Actuating circuit for microelectromechanical sound generator and sound generating system

Abstract

The invention relates to the actuation of an electrostatic sound transducer having a microelectromechanical component. A control circuit having a differential amplifier is provided, a bias voltage being provided on the intermediate attachment of the sound converter with respect to a common mode voltage of the differential amplifier. The supply voltage of the differential amplifier is matched according to the maximum signal amplitude of the input signal.

Description

Technical Field

[0001] The invention relates to a control circuit for a micro-electromechanical sound generator and a sound generating system having such a control circuit. In particular, the invention relates to the control of a micro-electromechanical sound generator having an electrostatically controllable membrane. Background Art

[0002] Sound generators can be used in loudspeakers, headphones or similar devices to generate sound waves from electrical signals. With the continuous development of miniaturization, sound generating elements based on microelectromechanical systems (MEMS) are also becoming more and more important. For example, there are sound generators in which the diaphragm can be excited by means of electrostatic forces.

[0003] For example, document EP 2 582 156 A2 describes an electrostatic loudspeaker which can be implemented as a micro-electromechanical system. Summary of the invention

[0004] The invention provides a control circuit for a micro-electromechanical sound generator and a sound generating system having the features of the independent claims. Further advantageous embodiments are the subject matter of the dependent claims.

[0005] According to this setup:

[0006] A control circuit for a micro-electromechanical sound generator. The sound generator can have two external attachments and one intermediate attachment. The control circuit includes a differential amplifier and a voltage generator circuit. The differential amplifier includes two output attachments. Each of the two output attachments is electrically coupled to a corresponding output attachment of the sound generator. The differential amplifier is designed to provide an output voltage between the two output attachments, which output voltage corresponds to an input signal between the two input attachments of the differential amplifier. The voltage generator circuit is designed to provide a predetermined, preferably constant DC voltage relative to the common mode voltage of the differential amplifier on the intermediate attachment of the sound generator. The control circuit is particularly designed to adjust the supply voltage for the differential amplifier according to the maximum amplitude of the input signal.

[0007] Additionally set:

[0008] A sound generating system having a micro-electromechanical sound generator and a drive control circuit according to the present invention. The sound generator comprises two external attachment parts and one intermediate attachment part. The external attachment parts of the sound generator are electrically coupled to the output attachment part of the drive control circuit. The intermediate attachment part of the sound generator is electrically coupled to the output end of the voltage generating circuit.

[0009] Advantages of the present invention

[0010] The invention is based on the recognition that voltages that exceed the voltage levels of conventional CMOS technology are often required to drive a sound generator based on MEMS with an electrostatically controllable membrane. Suitable control circuits are therefore required to drive such sound generators, which control circuits are able to provide voltages at a sufficient voltage level. However, conventional control circuits may have a relatively high energy requirement.

[0011] The idea of ​​the present invention is therefore to take this knowledge into account and to enable efficient control of an electrostatic sound generator having a MEMS which has a reduced energy requirement.

[0012] For this purpose, it is provided on the one hand that the voltage level is increased by means of an offset voltage generated by the voltage generator circuit. In addition, the supply voltage for the differential amplifier provided in the control circuit can be adapted as a function of the respective current signal amplitude, similar to a class H amplifier. It can be used here that the sound signal usually has high amplitudes, in particular maximum amplitudes, only very rarely. During the usually relatively long phases of low signal amplitudes, the differential amplifier can be operated with a lower supply voltage. This results in a significantly lower energy requirement. In particular in battery-operated systems, the operating time per battery charge can be significantly increased as a result.

[0013] In principle, any suitable differential amplifier circuit in the form of discrete components or integrated switching circuits can be used as differential amplifiers, which are suitable for providing an amplified output signal corresponding to the input signal and which can be operated with a variable supply voltage. As will be explained further below, the differential amplifier can be operated with a supply voltage between a reference potential (0 V) and a (positive) supply voltage or, in an alternative embodiment, can also be operated with negative and positive supply voltages.

[0014] The output voltage provided at the two output attachments of the differential amplifier can be provided at the external attachment of the electrostatic MEMS sound generator. In addition, a voltage boosted to a higher voltage level by means of a voltage generator circuit can be provided at the middle attachment of the sound generator. By means of this offset voltage (bias voltage, Bias-Spannung), the voltage at the middle attachment of the sound converter can be boosted, in particular with respect to the common mode voltage of the differential amplifier. As a result, a sufficiently high voltage suitable for operating the electrostatic sound converter is applied to the sound converter. The voltage provided by the voltage generator can in particular be a voltage with a predetermined constant DC voltage.

