Method for suppressing sensor-induced interference

Abstract

The invention relates to a method for generating a modulation signal (68) for a chopper using a delta-sigma modulation for damping critical frequencies, the method comprising at least the following steps: determining a transfer function, wherein a transfer function comprises a noise transfer function (56), generating an output sequence (69) by way of a delta-sigma modulator (55) by processing an input signal (63) by way of a quantizer (60) and a feedback path (61) of the delta-sigma modulator (55), using the generated output sequence (69) as a chopper sequence (53), integrating (34) a pseudo noise sequence (59) and the transfer function by way of an adding process in order to modify the input signal (63) before it is quantized, wherein a modified sequence (66) is generated, quantizing the modified sequence (66), wherein a modulation signal (68) is generated, feeding back the modulation signal (68) and repeating the determination (31) and quantizing to form the delta-sigma modulation and controlling the chopper based on the modulation signal (68).

Description

[0001] Description

[0002] title

[0003] Technical field

[0004] The invention relates to a method for generating a modulation signal for a chopper using delta-sigma modulation for attenuating critical frequencies. Furthermore, the invention relates to a delta-sigma modulator for generating a modulation signal. The invention also relates to a use of the delta-sigma modulator.

[0005] State of the art

[0006] A sensor, for example a Wheatstone bridge or a capacitive sensor, requires a control signal, which is typically a reference voltage V. re This sensor represents f, but can represent any other physical signal such as current, power, charge, and / or others. This sensor has a transfer function V. senseon, which is a function of both the control signal, namely a reference voltage V re f, as well as the sensor value sense vaiue is, which represents the physical sensor value, for example, for resistive or capacitive units. V sense For example, it can be detected by an analog-to-digital converter to enable a digital representation of the sensor value, which is not relevant within the scope of the present invention and is therefore not described further. In case of disturbances of V re f or V sense For example, electromagnetic interference can cause a distortion of the measured value.

[0007] An effective technique to eliminate such distortions is called "sensor chopping." Sensor chopping involves inverting the actuator signal, which simultaneously inverts the sensor signal V. senseThis occurs. A further inversion of the sensor signal corrects this inversion. It is important to note that, unlike the twice-inverted sensor signal, noise is only inverted once. Thus, the noise is modulated by the chopper, while the signal being evaluated remains unaltered.

[0008] The interference is typically modulated to a frequency above that of the sensor signal, which is determined by a chopper modulation frequency that can then be filtered into the signal path. Such modulation is detrimental if there is a frequency difference between the interference signal and the modulation frequency, or between the chopper modulation signal and the interfering signal, that is equal to the frequency difference between the interference signal and the chopper modulation frequency. In such a case, the interference is modulated to the same frequency as the sensor signal, thus distorting the sensor measurement.

[0009] To avoid a correlation between the interference signal and the chopper, the chopper's modulation signal can be designed as a random sequence. While a random sequence eliminates possible correlations between the chopper and the interference signal, it also exhibits spectral components at all frequencies. Consequently, V sense The signal is distorted by random frequency components and captured in a similar way to thermal noise. This is a disadvantage of the solution, but it is accepted because such distortion is generally less significant than distortion caused by a single tone.

[0010] Disclosure of the invention

[0011] According to the invention, a method for generating a modulation signal for a chopper using delta-sigma modulation for attenuating critical frequencies is proposed, comprising at least the following steps: a. Determining a transfer function which includes a noise transfer function, b. Generating an output sequence by a delta-sigma modulator by processing an input signal through a quantizer and a feedback path of the delta-sigma modulator, c. Using the generated output sequence as the chopper sequence, d. Integrating a pseudo-output sequence and the transfer function by an addition process to modify the input signal before it is quantized, generating a modified sequence, e. Quantizing the modified sequence, generating a modulation signal, f. Feeding back the resulting error signal and repeating the determination and quantization for delta-sigma modulation, and g.Controlling the chopper based on the modulation signal.

[0012] The solution according to the invention eliminates the distortion problem caused by the chopper with respect to the transfer function V. sense This is achieved by generating a modulation signal, namely a chopper sequence, for the chopper. This adjusts the chopper's frequency to a specific interference frequency to prevent the chopper from resonating during an interference event and thereby causing either DC distortion or increased noise.

