DETECTION OF NOISE-INDUCED ULTRASOUND SENSOR BLINDNESS

Abstract

Control for a piezoelectric transducer, the control comprising: a transmitter for driving a piezoelectric element during the actuation intervals to generate acoustic bursts; a receiver for detecting a response of the piezoelectric element to echoes of each acoustic burst, the receiver including a front-end amplifier; a processing circuit coupled to the transmitter and the receiver, the processing circuit operable to apply echo detection processing to the response; and a blindness detector for detecting the saturation of the front-end amplifier outside of the actuation intervals, wherein the blindness detector detects the saturation immediately before each actuation interval.

Description

BACKGROUND

[0001] Modern motor vehicles are equipped with an impressive number and variety of sensors. For example, cars are now routinely equipped with ultrasonic sensor arrays to monitor distances between the car and nearby people, animals, vehicles, or obstacles. Due to environmental noise and safety concerns, each of the sensors may be required to provide dozens of measurements per second while the car is in motion. It is important that such sensor arrays operate reliably or alert the operator if their performance appears suspect.

[0002] As the number of sensors increases, so does the incidence of sensor failures, and so does the importance of correctly diagnosing the fault so that the operator can be alerted and, if necessary, take appropriate action to correct or eliminate the fault. Illustrative measures may include: repairing a broken or disconnected converter, washing the vehicle to remove mud or dirt from the sensor surface, exercising caution when the converter is affected by snow or rain, and simply ignoring temporary noise if the sensor is otherwise operating correctly.

[0003] US 2019 / 0079173 A1, or US application 15 / 888,543, of the same assignee and by inventors J. Kutej, T. Suchy, M. Hustava, P. Horsky, and Z. Axman, entitled “Response-based determination of piezoelectric transducer state,” filed on February 5, 2018, and hereby incorporated herein in its entirety, discloses techniques for detecting various potential failure states of a piezoelectric transducer and for signaling the presence of such detected failure states. However, at least one potential failure state was not detected in the aforementioned application, and the inventors are not aware of any existing systems or prior art that enables the detection and reporting of this potential failure state. Nevertheless, this potential failure state may unnoticed blind the sensor.If this potential fault condition is not detected and diagnosed, the operator will not be aware of potential obstacles or hazards that the sensor is designed to detect.

[0004] DE 10 2012 201 920 A1 is known from the prior art and relates to a method and a measuring system for improving the detection capability of an ultrasonic sensor by means of a switchable transmission level. In particular, it concerns a method for detecting objects using ultrasound, in which ultrasonic pulses are emitted by a resonant transducer element and echo pulses reflected from the objects are received. The received signals comprising the echo pulses are amplified by means of a receiving amplifier and an associated measuring system. SUMMARY

[0005] Accordingly, various sensors, sensor controllers, and sensor control methods with noise-induced blindness detection are disclosed herein.

[0006] According to one aspect of the present application, a controller for a piezoelectric transducer is provided, the controller comprising: a transmitter for driving a piezoelectric element during actuation intervals to generate acoustic bursts; a receiver for detecting a response of the piezoelectric element to echoes of each acoustic burst, the receiver including a front-end amplifier; processing circuitry coupled to the transmitter and the receiver, the processing circuitry operable to apply echo detection processing to the response; and a blindness detector for detecting saturation of the front-end amplifier outside of actuation intervals.

[0007] The blindness detector detects saturation immediately before each actuation interval.

[0008] In another embodiment, the blindness detector includes: an envelope detector that measures a broadband envelope of the response outside the actuation interval; and a comparator that compares the broadband envelope to a threshold representing the saturation of the front-end amplifier.

[0009] In another embodiment, the controller further comprises: an analog-to-digital converter after the front-end amplifier, the analog-to-digital converter providing a digital response signal; a bandpass filter centered on a carrier frequency of the acoustic bursts to generate a filtered signal from the digital response signal; a second envelope detector that measures an envelope of the filtered signal during a noise measurement interval before each actuation interval; and a second comparator that compares the measured envelope of the filtered signal to a second threshold representing excessive environmental noise.

[0010] In another embodiment, the controller further comprises an I / O controller that communicates a sensor error when the blindness detector detects saturation and when the second comparator detects excessive environmental noise during the noise measurement interval.