[0015] The sound signal emitted by the sound generator usually has the maximum possible amplitude only relatively rarely. It is therefore possible to operate the differential amplifier with a lower operating / supply voltage during the time period in which the sound signal to be emitted has only a lower amplitude. This makes efficient and energy-saving operation possible. Here, in particular, the supply voltage for the differential amplifier can be adapted according to the corresponding real-time amplitude of the electrical signal. For example, the input signal can be continuously monitored or evaluated in order to determine the maximum amplitude within a predetermined time interval. Subsequently, the supply voltage of the differential amplifier can be adapted accordingly according to the maximum amplitude determined within this time interval. Here, for example, the supply voltage can be adjusted to the following voltage level, which can also achieve a sufficient safety margin for amplifying the input signal.

[0016] According to one embodiment, the drive control circuit includes a level converter. The level converter can be designed to match the signal level of the input signal. In addition, the level converter can also be designed to provide a matched input signal on the input attachment of the differential amplifier. In this way, the voltage range of the input signal can be matched to a voltage range suitable for subsequent amplification by the differential amplifier. For example, an input signal with positive and negative voltage components can be converted into a signal that no longer has a negative voltage component by corresponding level matching. Such a signal can then also be amplified, for example, by means of a differential amplifier, which in the case of this signal operates between 0V and a positive supply voltage.

[0017] According to one embodiment, the control circuit is designed to set the supply voltage for the level converter as a function of the maximum amplitude of the input signal. In this way, similar to the concept of the differential amplifier according to the invention, the level converter can also be operated accordingly with a supply voltage that is sufficient for the necessary level matching on the one hand and allows efficient and energy-saving operation by temporarily reducing the supply voltage on the other hand.

[0018] According to one embodiment, the control circuit is designed to provide a voltage between a reference potential and a predefined positive supply voltage as the supply voltage. In this way, it is sufficient to adapt only the positive supply voltage to the corresponding voltage level.

[0019] According to one embodiment, the driver circuit is designed to provide a voltage between a predetermined negative supply voltage and a predetermined positive supply voltage as a supply voltage. Although both the positive supply voltage and the negative supply voltage must be dynamically matched accordingly, in this solution, matching of the supply voltage can be omitted for upstream level matching if necessary. Instead, if negative voltages are also possible for the differential amplifier, upstream level matching can be implemented with a constant supply voltage.

[0020] According to one embodiment, the drive control circuit includes a signal processing device. The signal processing device is designed to receive a digital audio signal and convert the digital audio signal into an analog audio signal. In addition, the signal processing device can also provide the analog audio signal as an input signal to a level converter or a differential amplifier. In addition, the signal processing device is designed to determine the maximum amplitude of the input signal when using a digital input signal. Since "digital / analog conversion" and "determination of the maximum voltage amplitude when using a digital input signal" can be implemented in parallel here, the maximum amplitude of the input signal can be provided before the D / A conversion for the corresponding signal segment is completed due to the delay caused by the running time of the digital / analog conversion. Therefore, when the analog signal is output by the D / A converter, the corresponding supply voltage for the differential amplifier and, if necessary, for the level converter can be matched in a suitable manner.

[0021] According to one embodiment, the signal processing device is designed to process digital signals using a digital signal processor (DSP). The signal processed by the DSP can then be converted into an analog audio signal. For this purpose, a D / A converter connected downstream of the DSP can usually be used. In particular, due to the runtime delay occurring during the processing by the DSP, the maximum amplitude of the signal ascertained in parallel in the digital range is provided in time for matching the supply voltage of the differential amplifier and, if necessary, the level converter.

[0022] The above configurations and expansions can be combined with each other as much as they make sense. Other configurations, expansions and implementations of the present invention also include combinations not mentioned in detail, which are related to the combination of the features of the present invention described in the embodiments above or below. In particular, those skilled in the art also add individual aspects as improvements or supplements to the corresponding basic form of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further features and advantages of the invention are explained below with reference to the drawings.

[0024] Here it is shown:

[0025] Figure 1 A schematic diagram showing a principle circuit diagram of a sound generating system according to one embodiment;

[0026] Figure 2 A schematic diagram showing a principle circuit diagram of a drive circuit of a sound generator according to one embodiment;

[0027] Figure 3 a schematic diagram showing a block diagram of an audio system for a sound generating system according to one embodiment; and

[0028] Figure 4 A schematic diagram shows a basic circuit diagram of a control circuit for a sound generator according to another specific embodiment. DETAILED DESCRIPTION

[0029] Figure 1 A schematic diagram of a principle circuit diagram of a sound generating system with a control circuit 1 according to one embodiment is shown. In this case, the sound generation in the sound generating system is carried out by means of an electrostatic sound generator 2, in particular a sound generator 2 with a microelectromechanical system (MEMS). In this case, the diaphragm of the sound generator 2 can be deflected by providing a sufficiently high voltage. Figure 1 In FIG. 2 , the sound generator 2 is illustrated by two capacitors C1 and C2 , which are electrically connected to one another at an intermediate attachment M. The respective further attachments of the capacitors C1 and C2 form the outer attachments of the sound generator 2 .

