Time-varying templates for improved short-range performance in coded ultrasonic ranging

Abstract

Time-varying templates for improved short-range performance in ultrasonic ranging are disclosed. Ultrasonic ranging systems and methods that transmit a coded burst signal (802) and correlate converted acoustic echoes (808, 812, 816) of the burst signal (802) with a receive template that characterizes the burst code to determine time-of-flight information use a receive template of time-varying length to improve short-range object detection. The template length (810, 814, 818) is based on a time index measured from the start of transmission (804) of the burst signal (802). Detection can resolve a blind zone of transducer ringing (807) after the burst signal (802). A time-varying gain based on the time index can also be applied to the correlation signal. The length (810, 814, 818) and gain can be adjusted at a reduced time frequency to reduce computational cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to electronic processing systems and methods, and in particular to systems and methods of generating and using time-varying templates for improved short-range performance in coded ultrasonic ranging. BACKGROUND

[0002] Ultrasonic ranging is used in a variety of applications. For example, in automotive applications, ultrasonic transducers can be arranged in the bumper or fender of a car. The transducers emit ultrasonic signals that reflect off nearby objects, if present, and sense the reflections. The round-trip time of the ultrasonic signals is measured so that the distance to the object can be determined, or by processing the reflection information from multiple transducers, the position of the object can be inferred. Thus, for example, by presenting such determinations or inferences or navigation information based thereon to a warning system configured to present warning signals to a human driver or to an autonomous driving system configured to navigate the vehicle to avoid collision with detected obstacles, collision avoidance can be achieved. SUMMARY

[0003] An example ultrasonic ranging system includes a time-varying template generation circuit configured to generate a time-varying coded receive template based on a full-length template and a time index from a start of a burst signal provided to an ultrasonic transducer. The length of the time-varying coded receive template depends on the time index. The system also includes a correlator circuit coupled to the time-varying template generation circuit and configured to correlate a received converted reflection signal with the time-varying coded receive template to produce a correlation signal. An envelope of the correlation signal contains a peak indicative of a distance between the ultrasonic transducer and a detected object. A time-varying gain amplifier can be coupled to the correlator circuit and configured to adjust a gain of the correlation circuit by an amount based on the time index from the start of the burst signal.

[0004] In another example, a method of ultrasonic ranging includes emitting a coded ultrasonic acoustic burst signal encoded with a code from an ultrasonic transducer. Then, the ultrasonic transducer or another ultrasonic transducer converts a reflected acoustic signal encoded with the code. A time-varying receive template is generated that characterizes the code. The length of the receive template is based on a time index measured from the start of the emitted burst signal. The converted reflected signal is correlated with the time-varying receive template to produce a correlation signal. Based on the correlation signal, a time of flight of the reflected acoustic signal is computed. This time of flight represents a distance between the ultrasonic transducer and a detected object.

[0005] In yet another example, an ultrasonic detection system includes an excitation circuit configured to direct an ultrasonic transducer to emit a coded ultrasonic acoustic burst signal encoded with a code, and a listening circuit configured to receive a converted reflected acoustic signal encoded with the code from the ultrasonic transducer or another ultrasonic transducer. The system also includes a time-varying template generator configured to generate a time-varying receive template characterizing the code based on a time index measured from the emission of the burst signal. The system also includes a correlator coupled to the listening circuit and the time-varying template generator and configured to correlate the converted reflected signal with the time-varying receive template to produce a correlation signal. The system also includes a time-of-flight circuit coupled to the correlator and configured to compute a time-of-flight of the reflected acoustic signal based on the correlation signal, the time-of-flight being indicative of a distance between the ultrasonic transducer and a detected object. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 An example car with ultrasonic transducers to measure distance to objects is illustrated.

[0007] Figure 2 is a high-level diagram showing an example organization between a central controller and multiple ultrasonic sensor modules, each having an ultrasonic transducer and an electronic controller.

[0008] Figure 3 is a block diagram of an example portion of a controller and associated transducer in an ultrasonic sensing system.

[0009] Figure 4 is a waveform timing diagram of an example burst signal and corresponding example receiver template.

[0010] Figure 5 is a block diagram of a time-varying template generator coupled to a correlator.

[0011] Figure 6 is a waveform timing diagram of an example burst signal and corresponding example receiver template.

[0012] Figure 7 is a block diagram of a time-varying template generator coupled to a correlator.

[0013] Figure 8 is a waveform timing diagram of an example burst signal and corresponding example receiver template.

[0014] Figure 9 and 10 is a time diagram of an example converted receive echo signal.

[0015] Figure 11 is a graph showing example gain profiles for different template update segment lengths.

