Method for evaluating a sensor signal and evaluation device

Abstract

A method for evaluating a sensor signal from a sensor (1), wherein in a first method step an analog sensor signal (2) of the sensor (1) is converted into a digital sensor signal (3) and wherein in a second method step the digital sensor signal (3) is converted into a quantized first working signal (4) by means of a quantizer (16), characterized in that in a third method step a second working signal (5) is generated from the digital sensor signal (3) using a correction function (12) such that in the third method step a third working signal (7) is generated by taking the difference between the digital sensor signal (3) and the first working signal (4) and in the third method step the second working signal (5) is generated from the third working signal (7) using the correction function (12), wherein in a fourth method step an output signal (6) is generated both as a function of the first working signal (4),as well as depending on the second working signal (5), wherein the first working signal (4) is fed back to the sensor (1) as a feedback signal (8), wherein the feedback signal (8) is converted into an analog feedback signal (14) by means of a digital-to-analog converter (15).

Description

State of the art

[0001] The invention relates to a method for evaluating a sensor signal of a sensor according to the preamble of claim 1.

[0002] Such methods are generally known. For example, a circuit arrangement and a method for reading a sensor using a sigma-delta converter are known from German patent application DE 102005046699 A1. In this method, a measurement signal from a capacitive accelerometer is evaluated using an evaluation circuit, a filter structure, and a quantizer. The quantized and evaluated sensor signal is then fed back to the capacitive accelerometer. A disadvantage of this circuit arrangement is that the quantization of the measurement signal introduces quantization noise into the sensor signal, which impairs the signal-to-noise ratio of the output signal. According to the prior art, an increase in the signal-to-noise ratio can be achieved either by oversampling, the order of the control process, or by increasing the number of quantization stages.However, these solutions invariably lead to a significant increase in circuit complexity, thereby increasing the space requirements and power consumption of the circuit arrangement. Furthermore, faster and therefore more expensive semiconductor technologies are required, and stability problems arise. Further disclosures can be found in documents US 2002 / 0175846 A1, US 6 920 182 B2, DE 10 2005 003 630 A1, and DE 10 2007 007 551 A1. Disclosure of the invention

[0003] The inventive method and evaluation device according to the dependent claims have the advantage over the prior art that the output signal is not only formed by the quantized first operating signal, whose signal-to-noise ratio is affected by quantization noise, but is formed as a function of the first and second operating signals. The quantized first operating signal is advantageously modeled by the second operating signal in such a way that the quantization noise in the output signal is reduced and preferably minimized. The resulting increase in accuracy or improvement of the signal-to-noise ratio is achieved in a comparatively simple manner, without requiring significant additional circuitry.In particular, improving the signal-to-noise ratio does not require increasing the sampling rate, control order, or quantization levels, so that despite the improved signal-to-noise ratio, there is no significant increase in space or power requirements. A further advantage of the method according to the invention is that the correction of the first operating signal is performed entirely digitally. The processing of the first operating signal with the second operating signal is therefore comparatively easy to implement. Furthermore, the processing accuracy is increased (for example, no artifacts typical of analog data processing occur in the signal being processed). Moreover, the susceptibility to errors caused by external disturbances, such as alternating electric and magnetic fields, is significantly reduced.The sensor comprises in particular a micromechanical sensor, for example a micromechanical accelerometer or a micromechanical angular rate sensor, which is preferably based on a semiconductor and particularly preferably on a silicon substrate.

[0004] Advantageous embodiments and further developments of the invention can be found in the dependent claims and in the description with reference to the drawings.

[0005] According to the invention, in the third process step, a third working signal is generated by calculating the difference between the digital sensor signal and the first working signal, and in the third process step, the second working signal is generated from the third working signal using the correction function. Advantageously, this allows for a comparison between the quantized first working signal and the non-quantized digital sensor signal, whereby the quantization error in the first working signal, caused by the quantization of the digital sensor signal, is determined by calculating the difference. Knowledge of the quantization error therefore enables a subsequent correction of the first working signal, which is affected by the quantization error, in the fourth process step.

[0006] According to a further preferred embodiment, the fourth process step involves adding the first and second operating signals together. Advantageously, the second operating signal is generated in the third process step such that the quantization noise or quantization error in the first operating signal is minimized when the first and second operating signals are added. Ideally, this would be particularly effective, for example, if the second operating signal essentially follows the inverse curve of the quantization noise on the first operating signal. The output signal thus comprises the first operating signal at least partially cleansed of the quantization noise.