[0011] According to another aspect of the present application, a method of operating a piezoelectric sensor is provided, the method comprising: driving a piezoelectric transducer to generate a burst of acoustic energy during an actuation interval; during a measurement interval following the actuation interval, obtaining a response of the piezoelectric transducer with a receiver including a front-end amplifier; processing the response to detect echoes of the burst; and determining whether the response indicates sensor blindness during the measurement interval due to saturation of the front-end amplifier.

[0012] In one embodiment, determining includes using a reverberation detector to signal an end of the actuation interval.

[0013] In another embodiment, determining further includes: measuring a broadband envelope of the response; and comparing the broadband envelope to a threshold representing saturation of the front-end amplifier.

[0014] In another embodiment, the processing includes: digitizing an output of the front-end filter with optional gain control to obtain a digital response signal; measuring a narrowband envelope of the digital response signal during a noise measurement interval prior to the actuation interval; comparing the narrowband envelope to a threshold representing excessive environmental noise.

[0015] In another embodiment, determining includes: measuring a broadband envelope of the response; and communicating the broadband envelope measurement to a system controller for detecting sensor blindness. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a top view of an exemplary vehicle equipped with parking assistance sensors. Fig. 2 is a block diagram of an example parking assistance system. Fig. 3 is a circuit diagram of an example parking assistance sensor. Fig. Figure 4 is a diagram showing the control input and output signals. Fig. Figure 5 is a schematic diagram of an example parking assist sensor with additional details that enable detection and reporting of noise-induced sensor blindness. Fig. Figure 6 is a flowchart for an example detection method.

[0016] It should be understood that the drawings and the corresponding detailed description do not limit the disclosure, but on the contrary, they provide the basis for understanding all modifications, equivalents and alternatives that fall within the scope of the appended claims. DETAILED DESCRIPTION

[0017] As a context for a usage example, Fig. 1 shows a vehicle 102 equipped with a set of ultrasonic parking assistance sensors 104. The number and configuration of sensors in the sensor array is variable, and it would not be unusual to have six sensors at each buffer and two additional sensors on each side for blind spot detectors. The vehicle can use the sensor array to detect and measure distances to objects in the various detection zones, potentially using the sensors for individual measurements and cooperative (e.g., triangulation, multi-receiver) measurements.

[0018] The ultrasonic sensors are transceivers, meaning each sensor can transmit and receive ultrasonic bursts. Emitted bursts propagate outward from the vehicle until they encounter and reflect an object or other form of acoustic impedance mismatch. The reflected bursts return to the vehicle as "echoes" of the emitted bursts. The times between the emitted bursts and received echoes indicate the distances to the reflection points. In many systems, only one sensor transmits at a time, although all sensors can be configured to measure the resulting echoes. However, multiple simultaneous transmissions can be supported by using orthogonal waveforms or transmissions to non-overlapping detection zones.

[0019] Fig. Figure 2 shows an electronic control unit (ECU) 202 coupled to the various ultrasonic sensors 204 as the center of a star topology. Of course, other topologies, including serial, parallel, and hierarchical (tree) topologies, are also suitable and are contemplated for use in accordance with the principles disclosed herein. To provide automated parking assistance, the ECU 202 may be further connected to a group of actuators, such as a turn signal actuator 206, a steering actuator 208, a brake actuator 210, and an accelerator pedal actuator 212. The ECU 202 may be further coupled to an interactive user interface 214 to enable user input and provide a display of the various measurements and system status.Using the interface, sensors, and actuators, the ECU 202 can provide automated parking, assisted parking, lane change assistance, obstacle and blind spot detection, and other desirable features.

[0020] A potential sensor configuration is now described with reference to Fig. 3. (Other communication and power supply technologies, such as those provided in the DSI3, LIN and CAN standards, are also suitable and are contemplated for use in accordance with the principles disclosed herein.) In addition to the two power terminals (Vbat and GND) provided in the embodiment of Fig. 3, each of the illustrative ultrasonic sensors is connected only to the ECU 202 through a single input / output (“I / O” or “IO”) line. The I / O line may be biased by a pull-up resistor with supply voltage (“unset” or “unenabled” state) when not actively driven low by the ECU 202 or by the sensor controller 302 (“set” state). The communication protocol is designed so that only one of the two controllers (ECU 202 or sensor controller 302) is driving the I / O line at a given time.

