ACOUSTIC DUAL-CHANNEL DISTANCE MEASURING CIRCUIT AND METHOD

Abstract

Acoustic distance measuring circuit (800), comprising: a transmitter (810) having an output configured to be coupled to an acoustic transducer (820) to transmit a selected one of an amplitude modulation signal, AM signal, in an AM mode and provide a chirp signal in a chirp mode; a receiver (830) having an input configured to be coupled to the acoustic transducer (820) and an output for providing a digital received signal; and a control system that is operational during a first measurement period: Setting the transmitter (810) in one of the AM mode and the chirp mode using a first channel, selectively detecting a first direct echo in the first channel of the digital received signal of one of the AM signal and the chirp signal, and selectively detecting a first indirect echo in a second channel of the digital received signal of another of the AM signal and the chirp signal, where the first channel occupies a different frequency band than the second channel.

Description

AREA OF REVELATION

[0001] The disclosure relates generally to electrical and electronic circuits and, more particularly, to acoustic distance measuring circuits. BACKGROUND

[0002] Acoustic distance measurement systems can be used in a wide variety of applications. For example, acoustic distance measurement systems are used in parking assist sensors (PAS) for automobiles. PAS sensors detect the presence of an object within a range of distances from the motor vehicle and signal that the user may be able to take corrective action. Generally, acoustic distance measurement systems first transmit acoustic energy through sound waves and then measure the elapsed time until an echo is detected. The elapsed time is known as the time of flight and is proportional to the distance between the motor vehicle and the obstacle. Automotive applications that use acoustic distance measurement systems require reliable detection of the presence of obstacles over a wide measurement range, such as from a few centimeters to several meters.Currently, single modulating acoustic measurement sensors provide reliable detection at short intervals or long intervals, but not both, based on the type of acoustic signal used.

[0003] For example, acoustic sensors may use amplitude-modulated (AM) acoustic pulses, which provide good detection at short distances but have limited sensing capabilities at long distances. The limited detection of long distances results from a variety of factors. First, the sensitivity of conventional piezoelectric transducers is limited, preventing the detection of spurious AM echo signals reflected from distant objects. Second, the transducers themselves have limited bandwidths, and AM signals are susceptible to phase phenomena. For example, phase drift can occur due to overlapping echoes from complex objects, gravel, etc., causing interference. Third, AM signals are susceptible to limited beam durations, such as 500 microseconds (µs), which limit the amount of transmitted energy and therefore the maximum distance at which an echo can be reliably detected.

[0004] Because of these problems, AM signals, even when used with multiple channels, can only detect objects at distances of approximately 3.6 meters (m) or less.

[0005] On the other hand, acoustic sensors can use chirps instead of AM signals to achieve better detection of distant obstacles. A chirp is an electrical signal in which a frequency of the signal changes over a period of time, or is noisy. Chirp-based systems have problems when detecting objects at shorter distances. The minimum distance a chirp sensor can detect is limited by two factors. First, a high-quality transducer is required to match the surface impedance of the transducer to the surrounding air. However, the high-quality transducer still has a lot of energy remaining after the end of the beam period, which lengthens the reverberation period and increases the minimum distance at which the sensor can detect an obstacle.Secondly, to achieve object detection at a desirable long distance of 5 m, for example, the vehicle must drive the transducer with a lot of energy, which also lengthens the reverberation time and increases the minimum detectable distance.

[0006] The prior art can be found in US 2020 / 0 200 898 A1. This document generally relates to an acoustic distance measuring circuit comprising a frequency generator, a transmit amplifier, an acoustic transducer, and a sampling circuit. The sensor circuit includes an input that can be coupled to the acoustic transducer to receive an input signal. The detection circuit provides an in-phase portion and a quadrature portion of the input signal to a filter. The sensor circuit filters the in-phase portion and the quadrature portion and calculates a phase of the input signal depending on the filtered in-phase and quadrature portions. The detection circuit determines a frequency slope of the input signal in response to the phase calculation and provides the frequency slope of the input signal to an output. The prior art can also be found in US 2017 / 0 261 606 A1.This document generally relates to generating an acoustic signal for an acoustic transducer, wherein the acoustic transducer transmits the acoustic signal to determine a first position of an obstacle. In response to the acoustic signal encountering the obstacle within a predetermined distance, an echo or pulse is detected at the acoustic transducer. At a first time, a magnitude is detected in response to a rising edge of the pulse intersecting a certain threshold. A second magnitude is detected in response to detecting a first peak of the pulse. A time of flight of the acoustic signal within the predetermined distance is determined when a compensation time is extracted from a correction calculation algorithm in response to detecting the first magnitude and the second magnitude.The compensation time is subtracted from the first time, and the difference between the compensation time and the first time is the flight time. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present disclosure may be better understood, and its numerous features and advantages made more apparent to those skilled in the art, by reference to the accompanying drawings in which: Fig. 1 illustrates in block diagram form an acoustic distance measuring system according to various embodiments; Fig. 2 illustrates in block diagram form a dual-channel acoustic distance measurement system according to various embodiments of the present disclosure; Fig. 3 illustrates in block diagram form a dual-channel acoustic distance measurement system according to various embodiments of the present disclosure; Fig. 4 illustrates in block diagram form a low-height obstacle detection system that uses the dual-channel distance measuring system of Fig. 3 can be used; Fig. 5 timing diagrams are illustrated to help understand the operation of the dual-channel acoustic distance measurement system of Fig. 2 are useful for an object at a short distance; Fig. 6 timing diagrams are illustrated to help understand the operation of the acoustic distance measuring system of Fig. 2 are useful for an object at a great distance; Fig. 7 illustrates a set of timing diagrams that may be helpful in understanding the operation of the dual-channel acoustic distance measuring system of Fig. 3 and Fig. 4 are useful for an object with a small height; Fig. 8 illustrates in block diagram form an acoustic distance measuring circuit according to various embodiments of the present disclosure; and Fig. 9 illustrates in block diagram form an integrated circuit which incorporates the acoustic distance measuring circuit of Fig. 8 according to various embodiments of the present disclosure.

