Optimized control circuit for micro-electro-acoustic generator and sound generating system

Abstract

The invention discloses a control circuit for a micro-electro-acoustic generator. The micro-electro-acoustic generator is provided with a first central attachment end, a second central attachment end, a first outer attachment end and a second outer attachment end. The control circuit comprises a differential amplifier, which has a first output attachment end coupled to the first outer attachment end and a second output attachment end coupled to the second outer attachment end, and which is designed to control the first outer attachment end and the second outer attachment end by means of a differential signal corresponding to the input signal. The control circuit comprises a first voltage generator circuit designed to provide a predetermined first DC voltage to the first central attachment terminal relative to a common-mode voltage of the differential amplifier, and a second voltage generator circuit designed to provide a predetermined second DC voltage to the second central attachment terminal relative to a common-mode voltage of the differential amplifier. The second voltage generator circuit is designed to provide a predetermined second DC voltage to the second center attachment terminal relative to the common mode voltage of the differential amplifier. The invention also discloses a microcomputer electroacoustic generator and a sound generating system.

Description

Technical Field

[0001] The present invention relates to an optimized control circuit for a micro-electromechanical acoustic generator and a corresponding sound generating system. In particular, the present invention relates to a control device for a micro-electromechanical acoustic generator having a plurality of central attachment ends. Background Art

[0002] Sound generators can be used in loudspeakers, headphones or other devices in order to generate sound waves from electrical signals. In this regard, in the course of the development of miniaturization, sound generating elements based on microelectromechanical systems (MEMS) are also gaining in importance. 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 MEMS. In one embodiment, it is proposed to conduct the audio signal to an external capacitor plate by means of a differential amplifier, see Figure 1 , in order to drive the micro-electro-acoustic generator. Summary of the invention

[0004] The present invention provides an optimized control circuit for a micro-electromechanical sound generator and a corresponding sound generating system.

[0005] Preferred embodiments are described below.

[0006] According to a first aspect, the invention relates to a control circuit for a micro-electro-mechanical-acoustic generator, the micro-electro-mechanical-acoustic generator having a first central attachment terminal, a second central attachment terminal, a first external attachment terminal and a second external attachment terminal. The control circuit comprises a differential amplifier, the differential amplifier having a first output attachment terminal and a second output attachment terminal, the first output attachment terminal being coupled to the first external attachment terminal, the second output attachment terminal being coupled to the second external attachment terminal, and the differential amplifier being designed to control the first external attachment terminal and the second external attachment terminal by means of a differential signal, the differential signal corresponding to an input signal. The control circuit comprises a first voltage generator circuit and a second voltage generator circuit, the first voltage generator circuit being designed to provide a predetermined first DC voltage to the first central attachment terminal relative to a common mode voltage of the differential amplifier, the second voltage generator circuit being designed to provide a predetermined second DC voltage to the second central attachment terminal relative to the common mode voltage of the differential amplifier.

[0007] According to one embodiment, the control circuit is designed to set a supply voltage for the differential amplifier as a function of a maximum amplitude of the input signal.

[0008] According to one embodiment, the control circuit has a level converter which is designed to adapt a common-mode signal level of the input signal, wherein the level converter is coupled to the differential amplifier or is integrated in the differential amplifier in order to provide the adapted input signal.

[0009] According to one embodiment, the control circuit is designed to receive a supply voltage for the level converter as a function of the maximum amplitude of the input signal.

[0010] According to one embodiment, the control circuit is designed to receive a voltage between the reference potential and a predefined positive supply voltage as a supply voltage for the differential amplifier.

[0011] According to one embodiment, the control circuit is designed to receive a voltage between a predefined negative supply voltage and a predefined positive supply voltage as a supply voltage for the differential amplifier.

[0012] According to one embodiment, the differential amplifier is designed as a class G amplifier or a class H amplifier.

[0013] According to one embodiment, the first voltage generator circuit provides a predetermined first DC voltage relative to the common mode voltage of the differential amplifier via a first buffer circuit. The first buffer circuit preferably uses two supply voltages, preferably via a first potential-free charge pump (see Figure 5 The left part) keeps the voltage difference between the two supply voltages constant, and the first comparator compares two currents, such as a first current and a second current, the first current being a comparison current proportional to the voltage difference between the supply voltages, and the second current being a reference current proportional to a reference voltage.