[0016] Figure 12 is an expanded view of the plot of Figure 11

[0017] Figure 13 is a plot of the envelope of a plot showing a 64-pulse chirp burst signal for Figure 11

[0018] Figure 14 is an expanded view of the plot of Figure 13

[0019] Figure 15 is a flowchart illustrating an example method of coded ultrasonic ranging with time-varying template generation. DETAILED DESCRIPTION

[0020] Reflected ultrasonic signals can be detected by ultrasonic transducers and used to measure the round trip time, and thus the distance to the object that reflected the ultrasonic signal. For example, automotive applications can use one or more ultrasonic sensor modules to sense the distance of objects behind, along the way, or in front of the car. This application discloses systems and methods that provide enhanced ultrasonic detection of obstacles, particularly in conditions where the ranging detects targets very close to the detection system.

[0021] By encoding transmitted signal bursts and processing received echoes with knowledge of this encoding information, the discrimination of echoes of ultrasonic signals produced by different transducers can be improved. An example system for coded ultrasonic sensing is described in U.S. Patent Application No. 16 / 364,652, filed March 26, 2019, entitled “Time of Flight and Code Signature Detection for Coded Ultrasonic Transmission,” which is incorporated by reference herein. The encoding of the signal burst improves reflection detection by distinguishing the primary peaks in the envelope of the correlated reflection signal corresponding to true reflections from peaks (primary or secondary) corresponding to echoes sensed from other transducers. Correlators, envelopes, thresholding, peak searching, peak buffers, and peak rank logic arranged in multiple instances of the signal processing path (e.g., one signal processing path instance per burst code used in the ranging system, e.g., one per transducer) identify valid peaks in the correlator output. Verified peak information (e.g., amplitude and time) can be reported to a central controller and / or stored locally in fusion logic to use the peaks from multiple bursts to generate more intelligent information about possible targets or obstacles.

[0022] Figure 1 ​​​The use of an ultrasonic-based distance measurement (i.e., ranging) system is illustrated, i.e., in the car 100, which includes one or more ultrasonic transducers 105 in the front and / or rear bumpers. In Figure 1 In the example, four ultrasonic transducers 105 are shown, but in other examples, the number of transducers in each bumper can not be four. As used herein, "transducer" refers to an ultrasonic transducer. Any single transducer can function to emit an ultrasonic signal, convert an electrical signal to an acoustic signal, and sense a reflected signal, converting the acoustic signal to an electrical signal. Each transducer 105 can, for example, emit an acoustic wave, and subsequently detect a reflection of the emitted acoustic wave after it bounces off an object (e.g., object 120) and returns to the transducer. The elapsed time t between the initial emission of sound from the transducer ("burst") and the detection of the reflected acoustic wave at the transducer can be measured by a receiver circuit coupled to the transducer. The total distance traveled back and forth can be calculated as the product of the speed of sound through air c (approximately 344 meters / second or 1,129 feet / second) and the measured time t. The distance D1 between the transducer and the object is then given by the formula D1 = ct / 2, where the division by two represents the fact that the reflected acoustic wave travels back and forth to return to the transducer.

[0023] In some examples, the acoustic wave signal is emitted as a short burst of sound at a particular frequency, typically above 20 kHz, e.g., about 50 kHz. The emitted acoustic wave typically includes a number of pulses, e.g., between about 15 and 100 pulses, e.g., between about 20 and 65 pulses. A controller (not shown in Figure 1 The transducer 105 can then convert the electrical drive signal into an acoustic sound wave that is emitted from the transducer. The controller that directs its associated transducer to emit the burst is referred to herein as the "burst" transducer. The transducer 105 converts the received reflected acoustic wave into an electrical signal, and passes the converted signal to a receiver in the controller that is configured to process the received signal. The controller has a timer inside that starts when the burst sequence is emitted, and after a valid echo is received, the value of the timer is recorded as the time of flight (ToF) of the echo. As noted above, this time of flight divided by two and multiplied by the speed of sound in air yields the distance between the transducer 105 and the reflecting object 120.

[0024] In coded waveform burst signal systems and methods, rather than using a single tone burst signal, a frequency or phase modulated coded signal can be emitted by any one transducer, allowing disambiguation of returned echoes produced by multiple transducers.

[0025] In some examples using such encoding, each burst can consist, for example, of a sequence of pulses similar to a square wave, but with each pulse in the waveform having a different duration corresponding to a different frequency. In some examples, the frequencies used to produce a given sound burst can range between a first frequency and a second frequency, and thus have a difference referred to as Af. As an example, a first pulse in a burst can have a duration corresponding to a frequency of 48.0 kHz, a second pulse in the burst can have a duration corresponding to a frequency of 48.2 kHz, a third pulse in the burst can have a duration corresponding to a frequency of 48.4 kHz, and so on, up to a 21st and last pulse in the burst that can have a duration corresponding to a frequency of 52.0 kHz. The above represents only one example; other pulse frequencies and numbers of pulses per burst are possible, as is the arrangement of pulses of different frequencies within a burst, with the order of increasing frequencies beyond that in this example, or in other examples, with frequencies decreasing or increasing then decreasing, or frequencies decreasing then increasing.

