Patent Application
20120140930
This application claims priority to German Patent Application 10 2010 047 129.1, which was filed Sep. 30, 2010 and is incorporated herein by reference.
The present invention relates to a circuit for driving loudspeakers.
Various types of drives are used to drive loudspeakers. A simple type of drive is to drive each loudspeaker with a driver circuit via two cables. Thus, in the case of a simple drive with one driver circuit one cable with an audio signal is laid for the loudspeaker, while in this instance the other cable is the common ground (e.g., earth ground) of the loudspeaker and the driver circuit. A loudspeaker can be driven differentially by connecting the second cable not to a common ground, but to a second driver circuit.
The advantages of the simple drive over the differential drive are that fewer driver circuits are required, the result thus being that there is also a cost advantage of the simple drive over the differential drive. In the case of a simple drive, a plurality of loudspeakers can be operated with a common ground line. The outlay on the cabling can thereby be lowered, and so a further cost advantage is attained. A common ground line of a plurality of loudspeakers has the disadvantage, however, that each loudspeaker is disadvantageously influenced by the audio signals of the respective other loudspeakers owing to the common ground line. Particularly in the case of driver circuits which operate the loudspeakers with a bivalent signal, so called class D amplifiers, this leads to an audible deterioration in the acoustic signal output by the loudspeakers. A differential drive avoids this disadvantage by virtue of the fact that each loudspeaker is driven separately. However, this has the disadvantage of substantially higher costs.
An embodiment of the present invention provides a method for operating loudspeakers with a low outlay on loudspeaker drivers and cables, and provides the loudspeakers with an audio signal that exhibits a low mutual influence.
In an embodiment method for operating three loudspeakers having a provided stereo audio signal with one audio signal each for a right and a left channel, a third audio signal is extracted from the stereo audio signal. A drive signal of the left channel is produced for a loudspeaker connection from the audio signal for the left channel. A drive signal of the right channel is produced for a loudspeaker connection from the audio signal for the right channel. A first drive signal of the third audio signal is produced for a first loudspeaker connection. A second drive signal of the third audio signal is produced for a second loudspeaker connection. From the third audio signal, a first loudspeaker of the three loudspeakers is driven at a first loudspeaker connection with the drive signal of the left channel and the first drive signal of the third audio signal. The first loudspeaker of the three loudspeakers is driven at a second loudspeaker connection with the first drive signal of the third audio signal. A second loudspeaker of the three loudspeakers is driven at a first loudspeaker connection with the first drive signal of the third audio signal. The second loudspeaker of the three loudspeakers is driven at a second loudspeaker connection with the second drive signal of the third audio signal. A third loudspeaker of the three loudspeakers is driven at a first loudspeaker connection with the drive signal of the right channel and the second drive signal of the third audio signal. The third loudspeaker of the three loudspeakers is driven at a second loudspeaker connection with the second drive signal of the third audio signal.
This embodiment method can be used, for example, for a 2.1 sound system. The third channel for a 2.1 sound system, for example, a subwoofer channel, can be extracted from the audio signals of the left and right channels. The subwoofer channel can be driven by two drive signals in a fully differential fashion. The left and right stereo channels are, by contrast, driven only with one drive signal in each case. The second connection of the loudspeaker for the left and right stereo channels is made at in each case one connection of the loudspeaker for the subwoofer. This connection acts for the loudspeaker of the left and right channels like a virtual ground connection. The loudspeakers for the left and right channels are driven in a pseudo-differential fashion with this method. In the case of this method, the third audio signal acts like a common mode signal on the loudspeakers for the left and right channels, and therefore causes no deflections of any sort of the loudspeakers for the left and right channels.
In an embodiment method for operating three loudspeakers, the drive signal of the left channel, the drive signal of the right channel and the first and the second control signals of the third audio signal are signals with a bivalent level.
A bivalent drive signal can comprise, for example, the levels of positive and negative supply voltages, or supply voltage and ground. Audio systems which use a bivalent level to drive the loudspeakers are denoted as class D systems.
In an embodiment method for operating three loudspeakers, the drive signal of the left channel, the drive signal of the right channel and the first and the second drive signals of the third audio signal are pulse-width modulated signals.
In an embodiment method for operating three loudspeakers, the pulse width of the pulse-width modulated signal is a specific pulse-width value from a specific and bounded set of defined pulse-width values.
In an embodiment method for operating three loudspeakers, the third audio signal is extracted from the stereo audio signal in such a way that the third audio signal is a complement of the stereo audio signal.
With the aid of this embodiment drive by the drive signals, it is possible to achieve an uncorrupted audio signal at the outputs of the loudspeaker circuits, and thus a faithful reproduction of the audio signals by the loudspeaker per se. Complementary means that the addition of the third audio signal to the left or right audio signal leads to a linear transfer function. This method avoids overdriving the PWM.
In an embodiment method for operating three loudspeakers, the first drive signal of the third audio signal is a complement of the drive signal of the left channel, and the second drive signal of the third audio signal is a complement of the drive signal of the right channel.
