Method for operating a radar sensor system, corresponding circuit, system and vehicle

Abstract

The present disclosure relates to a method of operating a radar sensor system, corresponding circuits, systems and vehicles. A method of operating a radar sensor system includes: down-converting a received signal chirped modulated using a sequence of chirped ramps to an intermediate frequency signal; and high-pass filtering the intermediate frequency signal to produce a high-pass filtered signal. The high-pass filtering includes: performing a first high-pass filtering having a first corner frequency on the intermediate frequency signal at each chirp in the chirp modulation of the received signal; and replacing the first high-pass filtering with a second high-pass filtering having a second corner frequency, the first corner frequency being higher than the second corner frequency.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Italian Patent Application No. 102018000002649, filed on February 13, 2018, which is incorporated herein by reference. Technical Field

[0003] The present description relates generally to radar systems and, in particular embodiments, to methods of operating radar sensor systems, corresponding circuits, systems, and vehicles. Background Art

[0004] Frequency modulated continuous wave (FMCW) radar sensors are used in a variety of fields including automotive and consumer applications due to the possibility of achieving high accuracy using low-cost, relatively simple technology.

[0005] Despite the extensive activity in this field, further improved solutions are still desired that enable high precision at reduced cost, for example for automotive and consumer applications. Summary of the invention

[0006] It is an aim of one or more embodiments to help provide such an improved solution.

[0007] One or more embodiments may relate to corresponding circuits (eg, integrated circuits for use in implementing methods according to embodiments).

[0008] One or more embodiments may be directed to a corresponding system (eg, a radar sensor).

[0009] One or more embodiments may relate to a corresponding vehicle (eg, a motor vehicle equipped with a radar sensor according to an embodiment).

[0010] One or more embodiments were developed by focusing on possible usage in a receiver chain for 77 GHz radar applications with FMCW modulation.

[0011] However, one or more embodiments may be applied to nearly any possible operating frequency range that is compatible with the limitations of the technology involved.

[0012] One or more embodiments may provide a new method of high pass filter setting during operation of an FMCW modulator in a radar sensor and possible circuit implementations of the method.

[0013] One or more embodiments may include an autonomous switchable dual high-pass filter arranged downstream (ie, after or following) a down-conversion mixer of a radar receiver chain.

[0014] In one or more embodiments, in such a switchable architecture, the high-pass corner frequency (also called the "cutoff" or "breakpoint" frequency) can be set to a high value for a programmable time window and then to the value currently contemplated for the radar system.

[0015] One or more embodiments may produce a reduction in undesirably strong signals at the beginning of an FMCW chirp without causing signal degradation during the sampling of data.

[0016] One or more embodiments may advantageously employ fast signal ramps as desired for long-range applications and low intermediate frequencies (IFs) as desired for short-range applications. Thus, one or more embodiments are suitable for both long-range and short-range applications.

[0017] One or more embodiments are suitable for integration into a radar chip without negatively impacting the overall performance of the chip.

[0018] One or more embodiments may be used, for example, in integrated circuits on silicon (CMOS, bipolar, BiCMOS technologies) for radio frequency RF (eg microwave - MW) applications such as ultra-wideband (UWB) FMCW detection systems for automotive and consumer applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] One or more embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1 and Figure 2 is a general example of certain standards that are the basis for the operation of an FMCW radar system;

[0021] Figure 3 is an exemplary block diagram of circuit components of an illustrative embodiment, and

[0022] Figure 4 is an example of a possible temporal behavior of the received signal in an embodiment. DETAILED DESCRIPTION

[0023] In the following description, one or more specific details are described to provide a deeper understanding of the examples of the embodiments of the present specification. The embodiments can be obtained without one or more of the specific details or using other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail so that some aspects of the embodiments will not be obscured.

[0024] References to "an embodiment" or "one embodiment" in the framework of this description are intended to indicate that a particular configuration, structure, or feature described with respect to that embodiment is included in at least one embodiment. Thus, phrases such as "in an embodiment" or "in an embodiment" that may be present in one or more points of this description do not necessarily refer to the same embodiment. Additionally, in one or more embodiments, particular configurations, structures, or features may be combined in any appropriate manner.

