Amplifier circuit and method for amplifying audio signal

Abstract

To provide an amplifier circuit and an amplifying method for amplifying an audio signal which has no noise or distortion and is galvanic-insulated.SOLUTION: An amplifier circuit 1 comprises: an input stage I for receiving a first input signal Vin+; a transformer T including a primary winding L1 and a secondary winding L2 which define a first terminal m1, a second terminal m2 and a middle terminal m3; a differential amplifier U having a second input U- connected to a middle terminal of a first secondary winding connected to a first terminal of the secondary winding and output UOUT connected to a second terminal of the secondary winding; an additional transformer T' including an additional primary winding L1' and a secondary winding L2' that define the first terminal, the second terminal and the middle terminal; an additional differential amplifier U' having a first input U+' of the additional secondary winding, a second input U-' connected to the middle terminal of the additional secondary winding, and an output connected to the second terminal of the additional secondary winding; and an output circuit O for receiving as input the output signals from the differential amplifier U and the additional differential amplifier U' to generate a differential output signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an amplifier circuit and a method for amplifying an audio signal. [Background technology]

[0002] In the field of audio signal amplifiers, there is a need to minimize noise and distortion associated with the signal.

[0003] Traditionally, the prior art has taught the use of solutions that involve galvanically isolating the signal input stage from the signal amplification stage to make the amplifier circuit more robust against external signal noise.

[0004] An example of a solution involving galvanic isolation involves first digitizing the input signal, decoupling it via an optical transmission system (particularly an optocoupler), and then reconverting the digital signal to an analog signal and feeding it as input to the speaker. This solution uses active electronic elements (particularly operational amplifiers and / or analog-to-digital converters) that require a dedicated power supply before decoupling. This solution therefore has the disadvantage of requiring additional isolation of the power supply section.

[0005] Another solution involves the use of a transformer to galvanically isolate the input stage from the amplifier stage. However, the magnetic field induced in the transformer is not linear, which causes distortion of the signal passing through the transformer. Patent documents US4567443 and US3828269 describe examples of reducing the distortion generated by the transformer. In particular, in document US4567443, the output signal from the differential amplifier is fed to the secondary winding of an additional transformer electrically connected to the first transformer.

[0006] On the other hand, in document US 3828269, the output signal from the differential amplifier is fed to one end of the secondary winding of the transformer itself, but this solution tends to increase the sensitivity of the circuit to external noise, meaning that the transformer must be shielded with an inert material, making the system very expensive.

[0007] In addition, although examples of amplifier circuits are described in patent documents US2020 / 127620A1 and US2710312A, neither document can meet market needs. Summary of the Invention

[0008] SUMMARY OF THE INVENTION The present disclosure aims to provide an amplifier circuit and method for amplifying an audio signal to overcome the above-mentioned drawbacks of the prior art.

[0009] In particular, it is an object of the present disclosure to provide an amplifier circuit and method for amplifying an audio signal that can produce a noise-free, distortion-free, galvanically isolated output signal.

[0010] Another object of the invention is to propose an amplifier circuit that is able to suppress common-mode noise. The invention also makes it possible to extend the low-frequency response using a small transformer.

[0011] Furthermore, the present invention provides an amplifier circuit and method for amplifying audio signals that can reduce transformer distortion without the use of additional shielding.

[0012] These objects are fully achieved by the amplifier circuit and method for amplifying an audio signal according to the invention, as characterized in the appended claims.

[0013] In particular, an amplifier circuit for amplifying an audio signal comprises an input stage, which serves to receive a signal representative of the audio signal to be amplified.

[0014] The input stage comprises a first pin (defining a first input node) and a second pin (defining a second input node). In the following, the terms first input node and second input node are used synonymously with the terms first pin and second pin, respectively. The first input node is responsible for receiving a first input signal representing an audio signal. The second input node is responsible for receiving a second input signal representing an audio signal. Preferably, the second input signal is 180° out of phase with the first input signal.

[0015] In this way, the first input signal and the second input signal form a balanced signal.

[0016] The amplifier circuit includes a transformer. The transformer includes a primary winding and a secondary winding. The secondary winding defines (or includes) a first terminal and a second terminal. Preferably, the secondary winding defines (or includes) an intermediate terminal. The first terminal, the second terminal, and the intermediate terminal may define a first secondary winding and a second secondary winding. Two approaches are possible for forming the first secondary winding and the second secondary winding. In the first approach, the first secondary winding and the second secondary winding are (constitute) two separate windings. In the first approach, the first secondary winding is located between the first terminal and the intermediate terminal, and the second secondary winding is located between the intermediate terminal and the second terminal. In the second approach, there is a single winding between the first terminal and the second terminal (thus, the secondary winding is a single winding), and the intermediate terminal is defined by the central socket of the secondary winding (i.e., the single winding). Thus, in the second approach, a central socket (i.e., intermediate terminal) divides the secondary winding into a first secondary winding and a second secondary winding. The first terminal, the second terminal, and the intermediate terminal define a first end, a second end, and a central socket, respectively. Preferably, the secondary winding defines the central socket. In particular, the central socket is located between the first end and the second end. The central socket may divide the secondary winding into a first secondary winding and a second secondary winding to form a dual secondary winding.