[0013] According to the invention, a chopper is understood to be an electronic circuit or device used in sensors, particularly capacitive sensors, resistive bridges, or similar devices. For example, in such a technical solution, the chopper typically switches a sensor from one state to another at a specific frequency. Through these switching operations, the chopper is able to effectively reduce noise caused by a variety of noise sources, such as electrical noise, thermal noise, and environmental disturbances. This leads to improved separation of the useful signal from interfering noise signals, resulting in both higher accuracy and higher sensitivity of the sensor compared to operating without a chopper.

[0014] For the purposes of the present invention, a pseudo-noise sequence is understood to be a data sequence and / or a signal sequence that is generated by a deterministic process but appears like real noise. The pseudo-noise sequence can, for example, be generated by a digital generator. Advantageously, according to the method of the invention, the pseudo-noise sequence is fed in before quantization in order to protect the delta-sigma modulator from limit cycles. An additional advantage of using a pseudo-noise sequence before quantization is that this results in the shaping of the noise of the pseudo-noise sequence to frequencies outside the band of interest.

[0015] In the method according to the invention, a modulation signal, namely a chopper sequence, is generated for the chopper, whereby a critical frequency is suppressed. This results in a sequence whose spectrum has zeros at a given frequency f. Nua and its multiples. Does the noise consist exclusively of frequency components at a given frequency f? NuU and their multiples, a selection of choppers leads to a resulting noise spectrum shaped similarly to a chopper sequence. For example, a DC voltage has no signal components. If a DC voltage is additionally applied to a sensor signal, it remains unaltered. In the proposed method, a delta-sigma modulator is used to generate the sequence. By employing a quantizer, an output sequence with a frequency f is produced. sand values ​​of +1 / -1 derived from the delta-sigma modulator, which serves as a chopper sequence. The spectral properties of this chopper sequence are subject to a noise transfer function, which is determined, for example, by a loop filter. The noise transfer function is a filter function that affects quantization noise and improves the performance of the delta-sigma modulator.

[0016] In an advantageous further development of the method proposed according to the invention, the noise transfer function is determined by a loop filter.

[0017] In an advantageous further development of the method proposed according to the invention, the loop filter acts as a reduction element and dampens the resulting error signal.

[0018] In an advantageous further development of the method proposed according to the invention, the loop filter comprises a number of zeros, where the zeros are determined by the delay element z~ k at a frequency f zero = nx^- are generated, with n a positive integer, k a number of delay elements and fs a sampling frequency of the system, and where a position of the zeros is determined by the delay element.

[0019] Furthermore, the invention relates to a delta-sigma modulator for generating a modulation signal according to the proposed method, comprising at least the following components: a noise transfer function comprising at least a first adder and a delay element, a pseudo-noise sequence, a quantizer, a feedback path and at least a second adder, wherein the second adder is used to modify the input signal prior to quantization.

[0020] In a further development of the delta-sigma modulator proposed according to the invention, a noise transfer function comprises at least one loop filter.

[0021] In an advantageous further development of the delta-sigma modulator proposed according to the invention, a feedback path comprises a modulation signal of the quantizer, which is fed back to the noise transfer function.

[0022] In an advantageous further development of the delta-sigma modulator proposed according to the invention, the pseudo-noise sequence is fed into the input of the quantizer to protect against limit cycles.

[0023] Furthermore, the invention relates to the use of the delta-sigma modulator for generating a modulation signal for the chopper.

[0024] Furthermore, the invention relates to the use of the delta-sigma modulator for noise suppression of sensor-induced disturbances.

[0025] Advantages of the Invention: The solution according to the invention allows for improvements in both the performance and reliability of the sensor. By generating the modulation signal for the chopper from known noise frequencies, the distortion problem typically caused by the chopper is specifically counteracted. This enables more precise signal processing and avoids unwanted distortions.

[0026] By regulating the chopper in such a way that it never resonates at the interfering frequencies, the risk of interference such as DC distortion or increased noise is significantly reduced. This leads to an improvement in the acquired data or signals.

[0027] Precise control of the chopper through the chopper sequence ensures reliable system performance even under demanding conditions. Operation remains stable even in the event of disturbances, thus guaranteeing reliable signal processing.

[0028] By specifically adjusting the chopper frequency to known interference frequencies, the accuracy and reliability of measurements and / or signal processing are increased. This enables accurate and consistent results even in environments with variable interference.

[0029] Thus, the solution according to the invention enables the optimization of system performance by reducing distortions, minimizing interference, and ensuring robust operation under various conditions. This improves both the results and the quality of the acquired data or signals.