[0025] The references used herein are provided for convenience only and therefore do not limit the scope of protection or the scope of the embodiments.

[0026] One or more embodiments may be applied to, for example, a frequency modulated continuous wave (FMCW) radar sensor.

[0027] As described above, FMCW radar sensors are used in various fields including automotive applications and consumer applications due to the possibility of achieving high accuracy using low-cost, relatively simple technology.

[0028] The basic principle of operation of a conventional FMCW radar sensor involves generating a signal comprising a sequence of “chirps” (e.g., as in Figure 1 , Chirp_1, Chirp_2, . . . , Chirp_n) illustrated in FIG. , where the frequency of the signal is f and sweeps from a lower value to a higher value in a ramp-like manner (eg, linearly) during each chirp.

[0029] To do this, a "sawtooth" modulation signal may be applied to a voltage controlled oscillator (VCO), where a frequency modulated (FM) signal from the VCO is in turn applied to a transmitter (TX) amplifier to produce a signal that is sent toward the target.

[0030] The received signal (RX_signal) reflected from the target can be down-converted using the signal from the VCO, and the resulting intermediate frequency (IF) signal can have a frequency as shown in Figure 2 The amplitude (eg magnitude) versus frequency behavior illustrated in , depends on the distance of the target and the slope of the ramp in the FM "chirp" signal.

[0031] Thus, the IF signal indicates the range of the target, with lower frequencies corresponding to short range targets and higher frequencies corresponding to long range targets.

[0032] Operation of an FMCW radar sensor as outlined above may involve enabling the transmit (TX) amplifier only during the chirp signal ramp: see e.g. Figure 1 This facilitates optimizing the useful bandwidth, resulting in improved resolution of the target.

[0033] There is a continuing trend in FMCW radar applications to use "fast" chirp modulation for both short-range and long-range applications, with the ability to use the same equipment for both applications representing the desired characteristics.

[0034] Furthermore, to improve resolution, the goal is to use as much bandwidth as possible, which may involve dynamic management of the TX enable signal (TX_EN).

[0035] These operating conditions (e.g., power-up at the beginning of a ramp) may suddenly activate the IF signal and the associated process of charging a capacitor (e.g., a large capacitor) in a high-pass filter in the IF signal path. This may result in a (high) transient DC offset that may saturate the output of a variable gain amplifier (VGA) amplifying the IF signal, so that processing of the IF signal (in a conventional manner) is facilitated.

[0036] Various methods can be devised to solve this problem.

[0037] The first solution may involve reducing the VGA gain, which may compromise overall receiver sensitivity.

[0038] Another solution might involve increasing the TX enable window so that the saturation region is present before the useful signal is slightly "smoother". In this case, the bandwidth and resolution of the target distance will be reduced.

[0039] Yet another solution may involve adding a high pass filter turn when filtering the (small) IF signal. A possible consequence is that small nearby targets may be missed. Moreover, this approach may limit the use of detection equipment with fast ramp modulation (for both long-range and short-range applications).

[0040] One or more embodiments described herein use Figure 3 The switchable high-pass filter arrangement shown in .

[0041] Figure 3 A block diagram of an FMCW radar sensor 10 for detecting the presence, position (eg, distance), and possibly velocity of a target object T is shown.

[0042] For example, the radar sensor system 10 may be board-mounted on a vehicle V such as an automobile, with the ability to detect the presence / distance of other nearby vehicles, passing pedestrians, obstacles when parking, and the like.

[0043] The operation of such a sensor involves sending an RF (eg, microwave) signal towards a target T and collecting a corresponding received signal RF_signal reflected from the target.

[0044] The operating principles and various possible implementations of such sensor systems are well known in the art, so that a more detailed description need not be provided herein.

[0045] For purposes of illustrating an embodiment, it may be noted that the FMCW radar sensor system 10 may generate an FMCW transmission signal to be sent towards a (possible) target T to be detected.

[0046] The FMCW transmission signal includes a sequence of "chirps" (e.g., as in Figure 1 , Chirp_1, Chirp_2, . . . , Chirp_n) illustrated in FIG, where the frequency of the signal is f and sweeps from a lower value to a higher value in a ramp-like manner (eg, linearly) during each chirp.