[0007] Furthermore, according to the invention, the first operating signal is fed back to the sensor as a feedback signal, wherein the feedback signal is preferably converted into an analog feedback signal by means of a digital-to-analog converter. Advantageously, the sensor is controlled via the feedback signal in a known manner, wherein the feedback signal is determined from the first operating signal, which is quantized by means of the quantizer in a known manner, but has not yet been corrected for quantization noise by means of the second operating signal. The feedback to the sensor thus takes place in the usual way and does not need to be adapted in the inventive method for evaluating a sensor signal. In particular, the evaluation of a standard sensor is therefore possible with the inventive method.

[0008] According to a further preferred embodiment, in the first process step the analog sensor signal is converted into the digital sensor signal by means of an analog-to-digital converter, wherein, in particular, the analog sensor signal is converted into the digital sensor signal by means of the analog-to-digital converter and a filter element connected downstream of the analog-to-digital converter. Advantageously, this enables the conversion of the analog sensor signal into a digital sensor signal that is comparatively easy to evaluate and insensitive to external interference, such as external alternating electric and magnetic fields.

[0009] According to a further preferred embodiment, the first operating signal is modified by means of a transfer function before the fourth process step. Advantageously, this allows the quantized first operating signal to be modified in such a way that, when the first operating signal is modified with the second operating signal to generate the output signal in the fourth process step, the quantization noise in the output signal is minimized. In the simplest case, the transfer function is equal to 1, so that no modification of the first operating signal takes place and thus, advantageously, no influence on the sensor's measurement information via the rotation rate is to be feared. In certain cases, however, it is conceivable that the first operating signal is modified in such a way as to...It is explained that when mapping the second working signal onto the first working signal, the quantization noise can be reduced in a particularly simple way, for example by simply adding the second working signal to the first working signal.

[0010] According to a further preferred embodiment, the correction function and the transfer function are selected such that quantization noise from the output signal is minimized, at least in one frequency range. Advantageously, this significantly increases the signal-to-noise ratio of the output signal, as the impairment caused by quantization noise is reduced. The second operating signal is based, in particular, on the difference between the digital sensor signal and the first operating signal, so that the second operating signal is essentially dependent on the quantization noise on the first operating signal.The correction function and transfer function can now be selected such that this known component of the quantization noise is precisely compensated for when the second operating signal is appropriately mapped onto the first operating signal to generate the output signal, thus producing an output signal with reduced quantization noise. Simultaneously, the first operating signal is preferably fed back to the sensor for control purposes, without the compensation of the quantization noise in the first operating signal having any influence on this feedback.

[0011] According to a preferred embodiment, the correction function and the transfer function are selected such that, at least in one frequency range, the sum of the correction function and the product of the transfer function and a noise transfer function of the first operating signal is essentially zero. This ensures that the quantization error is minimized when mapping the second operating signal, modified by the correction function, onto the first operating signal, modified by the transfer function. This is achieved by a mathematical equation whereby the output signal is equal to the sum of the product of the correction function times the second operating signal and the product of the transfer function times the first operating signal (output signal = [correction function x second operating signal] + [transfer function x first operating signal]).The first operating signal corresponds to the sum of the product of the noise transfer function of the first operating signal and the quantization error, and the product of the signal transfer function of the first operating signal and the measurement signal (e.g., rotation rate signal) (First operating signal = [noise transfer function x quantization error] + [signal transfer function x rotation rate signal]). Furthermore, it is known that the second operating signal essentially corresponds to the quantization error (Second operating signal = quantization error, since the second operating signal is generated in the third process step by calculating the difference between the digital sensor signal and the first operating signal (also referred to as the third operating signal)).Setting the condition that the quantization error must be zero and substituting the equations into each other yields the mathematical condition that the sum of the correction function and the product of the transfer function and the noise transfer function must be zero if the quantization error is also to be zero (Math. condition: Correction function + [Transfer function x Noise transfer function] == 0). It can be seen that by appropriately choosing the correction function and the transfer function, the quantization error can be compensated, thus significantly improving the signal-to-noise ratio of the output signal. It is obvious to a person skilled in the art that it is sufficient if this condition holds within a narrow frequency band that is relevant for the evaluation of the sensor.

