FMCW-based distance measurement device

Abstract

The present invention relates to a distance measuring device (1) based on an FMCW radar that is particularly advantageous for measuring a filling level, and a method for operating the distance measuring device (1). The distance measuring device (1) is characterized in that, in addition to analog high-pass filtering and analog low-pass filtering, an evaluation signal (IF) that is typical for FMCW also undergoes subsequent digital filtering. In this case, the analog / digital conversion takes place by means of oversampling. As a result, according to the invention, all those frequencies (f IF ) above or below the frequency corresponding to the distance (d) of the object (2) in the evaluation signal (IF) are effectively suppressed. At the same time, the analog filters (131, 132, 133) can be constructed with a very low level of complexity. Thereby, the space requirements and costs of the analog components (131, 132, 133) are reduced. Additionally, the temperature dependence of the distance measuring device (1) is reduced thereby. A potentially high distance resolution is also maintained.

Description

Technical Field

[0001] The present invention relates to a distance measuring device based on FMCW. Background Art

[0002] In automation technology, especially for process automation, field devices are often used, which are used to detect various measured variables. The measured variables to be determined can be, for example, the filling level, flow rate, pressure, temperature, pH, redox potential, conductivity or dielectric value of the medium in a process device. To detect the corresponding measured values, field devices all include suitable sensors or are based on suitable measurement principles. Several different types of field devices are manufactured and sold by the Endress+Hauser group of companies.

[0003] For measuring the filling level of a filling material in a container, radar-based measurement methods have been established because they are robust and require minimal maintenance. Within the scope of the present invention, the term "container" is also understood to mean a non-closed container, such as, for example, a basin, a lake or a flowing body of water. The key advantage of radar-based measurement methods lies in their ability to measure the filling level quasi-continuously. In the context of this patent application, the term "radar" refers to microwave signals with frequencies between 0.03 GHz and 300 GHz. The typical frequency bands for which filling level measurements or distance measurements are usually performed are 2 GHz, 6 GHz, 26 GHz or 79 GHz. The higher the selected frequency band, the narrower the beam cone of the microwave signal being radiated or the smaller the antenna can be.

[0004] In the case of radar-based filling level measurement, FMCW ("Frequency Modulated Continuous Wave") forms an established measurement principle. The measurement principle is based on transmitting a continuous radar signal at a modulated frequency. In this case, the frequency of the radar signal lies within a defined frequency band within the standardized center frequency range. Here, the characteristic of FMCW is that the transmission frequency is not constant, but changes periodically within the defined frequency band. At a center frequency of 79 GHz, the frequency band is, for example, 2 GHz, i.e., from 78 GHz to 80 GHz. Similarly, for FMCW, the transmission and reception of the microwave signal are divided into successive measurement cycles.

[0005] For FMCW, by default, the frequency changes linearly over time and has a sawtooth or triangular shape. In principle, a sinusoidal change can be achieved. When the FMCW method is implemented, then, by mixing the corresponding radio-frequency electrical signals, a corresponding evaluation signal is generated, and based on the instantaneous frequency difference between the currently received radar signal and the instantaneously transmitted radar signal, the distance to the filling material or the filling level is determined. The distance can be determined based on the frequency of the evaluation signal because the frequency of the evaluation signal changes proportionally to the distance. The measurement principle of FMCW is described in more detail, for example, in "Radar Level Detection, Peter Devine, 2000".

[0006] Conventionally, the evaluation signal is then digitized by means of an analog / digital converter in order to be able to perform a Fourier transform of the evaluation signal for frequency determination. For this purpose, the evaluation signal must be low-pass filtered in practice in order to remove the radio-frequency interference components in the evaluation signal. In this case, the low-pass filtering takes place before the digitization of the evaluation signal in order to prevent aliasing effects during digitization.

[0007] Analog filters with sufficient filter sharpness must be designed with a corresponding high order, i.e., with a corresponding number of capacitor or inductor components. However, the implementation of analog filters is thus very costly. In addition, when the number of capacitor or inductor components increases, the robustness of the filter decreases, for example, with respect to component tolerances and temperature influences. This in turn reduces the potential accuracy of the distance measurement. However, especially for filling level measurements, a very high level of accuracy is required, at least in the case of tank metering. Summary of the Invention

[0008] Therefore, the present invention is based on the object of developing a cost-effective and robust filling level measuring device that achieves a high level of accuracy.