[0030] In order to drive the sound generator 2, the input signal V_in can be amplified by means of a differential amplifier 10. The two output attachments of the differential amplifier 10 can be electrically connected to the external attachments of the sound converter 2. In order to be able to provide a sufficiently high voltage for deflecting the diaphragm of the electrostatic sound generator 2, the following voltage is provided on the middle attachment M of the sound generator 2, which is increased by an offset voltage V_bias (bias voltage) relative to the common mode voltage V_CM of the differential amplifier 10. For this purpose, a voltage generator circuit 11 can be provided in the drive circuit 1 having the differential amplifier 10. The common mode voltage thus increased can be supplied to the middle attachment M of the sound generator 2 via a buffer circuit 12 when necessary.

[0031] The control circuit 1 must be dimensioned in such a way that the maximum expected amplitude of the input signal V_in can be amplified with sufficient quality according to the requirements. In order to amplify the signal with the maximum expected amplitude in the input signal V_in, a correspondingly high supply voltage must be provided at the differential amplifier 10 .

[0032] Figure 2A schematic diagram of a block diagram of a control circuit 1 for a sound generating system with an electrostatic MEMS sound generator 2 according to one embodiment is shown. In this case, the (analog) input signal V_in can be supplied, for example, first to a filter 30, optionally a filter 30 with suitable buffering, in particular a low-pass filter. The filter device 30 can be operated with a relatively low supply voltage VDD_LV. The output signal of the filter device 30 can then be supplied to a level converter 20. The level converter 20 can, for example, increase the signal provided by the filter device 30 by a DC voltage component, so that the output signal provided by the level converter 20 is suitable for amplification by a downstream differential amplifier 10 within a corresponding voltage range. In this case, the level converter 20 can be operated with a supply voltage VDD_MV, which is usually between the supply voltage VDD_LV of the filter device 30 and the supply voltage VDD_HV of the differential amplifier 10. For example, the voltage level of the input signal V_in can be increased to such an extent that no signal component with a negative voltage, i.e., less than 0V, is present in the increased signal.

[0033] Subsequently, the signal output by the level converter 20 is amplified by the differential amplifier 10 and combined with Figure 1 is supplied to the sound generator 2 as already described.

[0034] Here, the differential amplifier 10 and the level converter 20 must be designed for the maximum expected amplitude of the input signal V_in in principle. Accordingly, the input voltages of the differential amplifier 10 and the level converter 20 must also be provided with a sufficient safety margin corresponding to the amplitude of the input signal V_in.

[0035] However, since the maximum expected amplitude in the input signal V_in occurs only relatively rarely, especially in the case of sound signals, it is sufficient for signal segments with smaller amplitudes to operate the differential amplifier 10 and, if necessary, the level converter 20 at a lower supply voltage during these signal segments. According to the invention, it is therefore provided that the supply voltage VDD_HV of the differential amplifier 10 and, if necessary, also the supply voltage VDD_MV of the level converter 20 are adapted to the current amplitude of the input signal V_in, and that the supply voltage VDD_HV and, if necessary, VDD_MV are reduced, in particular in segments with smaller amplitudes in the input signal V_in.

[0036] In order to adapt the supply voltages VDD_MV and VDD_HV to the corresponding signal amplitudes in a timely manner, the input signal V_in can be analyzed, for example based on the digital signal, before the digital signal is converted into the analog input signal V_in. An exemplary approach for this is, for example, Figure 3 Shown in.

[0037] If you can Figure 3 As can be seen from the arrangement of , for example, a digital signal can be received by means of a corresponding input interface 110. If necessary, the sound intensity, i.e. the amplitude, can also be adapted in the digital range. Subsequently, the digital signal can be processed in the first signal path, for example, by means of a digital signal processor (DSP) 120, for example, filtered, etc. The prepared digital signal can then be converted into an analog signal V_in by means of a digital / analog converter (D / A) 130. In parallel with this, the maximum amplitude of the real-time audio signal can be realized in another signal path based on the digital data by means of a corresponding evaluation device 140. For this purpose, for example, the maximum amplitude can be determined within a predetermined time period. In principle, however, any other scheme for determining the corresponding real-time maximum amplitude in the digital data is also possible.