[0014] According to one embodiment, the second voltage generator circuit provides a predetermined second DC voltage relative to the common mode voltage of the differential amplifier via a second buffer circuit. The second buffer circuit preferably uses two supply voltages, preferably via a second potential-free charge pump (see Figure 6 The left part) keeps the voltage difference between the two supply voltages constant, and the first comparator compares two currents, such as a first current and a second current, the first current being a comparison current proportional to the voltage difference between the supply voltages, and the second current being a reference current proportional to a reference voltage.

[0015] According to one embodiment, the control circuit has a signal processing device which is designed to receive a digital audio signal, convert the digital audio signal into an analog audio signal and provide the analog audio signal as an input signal to a level converter or a differential amplifier. The signal processing device can also be designed to determine a maximum amplitude of the input signal when using a digital input signal.

[0016] According to one embodiment, the signal processing device is designed to process the digital signal using a digital signal processor and subsequently convert it into an analog audio signal.

[0017] According to a second aspect, the present invention relates to a micro-electro-acoustic generator, which has a first central attachment end, a second central attachment end, a first external attachment end and a second external attachment end, wherein the first external attachment end is arranged on a first substrate of the micro-electro-acoustic generator, and the second external attachment end is arranged on the first substrate; and wherein the first central attachment end is arranged on the second substrate of the micro-electro-acoustic generator, and the second central attachment end is arranged on the second substrate.

[0018] According to an extended scheme, the first substrate is configured to reduce the parasitic capacitance between the first external attachment terminal and the first substrate and the parasitic capacitance between the second external attachment terminal and the first substrate; and / or, the second substrate is configured to increase the parasitic capacitance between the first center attachment terminal and the second substrate and the parasitic capacitance between the second center attachment terminal and the second substrate.

[0019] According to one configuration, the first substrate is stationary and the second substrate is movable; or the first substrate is movable and the second substrate is stationary.

[0020] According to a third aspect, the invention relates to a sound generating system having a control circuit as described above and a micro-electromechanical sound generator.

[0021] The invention is based essentially on the recognition that, in order to control a sound generator based on MEMS with a membrane that can be controlled electrostatically, voltages that are greater than the voltage levels of conventional CMOS technology are generally required. In order to control a sound generator of this type, suitable control circuits are therefore required that can provide voltages of sufficient voltage height. Conventional control circuits may have a high energy requirement. Conventional control circuits may also not be able to efficiently control a sound generator with a plurality of central attachment terminals.

[0022] It is therefore an object of the present invention to provide a highly efficient control device for an electrostatic sound generator having a plurality of central attachment ends, which device has a reduced energy requirement.

[0023] For this purpose, it is provided on the one hand that the voltage level is increased by means of a bias voltage via a voltage generator circuit. In addition, the supply voltage for the differential amplifier provided in the control circuit can be adapted - similar to a class H amplifier - as a function of the respective current signal amplitude. In this case, it can be used that acoustic signals usually have high, in particular maximum, amplitudes only very rarely. In the event of long periods 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.

[0024] In principle, any suitable differential amplifier circuit can be used as the differential amplifier, which is in the form of discrete components or an integrated circuit, is 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 in more detail below, the differential amplifier can be operated with a supply voltage between a reference potential (0 volts) and a (positive) supply voltage or, in alternative embodiments, also with negative and positive supply voltages. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In the following, other features and advantages of the present invention are described with reference to the accompanying drawings. It is shown here:

[0026] Figure 1 : Schematic diagram of a control circuit and a MEMS acoustic generator having a central attachment end;

[0027] Figure 2 : A schematic diagram of a control circuit and a micro-electro-mechanical-acoustic generator according to one embodiment, wherein the micro-electro-mechanical-acoustic generator has a plurality of central attachment terminals;

[0028] Figure 3 : A schematic diagram of a control circuit for a micro-electro-acoustic generator according to one embodiment;

[0029] Figure 4 According to one embodiment, Figure 2 A schematic diagram of an exemplary MEAS generator;

[0030] Figure 5 : A schematic diagram of a charge pump for controlling a circuit according to one embodiment;

[0031] Figure 6 : A schematic diagram of a charge pump for controlling a circuit according to one embodiment;

[0032] Figure 7 According to one embodiment, Figure 5 and Figure 6 Schematic diagram of the charge pump comparator;

[0033] Figure 8 : A schematic diagram of a circuit for generating a reference current for a control circuit in a high voltage range according to one embodiment;

[0034] Fig. 9 : A schematic diagram of a circuit for generating a reference current for a control circuit in a low voltage range according to one embodiment;

[0035] Fig.10 : A schematic diagram of a circuit for generating a reference current for a control circuit in a low voltage range according to one embodiment;