Embodiments are explained in more detail below with reference to the following drawings.
In general, an embodiment circuit for operating loudspeakers having a provided audio signal comprises a first, second, third and fourth loudspeaker circuit, having one input each and one output each for connecting a loudspeaker input, the loudspeaker circuits being designed to amplify the injected signal and to provide the amplified signal at the outputs thereof. The loudspeaker circuits can, for example, be used for a 2.1 sound system. The three channels for a 2.1 sound system can be implemented by an amplifier circuit with four loudspeaker circuits, one loudspeaker circuit each being required for the two stereo channels left and right. A subwoofer channel can be driven differentially by two loudspeaker circuits. The left and right stereo channels are, by contrast, only still connected to one loudspeaker circuit each. The second connection of the loudspeaker for the left and right stereo channels is made at in each case one connection of the loudspeaker for the subwoofer. This connection acts for the loudspeaker of the left and right channels and the respective loudspeaker circuits like a virtual ground connection.
If digital, non-differential and/or single-phase class D amplifiers are used in the case of which the loudspeaker drivers of the loudspeaker circuit are not located in a feedback loop of the overall circuit, the result is a poorer rejection of the power supply interference (Power Supply Rejection, PSR or PSSR), since in comparison with the differential class D amplifiers, the additive interference component is not rejected. In the case of differential or pseudo-differential class D amplifiers, the interference signal is converted into a common mode signal so that the load, or the loudspeaker, does not perceive the additive interference.
A 2.1 sound system has three loudspeakers, a first loudspeaker reproducing a first audio signal. The first audio signal can be the audio signal of a right channel. A second loudspeaker can reproduce a second audio signal. The second audio signal can be the audio signal of a left channel. A third loudspeaker can reproduce a third audio signal. The third audio signal can be the audio signal of a subwoofer channel.
The first loudspeaker can be connected to a first loudspeaker connection at the output of the first loudspeaker circuit, and with its second loudspeaker connection to the connection of the second loudspeaker circuit. The second loudspeaker can be connected to a first loudspeaker connection at the output of the third loudspeaker circuit, and with its second loudspeaker connection to the connection of the fourth loudspeaker circuit. The third loudspeaker can be connected to a first loudspeaker connection at the output of the second loudspeaker circuit, and with its second loudspeaker connection to the connection of the third loudspeaker circuit. The first and the second loudspeakers therefore have a common connection each to a loudspeaker circuit.
Owing to a particular provision of the audio signals at the inputs of the loudspeaker circuits, it is possible to achieve an uncorrupted audio signal at the outputs of the loudspeaker circuits, and thus a faithful reproduction of the audio signals by the loudspeaker per se.
The circuit for operating loudspeakers can provide at the input of the first loudspeaker circuit a first audio signal and a first part of a third audio signal, the second loudspeaker circuit can provide at its input the first part of the third audio signal, the third loudspeaker circuit can provide at its input a second part of the third audio signal, and the fourth loudspeaker circuit can provide at its input a second audio signal and the second part of the third audio signal.
The effect of this circuit is that the third loudspeaker, the loudspeaker that reproduces the third audio signal, or the subwoofer signal, is driven fully differentially with the third audio signal. Since this loudspeaker is driven solely with the third audio signal, the reproduction of the third audio signal is not disturbed by the third loudspeaker.
This circuit equally has the effect that the first loudspeaker, which reproduces the first audio signal, or the right channel of the stereo signal, is driven in a pseudo-differential fashion with the first audio signal. The third audio signal is provided, via the first and the second loudspeaker circuits, to the first loudspeaker in the same way at the outputs of the first and the second loudspeaker circuits such that the third audio signal acts on the loudspeaker like a common mode signal, and therefore causes no deflections of any sort of the loudspeaker. The output of the second loudspeaker circuit therefore acts on the first loudspeaker like a virtual ground connection.
This circuit equally has the effect that the second loudspeaker, which reproduces the second audio signal, or the left channel of the stereo signal, is driven in a pseudo-differential fashion with the second audio signal. The third audio signal is provided, via the third and the fourth loudspeaker circuits, to the second loudspeaker in the same way at the outputs of the third and the fourth loudspeaker circuits such that the third audio signal acts on the loudspeaker like a common mode signal, and therefore causes no deflections of any sort of the loudspeaker. The output of the third loudspeaker circuit therefore acts on the second loudspeaker like a virtual ground connection.
The first and the second loudspeakers are driven by the circuit in a pseudo-differential fashion. The first and the fourth loudspeaker circuits drive the loudspeakers actively. The second and the third loudspeaker circuits act at their outputs on the loudspeakers like a virtual ground connection. The third audio signal is superimposed on the audio signals of the loudspeaker circuits in such a way that it acts on the first and second loudspeakers like a common mode signal via the outputs of the loudspeaker circuits. The first and the second loudspeaker circuits are superimposed thereby on the first part of the third audio signal, which is suitable for driving the first connection of the third loudspeaker. The second part of the third audio signal, which is suitable for driving the second connection of the third loudspeaker is in this case superimposed on the third and the fourth loudspeaker circuits.
