Class D audio amplifier and associated soundbar

Abstract

TITLE: Class D Audio Amplifier and Associated Soundbar The present invention relates to a Class D audio amplifier comprising: - a main input (10) for a digital signal to be amplified, - a digital amplification module (16), - a feedback loop (19) comprising a summing junction (32) one amplification input of which is connected to the output of the digital amplification module and another input of which is connected to the main input through a digital-to-analog converter suitable for providing an input current, the output of the summing junction being connected through an analog-to-digital converter to the input of a subtractor the other input of which is connected to the main input and the output of which is connected to the input of the digital amplification module, characterized in that the summing junction comprises means (38, 40,42) of conversion of the output voltage of the digital amplification module into a feedback current and is designed to ensure the sum of the input current and the feedback current. Figure for the abbreviation: Figure 1,

Description

Title of the invention: Class D audio amplifier and associated soundbar

[0001] The present invention relates to a class D audio amplifier.

[0002] Given the technologies available today, a person skilled in the art is able to manufacture high-performance audio amplifiers in order to obtain speakers and soundbars with very good sound quality or with easily accessible technology.

[0003] US patent 10256777 describes a digital Class D audio amplifier comprising a digital input signal, a digital amplification module, and a feedback loop. The digital input signal is first compared to a digital feedback signal from the feedback loop. The output signal from the feedback loop subtractor is then modulated by a modulation block, amplified by a push-pull configuration, and filtered using passive components. The input signal is also used within the feedback loop to improve the accuracy of the Class D audio amplifier.

[0004] However, the feedback loop is often very complex. Indeed, the feedback loop includes an analog summing junction, and this summing junction is designed to add two voltages: the output signal voltage and the input signal voltage. Since the input signal is a digital signal, a digital-to-analog converter is necessary to add the two voltages. Existing digital-to-analog converters on the market convert the digital signal into an analog output signal, but this latter signal is by default a current. A current-to-voltage converter is therefore also required.

[0005] In addition, in order to ensure that the summed signal is not disturbed, an analog filter is connected at the output of the summing ...

[0006] It is then observed that the class D audio amplifier has several complex and not very robust components which make it less functional.

[0007] The aim of the invention is therefore to provide a simpler and more efficient class D audio amplifier.

[0008] To this end, the invention relates to a class D audio amplifier comprising:

[0009] - a main input for a digital signal to be amplified,

[0010] - a digital amplification module,

[0011] - a feedback loop comprising a summing stump with an input The amplifier is connected to the output of the digital amplifier module and whose another input is connected to the main input through a dedicated digital-to-analog converter to provide an input current, the output of the summing stump being connected via an analog-to-digital converter to the input of a subtractor whose other input is connected to the main input and whose output is connected to the input of the digital amplification module,

[0012] the summing unit comprising means for converting the output voltage of the digital amplification module into a return current and is suitable for ensuring the summation of the input current and the return current.

[0013] The class D audio amplifier proposed by the invention makes it possible to create a summing device capable of adding two currents without the need for a current-voltage converter.

[0014] According to other advantageous aspects of the invention, the class D audio amplifier comprises one or more of the following features, taken individually or in any technically possible combination:

[0015] - the summing junction comprises a linear amplifier selected from the group consisting of operational amplifier and a transconductance amplifier;

[0016] - the summing junction includes an input resistor connected to the output of the module digital amplification, and a feedback resistor connected between an inverting input and the output of the linear amplifier;

[0017] - the amplification module includes a push-pull configuration and an analog filter connected to the output of the push-pull circuit and the amplification input of the summing amplifier is connected to the output of the analog filter;

[0018] - the amplification module includes a push-pull configuration connected to the output of a digital modulator connected to the output of the subtractor, said digital modulator comprising a low-pass digital filter;

[0019] - the digital modulator includes a programmable digital controller, the controller being suitable for implementing a type of controller chosen from the group consisting of: a phase-lead controller, an integral controller, a proportional controller, a differentiator controller, a proportional-differentiator-integral controller, and a phase-lag controller; and

[0020] - the proportional-integral controller is suitable for correcting a linear approximation or non-linear analog filter.

[0021] The invention also relates to a soundbar comprising a class D audio amplifier as defined above.

