Method and device for limiting power to protect a power supply from overload in a multi-channel audio amplifier

Abstract

A method for use in an audio system including a plurality of amplifier channels of a corresponding audio channel. Each of the amplifier channels receives a respective input audio signal and is powered by the same power supply. The method includes obtaining (810) a value of an indicator, the indicator representing an energy reserve of the power supply, and for each of the amplifier channels, determining (830) a gain to be applied to the respective input audio signal by an attenuation function and a clipping level to be applied to the output of the attenuation function by a clipping function, wherein when the value of the indicator is below a threshold, the gain decreases over time, when the value of the indicator is above the threshold, the gain increases over time to a maximum value, the threshold represents a nominal energy level at which the power supply is in a nominal operating state, and the clipping level is determined as a monotonic function of the value of the indicator.

Description

Technical Field

[0001] Various exemplary embodiments generally relate to methods and devices for use in audio systems including a plurality of amplifier channels.

Background Art

[0002] In current audio systems, the number of audio channels is constantly increasing. Starting from 2-channel stereo, currently 5+1 or 7+1 surround amplifiers are common. Modern line array speaker systems can use 48 channels. For scientific purposes as well as for best performance, there are wavefront synthesis arrays with up to 832 independent channels. For size and cost reasons, it makes sense to connect many amplifier channels to just one power supply. Since not all channels are driven at their maximum power capabilities simultaneously, the average power of the channels determines the long-term power capability of the common power supply.

[0003] The audio signal may represent, for example, music content. Since music content is dynamic, sizing the power supply for the maximum instantaneous power is costly and unnecessary. During power peaks, energy is provided by one or more bulk capacitors. The charge state of these bulk capacitors depends on the history of the power demand (e.g., whether the bulk capacitors were depleted by previous power draws or whether there was time to recharge during quiet parts of the audio signal).

[0004] To avoid switch-off, a typical solution is to use a dynamic range compressor or a limiter to limit the root mean square (RMS) level of the audio signal to be amplified. Since the impedance of the load is frequency-dependent and partially reactive, the relationship between the output signal level and the output power is not trivial. Therefore, to prevent the amplifier from switching off, the limiter needs to be set conservatively, potentially not utilizing the full output power capability of the system. Furthermore, by using such a limiter that operates independently on each audio channel, the multi-channel advantages of the shared power supply described above cannot be obtained.

[0005] In a multi-channel amplifier, it is common for the power supply and bulk capacitors to be shared among different amplification channels. If the power supply accidentally becomes overloaded, a protection mechanism switches off the circuit to prevent damage.

[0006] A limiting device is needed that takes into account the power demands of all amplification channels while minimizing audible distortion and preventing the power supply from switching off.

SUMMARY OF THE INVENTION

[0007] The scope of protection is indicated by the independent claims. Embodiments, examples, and features described herein that do not fall within the scope of protection, if any, should be construed as useful examples for understanding the various embodiments or examples that do fall within the scope of protection.

[0008] According to a first aspect, a device for use in an audio system comprising a plurality of amplifier channels for corresponding audio channels is disclosed. Each of the amplifier channels receives a respective input audio signal and is powered by the same power supply, and the device is an indicator, where the indicator represents an energy reserve of the power supply, the indicat Obtaining the value of the indicator, and for each of the amplifier channels, determining the gain to be applied to each input audio signal by an attenuation function and the clipping level to be applied to the output of the attenuation function by a clipping function, and means (e.g., signal processing means or a signal processor) for executing a method including the above are provided. When the value of the indicator is below the threshold, the gain decreases over time, and when the value of the indicator is above the threshold, the gain increases to the maximum value over time. The threshold represents the nominal energy level when the power supply is in the nominal operating state, and the clipping level is determined as a monotonic function of the value of the indicator.

[0009] The gain can decrease over time according to an attack rate. The attack rate can be a fixed attack rate corresponding to a fixed gain decrease per period on a logarithmic scale. The attack rate can also be a dynamic attack rate calculated as a function of the value of the indicator. The gain can increase over time according to a release rate. The release rate is a fixed release rate corresponding to a fixed gain increase per period on a logarithmic scale. When the value of the indicator is less than the threshold, the clipping level can be determined by applying a monotonic function of the output voltage of the power supply. The monotonic function can be a linear function of the output voltage of the power supply or a continuous function of the output voltage of the power supply.

[0010] The indicator can be proportional to the output voltage of the power supply or the square of the output voltage of the power supply. The indicator can also be proportional to the energy stored in the power supply. The gain varies between a minimum value and a maximum value. The monotonic function can be adjusted based on the trunk voltage level signal received from the power supply.

[0011] The means can include, for each amplifier channel, a clipping device connected to the input of the amplifier channel and configured to apply a clipping function, and an attenuation device having an output connected to the input of the clipping device and configured to apply an attenuation function.

[0012] According to a second aspect, there is disclosed a method for use in an audio system comprising a plurality of amplifier channels for corresponding audio channels, each of the amplifier channels receiving a respective input audio signal and being powered by the same power supply, the method comprising obtaining a value of an indicator, the indicator representing an energy reserve of the power supply, and for each of the amplifier channels, determining a gain to be applied to the respective input audio signal by an attenuation function and a clipping level to be applied to the output of the attenuation function by a clipping function, wherein when the value of the indicator falls below a threshold, the gain decreases over time, and when the value of the indicator exceeds the threshold, the gain increases over time to a maximum value, the threshold representing a nominal energy level at which the power supply is in a nominal operating state, and the clipping level being determined as a monotonic function of the value of the indicator.

[0013] The device according to the first aspect can comprise means for performing one or more or all of the steps of the method according to the second aspect. The means can comprise a circuit (e.g., a signal processor) configured to perform one or more or all of the steps of the method according to the first aspect. The means can comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the device to perform one or more or all of the steps of the method according to the first aspect.