[0026] Thus, in other examples, a burst can scan upward from a first frequency to a second, higher frequency, and again downward back to the first frequency or to a third frequency lower than the second frequency. In still other examples, a burst can switch between two or more frequencies using a predefined pattern to create a unique coded signature. In yet other examples, a burst can scan downward from a first frequency to a second, lower frequency, and then back to the first frequency or to a third frequency higher than the second frequency. Other modulation patterns are possible. Regardless of which pattern is employed, the particular scanning characteristics of a burst: pulse frequency, number of pulses, duration of pulses, and / or timing of pulses (e.g., by frequency, duration, or other manner) can act as a burst signature identifying the transducer that emitted the burst. Each transducer can have its own unique frequency modulation signature in the coded burst waveform it emits. Due at least in part to the burst encoding described above, there is no need to limit the overlap of the frequency ranges of the scans in the bursts from different transducers. The bursts can be phase-modulation encoded or frequency-modulation encoded.

[0027] The receiver circuit in the controller associated with a particular transducer can be equipped with a correlator. The correlator can be provided with a template, which can be sampled, for example, from the encoding signal used to create the drive signal. Each transducer can thus be correlated only with its own template. In particular, since each transducer has a distinct frequency or phase modulation pattern, the receiver circuit of each transducer can correlate the received signal only with the frequency or phase modulation signature of that transducer itself. Due to the differences in the different transducer burst strings, the encoded burst strings can be transmitted closer together in time than the unencoded. Since each transmitted sound signal is uniquely encoded for a particular transducer 105, the reflected sound signal is also unique and can be distinguished by the receiver circuit connected to each transducer.

[0028] The (full length) receive template can be generated in one of several ways. In each case, the fixed length N of the receive template approximately, but not necessarily exactly, matches the length of the burst signal (or the length of the burst signal plus the "dead zone" ringing period) M. As one example, the receive template can be generated computationally, for example, in real time from the transmitted burst signal, for example, by resampling from the excitation signal (i.e., the transmitted burst signal) at some point before it is converted to an acoustic signal. In this case, N is equal to M or slightly less than M, depending on implementation limitations of the correlator. For example, it can be the case that correlator template generation implemented in hardware can result in correlator templates having a fixed maximum length, and for some transducer and receive sampling rate configurations, M exceeds this maximum length.

[0029] Alternatively, a receive template can be generated based on the acoustic output of the encoded burst drive signal. For example, this can be done by measuring (e.g., using a microphone) and sampling (e.g., using an ADC) the acoustic burst pattern of the transducer output, then storing the generated template in memory for later use in correlation calculations. Another approach is to use another transducer and receiver circuit to record a template from the receiver circuit output. In this way, the recorded template also takes into account the receive response of the transducer and the response of the receiver circuit. Whichever way, the template generated from the acoustic output (as opposed to a computationally generated template by sampling the excitation signal) is able to account for the post-burst period of the transducer ringing (“dead zone”). In this case, N can be larger than M to account for some of the transducer ringing behavior. The correlator template size in hardware can be configured to have a maximum length to accommodate this difference in N vs. M size. A template generated in this way can perform better, e.g., in terms of signal-to-noise ratio (SNR), compared to a computationally generated template, because it matches the real acoustic signal emanating from the transducer, as opposed to the electrical excitation signal. The template generation method involving a user (e.g., system integrator) measuring the acoustic burst pattern using a microphone and storing the template in memory in the ranging device or system does not necessarily provide the convenience of performing dynamic computational generation of the template in real time based on the device configuration.

[0030] Figure 2 An organization of multiple ultrasonic sensor modules 202 directed by a central controller 204 (e.g., an electronic control unit (ECU)) is shown. Each sensor module 202 can include an associated individual controller (not specifically shown), which can be implemented, for example, as an integrated circuit (IC), and configured to drive an ultrasonic transducer (not specifically shown) in the sensor module 202 as well as to process received signals that can contain echoes corresponding to a target or obstacle. After processing, the transducer-associated controller can send the processed echo information back to the central controller 204, which can collect the processed echo information from multiple transducers (e.g., all four transducers in the illustrated example) and triangulate detected objects based on the information collected from the multiple transducers. The central controller 204 can also perform some additional high-level processing, including processing to deal with interference. In some examples, the central controller 204 can include circuitry to calculate the time of flight of detected echoes based on information (e.g., envelope information or peak position information) sent from the modules 202. In other examples, the time of flight can be calculated within the individual modules 202 and sent to the central controller 204.