[0009] The present invention achieves this object by means of a distance measuring device based on an FMCW radar for measuring the distance to an object. The distance measuring device according to the present invention at least comprises:

[0010] - A signal generation unit, which is designed to

[0011] ○ Generate a radio-frequency electrical signal according to the FMCW principle and

[0012] ○ Generate an evaluation signal by mixing the radio-frequency signal with the received signal,

[0013] - An antenna arrangement by means of which a radio-frequency signal can be transmitted as a radar signal in the direction of the object and received as a corresponding received signal after being reflected on the object,

[0014] - A first analog signal processing unit for processing an evaluation signal, the first analog signal processing unit having the following components arranged in series:

[0015] ○ A first analog high-pass filter,

[0016] ○ A first amplifier, and

[0017] ○ A first analog low-pass filter,

[0018] - A digital evaluation unit for processing the evaluation signal, wherein the digital evaluation unit is arranged downstream of the analog evaluation unit and has

[0019] ○ A first analog / digital converter, which is designed to digitize the evaluation signal processed by the analog signal processing unit by means of oversampling,

[0020] ○ A first digital low-pass filter for filtering the evaluation signal,

[0021] ○ Optionally, a first decimator for decimating the digitized evaluation signal,

[0022] ○ A first digital high-pass filter for filtering the optionally decimated evaluation signal,

[0023] ○ A calculation unit, which is designed to determine the distance, in particular by means of Fourier transform, based on the digitally filtered evaluation signal.

[0024] Thus, the distance measuring device according to the invention is based on the concept of performing not only analog filtering of the evaluation signal but also digital filtering thereof. The advantage of additional digital filtering is that it is possible to reduce the complexity of the analog signal processing unit without impairing the filtering of the evaluation signal. The oversampling provided according to the invention allows for simple analog filters and, moreover, improves the signal-to-noise ratio. Thus, it is also possible to use converters with only 10 or 12 bits implemented in a conventional microcontroller. The function of the analog filter is thereby limited to possible anti-aliasing in the evaluation signal during digitization and to adapting the analog evaluation signal to the dynamic range of the analog / digital converter.

[0025] Thus, additional digital filtering enables the construction of analog filters and analog-to-digital converters with very low complexity. For example, the first analog high-pass can be designed as a first-order filter only. For example, the analog low-pass filter can be designed as a filter of at most fourth order, and / or the analog / digital converter can be designed to have a maximum of 12 bits. This reduces the space required and the cost of the analog components. In addition, the temperature dependence of the distance measuring device is reduced. Nevertheless, a potentially high distance resolution is retained.

[0026] In order to set a high attenuation of more than 80 dB in the evaluation signal, the low-pass filter can be designed as, for example, a FIR filter with a decimator, where the decimator is designed to have, for example, at least 70 coefficients. The first digital high-pass filter can be designed as at least a second-order filter.

[0027] Within the scope of the present invention, the term "oversampling" with respect to the first analog / digital converter is defined such that the Nyquist frequency corresponding to the sampling rate is higher than the frequency of the evaluation signal corresponding to the distance, even for the frequency of the evaluation signal corresponding to the maximum distance to be measured. This is achieved when the sampling rate within the scope of the present invention is set to at least four times the frequency of the evaluation signal corresponding to the maximum distance to be measured.

[0028] With reference to the fill level measuring device, the term "unit" within the scope of the present invention is in principle understood to mean any electronic circuit that is suitably designed for the respective intended purpose. Thus, depending on the need, it can be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit, such as a microcontroller interacting with a program or a storage medium. In this case, the program is designed to execute the corresponding method steps or perform the necessary computational operations of the respective unit. In this context, different electronic units of the fill level measuring device in the sense of the present invention can also potentially access a common physical memory or be operated by means of the same physical digital circuit.