[0008] Similar or identical elements in the various drawings are designated by the same reference numerals. Unless otherwise noted, the word "coupled" and its associated verb forms refer to both direct connection and indirect electrical connection using means known in the art, and unless otherwise indicated, any description of a direct connection also includes alternative embodiments using suitable forms of indirect electrical connection. DETAILED DESCRIPTION

[0009] The invention is set out in the independent claims. Preferred embodiments of the invention are specified in the dependent claims.

[0010] Fig. Figure 1 illustrates, in block diagram form, an acoustic distance measuring system 100 according to various embodiments. The acoustic distance measuring system 100 generally includes a vehicle 102 and an obstacle 120.

[0011] Vehicle 102 includes an engine control unit (ECU) 104, a speaker 106, a set of conductors 112, and a set of acoustic sensor modules 110. A system controller, such as the ECU 104, is located on or within the motor vehicle 102 and provides an electrical warning signal that causes the speaker 106 to issue an audible warning to the driver to signal the presence and relative distance of an obstacle 120 with respect to the rear bumper of the motor vehicle 102. For example, the ECU 104 could signal the relative distance at the rate of beeps, and when the rear bumper is within a certain distance of the read bumper, it provides a continuous tone to warn the driver of the need to immediately stop the motor vehicle 102.In other embodiments, ECU could be replaced by a body control unit (BCU), an infotainment system controller, or the same controller that could interact with the driver.

[0012] ECU 104 also includes outputs connected to acoustic sensor modules 110 and inputs for receiving obstacle position information from acoustic sensor modules 110. Each of acoustic sensor modules 110 emits an ultrasonic acoustic signal, as described herein, which is reflected by obstacle 120 when obstacle 120 is within the sensing range between the rear bumper of motor vehicle 102 and obstacle 120. Each acoustic sensor module 110 also receives reflected signals, also known as echoes, processes them, and provides output signals to ECU 104. ECU 104 determines the time of flight and thus the distance to these signals.

[0013] In the illustrated embodiment, motor vehicle 102 has four acoustic sensor modules on its rear bumper, including an acoustic sensor module 110a, an acoustic sensor module 110b, an acoustic sensor module 110c, and an acoustic sensor module 110d. Each acoustic sensor module 110 is capable of emitting an acoustic pulse and receiving echoes from its or its neighboring transmissions. In the Fig. 1, the acoustic sensor module 110c emits an acoustic signal 114 and receives an echo 116 from obstacle 120. Echo 116 is known as a direct echo signal because it is directly reflected along the same path as the acoustic signal 114, and the time between the emission of the acoustic signal 114 and the reception of the echo 116 corresponds to the distance between the acoustic sensor module 110c on the rear bumper of the automobile 102 and the obstacle 120.

[0014] However, the acoustic signal 114 also generates another echo, which includes an echo 117 received by the acoustic sensor module 110b and an echo 118 received by the acoustic sensor module 110d. Echoes 117 and 118 are known as indirect echo signals because they are indirectly reflected along different paths to neighboring sensors. Because echoes 117 and 118 travel along indirect paths, they travel longer distances but also reflect the distance between the rear bumper and the obstacle 120. A more accurate distance measurement between the rear bumper of the automobile 102 and the obstacle 120 can be determined by triangulating the three signals based on the known and fixed physical separations between the acoustic sensor modules 110b, 110c, and 110d.

[0015] According to various embodiments described herein, an acoustic distance measurement system utilizes these properties of direct and indirect measurement to achieve both accurate detection of obstacles at a short distance and accurate detection of obstacles at a long distance. Furthermore, it utilizes distinct and complementary properties of different sensor types to measure the presence of low-height objects, such as a very low curb that tends to obscure a high-height object, such as a pole, behind it. Both capabilities are described in detail below.

[0016] Fig. Figure 2 illustrates, in block diagram form, a dual-channel acoustic distance measuring system 300 according to various embodiments of the present disclosure. The dual-channel acoustic distance measuring system 200 includes acoustic sensor modules 210, 220, 230, and 240, illustrated as circles and corresponding, for example, to the Fig. 1 acoustic sensor modules 110d, 110c, 110b and 110a. As shown in Fig. 2, the acoustic sensor module 210 transmits an AM signal from a low-frequency channel, labeled "01," and detects the direct echo of the AM signal and an indirect chirp signal from a high-frequency channel, labeled "10," transmitted by the acoustic sensor module 220. The acoustic sensor module 220 transmits a chirp signal on the high-frequency channel and detects a direct echo of the chirp signal and an indirect echo of the AM signal on the low-frequency channel, transmitted by each of the acoustic sensor modules 210 and 230. The acoustic sensor module 230 transmits an AM signal on the low channel and detects a direct echo of the AM signal and an indirect echo of the chirp signal transmitted by the acoustic sensor module 220.The acoustic sensor module 240 transmits a chirp signal on the high channel and detects a direct echo of the chirp signal and an indirect echo of the AM signal transmitted by the acoustic sensor module 230.

[0017] The inventors discovered that a low-frequency AM signal can accurately measure short distances up to approximately 16 cm, but cannot provide accurate detection of obstacles beyond approximately 3 m. On the other hand, the high-frequency chirp signal can accurately detect the presence of obstacles at short distances up to 16 cm, but cannot accurately determine their distances and can indicate the location of obstacles at distances up to approximately 5 m.