[0017] According to one embodiment, the secondary winding may include a first secondary winding and a second secondary winding, where the first secondary winding and the second secondary winding are separate windings, and in this case, the central socket may not be present.

[0018] The amplifier circuit includes a differential amplifier having a first input, a second input, and an output. Specifically, the first input is electrically connected to a first terminal of a secondary winding by a first connecting branch. The second input is electrically connected to an intermediate terminal of the secondary winding by a second connecting branch. The output is connected to a second terminal of the secondary winding.

[0019] The amplifier circuit includes an additional transformer. The additional transformer includes an additional primary winding and an additional secondary winding. The additional secondary winding defines (or includes) a first terminal and a second terminal. Preferably, the additional secondary winding defines (or includes) an intermediate terminal. The first terminal, the second terminal, and the intermediate terminal may define an additional first secondary winding and an additional second secondary winding. Two approaches are possible for forming the additional first secondary winding and the additional second secondary winding. In the first approach, the additional first secondary winding and the additional second secondary winding are (constitute) two separate windings. In the first approach, the additional first secondary winding is between the first terminal and the intermediate terminal, and the additional second secondary winding is between the intermediate terminal and the second terminal. In the second approach, there is an additional single winding between the first terminal and the second terminal (thus, the additional secondary winding is a single winding), and the intermediate terminal is defined by the central socket of the additional secondary winding (i.e., the single winding). Therefore, in the second approach, a central socket (i.e., intermediate terminal) divides the additional secondary winding into an additional first secondary winding and an additional second secondary winding. The first terminal, the second terminal, and the intermediate terminal define a first end, a second end, and a central socket, respectively. The additional secondary winding defines a first end and a second end. Preferably, the additional secondary winding defines a central socket. In particular, the central socket is located between the first end and the second end of the additional secondary winding. The central socket may divide the additional secondary winding into an additional first secondary winding and an additional second secondary winding to form an additional double secondary winding. According to one embodiment, the secondary winding may include a first secondary winding and a second secondary winding, each of which is a separate winding. In this case, the central socket may not be present.

[0020] In particular, the primary winding and the additional primary winding are electrically connected (in particular, electrically connected in series) between the first input node and the second input node.

[0021] The amplifier circuit includes an additional differential amplifier. The additional differential amplifier includes a first input, a second input, and an output. Specifically, the first input is electrically connected to a first terminal of an additional secondary winding of the additional transformer by a first connecting branch. The second input is electrically connected to an intermediate terminal of the additional secondary winding by a second connecting branch. The output is connected to a second terminal of the additional secondary winding.

[0022] Thus, the differential amplifier and the additional differential amplifier each amplify the voltage difference existing between their own inputs, and the output signal is fed, i.e., injected, into the second end (i.e., second terminal) of the respective transformer. In this way, the voltage difference is cancelled and the induction of the respective transformer core becomes nearly zero.

[0023] The amplifier circuit includes a differential amplifier and an output circuit that receives as input the output signal from the additional differential amplifier and generates a differential output signal.

[0024] In particular, to generate a differential output signal, the output circuit may comprise a differential output amplifier. The differential output amplifier receives as input the output signals from the differential amplifier and the further differential amplifier and generates the differential output signal. However, the differential output signal may also be generated in other ways, such as by analog or digital circuits (e.g., the output signal from the differential amplifier and the output signal from the further differential amplifier may be digitized and processed to obtain the differential output signal).

[0025] The output signal from the differential amplifier and the output signal from the further differential amplifier may be 180 degrees out of phase with each other. The output circuit may be operable to generate a differential output signal proportional to the difference between the output signal from the differential amplifier and the output signal from the further differential amplifier. In this way, the output signal from the differential amplifier is further filtered out of common-mode noise between the output signal from the amplifier and the output signal from the further amplifier.

[0026] Therefore, the amplifier circuit has the advantage of suppressing noise caused by stray capacitance occurring between the windings of the transformer.

[0027] In one example, the primary winding of the transformer and the additional primary winding of the additional transformer are configured to generate a magnetic flux and an opposing additional magnetic flux. In other words, the primary winding and the additional primary winding are connected so that their polarities do not match. Therefore, the magnetic flux generated by the primary winding of the transformer and the magnetic flux generated by the additional primary winding of the additional transformer cancel each other out.

[0028] Preferably, in both the differential amplifier and the further differential amplifier, the first input is a non-inverting input and the second input is an inverting input.

[0029] In both the differential amplifier and the additive differential amplifier, the first and second secondary windings have matching polarities. In both the transformer and the additive transformer, the primary and secondary windings can have matching, or additive, polarities.

[0030] In one example, the transformer and the additional transformer are identical, placed side by side, and oriented in the same direction, so that the external magnetic flux generates identical currents in the transformer and the additional transformer. In other words, the turns of the transformer winding and the additional transformer winding must be wound along parallel axes, i.e., the turns of the transformer winding and the additional transformer winding must be wound on parallel portions of their cores.