[0029] The distance measuring device can advantageously be developed by differentially designing the signal generation unit. In this case, it is necessary that at least the first analog signal processing unit is capable of processing a differential evaluation signal, or that a second structurally identical signal processing unit is arranged in parallel with the first analog signal processing unit. In both cases, the digital signal processing unit must be designed for the differential evaluation signal. Therefore, the first analog / digital converter must also be designed differentially. However, for cost reasons, it is advantageous if the digital signal processing unit includes a second grounded analog / digital converter that is arranged in parallel with and synchronized with the first grounded analog / digital converter. Downstream of the first analog / digital converter or both analog / digital converters, the differential evaluation signals are combined by subtraction at a summing point and further processed as a non-differential evaluation signal.

[0030] The advantage of differential design is reduced quantization noise and higher resistance of the measuring device to electromagnetic interference, also known by the acronym EMC (or "electromagnetic compatibility").

[0031] In another variant of the distance measuring device according to the invention, the signal generation unit can also be designed to generate the evaluation signal as a two-phase signal with a 90° phase shift relative to each other. In this variant, the following components must be added to the distance measuring device to process the second phase:

[0032] - A second analog signal processing unit for evaluating the second phase of the signal, the second analog signal processing unit having

[0033] ○ A second analog high-pass filter,

[0034] ○ A second amplifier, and

[0035] ○ A second analog low-pass filter.

[0036] In this case, the digital evaluation unit must include the following components corresponding to the original components for evaluating the second phase of the signal:

[0037] - A second analog / digital converter,

[0038] - A second decimator, and

[0039] - A second digital high-pass filter.

[0040] The advantage of this is that the calculation unit can subject the two phases of the evaluation signal to a fast Fourier transform in a quasi-complex value manner, thus further improving the sensitivity of the distance measurement.

[0041] According to the object of the invention, it is particularly advantageous to use the distance measuring device according to the invention according to one of the above variants as a fill level measuring device or as a dielectric value measuring device. Similar to the distance measuring device according to the invention, the object of the invention is also achieved by a method for operating a measuring device according to one of the above variants. Therefore, the method includes the following method steps:

[0042] - Generating a frequency-modulated radio frequency electrical signal according to the FMCW principle,

[0043] - Transmitting the radio frequency signal in the direction of the object as a radar signal,

[0044] - Receiving the reflected radar signal as an electrical received signal after reflection on the object,

[0045] - Generating an evaluation signal by mixing the received signal with the radio frequency signal,

[0046] - Amplifying and filtering the analog evaluation signal, wherein at least the frequency corresponding to the distance of the evaluation signal is allowed to pass through,

[0047] - Digitizing the evaluation signal by means of oversampling,

[0048] - Filter and optionally decimate the digitized evaluation signal, wherein in particular the frequencies of the evaluation signal corresponding to the distance are allowed to pass, and

[0049] - Determine the distance or the dielectric value, for example by means of a (fast) Fourier transform, based on the digitized and filtered evaluation signal. Description of the Drawings

[0050] The invention is explained in more detail with reference to the following drawings. As shown below:

[0051] Figure 1 is a typical arrangement of a radar-based fill level measuring device on a container,

[0052] Figure 2 is a circuit design of a distance measuring device based on an FMCW radar according to the prior art,

[0053] Figure 3 is a typical signal generation unit for an FMCW radar,

[0054] Figure 4 is a circuit design of a possible variant of the distance measuring device according to the invention, and

[0055] Figure 5 is a circuit design of another variant of the distance measuring device according to the invention. Detailed Description of the Invention

[0056] For a basic understanding of the invention, Figure 1 shows a typical arrangement of a free-radiation radar-based fill level measuring device 1 on a container 3. In the container 3 there is a filling material 2, the fill level L of which is to be determined by the fill level measuring device 1. For this purpose, the fill level measuring device 1 is mounted above the maximum admissible fill level L on the container 3. Depending on the application area, the height h of the container 3 can be between 30 cm and 125 m.

[0057] Typically, the fill level measuring device 1 is connected via a bus system such as "Ethernet", "Fieldbus (PROFIBUS)", "HART" or "Wireless HART" to a superior level unit 4, such as a process control system or a decentralized database. Thereby, information about the operating state of the fill level measuring device 1 can be communicated. On the other hand, information about the level L can also be sent via the bus system in order to control any inflows or outflows that may be present at the container 3.