[0047] To this end, a modulator circuit 12 may be provided to generate a “sawtooth” modulation signal which is applied to a voltage controlled oscillator (VCO) circuit 14 .

[0048] The frequency modulated (FM) signal from the VCO 14 is applied to a transmitter (TX) amplifier 16 to generate a signal that is transmitted toward a destination (e.g., via a transmitter antenna TXA). The TX amplifier is enabled by a signal TX-EN (e.g., obtained from the modulator circuit 12) to become active during the ramping of the FMCW signal over a time window that is (slightly) delayed relative to the start time of the ramp.

[0049] The received signal (RX_signal) as reflected from target T (eg, received via receiver antenna RXA) will be a chirped modulated signal suitable for down-conversion by the mixer circuit stage using the signal from VCO 14 to produce a resulting intermediate frequency (IF) signal.

[0050] As discussed above, the amplitude versus frequency behavior of the IF signal indicates the distance of the target. Processing such a signal can facilitate obtaining various other target-related parameters besides the distance, such as position (radial / angular), velocity, etc. For this purpose, various corresponding processing techniques are known in the art, which techniques themselves are not relevant to the embodiments.

[0051] For purposes of this document, it will suffice to recall that such processing is facilitated by avoiding the possibility that amplifier 20 that amplifies the IF signal (e.g., the variable gain of amplifier 20) might experience undesirable phenomena caused by sudden activation of the IF signal (e.g., a transient DC offset that causes output saturation as discussed previously).

[0052] One or more embodiments may address this problem by providing a dual filter arrangement 22 in the IF signal path from the mixer circuit 18 to the output amplifier (e.g., VGA) 20, the dual filter arrangement 22 comprising a first high pass filter (HPF1) 221 and a second high pass filter (HPF2) 222, wherein the first filter 221 has a (low end) corner frequency that is higher than the corresponding frequency of the second filter 222.

[0053] As is well known, the corner frequency (also known as the "cutoff" or "breakpoint" frequency) is a fundamental parameter in filters such as high-pass filters. A high-pass filter is an electronic filter that passes signals with frequencies higher than a certain cutoff / corner / breakpoint frequency and attenuates signals with frequencies lower than the cutoff / corner / breakpoint frequency.

[0054] One or more embodiments may envisage that, at each ramp, filtering of the IF signal is first performed by the first HF filter 221 (the filter with the higher corner frequency HPF1) and then, after a (programmable) time, by the second HF filter 222 (the filter with the lower corner frequency HPF2).

[0055] In such Figure 3 In one or more embodiments illustrated in FIG. 1 , two filters 221 and 222 may be arranged in the circuit portion between the mixer circuit 18 and the output amplifier 20 together with two switches 223, 224 (e.g., controlled by the modulator 12 to facilitate synchronization with the ramp of the FMCW signal), the two switches 223, 224 causing the IF from the mixer circuit 18 to follow:

[0056] First (eg during a time window located in the initial part of the ramp), a first path through the first HF filter 221 to the amplifier 20, and

[0057] Then (eg after a programmable time set by the modulator circuit 12 ) a second path to the amplifier 20 is provided via the second HF filter 221 .

[0058] It can be understood in another way. Figure 3 The implementation shown in is merely exemplary, and various alternatives may be devised by those skilled in the art.

[0059] To mention just two possible non-limiting examples, in one or more embodiments:

[0060] The two filters 221 and 222 may be replaced by a single filter having a selectively variable transfer function, i.e. a single filter having a corner frequency that may be selectively varied between a first higher value (HPF1) and a second lower value (HPF2);

[0061] The switching between the two HF filter characteristics synchronized with the ramp of the FMCW signal may be obtained with other circuits than the modulator circuit 12 (eg via a PLL circuit locked to the RF_signal).

[0062] Regardless of the specific implementation, one or more embodiments can facilitate obtaining the Figure 4 The output signal OS illustrated in FIG. 1 is a signal in which any DC offset may, for example, be quickly "smoothed" before the signal OS can be used for further processing, such as by sampling by an analog-to-digital converter (ADC - not visible in the figure).