[0021] The sensor controller 302 includes an I / O interface 303 that, when placed in a recessive mode, monitors the I / O line for setting or activation by the ECU 202, and when placed in a dominant mode, controls the status of the I / O line. The ECU communicates a command to the sensor via setting the I / O line, with the different commands being represented by setting operations of different lengths. The commands can include a "send and receive" command, a "receive only" command, and a "data mode" command.

[0022] The sensor controller 302 includes core logic 304, which operates according to firmware and parameters stored in non-volatile memory 305 to search for commands from the ECU and perform the corresponding operations, including the transmission and reception of ultrasonic bursts. To transmit an ultrasonic burst, the core logic 304 is coupled to a transmitter 306, which drives a set of transmit terminals on the sensor controller 302. The transmit terminals are coupled to a piezoelectric element PZ via a transformer M1. The transformer M1 transforms the voltage from the sensor controller (e.g., 12 volts) to a suitable level for driving the piezoelectric element (e.g., tens of volts). The piezoelectric element PZ has a resonant frequency that can be adjusted to a desirable value (e.g.,48 kHz) and has a resonant quality factor (Q) tuned with a parallel resistor R1. An illustrative purpose of the tuning capacitor and tuning resistor is to tune the parallel resonant frequency to a value close to the series resonant frequency of the piezoelectric element.

[0023] As used in this document, the term "piezoelectric transducer" includes not only the piezoelectric element, but also the supporting circuit elements for tuning, driving, and sensing the piezoelectric element. In the illustrative embodiment, these supporting elements are the transformer M1, the tuning resistor and capacitor, and the DC isolation capacitors. Optionally, the output and input capacitance of the transmitter 306 and amplifier 308, respectively, may also be included as parasitic properties of the supporting circuit elements considered part of the transducer. However, the use of the term "piezoelectric transducer" does not necessarily require the presence of supporting circuit elements, because a piezoelectric element can be used alone, without such supporting elements.

[0024] A pair of DC isolation capacitors C1, C2 couples the piezoelectric element to the pair of receive terminals of the sensor controller to protect against high voltages. Further protection is provided with internal voltage clamps on the receive terminals. This protection may be desired for the intervals when the piezoelectric element is transmitting. Since the received echo signals are typically in the millivolt or microvolt range, a low-noise amplifier 308 (also referred to herein as a "front-end amplifier") amplifies the signal from the receive terminals. The amplified receive signal can be digitized and processed by a digital signal processor (DSP) 310 with an integrated analog-to-digital converter (ADC).

[0025] The DSP 310 applies programmable techniques to measure the actuation duration of the piezoelectric transducer during the transmission of a discharge (including the subsequent reverberation or "ring" duration) and to detect and measure the timing of received discharges or "echoes." Such techniques may utilize threshold comparisons, as well as minimum intervals, peak detection, zero-crossing detection and counting, noise level determinations, and other customizable techniques aimed at improving reliability and accuracy. The DSP 310 can further process the amplified received signal to analyze transducer characteristics, such as resonant frequency and quality factor, and can also detect transducer fault conditions, as indicated below. Some fault conditions may, for example,Some faults may be indicated by an excessively short actuation duration (which may be due to a disconnected or defective transducer, suppressed vibration, or the like), while others may be indicated by an excessively long actuation duration (due to incorrect assembly, insufficient damping resistance, or the like). Still other fault conditions may be indicated by the presence of excessive noise during the non-transmitted portions of the measurement cycle.

[0026] Commands received via the I / O line trigger core logic 304 to operate the transmitter and receiver, and provide the measurement results to ECU 202 via the I / O line, as explained below. In addition to the transducer fault conditions that can be detected by DSP 310, core logic can monitor other sensor fault conditions, such as a supply voltage "undervoltage" or "overvoltage" when transmitting an ultrasonic burst, a thermal shutdown of the transmitter, a device failure, an incomplete power-on reset, or the like. Core logic 304 can detect and classify several of these transducer fault conditions and error states, storing the appropriate error codes in internal registers or non-volatile memory 305.

