Patent ID: 12209885

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The circuit shown inFIG.1includes a sensor element2for acquiring a measuring signal, and a readout circuit3for converting the measuring signal into an analog electrical sensor signal. In the described embodiment, sensor element2is the sensor element of an MEMS gyroscope. Sensor element2includes at least one seismic mass which is excited to a defined oscillation movement for the purpose of acquiring a measuring signal. In case of a rotary movement of sensor element2about an axis perpendicular to the oscillation direction of the seismic mass, a Coriolis force acts on the oscillating seismic mass. In the exemplary embodiment described here, the deflection of the seismic mass perpendicular to the oscillation direction and perpendicular to the axis of rotation caused by this force is acquired capacitively. The deflection of the seismic mass caused by a rotary movement of sensor element2is proportional to the yaw rate and is referred to as the useful signal component11in the following text. The frequency of this useful signal component11is a function of the excitation frequency, that is, the frequency of the defined oscillation movement of the seismic mass. The frequency range of useful signal component11, which is termed the useful signal frequency range30, is therefore able to be defined very well.

In addition to the useful signal component, the measuring signal includes at least one interference signal component30which superposes useful signal component11. In the described exemplary embodiment, an interference signal caused by a vibration of sensor element2is superposed to the yaw rate signal. This is sketched inFIG.1by the frequency representation of vibration20acting on sensor element2.

In addition to desired yaw rate signal11as the useful signal, the measuring signal output by sensor element2thus includes also undesired vibration signal20as an interference signal component. The frequency range of this vibration signal20, hereinafter referred to as interference signal frequency range, is likewise clearly defined, does not overlap with the useful signal frequency range and lies clearly above useful signal frequency range30, which may be gathered from the frequency representation10aof the measuring signal.

Measuring signal10aacquired by sensor element2is converted into an analog electrical measuring signal with the aid of readout circuit3. In this particular case, the acquisition of the measuring signal takes place capacitively, and readout circuit3includes a capacitance-voltage converter having transmission function A(s)3′ for converting measuring signal10into an analog electrical signal.

Situated between an output3bof capacitance-voltage converter3and an input3aof capacitance-voltage converter3is a feedback circuit5which applies a feedback circuit transmission function F(s)5′ to the output signal of capacitance-voltage converter3that has the largest possible amplification outside the useful signal frequency range30, in particular in the interference signal frequency range. The amplification thus occurs in the frequency range in which an undesired signal, e.g., vibration signal20or the like, appears. Conversely, the lowest possible amplification is used in the range of the useful signal frequency range30. The signal amplified in this way is fed back to input3aof capacitance-voltage converter3by being subtracted from an input signal at input3a. This reduces undesired interference signal component20.

As a whole, the transmission functions A(s)3′ and F(s)5′ result in a total transmission function H(s) for the two circuit components evaluation circuit3and feedback circuit5of sensor1according to

H⁡(s)=A⁡(s)1+A⁡(s)·F⁡(s)

In the described exemplary embodiment, the total transmission function H(s) thus has the following characteristics:

The total transmission function H(s)→A(s) if the feedback circuit transmission function F(s) goes→0, or in other words, yaw rate signal11is converted into an analog electrical voltage signal10bessentially without any effect by feedback circuit5.

Total transmission function H(s)→0 if feedback circuit transmission F(s) goes→∞, or in other words, the undesired signal or interference signal component20is suppressed for the most part.

For example, feedback circuit transmission function F(s)5′ is able to be provided with the aid of a notch filter in a useful signal frequency range30, a resonator at a frequency of an undesired interference signal to be expected, and/or with the aid of a high-pass filter for frequencies above useful signal frequency range30in feedback circuit5.

The analog measuring signal, largely purged of the interference signal component in the above-described manner, is then converted with the aid of an analog-to-digital converter4, ADC, into a digital signal that in essence is ultimately based on the useful signal component of the MEMS gyroscope.

In comparison,FIG.2shows the frequency representation of two gyroscope measuring signals that were recorded under identical test conditions, one without and one with the compensation according to the present invention of a vibration-related interference signal component. In other words,FIG.2illustrates the effects of the measures by comparing frequency representations20and20′ of two gyroscope measuring signals that were acquired under identical test conditions. The x-axis denotes the frequency, the y-axis denotes the frequency components in the measuring signal. The gyroscope was exposed to a mechanical vibration in this case, i.e., in a defined frequency range about the frequency X, in order to simulate an interference signal component in the gyroscope measuring signal. A DC voltage was applied as the useful signal component so that the frequency range of useful signal component11lies at zero here. In one case—frequency representation20—no measures were taken to attenuate or compensate the vibration-related interference signal component in the gyroscope measuring signal. In the other case—frequency representation20′—the measures for compensating for a vibration-related interference signal component as described in connection with the embodiments ofFIG.1were applied, i.e., using an amplification factor of 100 in feedback circuit5. The comparative illustration ofFIG.2demonstrates that the measures attenuate the interference signal component by a factor of approximately 100 in each case while useful signal component11is essentially unaffected by feedback circuit5.

FIG.3shows steps of a method for reducing undesired signals in a sensor signal.

The method includes the following steps:

In a first step S1, a measuring signal is acquired with the aid of the sensor, the measuring signal including at least one useful signal component in a useful signal frequency range and at least one interference signal component in an interference signal frequency range.

In a further step S2, the measuring signal is converted into an analog electrical sensor signal with the aid of a readout circuit.

In a further step S3, the output signal of the readout circuit is fed back to the input of the readout circuit at which the measuring signal is applied with the aid of a feedback circuit, and the total transmission function H(s) of the readout circuit and feedback circuit induces an attenuation of the analog electrical sensor signal in the interference signal frequency range, while the analog sensor signal in the useful signal frequency range is not attenuated.

In summary, at least one of the embodiments of the present invention offers at least one of the following advantages:a suppression of interference signals in a measuring signal essentially without an adverse effect on useful signals in the measuring signal,an improvement of the signal-to-noise ratio,an easier demodulation of sensor signals,an increased reliability of the sensor.

Although the present invention was described on the basis of preferred exemplary embodiments, it is not restricted to such but is able to be modified in a multitude of ways.