[0018] The dual-channel acoustic distance measuring system 200 simultaneously uses two types of acoustic signals, each provided on one of two channels, to provide more accurate detection of obstacles over a wider range of distances. Specifically, the dual-channel acoustic distance measuring system 200 simultaneously transmits on two channels, in the illustrated embodiment, a low-frequency AM signal channel and a high-frequency chirp signal channel, using alternating piezoelectric transducers along the rear bumper of a motor vehicle. The dual-channel acoustic distance measuring system 200 uses the chirp signal to detect the presence of obstacles at short distances, while the AM signal is used to determine their location to provide fast and accurate detection of obstacles up to approximately 16 cm, which is shorter than prior art systems.The dual-channel acoustic distance measuring system 200 also uses AM distances measured by two sensors to trigger the position and distance of obstacles relative to, for example, the rear bumper of a motor vehicle.

[0019] The dual-channel acoustic distance measurement system 200 also uses chirp signals to measure the distance to obstacles at greater distances. Like the AM signals, it uses distances measured by two sensors to triangulate the precise position of an obstacle relative to, for example, the vehicle's read bumper.

[0020] As from Fig. As can be seen in Figure 2, the rear bumper of the motor vehicle uses a pattern of sensors that alternate between AM and chirp acoustic signal transmissions and between low and high frequencies. Each transducer fires (i.e., transmits an acoustic signal) and measures the echo signal on its respective channel in a given mode. During an indirect measurement period, each transducer fires and measures the indirect signals received in the opposite mode. To measure an echo generated by signal reflections from an obstacle up to approximately 5 m from the rear bumper, each period lasts approximately 40 milliseconds (ms), which represents the time from the beginning to the end of the transmission and the round-trip flight time of the acoustic signal at the longest measurable distance.

[0021] The dual-channel acoustic distance measurement system 200 uses data from consecutive, alternating dual AM and dual chirp measurements to obtain a precise measurement up to a closer distance than would be obtained in a dual chirp mode alone. A chirp signal alone cannot provide an accurate distance if the object is detected at less than approximately 28 cm. However, if a dual chirp signal detects that an obstacle is present at less than approximately 28 cm, then a subsequent dual AM signal can provide an accurate measured distance well below approximately 28 cm. In particular, the inventors have discovered that by using the dual-sensor detection technique, distances as close as approximately 16 cm are achievable.

[0022] Similarly, the dual-channel acoustic distance measurement system 300 utilizes data from consecutive, alternating dual AM and dual chirp measurements to obtain a precise measurement up to a distance greater than would be obtainable using dual AM mode alone. An AM signal alone cannot provide an accurate distance if the object is detected beyond approximately 3.6 m. However, if an AM signal detects that an obstacle is present beyond approximately 3.6 m, then a subsequent dual chirp signal can provide an accurate measured distance well beyond approximately 3.6 m. In particular, the inventors have discovered that by using the dual-sensor sensing technique, distances as close as approximately 5 m can be accurately measured. Therefore, using dual AM / dual chirp measurements, an obstacle can be detected within a total range of approximately 16 cm to approximately 5 m.

[0023] Sequential direct and indirect measurements can also be used to detect low-level objects. For example, the dual-channel acoustic distance measurement system 300 can detect a low curb that is 9 cm high, even in the presence of background objects, such as a 20 cm diameter pole located 50 cm behind the curb.

[0024] Fig. 3 illustrates a block diagram of a dual-channel acoustic distance measuring system 300 using a combination of amplitude modulation signals and chirp signals. The dual-channel acoustic distance measuring system 300 includes acoustic sensor modules 310, 320, 330, and 340, illustrated as circles, corresponding, for example, to the acoustic sensor modules 110d, 110c, 110b, and 110a on the rear bumper, as shown in Fig. 1. The two-channel acoustic distance measuring system 300 has a first measurement period in which it transmits and then detects AM signals on both the low and high channels. Thus, as shown in Fig. 3, acoustic sensor modules 310 and 330 transmit AM signals on the low (01) channel, and acoustic sensor modules 320 and 340 transmit AM signals on the high (10) channel. Similarly, dual-channel acoustic distance measurement system 300 has a second measurement period in which it transmits and then detects chirp signals on both the low and high channels. It uses each transducer to measure both direct and indirect echoes and combines these measurements to detect the presence of a low-level object (such as a curb) and possibly a high-level object (such as a pole) behind the curb.

[0025] Specifically, the acoustic sensor module 310 transmits an AM signal on the low channel during the first measurement period and receives an acoustic signal after the end of the reverberation period. It detects echoes of the direct AM signal on the low (01) channel and echoes of the indirect AM signal on the high (10) channel, which are received by the acoustic sensor module 320 using digital processing on the received acoustic signal. The acoustic sensor module 310 analyzes the acoustic signal in the digital domain to search for echoes from which the presence of objects and their time of flight can be determined. The acoustic sensor module 320 transmits an AM signal on the high (10) channel and receives an acoustic signal after the end of the reverberation period. It detects echoes of the direct AM signal on the high (10) channel and echoes of the AM signal on the low (01) channel, which are indirectly received by the acoustic sensor modules 310 and 330.The acoustic sensor module 330 transmits an AM signal on the high channel and receives an acoustic signal after the end of the reverberation period. It detects echoes of the direct AM signal on the low (01) channel and echoes of the indirect AM signal on the high (10) channel received by the acoustic sensor module 320 using digital processing on the received acoustic signal. The acoustic sensor module 340 transmits an AM signal on the low channel and receives an acoustic signal after the end of the reverberation period. It detects echoes of the direct AM signal on the low (01) channel and echoes of the indirect AM signal on the high (10) channel received by the acoustic sensor module 320 using digital processing on the received acoustic signal.

