Sensing method and controller for acoustic transducers

Abstract

This disclosure relates to a sensing method and controller for an acoustic transducer. The acoustic sensing method and controller for an acoustic transducer can combine responses from acoustic pulse trains having different characteristic frequencies to improve the sensing of nearby obstacles. An exemplary controller includes: a transmitter for driving an acoustic transducer to generate a first acoustic pulse train and a second acoustic pulse train; a receiver coupled to the acoustic transducer for sensing a first response to the first acoustic pulse train and a second response to the second acoustic pulse train; and processing circuitry for deriving output data from the first and second responses, in part by determining an offset frequency difference between the first and second responses, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency.

Description

Technical Field

[0001] This disclosure generally relates to acoustic sensing methods and controllers for acoustic transducers, and more specifically to methods and controllers for combining responses from acoustic pulse trains with different characteristic frequencies to improve the sensing of nearby obstacles. Background Technology

[0002] Modern cars are equipped with a wide variety of sensors. For example, cars are now typically equipped with arrays of ultrasonic sensors to monitor the distance between the car and any nearby people, pets, vehicles, or obstacles. Due to noise and safety concerns, each sensor in the array may be required to provide dozens of measurements per second as the car moves. Reliably performing such sensor arrays is important even in environments that change in complex ways. Seemingly minor differences, such as temperature variations or aging of sensor components, can significantly alter the sensor's response characteristics.

[0003] Ultrasonic sensors, and other forms of acoustic sensors, are typically configured to simultaneously transmit a train of acoustic pulses and receive the resulting reflections or "echoes." The acoustic transducers used in such sensors are susceptible to residual reverberation from the transducer and structural noise (i.e., vibrations from any housing or overlying surface), which can render the sensor insensitive to reflections from nearby obstacles. The authors have found that these effects are strongly temperature-dependent and influenced by variations in other parameters of the sensor components, including those due to aging, making it difficult to provide reliable minimum distance detection and consistent distance measurements to nearby obstacles (e.g., within 15 cm, or alternatively within 10 cm, 5 cm, 3 cm, or 2 cm). Summary of the Invention

[0004] Therefore, this paper discloses exemplary sensor controllers, sensors, sensing systems, and sensing methods that at least partially solve the above-mentioned problems.

[0005] According to one aspect of this disclosure, a controller for an acoustic transducer is provided, the controller being characterized by: a transmitter for driving the acoustic transducer to generate a first acoustic pulse train and a second acoustic pulse train; a receiver coupled to the acoustic transducer for sensing a first response to the first acoustic pulse train and a second response to the second acoustic pulse train; and processing circuitry for deriving output data from the first response and the second response, in part by determining an offset frequency difference between the first response and the second response, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency.

[0006] In one embodiment, the controller for the acoustic transducer is characterized in that the transmitter is configured to drive the acoustic transducer to generate a third acoustic pulse train having the first characteristic frequency, wherein the receiver is configured to sense a third response to the third acoustic pulse train, and wherein the processing circuitry is configured to determine an alignment frequency difference between the first response and the third response.

[0007] In one embodiment, the controller for the acoustic transducer is characterized in that the processing circuit is configured to compare the amplitude of the offset frequency difference and the amplitude of the alignment frequency difference with a threshold to detect any nearby obstacles.

[0008] In one embodiment, the controller for the acoustic transducer is characterized in that it obtains a third response from the second acoustic pulse train, the third response indicating an offset between the first characteristic frequency and the second characteristic frequency, wherein the processing circuit is configured to determine an alignment frequency difference between the first response and the third response, and wherein the processing circuit is configured to compare the magnitude of the offset frequency difference and the magnitude of the alignment frequency difference with a threshold to detect any nearby obstacles.

[0009] In one embodiment, the controller for the acoustic transducer is characterized in that, in a series of acoustic pulse trains having characteristic frequencies alternating between the first characteristic frequency and the second characteristic frequency, the first acoustic pulse train and the second acoustic pulse train are adjacent.

[0010] According to another aspect of this disclosure, a sensing method is provided, characterized by: sensing the response of an acoustic transducer to each of a series of acoustic pulse trains, the series including a first acoustic pulse train and a second acoustic pulse train; determining an offset frequency difference between the response to the first acoustic pulse train and the response to the second acoustic pulse train, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency; and operating on the offset frequency difference to determine whether an obstacle is present in the vicinity.