[0031] Preferably, the transformer and the additional transformer are placed at a distance from each other such that the external magnetic flux generates identical currents in the transformer and the additional transformer.

[0032] The transformer and the additional transformer are therefore geometrically arranged relative to one another in such a way that noise generated by external magnetic fields is suppressed. In other words, the purpose of such an arrangement is that noise generated by external sources is common to both transformers and is rejected by electronic circuits that are inherently sensitive to differential type signals.

[0033] Generally speaking, it should be noted that since a differential amplifier is an active element that utilizes an external power source to generate voltage and current (power) gain, when it acts on a transformer, it makes the transformer more sensitive to external electromagnetic fields. Using a double isolation system (a first system with a transformer and amplifier, and a second system with an additional transformer and additional amplifier) ​​has the advantage of reducing noise caused by external electromagnetic fields without the need for expensive shielding systems.

[0034] With respect to the secondary winding and the additional secondary winding, the inductance of the first secondary winding and the inductance of the second secondary winding may be the same or different. Preferably, the inductance of the first secondary winding is greater than the inductance of the second secondary winding. More preferably, the inductance of the first secondary winding is 100 times greater than the inductance of the second secondary winding. The asymmetry in inductance values ​​between the first secondary winding and the second secondary winding has the advantage of improving the signal-to-noise ratio in that it can lower the impedance of the active cancellation circuit, thereby reducing the overall thermal noise of the component during operation.

[0035] In one example, in both the differential amplifier and the further differential amplifier, the output is connected to the second input by a first impedance.

[0036] In both the differential amplifier and the further differential amplifier, the second connection branch may include a second impedance, such that the second input may be connected to the intermediate terminal of the respective secondary winding via the second impedance. In both the differential amplifier and the further differential amplifier, the output may be connected to the second terminal of the respective secondary winding via a third impedance.

[0037] Preferably, the amplifier circuit comprises a ground connection between the second impedance and the intermediate terminal in both the differential amplifier and the further differential amplifier.

[0038] In one example, the first and / or second and / or third impedances comprise a resistive component. The first and / or second and / or third impedances may include a capacitive component.

[0039] Preferably, the transformer and the additional transformer are identical. Preferably, the transformer comprises a core and the additional transformer comprises an additional core different from the core of the transformer.

[0040] In one example, the output circuit comprises a differential output amplifier that generates a balanced differential output signal.

[0041] The present disclosure also provides a method for amplifying an audio signal, the method comprising receiving an input signal representing the audio signal. Preferably, the method comprises receiving a first input signal representing the audio signal at a first input node of an input stage. Preferably, the method comprises receiving a second input signal representing the audio signal and being 180° out of phase with the first input signal at a second input node of the input stage.

[0042] The method includes providing a transformer including a primary winding and a secondary winding. The secondary winding defines (or includes) a first terminal and a second terminal. Preferably, the secondary winding defines (or includes) an intermediate terminal. The first terminal, the second terminal, and the intermediate terminal may define a first secondary winding and a second secondary winding. The first terminal, the second terminal, and the intermediate terminal define a first end, a second end, and a central socket, respectively.

[0043] The method includes providing a differential amplifier having a first input electrically connected to a first terminal of the secondary winding by a first connecting branch, a second input electrically connected to an intermediate terminal of the secondary winding by a second connecting branch, and an output connected to a second terminal of the secondary winding.

[0044] The method includes providing an additional transformer including an additional primary winding and an additional secondary winding. The secondary winding defines (or includes) a first terminal and a second terminal. Preferably, the additional secondary winding defines (or includes) an intermediate terminal. The first terminal, the second terminal, and the intermediate terminal may define an additional first secondary winding and an additional second secondary winding. The first terminal, the second terminal, and the intermediate terminal define a first end, a second end, and a central socket, respectively.

[0045] Preferably, the primary winding and the additional primary winding are electrically connected in series between the first input node and the second input node.

[0046] The method includes providing an additional differential amplifier having a first input electrically connected to a first terminal of the additional secondary winding by a first connecting branch, a second input electrically connected to an intermediate terminal of the additional secondary winding by a second connecting branch, and an output connected to a second terminal of the additional secondary winding of the additional transformer.

[0047] Preferably, the method includes the step of generating a balanced differential output signal from the output signal from the differential amplifier and the output signal from the further differential amplifier, and providing the balanced differential output signal to the output stage.

[0048] In one example, the method includes generating a magnetic flux through a primary winding of a transformer and generating an additional magnetic flux opposing the magnetic flux through an additional primary winding of an additional transformer.

[0049] In both the differential amplifier and the additional differential amplifier, the output may be connected to the second input of the respective differential amplifier via a first impedance. In both the differential amplifier and the additional differential amplifier, the second connection branch includes a second impedance, so that the second input can be connected to the center socket of the respective secondary winding via the second impedance. Preferably, the second impedance is connected to the intermediate terminal by a ground connection. In both the differential amplifier and the additional differential amplifier, the output may be connected to the second terminal of the respective secondary winding via a third impedance.