[0014] According to another aspect, there is disclosed a computer program comprising instructions that, when executed by at least one processor, cause a device to perform the method according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Exemplary embodiments will be more fully understood from the detailed description given hereinbelow and the accompanying drawings. The accompanying drawings are given by way of example only and thus do not limit the present disclosure. ​Note that these figures illustrate general features of methods, structures, and / or materials utilized in certain exemplary embodiments and are intended to supplement the written description provided below. The use of like or identical reference numbers in the various drawings is intended to indicate the presence of like or identical elements or features.

[0016]

Fig. 1

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Fig. 5B

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DETAILED DESCRIPTION OF THE INVENTION

[0017] Next, various exemplary embodiments will be described in more detail with reference to the accompanying drawings which show some exemplary embodiments. However, the specific structural and / or functional details disclosed herein are merely representative examples for the purpose of explaining the exemplary embodiments. Therefore, these embodiments are shown as exemplary examples in the drawings and are described in detail herein to provide a complete understanding of the various aspects. However, it will be understood by those skilled in the art that the exemplary embodiments are capable of various modifications and alternative forms and can be implemented without all of the specific details. In addition, the systems and processes may be shown in block diagrams so as not to obscure the exemplary embodiments with unnecessary details. In other instances, well-known processes, structures, and techniques may be shown without unnecessary detail so as to avoid obscuring the exemplary embodiments.

[0018] FIG. 1 shows a multi-channel amplification having a power supply 110 that supplies power to several amplifier channels 120, 130, 140 having a full-bridge output stage that drives a bridge-coupled load It is a schematic block diagram of system 100. Both expressions "amplifier channel" and "amplification channel" used in this specification relate to an audio channel and indicate a functional block (s) configured to perform amplification of a corresponding input audio signal.

[0019] In the exemplary audio system 100 shown in FIG. 1, a multi-channel audio amplifier includes a power supply 110 connected to a power grid by a plug or a fixed connection. The power supply 110 supplies power to a group of amplifier channels 120, 130, 140.

[0020] The amplifier channels 120, 130, 140 are connected to the power supply by at least a positive power connection 111 and a negative power connection 112. A bulk capacitor 115 at the output of the power supply is connected between the positive power connection 111 and the negative power connection 112. Each amplifier channel 120, 130, 140 receives its respective input audio signal 121, 131, 141 and supplies its respective output audio signal to its respective load 129, 139, 149. Such a load is typically a speaker.

[0021] FIG. 2 is a schematic block diagram of a multi-channel amplification system 200 having a power supply 210 with two symmetric supply voltages that supplies power to some amplifier channels 220, 230, 240 having a half-bridge output stage driving a single-ended load.

[0022] The exemplary audio system 200 shown in FIG. 2, similar to FIG. 1, includes a group of amplifier channels 220, 230, 240, but in this example, the amplifier channels have a push-pull output configuration as shown by FIG. 2 and there is a positive power connection 211, a negative power connection 212, and a third central connection 213 to circuit ground potential. A first bulk capacitor 216 is connected between the positive power connection 211 and the central connection 213. A second bulk capacitor 217 is connected between the central power connection 213 and the negative power connection 212.

[0023] In situations where several input audio signals and amplifier channel gains cause each amplifier channel to output power higher than the average, the power supply can become overloaded, and the maximum power supplied by power supply 110 or 210 is less than the total power drawn together by all amplifier channels. In this case, the bulk capacitors 115 or 216, 217 of the power supply discharge to supply power from their stored energy, thereby reducing the supply voltage. Another reason for the supply voltage to drop is that in the case of a precisely regulated power supply, the power supply goes out of regulation because the maximum output current limit is reached. In this case, the power supply is no longer a regulated voltage source but a current source with a maximum output current smaller than the load current. When the lower threshold of the supply voltage is reached, the power supply switches off to prevent irregular operation or even damage. The interruption of power supply causes the mute of the output of the audio system.

[0024] To limit the power drawn by the amplifier channels, a limiting device operating under the control of a common control device is introduced. Such a device is configured to limit the sum of the power consumption of all channels to the maximum value that the power supply can provide. Typically, a short-term overload of the power supply can be possible until the energy storage of the power supply is discharged to its minimum value.

[0025] The common control device is configured to implement a control function (also referred to herein as a control law) to determine the amount of power limit to be applied. The control function can be based on one or more values of an indicator that can be calculated dynamically. The indicator may represent the energy reserve stored in the bulk capacitor that supports the output of the power supply. The physical parameter used to calculate the value of the indicator can be voltage or energy. The lower the value of the indicator, the more power limit is applied by the limiting device. The indic ator may be proportional to the output voltage of the power supply or the square of the output voltage of the power supply. The indicator may be proportional to the energy stored in the power supply.

[0026] Each limiting device can include an attenuation device configured to apply an attenuation function and a clipping device configured to apply a clipping function.

[0027] The attenuation device can be implemented by any type of attenuator / amplifier suitable for applying a gain (less than or equal to 1 in the linear region, or equivalently, less than or equal to 0 dB in the logarithmic region) to the input signal to reduce the magnitude of the input signal (e.g., voltage reduction in the analog domain or numerical reduction in the digital domain). The attenuation device can be, for example, a voltage-controlled attenuator (VCA), a gain multiplier in a digital signal processing implementation, and the like.

[0028] The clipping device can be implemented by any type of clipper suitable for reducing the magnitude (amplitude in absolute value) of the input signal to a given clipping level.

[0029] The clipping device can include, for example, a series resistor having two clamping diodes connected to a positive threshold voltage and a second clamping diode connected to an inverted (negative) threshold voltage. An improved version can use an operational amplifier for each clamping diode to compensate for the diode forward voltage.

[0030] It is also possible to emulate the clipping function of the clipping device using the attenuation device. When the magnitude of the input signal exceeds the threshold, the threshold is divided by this magnitude. The result is the gain (limited to a value above 0 dB) that should be applied to obtain the clipped output signal.

[0031] For each audio channel, the output of the clipping device is connected to the input of the corresponding amplifier channel, and the output of the attenuation device is connected to the input of the corresponding clipping device. Each attenuation device is configured to apply a gain to the corresponding input audio signal. The gain is applied by the attenuation device and is negative or zero when expressed, for example, in dB, or greater than zero and less than or equal to 1 when expressed in the linear region. Each clipping device is configured to apply a clipping level to the signal generated by the attenuation device. The output signal of the clipping device is used in place of the input audio signal and is supplied to the corresponding amplifier channel.