[0027] Fig. Figure 4 provides an example timing diagram to better understand the operation of the example sensor embodiments, particularly with respect to communication on the I / O line. An ECU formulates a signal pulse "CMD" with a duration representing a desired command. In this case, the duration is "TS" to represent a "send and receive" command. (Example command pulse durations may range from 300 ms to 1300 ms.) During a time 400, when the sensor is inactive (i.e., not taking a measurement or otherwise responding to a command from the ECU), the I / O line is "high" (not asserted). During this time 400, the ECU may control the I / O line. The ECU asserts the I / O signal by actively driving the line low for the duration representing the command. There is a small propagation delay due to limited slew rates in the I / O line, and a debounce interval (“TDB ") follows activation and deactivation to ensure that the timing of the line's return to battery voltage is intentional and not the result of transient noise. (Example debounce intervals can range from 40 ms to 80 ms.)

[0028] When the debounce interval expires, the sensor controller decodes the command and assumes control of the I / O line for a predetermined interval 401, which may be dependent on the command. For a "transmit and receive" command, the sensor controller begins the predetermined interval 401 by transmitting an acoustic burst 402 and maintains control until a programmed measurement interval has elapsed. Before discussing the operation of the I / O line during this measurement interval 401, we consider the operation of the piezoelectric transducer and the corresponding amplified receive signal RX.

[0029] The operation of the piezoelectric transducer is illustrated here as a vibration signal VIBR, which represents a mechanical vibration of the piezoelectric element. (Note that the signal is not drawn to scale because the transmitted burst 402 may be orders of magnitude larger than the echo 410.) Electrically, the mechanical vibration of the piezoelectric element can be detected as a voltage or current. The mechanical vibration amplitude increases when the controller 302 drives the transducer (the "drive" stage 404) and decreases after the drive operation is complete (the "reverberation" stage 406). The controller 302 may employ active and / or passive damping to shorten the duration of the reverberation stage.

[0030] In the sensor embodiment of Fig. 3, the oscillation is detected as a clamped, amplified version of the secondary voltage VX via the amplifier 308. For the purposes of explanation, the Fig. The RX signal shown in Figure 4 is an envelope of this clamped amplified voltage signal, but the amplified oscillation signal can also be used.

[0031] The sensor controller measures a noise level during a pre-transmission period 403, which may begin a debounce interval after the ECU asserts the I / O line and end when the transmit burst is sent. Actuation of the transducer for transmitting the burst saturates the RX signal. (In at least some implementations, internal voltage clamps on the sensor controller's receive terminals prevent excessive voltages from being received from amplifier 308.) The transmit burst floods the receiver and prevents meaningful echo measurements from being acquired during this interval. Because the receive signal is above a threshold 411 (and / or compatible with other implementation-specific requirements not relevant here), the sensor controller drives the I / O line low. Thus, the controller asserts the IO signal during the actuation interval T TX, which corresponds to the interval 412, while the RX signal exceeds the threshold 411. This activation during the transmission discharge allows the ECU to determine the reverberation interval (“T TX “) of the converter and thus enable him to test the converter operation.

[0032] Note that the actuation interval 412 includes not only the acoustic burst drive stage 404, but also part of the acoustic burst reverberation stage 406. The time required for the reverberation amplitude to fall below the threshold 411 indicates the losses in the transducer and can accordingly be used as an indicator of the quality factor (Q). The actuation interval can be used directly and converted into a decay rate (potentially expressed as a damping factor or a value for the series resistance RS in the representation of the equivalent circuit of the piezoelectric element) or combined with a resonant frequency measurement to derive a measure of the quality factor (Q).

[0033] If the received signal falls below a threshold 411, it becomes possible to detect echoes, and the I / O line is disabled until the sensor controller detects a valid echo. The requirements for a valid echo can include, for example, a minimum time (“T DLY “) above a threshold 411, with the minimum time equal to or greater than the debounce interval T DB Such a requirement necessarily requires that the setting of the I / O line in response to an echo is delayed by the minimum time T DLY The setting extends over a period of time (“T DET "), which is equal to the detected length 414 of the echo burst. At least in some embodiments, the multiple echoes can be detected and played back by setting the I / O line accordingly. Upon expiration of the programmed measurement interval 401, the sensor controller 302 releases control of the I / O line.