[0022] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0023] [Fig-1] [Fig.1] is a schematic diagram of a class D audio amplifier; and

[0024] [Fig.2] [Fig.2] is a Bode plot of the gain of the amplifier filter Class D audio, with a gain from the Class D audio amplifier corrector and a gain from the Class D audio amplifier.

[0025] The Class D audio amplifier 8 illustrated in [Fig. 1] is, for example, integrated into a soundbar. The amplifier 8 includes a main input 10 for a digital signal to be amplified. The signal to be amplified is, for example, a voltage.

[0026] The main input 10 is connected to a digital subtractor 14. The output of the subtractor 14 is connected to the input of a digital amplifier module 16. The subtractor 14 is capable of performing a subtraction between the main input 10 and another input 18 from a feedback loop 19.

[0027] Preferably, the digital amplification module 16 includes a digital modulator 20 connected at the output of the subtractor 14.

[0028] Preferably, the digital amplifier module 16 also includes a push-pull circuit 22 connected to the output of the digital modulator 20. The push-pull circuit 22, as known per se, comprises two transistors 22A, 22B connected in series between two supply potentials. The output of the push-pull circuit 22 is taken from a midpoint 22M between the two transistors. The gates of the two transistors 22A, 22B are connected to a control circuit 23, which is itself connected to the output of the digital modulator 20.

[0029] For example, a modulation method used by the digital modulator 20 is pulse-width modulation (PWM). This type of modulation is used to discretize a signal at the output of the subtractor 14 using a digital circuit (not shown). The modulation method used by the digital modulator 20 serves to generate a pseudo-analog signal for controlling the transistors 22A, 22B of the push-pull circuit 22 (in their open or closed states).

[0030] The digital amplification module 16 includes at the output of the push-pull circuit 22 an analog filter 24. By way of example, in [Fig.1] the analog filter 24 comprises a coil 25 connected to the midpoint 22M between the two transistors 22A, 22B on one side and is connected, on the other side, to a capacitor 26. The analog filter 24 is, for example, a low-pass filter itself connected to ground M.

[0031] A loudspeaker 27 is connected at the output of the filter between the coil 25 and the capacitor 26.

[0032] Alternatively, the digital amplification module 16 does not include an analog filter 24 and the midpoint between the two transistors 22A, 22B is connected directly to the loudspeaker 27. In this case, the digital modulator 20 includes a digital low-pass filter 30 in order to reproduce the integrating effect of the analog filter 24.

[0033] Preferably, the digital modulator 20 comprises a 28. [Fig. 2]. [Fig. 2] shows a curve Cl corresponding to the gain of the class D audio amplifier 8 for several frequencies. A bandwidth 29 of the amplifier 8 is also shown in [Fig. 2]. A curve C2 shows the gain of the low-pass filter 24 and a curve C3 shows the gain of the corrector.

[0034] Curves C2 and C3 have the same slopes but opposite signs between 40 kHz and 400 kHz. Since the gain of amplifier 8 depends on the gain of the low-pass filter 24 and the corrector of curves C2 and C3, it follows that the curve Cl of the gain of amplifier 8 gives a straight line 32 with a slope of zero between 40 kHz and 400 kHz.

[0035] By way of example, the 28 has 2, 3, or 4 poles allowing the bandwidth of the Class D audio amplifier 8 to be modified. Indeed, if the number of poles increases, the shape and therefore the slope of the C3 curve is modified across all frequencies. Consequently, the shape of the Cl curve and the bandwidth 29 are also modified across all frequencies.

[0036] Advantageously, the 28 is suitable for correcting a linear or non-linear approximation of the analog filter 24.

[0037] Depending on the type of corrector chosen for the adapter 28, the shape of the C3 curve is different.

[0038] Figure 2 shows an example where the corrector has two pairs of poles. Depending on the number of poles, the slope of the curves Cl and C2 is modified.

[0039] The feedback loop 19 includes a summing 32, one amplification input 34 of which is connected to the output of the digital amplification module 16 and the other input 35 of which is connected to the main input 10 through a digital-to-analog converter 36 suitable for providing an input current II.

[0040] The digital-to-analog converter 36 is, for example, adapted to have a fairly high signal-to-noise ratio (SNR). The signal-to-noise ratio is considered fairly high when it is greater than a value between 100 dB and 1 10 dB.