[0032] The indicator can be compared to a threshold value to calculate the gain to be applied to each audio channel in order to limit the total power drawn by the amplifier channel. The threshold value may represent the nominal energy level when the power supply is in the nominal operating state. The threshold value may represent the nominal voltage reflecting the nominal energy level.

[0033] The common control device is configured to generate control signals for the attenuation device and the clipping device corresponding to the gain and the clipping level determined by the control function based on the current value of the indicator, respectively.

[0034] When the value of the indicator is below the threshold value, the gain decreases (more attenuation), and when the value of the indicator is above the threshold value, the gain increases to the maximum value (less attenuation). The gain can decrease over time by the attack rate. The attack rate can be a fixed attack rate corresponding to a fixed gain decrease per period on a logarithmic scale. The attack rate can also be a dynamic attack rate calculated as a function of the value of the indicator. The gain is It can increase over time depending on the release rate. The release rate may be a fixed release rate corresponding to a fixed gain increase per period on a logarithmic scale. The gain may vary between a minimum value (e.g., a fixed minimum value) and a maximum value (e.g., a fixed maximum value).

[0035] The clipping level is determined as a monotonic function of the value of the indicator. For example, the clipping level decreases (more clipping) when the value of the indicator decreases (lower energy reserve), and vice versa. For example, when the value of the indicator is less than a threshold, the clipping level is determined by applying a monotonic function of the output voltage of the power supply. The monotonic function may be a linear function of the output voltage of the power supply, or may have another shape or a continuous (e.g., piecewise linear) function of the output voltage of the power supply. The monotonic function may be determined based on a trunk voltage level signal received from the power supply.

[0036] The clipping level can be determined by applying a linear function to the voltage at the output of the power supply when the indicator is proportional to the voltage at the output of the power supply. The clipping level may be determined such that as long as the value of the indicator exceeds a threshold representing the nominal energy level, the clipping function does not affect the audio signal supplied to the clipping function (the clipping level is higher than the maximum value). The clipping function may act gradually around the clipping level (sometimes called "soft clipping").

[0037] The values of the clipping level and / or the gain may be dynamically adjusted by a common control device. The clipping level and / or the gain may be dynamically adjusted as a function of the value of the indicator.

[0038] If the total power consumption of all amplifier channels is too high temporarily, the energy reserve can decrease very rapidly, so gain reduction alone may not be sufficient. An attenuation device that applies gain at an attack rate may not prevent the power supply from being switched off before sufficient gain reduction is achieved. Therefore, an instantaneous operating mechanism is required. To operate instantaneously, a clipping device is used in combination with the attenuation device and is configured to apply a clipping level at the start of the power peak, giving the attenuation device time to take over, i.e., reach a sufficiently reduced gain, so that the value of the indicator does not drop further.

[0039] However, the drawback of heavy clipping is audible artifacts for longer durations. Here, the attenuation performed by an attenuation device with an attack ramp can, for example, after a first period (attack phase), e.g., after 250 ms, limit the signal to a level where clipping no longer occurs. This means that during a second period (release phase) after the first period, no clipping occurs (the clipping function does not affect the signal received by the clipping device), and the limitation of the audio signal results from the gain applied by the attenuation function while the energy reserve is still in the attack phase where it has not reached the nominal energy level. After an event with high peak power simultaneously in several channels, the instantaneously operating clipping device can return to a clipping level above the maximum signal amplitude. During a third period, when the energy reserve reaches the nominal energy level, the gain increases (e.g., slowly to avoid pumping effects in the audio signal) to the maximum gain level (e.g., 0 dB).

[0040] The attack phase can start after the occurrence of a power consumption peak that results in the discharge of the energy of the bulk capacitor, and this discharge is detected based on one or more values of the indicator. The release phase can be interrupted by a second attack phase if a new power consumption peak occurs. The release phase and the attack phase may alternate in time as a function of the variation of the values of the indicator. The combination of clipping and dynamic attenuation can maintain a high average power level, and thus loudness, with an output signal having sufficiently low audible artifacts. This combination can react quickly enough to protect the power supply from being switched off during high power output.

[0041] Figure 3 is a schematic block diagram of a multi-channel amplification system 300. The multi-channel amplification system 300 includes limiting devices 322, 332, 342 in front of each amplifier channel 320, 330, 340, and each limiting device 322, 332, 342 is controlled by a common control device 390 that is common to all amplifier channels and uses information on the state of the supply voltage. In the example of Figure 3, similar to Figure 1, the full-bridge output stage is driving a bridge-coupled load.

[0042] Figure 4 is a schematic block diagram of a multi-channel amplification device 400. The multi-channel amplification system 400 includes limiting devices 422, 432, 442 in front of each amplifier channel 420, 430, 440, and each limiting device 422, 432, 442 is controlled by a common control device 490 that is common to all amplifier channels and uses information on the supply voltage. In the example of Figure 4, similar to Figure 2, the half-bridge output stage is driving a single-ended load.

[0043]

[0044] ​To simplify FIG. 3, the figure depicts a power supply 310 having only one supply voltage (between 311 and 312) that powers a group of amplifier channels 320, 330, 340 using bridge-coupled loads 329, 339, 349 that require only one power supply voltage.

[0045] It is also possible to have a single-ended push-pull output stage in an amplifier that requires positive and negative supply voltages, such as the system 400 of FIG. 4. Here, the power supply 410 has a positive supply voltage (between 411 and 413) and a negative supply voltage (between 412 and 413), which share a common ground at their central connection 413. In this case, the state of the power supply is given by the minimum value of the absolute value of both the positive and negative supply voltages.

[0046] In each audio channel of FIG. 3 or FIG. 4, the limiting devices 322, 332, 342, 422, 432, 442 receive the respective input audio signals 321, 331, 341, 421, 431, 441 of the associated audio channel and supply the respective limited audio signals 324, 334, 344, 424, 434, 444 that replace the respective input audio signals 321, 331, 341, 421, 431, 441 to the respective amplifier channels 320, 330, 340, 420, 430, 440.