[0036] Fig.11 : A schematic diagram of a circuit for generating a comparison current for a control circuit in a high voltage range according to one embodiment;

[0037] Fig.12 : A schematic diagram of a current subtractor for controlling a circuit according to one embodiment;

[0038] Fig.13 : A schematic diagram of a current subtractor for controlling a circuit according to one embodiment;

[0039] Fig.14 : A schematic diagram of a current comparator for controlling a circuit according to one embodiment;

[0040] Fig.15 : Fig.14 The operating characteristics of the current comparator;

[0041] Fig.16 : A schematic diagram of a current comparator for controlling a circuit according to one embodiment;

[0042] Fig.17 : Fig.16 The operating characteristics of the current comparator;

[0043] Fig.18 : A schematic diagram of a current comparator for controlling a circuit according to one embodiment;

[0044] Fig.19 : Fig.18 The operating characteristics of the current comparator.

[0045] In all the figures, identical or functionally identical elements and devices are provided with the same reference symbols. DETAILED DESCRIPTION

[0046] Figure 1A schematic diagram showing a control circuit 1200 and a micro-electro-acoustic generator 1100 having a central attachment terminal E 0 .

[0047] The sound generation in the sound generating system can be realized, for example, by means of a micro-electromechanical acoustic generator 1100. In this case, the diaphragm of the micro-electromechanical acoustic generator 1100 can be deflected by providing a sufficiently high voltage. Figure 1 Through two capacitors C 1 and C 2 The micro-electro-acoustic generator 1200 is shown, wherein the capacitor is connected to the micro-electro-acoustic generator 1200 via a single central attachment terminal E. 0 are electrically connected to each other. Capacitor C 1 and C 2 The corresponding other attachment ends form the external attachment ends of the micro-electro-acoustic generator 1100 .

[0048] In order to control the MEAS generator 1100, the input signal V can be amplified by means of the differential amplifier 1210. IN The two output attachment terminals of the differential amplifier 1210 can be electrically connected to the outer attachment terminals of the micro-electromechanical acoustic generator 1100. In order to provide a sufficiently high voltage for deflecting the diaphragm of the micro-electromechanical acoustic generator 1100, the central attachment terminal E 0 The following voltage is provided on the differential amplifier 1210: This voltage is relative to the common mode voltage V CM With bias voltage V BIAS (Bias voltage) is increased. For this purpose, a voltage generator circuit 1211 can be provided in the control circuit 1200 with the differential amplifier 1210. If necessary, the common mode voltage thus increased can be supplied to the central attachment terminal E via the buffer circuit 1212. 0 .

[0049] The control circuit 1200 must be dimensioned so that the input signal V IN The maximum expected amplitude of can be amplified according to the requirements and with sufficient quality. In this case, in order to amplify the input signal V IN In order to obtain a signal with the maximum expected amplitude in , a correspondingly high supply voltage must be provided at the differential amplifier 1210 .

[0050] In practice, Figure 1 Mechanical movement of the capacitor plates of the microelectroacoustic generator 1100 shown in FIG. 1 may result in a change in capacitance over time, which may result in a current load at the center attachment terminal because the changes at the upper and lower capacitors may have opposite signs.

[0051] Figure 2A schematic diagram showing a control circuit 2200 and a micro-electro-acoustic generator 2100 according to one embodiment, the micro-electro-acoustic generator having a plurality of central attachment terminals E 0 and E 3 .

[0052] The sound generation in the sound generating system can be realized, for example, by means of a micro-electromechanical acoustic generator 2100. The diaphragm of the micro-electromechanical acoustic generator 2100 can be deflected by providing a sufficiently high voltage. Figure 2 Through the capacitor C 1 , C 2 , C 3 and C 4 A micro-electro-acoustic generator 2200 is shown. The capacitors can be electrically connected to each other in pairs via a central attachment terminal. Figure 4 Describe the parasitic capacitor C in detail p0 , C p1 , C p2 and C p3 .

[0053] like Figure 2 As shown in 1 and C 2 The first center attachment end E 0 are electrically connected to each other, and the capacitor C 3 and C 4 The second center attachment end E 3 Electrically connected to each other.

[0054] The other end of the capacitor C 1 and C 3 The first external attachment end E 1 The other attachment terminal C of the capacitor 2 and C 4 The second external attachment end E 2 Electrically connected to each other.

