates the difference voltage between the signal output by the differential amplifier 11 and a voltage-divided first feedback signal supplied from an intermediate node between resistors R9 and R7, which will be described later, and outputs the integrated signal as a first output signal amplified by the input amplifier circuit 10.

[0011] The modulation circuit 20 has a comparator 21 and a triangular wave generating section 22 that outputs a triangular wave signal of a predetermined frequency as a carrier signal. The comparator 21 compares the first output signal with the triangular wave signal output by the triangular wave generating section 22, thereby generating and outputting a first pulse that is pulse width modulated by the first output signal.

[0012] The separator 30 is a circuit that transmits the first pulse to the input of the output amplifier circuit 40 while electrically isolating the input of the output amplifier circuit 40 from the output of the modulation circuit 20, and is configured, for example, by a photocoupler or a transformer. More specifically, the separator 30 generates a voltage proportional to the voltage difference between the output of the modulation circuit 20 and the input earth G1 as an isolated first pulse between the input of the output amplifier circuit 40 and the low-potential power supply line 102. Note that, instead of such a separator 30, a level shifter that shifts the voltage of the first pulse and outputs the shifted first pulse may be used.

[0013] The output amplifier circuit 40 includes a driver 43 and output stage transistors 41 and 42 capable of switching power at a high frequency (1.7 MHz or more). For example, the output stage transistors 41 and 42 are GaN transistors (Gallium nitride transistors). A positive voltage is supplied to the drain of the output stage transistor 41 from an external positive power supply B101 via a power supply line 101 and a power supply terminal 17p. A source of the output stage transistor 41 is connected to the drain of the output stage transistor 42, and the common connection node is the output of the output amplifier circuit 40. A negative voltage is supplied to the source of the output stage transistor 42 from an external negative power supply B102 via a power supply line 102 and a power supply terminal 17n. The reference potential of the positive power supply B102 and the negative power supply B101 is the output earth G2. A power supply capacitor C101 is connected in parallel to the positive power supply B101, and a power supply capacitor C102 is connected in parallel to the negative power supply B102.

[0014] The driver 43 is a circuit that drives the output stage transistors 41 and 42 based on the isolated first pulse. More specifically, when the voltage of the isolated first pulse is lower than a predetermined reference voltage, for example, the driver 43 turns the output stage transistor 41 ON and turns the output stage transistor 42 OFF. When the voltage of the isolated first pulse is higher than a predetermined reference voltage, for example, the driver 43 turns the output stage transistor 41 OFF and turns the output stage transistor 42 ON. Due to the high-speed switching of the output stage transistors, a large current of a high frequency flows in the output section of the class-D amplifier circuit 100. In order to increase power efficiency and reduce unnecessary radiation, it is desirable to make the current path of the printed circuit board 300 as short as possible.

[0015] Therefore, when a first pulse is provided to the driver 43 of the output amplifier circuit 40 via the separator 30, a second pulse is output from the output of the output amplifier circuit 40. This second pulse is a pulse having an H level corresponding to the positive voltage of the power supply line 101 and an L level corresponding to the negative voltage of the power supply line 102. In this manner, the output amplifier circuit 40 power amplifies the first pulse and outputs it as the second pulse.

[0016] The output filter 50 is composed of an inductance 51 and a capacitor 52 connected in series and inserted between the output of the output amplifier circuit 40 and the output earth G2. A common connection node of the inductance 51 and the capacitor 52 is connected to the output terminal 16p of the class D amplifier 100, and a connection node between the inductance 51 and the capacitor 52 at the output earth G2 is connected to the output terminal 16n of the class D amplifier 100. A load 53 is connected between the output terminals 16p and 16n. The load 53 is, for example, a speaker, but may also be a motor or a light-emitting element. The output filter 50 passes the low-frequency components of the PWM pulse (second pulse) amplified by the output amplifier circuit 40, and generates an output signal to be supplied to the load 53. When the input signal is an audio signal, the audio signal obtained by power-amplifying the input signal is generated as the output signal.

[0017] A low-pass filter F8, which is a series connection of a resistor R8 and a capacitor C8, is connected in parallel to the output filter 50. Resistors R9 and R7 are connected in series between a common connection node of the resistor R8 and the capacitor C8 and the input earth G1, and the common connection node of the resistors R9 and R7 is connected to the inverting input of the differential amplifier 12 of the input amplifier circuit 10. In the class D amplifier circuit 100, the low-frequency component of the second pulse output from the output amplifier circuit 40 passes through the low-pass filter F8 as a first feedback signal, and the first feedback signal is divided by the resistors R9 and R7 and negatively fed back to the input of the differential amplifier 12. This negative feedback improves the linearity of amplification from the differential amplifier 12 to the output terminal of the class D amplifier circuit 100.