[0047] Each limiting device 322, 332, 342, 422, 432, 442 comprises an attenuation device followed by a clipping device.

[0048] Each attenuation device receives an input control signal configured to control, from a common control device 390, 490, the value of the gain applied by the associated attenuation device. The control signal may be the same for all audio channels. When the gain is set to a maximum of 0 dB (i.e., corresponding to a multiplication factor of 1), the input audio signal remains unchanged.

[0049] Each clipping device receives an input control signal configured to control, from the common control devices 390, 490, the values of the positive and negative clipping levels applied by the associated clipping device. For each clipping device, the maximum positive and negative saturation thresholds (i.e., the maximum positive and negative values of the clipping levels) are set to the maximum signal levels that can be processed at its input by the respective amplifier stages. Typically, this maximum signal level is limited by the supply voltage divided by the amplifier voltage gain of the amplifier channel. The common control devices 390, 490 can use different information available for generating the input control signal.

[0050] In the embodiment of FIG. 3, the supply voltage (between 311 and 312) at the bulk capacitor of the power supply is used and sent to the common control device 390. In a two-symmetric power supply voltage and push-pull configuration as in FIG. 4, two power supply voltages (between 411 and 413, and between 412 and 413) are used, and the minimum value of the absolute value of these two voltages is sent to the common control device 490.

[0051] Several types of control signals can be generated by the common control device to control the gain and the clipping level.

[0052]

[0053] ​The gain can be adjusted by applying an attack rate (e.g., a linear decrease as a function of time if the gain is expressed in dB) during the attack phase and / or by applying a release rate (e.g., a linear increase as a function of time if the gain is expressed in dB) during the release phase. The gain control signal is the same for all audio channels. The gain can vary between a maximum value (e.g., equal to 0 dB, i.e., no attenuation) and a minimum value. The attack rate and / or the release rate can be fixed or determined based on the difference between an indicator and a threshold representing a nominal energy level. The release rate may have a smaller absolute value than the attack rate such that the release phase lasts longer than the attack phase. A trade-off can be found between the reaction being too fast (causing low average power) or the reaction being too slow (too long a period of gain reduction with additional clipping of the input audio signal). As long as the energy reserve represented by the indicator exceeds the threshold, the gain is in the release phase and is limited to the maximum gain (e.g., equal to 0 dB, i.e., no attenuation).

[0054] The gain may decrease as a function of time (i.e., more attenuation) during a first period (attack phase) and may increase as a function of time (i.e., less attenuation) during a second period (release phase). For example, during the attack phase, the gain decreases at a constant attack rate (e.g., a predefined attack rate) or a dynamic attack rate. The attack rate and the release rate represent the change in gain over time (increase or decrease respectively). The dynamic attack rate can be adjusted as a function of the difference between the threshold and the current value of the indicator.

[0055] For example, as represented by FIG. 5A, the attack rate (AR) and the release rate (RR) are fixed, and the attack phase alternates with the release phase. During the release phase, the gain is limited to the maximum gain value (MG, e.g., 0 dB). This limitation can cause a part of the release phase to have a gain change rate of 0 (R = 0) while the gain remains at its maximum gain value (MG).

[0056] For example, as shown in FIG. 5B, the dynamic attack rate is adjusted according to the difference between the indicator value and the threshold value. When the energy reserve represented by the indicator decreases, the difference increases, and the dynamic attack rate also increases, and vice versa.

[0057] FIG. 5B shows a curve indicating the variation of the gain. The first slope corresponds to the first attack rate AR1 (when represented in dB, a linear decrease in the gain) during the first period, and corresponds to the second attack rate AR2 during the second period. Similarly, other attack rates AR3, AR4, AR5 may be used during subsequent corresponding periods. In this example, the dynamic attack rate is updated at transitions such as from AR1 to AR2, from AR2 to AR3, etc. The update of the dynamic attack rate may be performed at a control update rate at which the value of the indicator is evaluated by a common control function.

[0058] FIG. 6 shows a flowchart of a method for determining the gain of an attenuation function according to an example. In step 650-1, the value of the indicator is obtained. The indicator may be the measured supply voltage in the bulk capacitor, in this example the supply voltage V supply . In step 650-2, the indicator value is compared with the threshold value V th , which is here the voltage level of the nominal operation.

[0059] If the value of the indicator is less than the threshold value, step 650-3 is executed after step 650-2. Otherwise, if the value of the indicator is greater than or equal to the threshold value, step 650-6 is executed after step 650-2.

[0060] If the indicator is below the threshold, the method continues to step 650-3, and an attack rate is determined. This can be a fixed attack rate as in FIG. 5A. This can also be a dynamic attack rate as in FIG. 5B. In the case of a dynamic attack rate, the weighting factor w may be calculated as the ratio of two differences, where w = (V th -V supply ) / (V th -V min ). In this example, the nominal voltage is V th = 155V, and the minimum voltage for safe operation is V min = 130V. Thus, the weighting factor w is a number between 0 and 1. For a (logarithmic) maximum attack rate of -0.2085 dB / ms and a gain update rate of 24 kHz, the maximum attack rate corresponds to a coefficient FA max = 0.999 on a linear scale. Using the current value of w, a dynamic attack rate corresponding to the coefficient FA d = 1 - w·(1 - FA max ) is calculated.

[0061] In step 650-4, the gain is decreased by only this coefficient such that the updated value of the gain is gain·FA d . As an optional step 650-5, the gain may be limited to a minimum gain value, for example, a value of 0.01. The minimum gain value can help shorten the duration of the subsequent release phase. As shown in step 650-8, this gain is used for all attenuation devices until the next control update, for example, the next execution of step 650-1 where a new value of the indicator is obtained. The control update rate at which the value of the indicator is evaluated may be slower than the gain update rate at which the value of the gain is updated.