[0055] In order to control the MEAS generator 2100, the input signal V can be amplified by means of the differential amplifier 2210. IN Here, two output attachment terminals of the differential amplifier 2210 may be electrically connected to external attachment terminals of the micro-electro-acoustic generator 2100 .

[0056] exist Figure 2 In the example, two electrodes are driven by an amplified audio signal, while the other two electrodes are driven by a constant voltage. AC and common mode voltage V CM The differential signal controls the first external attachment terminal E 1 and the second outer attachment end E 2. Through a constant voltage V CM +V DC Manipulate the first center attachment end E 0 . Through a constant negative voltage V CM -V DC Manipulate the second center attachment end E 3 . V CM Less than V DC , and V CM 、V AC and V DC All are positive numbers. AC can be, for example, in the order of about 20 V, while V DC It may be, for example, in the order of magnitude of approximately 30 V.

[0057] A first voltage generator circuit 2211 may be provided in the control circuit 2200 to increase the common mode voltage V CM And the increased voltage V CM +V DC Supplied to the first center attachment terminal E via the optional first buffer circuit 2212 0 In addition, a second voltage generator circuit 2213 may be provided in the control circuit 2200 to reduce the common mode voltage V CM And the reduced voltage V CM -V DC Supplied to the second center attachment terminal E via the optional second buffer circuit 2214 0 .

[0058] Typically, the audio input signal is in the low voltage range. The common mode of the audio input signal must be moved to a level that is equal to the common mode voltage V CM This function can be implemented in a circuit such as Figure 3 Alternatively or at least partially, this functionality can also be integrated directly into the differential amplifier 2210 .

[0059] High-pass filtering and / or low-pass filtering and / or buffering of the audio signal may be implemented in the device or may not be implemented in the device if the corresponding functions are implemented elsewhere in the signal path.

[0060] Figure 3 A method for a micro-electro-acoustic generator (not shown, see for example) according to one embodiment is shown. Figure 2 or Figure 4 ) is a schematic diagram of a control circuit 3200.

[0061] Here, the (analog) input signal V INFor example, it can first be supplied to a filter 3230, in particular a low-pass filter, optionally with suitable buffering. The filter device 3230 can be supplied with a low supply voltage VDD LV Then, the output signal of the filter device 3230 may be supplied to the level converter 3220 .

[0062] The level converter 3220 can, for example, partially boost the signal provided by the filter device 3230 with a DC voltage, so that the output signal provided by the level converter 3220 is suitable for being amplified in a corresponding voltage range by the downstream differential amplifier 3210. The level converter 3220 can be operated with a supply voltage VDD. MV operation, the supply voltage is usually at the supply voltage VDD of the filter device 3230 LV The supply voltage VDD of the differential amplifier 3210 HV For example, the input signal V IN The voltage level of is increased to such an extent that no signal parts with negative voltage, ie, less than 0 volts, are present in the increased signal.

[0063] The signal output by the level converter 3220 can be amplified by the differential amplifier 3210 and supplied to the micro-electro-acoustic generator, such as, for example, referring to Figure 2 Just as described.

[0064] Here, in principle, the differential amplifier 3210 and the level converter 3220 can be designed for the input signal V IN The maximum expected amplitude of . Accordingly, it can also be based on the input signal V IN The amplitude of is provided in a manner that provides the input voltage of the differential amplifier 3210 and the level converter 3220 with sufficient safety margin.

[0065] Since the input signal V may rarely appear in the case of acoustic signals IN , so for signal segments with lower amplitudes it may be sufficient to operate the differential amplifier 3210 and, if necessary, the level converter 3220 at a lower supply voltage during these signal segments. IN The current amplitude adapts the supply voltage VDD of the differential amplifier 3210 HV and VSS HV and the supply voltage VDD of the level converter 3220 when necessary MV , and especially with input signal V IN The supply voltage VDD is reduced in the low amplitude section HV and VSS HVAnd if necessary, reduce the supply voltage VDD MV .

[0066] In order to make the supply voltage VDD MV and VDD HV and VSS HV Adapting to the corresponding signal amplitude in time can be done, for example, when converting a digital signal into an analog input signal V IN Previously, based on the digital signal, the input signal V IN Conduct analysis.

[0067] Suitably, the supply voltage for the level shifting function performed by the level converter 3220 may be at an average voltage level VDD MV The common-mode voltage V at the amplifier output is 5 V, for example, which is compatible with the common-mode voltage at the amplifier input. CM Can have ground and VDD MV any value between , but preferably, can be set to VDD MV / 2 The supply voltage VDD of the differential amplifier 3210 HV and VSS HV can be compared with the common-mode voltage V CM Arranged symmetrically.