[0012] A further object of the present invention is an evaluation device for evaluating a sensor signal of a sensor, wherein the evaluation device comprises an analog-to-digital converter for converting an analog sensor signal of the sensor into a digital sensor signal, wherein the evaluation device comprises a quantizer for converting the digital sensor signal into a quantized first working signal, and wherein the evaluation unit comprises a first modulation unit which is configured to generate a second working signal from the digital sensor signal by means of a correction function, wherein the evaluation unit further comprises an output element for generating an output signal depending on the first and second working signals.Advantageously, the evaluation device for carrying out the inventive method for evaluating a sensor signal is configured such that the above-described increase in the signal-to-noise ratio can be achieved when evaluating the sensor signal with this evaluation unit. In particular, no additional circuitry is required to improve the signal-to-noise ratio. The output element is preferably configured to generate the output signal by adding the first and second operating signals.

[0013] According to a preferred embodiment, the evaluation device includes a second modulation unit configured to modulate the first operating signal using a transfer function, wherein the first and second modulation units are configured to minimize quantization noise in the output signal. In particular, the first modulation unit is configured to modify the operating signal with a transfer function that conditions the first operating signal such that mapping the second operating signal onto the first operating signal results in an output signal with reduced quantization error.Furthermore, the second modulation unit is designed in such a way that the second operating signal is modified by means of the correction function so that the condition, according to which the sum of the correction function and the product of the noise transfer function of the first operating signal and the transfer function is equal to zero, is fulfilled at least in a certain frequency range.

[0014] Exemplary embodiments of the present invention are shown in the drawings and explained in more detail in the following description. Brief description of the drawings

[0015] It shows Fig. 1 A schematic illustration of a method and an evaluation device for evaluating a sensor signal according to an exemplary embodiment of the present invention. embodiment of the invention

[0016] In Fig. Figure 1 shows a schematic view of the individual process steps of a method for evaluating a sensor signal 2 from a sensor 1 according to an exemplary embodiment of the invention. An analog sensor signal 2 is generated by a sensor 1, which in particular comprises a silicon-based micromechanical angular rate sensor. The analog sensor signal 2 is proportional to an angular rate applied to the sensor 1 and to be measured. The analog sensor signal 2 is converted into a digital sensor signal 3 by means of an analog-to-digital converter 9. Optionally, the digital sensor signal 3 is further modified after the analog-to-digital converter by means of a filter element 10. Subsequently, the digital sensor signal 3 is converted into a quantized first operating signal 4 by means of a quantizer 16. The quantization is carried out, for example, by means of a formula from a lookup table and / or a simple rounding operation.The first working signal 4 is fed back to the sensor 1 as feedback signal 8, whereby the feedback signal 8 is converted into an analog feedback signal 14 by means of a digital-to-analog converter 15.

[0017] A third operating signal 7 is generated from the difference between the digital sensor signal 3 and the quantized first operating signal 4. The third operating signal 7 thus essentially corresponds to the quantization error that arose from the quantization of the digital sensor signal 3 in the first operating signal 4. A second operating signal 5 is generated from the third operating signal 7 by means of a first modulation unit 12'. In this process, the third operating signal 7 is modified by a correction function 12. The first operating signal 4 is modified analogously in a second modulation unit 11' by a transfer function 11. Subsequently, an output signal 6 is generated by an output element 14 by mapping the second operating signal 5 onto the first operating signal 4.

[0018] By appropriately choosing the transfer function 11 and the correction function 12, it is possible to generate an output signal 6 in which the quantization error is reduced or minimized. This is particularly the case when the mathematical condition is met, according to which the sum of the correction function 12 with the product of the transfer function 11 and the noise transfer function of the first operating signal 4 must equal zero if the quantization error is also to be zero (Mathematical condition: Correction function 12 + [Transfer function 11 x Noise transfer function of the first operating signal 4] == 0). In the simplest case, the transfer function 11 equals one, i.e., that only the identity of the first operating signal 4 is mapped.In this case, the mathematical condition dictates that the correction function 12 must be equal to the inverse noise transfer function of the first operating signal 4 in order to reduce the quantization noise. However, other transfer and correction functions 11, 12 are also conceivable. The mathematical condition only needs to be satisfied for the frequency range that is relevant for evaluating the measurement signal. Furthermore, it is conceivable that the evaluation process can be monitored by correlating the output signal 6 with the quantization error, since if the model description does not correspond to the actual sensor behavior, noise components of the quantization noise must be present and measurable in the output signal 6.