[0011] In one embodiment, the sensing method is characterized in that the series includes a third acoustic pulse train having the first characteristic frequency, and the method further includes: determining an alignment frequency difference between the response to the first acoustic pulse train and the third response; and operating on the alignment frequency difference to determine whether an obstacle is present in the vicinity.

[0012] In one embodiment, the sensing method is characterized in that the operation on the offset frequency difference includes comparing the amplitude of the offset frequency difference with a threshold, and the operation on the alignment frequency difference includes comparing the amplitude of the alignment frequency difference with the threshold.

[0013] In one embodiment, the sensing method is further characterized by: obtaining a compensated response to the second acoustic pulse train, the compensated response indicating an offset between the first characteristic frequency and the second characteristic frequency; determining an alignment frequency difference between the response to the first acoustic pulse train and a third response; and operating on the alignment frequency difference to determine whether an obstacle is present in the vicinity.

[0014] In one embodiment, the sensing method is characterized in that the series includes at least two acoustic pulse trains of different pulse train lengths for obstacle detection at different distances. Attached Figure Description

[0015] Figure 1 This is a top view of an exemplary vehicle equipped with ultrasonic sensors.

[0016] Figure 2 This is a block diagram of an exemplary driving / parking assistance system.

[0017] Figure 3 This is a circuit diagram of an illustrative acoustic obstacle sensor.

[0018] Figure 4 This is a block diagram of an exemplary sensor controller with single-channel sensing.

[0019] Figure 5 This is a block diagram of an exemplary sensor controller with multi-channel sensing.

[0020] Figure 6 This is a flowchart of a first exemplary sensing method for nearby obstacles.

[0021] Figure 7 This is a flowchart of a second exemplary sensing method for nearby obstacles. Detailed Implementation

[0022] It should be understood that the accompanying drawings and the following description are not limiting of this disclosure, but rather, they provide a basis for those skilled in the art to understand all modifications, equivalents, and alternatives falling within the scope of the language of the claims. Ultrasonic sensors are used to provide illustrative context, but the principles of this disclosure can be applied to sonar systems, radar systems, and any system that actually employs pulse-echo sensing technology.

[0023] Use the context as an example. Figure 1A vehicle 102 equipped with a set of ultrasonic sensors 104 is shown. The number and configuration of sensors in the sensor arrangement vary, and it is not uncommon to have six sensors on each bumper, with additional sensors on each side acting as blind spot detectors. The vehicle can employ this sensor arrangement to detect and measure the distance to objects in various detection areas, where individual measurements and collaborative measurements (e.g., triangulation, multi-receiver measurements) are possible.

[0024] An ultrasonic sensor is a transceiver, meaning each sensor can transmit and receive a train of ultrasonic sounds. The transmitted train of sounds propagates outward from the vehicle until it encounters an object or some other form of acoustic impedance mismatch and is reflected. The reflected train of sounds returns to the vehicle as an "echo" of the transmitted train of sounds. The time between the transmitted train of sounds and the received echo indicates the distance to the point of reflection. In many systems, only one sensor transmits at a time, but all sensors can be configured to measure the resulting echoes. However, multiple simultaneous transmissions can be supported using orthogonal waveforms, transmissions to non-overlapping detection zones, or transmissions with markers that allow filtering of any echoes from different transmitters.

[0025] In various implementations, chirped modulated signals, such as linear frequency modulation (“LFM”) chirps, are used. A chirp is a pulse that changes frequency during transmission. An upper chirp is a single pulse that increases the frequency during transmission, and a lower chirp is a single pulse that decreases the frequency during transmission. For clarity, the examples used herein will consider linear increases or decreases; however, in various implementations, this increase or decrease is not linear. The echo of a chirped signal can be compressed in a correlator without introducing significant or any correlated noise. Therefore, peak detection of the echo is advantageous without reducing time resolution. Furthermore, LFM chirps can withstand Doppler shifts without any increase in correlated noise or only a minimal increase. LFM chirps can be used as transmitted pulses for measuring the distance to obstacles or objects within the sensing range of a sensor system.