[0062] If the indicator is above the threshold value, the method continues with step 650-6. The gain is increased at a release rate corresponding to a coefficient FR = 1.0001 on a linear scale, for example, a fixed release rate of 20.85 dB / s and a gain update rate of 24 kHz. The gain is increased by this coefficient gain = gain·FR. In step 650-7, the gain is limited to a maximum gain value, for example, a value of 1 on a linear scale. As shown in step 650-8, this gain is used for all attenuation devices until the next control update.

[0063] Figure 7 shows a flowchart of a method for calculating the clipping level of a clipping function using a control function, according to an example. In step 750-1, the calculation is based on the measured supply voltage in the bulk capacitor. In step 750-2, a new voltage level is calculated as a function of V new =c·V supply +V offset using the linear control law V supply . The coefficients c and the voltage V offset may be pre-calculated according to the mains voltage RMS level at the input of the power supply and the load impedance connected at the output of a given amplifier channel.

[0064] For example, two operating points are used to determine the coefficients of the linear control law. The first operating point is when the supply voltage is at the nominal level (V supply =V th ), and the linear control law returns V new =V th +V ripple . Here, the power supply has a nominal voltage of V th = 155 V, and for example, V ripple = 5 V varies from 150 V to 160 V. The second operating point is when the supply voltage is at the minimum level (V supply =V min ), and the linear control law is the voltage level V newis returned. Thus, the connected load impedance can operate with any signal at that voltage level without exceeding the long-term maximum average power level per channel. V new These two conditions for [V] offset offset enable pre-calculation of both c and [V] offset

[0065] As two optional steps 750-3 and 750-4, the current clipping level is increased by a fixed clipping release rate (in dB / s), e.g., CRR = 16 dB / s, in step 750-3. For discrete-time implementations, the value of the clipping level release factor can be selected according to the control update rate. In step 750-4, the new voltage level V new is limited below the clipping level. In this way, the impact of the supply voltage V supply variation on the clipping level is reduced. However, if CRR is selected too slow, clipping may continue for an unnecessarily long period until attenuation by gain reduction takes over. Steps 750-3 and 750-4 may both be used or both may be omitted.

[0066] As shown in step 750-5, the new voltage level V new is then used as the clipping level for all clipping devices until the next control update, e.g., until a new value of the supply voltage in the bulk capacitor is evaluated by a common control function.

[0067] The clipping level can be determined by a common control device based on an indicator. The clipping level can be determined for each audio channel depending on the connected load impedance of the amplifier channel under consideration and the supply voltage which is the voltage at the output of the power supply.

[0068] As long as the indicator exceeds the threshold value, the gain is limited to its maximum value (e.g., 0 dB, no attenuation) during the release phase. Similarly, the clipping level is set to a level at which clipping is inactive (it may be limited to the maximum level).

[0069] Regarding the determination of the indicator, several algorithms can be used separately or in combination.

[0070] According to the algorithm, the value of the indicator is obtained by sampling the voltage at the output of the power supply. A good marker of the available energy reserve is the power supply output voltage (between 311 and 312 in FIG. 3, or between 411 and 413, and between 412 and 413 in FIG. 4; in FIG. 4, the minimum value of the absolute value of the positive and negative power supply voltages is taken). Thus, the available energy reserve can be calculated as E = 0.5·C B ·(V supply ) 2 where C B is the effective capacitance of the bulk capacitor and V supply is the voltage at the output of the power supply. The control function is configured to calculate the gain and clipping level applied to some or all of the audio channels based on the available energy reserve.

[0071] The common control device may receive, as input, the value of the indicator representing the bulk capacitor voltage and calculate the gain and clipping level applied to some or all of the audio channels.

[0072] Exemplary embodiments of the control function and the adjustment of the threshold and parameters are provided below.

[0073] The control function can compare the measured supply voltage with a threshold value set to 155V. If the measured supply voltage is higher than 155V, the gain release phase is applied.

[0074] When the measured supply voltage is less than 155V, more attenuation is applied to the gain over time by an amount (using the "gain update" rate). The typical attack rate for a dynamic compressor of a music signal ranges from 0.04 dB / ms to 3 dB / ms. In an embodiment suitable for a music signal, the attack rate of the gain is calculated dynamically and not set to a fixed value. A linear control equation may be used. This reaches the maximum attack rate at 130V, which is 25V lower than the 155V threshold. For example, this attack rate may be set to 0.25 dB / ms. When the measured voltage is only 5V lower than the threshold (the measured supply voltage is 150V), the attack rate is set to 0.05 dB / ms. Using an analog hardware circuit, the control function may be implemented using several comparators, differential amplifiers, and integrators to match the requirements of an attenuation device (e.g., voltage controlled attenuator, VCA). The control function may be implemented in a programmable device such as a microcontroller, FPGA or CPLD with memory, or a DSP. In this case, the power supply voltage may be provided by an analog-to-digital converter.

[0075] When the measured voltage is greater than the nominal operating voltage of 155V, less attenuation should be applied and it returns from its current value to 0 dB (no attenuation) by a fixed release rate within the range of 5 dB / s to 250 dB / s, and the preferred release rate is 25 dB / s.

[0076] In one or more embodiments, this calculated attenuation is applied to all channels of the multi-channel amplifier. However, in other embodiments, since some audio channels are known not to consume much power, it may be interesting to exclude them from attenuation using prior knowledge. Thus, when the audio system drives an active crossover speaker system, it may only make sense to attenuate the subwoofer and bass channels of the system and maintain the loudness of the mid-frequency and high-frequency channels (which draw only a small amount of power by design). In other embodiments, channels with the highest instantaneous output power can be selected and attenuated first.

[0077] The control method described above enables a good and musical-sounding power supply, but the supply voltage-dependent attenuation of music signals in different audio channels may not prevent the off state in any case. The reason is that good sound quality is typically achieved only at a moderate attack rate of 0.25 dB / ms. An additional instantaneous operating mechanism is required to fix the system.

[0078] Here, a clipping level (corresponding to the clipping voltage) calculation is used. There may be a linear control function between the power supply voltage and the clipping level corresponding to the maximum output signal voltage that the clipping device can reach before clipping its input signal accordingly. Other control functions other than the linear control function are possible for this control function, but they should increase monotonically as a function of the value of V supply should increase monotonically as a function of the value of V.