[0018] The feedback section 60 includes a feedback circuit 61 in which a resistor R5 and a capacitor C5 are connected in parallel, and a feedback circuit 62 in which a resistor R6 and a capacitor C6 are connected in parallel. The feedback circuit 61 negatively feeds back the potential of the output earth G2 (potential on the cold side of the output signal) as a third feedback signal to the non-inverting input of the differential amplifier 11 of the input amplifier circuit 10. The feedback circuit 62 negatively feeds back the potential of the common connection node of the inductance 51 and the capacitor 52 (potential on the hot side of the output signal) as a second feedback signal to the inverting input of the differential amplifier 11 of the input amplifier circuit 10. That is, the feedback section 60 negatively feeds back to the input of the class D amplifier 100 the voltage of a connection point (common connection node of the inductance 51 and the capacitor 52) with one end of the load 53 in the output filter 50, and also negatively feeds back the voltage of a connection point (connection point with the capacitor 52) with the other end of the load 53 in the output earth G2. This negative feedback improves the linearity of amplification for the entire class D amplifier circuit 100 (from the input terminal to the output terminal). Since the voltage of the output terminal 16n is negatively fed back in addition to the voltage of the output terminal 16p, even if the potential of the output earth G2 connected to the output terminal 16n changes dynamically at a high switching frequency, the adverse effect of this on the output signal can be suppressed.

[0019] Fig. 2 is a layout diagram showing the configuration of the class D amplifier 100 mounted on one printed circuit board 300. As shown in Fig. 2, the input amplifier circuit 10, the modulation circuit 20, the separator 30, the output amplifier circuit 40, the output filter 30, and the power supply capacitors C101 and C102 of Fig. 1 are mounted on the printed circuit board 300. In order to shorten the current path at the output of the class D amplifier circuit 100, the output amplifier circuit 40, the output filter 50, and the power supply capacitors C101 and C102 are arranged close to each other.

[0020] The printed circuit board 300 is also provided with input terminals 15p and 15n, output terminals 16p and 16n, and power supply terminals 17p and 17n shown in FIG. 1. For example, an audio signal transmitted in a balanced manner from a sound source (not shown) is applied as an input signal to the input terminals 15p and 15n. An external load 53 such as a speaker is connected between the output terminals 16p and 16n. An external positive power supply B101 and a negative power supply 17n are connected to the power supply terminals 17p and 17n, respectively.

[0021] In addition, the printed circuit board 300 is formed with a feedback path 311 for a first feedback signal from the output filter 50 to the input amplifier circuit 10, a feedback path 312 for a second feedback signal from the output terminal 16p to the input amplifier circuit 10, and a feedback path 313 for a third feedback signal from the output terminal 16n connected to the output earth G2 to the input amplifier circuit 10.

[0022] Here, the feedback path 311 includes the low-pass filter F8 and resistors R9 and R7 in FIG. 1 in the vicinity of the input amplifier circuit 10. The feedback path 312 includes the feedback circuit 62 in FIG. 1 in the vicinity of the input amplifier circuit 10. The feedback path 313 includes the feedback circuit 61 in FIG. 1 in the vicinity of the input amplifier circuit 10. The printed circuit board 300 is formed with a solid pattern 302 of the input amplifier circuit 10, the modulation circuit 20, the separation unit 30, the output amplifier circuit 40, the output filter 50, the power supply capacitors C101 and C102, and an output earth G2 that spans the entire feedback paths 311 to 313. The printed circuit board is multi-layered, and the solid pattern 302 is provided in a layer different from the wiring of the other circuits including the feedback paths. In this embodiment, the feedback path 312 negatively feeds back the second feedback signal to the inverting input of the input amplifier circuit 10, and the feedback circuit 313 negatively feeds back the third feedback signal to the non-inverting input of the input amplifier circuit 10.

[0023] According to this embodiment, the solid pattern 302 of the output earth G2 is formed across the entire circuit constituting the class D amplifier 100, particularly across the input amplifier circuit 10, the modulation circuit 20, the output amplifier circuit 40, and the output filter 50. Therefore, even if an output current with a frequency one order of magnitude higher than that of a general class D amplifier flows, unwanted radiation of the class D amplifier 100 can be suppressed.

[0024] 3 is a layout diagram showing a mounting state on a printed circuit board 300 of a general class-D amplifier 100' with a low switching frequency (less than 1.7 MHz) as a comparative example of this embodiment. In a class-D amplifier with a low switching frequency, unnecessary radiation can be sufficiently suppressed by providing a solid pattern 302 of the output earth G2 so as to straddle the output amplifier circuit 40 and the output filter 50 after the separation unit 30. In addition, in order to prevent noise from jumping into the input signal, a solid pattern 301 of the input earth G1 is provided that straddles the input amplifier circuit 10 and the modulation circuit 20, separate from the solid pattern 302. In addition, when the switching frequency is low, the effect of inductance in the current path is small, so the feedback path 313 in this embodiment is not necessary.