[0030] Brief description of the drawings

[0031] Embodiments of the invention are explained in more detail with reference to the drawings and the following description.

[0032] Figure 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography.

[0033] Figure 2 shows a schematic representation of a method for generating a modulation signal for a chopper,

[0034] Figure 3 shows a schematic representation of a circuit of a sensor noise reduction system.

[0035] Figure 4 shows a diagram of a sequence and

[0036] Figure 5 shows a schematic representation of a circuit of a delta-sigma modulator.

[0037] Embodiments of the invention

[0038] In the following description of embodiments of the invention, identical or similar elements are designated by the same reference numerals, and repeated descriptions of these elements are omitted in individual cases. The figures represent the subject matter of the invention only schematically.

[0039] The following section describes, with reference to Figure 1, the essential components of a projection exposure system 1 for microlithography. The description of the basic structure of the projection exposure system 1 and its components is not intended to be restrictive.

[0040] One embodiment of a lighting system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optic 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the radiation source 3 can also be provided as a separate module from the rest of the lighting system 2. In this case, the lighting system 2 does not include the radiation source 3. A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be moved, particularly in a scanning direction, by means of a reticle displacement drive 9.

[0041] Figure 1 shows a Cartesian xyz coordinate system for illustrative purposes. The x-direction runs perpendicular to the plane of the drawing. The y-direction runs horizontally, and the z-direction runs vertically. In Figure 1, the scan direction runs along the y-direction. The z-direction runs perpendicular to the object plane 6.

[0042] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 is parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0043] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0044] Radiation source 3 is an EUV radiation source. Radiation source 3 emits, in particular, EUV radiation, which is also referred to below as useful radiation, illumination radiation 16, or illumination light. The useful radiation has a wavelength in the range between 5 nm and 30 nm. Radiation source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. Radiation source 3 can be a free-electron laser (FEL). Radiation source 3 can be a tin-based or xenon-based EUV radiation source. The illumination radiation 16, which emanates from the radiation source 3, is focused by a collector 17.The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated by the illuminating radiation 16 at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0045] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the radiation source 3 and the collector 17, and the illumination optics 4.

[0046] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted mirror 20 comprises a plurality of individual first facets 21, which are hereinafter also referred to as field facets. Only a few of these facets 21 are shown in Figure 1 as examples.

[0047] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular border contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0048] As is known, for example, from DE 10 2008 009 600 Al, the first facets 21 can themselves each be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can in particular be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 Al.

[0049] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction.

[0050] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first faceted mirror 20 and the second faceted mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0051] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0052] The second facets 23 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 Al in this regard.

[0053] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0054] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (Fly's Eye Integrator).

[0055] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second faceted mirror 22, for example a pupil faceted mirror, can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220586 A1.

[0056] With the aid of the second faceted mirror 22, the individual first facets 21 are imaged into the object field 5. The second faceted mirror 22 is the last beam-shaping, or indeed the last, mirror for the illumination radiation 16 in the beam path before the object field 5.

[0057] In another embodiment of the illumination optics 4, not shown, a transmission optic can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to imaging the first facets 21 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optic can in particular comprise one or two mirrors for normal incidence (Nl mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (Gl mirrors, grazing incidence mirrors).

[0058] In the embodiment shown in Fig. 1, the lighting optics 4 has exactly three mirrors after the collector 17, namely the deflecting mirror 19, the first faceted mirror (field faceted mirror) 20 and the second faceted mirror (pupil faceted mirror) 22.

[0059] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0060] The mapping of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate mapping.

[0061] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure unit 1. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The projection optics 10 is a double-obscured optic. The penultimate mirror M5 and the last mirror M6 each have an aperture for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0062] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0063] The projection optics 10 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0064] The projection optics 10 can be anamorphic. In particular, they have different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, ± 0.125). A positive image scale β indicates an image without image inversion. A negative value for the image scale β indicates an image with image inversion.

[0065] The projection optics 10 thus lead to a reduction in the x-direction, that is, in the direction perpendicular to the scan direction, by a ratio of 4:1. The projection optics 10 lead to a reduction in the y-direction, that is, in the scan direction, by a ratio of 8:1.

[0066] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute values ​​in the x and y directions, for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0067] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 5 and the image field 11 can be the same or, depending on the design of the projection optics 10, different. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A.

[0068] Each of the first facets 23, namely pupil facets, is assigned to exactly one of the second facets 21, namely field facets, to form an illumination channel for illuminating the object field 5. This can result in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 with the help of the field facets. The field facets generate a plurality of images of the intermediate focus on the pupil facets assigned to them.