[0079] As a numerical example, an audio system with N ch = 8 channels and a common power supply supplying P supply = 2500 W is used. The power supply has a nominal voltage of V th = 155 V, changes from 150 V to 160 V at V ripple = 5 V, and has an idle voltage V idle= 177V. When no power is drawn from the power supply, the supply voltage V supply rises to V idle . The power supply is assumed to supply a constant power value P supply = V th + V ripple for all power supply voltages below. Assuming that the losses in the amplifier stage can be ignored, each channel has a steady-state output power budget of P supply = P ch = P supply / N ch = 312.5W. For the safe operation of the amplifier, the supply voltage cannot drop below V min = 130V. A load impedance of R load = 8Ω is assumed for all audio channels.

[0080] There must always be at least a margin (or voltage difference) of V diff = 5V between the supply voltage and the maximum signal voltage at the amplifier output. Two operating points can be defined to set the linear control law for the clipping level voltage. First, at the nominal supply voltage V th , the signal voltage corresponding to the high clipping level is V high = V th - V diff = 150V. Second, at the minimum supply voltage V min , the power consumption per channel, even in the case of a square wave (rectangular) output signal shape, must not exceed P ch . Therefore, the voltage corresponding to the low clipping level is V ch · R load calculated as the square root of the product P low , where R load is the total load impedance of the channel, giving V load = sqrt(P ch · R load ) = 50V. Using these two operating points, a linear control function can be defined to calculate the clipping level depending on the supply voltage. V clip = c· V supply - V offsetand here V supply is the current value of the supply voltage used as an indicator. The coefficient of this linear control function is c = (V high - V low ) / (V th - V min ) = 4. The offset of this linear control function is V offset = c·V th - V high = 470V.

[0081] Therefore, at a supply voltage of 130V (switch-off threshold), the clipping device allows only a maximum voltage of 50V at the amplifier channel output. For a signal with an 8Ω load and a clipped rectangular shape, the power per channel is (50V) 2 / (8Ω) = 312.5W. Multiplying by the number of channels gives the total power that the power supply must provide at a supply voltage of 130V. In this way, an audio system with 8 channels is protected when the power supply can provide 2500W at a supply voltage of 130V. The power must be slightly higher due to the efficiency of the amplifier channels. One skilled in the art designing such an amplification system can easily adapt these exemplary values to the requirements of a particular audio system.

[0082] At a supply voltage of 155V, the clipping level is calculated by a linear equation for an output clipping voltage of 150V. This is a reasonable margin to be considered between the supply voltage and the output voltage that a typical amplifier can reach. When the clipping level is above the maximum output level, the clipping device has no effect, i.e., it does not change the output signal.

[0083] Figure 8 shows a flowchart of a method implemented by a limiting device according to an example. This method is for use in an audio system including a plurality of amplifier channels of corresponding audio channels. Each of the amplifier channels receives its respective input audio signal and is powered by the same power supply.

[0084] In step 810, the value of the indicator is obtained. The indicator represents the energy reserve of the power supply. of the power supply.

[0085] In step 830, for each amplifier channel, the gain applied to each input audio signal by the attenuation function and the clipping level applied to the output of the attenuation function by the clipping function are determined. The gain decreases when the value of the indicator falls below a threshold, and the gain increases to a maximum value when the value of the indicator exceeds the threshold. The threshold may represent the nominal energy level at which the power supply is in a nominal operating state. The clipping level may be determined as a monotonic function of the value of the indicator.

[0086] To illustrate the operation, FIG. 9 shows a supply voltage 901 that decreases as the system response to a burst signal at all audio inputs. FIG. 9 is a screenshot of an oscilloscope of a sine wave burst signal 902, showing the effect of the limiting device on the output signal of the multi-channel amplification device and the voltage of the bulk capacitor.

[0087] First, the output signal 902 is clipped by the clipping device due to the low supply voltage value after a sudden voltage drop as a response to a high power demand. After 100 ms, the gain reduction is taken over, which means that signal clipping no longer occurs after this point. Here, the output signal is a sine wave again. The reduced amplitude (and thus reduced output power) has brought about a recovery of the supply voltage. When the supply voltage reaches V supply =V th , the control function releases the gain and the sine wave output voltage rises slightly. In the steady state region, the attack and release time intervals may alternate such that the attenuation level is approximately constant. (If the indicator remains above the threshold, i.e., V supply >V thIf so, the gain can remain in the release phase while it is limited to its maximum value. In many cases, the supply voltage drops below the threshold of 155V. Therefore, the gain is reduced again by an attack rate of 0.01 dB / ms at 154V and then 0.05 dB / ms at 150V, reaching 0.25 dB / ms at a supply voltage of 130V.

[0088] If the load impedance is 4Ω instead of 8Ω for example, different control laws must be evaluated. The power of 312.5W is reached at 4Ω with a clipping voltage of 35.36V. This must be reached at a supply voltage of 130V.

[0089] In an audio system with different load impedances, one or more clipping levels can be calculated for each load impedance. Also, for each different load impedance, a respective control signal is generated from a common control device to the clipping device within the amplifier channel. The gain can be the same for all channels, but the clipping level can depend on the attached load, and the load can be different for different channels (e.g., 4 ohms or 8 ohms).

[0090] Depending on the characteristics of the power supply, the maximum power rating of the power supply can depend on the available mains voltage. Worldwide, operating ranges of 100V, 120V, and 230V are used. The clipping level calculation can be adapted to these ranges. To achieve this, information about the mains voltage is passed to the clipping level calculation device using signals 350, 450. Thus, in a particular embodiment, there can be three sets of control equations for 100V, 120V, and 230V for different loads of 4Ω and 8Ω. The clipping level calculation formula is selected according to the actual operating conditions. Even a continuous adaptation of the clipping level calculation formula is possible according to the mains voltage. A person skilled in the art can adapt this clipping level calculation to the requirements of the power supply used in a multi-channel amplification system.