[0050] In one example, the method includes providing a differential output amplifier in the output circuit to generate a balanced differential output signal.

[0051] In embodiments of the method, the transformer and the additional transformer, the differential amplifier and the additional differential amplifier may be manufactured according to one or more of the features described in this disclosure.

[0052] The present disclosure also provides an audio amplifier.

[0053] The audio amplifier comprises an amplifier circuit manufactured in accordance with one or more aspects of the present disclosure.

[0054] The audio amplifier comprises a power amplifier. The amplifier circuit may be located upstream or downstream of the power amplifier (relative to the direction of signal travel inside the audio amplifier). In other words, the amplifier circuit may be configured to (directly or indirectly) provide an output signal (i.e., a balanced differential output signal) from the amplifier circuit to the power amplifier, or to receive an (amplified) output signal from the power amplifier.

[0055] When placed upstream of a power amplifier, an amplifier circuit constitutes or defines a system for galvanic isolation of the input signal to the audio amplifier. Such a circuit may therefore be used to increase the common-mode rejection ratio and shield signal lines, to reduce or eliminate ground loops caused by potential differences between two parts of a circuit, or to shield a circuit from external electromagnetic fields.

[0056] Such an amplifier circuit may also be used to isolate conductive, user-accessible components from the mains power supply to ensure electrical safety.

[0057] For example, an audio amplifier may be configured to amplify an input signal to a speaker (i.e., to provide an amplified signal to the speaker). The audio amplifier, and in particular the amplifier circuit of the audio amplifier, may be configured to receive a mains signal via a (user-accessible) input connector. In particular, the power amplifier of the audio amplifier may be configured to provide the amplified signal to the speaker. The amplifier circuit is therefore located upstream of the power amplifier. When used in this manner, the amplifier circuit is configured to galvanically isolate the input connector from the mains power supply. It should be noted that the system consisting of the input connector, the audio amplifier, and the speaker constitutes an active diffuser.

[0058] When located downstream of a power amplifier, the amplifier circuitry constitutes or defines a system for galvanic isolation of the output signal from the power amplifier. Such circuitry may be used to perform current and / or voltage measurements of the output signal from the power amplifier.

[0059] For example, the audio amplifier may be configured to perform a current and / or voltage measurement of the signal output from the power amplifier. The amplification circuit of the audio amplifier may be configured to receive the output signal from the power amplifier. The amplification circuit of the audio amplifier may be configured to generate an output signal representing the value of the current and / or voltage output by the power amplifier. The audio amplifier may include a shunt resistor disposed at the output of the power amplifier (i.e., the shunt resistor is configured to receive the output signal from the power amplifier). The amplification circuit may be connected across the shunt resistor.

[0060] Therefore, when the amplifier circuit is arranged in this manner, the purpose is to reduce the common mode rejection ratio and thus perform a more accurate measurement across the shunt resistor.

[0061] According to one aspect of the present disclosure, an audio amplifier includes a first stage including an amplifier circuit according to one or more aspects of the present disclosure and a second stage including a power amplifier according to one or more aspects of the present disclosure. The first stage can be located upstream or downstream of the second stage. Thus, the amplifier circuit can be located upstream or downstream of the power amplifier, allowing the amplifier circuit to operate in any of the above modes.

[0062] In one example, the second stage is configured to receive a balanced differential output signal from the first stage. The first stage thus defines a stage that preconditions the input signal to the power amplifier. The audio amplifier may include a third stage that includes an additional amplifier circuit according to one or more aspects of the present disclosure. The third stage, and in particular the additional amplifier circuit, may thus operate the amplifier circuit in any of the above modes.

[0063] In one example, the third stage is configured to receive the output signal from the power amplifier, ie, from the second stage.

[0064] In particular, the third stage, ie the additional amplifier circuit, is configured to perform measurements of the output current and / or voltage from the second stage.

[0065] It should therefore be noted that there are at least three different modes in which an audio amplifier can be implemented. In the first mode, the audio amplifier comprises one (single) amplifier circuit located upstream of a power amplifier. In this mode, there is a first stage comprising an amplifier circuit and a second stage comprising a power amplifier. In the second mode, the audio amplifier comprises one (single) amplifier circuit located downstream of the power amplifier. In this mode, there is a second stage comprising a power amplifier and the first stage (downstream of the second stage) comprising an amplifier circuit. In the third mode, the audio amplifier comprises an amplifier circuit located upstream of the power amplifier and an additional amplifier circuit located downstream of the power amplifier. In this mode, there is a first stage comprising an amplifier circuit, a second stage comprising a power amplifier and located downstream of the first stage, and a third stage comprising an additional amplifier circuit and located downstream of the second stage.