[0026] In other implementations, amplitude modulation (AM) signals are used, such as shaped pulses of a fixed-frequency carrier. AM signaling modes allow for the use of shorter pulse trains (e.g., approximately 200 to 300 microseconds), thereby reducing transmission time and increasing sensitivity to nearby obstacles. Other implementations may employ pulses with a modulated carrier (e.g., using binary phase-shift keying (BPSK) modulation). For clarity, the term "pulse train" as used herein refers to an AM (fixed-frequency), BPSK (modulated), or chirped (sweep) pulse, which can be one of a series of pulse trains generated by driving a piezoelectric element or other acoustic transducer. Chirped modulated pulses can have a longer duration than typical AM pulses, for example, greater than 1 millisecond, such as in the range of 2 to 3 milliseconds. Note that the pulse train length can be varied; shorter pulse trains are used to facilitate the detection of nearby obstacles, while longer pulse trains are used to increase the pulse train energy (and echo energy) for obstacles at greater distances. The pulse train length used for detecting nearby obstacles can be half or possibly a quarter of the pulse train length used for distant obstacles. The sensor can switch between modes for different detection distances.

[0027] While systematically altering the characteristic frequencies (e.g., start frequencies, or equivalent center or end frequencies) of chirped modulated pulses in a sequence is considered particularly useful, such frequency variations can also be applied to the carrier frequencies of AM pulses in the sequence. The frequency change of each pulse can be expressed as a frequency shift from the nominal characteristic frequency (e.g., the nominal start frequency or the nominal carrier frequency).

[0028] Figure 2 An electronic control unit (ECU) 202, coupled to various ultrasonic sensors 204 as the center of a star topology, is shown. Of course, other topologies, including serial, parallel, and hierarchical (tree) topologies, are also suitable and are envisioned for use according to the principles disclosed herein. To provide automatic parking or driving assistance, the ECU 202 can be further connected to a set of actuators, such as a turn signal actuator 206, a steering actuator 208, a brake actuator 210, and a throttle actuator 212. The ECU 202 can be further coupled to a user interactive interface 214 to accept user input and provide displays of various measurements and system status. Using the interface, sensors, and actuators, the ECU 202 can provide automatic parking, assisted parking, lane change assist, obstacle and blind spot detection, and other desired features.

[0029] Now refer to Figure 3One possible sensor configuration is described. The illustrated sensor configuration uses the DSI3 communication and power standard, but other communication technologies such as those provided in the LIN, CAN, and SENT standards will also be suitable, and it is envisioned that these technologies will be used according to the principles disclosed herein. In addition... Figure 3 In addition to the two power terminals (Vbat and GND) shown in the specific implementation, each of the exemplary ultrasonic sensors is connected to ECU 202 via a single input / output (“I / O” or “IO”) line. When the I / O line is not actively driven low (“active” state) via ECU 202 or sensor controller 302, it can be biased to the supply voltage via a pull-up resistor (“deactivated” state). The communication protocol is designed so that at any given time only one of the two controllers (ECU 202 or sensor controller 302) activates the I / O line.

[0030] The sensor controller 302 includes an I / O interface 303 that monitors the activation of the I / O lines caused by the ECU 202 when in recessive mode, and drives the state of the I / O lines when in dominant mode. The ECU transmits commands to the sensor by activating the I / O lines, with different commands represented by activation lengths. Commands may include "send and receive" commands, "receive only" commands, and "data mode" commands.

[0031] Sensor controller 302 includes a core logic unit 304 that operates according to firmware and parameters stored in non-volatile memory 305 to parse commands from the ECU and perform appropriate operations, including the transmission and reception of ultrasonic pulse trains. To transmit the ultrasonic pulse train, core logic unit 304 is coupled to transmitter 306, which drives a set of transmit terminals on sensor controller 302 using a suitably modulated local oscillator signal from voltage-controlled oscillator 307. The transmitter terminals are coupled to piezoelectric element PZ via transformer M1. Transformer M1 progressively increases the voltage from the sensor controller (e.g., 12 volts) to a suitable level (e.g., tens of volts) for driving the piezoelectric element. Piezoelectric element PZ has a resonant frequency tuned to a desired value (e.g., 48 kHz) using a parallel capacitor C3 and a resonant quality factor (Q) tuned using a parallel resistor R1. An exemplary purpose of the tuning capacitor and tuning resistor is to tune the parallel resonant frequency to be close to the series resonant frequency of the piezoelectric element.

[0032] As used herein, the term "piezoelectric transducer" includes not only the piezoelectric element but also the supporting circuitry for tuning, driving, and sensing the piezoelectric element. In an exemplary embodiment, these supporting elements are a transformer M1, a tuning resistor and a tuning capacitor, and a DC isolation capacitor. Optionally, the output and input capacitances of the transmitter 306 and amplifier 308 may also be included as parasitic characteristics of the supporting circuitry considered part of the transducer. In an exemplary embodiment, a pair of DC isolation capacitors C1, C2 couple the piezoelectric element to a pair of receiving terminals of a sensor controller to prevent high voltage. Further protection is provided by an internal voltage clamp on the receiving terminals. Such protection may be desired for intervals during which the piezoelectric element is transmitting.