[0068] It is possible to connect ground and VDD in differential amplifier 3210. MV is used as an intermediate supply. In this way, the differential amplifier 3210 can be implemented as a class G amplifier. On the other hand, the high voltage supply VDD HV and VSS HV It can be increased or decreased depending on the input signal, thus realizing a class H amplifier.

[0069] If the audio signal is small, for example 20dB below the maximum value, it is possible to increase VDD HV Reduce to VDD MV And VSS HV to ground, whereby the differential amplifier 3210 is operated in a reduced voltage range and can have significantly lower power consumption.

[0070] The advantage of the control circuit 3200 is that the power required for the buffer device in order to connect the first central attachment terminal E 0 and the second center attachment end E 3The buffer device 3200 is maintained at a constant voltage in each case. Strictly speaking, this is suitable if the capacitor remains linear and does not change in time. In the case of large mechanical movements, this assumption is not entirely suitable and the buffer device needs to be able to carry a certain current load. However, the control circuit 3200 can minimize the current load in the MEMS under certain symmetry conditions.

[0071] Figure 4 According to one embodiment, Figure 2 A schematic diagram of an exemplary acoustic generator 4100 is shown. Figure 4 Seen in the sound generator 4100 Figure 3 The capacitor C 1 , C 2 , C 3 and C 4 , and the parasitic capacitor C p0 , C p1 , C p2 and C p3 .

[0072] Figure 4 The structure of the capacitor used in the electrostatically driven sound generator 4100 is shown. Figure 4 The electrode voltage V shown in CM Quantity. Figure 4 As can be seen in the figure, the parasitic capacitor C p0 and C p3 can have a common attachment terminal, and the parasitic capacitor C p1 and C p2 It is also possible to have a common attachment end.

[0073] As described in detail below, for example, under condition C 1 =C 2 =C 3 =C 4 and C p0 =C p3 If the first external attachment terminal E 1 The voltage on the second external attachment terminal E 2 The voltage on the capacitor C 1 and C 4 decreases, and the capacitance C 2 and C 3 That is, the net current from the first center attachment terminal E 0 Flow to the second center attachment end E 3 First center attachment end E 0 tends to reduce its voltage, while the second center attachment terminal E 3Tends to increase its voltage. Parasitic capacitor C p0 and C p3 The series connection (Reihe) gives the first center attachment end E 0 supply charge, and the second center attached terminal E 3 Considering its beneficial effect, capacitor C p0 and C p3 Large dimensions are intended, wherein the requirements on the bandwidth of the buffer device may set limits.

[0074] According to a particular aspect, the first central attachment end E can be provided with a relatively high impedance 0 and the second center attachment end E 3 The substrate, namely C p0 and C p3 The common attachment terminal of the capacitors is biased, but the two capacitors still behave like two separately grounded capacitors rather than like a series connection of capacitors.

[0075] Capacitor C p1 and C p2 It should be as small as possible to reduce the power consumption of the differential amplifier.

[0076] If reference Figure 4 ±V AC Voltage controls the electrodes on the movable part of the sound generator 4100 and the DC If the voltage is controlled on the electrodes on the stationary part of the sound generator 4100, the scheme can still be applied. Then, the first center attachment end E 0 Assigned to +V DC (+V CM ) The electrode being manipulated, the second center attachment end E 3 Assigned to -V DC (+V CM ) is the electrode to be manipulated, and the external attachment terminal E 1 and E 2 Assigned to ±V AC The electrodes being manipulated are sufficient.

[0077] In this redistributed configuration, the parasitic capacitor C p1 and C p2 Undertake C p0 and C p3 and must be renamed C p0 and C p3 In turn, the parasitic capacitor C Cp0 and C p3 Undertake C p1 and C p2 and must be renamed Cp1 and C p2 .

[0078] The buffer device consumes a certain amount of bias current in order to ensure a certain bandwidth. The buffer device can be fed via two voltage rails, which have a voltage greater than VDD. MV A small voltage difference, for example 2 V or a maximum of 5 V, preferably 4 V. Such a voltage difference can be generated by a potential-free charge pump, such as in Figure 5 and Figure 6 As schematically shown in .