[0091] In the example of FIG. 9, a burst signal is started at time 0 ms. The output voltage of the signal exceeds 150 V. As a result of this load, the supply voltage drops sharply from its idle voltage V idle = 177 V to V min = a supply voltage slightly higher than 130 V. The threshold is set at V th = 155 V. The common control device maps the supply voltage to the time-varying clipping level. In the time interval from 0 ms to 100 ms, the output signal is clipped and does not have a sine wave shape. Further, the gain applied by the attenuation device is reduced at an attack rate of approximately 0.25 dB / ms. Thus, after 100 ms, a gain reduction of approximately 25 dB is reached. At this time, the amplitude of the burst signal is attenuated until the signal peak is below the clipping level. Since the signals of all channels are reduced, the supply voltage returns to a steady state and fluctuates slightly around the nominal voltage. The calculation device reacts to voltages higher than the threshold by increasing the gain at a release rate of 25 dB / s. Therefore, the output signal amplitude rises slightly. As a result, the supply voltage becomes slightly lower. After 300 ms, the gain applied by the attenuation device is approximately constant. This is because the release phase is interrupted by the attack phase and the supply voltage is allowed to vary (within the ripple voltage range) around the nominal voltage (related to the threshold level).

[0092] FIG. 10 is a comparison of two music signals. The lower figure is the original signal 910 played at a low level. At the top is the same signal 920 played at a much higher level that overloads the power supply, and as a result, the common control device calculates the clipping level to cut the high output amplitude and calculates the gain to attenuate the music signal within all channels.

[0093] Here, the original signal 910 is at a sufficiently low level such that there is no drop in the power supply voltage to the range where the clipping and attenuation devices operate. When the input signal is supplied to the multi-channel amplification system with a very large gain, the supply voltage suddenly drops when the amplitude of the music signal changes to a large amplitude. Thereafter, the clipping level is instantaneously reduced. This results in a first period (attack phase) having a duration of 60 ms that exhibits severe clipping of the signal peaks. During that time, the gain applied by the attenuation device is further reduced. At the end of the first period, the signal is sufficiently attenuated to exhibit the same amplitude shape as the original signal shown below.

[0094] In FIGS. 9 and 10, it can be observed that the power supply voltage has several signals and trunk frequency-dependent ripples that "modulate" the calculated clipping level for the audio signal. In another embodiment, it is possible to store the minimum value of the previously calculated clipping level and apply, for example, a clipping release rate of 16 dB / s thereto. If there is a new minimum value of the clipping level, the stored clipping level is overwritten. This can be realized as an approximation by a capacitor charged by a current source and a diode that can directly discharge or clamp the capacitor voltage to the calculated clipping voltage calculated from the power supply voltage. Next, the capacitor voltage is used to set the clipping voltage in each amplification channel. Of course, this can also be realized in software if the signal chain is digitally implemented, the amplifier has a digital input, and a digital-to-analog converter or digital PWM modulator that receives a digital input signal is used.

[0095] FIG. 11 is a screenshot of an oscilloscope of a burst signal showing the effect on the output signal 940 of a multi-channel amplification device that uses a fixed release rate for the calculated clipping level in combination with the minimum operation with respect to the clipping level derived from the instantaneous power supply voltage 930.

[0096] During the period when the output signal 940 is clipped, there is a "flat top" from this clipping operation. Modulation from the supply voltage ripple is not seen. A drawback of this embodiment is that the time interval during which the signal is clipped can be long. The reason is that by instantaneously calculating the clipping level according to the supply voltage, the level of clipping rises more quickly.

[0097] Any functions, engines, block diagrams, flowcharts, state transition diagrams, flowcharts, and / or data structures described herein should be understood by those skilled in the art to represent conceptual diagrams of exemplary circuitry embodying the principles of the present invention. Similarly, any flowchart, flowchart, state transition diagram, pseudocode, etc. is substantially represented in a computer-readable medium and, thus, represents various processes that can be executed by such a computer or processor, whether or not the computer or processor is explicitly shown.

[0098] A flowchart can describe operations as sequential processes, but many of the operations can be executed in parallel, concurrently, or simultaneously. Also, some operations may be omitted, combined, or executed in a different order. A process may end when its operations are completed, but may also have additional steps not disclosed in the figure or description. A process can correspond to a method, function, procedure, subroutine, subprogram, etc. When a process corresponds to a function, its end can correspond to the return of the function to the calling function or main function.

[0099] Each described function, engine, block, step described herein can be implemented in hardware, software, firmware, middleware, microcode, or any suitable combination thereof.

[0100] When implemented in software, firmware, middleware or microcode, the instructions for performing the required tasks may be stored on a computer-readable medium that may or may not be included in the host device or host system. The instructions may be transmitted via the computer-readable medium and loaded into the host device or host system. The instructions are configured to cause the host device or host system to perform one or more functions disclosed herein. For example, as described above, according to one or more examples, at least one memory may contain or be capable of storing the instructions, and the at least one memory and the instructions may be configured to cause one or more functions to be performed by the host device or host system using at least one processor. Further, the processor, memory, and instructions act as means for providing or causing the execution of one or more functions by the host device or host system disclosed herein.

[0101] The host device or host system may be a general-purpose computer and / or computing system, a dedicated computer and / or computing system, a programmable processing device, an audio system, a machine, etc.

[0102] The instructions may correspond to computer program instructions, computer program code, and may include one or more code segments. A code segment may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or hardware circuit by passing and / or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, transferred, or transmitted via any suitable technique including memory sharing, message passing, token passing, network transmission, etc.

