Signal processing device, acoustic wave system, and vehicle

Abstract

This signal processing device is configured to output to an acoustic wave transmitting device, via a transformer, a transmission signal for transmitting an acoustic wave. The signal processing device includes a resonance frequency measuring unit. The resonance frequency measuring unit is configured to obtain a resonant frequency of the acoustic wave transmitting device from at least one of a first frequency at which the amplitude of a secondary voltage of the transformer is minimum when the frequency of the transmission signal is being down-chirped, and a second frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is being up-chirped.

Description

Signal processing device, acoustic wave system, and vehicle

[0001] The invention disclosed in this specification relates to a signal processing device that processes a transmission signal for transmitting a sound wave, a sound wave system including the signal processing device, and a vehicle including the sound wave system.

[0002] Conventionally, ultrasonic systems have been known that measure the distance to an obstacle by measuring the time of flight (TOF) between when an ultrasonic wave is emitted and when the reflected wave returns from the obstacle. Such ultrasonic systems are often installed in vehicles, and an example of such an ultrasonic system is an in-vehicle clearance sonar (see, for example, Patent Document 1).

[0003] International Publication No. 2020 / 004609

[0004] In an ultrasonic system, the sound pressure of the transmitted wave attenuates as the frequency of the transmitted wave signal deviates from the resonant frequency of the ultrasonic transmitter, so transmitting waves at a high sound pressure requires transmitting waves at the resonant frequency. Since the resonant frequency of an ultrasonic transmitter depends on the ultrasonic transmitter, it is necessary to measure the resonant frequency of the ultrasonic transmitter for each ultrasonic system.

[0005] The signal processing device disclosed in this specification is configured to output a transmission signal for transmitting sound waves to an acoustic wave transmitting device via a transformer. The signal processing device includes a resonant frequency measurement unit. The resonant frequency measurement unit is configured to determine the resonant frequency of the acoustic wave transmitting device from at least one of a first frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is down-chirped and a second frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is up-chirped.

[0006] The sonic system disclosed in this specification is configured to include the signal processing device configured as described above, the transformer, and the sonic transmitting device.

[0007] The vehicle disclosed in this specification is configured to include the sonic system configured as described above.

[0008] The signal processing device, sonic system, and vehicle disclosed herein allow for the measurement of the resonant frequency of a sonic transmitting device.

[0009] Fig. 1 is a diagram schematically showing a vehicle equipped with an ultrasonic system according to an embodiment and an object. Fig. 2 is a diagram showing the configuration of the ultrasonic system according to an embodiment. Fig. 3 is a diagram showing an equivalent circuit of an ultrasonic transmission device. Fig. 4 is a diagram showing the waveform of the secondary voltage of a transformer when the frequency of a transmission signal is down-chirped. Fig. 5 is a diagram showing the waveform of the secondary voltage of a transformer when the frequency of a transmission signal is up-chirped. Fig. 6 is a diagram showing the configuration of an ultrasonic system according to a modified example.

[0010] The following describes embodiments with reference to the drawings. The ultrasonic system according to the embodiments described below is intended to be mounted on a vehicle, for example, and can be used for alarm functions, automatic braking functions, automatic parking functions, etc., by measuring the distance between the vehicle and an object.

[0011] 1 is a schematic diagram showing a vehicle 200 equipped with an ultrasonic system 100 according to an embodiment, and an object (obstacle) 300. Ultrasonic waves transmitted from the ultrasonic system 100 according to an embodiment are reflected by the object 300 and received as reflected waves by the ultrasonic system 100 according to an embodiment. At this time, the ultrasonic system 100 also receives environmental noise N. The environmental noise N includes ultrasonic waves (other waves) transmitted from other ultrasonic systems.

[0012] FIG. 2 is a diagram showing the configuration of an ultrasound system 100 according to an embodiment.