[0026] During the second measurement period, the acoustic sensor modules transmit opposing signals. Acoustic sensor module 310 transmits a chirp signal on the low channel and receives and analyzes an acoustic signal after the end of the reverberation period. It detects direct echoes of the chirp signal on the low (01) channel and indirect echoes of the chirp signal on the high (10) channel received from acoustic sensor module 320 using digital processing on the received acoustic signal. Acoustic sensor module 310 analyzes the acoustic signal in the digital domain to search for echoes from which the presence of objects and their flight times can be determined. Acoustic sensor module 320 transmits a chirp signal on the high (10) channel and receives an acoustic signal after the end of the reverberation period.It detects direct echoes of the chirp signal on the high (10) channel and echoes of the chirp signal on the low (01) channel indirectly received by the acoustic sensor modules 310 and 330. The acoustic sensor module 330 transmits a chirp signal on the high channel and receives an acoustic signal after the end of the reverberation period. It detects echoes of the direct chirp signal on the low (01) channel and indirect echoes of the chirp signal on the high (10) channel received from the acoustic sensor module 320 using digital processing on the received acoustic signal. The acoustic sensor module 340 transmits a chirp signal on the low channel and receives an acoustic signal after the end of the reverberation period.It detects direct echoes of the direct chirp signal on the high (10) channel and indirect echoes of the chirp signal on the low (01) channel received by the acoustic sensor module 330 using digital processing on the received acoustic signal.

[0027] In other embodiments, chirp signals could be used during the first measurement period and AM signals during the second measurement period.

[0028] The dual-channel acoustic distance measurement system 300 utilizes a difference between AM and chirp echoes to detect the presence of a low-altitude object. As mentioned above, AM measurements are accurate for detecting objects at short distances, but less accurate for detecting objects at long distances. However, while AM ​​can be used to detect objects at close distances, their amplitudes are smaller at shorter distances when the AM signals are reflected off low-altitude objects. The inventors have discovered that a significant difference in the amplitude of the near-end echoes between AM and chirp echoes accurately indicates the presence of a low-altitude object. In particular, an echo from a low-altitude object has a significantly smaller amplitude at distances less than approximately 1 m in the dual-channel AM mode compared to that in the dual-chirp mode.These distances are the distances at which the detection of a low-height object, primarily a curb, becomes important.

[0029] Each acoustic sensor module analyzes the received acoustic signal by converting it to the digital domain and analyzing the received signal in the digital domain to observe echoes, from which the presence of objects and their time of flight can be determined. Using two channels, two signals can be distinguished by overlapping time but not by frequency.

[0030] Thus, for each acoustic distance measurement, the two-channel acoustic distance measurement system 300 generally operates during two measurement periods. During a first measurement period, a transmitter is set to one of the AM mode and the chirp mode and uses a first channel of the AM mode or the chirp mode, as appropriate. A first direct echo is selectively detected in the first channel of a digital receive signal. A first indirect echo is selectively detected in a second channel of the digital receive signal. During a second measurement period following the first measurement period, the transmitter is set to the other of the AM mode and the chirp mode and uses a second channel of the AM mode or the chirp mode, as appropriate. A second direct echo is selectively detected in the second channel of a digital receive signal or the other of the AM signal and the chirp signal.This pattern is repeated on alternating channels in adjacent sensors as described above.

[0031] Fig. Figure 4 illustrates in block diagram form a low-level obstacle detection system 400 that is compatible with the dual-channel acoustic distance measuring system 300 of Fig. 3. The low-height obstacle detection system 400 includes distance measurement blocks 410 and 420 and low-height object detection blocks 430 and 440. The distance measurement block 410 has a first input for receiving a previously measured dual AM direct measurement (in the present example, one measured in the first measurement period), a second input for receiving a current (or "actual") measured dual chirp direct measurement, and an output for providing a signal labeled "direct distance."The indirect distance measurement block 420 has a first input for receiving a previously measured dual AM direct measurement (in the present example, one measured in the first measurement period), a second input for receiving a current (or "actual") measured dual chirp direct measurement, and an output for providing a signal labeled "indirect distance." The low height object detection block 440 uses the previous dual indirect AM distance measurement, and the current dual indirect chirp measurement generates an indirect low height flag.

[0032] Low-height object detection system 400 uses sequential alternating dual AM / dual chirp measurements to detect a combination of low-height and high-height objects. A low-height object will have a dual AM echo that is measurably different from the low-height object in chirp mode because the low-height object's echo is significantly smaller than that of the high-height object. This system is therefore capable of effectively detecting low height at distances shorter than 1 m, which are distances where detection of an approaching curb is important.

[0033] Fig. 5 illustrates a set of timing diagrams 500 useful in understanding the operation of the dual-channel acoustic distance sensing system 200 of Fig. 2 are useful for an object at a short distance. Timing diagrams 500 include a timing diagram 510 and a timing diagram 520. In each of the timing diagrams 500, the horizontal axis represents time in milliseconds (ms) and the corresponding distance in centimeters (cm), and the vertical axis represents amplitude in millivolts (mV). Timing diagram 510 shows a waveform 511 associated with an acoustic sensor emitting a chirp signal. The transducer emits a chirp pattern 512 that lasts until a time instant designated "t 0 ” is marked, where the time t 0 represents the end of the reverberation. After t 0the transducer detects a direct echo, showing peaks 513 and 514. These peaks indicate the presence of a near-range obstacle, but do not provide a reliable indication of its position due to the complex shape of the reflection shown by peaks 513 and 514. Timing diagram 520 shows a waveform 521, with the acoustic sensor emitting a chirp signal 522, which persists until the end of the reverberation at time t 0 lasts. In this case, however, the acoustic sensor detects an indirect echo of an AM signal emitted by a neighboring sensor. After time t 0The transducer detects the indirect echo, which exhibits a single, well-defined peak 523, which accurately identifies the time of flight and thus the distance. By using data from consecutive alternating AM and chirp measurements on different channels, the dual-channel acoustic distance measurement system 200 improves precision over the dual chirp measurement alone, and an object can be accurately detected at a distance of approximately 16 cm.