[0031] Figure 3This is a simplified diagram of an example system 300 or a portion thereof for coded ultrasonic ranging, including an ultrasonic transducer 302 capable of transmitting coded ultrasonic signals based on electrical signals and listening for echoes to convert them back to electronic signals. The upper part of the diagram shows the excitation circuitry constituting the transmission path, and the lower part shows the listening circuitry constituting the receiver path. On the excitation circuitry side, a burst generator 310 can generate an coded (e.g., frequency-modulated) excitation signal that drives both sides of a transformer 320 via drivers 312, 314 and field-effect transistors (FETs) 316, 318. On the other side of the transformer 320 is the transducer 302. During excitation, the transformer 320 drives the transducer 302 to transmit coded ultrasonic bursts. Once excitation stops, there is a transducer ringing period after which the transducer 302 can begin receiving echoes from one or more targets in the environment (e.g., [targets]). Figure 1 The target 120 shown is reflected back to system 300.

[0032] On the listening circuit side, the received acoustic signal can be converted into an analog electrical signal by transducer 302 and then fed to coupling network 322 and time-varying gain (TVG) amplifier 324, where it can be sampled by analog-to-digital converter 326. The sampled signal can then be correlated with transmit template 330 via correlator 328. Transmit template 330 can be generated, for example, from burst signals generated by burst generator 310 driving transducer 302, or retrieved from memory after previous acoustic sampling, as described above. After the correlator, envelope extractor 332 can extract envelope information from the correlated signal, which can be compared with a threshold to provide time-of-flight information. The threshold can be set, for example, above a certain noise level to avoid false alarms triggered by fundamental electrical noise in the received signal path or acoustic noise in the environment. In some cases, it may also be desirable to avoid triggering from certain types of objects and / or objects at a certain distance. The threshold can be set higher to suppress the detection of such objects. The threshold does not have to be a constant value relative to time; rather, the threshold itself can be a time-varying signal that can be predefined and / or dynamically generated.

[0033] System 300 can be configured to accommodate any number of different codes (e.g., four codes), one such path per code, by implementing additional parallel processing receiver paths between analog-to-digital converter 326 and the peak-level (not shown) following envelope generator 332. The basic system 300 for encoding ultrasound transmission enables simultaneous sensor bursts and increased scan time while improving signal-to-noise ratio and echo stability.

[0034] exist Figure 4 The text describes the problem solved by the system and method described herein. Figure 4Three example time-domain acoustic waveforms 402, 408, 410 converted by a transducer such as transducer 302 are shown. The coded burst signal 402 (which can also be referred to as an excitation signal) begins at an excitation start time 404 and ends at an excitation end time 406. The duration of the burst signal 402 shown is approximately 64 pulses at an average of approximately 55 kHz, or approximately 1.2 milliseconds, but can have a different duration, number of pulses, or average frequency in other examples. As described above, a received signal is correlated with a template that identifies the coding of the burst signal, and the template can be generated from the burst signal. The problem that is determined is that a target that is close to the ranging system will generate a return echo before the burst signal ends, and a significant portion of the echo is not effectively received by the ranging system because this portion falls within the excitation period, rather than the subsequent listening period.

[0035] In Figure 4 Case 1 of the illustrative example, a target object 10 centimeters away from the burst transducer 10 begins returning a first echo signal 408 588 microseconds after the excitation signal 402 begins, with a speed of sound of 340 meters / second. Thus, the first echo signal 408 partially overlaps in time with the excitation signal 402. Because the transducer that produces the burst signal 402 is driven by a transformer during the excitation, the electrical signal is directly coupled to the receiver side of the system before the burst signal ends, and thus the system cannot effectively listen for echoes until some time after the excitation is completed at the excitation end time 406. As described above, in the previously described systems and methods for coded ultrasonic ranging, the receive template approximately matches the length of its corresponding burst signal. However, in Figure 4 Case 1, assuming only a portion of the received echo signal 408 is "heard" (i.e., converted to an electrical signal for correlation and peak detection) after time 406, the full receive template for the burst signal 402 (the length of the burst signal 402 is indicated above the received signal 408) does not have a good correlation with the received signal 408. Thus, in Case 1, it is desirable to correlate the received echo 408 with a template that only corresponds in length to the portion of the echo 408 that the system "heard."

[0036] In contrast, Figure 4Case 2 describes the reception of the echo 410 of the burst signal 402 from a target object 25 cm from the burst transducer at 1.47 ms after the start of the burst signal 402 (duration 1.2 ms). This ensures that the received signal 410 effectively eliminates the time following the end of the burst signal 406 and falls entirely within the transducer's listening period. In Case 2, it is desirable to associate the received echo 410 with a full-length template that corresponds in length to the entire portion of the echo 410 "heard" by the system, i.e., to the full length of the burst signal 402. While in Case 1, it is desirable that the template is "active" only after the end of the burst signal 406, in Case 2, it is desirable that the template is active along its entire length.