[0066] The amplifier circuit may include a processing stage. The processing stage may be located between the amplifier circuit and the power amplifier (i.e., between the first stage and the second stage). Thus, the processing stage is configured to process an output signal from the first stage and provide the processed output signal from the first stage to the second stage (particularly according to the first mode and the second mode). In one example, the processing stage may be located between the amplifier circuit and the power amplifier, and / or between the power amplifier and an additional amplifier circuit (i.e., between the first stage and the second stage, and / or between the second stage and the third stage). The processing stage may include at least an analog-to-digital converter and a digital signal processor. The processing stage may include at least a digital-to-analog converter. [Brief explanation of the drawings]

[0067] This and other features will become more apparent from the following description of preferred embodiments, illustrated by way of non-limiting example in the accompanying drawings, in which: [Figure 1] 1 illustrates an amplifier circuit according to one or more embodiments of the present disclosure. [Figures 2A-2C] 1 illustrates an audio amplifier according to one or more aspects of the present disclosure. [Figure 3A-3B] 1 illustrates an audio amplifier according to one or more aspects of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0068] The number 1 in the figure indicates an amplifier circuit. The amplifier circuit 1 receives an audio signal V in The input stage I comprises an input stage I for receiving a first input signal V in+ The first input node IN is responsible for receiving + The input stage I receives a second input signal V in- The second input node IN is responsible for receiving - Thus, the input stage I receives the input audio signal V in The input stage is used to balance the second input signal V in- is the first input signal V in+ and are 180° out of phase.

[0069] The amplifier circuit 1 comprises an isolation stage TI connected to an input stage I.

[0070] The isolation stage TI comprises a transformer T and an additional transformer T'. The transformer T includes a primary winding L1 having a first terminal m1 (i.e., a first end) and a second terminal m2 (i.e., a second end). The first terminal m1 of the primary winding L1 is connected to a first input signal V in+ The first input node IN receives + The additional transformer T' includes an additional primary winding L1' having a first terminal m1 (i.e., a first end) and a second terminal m2 (i.e., a second end). The first terminal m1 of the additional primary winding L1' is connected to a second input node IN - The transformer T and the additional transformer T' are connected to the first input node IN + and IN - The second terminal m2 of the primary winding L1 and the second terminal m2 of the additional primary winding L1′ are electrically connected in series such that the second terminal m2 of the primary winding L1 is electrically connected in series between the first input resistor R in+ via the first input node IN + and the second terminal m2 of the additional primary winding L1' is connected to the second input node IN - In particular, the primary winding L1 and the additional primary winding L1' are connected to each other with opposite polarities, i.e., the magnetic flux generated by the primary winding L1 is opposite to the magnetic flux generated by the additional primary winding L1'.

[0071] The transformer T includes a secondary winding L2 having a first terminal m1 (i.e., a first end) and a second terminal m2 (i.e., a second end). The secondary winding L2 is connected to a first secondary winding L2 having a first terminal m1 of the secondary winding L2. 21 and the second secondary winding L including the second terminal m2 of the secondary winding L 22 The first secondary winding L 21 and the second secondary winding L 22 are connected to each other by the intermediate terminal m3 of the secondary winding L2. 21 and the second secondary winding L 22are connected to each other with matching polarities. The primary winding L1 and secondary winding L2 of the transformer T have matching polarities, i.e. additive polarity.

[0072] The additional transformer T' comprises a secondary winding L2' having a first terminal m1 (i.e., a first end) and a second terminal m2 (i.e., a second end). The secondary winding L2 is connected to an additional first secondary winding L2' having a first terminal m1 of the additional secondary winding L2'. 21 ' and the second secondary winding L2' including the second terminal m2 22 ' and an additional first secondary winding L 21 ' and an additional second secondary winding L 22 The additional first secondary winding L' is connected to the intermediate terminal m3 of the additional secondary winding L2'. 21 ' and an additional second secondary winding L 22 The additional primary winding L1' and the additional secondary winding L2' of the additional transformer T' have matching polarities, i.e. additive polarities.

[0073] The transformer T and the additional transformer T' define a transformer pair. In one example, the amplifier circuit 1 may include multiple transformer pairs.

[0074] The primary winding L1 of the transformer T and the additional primary winding L1' of the additional transformer T' are connected in such a way that their polarities do not match.

[0075] As an example, Figure 1 shows a case where the primary winding L1 of the transformer T and the additional primary winding L1' of the additional transformer T' are connected in such a way that their polarities do not match, and the first primary winding L 21 and L 21 ' and ' are connected to the second secondary winding L 22 , L 22 The polarity of both the primary winding L1 of the transformer T and the additional primary winding L1' of the additional transformer T' may be reversed from that shown in FIG. 1. The polarity of all windings may also be reversed from that shown in FIG. 1.

[0076] In particular, it should be noted that the secondary winding L2 and the additional secondary winding L2' are in separate magnetic circuits.

[0077] In the figure, the primary winding L1 of the transformer T and the secondary winding L 21 between the primary winding L1 of the transformer T and the secondary winding L2 22 The stray capacitances between the additional primary winding L1' and the additional first secondary winding L of the additional transformer T' are denoted as C1 and C2, respectively. 21 ', and the additional primary winding L1' and the additional second secondary winding L of the additional transformer T'. 22 The stray capacitances between ' and ' are denoted as C3 and C4, respectively.