[0033] Commands received via the I / O line trigger the core logic unit 304 to operate the transmitter and receiver, and provide measurement results to the ECU 202 via the I / O line, also referred to herein as the communication bus. The measurement results are also referred to herein as output data. The core logic unit 304 can monitor the status of other sensors, such as undervoltage or overvoltage of the supply voltage during the transmission of ultrasonic pulse trains, thermal shutdown of the transmitter, hardware errors, incomplete power-on resets, etc. The core logic unit 304 can detect and classify multiple such transducer fault states and error conditions, storing appropriate fault codes in an internal register or non-volatile memory 305.

[0034] Since the received echo signal is typically in the millivolt or microvolt range, the front-end amplifier 308 buffers and amplifies the signal from the receiving terminal. The received echo signal is then processed by an analog-to-digital converter (ADC) and down-converted by a digital mixer 309. The mixer 309 multiplies the amplified and digitized received signal with a local oscillator signal to down-convert the modulated signal to baseband for further filtering and processing by a digital signal processor (DSP) 310. In one specific implementation, the mixer 309 is an in-phase / quadrature (I / Q) digital mixer that outputs zero-intermediate-frequency (ZIF) IQ data. (Although the term "ZIF" is used herein, the down-converted signal may be a low-intermediate-frequency or "near-baseband" signal in the implementation.)

[0035] The DSP 310 employs programmable methods to monitor piezoelectric transducers during pulse train transmissions, detecting any echoes and measuring their parameters, such as time-of-flight (ToF), duration, and peak amplitude. These methods can employ threshold comparison, minimum interval, peak detection, zero-crossing detection and counting, noise level determination, and other customizable techniques tailored to improve reliability and accuracy. Notably, the peak detection process itself has variations, some of which perform rising-edge detection, falling-edge detection, or peak maximum detection. The DSP 310 can further process the amplified received signal to analyze transducer characteristics, such as resonant frequency and quality factor, and can further detect transducer fault conditions.

[0036] As described above, in one specific embodiment, mixer 309 is a quadrature mixer. This I / Q digital mixer 309 has an input connected to the output of an analog-to-digital converter (not shown) for receiving a mixed signal F. TX The DSP 310 includes inputs and first and second outputs, respectively, for providing in-phase and quadrature signals corresponding to the amplitude and phase of the signal input from the acoustic transducer in the complex plane. The DSP 310 may include one or more digital filters configured to retrieve and use filter coefficients stored in memory for operation on the ZIF-IQ signal. More specifically, the digital filters may include low-pass filters and correlators. The DSP may include programmable modules or dedicated circuitry for other operations, including phase derivation, magnitude measurement, downsampling, amplitude scaling (attenuation control), noise suppression, peak detection, reverberation monitoring, and transducer diagnostics, as well as an interface for host communication.

[0037] Figure 4 This is a block diagram of a controller 302 in an exemplary single-channel implementation. Nearby obstacle detection processing can be performed entirely within the controller 302, or it can be shared with or delegated to an ECU or host processor that receives certain data via a communication bus, as previously referenced. Figure 2 and Figure 3 As stated above. For simplicity, Figure 4 Not all features of the controller 302, such as, for example, the power electronics section, are shown.

[0038] As referenced above Figure 3 As discussed, controller 302 includes both a receiver and a transmitter, as well as processing circuitry coupled to the receiver for converting the received response into output data. This processing circuitry can be implemented as a dedicated circuit or a programmable module in a digital signal processor (DSP).

[0039] An oscillator 307 for generating a carrier frequency signal is coupled to a transmit controller 402 and a mixer 309. The oscillator 307 can provide, for example, a nominal carrier frequency of 50 kHz. The TX controller 402 uses the carrier frequency signal to derive a series of AM or chirped burst signals, thereby applying a frequency offset specified by a frequency offset controller 403. In the illustrated single-channel implementation, the unoffset chirped burst signal can be swept upwards from 7 kHz below the carrier frequency to 7 kHz above the carrier frequency. Alternatively, a lower chirp can be used instead of an upper chirp. A digital-to-analog converter 404 converts the digital acoustic burst into an analog drive signal for the acoustic transducer.