[0013] The ultrasound system 100 includes a signal processing device 1, a transformer Tr, capacitors C1 and C2, and an ultrasound transmitting device 2. The ultrasound transmitting device 2 is externally connected to the signal processing device 1 via the transformer Tr and the capacitors C1 and C2.

[0014] The signal processing device 1 is a semiconductor integrated circuit device and includes a DAC (Digital to Analog Converter) 11, a driver 12, an LNA (Low Noise Amplifier) ​​13, a PGA (Programmable Gain Amplifier) ​​14, an ADC (Analog to Digital Converter) 15, a digital processing unit 16, an attenuation unit ATT1, a selector SEL1, and external terminals T1 to T7.

[0015] The DAC 11 converts the digital wave signal output from the transmission wave signal generating unit 161 included in the digital processing unit 16 from a digital signal to an analog signal, and outputs the D / A converted signal to the driver 12 .

[0016] The output terminals of the differential pair of the driver 12 are connected to the primary side of a transformer Tr via external terminals T1 and T2. The secondary side of the transformer Tr is connected to the ultrasonic transmission device 2. The driver 12 drives the ultrasonic transmission device 2 based on the output signal of the DAC 11.

[0017] The ultrasonic transmitting device 2 has a piezoelectric element (not shown) and transmits and receives ultrasonic waves. In other words, the ultrasonic transmitting device 2 is an ultrasonic transmitting / receiving device that functions as both a sound source and a receiver. The ultrasonic transmitting device 2 may have a common piezoelectric element for transmitting and receiving waves, or may have a piezoelectric element dedicated to transmitting and a piezoelectric element dedicated to receiving waves. FIG. 3 is a diagram showing an equivalent circuit of the ultrasonic transmitting device 2. The equivalent circuit of the ultrasonic transmitting device 2 includes a capacitor 21, a resistor 22, an inductor 23, and a capacitor 24. A first end of the capacitor 21 and a first end of the resistor 22 are connected to a first end of a secondary winding of a transformer Tr. A second end of the resistor 22 is connected to a first end of the inductor 23. A second end of the inductor 23 is connected to a first end of the capacitor 24. A second end of the capacitor 21 and a second end of the capacitor 24 are connected to a second end of the secondary winding of the transformer Tr.

[0018] The input terminals of the differential pair of the LNA 13 are connected to the secondary side of the transformer Tr via external terminals T3 and T4 and capacitors C1 and C2. The LNA 13 amplifies the differential signal received from the external terminals T3 and T4, converts it to a single-ended signal, and outputs it to the PGA 14. The LNA 13 also performs clipping to prevent the single-ended signal from exceeding a predetermined level. The PGA 14 amplifies the signal received from the LNA 13 and outputs it to the ADC 15 via the selector SEL1. The ADC 15 A / D converts the output signal of the PGA 14 from an analog signal to a digital signal, and outputs the A / D converted signal to the BPF 162 and the resonant frequency measurement unit 168. The sampling frequency of the ADC 15 is higher than the frequency of the transmission signal.

[0019] The selector SEL1 selects the output signal of the PGA 14 and supplies it to the ADC 15 when the signal processing device 1 is in a mode for receiving ultrasonic waves, and selects the output signal of the attenuation unit ATT1 and supplies it to the ADC 15 when the signal processing device 1 is in a mode for measuring the resonant frequency.

[0020] The digital processing unit 16 includes a transmission signal generating unit 161, a BPF (Band Pass Filter) 162, an ABS (Absolute value processing unit) 163, an envelope unit 164, a lower threshold determining unit 165, a TOF measuring unit 166, an interface 167, and a resonant frequency measuring unit 168.

[0021] The transmission signal generating unit 161 is configured to generate a transmission signal for transmitting ultrasonic waves. More specifically, when the transmission signal generating unit 161 receives a wave transmission command from an ECU (Electronic Control Unit) (not shown) mounted on the vehicle 200 (see FIG. 1 ) via the interface 167, the transmission signal generating unit 161 generates a transmission signal including a predetermined number of waves and outputs the transmission signal to the DAC 11.