[0063] As a non-limiting example only, the following exemplary numbers may apply to a 77 GHz radar application for the consumer automotive industry with FMCW modulation:

[0064] -Chirp slope: from 0.003 GHz / μs to 0.05 GHz / μs;

[0065] -Chirp modulation (sweep) range: from 0.2Ghz to 4GHz;

[0066] -VCO frequency range: from 76 GHz to 81 GHz;

[0067] - First corner frequency (HPF1 - filter 221): maximum 5 MHz;

[0068] - Second corner frequency (HPF2 - filter 222): minimum 50KHz;

[0069] - Programmable time delay for switching to the second filtering (filter 222, corner frequency HPF2) after the start of the chirp ramp: from 0 μs to 5 μs.

[0070] Thus, one or more embodiments may be directed to a method of operating a radar sensor system, wherein a sequence of chirped ramps (see, e.g. Figure 1A received signal (e.g., RF_signal) chirped modulated by chirp_1, chirp_2, ..., chirp_n) in the received signal is down-converted (e.g., at the mixer 18) to an intermediate frequency signal, and the intermediate frequency signal is high-pass filtered (e.g., 221, 222) to produce a high-pass filtered signal (OS, e.g., for further processing such as ADC conversion) therefrom. The method may include: at each chirp in the chirp modulation of the received signal, applying high-pass filtering to the intermediate frequency signal, the high-pass filtering starting with a first high-pass filtering (e.g., filter 221) having a first corner frequency (e.g., HPF1), which is subsequently replaced (e.g., after a possibly adjustable time interval) by a second high-pass filtering (e.g., filter 222) having a second corner frequency (e.g., HPF2), the first corner frequency being higher than the second corner frequency.

[0071] One or more embodiments may include generating (e.g., using a modulator 12 and a VCO 14) a transmission signal to produce a received signal due to reflection of the transmission signal at a detection target (e.g., a target object T), chirping the transmission signal using a sequence of chirped ramps (so that the received signal reflected back from the target T is similarly chirped modulated), and the method may include controlling (e.g., via the modulator 12 and switches 223, 224) replacing a first high-pass filter with a second high-pass filter according to the sequence of chirped ramps that chirp modulate the transmission signal.

[0072] One or more embodiments may include amplifying the transmit signal by a discontinuously activated transmit amplifier (eg, amplifier 16), wherein the transmit amplifier is enabled (eg, TX_EN) during the chirp ramp.

[0073] One or more embodiments may include: an input node (e.g., mixer circuit 18) configured to receive a radar receive signal chirped modulated with a sequence of chirp ramps and down-convert the receive signal to an intermediate frequency signal; and a high-pass filter circuit configured to receive the intermediate frequency signal and generate a high-pass filtered signal therefrom. The high-pass filter circuit includes first and second high-pass filter devices (e.g., two filters such as 221, 222 or a single adjustable filter) having first and second corner frequencies, respectively, the first corner frequency being higher than the second corner frequency. The high-pass filter circuit is configured (see, e.g., switches 223, 224) to provide high-pass filtering at each chirp in the chirp modulation, the high-pass filtering starting with a first high-pass filtering having a first corner frequency, and subsequently replaced by a second high-pass filtering having a second corner frequency, the first corner frequency being higher than the second corner frequency.

[0074] One or more embodiments may include: an output node (e.g., amplifier 20), wherein a high-pass filter circuit is located between the input node and the output node, wherein the high-pass filter circuit includes a first high-pass filter having a first corner frequency and a second high-pass filter having a second corner frequency; a first switch (e.g., switch 223), which can be activated to guide an intermediate frequency signal from the input node toward either the first high-pass filter and the second high-pass filter; a second switch (e.g., switch 224), which can be activated to guide a high-pass filtered signal from either the first high-pass filter and the second high-pass filter toward the output node; the first switch and the second switch can be activated together to provide a first filtering path and a second filtering path from the input node to the output node via the first high-pass filter and the second high-pass filter, respectively, for the intermediate frequency signal.

[0075] One or more embodiments may include a chirp modulator (e.g., modulator 12 and VCO 14) configured to generate a transmission signal to produce a reception signal due to reflection of the transmission signal at a detection target, the chirp modulator being configured to generate a sequence of chirped ramps, wherein a high pass filter circuit is coupled to the chirp modulator to provide alternating activation of a first high pass filtering device and a second high pass filtering device at each chirp in the chirp modulation.