[0038] Since processing of the digital signal in DSP 120 and in downstream D / A converter 130 may result in a runtime delay that is longer than the time required for determining the maximum amplitude in device 140 at the current time, based on this determination of the maximum amplitude, supply voltage VDD_HV for differential amplifier 10 and, if necessary, for level converter 20 can be adapted in a timely manner to the signal profile of (analog) input signal V_in.

[0039] Figure 4 A schematic diagram of a block diagram of a drive circuit 1 for a sound generating system having an electrostatic MEMS sound generator 2 according to another embodiment is shown. The drive circuit 1 in this embodiment is different from the previously described drive circuit 1 according to Figure 2 The difference of the described control circuit 1 is in particular that the differential amplifier 10 is not operated here with a supply voltage between the reference potential (0V) and the positive supply voltage VDD_HV, but with a supply voltage between the negative supply voltage VSS_HV and the positive supply voltage VDD_HV. In this case, these supply voltages VSS_HV and VDD_HV can be adapted in accordance with the respective current signal amplitude in the input signal V_in, similar to the previously described approach.

[0040] Due to the possibility that a negative supply voltage can also be provided for the differential amplifier and thus the output signal can also be in the negative voltage range, the signal no longer needs to be so greatly boosted by the level converter 20, especially in the case of input signals V_in with large amplitudes. Therefore, the level converter 20 can be continuously operated with a constant supply voltage VDD_MV. Thus, the matching of the supply voltage for the level converter 20 can be omitted.

[0041] Apart from this, in particular in the case of matching supply voltages VSS_HV and VDD_HV, the above explanations also apply to determining the corresponding real-time amplitude in the digital input signal.

[0042] In summary, the present invention relates to the control of an electrostatic sound transducer having a micro-electric structure element. For this purpose, a drive circuit having a differential amplifier is provided, wherein a bias voltage relative to the common mode voltage of the differential amplifier is provided at a central attachment of the sound transducer. In this case, the supply voltage of the differential amplifier can be adapted according to the signal amplitude of the input signal.

Claims

1. A control circuit (1) for a micro-electromechanical sound generator (2), the sound generator having two external attachment parts and one middle attachment part (M), the sound generator comprising: a differential amplifier (10) having two output attachments, the output attachments being electrically coupled to the two external attachments of the sound generator (2) and the differential amplifier being designed to provide an output voltage between the two output attachments, the output voltage corresponding to an input signal (V_in) between the two input attachments of the differential amplifier (10); and a voltage generator circuit (11) designed to provide a predetermined DC voltage (V_bias) relative to the common mode voltage of the differential amplifier (10) on the middle attachment portion (M) of the sound generator (2); The drive control circuit (1) is designed to adjust a supply voltage (VDD_HV, VSS_HV) for the differential amplifier (10) according to a maximum amplitude of the input signal (V_in).

2. The drive control circuit (1) according to claim 1 has a level converter (20), which is designed to match the signal level of the input signal (V_in) and provide a matched input signal at the input attachment part of the differential amplifier (10).

3. The drive control circuit (1) according to claim 2, wherein: The driver control circuit (1) is designed to adjust a supply voltage (VDD_MV) for the level converter (20) according to a maximum amplitude of the input signal (V_in).

4. The drive control circuit (1) according to any one of claims 1 to 3, wherein: The control circuit (1) is designed to provide a voltage between a reference potential and a predefined positive supply voltage as a supply voltage (VDD_HV) for the differential amplifier (10).

5. The drive control circuit (1) according to any one of claims 1 to 3, wherein: The control circuit (1) is designed to provide a voltage between a predetermined negative supply voltage and a predetermined positive supply voltage as a supply voltage (VSS_HV, VDD_HV) for the differential amplifier (10).

6. The driver control circuit (1) according to claim 1, comprising a signal processing device (100) which is designed to receive a digital audio signal, to convert the digital audio signal into an analog audio signal and to provide the analog audio signal as an input signal to the level converter (20) or to the differential amplifier (10). in, The signal processing device (100) is further designed to determine a maximum amplitude of the input signal using the digital input signal.

7. The driving control circuit (1) according to claim 8, wherein: The signal processing device (100) is designed to process the digital signal using a digital signal processor (120) and subsequently convert it into an analog audio signal.

8. A sound generating system, comprising: a micro-electromechanical sound generator (2); and The drive control circuit (1) according to any one of claims 1 to 7; in, The sound generator (2) comprises two external attachment parts and one intermediate attachment part (M), wherein the external attachment parts are electrically coupled to the output attachment parts of the drive control circuit (1), and the intermediate attachment part (M) is electrically coupled to the output end of the voltage generating circuit (11).

9. The sound generating system according to claim 8, wherein: The sound generator (2) comprises a micro-electromechanical system having an electrostatically controllable membrane.

Images