[0040] The frequency offset controller 403 is configured to apply a frequency shift to the characteristic frequency of the digital burst signal (e.g., the carrier frequency for an AM burst, or the start frequency for a chirped burst). Such a frequency shift is, for example, in the range of 200 Hz to 2000 Hz, preferably 300 Hz to 1200 Hz, such as 600 Hz to 1000 Hz, 800 Hz, or 900 Hz. The shift of the characteristic frequency causes a corresponding Doppler-like frequency shift in the echo of the acoustic burst.

[0041] After each acoustic pulse train, controller 302 receives a signal from acoustic transducer PZ ( Figure 3 The input signal, which is optionally amplified by a front-end amplifier 308, is the response of the transducer. An analog-to-digital converter (ADC) 311 digitizes the input signal at a relatively high sampling rate (e.g., 400 kHz). A diagnostic block 442 analyzes the digitized response signal, either alone or in combination with a reverberation monitoring block 441, to detect and diagnose any transducer fault conditions. Some fault conditions may be indicated by, for example, an excessively short reverberation period (which could be due to a disconnected or defective transducer, suppressed vibration, etc.), while other fault conditions may be indicated by an excessively long reverberation period (installation defects, insufficient damping resistance, etc.). The diagnostic block 442 can detect and classify multiple such transducer fault conditions, storing appropriate fault codes in an internal register from which they can be transmitted to the ECU. The reverberation monitoring block 441 detects and signals the end of the transducer reverberation period, optionally initiating signal processing for echo detection.

[0042] The digitized response is then down-converted in a digital I / Q mixer 309. The digital I / Q mixer 309 converts the received signal into a sum frequency and a difference frequency, where the difference frequency is close to the baseband (zero intermediate frequency). The I / Q digital mixer 309 outputs a baseband signal containing both the in-phase and quadrature components of the received signal. A low-pass filter (LPF) 412 is arranged downstream of the mixer 309 to remove certain noise components (including the input signal image at the sum frequency) from the down-converted response. The filtered signal may be referred to herein as ZIF IQ data.

[0043] The exemplary controller 302 includes processing circuitry 414, a large portion of which can be bypassed (via multiplexers 426, 430) if it is desired to transmit ZIF IQ data off-chip via I / O interface 303 so that an ECU or host processor can process the signal (e.g., analyze the timing of peaks in the signal to determine the travel time of reflections and thus the distance to an obstacle). Furthermore, peak amplitude and width can be analyzed to determine saliency. To reduce I / O bandwidth requirements, a compressor block 428 may be included to reduce the number of bits required to represent the ZIF IQ data or the output of amplitude block 422, which represents the IQ component data converted into signal amplitude. (Amplitude block 422 operates by squaring the in-phase component signal, squaring the quadrature phase component signal, and summing the two, optionally taking the square root or logarithm of the summed signal.) To further reduce bandwidth requirements, controller 302 may perform on-chip processing with detection block 424, which performs peak detection and distance estimation processing.

[0044] As mentioned in the background section, sensors are affected by residual reverberation of the transducer and structural noise that masks echoes from nearby obstacles. The authors have found that these effects are strongly temperature-dependent and influenced by variations in other parameters of the sensor components, including those due to aging. However, for “concealed” sensors mounted behind fenders or other covering surfaces, these effects have also been found to be largely independent of the characteristic frequency of the acoustic pulse train. Since echoes are sensitive to characteristic frequencies while structural noise is not, the sensor’s ability to reliably detect nearby obstacles can be enhanced by identifying the differences between the transducer responses to acoustic pulse trains with different characteristic frequencies.

[0045] Therefore, the controller 302 shown includes a delay buffer 418 in each branch of the processing circuitry to capture ZIF IQ data from each burst, such that data from previous bursts can be used by the subtraction element 420 to determine the difference between ZIF IQ data from adjacent bursts with different frequency offsets. Because it is frequency-insensitive, structural noise is essentially removed, while the echo is enhanced. The difference signal can be passed to a compressor or I / O interface for off-chip processing, or to the amplitude block 422 and the detection block 424 for on-chip detection of nearby obstacles.