[0022] The BPF 162 passes only a predetermined frequency band of the output signal from the ADC 15 and attenuates frequency bands other than the predetermined frequency band. The BPF 162 has frequency characteristics according to the frequency setting of the transmission signal. For example, the predetermined frequency band is set to match the frequency band of the transmission signal. Since the frequency band of the environmental noise N is highly likely to differ from the frequency band of the transmission signal, the BPF 162 can basically remove the environmental noise N.

[0023] The ABS 163 performs absolute value processing on the output signal of the BPF 162. That is, the ABS 163 performs inversion processing on the negative output signal of the BPF 162 to convert it into a positive signal.

[0024] The envelope section 164 outputs a signal obtained by detecting the envelope of the output signal of the ABS 163 .

[0025] The lower threshold determination unit 165 compares the output signal of the envelope unit 164 with the lower threshold. The lower threshold determination unit 165 detects a reflected wave from the object 300 when the output signal of the envelope unit 164 becomes larger than the lower threshold.

[0026] The TOF measurement unit 166 uses the counter 166A to measure the time (TOF) from when an ultrasonic wave is transmitted until when a reflected wave reflected by the object 300 is received.

[0027] The interface 167 is compliant with, for example, LIN (Local Interconnect Network) and communicates with an ECU (not shown) mounted on the vehicle 200 (see FIG. 1) via an external terminal T5.

[0028] The input terminals of the differential pair of the attenuation unit ATT1 are connected to the secondary side of the transformer Tr via external terminals T6 and T7. The attenuation unit ATT1 attenuates the amplitude of the differential signal received from the external terminals T6 and T7, converts it to a single-ended signal, and outputs it to the ADC 15 via the selector SEL1. The ADC 15 A / D converts the output signal of the PGA 14 from an analog signal to a digital signal, and outputs the A / D converted signal to the BPF 162 and the resonant frequency measurement unit 168. The provision of the attenuation unit ATT1 makes it possible to measure the amplitude of the secondary side voltage of the transformer Tr without increasing the withstand voltage of the digital processing unit 16.

[0029] Here, the operation of the signal processing device 1 when it is in a mode for measuring the resonance frequency will be described.

[0030] The transmission signal generator 161 down-chirps the frequency of the transmission signal. For example, the transmission signal generator 161 reduces the frequency of the transmission signal from 63 kHz to 51 kHz at equal intervals for each pulse, outputting a transmission signal of 64 pulses. At this time, the waveform of the secondary voltage of the transformer Tr becomes as shown in the upper diagram of FIG. 4 .

[0031] The equivalent circuit of the ultrasonic transmission device 2 (see FIG. 3) has a complex impedance. This complex impedance is minimized at the resonant frequency of the ultrasonic transmission device 2. When the complex impedance of the equivalent circuit of the ultrasonic transmission device 2 is minimized, the secondary voltage of the transformer Tr is also minimized. Therefore, the resonant frequency measurement unit 168 measures the amplitude of the secondary voltage of the transformer Tr for each frequency of the transmission signal.

[0032] However, the ultrasonic transmission device 2 has poor tracking ability, and the vibration of the ultrasonic transmission device 2 follows the frequency of the transmission signal with a delay. Therefore, when the amplitude of the secondary voltage of the transformer Tr shown in Fig. 4 is minimum, the frequency of the transmission signal becomes a value slightly smaller than the resonant frequency of the ultrasonic transmission device 2 (55.35 kHz in the example shown in Fig. 4).

[0033] Next, the transmission signal generator 161 up-chirps the frequency of the transmission signal. For example, the transmission signal generator 161 increases the frequency of the transmission signal from 51 kHz to 63 kHz at equal intervals for each pulse, outputting a transmission signal of 64 pulses. At this time, the waveform of the secondary voltage of the transformer Tr becomes as shown in the upper diagram of FIG. 5 .