[0076] One or more embodiments may include an output node wherein the high pass filter circuit is located between the input node and the output node, wherein the output node includes an amplifier (eg, amplifier 20), optionally a variable gain amplifier, operative for the high pass filtered signal from the high pass filter circuit.

[0077] One or more embodiments may include: a chirp modulator configured to generate a transmission signal to produce a reception signal due to reflection of the transmission signal at a detection target, the chirp modulator configured to generate a sequence of chirped ramps; and a transmission amplifier (e.g., amplifier 16) configured to amplify the transmission signal, the transmission amplifier being discontinuously activated, wherein the transmission amplifier is configured to be enabled during the chirped ramps.

[0078] One or more embodiments may relate to a radar sensor system, comprising: a circuit according to one or more embodiments (e.g., radar sensor 10); a transmitter antenna (e.g., TXA) configured to transmit a transmission signal to generate a reception signal due to reflection of the transmission signal at a detection target; and a receiver antenna (e.g., RXA) configured to receive the reception signal, the receiver antenna being coupled to an input node of the circuit to transmit the reception signal thereto.

[0079] One or more embodiments may relate to a vehicle (eg, V, such as a motor vehicle) equipped with a radar sensor system (eg, TXA, RXA, radar sensor 10 ) according to one or more embodiments.

[0080] The details and embodiments may vary, even significantly, with respect to what is described merely as an example, without prejudice to the underlying principle and without departing from the scope of protection.

Claims

1. A method of operating a radar sensor system, the method comprising: down-converting a received signal chirped modulated by a sequence of chirped ramps into an intermediate frequency signal; as well as The intermediate frequency signal is subjected to high-pass filtering to generate a high-pass filtered signal, wherein the high-pass filtering comprises: At each chirp in the chirp modulation of the received signal, performing a first high-pass filter having a first corner frequency on the intermediate frequency signal; as well as The first high pass filter is replaced by a second high pass filter having a second corner frequency, the first corner frequency being higher than the second corner frequency.

2. The method according to claim 1, further comprising: A transmission signal is generated to produce the reception signal, the reception signal being a result of reflection of the transmission signal at a detection target, wherein the transmission signal is chirp modulated with a sequence of chirp ramps.

3. The method according to claim 2, further comprising: According to the sequence of the chirp ramps for chirping the transmission signal, the use of the second high-pass filtering to replace the first high-pass filtering is controlled.

4. The method according to claim 2, further comprising: A transmission amplifier is discontinuously activated, and the transmission signal is amplified using the transmission amplifier.

5. The method according to claim 4, further comprising: The transmit amplifier is activated during the sequence of chirp ramps.

6. A circuit comprising: An input node configured to receive a received signal chirped modulated using a sequence of chirped ramps and down-convert the received signal to an intermediate frequency signal; a high-pass filter circuit configured to receive the intermediate frequency signal and generate a high-pass filtered signal; in: The high-pass filter circuit comprises a first high-pass filter device having a first corner frequency and a second high-pass filter device having a second corner frequency, the first corner frequency being higher than the second corner frequency; and The high pass filter circuit is configured to provide high pass filtering starting with the first high pass filtering means having the first corner frequency at each chirp in the chirp modulation, wherein the first high pass filtering means is subsequently replaced by the second high pass filtering means having the second corner frequency.

7. The circuit according to claim 6, further comprising: an output node coupled to an output of the high pass filter circuit, wherein the high pass filter circuit is located between the input node and the output node, wherein the high pass filter circuit includes a first high pass filter having the first corner frequency and a second high pass filter having the second corner frequency.

8. The circuit according to claim 7, further comprising: a first switch activatable to direct the intermediate frequency signal from the input node toward either the first high pass filter or the second high pass filter; as well as A second switch is activatable to direct the high pass filtered signal from either the first high pass filter or the second high pass filter toward the output node.

9. The circuit of claim 8, wherein the first switch and the second switch are jointly activatable to provide a first filtering path and a second filtering path from the input node to the output node via the first high pass filter and the second high pass filter, respectively, for the intermediate frequency signal.