[0046] Figure 5This is a block diagram of a controller 302 in an exemplary multi-channel implementation, wherein the processing circuitry has branches 414, 415 for each channel. The transmit controller 402 can be configured to generate a lower channel chirp sweeping upwards from 7 kHz below the carrier frequency to 1 kHz below the carrier frequency and a higher channel chirp sweeping upwards from 1 kHz above the carrier frequency to 7 kHz above the carrier frequency. Alternatively, a lower chirp can be used instead of any or all of the upper chirps. Depending on the system configuration, the TX controller 402 can operate in only one channel or can alternately or otherwise employ both upper and lower channels. Each branch can be provided with a corresponding channel filter 416, 417 to limit the signal spectrum of the ZIF IQ data to the frequency range of that channel. The previously described processing steps can then be performed on the portion of the ZIF IQ data energy residing in the corresponding channel. The filters can each take the form of a programmable finite impulse response (FIR) filter with complex-valued coefficients retrievable from memory. Although not shown here, the processing circuitry may be configured with additional filters to provide correlation or matched response filtering, thereby enhancing the signal-to-noise ratio.

[0047] It should be noted here that the specific implementation of single channel ( Figure 4 This maximizes sensitivity to nearby obstacles and is therefore particularly well-suited for detecting such obstacles and providing alarms or setting up markers to indicate that such obstacles have been detected. This specific implementation is used to detect nearby obstacles even when the distance to the transducer is essentially 0 cm, and the resulting detection marker can be called a 0 cm marker. Multi-channel implementation ( Figure 5 It may lose some detection sensitivity, making reliable detection require a larger minimum distance to the transducer, but conversely, multi-channel measurements can more accurately determine the distance to any nearby obstacles.

[0048] Figure 6 This is a flowchart of a first exemplary sensing method that utilizes the characteristic frequency insensitivity of the transducer's structural noise to provide enhanced proximity sensing. While this method can be implemented by an ECU, a sensor controller, or distributed across both, the following description uses the controller for illustrative purposes.

[0049] In block 502, the controller obtains the response to a first acoustic pulse train emitted without any frequency offset, and then in block 504 obtains the response to a second acoustic pulse train emitted with a frequency offset of, for example, 900 Hz. In some specific implementations, if the transducer's response is sensitive to frequency offset, the controller uses the frequency offset to scale the response. The controller loops through blocks 502 and 504, thereby obtaining a series of responses with alternating frequency offsets. Blocks 510 and 511 buffer the responses obtained in blocks 502 and 504, respectively, so that they can be used to subtract from later responses.

[0050] In block 520, the controller subtracts the previous response to an acoustic pulse train without frequency offset from the current response to the previous ...

[0051] Since structural noise is insensitive to frequency shifts, it is not present in the offset frequency and alignment frequency difference signals. (Since temperature and other factors do not change significantly within the small intervals between pulse trains, sensitivity to temperature and other factors in structural noise is eliminated by using adjacent acoustic pulse trains.) However, echoes from any nearby obstacles are sensitive to frequency shifts, causing them to be amplified in the offset frequency difference signal unless the obstacle moves in a manner that produces a Doppler shift that precisely cancels out the effect of the frequency shift. Conversely, echoes from any nearby obstacle should not be present in the alignment frequency difference signal unless the obstacle is moving. Then, as a precaution, both the offset frequency difference signal and the alignment frequency difference signal can be evaluated to determine the presence of a nearby obstacle (e.g., within 15 cm, or alternatively within 10 cm, 5 cm, 3 cm, or 2 cm).

[0052] Therefore, in blocks 530 to 533, the controller converts the IQ components of the various difference signals into amplitude signals, and in block 540, the controller compares the amplitude signals with a threshold to detect any peaks representing echoes from an obstacle. This threshold may vary with elapsed time to account for the expected attenuation of echoes returning from a greater distance. When any peak indicating that an obstacle is too close is detected, the controller may issue an alert to the ECU or the driver. In some implementations, the controller determines the obstacle distance associated with each peak.

[0053] Figure 5 An exemplary sensing method derives the alignment frequency difference signal from non-adjacent acoustic pulse trains. Figure 7A second exemplary method is provided for deriving offset frequency difference signals and alignment frequency difference signals from a given pair of adjacent acoustic pulse trains. Similar to the first method, in block 502, the controller obtains the response to a first acoustic pulse train emitted without any frequency offset, and then in block 704 obtains the response to a second acoustic pulse train emitted with, for example, a frequency offset of 900 Hz. Additionally, in block 704, the controller obtains a compensated response to the second acoustic pulse train. For example, the compensated response can be obtained by adjusting the local oscillator signal provided to mixer 309 to match the characteristic frequency of the emitted pulse train, and by repeatedly down-converting using the adjusted local oscillator signal. (Alternatively, a second mixer element can be used to enable the two down-conversions to be performed in parallel.) If the transducer response is sensitive to frequency offset, the controller can scale the response using the frequency offset and the compensated response. The controller cycles through blocks 502 and 704 to obtain a series of responses to pulse trains with alternating frequency offsets.