[0025] In this embodiment (Figure 2), in order to suppress unwanted radiation at high switching frequencies, a solid pattern 302 of the output earth G2 having a larger area than that of the comparative example is formed across the input amplifier circuit 10, the modulation circuit 20, the output amplifier circuit 40 and the output filter 50.

[0026] In this embodiment, since the solid pattern 302 is wide, it is difficult to identify the output current path, and furthermore, since the switching frequency is high, the adverse effect of inductance in the current path becomes large.

[0027] However, in this embodiment, the feedback path 312 negatively feeds back the second feedback signal of the output terminal 16p (the connection point of the output filter 50 with one end of the load 53) to the input amplifier circuit 10, and the feedback path 313 negatively feeds back the third feedback signal of the output terminal 16n (the connection point of the solid pattern 302 of the output earth G2 with the other end of the load 53) to the input amplifier circuit 10, so that even in the severe conditions of the wide solid pattern 302 and the high switching frequency, the input signal can be amplified without deteriorating the distortion rate. Also, in this embodiment, the output stage transistors 41 and 42 perform power switching at a high frequency of 1.7 MHz or more, so there is an advantage that the frequency of the switching noise is outside the band of AM (Amplitude modulation) radio and no interference with AM radio occurs.

[0028] <Other embodiments> Although the embodiment of the present invention has been described above, other embodiments of the present invention are also possible. For example, the following embodiments are possible.

[0029] (1) In the above embodiment, the modulation circuit 20 outputs a PWM pulse that is pulse width modulated by the signal amplified by the input amplifier circuit 10. However, the modulation circuit 20 may output a PDM (Pulse Density Modulation) pulse that is pulse density modulated by the signal amplified by the input amplifier circuit 10.

[0030] (2) The input earth G1 may be a solid pattern or may be a normal earth wiring. Regardless of whether the input earth G1 is a solid pattern or not, the input earth G1 is connected to the solid pattern 302 of the output earth G2 by a low impedance.

[0031] (3) In the above embodiment, GaN transistors are used as the output stage transistors 41 and 42. However, if there are other transistors capable of equivalent high-speed and efficient power switching, they may be used.

[0032] (4) In the above embodiment, a triangular wave is used as the carrier signal. However, a signal having a different shape, such as a sawtooth wave, may be used. [Explanation of symbols]

[0033] 100,100'...Class D amplifier, 15p,15n...input terminal, 10...input amplifier circuit, 11,12...differential amplifier, 13,52,C8,C5,C6...capacitor, R1,R2,R3,R4,R5,R6,R7,R8,R9...resistor, 20...modulation circuit, 21...comparator, 22...triangular wave generator, 30...separator, 40...output amplifier circuit, 41,42...output stage transistor, 16p,16n...output terminal, 50...output filter, 51...inductance, 53...load, G1...input earth, G2...output earth, B101,B102...DC power supply, 17p,17n...power supply terminal, C101,C102...power supply capacitor, F8...low-pass filter, 60...feedback circuit, 61,62...feedback filter, 301,302...solid patterns.

Claims

1. A class D amplifier including an input amplifier circuit, a modulation circuit, an output amplifier circuit, and an output filter, which are mounted on a single printed circuit board, The input amplifier circuit amplifies an input signal using an input ground as a reference potential, the modulation circuit outputs a pulse having a switching frequency of 1.7 MHz or more, the pulse being modulated by the signal amplified by the input amplifier circuit; the output amplifier circuit amplifies the pulse with an output ground as a reference potential; the output filter passing a low-pass component of the amplified pulse to generate an output signal; In the printed circuit board, a solid pattern of the output earth is formed across the input amplifier circuit, the modulation circuit, the output amplifier circuit, and the output filter.

2. A class D amplifier including an input amplifier circuit, a modulation circuit, an output amplifier circuit, and an output filter, which are mounted on a single printed circuit board, The input amplifier circuit amplifies an input signal using an input ground as a reference potential, the modulation circuit outputs a pulse modulated by the signal amplified by the input amplifier circuit; the output amplifier circuit amplifies the pulse with an output ground as a reference potential; the output filter passing a low-pass component of the amplified pulse to generate an output signal; In the printed circuit board, the solid pattern of the output earth is formed across the input amplifier circuit, the modulation circuit, the output amplifier circuit, and the output filter, The class D amplifier further includes a feedback circuit that negatively feeds back the voltage at a connection point between the output filter and one end of the load to the inverting input of the input amplifier circuit, and a feedback circuit that negatively feeds back the voltage between the connection point between the solid pattern and the other end of the load to the non-inverting input of the input amplifier circuit.

3. 3. The class D amplifier according to claim 1, wherein the output amplifier circuit amplifies the pulse using a GaN transistor.

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