[0034] With the above protocol, it is possible for the ECU to detect certain sensor error conditions during measurements, but not other measurement conditions. Errors such as excessive noise, under / overvoltage conditions, and the like could only be detected if the ECU interrupts the measurement sequence and takes the time to send a "data" command to poll the appropriate sensor controller registers. Without this polling, the ECU may inadvertently rely on unreliable measurements, but with such polling, the measurement repetition rate may become unreasonable. In jointly assigned U.S. patent 9,810,778, titled "Triggered-event signaling with digital error reporting," filed September 14, 2015, which is hereby incorporated by reference, the sensor controller embeds digital bits during a reporting period 407 at the beginning of the actuation interval to report error conditions to the ECU.These bits can also, or alternatively, be used by the sensor controller to communicate identified converter states to the ECU. In any case, it is expected that the sensor controller will use internal registers to store codes representing the converter state and other detected fault conditions, and that the ECU can use a data command to retrieve this information via the I / O line.

[0035] In one contemplated embodiment, setting during the first bit interval during the reporting period 407 indicates an excessive noise level during the pre-transmission period 403, setting during the second bit interval indicates an acceptable reverberation period (relative to the previous transmit pulse, since the measurement of the current reverberation period is not yet complete), and setting the third bit interval indicates the absence of other errors (such as under / overvoltage, thermal shutdown, hardware failure, power-on reset, etc.). Thus, during a successful, error-free measurement, the I / O signal would be high during the first bit interval of the reporting period 407 and low during the second and third bit intervals. However, if an error is detected, the ECU is immediately alerted to the presence of the error without reducing the maximum measurement repetition rate.To explain a preferred noise-induced blindness technique and how it differs from existing systems, we now turn to . Fig. 5 to. Fig. Figure 5 shows a sensor controller 502 with some additional implementation details and some additional functional blocks that can be implemented by the DSP 310 or by application-specific hardware modules. We begin with the transmit chain. An oscillator 504 generates a signal with a desired carrier frequency in the ultrasonic range. When triggered, a transmit control module 306B delivers a pulse of the carrier signal frequency to a transmit driver 306A, which supplies the piezoelectric element PZ with AC drive voltage or current via transformer M1.

[0036] As previously mentioned, the piezoelectric element converts the oscillating signal into an ultrasonic sound burst that propagates away from the transducer until it encounters obstacles. The sound burst is reflected by the obstacles and returns to the transducer in the form of echoes. These, along with other noise impinging on the piezoelectric element, are converted into an electrical received signal, which is amplified by a low-noise amplifier (LNA) 308A. Since the LNA typically has a fixed gain, a subsequent variable gain amplifier 308B provides further amplification with a variable gain to optimize the range of the received signal relative to the range of the analog-to-digital converter 506. A gain controller 508 determines the variable gain provided by the variable gain amplifier 308B.Gain controller 508 can provide adaptive gain to compensate for operating conditions and aging of the transducer components. Temperature compensation can also be integrated. In at least some embodiments, the input of ADC 506 can be multiplexed between the acoustic receive chain and other sensors, such as a temperature sensor 509. A low-pass filter (LPF) 510 can combine the temperature sensor measurements to obtain an averaged temperature measurement.

[0037] A measurement controller 512 may periodically record the averaged temperature value, and as with the other measurements to be described below, the controller 512 may store the measurements in memory 305. The memory may further include one or more configuration registers for holding parameters that control the operation of the sensor controller 502. For example, the configuration register may control the carrier frequency and length of the transmitted sound bursts. The memory 305 may further track historical magnitude information of the received signal, which is used by the gain controller 508. Finally, the memory 305 may be used as an I / O buffer when the I / O controller 303A is operating in a data mode. The I / O transceiver 303B captures and drives signals on the I / O line and serves as an analog interface for use by the digital I / O controller 303A.

[0038] When the ADC 506 digitizes the acoustic receive signal from the control amplifier 308B, it can sample the receive signal at a multiple (e.g., 4x) of the carrier frequency provided by the oscillator 504. This sampling rate, combined with the bandwidth limitations of the converter and the front-end amplifiers 308A, 308B, reduces aliasing effects. A narrowbandpass filter 514 extracts the receive signal frequencies directly around the carrier frequency. In some embodiments, the bandpass filter has an adjustable quality factor Q or bandwidth, but an exemplary value could be Q=20, which at a carrier frequency of 50 kHz would provide a bandwidth of approximately 2.5 kHz. In some contemplated embodiments, the narrowbandpass filter is a correlator or a matched filter. An envelope detector 516 extracts the narrowband envelope of the filtered receive signal.An optional noise filter 518 performs a nonlinear transformation to suppress low-amplitude signals or, correspondingly, to preferentially amplify higher-amplitude signals. The noise suppression level can be adaptively determined based on the noise level measured before each transmitted burst. Typically, the noise level is measured at the output of the bandpass filter 514 or the envelope detector 516. If excessive noise levels are detected, the sensor controller can abort the transmission of the acoustic burst and / or signal a sensor error to the ECU.