[0034] The equivalent circuit of the ultrasonic transmission device 2 (see FIG. 3) has a complex impedance. This complex impedance is minimized at the resonant frequency of the ultrasonic transmission device 2. When the complex impedance of the equivalent circuit of the ultrasonic transmission device 2 is minimized, the secondary voltage of the transformer Tr is also minimized. Therefore, the resonant frequency measurement unit 168 measures the amplitude of the secondary voltage of the transformer Tr for each frequency of the transmission signal.

[0035] However, the ultrasonic transmission device 2 has poor tracking ability, and the vibration of the ultrasonic transmission device 2 follows the frequency of the transmission signal with a delay. Therefore, when the amplitude of the secondary voltage of the transformer Tr shown in Fig. 5 is minimum, the frequency of the transmission signal becomes a value slightly larger than the resonant frequency of the ultrasonic transmission device 2 (58.02 kHz in the example shown in Fig. 5).

[0036] The resonant frequency measurement unit 168 calculates the resonant frequency of the ultrasonic transmission device 2 from the average of a first frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is down-chirped, and a second frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is up-chirped. Specifically, the resonant frequency measurement unit 168 calculates the resonant frequency of the ultrasonic transmission device 2 as the simple average (56.68 kHz = (55.35 kHz + 58.02 kHz) / 2 in the example shown in Figures 4 and 5) of the first frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is down-chirped and the second frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is up-chirped.

[0037] In this embodiment, the transmission signal generating unit 161 sets the frequency change rate in the down-chirp to be the same as the frequency change rate in the up-chirp.

[0038] The above-described averaging process in the resonant frequency measuring unit 168 virtually cancels out the tracking delay of the ultrasonic wave transmitting device 2, improving the measurement accuracy of the resonant frequency of the ultrasonic wave transmitting device 2.

[0039] Unlike the present embodiment, the resonant frequency measurement unit 168 may determine a weighted average of a first frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is down-chirped, and a second frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is up-chirped, as the resonant frequency of the ultrasonic transmission device 2. The weighted average is useful when the tracking delay of the ultrasonic transmission device 2 differs between down-chirping and up-chirping.

[0040] Examples of cases in which the tracking delay of the ultrasonic transmission device 2 differs between down-chirp and up-chirp include when the transmission signal generation unit 161 sets the frequency change rate for down-chirp and the frequency change rate for up-chirp to be different from each other, when the surrounding environment is significantly different between down-chirp and up-chirp, etc. In such cases, the resonant frequency measurement unit 168 can calculate a weighted average.

[0041] In this embodiment, the ADC 15 is shared between a mode in which the signal processing device 1 receives ultrasonic waves and a mode in which the signal processing device 1 measures the resonance frequency. However, as in a modified example shown in Fig. 6, the signal processing device 1 may be configured without the selector SEL1, and may include an ADC 15 dedicated to the mode in which the signal processing device 1 receives ultrasonic waves and an ADC 15' dedicated to the mode in which the signal processing device 1 measures the resonance frequency.

[0042] <Others> In addition to the above-described embodiments, various modifications can be made to the configuration of the present invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0043] In the above embodiment, the ultrasonic system 100 that transmits ultrasonic waves (sound waves with a high frequency exceeding audible sound) has been described, but the present invention can also be applied to an ultrasonic system that transmits sound waves other than ultrasonic waves.

[0044] In the above embodiment, the resonant frequency measurement unit 168 calculates the resonant frequency of the ultrasonic transmission device 2 from the average of a first frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is down-chirped, and a second frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is up-chirped. However, the resonant frequency measurement unit 168 may calculate the resonant frequency of the ultrasonic transmission device 2 from either the first frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is down-chirped, or the second frequency at which the amplitude of the secondary voltage of the transformer Tr is minimum when the frequency of the transmission signal is up-chirped.