[0054] Block 510 buffers the non-offset response obtained in block 502, making it available in blocks 521 and 523 for subtraction from the response obtained in block 704. In block 521, the controller subtracts the buffered response signal from the offset response signal to obtain the offset frequency difference signal, while in block 523, the controller subtracts the buffered response signal from the compensation response signal to obtain the alignment frequency difference signal. In blocks 531 and 533, the controller converts the IQ components of the various difference signals into amplitude signals, and in block 540, the controller compares the amplitude signals to a threshold to detect any peaks representing echoes from an obstacle. This threshold may vary with elapsed time to account for the expected attenuation of echoes returning from a greater distance. When any peak indicating that an obstacle is too close is detected, the controller may provide an alert to the ECU or the driver. In some implementations, the controller determines the obstacle distance associated with each peak.

[0055] The method is used in single-channel systems. In multi-channel systems, processing can be performed in selected channels or in all channels to improve distance determination accuracy. Although described in the context of ultrasonic sensing, the disclosed techniques are applicable to radar systems, sonar systems, and more generally to all systems employing pulse-echo sensing.

[0056] In summary, an exemplary controller has been disclosed, comprising: a transmitter for driving an acoustic transducer to generate a first acoustic pulse train and a second acoustic pulse train; a receiver coupled to the acoustic transducer for sensing a first response to the first acoustic pulse train and a second response to the second acoustic pulse train; and processing circuitry for deriving output data from the first and second responses, in part by determining an offset frequency difference between the first and second responses, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency.

[0057] An exemplary obstacle detection method is also disclosed, comprising: sensing the response of an acoustic transducer to each of a series of acoustic pulse trains, the series including a first acoustic pulse train and a second acoustic pulse train; determining an offset frequency difference between the response to the first acoustic pulse train and the response to the second acoustic pulse train, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency; and operating on the difference to detect any nearby obstacles.

[0058] An exemplary sensor is also disclosed, comprising: an acoustic transducer; and a controller coupled to the acoustic transducer to generate a series of acoustic pulse trains with alternating frequency offsets and to measure the response of the acoustic transducer to each acoustic pulse train in the series, the controller being configured to determine the offset frequency difference between each pair of responses to adjacent acoustic pulse trains in the series, the offset frequency difference having an amplitude sensitive to the presence of any nearby obstacles.

[0059] Each of the aforementioned controllers, methods, and sensors may be used individually or in combination, and any suitable combination may include one or more of the following features: 1. The transmitter is configured to drive the acoustic transducer to generate a third acoustic pulse train having the first characteristic frequency. 2. The receiver is configured to sense a third response to the third acoustic pulse train, and the processing circuitry is configured to determine an alignment frequency difference between the first response and the third response. 3. The processing circuitry is configured to compare the amplitude of the offset frequency difference and / or the alignment frequency difference with a threshold to determine the presence of a nearby obstacle. 4. The processing circuitry is configured to compare the amplitude of the offset frequency difference and / or the alignment frequency difference with a threshold to determine the distance to a nearby obstacle. 5. The receiver is configured to down-convert the received signal to a baseband signal and apply a correlation filter as part of the sensing. 6. In a series of acoustic pulse trains having characteristic frequencies alternating between the first characteristic frequency and the second characteristic frequency, the first acoustic pulse train and the second acoustic pulse train are adjacent. 7. The first and second acoustic pulse trains each have a pulse train length less than 50% of the other acoustic pulse trains generated by the acoustic transducer, for detecting obstacles at a greater distance. 8. Each acoustic pulse train in the acoustic pulse train is either an up-chirped or down-chirped sound. 9. The controller is configured to determine the offset frequency difference in each of a plurality of individual frequency bands.

Claims

1. A controller for an acoustic transducer used to detect obstacles near a vehicle, the controller comprising: A transmitter for driving the acoustic transducer to generate a first acoustic pulse train and a second acoustic pulse train; A receiver coupled to the acoustic transducer to sense a first response to the first acoustic pulse train and a second response to the second acoustic pulse train, each response including a structure noise component; and A processing circuit is configured to derive output data from the first response and the second response in part by determining an offset frequency difference between the first response and the second response, wherein the structure noise components at least partially cancel each other out, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency.