[0079] Manipulate the first center attachment end E 0 The buffer device uses VDD_HVBP as a low supply voltage and VDD_HVBP_HI as a high supply voltage. The bias current flows from the high voltage to the lower voltage, thereby reducing the voltage difference between the two nodes VDD_HVBP_HI and VDD_HVBP. The potential-free charge pump can detect when the difference VDD_HVBP_HI-VDD_HVBP becomes smaller than a predetermined threshold, such as 2V, by means of a comparator. If the difference is smaller than the threshold, the pumping process starts in order to make the voltage difference greater than the threshold.

[0080] Manipulate the second center attachment end E 3 The buffer device uses VDD_HVBN as a high supply voltage and VDD_HVBN_LO as a low supply voltage. The bias current flows from the high voltage to the lower voltage, thereby reducing the voltage difference between the two nodes VDD_HVBN and VDD_HVBN_LO. The potential-free charge pump can detect with the help of a comparator when the difference VDD_HVBN-VDD_HVBN_LO becomes smaller than a predetermined threshold, for example 2V. If the difference is smaller than the threshold, the pumping process starts in order to make the voltage difference greater than the threshold.

[0081] Figure 7 A schematic diagram of a comparator is shown. According to one embodiment, the comparator can be used to Figure 5 and Figure 6 The comparator shown implements the comparison function VDD_HVBP_HI–VDD_HVBP>γV ref , where γV ref =2V is applicable; and VDD_HVBN–VDD_HVBN_LO>γV ref , where γV ref =2V can be applied.

[0082] Based on this comparison, an ON signal or an OFF signal is generated for each potential-free charge pump.

[0083] In order to achieve the desired functionality of generating a voltage difference and comparing the difference with another voltage reference, different solutions can be used. For example, it is possible to use a standard differential amplifier and a standard comparator and then a dedicated analog level shifter to either shift the voltage difference into the low voltage range and perform the comparison there, or to compare the voltage difference with the reference voltage V ref Shifting to the higher voltage range of the potential-free comparator. However, these implementations may be less favorable in terms of their area and / or power consumption.

[0084] For the intended application, further solutions are proposed for generating supply voltage differential signals and analog level shifting. Preferably, the level shifting can be performed towards the low voltage range in order to control a clock control circuit for each charge pump by means of an ON signal or an OFF signal, which clock control circuit also operates in the low voltage range.

[0085] A comparison current proportional to the voltage difference between the supply voltages of the potential-free charge pump and a reference current proportional to the reference voltage are generated. The comparison current generated in the high voltage range can be moved to the low voltage range, where it is compared with the reference current.

[0086] Figure 8 A voltage divider with fixed resistors R1_high and R2_high generates a reference voltage vref_high according to the ratio of supply voltages Vdd_high to Vss_high, which corresponds to the above-mentioned supply voltages VDD_HVBP_HI and VDD_HVBP.

[0087] This voltage is then used in conjunction with a standard operational amplifier that can only operate in a local voltage range and does not need to see high voltages in order to bias PFET_high so that the same current that passes through R1_high also flows through R3_high. That is, R1_high and R3_high have the same fixed resistance, while R2_high can be selected to have a very high impedance in order to achieve low current consumption. In this circuit, the current i_high corresponds to the actual voltage difference between the potential-free supply voltages Vdd_high and Vss_high.

[0088] In the high negative voltage range, a complementary circuit can be used in which the roles of Vdd_high and Vss_high are interchanged and the PFET is replaced by an NFET. In this case, Vdd_high and Vss_high correspond to VDD_HVBN and VDD_HVBN_LO, respectively.

[0089] Fig. 9 A schematic diagram of a circuit for generating a reference current for a control circuit in the low voltage range according to one embodiment is shown. A similar scheme can be used in the low voltage range to generate a reference for further comparison. The working principle of the circuit is similar to that of the reference Figure 8 The working principle described is similar. Resistors R2_low and R3_low have the same resistance value and may also be equal to R1_high and R3_high. R1_low may be selected to have a very high impedance in order to achieve low current consumption and may be equal to R2_high.

[0090] For example, in Figure 8 The two separate circuits shown in can be used for two potential-free comparators in the high voltage range. Thus, the difference in the corresponding supply rails can be converted into a current and moved to the low voltage range in a much simpler manner with low current consumption. In the low voltage range, a reference current is also generated, which can be used instead of the previously mentioned reference voltage Vref. However, other variants are also possible in order to generate a reference current in the voltage range.

[0091] Fig.10 The following circuit is shown, for example, in which an NFET current mirror and a resistor R1_low with a fixed high impedance can be used to generate a reference current. Fig.11 The following circuit is shown, for example, in which a PMOS current mirror and a resistor R1_high with a fixed high impedance can be used to generate the current.