Loudspeaker circuits of the circuit for operating loudspeakers can comprise one loudspeaker driver each with one output each which is connected to the output of the loudspeaker circuit, the loudspeaker driver providing at its outputs a signal with a bivalent level.
A bivalent drive signal can comprise, for example, the levels of positive and negative supply voltages, or supply voltage and ground. The loudspeaker driver can therefore, by way of example, be designed as a simple half bridge, the half bridge having two switches which are configured in such a way that the output of the loudspeaker driver can be switched to the first or to the second level.
Audio systems which use a bivalent level to drive the loudspeakers are denoted as class D systems.
The loudspeaker circuits of the circuit for operating loudspeakers can comprise one pulse width modulator each, having one output each and one input each. The respective input of the pulse width modulator is connected to the respective input of the loudspeaker circuit. The respective output of the pulse width modulator is connected to the respective input of the loudspeaker driver. The pulse width modulators provide a pulse-width modulated signal at their outputs. By way of example, such a pulse-width modulated signal can be provided by the pulse width modulator by virtue of the fact that the pulse width modulator samples the signal at its input and, for example, determines a pulse width with the aid of a comparator. The pulse width can assume any desired value in such a pulse-width modulated system.
The pulse-width modulator of the circuit for operating loudspeakers can provide one pulse width, the pulse width being a specific pulse width value from a specific and bounded set of defined pulse width values. The set of defined pulse width values can, for example, comprise 2n values, the result being 21−1 intervals. These pulse width values can have an equal temporal spacing.
The circuit for operating loudspeakers can have a filter for converting signals. The filter has at least one input and a first, second, third and fourth output. The first to fourth outputs of the filter is connected to the respective input of the first to fourth loudspeaker drivers. The filter is provided at its input with a first and a second audio signal. The filter uses the first and the second audio signals to produce the third audio signal and to provide it at its outputs.
The filter of the circuit for operating loudspeakers can extract the third signal from the first and the second signals in such a way that the third signal is a complement of the first and the second signals.
The filter of the circuit for operating loudspeakers can extract the first part of the third signal from the first signal, and extract the second part of the third signal from the second signal in such a way that the first part of the third signal is a complement of the first signal, and that the second part of the third signal is a complement of the second signal.
The filter of the circuit can split a stereo PCM signal into a left and right as well as into a subwoofer signal. After this splitting, the audio signals may be supplied to the corresponding pulse width modulators of the loudspeaker circuits.
The pulse width modulators of the loudspeaker circuits for the stereo channels respectively receive a superimposed PCM signal from the respective channel and the subwoofer signal, such that the loudspeakers which can be connected for the channels receive the superimposed subwoofer signal as common mode signal. This superimposition leads to the extinction of the subwoofer signals in the left and right channels. The result at the outputs of the loudspeaker circuits and at the loudspeakers is a pseudo-differential class D signal without subwoofer components. The subwoofer loudspeaker can be driven fully differentially.
In order to avoid overdriving in the PWM modulators, the separation of the subwoofer signal and the signals of the right or the left channels can be performed with a complementary filter structure. Complementary means that the addition of the subwoofer signal to the left or right audio signal leads to a linear transfer function.
The method for operating three loudspeakers converts a provided stereo audio signal which has an audio signal for a right and a left channel in such a way as to extract from the provided stereo audio signal a third audio signal which can be used to operate a subwoofer loudspeaker. The third audio signal is added to the audio signals for the left and right channels.
A third loudspeaker is driven with the third audio signal in a fully differential fashion. A virtual reference point is provided for the first and the second loudspeakers with the aid in each case of a connection of the third loudspeaker.
A first loudspeaker is driven in a pseudo-differential fashion with the audio signal for the right channel and the third audio signal.
A second loudspeaker is driven in a pseudo-differential fashion with the audio signal for the left channel and the third audio signal.
The provided stereo audio signal and the third audio signal are converted into PWM signals in the method for operating three loudspeakers.
In the method for operating three loudspeakers, the third audio signal is extracted from the provided stereo audio signal in such a way that the third audio signal is a complement of the provided stereo audio signal.
By way of example, the low-frequency subwoofer signal can be separated with a linear-phase FIR filter 711, 712 from a stereo signal 701, 702 on the right and left channels. In this example embodiment, a filter frequency of 400 Hz is applied in the linear-phase FIR filters 711, 712. The subwoofer signal is then produced by subtracting the right and left stereo input signals. It can be ensured thereby that the digital pulse width modulators of the loudspeaker circuits are not overdriven when the latter are designed for the maximum stereo input signal. What then results is a maximum modulation degree in conjunction with a maximum level of the stereo input signal.
When the separation of the audio signals is not performed in an entirely complementary fashion, this leads to a reduced driving of the pulse width modulators of the loudspeaker circuits, and thus to a lower modulation degree. The separation should therefore be performed as far as possible with linear-phase filter structures.
The splitter 740 in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2010 047 129.1 | Sep 2010 | DE | national |