10. The circuit of claim 6, further comprising a chirp modulator configured to generate a transmission signal to produce the received signal as a result of reflection of the transmission signal at a detection target, wherein the chirp modulator is configured to produce a sequence of the chirp ramps, wherein the high pass filter circuit is coupled to the chirp modulator to provide alternating activation of the first high pass filtering means and the second high pass filtering means at each chirp of the chirp modulation.

11. The circuit of claim 6 further comprising an output node, wherein the high pass filter circuit is located between the input node and the output node, and wherein the output node includes an amplifier active for the high pass filtered signal from the high pass filter circuit.

12. The circuit of claim 11, wherein the amplifier comprises a variable gain amplifier.

13. The circuit according to claim 6, further comprising: a chirp modulator configured to generate a transmission signal to produce the received signal as a result of reflection of the transmission signal at a detection target, wherein the chirp modulator is configured to generate the sequence of chirp ramps; as well as A transmission amplifier is configured to amplify the transmission signal, and the transmission amplifier can be activated discontinuously.

14. The circuit of claim 13, wherein the transmit amplifier is configured to be enabled during the sequence of chirped ramps.

15. A radar sensor system comprising: Circuit, including: An input node configured to receive a received signal chirped modulated using a sequence of chirped ramps and down-convert the received signal to an intermediate frequency signal; a high-pass filter circuit configured to receive the intermediate frequency signal and generate a high-pass filtered signal; in: The high-pass filter circuit comprises a first high-pass filter device having a first corner frequency and a second high-pass filter device having a second corner frequency, the first corner frequency being higher than the second corner frequency; and The high pass filter circuit is configured to provide high pass filtering starting with the first high pass filtering means having the first corner frequency at each chirp in the chirp modulation, wherein the first high pass filtering means is subsequently replaced by the second high pass filtering means having the second corner frequency; a transmitter antenna configured to transmit a transmission signal to generate the reception signal as a result of reflection of the transmission signal at a detection target; and A receiver antenna is configured to receive the receive signal, the receiver antenna being coupled to the input node of the circuit to transmit the receive signal to the circuit.

16. The radar sensor system of claim 15, wherein the circuit further comprises: an output node coupled to an output of the high pass filter circuit, wherein the high pass filter circuit is located between the input node and the output node, wherein the high pass filter circuit includes a first high pass filter having the first corner frequency and a second high pass filter having the second corner frequency.

17. The radar sensor system of claim 16, wherein the circuit further comprises: a first switch activatable to direct the intermediate frequency signal from the input node toward either the first high pass filter or the second high pass filter; as well as A second switch is activatable to direct the high pass filtered signal from either the first high pass filter or the second high pass filter toward the output node.

18. The radar sensor system of claim 17, wherein the first switch and the second switch are jointly activatable to provide a first filtering path and a second filtering path from the input node to the output node via the first high pass filter and the second high pass filter, respectively, for the intermediate frequency signal.

19. The radar sensor system of claim 15, wherein the circuit further comprises a chirp modulator configured to generate a transmission signal to produce the received signal as a result of reflection of the transmission signal at a detection target, wherein the chirp modulator is configured to produce a sequence of the chirp ramps, wherein the high pass filter circuit is coupled to the chirp modulator to provide alternating activation of the first high pass filtering means and the second high pass filtering means at each chirp in the chirp modulation.

20. A vehicle equipped with a radar sensor system, the radar sensor system comprising: Circuit, including: an input node configured to receive a received signal chirped modulated with a sequence of chirped ramps and down-convert the received signal to an intermediate frequency signal; and a high-pass filter circuit configured to receive the intermediate frequency signal and generate a high-pass filtered signal; in: The high-pass filter circuit comprises a first high-pass filter device having a first corner frequency and a second high-pass filter device having a second corner frequency, the first corner frequency being higher than the second corner frequency; and The high pass filter circuit is configured to provide high pass filtering starting with the first high pass filtering means having the first corner frequency at each chirp in the chirp modulation, wherein the first high pass filtering means is subsequently replaced by the second high pass filtering means having the second corner frequency; a transmitter antenna configured to transmit a transmission signal to generate the reception signal as a result of reflection of the transmission signal at a detection target; and A receiver antenna is configured to receive the receive signal, the receiver antenna being coupled to the input node of the circuit to transmit the receive signal to the circuit.

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