[0078] The amplifier circuit 1 comprises an amplifier stage A connected to an isolation stage TI.

[0079] The amplifier stage A comprises a differential amplifier U having a first input U which defines the non-inverting input of the differential amplifier U. + , a second input U that defines the inverting input of the differential amplifier U - , and the first output node OUT + Output U for generating a differential signal at out First input U + is connected by a first connecting branch r1 to the first terminal m1 of the secondary winding L2, and the second input U - is connected to the intermediate terminal m3 of the secondary winding L2 by the second connecting branch r2, and to the output U out Connected to the output U out is also connected to the second terminal m2 of the secondary winding L2.

[0080] In particular, the output U out is connected to the second input U via the first impedance Z1. - and the second input U + is connected to intermediate terminal m3 through a second impedance Z2, which is connected to intermediate terminal m3 of secondary winding L2 by a ground connection M. out is connected to the second terminal m2 of the secondary winding L2 via a third impedance Z3.

[0081] The amplifier stage A comprises an additional differential amplifier U' having a first input U' which defines the non-inverting input of the additional differential amplifier U'. + ', a second input U' that defines the inverting input of an additional differential amplifier U' - ', and the second output node OUT - Output U for generating an additional differential signal at out '. First input U + ' is connected by a first connecting branch r1 to the first terminal m1 of the secondary winding L2, and the second input U - ' is connected by the second connecting branch r2 to the intermediate terminal m3 of the secondary winding L2, and to the output U out ' is connected to the output U out ' is also connected to the second terminal m2 of the additional secondary winding L2'.

[0082] In particular, the output U of the additional differential amplifier U' out is connected to the second input U of the additional differential amplifier U' through an additional first impedance Z1' - ' and the second input U of the additional differential amplifier U' + The output U of the additional differential amplifier U' is connected to the intermediate terminal m3 through an additional second impedance Z2', which is in turn connected to the intermediate terminal m3 of the additional secondary winding L2' by an additional ground connection M'. out ' is connected to the second terminal m2 of the additional secondary winding L2' via an additional third impedance Z3'.

[0083] The amplifier circuit 1 includes an output circuit O connected to the amplifier stage A. The output circuit O receives an output signal U from the differential amplifier U. out The first output node OUT receives + The output circuit O receives the output signal U from the additional differential amplifier U'. out The second output node OUT receives - Equipped with.

[0084] The output circuit O comprises a differential output amplifier U1 having a first output node OUT1 that defines a non-inverting input of the differential output amplifier U1 and is coupled to a first output node OUT2 through a first resistor R1. +The first input U1 is connected to + The differential output amplifier U1 defines an inverting input of the differential output amplifier U1 and is coupled to a second output node OUT through a second resistor R2. - The second input U1 is connected to - The differential output amplifier U1 outputs a differential output signal V out Output U1 to generate out Includes output U1 out is connected to the second input U of the differential output amplifier U1 through the third resistor R3. - First output U1 + is connected to the ground output M1 via a fourth resistor R4.

[0085] The number 100 in the figure indicates an audio amplifier.

[0086] The audio amplifier 100 comprises an amplifier circuit 1. The audio amplifier 100 comprises a power amplifier 2. In one example, the audio amplifier 100 comprises a first stage S1 including the amplifier circuit 1 and a second stage S2 including the power amplifier 2. The first stage S1 may be placed upstream of the second stage S2, so that the amplifier circuit 1 outputs a balanced differential signal V out is supplied to the audio amplifier 100. Alternatively, the amplified signal V a The first stage S1 may be located downstream of the second stage S2 so as to receive

[0087] If the first stage S1 is placed upstream of the second stage S2, the first stage S1 constitutes a stage for preconditioning the signal (before the power amplification stage). If the first stage S1 is placed downstream of the second stage S2, the first stage S1 constitutes a stage for measuring the output signal from the power amplifier 2.

[0088] The audio amplifier 100 comprises a processing stage S4 located between the first stage S1 and the second stage S2. The processing stage S4 therefore receives the differential output signal V from the first stage S1. out and receives the processed differential output signal V outto the second stage S2. Preferably, the processing stage S4 includes an analog-to-digital converter ADCl and a digital signal processor PD, and further the processing stage includes a digital-to-analog converter ADC2.

[0089] FIG. 2A shows, by way of example, an audio amplifier 100 in which a first stage S1 is placed upstream of a second stage S2.

[0090] 2B shows, by way of example, an audio amplifier 100 in which a first stage S1 is placed downstream of a second stage S2. The audio amplifier 100 includes a shunt resistor R sh The amplifier circuit 1 may include a shunt resistor R sh and a shunt resistor R sh Perform current and / or voltage measurements across the

[0091] FIG. 2C shows, as an example, an audio amplifier 100 in which a first stage S1 is placed upstream of a second stage S2, and the audio amplifier 100 receives an amplified output signal V from a power amplifier 2. a to speaker A. In particular, FIG. 2C shows an input power signal V from a mains power supply R via an input connector. i 1 shows an active sound diffuser comprising an audio amplifier 100 configured to receive an input power signal V. i and supplies a balanced differential output signal V to the processing stage S4. out The power amplifier 2 is configured to provide a balanced differential output signal V from the processing stage S4. out and receives the amplified output signal V a and supplies it to the speaker A. In this case, the amplifier circuit 1 of the first stage S1 therefore constitutes a stage that isolates the input connector from the external power supply.