[0034] Thus, by alternating between a direct chirp measurement and an indirect AM measurement, the near-range peak can be detected but not measured using the chirp measurement, and then the consecutive indirect measurement with an AM neighbor can be used to improve the minimum distance measurement to the same performance using an AM pulse.

[0035] Fig. 6 illustrates a set of timing diagrams 600 useful in understanding the operation of the dual-channel acoustic distance measuring system 200 of Fig. 2 are useful for a long-distance obstacle. Timing diagrams 600 include a timing diagram 610 and a timing diagram 620. In each of the timing diagrams 600, the horizontal axis represents time in ms and the corresponding distance in cm, and the vertical axis represents amplitude in mV. Timing diagram 610 shows a waveform 611 associated with an acoustic sensor emitting a dual AM signal. An obstacle at a long distance causes an echo 612 to be detected. Note that the magnitude of the echo 612 is just above the noise floor 613. However, the acoustic sensor detects a chirp in waveform 621 in indirect mode that has a peak 622 significantly higher than the noise floor 623, and thus the acoustic sensor can reliably detect it. Thus, by using an indirect chirp measurement, an obstacle at a long distance can be reliably detected.

[0036] Fig. 7 illustrates a set of timing diagrams 700 useful in understanding the operation of the dual-channel acoustic distance measuring system 300 of Fig. 3 are useful for a low-altitude object. Timing diagrams 700 include a timing diagram 710, a timing diagram 720, and a timing diagram 730. In each of the timing diagrams 700, the horizontal axis represents time in microseconds (µs) and the corresponding distance in centimeters (cm), and the vertical axis represents amplitude in volts (V). A time window 740 corresponds to the time of flight and distance between the acoustic distance measuring circuit and a low-altitude object at various times of flight and distances.

[0037] Timing diagram 710 shows a waveform 711 associated with an AM direct signal and a waveform 712 associated with a chirped direct signal, corresponding to a low-elevation object, such as a curb, located 0.6 m from the acoustic distance measuring circuit with a high-elevation object behind it. Within a time window 740, acoustic distance measuring circuits emitting an AM signal and a dual chirped signal receive small direct echoes that are barely distinguishable from the noise floor and from each other. However, both the AM direct echo signal and the chirped direct echo signal indicate the presence of the high-elevation object at approximately the same distance.

[0038] Timing diagram 720 shows a waveform 721 associated with an AM direct signal and a waveform 722 associated with a chirped direct signal, corresponding to a low-elevation object, such as a curb, located 0.8 m from the acoustic distance measuring circuit with a high-elevation object behind it. Waveforms 721 and 722 have been shifted so that the two direct echoes from the low-elevation object occur at corresponding points within the time window 740. The acoustic distance measuring circuit emitting the AM signal still receives a small direct echo that is barely distinguishable from the noise floor. However, the acoustic distance measuring circuit emitting the chirped signal is able to measure a significant echo in the low-elevation obstacle. Furthermore, the difference in amplitudes between the chirped signal and the AM signal indicates that it is believed to be a low-elevation object.Thus, in the low-height object obstacle detection system 400, the detection block 430 outputs the LOW HEIGHT DIRECT FLAG signal, which causes the system controller, such as the ECU 104, to warn the driver that a low-height object has been detected. However, both the AM direct echo signal and the chirped direct echo signal indicate the presence of the high-height object at approximately the same distance.

[0039] Timing diagram 730 shows a waveform 731 associated with an AM direct signal and a waveform 732 associated with a chirped direct signal, corresponding to a low-elevation object, such as a curb, located 1.0 m from the acoustic distance measuring circuit with a high-elevation object behind it. Waveforms 731 and 732 have been shifted so that the two direct echoes from the low-elevation object occur at corresponding points within time window 740. In timing diagram 730, the acoustic distance measuring circuit emitting the AM signal receives a direct echo that has approximately the same peak amplitude as the chirped echo. However, both the AM direct echo signal and the chirped direct echo signal indicate the presence of the high-elevation object at approximately the same distance.

[0040] At the same time, the acoustic distance measuring circuit receives alternative indirect echoes. Although Fig. 7 not shown, the received indirect echo signals have the same relative characteristics, which allows the system to alert the driver to the presence of the low height object around 0.8 m.

[0041] In a normal driving situation where the driver is parking the vehicle, the acoustic distance measuring system can detect the presence of the low height object such as a curb when the object is relatively far away from the vehicle, and alert the driver of the presence of the low height object, giving him or her enough time to take appropriate corrective action even in the presence of a high height object behind the low height object.

[0042] Fig. Figure 8 illustrates, in block diagram form, an acoustic distance measurement circuit 800 according to various embodiments of the present disclosure. The acoustic distance measurement circuit 800 includes a transmitter 810, an acoustic transducer 820, a receiver 830, and a sensor controller and digital signal processor 840.

[0043] Transmitter 810 includes a signal generator 811 and a transmitter amplifier 812. Signal generator 811 has an input and an output for providing a selected one of a dual AM signal and a dual chirp signal. Transmitter amplifier 812 has an input connected to the output of signal generator 811 and an output adapted to be connected to acoustic transducer 820.

[0044] Receiver 830 includes an amplifier 831 and a mixer 832. Receiver amplifier 831 has an input for connection to a transducer 820 and an output. Mixer circuit 832 has an input connected to the output of receiver amplifier 831 and an output for providing a digital received signal. Sensor controller and digital signal processor 840 have an input connected to the output of receiver 830, an output connected to the input of transmitter 810, and provide an output to ECU 104 to enable ECU 104 to signal appropriate alerts to the driver.