[0069] The field facets are each superimposed on the reticulum 7 by an associated pupil facet to illuminate the object field 5. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0070] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, in particular the subset of pupil facets that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill. A similarly desirable pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

[0071] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0072] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0073] The entrance pupil of the projection optics 10 cannot always be illuminated exactly by the second faceted mirror 22. When the projection optics 10 image the center of the second faceted mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0074] The projection optics 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second faceted mirror 22 and the reticle 7. This optical element can accommodate the different positions of the tangential and sagittal entrance pupils.

[0075] In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second faceted mirror 22 is arranged in a plane conjugate to the entrance pupil of the projection optics 10. The first field faceted mirror 20 is arranged tilted relative to the object plane 6. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the deflecting mirror 19.

[0076] The first faceted mirror 20 is tilted relative to an arrangement plane defined by the second faceted mirror 22. Using the projection exposure system 1, at least a portion of the reticulum 7 in the object field 5 is imaged onto a region of a photosensitive layer on the wafer 13 in the image field 11 for the lithographic fabrication of a micro- or nanostructured component, in particular a semiconductor component, for example, a microchip. Depending on whether the projection exposure system 1 is configured as a scanner or a stepper, the reticulum 7 and the wafer 13 are moved continuously in the y-direction in scanner mode or stepwise in stepper mode, synchronized over time.

[0077] Depending on the design, individual components or component assemblies described above, such as the EUV collector 17, the illumination optics 4, or the projection optics 10, can also be components of a mask inspection device or a mask metrology device. A mask inspection system is generally known from US 10,042,248 B2, DE 102 20 815 Al, and WO 2012 / 101 269 Al.

[0078] The projection optics 10 or imaging optics of such a mask inspection device or mask metrology device can be designed in such a way that a magnifying projection or imaging from the object field 5 into the image field 11 takes place.

[0079] For example, during lithography, undesirable disturbances such as artifacts can occur, caused by the radiation source 3. These disturbances can be introduced by faulty ground connections in the sensor front end, which are reduced by the method 30 presented in the present invention.

[0080] Figure 2 shows, in schematic form as a block diagram, an exemplary method 30 according to the invention for generating a modulation signal 68 for a chopper 42, 43. In the first step, a transfer function 31 is determined, wherein a transfer function comprises a noise transfer function 56. In a second step, an output sequence 32 is generated by a delta-sigma modulator 55 by processing an input signal 63 through a quantizer 60 and a feedback path 61 of the delta-sigma modulator 55. In the third step of the method 30 according to the invention, the generated output sequence 69 is used 33 as a chopper sequence 53. In the fourth step, a pseudo-noise sequence 59 and the transfer function are integrated 34 by an addition process to modify the input signal 63 before it is quantized, generating a modified sequence 66.In the fifth step of the inventive method 30, the modified sequence 66 is quantized 36, generating a modulation signal 68. In the sixth step, the modulation signal 68 is fed back 37, and the comparison 35 is repeated, followed by quantization 36 to achieve delta-sigma modulation. In the final eighth step, the chopper 42, 43 is controlled 38 based on the modulation signal 68.

[0081] Figure 3 shows a representation of a sensor noise reduction system 40 in the form of a circuit. The circuit comprises a series of components arranged sequentially from left to right. At the beginning of the circuit, a positive reference voltage V is applied. re f P 44 and a negative reference voltage V ref>nReference voltages 44 and 45 are fed into the first chopper 42. These reference voltages serve, for example, as reference values ​​for a sensor 41 and are modulated to minimize the susceptibility of measurements to interference. The two reference voltages 44 and 45 are fed into the first chopper 42. The first chopper 42 modulates the incoming reference voltages 44 and 45 using a "colored noise sequence," namely a modulation signal 68, provided by a delta-sigma modulator 55, to generate a differential reference voltage 46. This differential reference voltage 46 forms the basis for a subsequent measurement by the sensor 41 and enables precise acquisition of the measured values. Subsequently, the sensor 41, for example in the form of a Wheatstone bridge, receives the differential reference voltage 46 and converts it into a sensor signal 47. The sensor signal 47 is fed to a second chopper 43.This second chopper 43 further processes the sensor signal 47 and splits it into a positive sensor signal component 48 and a negative sensor signal component 49. Processing by the second chopper 43 suppresses noise in the sensor signal 47, resulting in improved signal quality.