[0092] In one example, the audio amplifier 100 comprises an amplifier circuit 1 located in a first stage S1, a power amplifier 2 located in a second stage S2 downstream of the first stage S1, and an additional amplifier circuit located in a third stage downstream of the second stage S2 and configured to perform measurements of the output current and / or voltage from the power amplifier 2.

[0093] FIG. 3A shows, by way of example, an electronic card provided with an amplifier circuit 1, an analog-to-digital converter ADC1, a number of relays RE, and a pin MO. The transformer T and the additional transformer T' are mounted side by side and oriented in the same direction. In particular, the winding turns of the transformer T and the additional transformer T' are wound along axes parallel to each other. Furthermore, the transformer T and the additional transformer T' are mounted at a distance from each other such that an external magnetic flux generates identical currents in the transformer T and the additional transformer T'. Thus, each transformer T and T' of a transformer pair has the same common orientation (for example, as shown in FIG. 3B). [Prior art documents] [Patent documents]

[0094] [Patent Document 1] US4567443 [Patent Document 2] US3828269 [Patent Document 3] US2020 / 127620A1 [Patent Document 4] US2710312A

Claims

1. An amplifier circuit (1) for amplifying an audio signal, comprising: a first input signal (V ｉｎ＋ ) to receive the first pin (IN ＋ ), and a second input signal (Vin+) representing the audio signal and 180° out of phase with the first input signal (Vin+). ｉｎ－ ) and a second pin (IN － an input stage (I) having - Primary winding (L １ ) and the secondary winding (L ２ ) and a transformer (T) including the secondary winding (L ２ ) is the first terminal (m １ ), second terminal (m ２ ) and intermediate terminal (m ３ ) a transformer (T) defining a differential amplifier (U), The first connecting branch (r １ ) by the secondary winding (L ２ ) the first terminal (m １ ) electrically connected to the first input (U ＋ )and, The second connecting branch (r ２ ) by the secondary winding (L ２ ) of the intermediate terminal (m ３ a second input (U) electrically connected to the The secondary winding (L ２ ) of the second terminal (m ２ ) connected to the output (U ｏｕｔ a differential amplifier (U) having - Additional primary winding (L １ ') and an additional secondary winding (L ２ an additional transformer (T′) including said additional secondary winding (L ２ ') is the first terminal (m １ ), second terminal (m ２ ) and intermediate terminal (m ３ ) and the primary winding (L １ ) and the additional primary winding (L １ ') is the first pin (IN ＋ ) and the second pin (IN － an additional transformer (T') electrically connected in series between the an additional differential amplifier (U'), The first connecting branch (r １ ) by the additional secondary winding (L ２ The first terminal (m １ ) electrically connected to the first input (U ＋ ')and, The second connecting branch (r ２ ) by the additional secondary winding (L ２ The intermediate terminal (m ３ a second input (U') electrically connected to the The additional secondary winding (L ２ The second terminal (m ２ ) connected to the output (U ｏｕｔ an additional differential amplifier (U′) having - receiving as input the output signals from said differential amplifier (U) and said further differential amplifier (U') and generating a differential output signal (V ｏｕｔ and an output circuit (O) for generating a first input signal.

2. The primary winding (L １ ) and the additional primary winding (L １ 2. The amplifier circuit (1) of claim 1, wherein the first magnetic flux generator (1) is configured to generate an additional magnetic flux opposite to the magnetic flux generator (1).

3. 3. An amplifier circuit (1) according to claim 1 or 2, wherein the transformer (T) and the additional transformer (T') are identical, arranged side by side and oriented in the same direction, so that an external magnetic flux generates identical currents in the transformer (T) and the additional transformer (T').

4. For each of the differential amplifier (U) and the additional differential amplifier (U′), ｏｕｔ , U ｏｕｔ ') is the first impedance (Z １ , Z １ 3. An amplifier circuit (1) according to claim 1 or 2, wherein said amplifier circuit (1) is connected to said second input (U, U') by a first input (U, U').

5. For each of the differential amplifier (U) and the additional differential amplifier (U′), - the second connecting branch (r ２ ) is the second impedance (Z ２ , Z ２ '), so that the second input (U, U') is coupled to the second impedance (Z ２ , Z ２ ') by the respective secondary windings (L ２ , L ２ The intermediate terminal (m ３ ) and - the output (U ｏｕｔ , U ｏｕｔ ') is the third impedance (Z ３ , Z ３ ') by the respective secondary windings (L ２ , L ２ The second terminal (m ２ 5. The amplifier circuit (1) according to claim 4, wherein the amplifier circuit (1) is connected to a

6. The second impedance (Z ２ , Z ２ ') and the intermediate terminal (m ３ 6. An amplifier circuit (1) according to claim 5, comprising a ground connection (M, M') between said amplifier circuit (1) and said first amplifier circuit (1).