[0037] Figure 5 Block diagram 500 illustrates an example receive template generator that can time-varyrate the length of the receive template based on elapsed time to generate a receive template with a length that more perfectly matches the length of the desired "heard" echo signal. Not in all cases is the full-length template of static length passed to the correlator, such as... Figure 3 As shown, the time-varying template generator 502 can output a time-varying template 504, which can be based on a full-length template 506 and a time index 508 measured from the start of the burst signal. The time-varying template 504 can then be passed to a correlator 510, which can correspond to... Figure 3 Correlator 328 in the middle. Correlator 510 can provide correlator output signal 512 based on time-varying template 504 and sampled received signal 514. TVG multiplier 516 (in Figure 3 (Not present in and not confused with TVG amplifier 324) may also be included to transmit the TVG-adjusted correlator output 518 to the envelope extractor (e.g. Figure 3 Before the envelope extractor 332 shown, a time-varying gain is applied to the correlator output to adjust for any gain changes caused by the varying template size.

[0038] As an example, this illustrates how the time-varying template generator 502 can calculate the length 504 of the template to be output, where the burst length is M based on the received samples, and then for a template of total length N, the time-varying template at time index n (where M+1≤n≤2M) is...

[0039]

[0040] Where r0(i) is the original full-length template 506, and i is the template index. Note that N can be greater than M in cases where some portions of the transducer ringing are also included in the templates used for correlation. As described above, in such cases, the templates can be constructed and stored in memory rather than being generated in real time from the excitation signal. When n ≥ 2M + 1, the template is equal to r0(i). It has a fixed length and is no longer time-varying. When n < M + 1, the template can be a complete or incomplete template while it is still being generated. Generating the template completely in this case is not crucial because the correlator output is based on the electrical signal coupling rather than the reflected echoes from the object. In other words, during n < M + 1, the system may not "listen" for echoes with the transducer because the transducer is still in the burst.

[0041] To compensate for the gain difference caused by the varying template length, the TVG 516 can provide the following gain compensation g(n) at time index n, where M + 1 ≤ n ≤ 2M:

[0042]

[0043] Thus, when the time index n is equal to twice the burst length M, i.e., when n = 2M, the gain g(n) reaches N / N = 1.

[0044] For example, for a burst signal of M = 64 pulses, the length of the received template can be 64 × 7 = 448 (assuming the receive sampling rate is 7 times the transducer frequency). The generation of the normal template is completed at sample number 448. For the next received sample that enters at sample n = 449, the received template is all zero except for the last value. The gain applied to the correlator output is 448. For the sample immediately following, i.e., n = 450, the template is non-zero only for the last two values. The gain applied to the correlator output is 224. This continues until sample n = 448 × 2, at which point the template is full again and the gain applied to the correlator output is 1.

[0045] Figure 6 Illustrates Figure 5 how the arrangement 500 provides an adjusted length for the received template that is adjusted based on the time elapsed since the end of the burst signal, such that the received template grows in time length until it becomes full length. The burst signal 602 is approximately 64 pulses and has a time length of approximately 1.2 milliseconds at an average frequency of approximately 55 kHz. The burst signal 602 starts at the excitation start time 604 and ends at the excitation end time 606. The full length of the received template 608 is shown (corresponding to Figure 5the length of the receive template at the time of the end of the burst signal 606 (e.g., computed by the time-varying template generator 502) is shown as length 610. For an echo 612 that returns after a time Ati that is less than the duration of the burst signal 602, the computed length 614 of the receive template is length 610 plus Ati. For an echo 616 that returns after a time At2 that is greater than the duration of the burst signal 602, the computed length 618 of the receive template is its full length. From the end of the burst until one burst interval after the end of the burst, the receive template is time-varying.

[0046] Figure 7 The block diagram 700 illustrates another example receive template generator that can time-vary the length of the receive template based on elapsed time to generate a receive template with a length that more perfectly matches the length of the expected "heard" echo signal. Rather than delivering a full-length template of static length to the correlator in all cases, as Figure 3 shown, the time-varying template generator 702 can output a time-varying template 704 based on a full-length template 706, a time index 708 measured from the start of the burst signal, and a blind time duration, which can be, for example, a programmed parameter based on measurements to determine how long the transducer will ring after a burst. The resulting time-varying template 704 can be delivered to a correlator 710, which can correspond to Figure 3 the correlator 328 in FIG. 3. The correlator 710 can provide a correlator output signal 712 based on the time-varying template 704 and a sampled receive signal 714. A TVG multiplier 716 (not present in FIG. 3 and not to be confused with the TVG amplifier 324) can also be included to apply a time-varying gain to the correlator output to adjust for any gain variations due to the changing template size before delivering a TVG-adjusted correlator output 718 to an envelope extractor (e.g., the envelope extractor 332 shown in Figure 3 FIG. 3). Figure 3

[0047] As an example, it is illustrated how the time-varying template generator 702 can compute the length 704 of the template to output, where M is the burst length plus the blind time duration in terms of receive samples, the time-varying template generator 702 can be configured to consider two separate cases, the first case where the template length N is greater than or equal to M, and the second case where the template length N is less than M.

[0048] If N > M, that is, the full template length is greater than or equal to the burst length, then for a receive template of full length N, the time-varying template at time index n, where M + 1 < n < 2M, is

[0049] ​

[0050] where r0(i) is the original full-length template 706, and i is the template index. When n ≥ 2M + 1, the template is equal to r0(i). It has a fixed length and is no longer time-varying.