2. The controller according to claim 1, wherein, The transmitter is configured to drive the acoustic transducer to generate a third acoustic pulse train having the first characteristic frequency, wherein the receiver is configured to sense a third response to the third acoustic pulse train, and wherein the processing circuitry is configured to determine an alignment frequency difference between the first response and the third response.

3. The controller according to claim 2, wherein, The processing circuit is configured to compare the amplitude of the offset frequency difference and the amplitude of the alignment frequency difference with a threshold to detect any nearby obstacles.

4. The controller according to claim 1, wherein, A third response is obtained from the second acoustic pulse train, the third response indicating an offset between the first characteristic frequency and the second characteristic frequency, wherein the processing circuit is configured to determine an alignment frequency difference between the first response and the third response, and wherein the processing circuit is configured to compare the magnitude of the offset frequency difference and the magnitude of the alignment frequency difference with a threshold to detect any nearby obstacles.

5. The controller according to claim 1, wherein, The processing circuit is configured to compare the amplitude of the offset frequency difference with a threshold to detect any nearby obstacles.

6. The controller according to claim 1, wherein, The processing circuit is configured to compare the amplitude of the offset frequency difference with a threshold to determine the distance to the obstacle.

7. The controller according to claim 1, wherein, In a series of acoustic pulse trains having characteristic frequencies that alternate between the first characteristic frequency and the second characteristic frequency, the first acoustic pulse train and the second acoustic pulse train are adjacent.

8. The controller according to claim 1, wherein, The first and second acoustic pulse trains each have a shorter pulse train length than the acoustic pulse train generated by the acoustic transducer, in order to detect obstacles at greater distances.

9. A sensing method for detecting obstacles near a vehicle, comprising: The response of a sensing acoustic transducer to each of a series of acoustic pulse trains, the series including a first acoustic pulse train and a second acoustic pulse train, each response including a structure noise component; Determine the offset frequency difference between the response to the first acoustic pulse train and the response to the second acoustic pulse train, wherein the structural noise components at least partially cancel each other out, wherein the first acoustic pulse train has a first characteristic frequency and the second acoustic pulse train has a second characteristic frequency, the second characteristic frequency being different from the first characteristic frequency; as well as The offset frequency difference is manipulated to determine whether there are obstacles nearby.

10. The sensing method according to claim 9, wherein, The series includes a third sound pulse train having the first characteristic frequency, and the method further includes: Determine the alignment frequency difference between the response to the first acoustic pulse train and the third response; and The alignment frequency difference is manipulated to determine whether there are obstacles nearby.

11. The sensing method according to claim 10, wherein, The operation on the offset frequency difference includes comparing the amplitude of the offset frequency difference with a threshold, and the operation on the alignment frequency difference includes comparing the amplitude of the alignment frequency difference with the threshold.

12. The sensing method according to claim 9, further comprising: Obtain a compensated response to the second acoustic pulse train, the compensated response indicating the offset between the first characteristic frequency and the second characteristic frequency; as well as Determine the alignment frequency difference between the response to the first acoustic pulse train and the compensation response; as well as The alignment frequency difference is manipulated to determine whether there are obstacles nearby.

13. The sensing method according to claim 9, wherein, The operation on the offset frequency difference includes comparing the magnitude of the offset frequency difference with a threshold.

14. The sensing method according to claim 9, wherein, The operation includes determining the distance to the obstacle.

15. The sensing method according to claim 9, wherein, The series includes at least two acoustic pulse trains of different pulse train lengths for obstacle detection at different distances.

16. A sensor for detecting obstacles near a vehicle, comprising: Acoustic transducer; and A controller coupled to the acoustic transducer generates a series of acoustic pulse trains with alternating frequency offsets and measures the transducer’s response to each of the acoustic pulse trains in the series, each response including a structural noise component. The controller is configured to determine an offset frequency difference between each pair of responses to adjacent acoustic pulse trains in the series, wherein the structural noise components at least partially cancel each other out, the offset frequency difference having an amplitude sensitive to any obstacles in the vicinity of the sensor.

17. The sensor according to claim 16, wherein, The controller is configured to determine the amplitude.

18. The sensor according to claim 17, wherein, The controller is configured to compare the amplitude with a threshold.

19. The sensor according to claim 16, wherein, Each of the acoustic pulse trains is either an up-chirp or a down-chirp.

20. The sensor according to claim 16, wherein, Each of the acoustic pulse trains is an amplitude-modulated or phase-modulated pulse.

21. The sensor according to claim 16, wherein, The controller is configured to determine the offset frequency difference in each of the plurality of channels.

Images