[0039] A comparator 522 compares the narrowband envelope signal to a threshold provided by a threshold controller 520. The threshold controller 520 varies the threshold, decreasing the value at a rate designed to compensate for the expected attenuation caused by the greater distance traveled by later-arriving echoes. A debounce unit 524 may be included to ensure that the envelope remains above the threshold long enough to correspond to a true echo. Any deviations beyond the threshold that are detected as true echoes are forwarded to the measurement controller 512.

[0040] As previously mentioned, the echo amplitudes can be orders of magnitude smaller than those of the transmitted bursts. By the time the burst transmission is complete and the piezoelectric element returns to a resting state, the LNA 308A is saturated, meaning its outputs (if not its inputs) are routed to one or the other of the voltage rails. The amplifier's behavior in this mode is decidedly nonlinear, so it does not respond to any echo signals that may be detected during this interval. Fortunately, the reverberation interval is relatively short and well-defined, so it serves as an indicator of the healthy condition of the piezoelectric element. Accordingly, the sensor controller 502 includes a reverberation length detector 526 for measuring the length of the reverberation interval (alone or in combination with the drive interval).In at least some implementations, the reverberation length detector counts a number of carrier frequency cycles (from oscillator 504) from the beginning of a transmitted burst until the envelope of the received signal falls below a threshold within the range of ADC 506 (e.g., 80% of the maximum digitized value). Measurement controller 512 may record the reverberation interval length measurement once with each measurement cycle.

[0041] The inventors have observed that the LNA 308A can also become saturated under other circumstances, such as high ambient noise levels (including acoustic noise and electromagnetic noise), and that this condition is difficult to detect with a narrowband noise measurement near the carrier frequency. Thus, it may be possible for a sensor to be blinded by ambient noise without the fault being detected by the narrowband noise measurement. Accordingly, the sensor controller 502 includes a broadband noise detector 528 to detect amplifier saturation either during the pre-transmission interval 403 or, more generally, outside the actuation interval 412 for the piezoelectric transducer. The detector 528 may include an envelope detector to measure an envelope of the unfiltered output signal of the ADC.In some embodiments, the broadband envelope measurement is stored in an internal register and reported to the ECU so the ECU can determine whether the noise is excessive. In further embodiments, the detector includes a comparator for comparing the broadband envelope to a threshold (possibly taking into account the control amplifier setting) and a debounce circuit for shielding transient events shorter than, for example, 10% of the measurement cycle. A suitable threshold may be 98% of the maximum digitized value.

[0042] In an alternative implementation, broadband noise detector 528 is an analog circuit operating directly at the output of front-end amplifier 308A to measure the broadband envelope and optionally detect when the amplifier is operating outside a desired range for detecting echo signals. In at least some implementations, the analog noise detector uses an envelope detector, a low-pass RC filter, and a threshold comparator. In both cases, the operation of the broadband noise detector during the actuation period (i.e., the drive and reverberation intervals) can be suppressed by reverberation detector 526.

[0043] Fig. Figure 6 is a flowchart for an exemplary sensor control method. It begins in block 602 with the initialization (and then updating) of the control logic registers used to store codes representing the converter's state and any detected errors. These registers are reset when read by the ECU. In block 604, the control logic determines whether the ECU has asserted the I / O line to initiate a command. (As previously noted, other communication and power supply techniques are also suitable and are contemplated for use.) If not, blocks 602 and 604 are repeated while the control logic waits for a command.

[0044] Upon detecting the initiation of a command, the control logic requests the receiver to perform a noise level detection in block 606. This noise level detection can include both a narrowband and a wideband envelope measurement. In block 608, the control logic determines whether the command has been completely received. If not, blocks 604 and 606 are repeated while the control logic waits for the command to complete.

[0045] After the command is fully received, the control logic determines in block 610 whether it is a "data" command. If so, the control logic 612 searches the digital data to determine what the command is and executes it. For example, the command may specify that a specific value should be written to a specified memory address or that the contents of a specified register should be sent to the ECU. The control logic executes the command and signals completion to the ECU. After the data operations have been completed, the control logic returns to block 602.