[0051] To compensate for the gain difference caused by the varying template length, TVG 716 can provide the following gain compensation g(n) at time index n, where M + 1 ≤ n ≤ 2M:

[0052]

[0053] If N < M, that is, the entire template length is less than the burst length, then for a received template of full length N, the time-varying template at time index n (where 2M - N + 1 ≤ n ≤ 2M) is

[0054]

[0055] where r0(i) is the original full-length template, and i is the template index. When n ≥ 2M + 1, the template is equal to r0(i). It has a fixed length and is no longer time-varying.

[0056] To compensate for the gain difference caused by the varying template length, TVG 716 can provide the following gain compensation (where 2M - N + 1 ≤ n ≤ 2M):

[0057]

[0058] Figure 8 illustrates Figure 7 an example of how the arrangement 700 can provide an adjusted length to a received template that is adjusted based on the time elapsed since the end of the burst signal and the blind zone duration such that the received template grows in time length until it becomes its full length. The burst signal 802 is approximately 64 pulses, having a time length of approximately 1.2 milliseconds at an average frequency of approximately 55 kHz. The burst signal 802 starts at the excitation start time 804 and ends at the excitation end time 806. The blind zone caused by transducer ringing persists for a specified period 807 after the end 806 of the burst signal 802. The full length of the received template 808 is shown (corresponding to Figure 7the computed length of the receive template at the time of the end 806 of the burst signal 802 (e.g., computed by the time-varying template generator 702) is shown as length 810. For echoes 812 that return after a time Ati that is less than the duration of the burst signal 802 plus the duration of the blind zone 807, the computed length 814 of the receive template is length 810 plus Ati. For echoes 816 that return after a time At2 that is greater than the duration of the burst signal 802 plus the duration of the blind zone 807, the computed length 818 of the receive template is its full length. From the end of the burst signal plus the duration of the blind zone until one burst interval after the end of the burst signal, the receive template is time-varying.

[0059] Figure 9 and Figure 10 The plots illustrate a correlator output comparison for a 64-pulse chirped burst signal. Figure 9 The results are shown for a fixed-length template, while Figure 10 The results are shown for a time-varying template generated as described above. The different curves plotted in each plot correspond to envelopes that are the result of echoes from target objects at different distances, as indicated by the respective legends of each plot. For a threshold set to 5 x 104, short-range ranging is improved from about 13 centimeters to about 9 centimeters using a time-varying template design of the type described herein.

[0060] With respect to the update frequency of the template r(i) performed by the template generator 502 or 702 (i.e., the length of the template) and / or the gain factor g(n) of the template r(i) performed by the TVG 516 or 716, in some examples, the template length and / or its gain can be updated every sample, while in other examples, the template length and / or its gain can be updated at a smaller frequency (e.g., every 8 samples) to reduce computational cost. In such examples, the template length and / or its gain can be set according to a template that terminates in the center of an 8-sample window. For example, for a template of full length N, the time-varying template r(i) at time indices N+1 to N+8 can be computed as t (i) = r(i - N) (1)

[0061]

[0062] where r0(i) is the original full-length template. The gain g(n) can be computed as N / 4, since the template has 4 values. The next template length / gain will be updated at time indices N+9 to N+16. The time-varying template r(i) at time indices N+9 to N+16 can be computed as t (i) = r(i - N) (1)

[0063]

[0064] In this case, the gain g(n) is N / 12, since the template has 12 values.

[0065] Further regarding this frequency of template length / gain update, Figures 11-14 Gain profiles and envelope outputs are shown for a 13 cm distant target for various segment sizes (i.e. 1 sample segment, 8 sample segment, 16 sample segment and 32 sample segment). In the illustrated graphs, with a 1 sample segment, the receive template length and its time-varying gain are updated every 1 sample, while with a 32 sample segment, the receive template length and its time-varying gain are updated every 32 samples. Figure 11 Gain profiles for different segment lengths are shown. Figure 12 Figure 11 is a zoomed in view of Figure 11 and 12 As can be seen in

[0066] Figure 13 and 14 show the effect of update frequency on the measured echo. Figure 13 shows the envelope of the plot of Figure 11 In Figure 13 the peaks in the portion of the envelope between 1.2 and 1.6 milliseconds can be attributed to transducer ringing rather than detected acoustic reflections. The peak centered at about 2.16 milliseconds represents the echo from the 13 cm distant object. Figure 14 is a zoomed in view of Figure 13 shows the zoomed in envelope of the 13 cm echo of the 64 pulse chirp burst signal at the peak between 2.0 and 2.3 milliseconds. According to Figures 11-13 the plot, a 32 sample segment can be used to point out the apparent distortion of the echo signal. Although a hardware trade-off analysis can determine the precise segment sample size to use in any individual case, in some examples, an 8 sample segment will be found to be optimal. In the case of 128 pulses, the oversampling rate is 3.5 times.