[0058] Since Figure 1The filling level measuring device 1 shown is designed as a freely radiating radar measuring device and thus includes a corresponding transmit / receive antenna 12. As indicated, the antenna 12 can be designed, for example, as a horn antenna. Regardless of the design, the transmit / receive antenna 12 is oriented such that a corresponding radar signal S is transmitted in the direction of the filling material 3 according to the FMCW principle HF .

[0059] The radar signal S HF is reflected at the surface of the filling material 3 and, after a corresponding signal propagation delay, is accordingly received by the transmit / receive antenna 12 as an electrical received signal e HF . The radar signal S HF , E HF 's signal propagation delay depends on the distance d = h - L of the filling level measuring device 1 from the surface of the filling material

[0060] Compared to the variant shown, it is also possible to use two separate antennas instead of a single transmit / receive antenna 12 for the separate transmission and reception of the radar signals S HF , E HF . Another alternative consists in using a conductive probe extending towards the bottom of the container, such as a waveguide or a coaxial cable. This variant is referred to by the term "guided wave radar". In the case of a guided wave radar, in addition to or instead of the distance d or the filling level L, it is also possible to determine the dielectric value of the filling material 2 with the aid of the measuring device 1 based on the received signal e HF .

[0061] Figure 2 The basic circuit design of a known filling level measuring device 1 operating according to the FMCW method is illustrated in HF . To generate the radar signal S HF , the measuring device 1 includes a signal generation unit 11 which generates a corresponding radio frequency electrical signal s HF and supplies it to the antenna 12. The frequency of the radio frequency signal s HF defines the frequency of the radar signal S HF in the microwave range. Therefore, the radio frequency signal generation units 11, 12 must be designed to generate a radio frequency electrical signal s with a ramp-shaped frequency change required in FMCW

[0062] In the case of a ramp-shaped frequency change according to the FMCW principle, the frequency f increases in a periodically repeating manner within a predefined frequency band Δf with a constant rate of change. The periodicity of the individual frequency ramps can be in the range of approximately 100 ms. The period of an individual ramp can be in the range between 100 μs and 100 ms. The position of the frequency band Δf must be set taking into account regulatory requirements, and thus preferably the ISM bands at 6 GHz, 26 GHz, 79 GHz or 120 GHz are implemented as the frequency band Δf. The bandwidth is in particular between 0.5 GHz and 10 GHz, depending on the position of the frequency band Δf.

[0063] As Figure 3 shown in detail in, the signal generation unit 11 includes a radio frequency oscillator 122, which is adjusted by means of a ramp generation unit 121 for generating a radio frequency signal s HF . This adjustment takes place in the form of phase control (referred to as "phase-locked loop, PLL"). Thus, on the one hand, the frequency f of the radio frequency oscillator 122 is stable with respect to fluctuations in the ambient temperature. On the other hand, the ramp-shaped frequency change of the radio frequency signal s HF is thereby set.

[0064] According to Figure 3 the signal generation unit 11 in, the radio frequency electrical signal s HF is supplied to the antenna 12 via a signal divider 123 and a transmit / receive switch 124 for transmission.

[0065] The incoming radar signal E reflected by the surface of the filling material HF is converted back by the transmit / receive antenna 12 into the received pure electrical signal e HF , and optionally amplified by a receive amplifier ( Figure 3 not shown in) of the signal generation unit 11. Then, the received signal e HF is mixed with the radio frequency signal s HF to be transmitted by means of a mixer 125, where for this purpose the radio frequency signal s HF is branched off from the signal divider 123. This operation generates an evaluation signal IF, which is typical in the FMCW method and forms the basis for determining the distance d or the filling level L. In this case, the frequency of the evaluation signal IF according to the FMCW principle is proportional to the distance d.

[0066] Figure 2It is clearly shown that the frequency of the evaluation signal IF is determined by the digital evaluation unit 14 of the distance measurement device 1. For this purpose, the first analog / digital converter 141 of the evaluation unit 14 digitizes the evaluation signal IF. In order to comply with the sampling theorem, the first analog / digital converter 141 samples at a frequency that is slightly more than twice the frequency of the evaluation signal IF corresponding to the distance d. Thus, the correspondingly designed calculation unit 143 of the evaluation unit 14 can subject the digitized evaluation signal to a (fast) Fourier transform, or simply FFT for short. The frequency of the global maximum of the corresponding FFT spectrum ideally corresponds to the distance d. In order to suppress any unwanted secondary maxima that occur due to the finite length of the evaluation signal IF, the evaluation unit 14 subjects the digitized evaluation signal IF d to a first windowing 142 before the Fourier transform.