[0045] In operation, the sensor controller and digital signal processor 840 are operable to set the transmitter 810 to one of the AM mode and the chirp mode and detect a received signal during an echo period. The sensor controller and digital signal processor 840 analyze the digital received signal to selectively detect a direct echo on the first channel and an indirect echo on the second channel. During the detection of low-altitude objects, the sensor controller and digital signal processor 840 are further operable during a second measurement period following the first measurement period to set the transmitter 810 to another of the AM mode and the chirp mode, i.e.in the opposite mode to that used in the first measurement period, and to selectively detect a second direct echo in the first channel of the digital receive signal of the other of the AM signal and the chirp signal, and to selectively detect a second indirect echo in the second channel of the digital receive signal of the same of the AM signal and the chirp signal used in the first measurement period. In exemplary embodiments, each of the first and second measurement periods lasts approximately 40 milliseconds (ms).

[0046] In the exemplary embodiment, the sensor controller and digital signal processor 840 perform the DSP-related tasks, including digital filtering and correlation of the received echoes to the AM and chirp patterns, as well as magnitude scaling and noise filtering. However, in other embodiments, various portions of the signal analysis functions may be performed by the vehicle controller, e.g., ECU 104.

[0047] Fig. 9 illustrates in block diagram form an acoustic distance measuring circuit 900 having an integrated circuit 910 incorporating portions of the acoustic distance measuring circuit 800 of Fig. 8 according to various embodiments. Acoustic distance measurement circuit 900 generally includes an integrated circuit 910, a transducer driver interface circuit 920, and a resistor 930.

[0048] In the illustrated embodiment, the integrated circuit 910 is a monolithic silicon chip that may be packaged for attachment or soldering to a circuit board that connects device contacts to other electronic components or wire connectors. As in Fig. As shown in Figure 9, the integrated circuit 910 is connected to two power supply terminals, VBAT and GND, and has a single input / output line labeled "I / O" for bidirectional communication with the ECU 104, three terminals for connection to the transducer driver interface circuit 920, and two terminals connected to the piezoelectric transducer 921, in which the resistor 930 is connected between the two terminals. The integrated circuit 910 generally includes a transmitter 911, labeled "TX," a receiver amplifier 912, an analog-to-digital converter (ADCO) 913, a core logic and DSP block 914, a memory 915, and an I / O controller 916.

[0049] Transmitter 911 corresponds to transmitter 810 of Fig. 8 and has an input and an output connected to a piezoelectric transducer 921 through a transformer 923 having connections to two ends of a winding and a connection to a center tap. Receiver 912 corresponds to the receiver amplifier 831 of Fig. 8 and has a first input connected to the first terminal connected to the piezoelectric transducer 921, a second input connected to the second terminal of the piezoelectric transducer 921, and an output. ADC 913 corresponds to ADC in ADC and mixer 832 of Fig.8 and has an input connected to the output of receiver 912 and an output. Core logic and DSP block 914 have an input connected to the input of transmitter 911, a bidirectional connection to ADC 913, a signal output, a signal input, and a bidirectional connection to memory 915. Memory 915 has memory locations for storing programs, firmware, data, and the like and is bidirectionally connected to core logic and DSP block 914. I / O controller 916 has an input connected to the signal output of core logic and DSP block 914, an output connected to the signal input of core logic and DSP block 914, and a bidirectional connection to the I / O port of integrated circuit 910.

[0050] Core logic and DSP block 914 control the sequence of operations according to the techniques and operations described above. They report measurement results to a vehicle controller, such as ECU 104, which then combines the measurements from multiple acoustic sensor modules to provide precise acoustic distance measurements over a wide range of obstacles from 16 cm to 5 m. To enable this operation, core logic and DSP block 914 perform some signal analysis on the digital received signals to detect received AM and chirp signal strengths, which can be used to detect echo times and obstacle flight times. To enable these operations, they discriminate echoes in the digital received signals using correlators on selected channels of the dual channel AM signals and dual channel chirp signals.An example of a DSP-based processing engine capable of performing all these operations is described in US 2021 / 0352412, but other DSP processing engines are possible and would be obvious to those skilled in the art.

[0051] The above-disclosed subject matter is to be considered illustrative and not restrictive, and the appended claims are intended to encompass all modifications, improvements, and other embodiments that fall within the true scope of the claims. For example, the signal processing functions to detect a valid echo from an obstacle within the range of the sensor may determine flight times and distance by the acoustic sensor itself or by a vehicle control unit, or by various combinations of the two. The vehicle control unit may be part of another control unit, such as an engine control unit (ECU), a body control unit (BCU), an infotainment controller, and the like.While the embodiments have been described with respect to a motor vehicle with four rear sensors and four front sensors, other numbers of sensors and positions for the sensors are possible. The overall function of the acoustic distance measurement system could be for a parking assist sensor (PAS), a forward detection camera, a collision detection system, and the like. Furthermore, the distance enhancement and low-height object detection systems can be used together or individually, while both utilizing dual-channel, dual-mode distance sensing techniques.

[0052] In one form, an acoustic distance measuring circuit includes a transmitter, a receiver, and a controller. The transmitter has an output configured to be coupled to an acoustic transducer for providing a selected one of an amplitude modulation (AM) signal in an AM mode and a chirped signal in a chirped mode. The receiver has an input configured to be coupled to the acoustic transducer and an output for providing a digital received signal.The controller operates during a first measurement period to: set the transmitter in one of the AM mode and the chirp mode using a first channel, selectively detect a first direct echo in the first channel of the digital received signal of one of the AM signal and the chirp signal, and selectively detect a first indirect echo in a second channel of the digital received signal of another of the AM signal and the chirp signal.

[0053] According to one aspect, the transmitter comprises a signal generator having an output for providing the selected one of the amplitude modulation (AM) signal and the chirp signal, and a transmitter amplifier having an input coupled to the output of the signal generator and an output configured to be coupled to the acoustic transducer.

[0054] According to another aspect, the receiver comprises a receiver amplifier having an input configured to be coupled to the acoustic transducer and an output and a mixer circuit having an input coupled to the output of the receiver amplifier and an output for providing the digital receive signal.