[0046] If the command is not a data command, the control logic determines whether it is a "receive-only" command in block 614. If so, the DSP performs echo detection in block 615 (by driving the I / O line as previously described), and after the measurement period expires, the sensor controller releases control of the I / O line. During the measurement period in block 615, the blindness detector monitors the saturation of the front-end amplifier as previously described. (As previously mentioned, some embodiments perform the broadband envelope measurement check during the pre-transmission interval in block 606.) In block 616, the DSP checks whether the blindness detector has observed any saturation events, and if not, control returns to block 602.Otherwise, in block 617, the DSP determines the status code information about this sensor error in block 617 for storage in an internal register in block 602 and for potential reporting in the subsequent block 618. Control then returns to block 602. .

[0047] If it is determined in block 614 that the command is a transmit and receive command (rather than a receive-only command), the control logic causes the transmitter to send a transmit burst to block 618 and assumes control of the I / O line, as previously described. As described in the related application, after assuming control of the I / O line, the control logic may send a digital status word (consisting of one or more bit intervals) to the ECU. The digital status word may be derived from the codes stored in the internal registers.

[0048] In block 620, DSP measures the response of the piezoelectric transducer during the drive stage and / or during the reverberation stage of acoustic burst transmission and derives one or more response parameters such as resonant frequency, quality factor, magnitude, phase shift, actuation interval, damping rate, series resistance, damping factor, etc. As previously described, the digital status word is derived from a noise level measurement and error conditions that may be stored in the hardware registers. (In certain alternative embodiments, the response measurement and parameter determination may be decoupled from the sensor's echo measurement operation, so that most echo measurements are performed without measuring the response parameters.)The response parameters can then be determined, if necessary, using the disclosed principles via a special command or calibration procedure that is independent of the echo measurement process.

[0049] In block 622, the DSP optionally adjusts the drive frequency, amplitude, and / or waveform to optimize the efficiency of the acoustic burst transmission. In block 624, the DSP analyzes the measured parameter(s) to determine whether they indicate that a new fault or a change in converter state has occurred. The DSP then performs echo detection in block 616 and drives the I / O line accordingly. Otherwise, in block 626, before performing echo detection in block 616, the DSP analyzes the measured parameters to classify any faults and identify the converter state (e.g., normal, charged, degraded, or faulty). The status code for such diagnosed faults or state conditions is stored in internal registers in block 602 and can be communicated to the ECU, which in turn can alert the vehicle driver via a dashboard display or an alarm tone.Preferably, the driver is informed about the converter status and is given an indication as to whether increased caution is sufficient, whether sensor impairments need to be remedied, or whether a trip to a workshop is recommended.

[0050] In summary, in one embodiment, a sensor controller has been disclosed herein, including: a transmitter for driving a piezoelectric element during actuation intervals to generate acoustic bursts; a receiver for detecting a response of the piezoelectric element to echoes of each acoustic burst, the receiver including a front-end amplifier; processing circuitry coupled to the transmitter and the receiver, the processing circuitry operable to apply echo detection processing to the response; and a blindness detector for detecting saturation of the front-end amplifier outside of actuation intervals.

[0051] In one embodiment of a method of operating a piezoelectric sensor, the method includes: driving a piezoelectric transducer to generate a burst of acoustic energy during an actuation interval; during a measurement interval following the actuation interval, obtaining a response of the piezoelectric transducer with a receiver including a front-end amplifier; processing the response to detect echoes of the burst; and determining whether the response indicates sensor blindness due to saturation of the front-end amplifier.

[0052] A sensor embodiment includes: a piezoelectric transducer; and a controller that drives the piezoelectric transducer to generate bursts of acoustic energy during actuation intervals and receives the responses of the piezoelectric transducer during the measurement intervals with a receiver that includes a front-end amplifier, the controller including a blindness detector that detects saturation of the front-end amplifier outside of the actuation intervals