[0092] The comparison operation can be performed with the aid of currents representing the difference in the supply lines. By providing the currents, it is possible to use Fig.12 A simple current subtractor is shown in FIG.

[0093] The reference current i_low from the low voltage range can be mirrored on the same path as the corresponding current i_high from the potential-free high voltage domain, where both converge to i_diff. Assuming a constant mirror ratio of 1:1 for all circuits, the voltage at i_diff varies according to the resulting current difference i_low-i_high.

[0094] Fig.13A more advanced current subtractor is shown, which also implements this function. Here, the currents from the two voltage ranges are first decoupled from the outside by means of self-amplifying current mirrors P1, P2, N1 and N2 for i_low and self-amplifying current mirrors P5, P6, N5 and N6 for i_high. The current from the outside sets the stable operating point. Then, as described with reference to Fig.12 As described, these buffered currents can be subtracted in order to obtain the corresponding voltage at i_diff again.

[0095] The voltage at i_diff must now be converted into a logic signal which represents the desired ON and OFF functions for the clock control and thus for the charge pump and the potential-free supply rail itself. Figures 14 to 19 Three different implementations of a current comparator are shown and described.

[0096] Fig.14 A current comparator with a cross-coupled inverter input stage is shown in which N1 and P1 are interchanged from their standard positions. In this configuration, the potential i_diff is kept near the switching threshold of the inverter configuration. When the current at i_diff is changed by the previously described current subtractor, the input voltage for the next inverter P3 / N3 changes so slightly that it is greater than the switching threshold and causes a change in the potential at comp_out from low to high or from high to low.

[0097] Fig.15 Show Fig.14 . The working principle of the current comparator in FIG. By changing the Vdd_high potential from 5.5V to 6.5V (Vss_high is stable at 4V), the current i_high changes linearly, while the current i_low in the low voltage range is kept stable by not changing the low voltage supply Vdd_low = 2V (Vss_low = 0V). The two supply ranges produce the same current with a potential difference of 2V. The voltage at i_diff on the voltage subtractor also changes accordingly. In the illustrated implementation, if i_high is less than i_low, the resulting signal comp_out remains logically low, and switches to logically high as soon as i_high is greater than i_low.

[0098] exist Fig.16A second implementation variant for the current comparator is shown in . Here too, two cross-coupled inverter stages are used, but they form a correct latch in such a way that the positions of P1 and N1 are not interchanged. In this configuration, i_diff is not kept near the switching threshold of the inverter. With regard to the current consumption, this has the advantage that i_diff can move more freely in the direction of the supply rails Vdd_low / Vss_low and bias the inverters P1 / N1 and P2 / N2 in their respective ON and OFF states, without a direct current being able to flow between the supply rails. This behavior can also be Fig.17 . With such a latch structure, an internal hysteresis for the comp_out decision can be implemented, which in this example is set to a threshold between 6.15V and 6.2V compared to the same current in the case of 6V. Such a hysteresis can be useful in order to avoid undesired switching of ON / OFF (=comp_out) in terms of supply rail peaks and supply rail ripples and in order to make a decision only in case of a stable rail voltage.

[0099] The current comparator can also be used as Fig.18 The simpler implementation shown in Fig.18 In an implementation of , the potential at i_diff is directly connected to the input of the inverter having P1 and N1.

[0100] Fig.19 and Fig.15 The comparison shows that according to Fig.18 The behavior of the current comparator is based on Fig.14 The behavior of the current comparator is similar, but in this case, i_diff can move freely as in the latch variant. Fig.19 There is no hysteresis in , and as soon as i_high is greater than i_low, the signal comp_out starts to change its logic level.

Claims

1. A control circuit (2200; 3200) for a micro-electro-mechanical-acoustic generator (2100; 4100), the micro-electro-mechanical-acoustic generator having a first central attachment end (E0), a second central attachment end (E3), a first external attachment end (E1) and a second external attachment end (E2), the control circuit comprising: Differential amplifier (2210; 3210), the differential amplifier having a first output attachment terminal and a second output attachment terminal, the first output attachment terminal is coupled to the first external attachment terminal (E1), the second output attachment terminal is coupled to the second external attachment terminal (E2), and the differential amplifier is designed to operate the first external attachment terminal (E1) and the second external attachment terminal (E2) by means of a differential signal, the differential signal corresponding to the input signal (V IN ); A first voltage generator circuit (2211) and a second voltage generator circuit (2213), wherein the first voltage generator circuit is designed to be used for a common mode voltage (V CM ) provides a predetermined first DC voltage (+V DC ), the second voltage generator circuit is designed to be used for a common mode voltage (V CM ) provides a predetermined second DC voltage (-V DC ).