[0019] The Fig.Figure 1 further shows a schematic representation of an evaluation device 13, which is provided for evaluating a sensor signal from a sensor 1. For this purpose, the evaluation device 13 includes the analog-to-digital converter 9 for converting the analog sensor signal 2 into the digital sensor signal 3.

[0020] Optionally, the evaluation device 13 also includes the filter element 10, which filters the digital sensor signal 3. The evaluation device 13 comprises the quantizer 16, which is provided for converting the digital sensor signal 3 into the quantized first operating signal 4. The evaluation device 13 further comprises the first modulation unit 12' and the second modulation unit 11'. The first modulation unit 12' is provided for modulating the third operating signal 7 by means of the correction function 12, while the second modulation unit 11' is provided for modulating the first operating signal 4 by means of the transfer function 11. The evaluation device 13 further comprises an output element 14, which is provided for generating the output signal 6 as a function of the first and second operating signals 4, 5.Furthermore, the evaluation device 13 includes a digital-to-analog converter 15, which is provided for the feedback of the first working signal 4 as a feedback signal 8 to the sensor 1 and converts the feedback signal 8 into an analog feedback signal 14.

Claims

[1] Method for evaluating a sensor signal of a sensor (1), wherein in a first method step an analog sensor signal (2) of the sensor (1) is converted into a digital sensor signal (3) and wherein in a second method step the digital sensor signal (3) is converted into a quantized first working signal (4) by means of a quantizer (16), characterized by, that in a third process step a second working signal (5) is generated from the digital sensor signal (3) using a correction function (12) such that in the third process step a third working signal (7) is formed by calculating the difference between the digital sensor signal (3) and the first working signal (4) and in the third process step the second working signal (5) is generated from the third working signal (7) using the correction function (12), wherein in a fourth process step an output signal (6) is generated as a function of both the first working signal (4) and the second working signal (5), wherein the first working signal (4) is fed back to the sensor (1) as a feedback signal (8), wherein the feedback signal (8) is converted into an analog feedback signal (14) using a digital-to-analog converter (15). [2] Method according to claim 1, characterized by, that in the fourth process step the first and the second working signal (4, 5) are added together. [3] Method according to any one of the preceding claims, characterized by , that in the first process step the analog sensor signal (2) is converted into the digital sensor signal (3) by means of an analog-to-digital converter (9) and a filter element (10) connected downstream of the analog-to-digital converter (9). [4] Method according to any one of the preceding claims, characterized by , that the first working signal (4) is modified before the fourth process step by means of a transfer function (11). [5] Method according to claim 4, characterized by , that the correction function (12) and the transfer function (11) are chosen such that quantization noise in the output signal (6) is minimized. [6] Method according to one of claims 4 or 5, characterized by, that the correction function (12) and the transfer function (11) are chosen such that at least in one frequency range the sum of the correction function (12) and a product of the transfer function (11) and a noise transfer function of the first operating signal (4) is essentially equal to zero. [7] Evaluation device (13) for evaluating a sensor signal from a sensor (1), wherein the evaluation device (13) comprises an analog-to-digital converter (9) for converting an analog sensor signal (2) from the sensor (1) into a digital sensor signal (3), wherein the evaluation device (13) comprises a quantizer (16) for converting the digital sensor signal (3) into a quantized first operating signal (4), characterized by, that the evaluation unit (13) has a first modulation unit (12') which is configured to generate a second working signal (5) from the digital sensor signal (3) using a correction function (12) such that a third working signal (7) is formed by calculating the difference between the digital sensor signal (3) and the first working signal (4) and the second working signal (5) is generated from the third working signal (7) using the correction function, wherein the evaluation unit (13) further comprises an output element (14) for generating an output signal (6) depending on the first and second working signals (4, 5) and wherein the first working signal (4) is fed back to the sensor (1) as a feedback signal (8), wherein the feedback signal (8) is converted into an analog feedback signal (14) by means of a digital-to-analog converter (15). [8] Evaluation device (13) according to claim 7, characterized by, that the evaluation device (13) has a second modulation unit (11') which is configured to modulate the first operating signal (4) using a transfer function (11), wherein the first and second modulation units (11', 12') are configured such that quantization noise in the output signal (6) is minimized.

Images