[0053] Any of the foregoing embodiments may be employed in conjunction with any one or more of the following optional features: 1. The blindness detector includes: an envelope detector that measures a broadband envelope of the response during the measurement intervals; and a comparator that compares the broadband envelope to a threshold representing the saturation of the front-end amplifier. 2. An I / O controller that transmits broadband envelope measurements to a system controller for detecting sensor blindness. 3. An analog-to-digital converter after the front-end amplifier, the analog-to-digital converter providing a digital response signal. 4. A bandpass filter centered on a carrier frequency of the acoustic bursts for generating a filtered signal from the digital response signal. 5.a second envelope detector that measures a narrowband envelope of the filtered signal during a noise measurement interval before each actuation interval. 6. a second comparator that compares the narrowband envelope to a second threshold representing excessive ambient noise. 7. an I / O controller that communicates a sensor error when the blindness detector detects saturation and / or when the second comparator detects excessive ambient noise during the noise measurement interval. 8. the blindness detector is powered by the digital response signal. 9. the blindness detector is powered by an analog output signal from the front-end amplifier. 10. using a reverberation detector to signal an end of the actuation interval. 11. measuring a broadband envelope of the response; and comparing the broadband envelope to a threshold representing saturation of the front-end amplifier. 12.a reverberation detector that determines the beginning of each measurement interval.

[0054] Although the Fig.6 are treated as sequential for the purpose of illustration, in practice the method may be carried out across multiple integrated circuit components operating simultaneously, and perhaps even speculatively to enable repair operations in the event of defects. The sequential discussion is not intended to be limiting. Furthermore, the foregoing description assumes the use of a LIN bus, but other bus implementations are also contemplated, including CAN and DSI3, where wideband envelope measurements may be communicated directly to the ECU to enable the ECU to determine whether the front-end saturation level is effectively blinding the sensor. Furthermore, the foregoing discussions focused on ultrasonic sensors, but the principles apply to any sensors that might be blinded by front-end saturation effects.These and numerous other modifications, equivalents, and alternatives will become apparent to those skilled in the art after a full understanding of the above disclosure. The following claims are intended to be interpreted to encompass all such modifications, equivalents, and alternatives, as appropriate.

Claims

[1] A control system for a piezoelectric transducer, the control system comprising: a transmitter for driving a piezoelectric element during the actuation intervals to generate acoustic bursts; a receiver for detecting a response of the piezoelectric element to echoes of each acoustic burst, the receiver including a front-end amplifier; a processing circuit coupled to the transmitter and the receiver, the processing circuit operable to apply echo detection processing to the response; and a blindness detector for detecting the saturation of the front-end amplifier outside of the actuation intervals, wherein the blindness detector detects the saturation immediately before each actuation interval. [2] The controller of claim 1, wherein the blindness detector includes: an envelope detector that measures a broadband envelope of the response outside the actuation interval; and a comparator that compares the broadband envelope with a threshold value that represents the saturation of the front-end amplifier. [3] The controller of claim 2, further comprising: an analog-to-digital converter after the front-end amplifier, the analog-to-digital converter providing a digital response signal; a bandpass filter centered on a carrier frequency of the acoustic bursts to generate a filtered signal from the digital response signal; a second envelope detector that measures an envelope of the filtered signal during a noise measurement interval before each actuation interval; and a second comparator that compares the measured envelope of the filtered signal with a second threshold representing excessive environmental noise. [4] The controller of claim 3, further comprising an I / O controller that communicates a sensor error when the blindness detector detects saturation and when the second comparator detects excessive environmental noise during the noise measurement interval. [5] A method for operating a piezoelectric-based sensor, the method comprising: Driving a piezoelectric transducer to generate a burst of acoustic energy during an actuation interval; during a measurement interval following the actuation interval, obtaining a response of the piezoelectric transducer with a receiver including a front-end amplifier; Processing the response to detect echoes of the burst; and Determining whether the response indicates sensor blindness during the measurement interval due to saturation of the front-end amplifier, wherein the determination includes detecting saturation immediately before each actuation interval. [6] The method of claim 5, wherein determining includes using a reverberation detector to signal an end of the actuation interval [7] The method of claim 5, wherein determining further comprises: Measuring a broadband envelope of the response; and Comparing the broadband envelope with a threshold value that represents the saturation of the front-end amplifier. [8] The method of claim 7, wherein the processing comprises: Digitizing an output of the front-end filter with optional gain control to obtain a digital response signal; Measuring a narrowband envelope of the digital response signal during a noise measurement interval prior to the actuation interval; Comparing the narrowband envelope to a threshold representing excessive ambient noise. [9] The method of claim 5, wherein determining comprises: Measuring a broadband envelope of the response; and Transmit the broadband envelope measurement to a system controller for sensor blindness detection.

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