[0067] As Figure 2 shown, the first analog signal processing unit 13 for filtering the analog evaluation signal IF is connected upstream of the digital evaluation unit 14. First, here the analog evaluation signal IF is subjected to an analog high-pass filter 131 mainly to suppress the so-called low-frequency "ringing" in the near range. For example, a first-order high-pass filter 131, i.e., a single capacitor, can be used as the analog filter here. Another advantage of using the first analog high-pass filter is that the analog / digital converter 141 can be designed to have low dynamic range, for example, thus having a maximum of 12 bits. After subsequent signal amplification by means of the corresponding first amplifier 132, the first analog low-pass filter 133 of the first analog signal processing unit 13 filters the evaluation signal IF. On the one hand, this cancels out the aliasing effect during the subsequent digitization of the evaluation signal IF. However, most importantly, the first analog low-pass filter 133 must be designed to have a high order of at least 8, for example, so as to suppress as much as possible all frequencies higher than the frequency of the evaluation signal IF corresponding to the distance d. However, the impedance or capacitance required for the first analog low-pass filter 133 to achieve a high order results in high temperature dependence and high tolerance dependence during filtering. In addition, the implementation cost of the first analog low-pass filter 133 with a high order is very high. The transient recovery time and thus the required minimum measurement time also increase with the increase in the order.

[0068] In Figure 4 more detail, the FMCW-based distance measurement device 1 according to the present invention is described, which only requires an analog low-pass filter 133 of low order - for example, third order. Compared with Figure 2 the measurement device 1 shown in, it is additionally based on a first decimator 144 in the digital evaluation unit 14, which on the one hand performs digital low-pass filtering and at the same time decimates the digitized evaluation signal IF dThe data rate. In this case, the first analog low-pass filter 133 ensures anti-aliasing during the digitization of the evaluation signal IF, while the first decimator 144 filters out all frequencies above the frequency corresponding to the maximum distance d of the evaluation signal IF. In order to use the frequency f IF Up to the Nyquist frequency of the reduced sampling rate. Therefore, it is advantageous to design the decimator 144 with at least 70 coefficients.

[0069] In Figure 4 In the variant of the fill level measuring device 1 according to the invention shown, the first digital high-pass filter 145 is additionally arranged downstream of the first decimator 144 in the signal path of the digitized evaluation signal IF d In the digital evaluation unit 14. This is correspondingly used with the first analog high-pass filter 131 to filter the low-frequency component f d In the evaluation signal IF IF Which is caused by internal reflections in the device in RF components such as the antenna 12. Here, it is advantageous to design the digital high-pass filter 145 with a variable order (at least second order) and an adjustable limit frequency.

[0070] Although of low order, in the context of the present invention, in order for the first analog low-pass filter 133 to also be able to prevent any aliasing of the first analog / digital converter 141, it is essential that the first analog / digital converter 141 digitizes the evaluation signal IF by means of oversampling with respect to the frequency corresponding to the distance d of the object 3. This means that even at this frequency f IF Of the evaluation signal IF corresponding to the maximum distance d to be measured, the sampling rate r of the analog / digital converter 141 must also be, according to the following formula

[0071] r > 2*f IF ,

[0072] Higher than the frequency f corresponding to the distance of the evaluation signal IF IF . Therefore, after filtering in the decimator 144, the aliasing components in the digitized evaluation signal IF d Are suppressed until they are below the resolution limit.