[0103] When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. The term "processor" should not be construed to refer exclusively to hardware capable of executing software, but may implicitly include one or more processing circuits, whether programmable or not. A processor, or similar processing circuit, may be any type of device, including, but not limited to, a Digital Signal Processor (DSP), a network processor, an Application Specific Integrated Circuit (ASIC), a Fieldbus, a 32-bit or 64-bit processor ... Field Programmable Gate Array (FPGA), system System-on-Chips (SoC), Central Processing Unit (CPU), Quantum Processor, Arithmetic Logic Unit (ALU), Programmable Logic Unit (PLU), processing core, program The processor or processing circuitry may correspond to programmable logic, a microprocessor, a controller, a microcontroller, a microcomputer, any device capable of responding to and / or executing instructions in a defined manner and / or according to defined logic. Other hardware, conventional or custom, may also be included. The processor or processing circuitry may be configured to execute instructions adapted to cause a host device or host system to perform one or more functions disclosed herein for the host device or host system.

[0104] A computer-readable medium or computer-readable storage medium may be any storage medium suitable for storing instructions readable by a computer or processor. More generally, a computer-readable medium may be any storage medium capable of storing and / or containing and / or carrying instructions and / or data. A computer-readable medium may be a portable or fixed storage medium. A computer-readable medium may include one or more storage devices such as a permanent mass storage device, a magnetic storage medium, an optical storage medium, digital storage disks (such as CD-ROM, DVD, Blue Ray, etc.), a USB key or dongle or peripheral device, a permanent mass storage device such as a disk drive, a hard disk drive (HDD), a solid state drive (SSD), a memory card, a read only memory (ROM), core memory, flash memory, or any other non-volatile memory device, or any combination thereof.

[0105] In this description, the expression "means configured to perform one or more functions" or "means for performing one or more functions" may correspond to one or more functional blocks comprising circuitry adapted or configured to perform the relevant function(s). The block may perform this function itself, or may cooperate and / or communicate with one or more other blocks to perform this function. "Means" may correspond to or be implemented as "one or more modules", "one or more devices", "one or more units", etc. Means may include circuitry configured to perform the relevant function. Means may comprise at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to cause the at least one processor to perform the relevant function in an apparatus or system.

[0106] As used in this application, the terms "circuit" or "circuit network" can refer to a circuit implementation form of only hardware, a combination of a hardware circuit and software, a hardware circuit(s) that requires software (e.g., firmware) for operation, or a processor. The terms "circuit" or "circuit network" can include, for example, digital signal processor (DSP) hardware, network processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), etc. A circuit network can be, for example, hardware, programmable logic, a programmable processor that executes software or firmware, and / or any combination thereof (e.g., a processor, control unit / entity

[0107]

[0108] controller), and can be or can include a memory that stores data and / or instructions. Terms such as first, second, etc. may be used herein to describe various elements, but these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, without departing from the scope of the present disclosure, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.The terms used in this specification are for the purpose of describing particular embodiments only and are not intended to be limiting. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", and / or "including", when used herein, specify the presence of the stated feature, integer, step, operation, element, and / or component, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0109] Aspects of the present disclosure have been specifically shown and described with reference to the above embodiments, but it will be understood by those skilled in the art that various additional embodiments may be contemplated by modifying the disclosed machines, systems, and methods without departing from the scope of what has been disclosed. Such embodiments are to be understood as being within the scope of the present disclosure as determined based on the claims and any equivalents thereof.

Claims

1. A device for use in an audio system including multiple amplifier channels of corresponding audio channels, wherein each of the amplifier channels receives its respective input audio signal and is powered by the same power supply, and the device, - An indicator, wherein the indicator represents the energy reserve of the power supply, and the value of the indicator is obtained (810), - For each of the amplifier channels, the gain to be applied to the respective input audio signal by the attenuation function and the clipping level to be applied to the output of the attenuation function by the clipping function are determined (830), The method includes means for performing a method that includes, A device in which the gain decreases over time when the value of the indicator falls below a threshold, and increases over time to a maximum value when the value of the indicator exceeds the threshold, the threshold representing the nominal energy level at which the power supply is in nominal operation, and the clipping level is determined as a monotonic function of the value of the indicator.

2. The device according to claim 1, wherein the gain decreases over time with respect to the attack rate.

3. The device according to claim 2, wherein the attack rate is a fixed attack rate corresponding to a fixed gain decrease per period on a logarithmic scale.

4. The device according to claim 2, wherein the attack rate is a dynamic attack rate calculated as a function of the value of the indicator.

5. The device according to any one of claims 1 to 4, wherein the gain increases over time with respect to the release rate.

6. The device according to claim 5, wherein the release rate is a fixed release rate corresponding to a fixed gain increase per period on a logarithmic scale.

7. When the value of the indicator is less than the threshold, the clipping level is determined by applying a monotonic function of the output voltage of the power supply, as per any one of claims 1 to 4. The devices described in item 1.

8. The device according to claim 7, wherein the monotonic function is a continuous function of the output voltage of the power supply.

9. The device according to claim 7, wherein the indicator is proportional to the output voltage of the power supply or the squared output voltage of the power supply.

10. The device according to any one of claims 1 to 4, wherein the indicator is proportional to the energy stored in the power supply.

11. The device according to claim 1, wherein the gain changes between a minimum value and a maximum value.

12. The device according to claim 1, wherein the monotonic function is adjusted based on the main line voltage level signals (350, 450) received from the power supply.

13. The means described above, for each amplifier channel, A clipping device connected to the input of the amplifier channel and configured to apply the clipping function, - An attenuation device whose output is connected to the input of the clipping device, wherein the attenuation device is configured to apply the attenuation function, The device according to claim 1, including the device described in claim 1.

14. A method for use in an audio system including multiple amplifier channels for corresponding audio channels, wherein each of the amplifier channels receives its respective input audio signal and is powered by the same power supply, and the method is - An indicator, wherein the indicator represents the energy reserve of the power supply, and the value of the indicator is obtained (810), - For each of the amplifier channels, the gain to be applied to the respective input audio signal by the attenuation function and the clipping level to be applied to the output of the attenuation function by the clipping function are determined (830), A method comprising: the gain decreasing over time when the value of the indicator falls below a threshold; the gain increasing over time to a maximum value when the value of the indicator exceeds the threshold; the threshold representing the nominal energy level at which the power supply is in nominal operation; and the clipping level being determined as a monotonic function of the value of the indicator.

15. A computer program, when executed by at least one processor, includes instructions that cause a device to perform the method described in claim 14.

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