[0055] According to yet another aspect, the transmitter, receiver and controller are combined on a single monolithic integrated circuit.

[0056] According to yet another aspect, the controller is further operable during a second measurement period after the first measurement period to set the transmitter in the other of the AM mode and the chirp mode using the first channel, selectively detect a second direct echo in the first channel of the digital received signal of the other of the AM signal and the chirp signal, and selectively detect a second indirect echo in the second channel of the digital received signal of the one of the AM signal and the chirp signal.

[0057] In this case, the acoustic distance measuring circuit may comprise a vehicle control unit coupled to the controller, the controller further operable to transmit information about the time of flight of the first direct echo, the second direct echo, the first indirect echo, and the second indirect echo to the vehicle control unit, and the vehicle control unit is responsive to the information to determine a distance of a low-level obstacle from a vehicle.The acoustic distance measuring circuit may further comprise a second transmitter having an output configured to be coupled to a second acoustic transducer for providing the selected one of the AM signal in the AM mode and the chirp signal in the chirp mode, wherein a second receiver has an input configured to be coupled to the second acoustic transducer and an output for providing a second digital received signal and a second controller.The second controller is operable during the first measurement period to set the second transmitter in the one of the AM mode and the chirp mode using the second channel, selectively detect a third direct echo in the first channel of the second digital received signal of the one of the AM signal and the chirp signal, and selectively detect a third indirect echo in the second channel of the digital received signal of the one of the AM signal and the chirp signal, and during the second measurement period to set the second transmitter in the other of the AM mode and the chirp mode using the second channel, selectively detect a fourth direct echo in the second channel of the digital received signal of the other of the AM signal and the chirp signal, and selectively detect a fourth indirect echo in the second channel of the second digital received signal of the one of the AM signal and the chirp signal.In this case, the second controller may be further operable to transmit second information about the time of flight of both the second direct echo and the second indirect echo to the vehicle control unit, and the vehicle control unit may be further responsive to the second information to determine a distance of the low-altitude obstacle from the vehicle.

[0058] Furthermore, in this case, the transmitter may comprise a signal generator having an output for providing the selected one of the amplitude modulation (AM) signal and the chirp signal, and a transmitter amplifier having an input coupled to the output of the signal generator and an output configured to be coupled to the acoustic transducer.

[0059] Still further in this case, the receiver may comprise a receiver amplifier having an input configured to be coupled to the acoustic transducer and an output and a mixer circuit having an input coupled to the output of the receiver amplifier and an output for providing the digital receive signal.

[0060] In another form, a method for measuring an acoustic distance of an obstacle from a vehicle comprises providing a selected one of an amplitude modulation (AM) signal in an AM mode and a chirp signal in a chirp mode using a transmitter configured to be coupled to an acoustic transducer. A digital received signal is received using a receiver configured to be coupled to the acoustic transducer. During a first measurement period, a transmitter is placed in one of the AM mode and the chirp mode using a first channel, and a direct echo is selectively detected in the first channel of the digital received signal of one of the AM signal and the chirp signal, and an indirect echo is selectively detected in a second channel of the digital received signal of another of the AM signal and the chirp signal.

[0061] According to one aspect, the method further includes providing the selected one of the AM signal in the AM mode and the chirp signal in the chirp mode using a second transmitter having an output configured to be coupled to a second acoustic transducer, and providing a second digital receive signal using a second receiver having an input configured to be coupled to the second acoustic transducer. During the first measurement period, the second transmitter is set to the other of the AM mode and the chirp mode using the second channel. A second direct echo is selectively detected in the second channel of the digital receive signal of the other of the AM signal and the chirp signal. A second indirect echo is selectively detected in the first channel of the digital receive signal of the one of the AM signal and the chirp signal.In this case, information about the time of flight of both the direct echo and the indirect echo may be transmitted using a controller configured to be coupled to a vehicle control unit, second information about the time of flight of both the second direct echo and the second indirect echo may be transmitted to the vehicle control unit, and a distance of the obstacle from the vehicle may be determined in response to the information and the second information.

[0062] According to the independent claims, the first channel occupies a frequency band which is different from the frequency band of the second channel.

[0063] In yet another form, a method for measuring a distance of a low-level obstacle from a vehicle comprises providing a selected one of an amplitude modulation (AM) signal in an AM mode and a chirp signal in a chirp mode using a transmitter configured to be coupled to an acoustic transducer. A digital received signal is received using a receiver configured to be coupled to the acoustic transducer. During a first measurement period, the transmitter is set in one of the AM mode and the chirp mode using a first channel, wherein a first direct echo is selectively detected in the first channel of the digital received signal of the one of the AM signal and the chirp signal, and a first indirect echo is selectively detected in a second channel of the digital received signal of the one of the AM signal and the chirp signal.During a second measurement period after the first measurement period, the transmitter is set to another of the AM mode and the chirp mode using the first channel, a second direct echo is selectively detected in the first channel of the digital received signal of another of the AM signal and the chirp signal, and a second indirect echo is selectively detected in the second channel of the digital received signal of the one of the AM signal and the chirp signal.

[0064] According to one aspect, the method further includes transmitting information about the time of flight of the first direct echo, the first indirect echo, the second direct echo, and the second indirect echo using a controller, and determining the distance of the low-level obstacle from the vehicle in response to the information using a vehicle control unit.