7. The first impedance (Z １ , Z １ '), the second impedance (Z ２ , Z ２ ') and the third impedance (Z ３ , Z ３ 6. The amplifier circuit (1) of claim 5, wherein each of the resistors (1') comprises a respective resistive component and a capacitive component.

8. 3. An amplifier circuit (1) according to claim 1 or 2, wherein the transformer (T) and the additional transformer (T') are identical.

9. 3. An amplifier circuit (1) according to claim 1 or 2, wherein the transformer (T) comprises a core and the additional transformer (T') comprises an additional core different from the core of the transformer (T).

10. The output circuit (O) outputs the differential output signal (V ｏｕｔ 3. An amplifier circuit (1) according to claim 1 or 2, comprising a differential output amplifier (U1) for generating a differential output voltage.

11. An audio amplifier (100), comprising: an amplifier circuit (1) according to claim 1 or 2, - a power amplifier (2).

12. The amplifier circuit (1) includes a first stage (S1) and a second stage (S2) includes the power amplifier (2), and the second stage (S2) outputs the differential output signal (V ｏｕｔ 12. The audio amplifier (100) of claim 11, configured to receive a

13. a third stage including an additional amplifier circuit (1) according to claim 1 or 2, said third stage receiving an amplified output signal (V ａ 13. The audio amplifier of claim 12, configured to receive a

14. 1. A method for amplifying an audio signal, comprising: - first pin of the input stage (I) (IN ＋ ), a first input signal (V ｉｎ＋ ) and the second pin (in － ) represents the audio signal and the first input signal (V ｉｎ＋ ) that is 180° out of phase with the second input signal (V ｉｎ－ ) and - Primary winding (L １ ) and the secondary winding (L ２ providing a transformer (T) including the secondary winding (L ２ ) is the first terminal (m １ ), second terminal (m ２ ) and intermediate terminal (m ３ ) a differential amplifier (U), The first connecting branch (r １ ) by the secondary winding (L ２ ) the first terminal (m １ ) electrically connected to the first input (U ＋ )and, The second connecting branch (r ２ ) by the secondary winding (L ２ ) of the intermediate terminal (m ３ a second input (U) electrically connected to the The secondary winding (L ２ ) of the second terminal (m ２ ) connected to the output (U ｏｕｔ providing a differential amplifier (U) having - Additional primary winding (L １ ') and an additional secondary winding (L ２ providing an additional transformer (T′) including said additional secondary winding (L ２ ') is the first terminal (m １ ), second terminal (m ２ ) and intermediate terminal (m ３ ) and the primary winding (L １ ) and the additional primary winding (L1') is connected to the first pin (IN ＋ ) and the second pin (IN － ) electrically connected in series between the steps; an additional differential amplifier (U'), The first connecting branch (r １ ) by the additional secondary winding (L ２ The first terminal (m １ ) electrically connected to the first input (U ＋ ')and, The second connecting branch (r ２ ) by the additional secondary winding (L ２ The intermediate terminal (m ３ a second input (U') electrically connected to the The additional secondary winding (L ２ The second terminal (m ２ ) connected to the output (U ｏｕｔ providing an additional differential amplifier (U′) having - a differential output signal (V ｏｕｔ ), and generating the differential output signal (V ｏｕｔ and providing a first input signal to an output stage.

15. - the primary winding (L) of the transformer (T) １ generating a magnetic flux through a the additional primary winding (L) of the additional transformer (T') １ ') through the primary winding (L １ and generating a magnetic flux opposite to the magnetic flux generated by the magnetic field.

16. 16. The method according to claim 14 or 15, wherein the transformer (T) and the additional transformer (T') are identical, arranged side by side and oriented in the same direction, so that an external magnetic flux generates identical currents in the transformer (T) and the additional transformer (T').

17. For each of the differential amplifier (U) and the additional differential amplifier (U′), - the output (U ｏｕｔ , U ｏｕｔ ') is the first impedance (Z １ , Z １ to the second inputs (U, U') of the respective differential amplifiers (U, U'), - the second connecting branch (r ２ ) is the second impedance (Z ２ , Z ２ '), so that the second input (U, U') is coupled to the second impedance (Z ２ , Z ２ ') by the respective secondary windings (L ２ , L ２ The intermediate terminal (m ３ ), and the second impedance (Z ２ , Z ２ ') is connected to the intermediate terminal (m ３ ) is connected. - Output (U ｏｕｔ , U ｏｕｔ ') is the third impedance (Z ３ , Z ３ ') by the respective secondary windings (L ２ , L ２ 16. The method of claim 15, wherein the second end of the first electrode is connected to the second end of the second electrode.

18. The differential output signal (V ｏｕｔ 16. A method according to claim 14 or 15, comprising the step of providing a differential output amplifier (U1) having an output circuit (O) for generating a

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