2. The control circuit (2200; 3200) according to claim 1, wherein: The control circuit (2200; 3200) is designed to control the input signal (V IN ) sets the maximum amplitude of the supply voltage (VDD_HV, VSS_HV) used for the differential amplifier (2210; 3210).

3. The control circuit (2200; 3200) according to claim 1, comprising a level converter (3220) which is designed to adapt the input signal (V IN ) of the common-mode signal level, where The level converter (3220) is coupled to the differential amplifier (2210; 3210) or integrated in the differential amplifier to provide an adapted input signal (V IN ).

4. The control circuit (2200; 3200) according to claim 3, wherein: The control circuit (2200; 3200) is designed to receive a supply voltage (VDD) for the level converter (3220) according to the maximum amplitude of the input signal (VIN). MV ).

5. The control circuit (2200; 3200) according to any one of claims 1 to 4, wherein: The control circuit (2200; 3200) is designed to receive a voltage between a reference potential and a predetermined positive supply voltage as a supply voltage (VDD) for the differential amplifier (2210; 3210). HV ).

6. The control circuit (2200; 3200) according to any one of claims 1 to 4, wherein: The control circuit (2200; 3200) is designed to receive a voltage between a predetermined negative supply voltage and a predetermined positive supply voltage as a supply voltage for the differential amplifier.

7. The control circuit (2200; 3200) according to any one of claims 1 to 6, wherein: The differential amplifier (2210; 3210) is implemented as a class G amplifier or a class H amplifier.

8. The control circuit (2200; 3200) according to any one of claims 1 to 7, in, The first voltage generator circuit (2211) is connected to the common mode voltage (V) of the differential amplifier (2210; 3210) via the first buffer circuit (2212). CM ) provides the predetermined first DC voltage (+V DC ), wherein the first buffer circuit (2212) preferably uses two supply voltages (VDD_HVBP, VDD_HVBP_HI), preferably maintaining a voltage difference between the two supply voltages constant by a first potential-free charge pump (5220) using a first comparator, the first comparator comparing two currents, namely a first current proportional to the voltage difference and a second current proportional to a reference voltage; and / or The second voltage generator circuit (2211) is connected to the common mode voltage (V CM ) provides the predetermined second DC voltage (-V DC ), wherein the second buffer circuit (2214) preferably uses two supply voltages (VDD_HVBN_LO, VDD_HVBN), and preferably maintains a voltage difference between the two supply voltages constant by a second potential-free charge pump (6230) using a second comparator, wherein the second comparator compares two currents, namely a first current proportional to the voltage difference and a second current proportional to a reference voltage.

9. The control circuit (2200; 3200) according to any one of claims 1 to 8, comprising a signal processing device, which is designed to receive a digital audio signal, convert the digital audio signal into an analog audio signal and provide the analog audio signal as an input signal to the level converter (3220) or the differential amplifier (2210; 3210), in, The signal processing device is furthermore designed to ascertain a maximum amplitude of the input signal using the digital input signal.

10. A micro-electromechanical acoustic generator (2100; 4100), the micro-electromechanical acoustic generator having a first central attachment end (E0), a second central attachment end (E3), a first outer attachment end (E1) and a second outer attachment end (E2), in, The first external attachment end (E1) is arranged on a first substrate of the micro-electro-acoustic generator (2100; 4100), and the second external attachment end (E2) is arranged on the first substrate; Wherein, the first central attachment end (E0) is arranged on the second substrate of the micro-electro-acoustic generator (2100; 4100), and the second central attachment end (E3) is arranged on the second substrate.

11. The micro-electro-acoustic generator (2100; 4100) according to claim 10, in, The first substrate is configured to reduce a parasitic capacitance (C p1 ) and a parasitic capacitance (C p2 ); and / or The second substrate is configured to increase the parasitic capacitance (C p0 ) and a parasitic capacitance (C p3 ).

12. The micro-electro-acoustic generator (2100; 4100) according to any one of claims 10 to 11, wherein: The first substrate is stationary and the second substrate is movable; or the first substrate is movable and the second substrate is stationary.

13. A sound generating system, comprising: The control circuit (2200; 3200) according to any one of claims 1 to 9; and The micro-electro-acoustic generator (2100; 4100) according to any one of claims 10 to 12.

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