[0067] ​Further hardware implementation efficiency can be achieved by quantizing the time-varying gains applied to the time-varying length receive templates to an appropriate or optimal number of bits. In the case of a 64-pulse burst signal (64 x 7 = 448 template samples) and 8-sample segments, the maximum gain is 448 / 4 = 112. The various gain levels to be applied can be represented as floating point numbers or using fewer bits representing the integer and fractional parts of the gain level. The integer part of the gain can be, for example, 7 bits, while the fractional part can be, for example, 2, 3, or 4 bits. The integer bit width can be reduced by increasing the length of the first template, which reduces the gain, but has the disadvantage of creating a small notch in the envelope. Note that in these figures, the subsequent templates after the first template are set to length 1 sample.

[0068] Figure 15 An example method 1500 of ultrasonic detection is illustrated. An ultrasonic transducer can emit an encoded ultrasonic acoustic burst signal encoded with a code (1502). In the presence of an object that reflects the emitted burst signal, the ultrasonic transducer (or a different ultrasonic transducer) can convert the reflected acoustic signal encoded with the code (1504). A time-varying receive template characterizing the code can be generated (1506), the length of the receive template (i.e., the length in time or the length in samples) being based on the length of time elapsed since the emission of the burst signal. (As used herein, the meaning of "time elapsed since the emission of the burst signal" includes the time index measured from the start of the burst signal. Thus, a receive template length based on the number of samples can be considered a "receive template length based on the length of time elapsed," even if the time in seconds is not measured as part of the method 1500.) The converted reflected signal can be correlated with the time-varying receive template characterizing the code (1508) to produce a correlation signal. The gain of the correlation signal can be adjusted based on the length of time elapsed since the emission of the burst signal (1510). The time of flight of the reflected acoustic signal can be computed (1512), the time of flight indicating the distance between the ultrasonic transducer and the detected object. The method can be performed, for example, by an ultrasonic detection system including Figure 1 、 2 some or all of the components illustrated in Figures 3, 5, and / or 7.

[0069] The encoded burst signal in the method 1500 can be frequency-modulation encoded or phase-modulation encoded. The use of time-varying templates in the method 1500 effectively improves short-range ultrasonic detection.

[0070] The systems described herein can be implemented using application specific integrated circuits (ASICs) or multiple ASICs, and can perform the methods described herein. In some examples, the systems and methods can be implemented or performed using a general purpose digital electronic computer that is programmed in accordance with the instructions of the software to perform the signal processing involved in the correlator, envelope stage, threshold stage, peak search stage, peak buffer stage, peak rank stage, and time of flight generation stage.

[0071] In this specification, the term "based on" means at least partially based on. In this specification, the term "coupled" means directly or indirectly connected. Thus, if a first device, element, or component is coupled to a second device, element, or component, that connection can be through a direct electrical, mechanical, or fluid connection, or through an indirect electrical, mechanical, or fluid connection via other devices, elements, or components and connections. Similarly, a device, element, or component that is coupled between a first component or location and a second component or location can be coupled directly, or by way of intervening devices, elements, or components and / or connections. A device configured to perform a task or function can be configured (e.g., programmed and / or hardwired) at a manufacturing time, by a manufacturer, to perform that function and / or can be configurable (or reconfigurable) by a user after manufacture to perform that function and / or other additional or optional functions. The configuration can be performed by firmware and / or software programming of the device, by the construction and / or layout of hardware components and interconnections of the device, or a combination thereof. Furthermore, a circuit or device that is said to include certain components can instead be configured to be coupled to those components to form the described circuit or device. For example, a structure described as including one or more semiconductor elements (e.g., transistors), one or more passive elements (e.g., resistors, capacitors, and / or inductors), and / or one or more sources (e.g., voltage and / or current sources) can instead include only the semiconductor elements (e.g., a semiconductor die and / or an integrated circuit (IC) package) within a single physical device, and can be configured to be coupled to at least some of the passive elements and / or sources to form the described structure at a time of manufacture or after manufacture (e.g., by an end user and / or a third party).

[0072] Modifications can be made in the described embodiments, and other embodiments can be made, within the scope of the claims.

Claims

1. An ultrasonic ranging system, comprising: a time-varying template generation circuit configured to generate a time-varying coded receive template based on a full-length template and a time index, including determining a length of the time-varying coded receive template based on the time index, the time index based on a time of receipt of a received transition reflection signal relative to a start of a coded burst signal provided to an ultrasonic transducer for transmission; and a correlator circuit coupled to the time-varying template generation circuit, the correlator circuit configured to correlate the received transition reflection signal to the time-varying coded receive template to produce a correlation signal.

2. The system of claim 1, further comprising a time-varying gain multiplier coupled to the correlator circuit, the time-varying gain multiplier configured to adjust a gain of the correlation signal by an amount based on the time index.