[0065] According to another aspect, the method further includes providing a selected one of a second amplitude modulation (AM) signal in the AM mode and a second chirp signal in the chirp mode using a second transmitter configured to be coupled to the acoustic transducer, and receiving a second digital receive signal using a second receiver adapted to be coupled to the acoustic transducer. During the first measurement period, the second transmitter is set in one of the AM mode and the chirp mode using the second channel, wherein a third direct echo is selectively detected in the second channel of the second digital receive signal of the one of the AM signal and the chirp signal, and a third indirect echo is selectively detected in the second channel of the second digital receive signal of the one of the AM signal and the chirp signal.During the second measurement period, the second transmitter is set in the other of the AM mode and the chirp mode using the second channel, wherein a fourth direct echo is selectively detected in the second channel of the second digital reception signal of the other of the AM signal and the chirp signal, and a fourth indirect echo is selectively detected in the second channel of the digital reception signal of the one of the AM signal and the chirp signal.In this case, the method may further comprise transmitting first information about the time of flight of the first direct echo, the first indirect echo, the second direct echo, and the second indirect echo using a first controller configured to be coupled to a vehicle control unit, transmitting second information about the time of flight of the third direct echo, the third indirect echo, the fourth direct echo, and the fourth indirect echo using a second controller configured to be coupled to the vehicle control unit, and determining the distance of the low-level obstacle from the vehicle in response to the first information and the second information using the vehicle control unit.

[0066] Thus, to the maximum extent permitted by law, the scope of the present invention is to be determined by the broadest interpretation of the following claims and their equivalents, and is not to be restricted or limited by the foregoing detailed description.

Claims

[1] Acoustic distance measuring circuit (800), comprising: a transmitter (810) having an output configured to be coupled to an acoustic transducer (820) to receive a selected one of an amplitude modulation signal, AM signal, in an AM mode and provide a chirp signal in a chirp mode; a receiver (830) having an input configured to be coupled to the acoustic transducer (820) and an output for providing a digital received signal; and a control system that is operational during a first measurement period: Setting the transmitter (810) in one of the AM mode and the chirp mode using a first channel, selectively detecting a first direct echo in the first channel of the digital received signal of one of the AM signal and the chirp signal, and selectively detecting a first indirect echo in a second channel of the digital received signal of another of the AM signal and the chirp signal, where the first channel occupies a different frequency band than the second channel. [2] The acoustic distance measuring circuit (800) of claim 1, further comprising: a vehicle control unit coupled to the controller, wherein the controller is further operable to transmit information about the time of flight of both the first direct echo and the first indirect echo to the vehicle control unit, and the vehicle control unit is responsive to the information to determine a distance of an obstacle from a vehicle. [3] The acoustic distance measuring circuit (800) of claim 2, further comprising: a second transmitter having an output configured to be coupled to a second acoustic transducer for providing the selected one of the AM signal in the AM mode and the chirp signal in the chirp mode; a second receiver having an input configured to be coupled to the second acoustic transducer and an output for providing a second digital received signal; and a second control system that is operational during the first measurement period to: Setting the second transmitter to the other of the AM mode and the chirp mode using the second channel, selectively detecting a second direct echo in the second channel of the digital received signal of the other of the AM signal and the chirp signal, and selectively detecting a second indirect echo in the first channel of the digital received signal of the one of the AM signal and the chirp signal. [4] Acoustic distance measuring circuit (800) according to claim 3, wherein: the second controller is further operable to transmit second information about the time of flight of both the second direct echo and the second indirect echo to the vehicle control unit, and the vehicle control unit is further responsive to the second information to determine the distance of the obstacle from the vehicle. [5] Acoustic distance measuring circuit (800) according to claim 1, wherein: the control is further operable during a second measuring period after the first measuring period to: Setting the transmitter to the other of the AM mode and the chirp mode using the first channel, selectively detecting a second direct echo in the first channel of the digital received signal of the other of the AM signal and the chirp signal, and selectively detecting a second indirect echo in the second channel of the digital received signal of the one of the AM signal and the chirp signal. [6] The acoustic distance measuring circuit (800) of claim 5, further comprising: a vehicle control unit coupled to the controller, the controller further operable to transmit time-of-flight information of the first direct echo, the second direct echo, the first indirect echo, and the second indirect echo to the vehicle control unit, and the vehicle control unit responsive to the information to determine a distance of a low-level obstacle from a vehicle. [7] A method for measuring an acoustic distance of an obstacle from a vehicle, comprising: Providing a selected one of an amplitude modulation (AM) signal in an AM mode and a chirp signal in a chirp mode using a transmitter configured to be coupled to an acoustic transducer; Receiving a digital received signal using a receiver configured to be coupled to the acoustic transducer; during a first measurement period: Setting a transmitter in one of the AM mode and the chirp mode using a first channel; selectively detecting a direct echo in the first channel of the digital received signal of one of the AM signal and the chirp signal; and selectively detecting an indirect echo in a second channel of the digital received signal of another of the AM signal and the chirp signal, where the first channel occupies a different frequency band than the second channel. [8] The method of claim 7, further comprising: Transmitting information about the time of flight of both the direct echo and the indirect echo using a controller; and Determining a distance of the obstacle from the vehicle in response to the information using a vehicle control unit. [9] A method for measuring a distance of a low-level obstacle from a vehicle, comprising: Providing a selected one of an amplitude modulation (AM) signal in an AM mode and a chirp signal in a chirp mode using a transmitter configured to be coupled to an acoustic transducer; Receiving a digital received signal using a receiver configured to be coupled to the acoustic transducer; and during a first measurement period: Setting the transmitter to one of the AM mode and the chirp mode using a first channel; selectively detecting a first direct echo in the first channel of the digital received signal of one of the AM signal and the chirp signal; and selectively detecting a first indirect echo in a second channel of the digital received signal of one of the AM signal and the chirp signal, and during a second measurement period after the first measurement period: Setting the transmitter to another of the AM mode and the chirp mode using the first channel; selectively detecting a second direct echo in the first channel of the digital received signal of another of the AM signal and the chirp signal; and selectively detecting a second indirect echo in the second channel of the digital received signal of one of the AM signal and the chirp signal, where the first channel occupies a different frequency band than the second channel.

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