[0082] Figure 4 shows a diagram of an exemplary sequence 53 of a switching sequence that can be used as a modulation signal 68 for the first and / or second chopper 42, 43 for noise suppression. A frequency 51 in Hertz is plotted on a horizontal X-axis, while a power spectral density 52 in decibels relative to a full scalar of the system and a noise bandwidth is plotted on a vertical Y-axis. The chopper sequence 53 shows a multitude of zeros 54, which, for example, indicate regions where there is no or minimal energy in the signal.

[0083] Figure 5 shows a schematic representation of a delta-sigma modulator 55 circuit. The delta-sigma modulator 55 circuit comprises a quantizer 60, a pseudo-noise sequence 59 element, and a transfer function element, which is implemented as a noise transfer function 56 with a loop filter 65. Figure 5 also shows that the delta-sigma modulator 55 includes a first adder 57 and a second adder 62. The first adder 57 is an associated component of the noise transfer function 56. The second adder 62 is an adder for integrating 34 a pseudo-noise sequence 59 and the noise transfer function 56 to provide an input signal 63, namely a modified sequence 66, for the quantizer 60.

[0084] Figure 5 further shows that the noise transfer function 56 also has a delay element 58, which has an exemplary form shown z. A -60 to create a delay of, for example, 60 sampling frequencies. This delays the modulation signal 68, which is fed to the noise transfer function 56 via the feedback path 61, by 60 sampling frequencies. The sampling frequency can vary depending on the requirements.

[0085] The invention is not limited to the embodiments described here and the aspects highlighted therein. Rather, within the scope specified by the claims, a multitude of modifications are possible that fall within the bounds of what is considered skilled in the art.

Claims

Claims 1. Method (30) for generating a modulation signal (68) for a chopper (42, 43) using delta-sigma modulation for attenuating critical frequencies, wherein the method (30) comprises at least the following steps: a. Determining (31) a transfer function, wherein a transfer function comprises a noise transfer function (56), b. Generating (32) an output sequence (69) by a delta-sigma modulator (55) by processing an input signal (63) through a quantizer (60) and a feedback path (61) of the delta-sigma modulator (55), c. Using (33) the generated output sequence (69) as a chopper sequence (53), d. Integrating (34) a pseudo-noise sequence (59) and the transfer function by an adding process to modify the input signal (63) before it is quantized, generating a modified sequence (66), e. Quantizing (36) the modified sequence (66), generating a modulation signal (68), f.Feedback (37) of the modulation signal (68) and repetition of determining (31) and quantizing (36) to achieve delta-sigma modulation and g. controlling (38) the chopper (42, 43) on a basis of the modulation signal (68).

2. Method (30) according to claim 1, wherein the noise transfer function (56) is determined by a loop filter (65).

3. Method (30) according to claim 2, wherein the loop filter (65) acts as a reduction element (58) and attenuates the resulting error signal (64).

4. Method (30) according to claim 3, wherein the loop filter (65) comprises a number of zeros (54), wherein the zeros (54) are defined by the delay element (58) z~ k at a frequency f zero = nx^ erzeu . werden, where n is a positive integer, k is a number of delay elements (58) and fs is a sampling frequency of the system, and where a position of the zeros (54) is determined by the delay element (58).

5. Delta-sigma modulator (55) for generating a modulation signal (68) according to the method (30) according to claims 1 to 4, comprising at least the following components: a noise transfer function (56) comprising at least a first adder (57) and a delay element (58), a pseudo-noise sequence (59), a quantizer (60), a feedback path (61) and at least a second adder (62), wherein the second adder (62) is used to modify the input signal (63) before quantizing (36).

6. Delta-sigma modulator (55) according to claim 5, wherein a noise transfer function (56) comprises at least one loop filter (65).

7. Delta-sigma modulator (55) according to claims 5 or 6, wherein a feedback path (61) comprises a modulation signal (68) of the quantizer (60) which is fed back to the noise transfer function (56).

8. Delta-sigma modulator (55) according to claims 5 to 7, wherein the pseudo-noise sequence (59) is fed into the input of the quantizer (60) to protect against limit cycles.

9. Use of the Delta-Sigma modulator (55) according to claims 5 to 8 for generating a modulation signal (68) for the chopper (42, 43).

10. Use of the Delta-Sigma Modulator (55) according to claims 5 to 8 for noise reduction of sensor-induced disturbances.

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