[0073] Figure 4 The signal generation unit 11 of the variant shown in is designed to output the evaluation signal IF differentially. Correspondingly, the first analog high-pass filter 131, the first amplifier 132, and the first analog low-pass filter 133 of the first analog signal processing unit 13 are in Figure 4The variants shown therein are also designed differentially. The digital evaluation unit 14 is also designed to process the evaluation signal IF differentially. For this purpose, the digital evaluation unit 14 includes a second analog / digital converter 141' in parallel with the first analog / digital converter 141, where the two converters 141, 141' are referenced to ground and are synchronized with each other, and digitize the respective phases of the evaluation signal IF. Downstream of the analog / digital converters 141, 141', the two components of the evaluation signal IF are combined by means of subtraction at the summing point 146. The advantage of the differential design is that the analog / digital conversion is additionally performed using actually one bit, thereby reducing the quantization noise. This increases the sensitivity of the distance measurement. Thus, objects 2 that are farther away or have poor reflectivity can be detected.

[0074] Figure 5 Another extended variant of the distance measurement device 1 is shown therein. In this variant, the signal generation unit 11 is designed to output an evaluation signal IF having two phases I, Q that have a phase shift of 90° relative to each other. For this purpose, the signal generation unit 11 includes a quadrature demodulator that outputs the evaluation signal IF as a so-called I component and Q component that have a phase shift of 90° relative to each other. To process the second phase Q, in this case, the distance measurement device 1 includes a second signal processing unit 13', such that the so-called I phase and Q phase of the evaluation signal IF are each separately supplied to one of the two signal processing units 13, 13'. As Figure 5 can be seen, in this case, the digital evaluation unit 14 includes a second analog / digital converter 141', a second decimator 144', a second digital high-pass filter 145', and a second windowing 142' for the additional Q phase of the evaluation signal IF. The digitized evaluation signal IF d of the two phases I, Q is combined in the calculation unit 143, where in this case the fast Fourier transform is performed in a correspondingly complex-valued manner. The advantage of this complex-valued evaluation is that the sensitivity of the distance measurement is thereby increased by approximately 3 dB.

[0075] In the case of the two-phase design of the signal generation unit 11, the latter can also be designed such that each of the phase I and phase Q that are shifted by up to 90° is output differentially in sequence. In this case, the analog signal processing units 13, 13' and the digital signal processing unit 14 are then designed differentially correspondingly, as explained in connection with Figure 4 is explained.

[0076] It goes without saying that the measurement device 1 described in connection with the fill level measurement can of course generally also be used for distance measurement. If the measurement device 1 is implemented based on guided radar, i.e., if the antenna 12 is designed as a probe immersed in the filling material 2 ( Figure 1If not shown in the figure (not shown), the measuring device 1 can also be used to determine the dielectric value of the filling material 2. In this case, the dielectric value can then be determined by means of the digital evaluation signal IF d since the probe length is known or constant.