3. The system of claim 1, the time-varying template generation circuit generating the time-varying coded receive template further based on a programmable blind duration parameter indicative of a period of transducer ringing after an end of the coded burst signal.

4. The system of claim 1, the time-varying template generation circuit further configured to regenerate the time-varying coded receive template at a frequency less than once per sample.

5. The system of claim 1, wherein generating the time-varying coded receive template includes subsampling the full-length template.

6. The system of claim 1, wherein generating the time-varying coded receive template is further performed based on twice a length of the full-length template minus the time index.

7. The system of claim 2, wherein the time-varying gain multiplier is further configured to adjust the gain of the correlation signal based on a length of the full-length template and based on a length of the coded burst signal.

8. An ultrasonic ranging method, comprising: transducing a coded burst signal by an ultrasonic transducer, the coded burst signal to be transduced being an acoustic signal; generating, by a time-varying template generator, a time-varying coded receive template, including determining a length of the time-varying coded receive template based on a time index, the time index based on a time of receipt of the transduced coded burst signal relative to a start of the coded burst signal being transmitted; correlating, by a correlator, the transduced coded burst signal to the time-varying coded receive template to produce a correlation signal; and based on the correlation signal, computing a time of flight of the transduced coded burst signal.

9. The method of claim 8, wherein generating the time-varying coded receive template is further performed based on a full-length template, the full-length template being resampled from a coded excitation signal at a point prior to the coded excitation signal being transduced into the coded burst signal.

10. The method of claim 8, further comprising adjusting a gain of the correlation signal based on the time index.

11. The method of claim 8, further comprising transmitting the coded burst signal coded with a code from the ultrasonic transducer.

12. The method of claim 8, wherein the ultrasonic transducer is a first ultrasonic transducer, the method further comprising transmitting the code-encoded encoded burst signal from a second ultrasonic transducer.

13. An ultrasonic detection system comprising: an excitation circuit configured to induce an ultrasonic transducer to transmit a code-encoded encoded burst signal, the encoded burst signal being an acoustic signal; a listening circuit configured to receive a reflected code-encoded encoded burst signal from the ultrasonic transducer or another ultrasonic transducer; a time-varying template generator configured to generate a time-varying encoded receive template characterizing the code based on a time index, the time index based on a time of receipt of the reflected encoded burst signal relative to a start of transmission of the encoded burst signal; a correlator coupled to the listening circuit and the time-varying template generator, the correlator configured to correlate the reflected encoded burst signal with the time-varying encoded receive template to produce a correlation signal; and a time-of-flight circuit coupled to the correlator, the time-of-flight circuit configured to compute a time-of-flight of the reflected encoded burst signal based on the correlation signal.

14. The system of claim 13, wherein the time-varying template generator is further configured to generate the time-varying encoded receive template based on a full-length template, the full-length template generated by sampling an acoustic output of the encoded burst signal including a period of transducer ringdown after an end of the encoded burst signal.

15. The system of claim 13, further comprising a time-varying gain multiplier coupled between the correlator and the time-of-flight circuit, the time-varying gain multiplier configured to adjust a gain of the correlation signal based on the time index.

16. The system of claim 13, the time-varying template generator generating the time-varying encoded receive template further based on a programmable blind zone duration parameter indicative of a period of transducer ringdown after an end of the encoded burst signal.

17. The system of claim 14, wherein generating the time-varying encoded receive template comprises subsampling the full-length template.

18. An ultrasonic detection system comprising: an excitation circuit configured to induce an ultrasonic transducer to transmit a code-encoded encoded burst signal, the encoded burst signal being an acoustic signal; a listening circuit configured to receive a reflected code-encoded encoded burst signal from the ultrasonic transducer or another ultrasonic transducer; a time-varying template generator configured to generate a time-varying encoded receive template characterizing the code based on a time index, the time index based on a time of receipt of the reflected encoded burst signal relative to a start of transmission of the encoded burst signal; a correlator coupled to the listening circuit and the time-varying template generator, the correlator configured to correlate the reflected encoded burst signal with the time-varying encoded receive template to produce a correlation signal; and a time-of-flight circuit coupled to the correlator, the time-of-flight circuit configured to compute a time-of-flight of the reflected encoded burst signal based on the correlation signal. a time-of-flight circuit coupled to the correlator, the time-of-flight circuit configured to determine a time-of-flight of the reflected coded burst signal based on the correlation signal; and a time-varying gain multiplier coupled between the correlator and the time-of-flight circuit, the time-varying gain multiplier configured to adjust a gain of the correlation signal based on the time index.

19. The system of claim 18, wherein the time-varying template generator generates the time-varying coded receive template further based on a programmable blind duration parameter indicative of a time period of a transducer ringdown after an end of the coded burst signal.

20. The system of claim 18, wherein the time-varying gain multiplier is further configured to adjust the gain of the correlation signal based on a length of the coded burst signal and a length of the time-varying coded receive template.

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