[0041] The summing 32 is suitable for converting the output voltage denoted V2 at the output of the digital amplification module 16 received on the input 34 into a return current 12 and is suitable for ensuring the summation of the input current II received on the input 35 and the return current 12.

[0042] The summing junction includes after the input 34 a resistance 37 for converting the voltage VI into the current II.

[0043] It further comprises a linear amplifier 38 whose inverting input is connected to the resistor 37 and to the input 35 to receive the sum of the currents II and 12.

[0044] The linear amplifier 38 is selected from the group consisting of an operational amplifier and a transconductance amplifier. The non-inverting input of the linear amplifier 38 is connected to a reference voltage Vref.

[0045] A feedback resistor 42 is connected between the inverting input 41 and the output of the linear amplifier 38 to receive the input current II and the feedback current 12 representative of the voltage VL

[0046] The output of the summing 32 is connected via an analog-to-digital converter 44 to the input 18 of the subtractor 14.

[0047] The input of the summing 32 is connected to the output of the analog filter 24.

[0048] Alternatively, the feedback loop 19, and consequently an input resistance 40, is connected at the output of the push-pull assembly 22 between the midpoint between the two transistors and the inverting input 41 of the linear amplifier 38.

[0049] The analog-to-digital converter 44 has a low resolution of between 4 and 10 bits maximum. This implies that the analog-to-digital converter 44 is fast and has a latency of between 0.1 and 1 microsecond.

[0050] Thanks to the characteristics described above, and more particularly thanks to the summing 32, the amplifier 8 is able to add two analog currents directly without needing a current-voltage converter.

[0051] In the case where the digital modulator 20 includes a digital low-pass filter, and therefore a filter much more precise than an analog filter, there is no longer any point in placing an analog filter at the output of the summing 32. The class D audio amplifier 8 then has the same functionalities as a classic class D audio amplifier for a smaller size.

[0052] In addition, the controller 28 is particularly advantageous since its parameters are not fixed and allow the amplifier 8 to be easily adaptable to any type of circuit.

Claims

Demands

1. Class D audio amplifier (8) comprising: - a main input (10) for a digital signal to be amplified, - a digital amplification module (16), - a feedback loop (19) comprising a summing junction (32) having one amplification input (34) connected to the output of the digital amplification module (16) and another input (35) connected to the main input (10) through a digital-to-analog converter (36) suitable for providing an input current (II), the output of the summing junction (32) being connected through an analog-to-digital converter (44) to the input of a subtractor (14) having the other input connected to the main input (10) and the output of which is connected to the input of the digital amplification module (16), characterized in that the summing junction (32) comprises means (38, 40,42) conversion of the output voltage (VI) of the digital amplification module (16) into a return current (12) and is suitable for ensuring the sum of the input current (II) and the return current (12).

2. Class D audio amplifier according to claim 1, wherein the summing junction (32) comprises a linear amplifier (38) selected from the group consisting of an operational amplifier and a transconductance amplifier.

3. Class D audio amplifier according to claim 1 or 2, wherein the summing junction (32) comprises an input resistor (40) connected to the output of the digital amplification module (16), and a feedback resistor (42) connected between an inverting input and the output of the linear amplifier (38).

4. Class D audio amplifier according to any one of the preceding claims, wherein the amplification module (16) comprises a push-pull assembly (22) and an analog filter (24) connected to the output of the push-pull assembly and the amplification input (34) of the summing junction (32) is connected to the output of the analog filter (24).

5. Class D audio amplifier according to any one of the preceding claims, wherein the amplification module (16) comprises a push-pull assembly (22) connected at the output of a digital modulator (20) connected at the output of the subtractor (14), said digital modulator (20) comprising a low-pass digital filter (28).

6. Class D audio amplifier according to claim 5, wherein the digital modulator (20) comprises a programmable digital controller (28), the controller (28) being suitable for implementing a type of corrector selected from the group consisting of: a phase-lead corrector, an integral corrector, a proportional corrector, a differentiator corrector, a proportional-differentiator, integral corrector and a phase-lag corrector.

7. Class D audio amplifier according to claims 4 and 6, wherein the integral proportional corrector is suitable for correcting a linear or non-linear approximation of the analog filter (24).

8. Soundbar comprising a class D audio amplifier (8) according to any one of claims 1 to 7.

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