[0077] List of reference numerals

[0078] 1 Filling level measuring device

[0079] 2 Object / filling material

[0080] 3 Container

[0081] 4 Higher-level liquid level unit

[0082] 11 Signal generation unit

[0083] 12 Antenna arrangement

[0084] 13, 13’ Analog signal processing unit

[0085] 14 Digital evaluation unit

[0086] 121 Ramp generation unit

[0087] 122 Radio frequency oscillator

[0088] 123 Signal divider

[0089] 124 Transmit / receive switch

[0090] 125 Mixer

[0091] 131, 131’ Analog high-pass filter

[0092] 132, 132’ Amplifier

[0093] 133, 133’ Analog low-pass filter

[0094] 141, 141’ Analog / digital converter

[0095] 142, 142’ Windowing

[0096] 143 Calculation unit

[0097] 144, 144’ Low-pass filter

[0098] 145, 145’ High-pass filter

[0099] 146 Summing point

[0100] d Distance

[0101] E HF and eHF Received radar signal or received signal

[0102] f HF Frequency of the RF signal

[0103] f IF Frequency of the evaluation signal

[0104] h Installation height or measuring range

[0105] IF Evaluation signal

[0106] IF d Digitized evaluation signal

[0107] L Filling level

[0108] r Sampling rate of the analog / digital converter

[0109] S HF 、s HF Radar signal or RF signal

Claims

1. An FMCW radar-based distance measurement device for measuring the distance (d) to an object (2), comprising: a signal generation unit (11), which is designed to Generate an electrical radio frequency signal (s HF ) according to the FMCW principle, and By mixing the radio frequency signal (s HF ) with the received signal (e HF ), an evaluation signal (IF) is generated. Antenna arrangement (12) by means of which the radio frequency signal (s HF ) can be transmitted as a radar signal (S HF ) in the direction of the object (2) and can be received as a corresponding received signal (E HF ) after being reflected on the object (2). a first analog signal processing unit (13) for processing the evaluation signal (IF), the first analog signal processing unit (13) having the following components arranged in series: a first analog high-pass filter (131), a first amplifier (132), and a first analog low-pass filter (133), a digital evaluation unit (14) for processing the evaluation signal (IF), wherein the digital evaluation unit (14) is arranged downstream of the first analog signal processing unit (13) and has a first analog / digital converter (141), which is designed to digitize the evaluation signal (IF) processed by the first analog signal processing unit (13) by means of oversampling, A first digital low-pass filter (144), the first digital low-pass filter (144) being configured to filter the evaluation signal (IF d ). A first digital high-pass filter (145), the first digital high-pass filter (145) being configured to filter the evaluation signal (IF d ). Calculation unit (143), the calculation unit (143) being designed to determine the distance (d) based on the filtered digital evaluation signal (IF d ) wherein the first analog high-pass filter (131) is designed as a first-order filter, and wherein the analog low-pass filter (133) is designed as a filter of at most fourth order.

2. The distance measuring device according to claim 1, wherein, The computing unit (143) is designed to determine the distance (d) on the basis of the filtered digital evaluation signal (IF d ) by means of a Fourier transform.

3. The distance measuring device according to claim 1, wherein, The low-pass filter (144) for extracting a digitized evaluation signal (IF d ) is designed as a FIR filter with an integrated decimator, wherein the decimator is designed to have at least 50 coefficients, and / or wherein the first digital high-pass filter (145) is designed as a filter of at least second order.

4. The distance measurement device according to one of claims 1-3, wherein the analog / digital converter (141) is designed to have a maximum of 12 bits.

5. The distance measuring device according to one of claims 1 to 3, wherein, The signal generation unit (11) is designed to output the evaluation signal (IF) differentially.

6. The distance measuring device according to claim 5, wherein, At least the first analog signal processing unit (13) is designed to process the evaluation signal (IF) differentially, and wherein the digital evaluation unit (14) includes a second analog / digital converter (141').

7. The distance measuring device according to one of claims 1-3, wherein, The signal generation unit (11) is designed to generate the evaluation signal (IF) as a two-phase signal (I, Q) having a phase shift of 90° relative to each other, including: a second analog signal processing unit (13') for the second phase (Q) of the evaluation signal (IF), the second analog signal processing unit (13') having a second analog high-pass filter (131'), a second amplifier (132'), and a second analog low-pass filter (133'), wherein the digital evaluation unit (14) for the second phase (Q) of the evaluation signal (IF) includes a second analog / digital converter (141'), a second decimator (144'), and a second digital high-pass filter (145').

8. A method for FMCW radar-based measurement of the distance (d) to an object (2) by means of a distance measurement device (1) according to one of claims 1-7, comprising the following method steps: Generate a frequency-modulated radio frequency electrical signal (s HF ) according to the FMCW principle Transmit the radio frequency signal (s HF ) in the direction of the object (2) as a radar signal (S HF ). Receiving the reflected radar signal (E HF ) as an electrical received signal (s HF ) after reflection on the object (2). By mixing the received signal (e HF ) with the radio frequency signal (s HF ), an evaluation signal (IF) is generated. amplifying and filtering the evaluation signal (IF), wherein at least the frequency corresponding to the distance (d) of the evaluation signal (IF) is allowed to pass through, digitizing the evaluation signal (IF) at a sampling rate that is at least four times higher than the frequency corresponding to the distance (d) of the evaluation signal (IF), Filter and compress the digitized evaluation signal (IF d ), and Based on the digitized evaluation signal (IF d ) to determine the distance (d).

9. The method according to claim 8, wherein The distance (d) is determined on the basis of the digitized evaluation signal (IF d ) by means of a fast Fourier transform.

10. A filling level measuring device comprising a distance measuring device (1) according to one of claims 1 to 7.

11. A dielectric value measuring device comprising a distance measuring device (1) according to one of claims 1 to 7.

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