[0045] When determining the resonant frequency of the ultrasonic transmitting device 2 from either the first frequency or the second frequency, the resonant frequency measurement unit 168 may estimate the tracking delay of the ultrasonic transmitting device 2 from an output signal of a sensor configured to detect the surrounding environment. This is because the tracking delay of the ultrasonic transmitting device 2 is determined by the circuit constants of the equivalent circuit of the ultrasonic transmitting device 2, but the circuit constants of the equivalent circuit of the ultrasonic transmitting device 2 vary depending on the surrounding environment of the ultrasonic transmitting device 2. An example of a sensor configured to detect the surrounding environment is a temperature sensor configured to detect the surrounding temperature. The sensor configured to detect the surrounding environment may be built into the signal processing device 1 or may be externally connected to the signal processing device 1. However, since installing the sensor configured to detect the surrounding environment near the ultrasonic transmitting device 2 improves the estimation accuracy of the tracking delay of the ultrasonic transmitting device 2, it is desirable to install the sensor configured to detect the surrounding environment near the ultrasonic transmitting device 2.

[0046] <Supplementary Note> Supplementary notes are provided for the present disclosure, the specific configuration examples of which have been shown in the above-described embodiments.

[0047] The signal processing device (1) of the present disclosure is a signal processing device configured to output a transmission signal for transmitting sound waves to an acoustic wave transmitting device (2) via a transformer (Tr), and is equipped with a resonant frequency measuring unit (168), and the resonant frequency measuring unit is configured to determine the resonant frequency of the acoustic wave transmitting device from at least one of a first frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is down-chirped, and a second frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is up-chirped (first configuration).

[0048] In the signal processing device of the first configuration described above, the resonant frequency measuring unit may be configured to calculate the resonant frequency of the ultrasonic transmitting device from the average of the first frequency and the second frequency (second configuration).

[0049] In the signal processing device of the second configuration, the average may be a simple average of the first frequency and the second frequency (third configuration).

[0050] The signal processing device of the third configuration may be configured (fourth configuration) such that the rate of frequency change in the down-chirp and the rate of frequency change in the up-chirp are the same.

[0051] In the signal processing device of the second configuration, the average may be a weighted average of the first frequency and the second frequency (fifth configuration).

[0052] The signal processing device of the fifth configuration may be configured (sixth configuration) such that the rate of change of frequency in the down-chirp and the rate of change of frequency in the up-chirp are different from each other.

[0053] In the signal processing device of the first configuration described above, the resonant frequency measuring unit may be configured to determine the resonant frequency of the ultrasonic transmitting device from either the first frequency or the second frequency and an output signal of a sensor configured to detect the surrounding environment (seventh configuration).

[0054] The signal processing device of any one of the first to seventh configurations may be configured (eighth configuration) to include an attenuation unit (ATT1) configured to attenuate the secondary voltage of the transformer.

[0055] The sonic system (100) of the present disclosure has a configuration (ninth configuration) including a signal processing device of any one of the first to eighth configurations, the transformer, and the sonic transmitting device.

[0056] The vehicle (200) of the present disclosure has a configuration (tenth configuration) that includes the sonic system of the ninth configuration described above.

[0057] REFERENCE SIGNS LIST 1 Signal processing device 2 Ultrasonic transmission device 11 DAC 12 Driver 13 LNA 14 PGA 15, 15' ADC 16 Digital processing unit 161 Transmission signal generation unit 162 BPF 163 ABS 164 Envelope unit 165 Lower threshold determination unit 166 TOF measurement unit 166A Counter 167 Interface 168 Resonance frequency measurement unit 100 Ultrasonic system according to embodiment 200 Vehicle 300 Object (obstacle) ATT1 Attenuation unit C1, C2 Capacitor SEL1 Selector T1 to T7 External terminal Tr Transformer

Claims

1. A signal processing device configured to output a transmission signal for transmitting an acoustic wave to an acoustic wave transmitting device via a transformer, A resonance frequency measuring unit is provided, The resonance frequency measurement unit a first frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is down-chirped; a second frequency at which the amplitude of the secondary voltage of the transformer is minimum when the frequency of the transmission signal is up-chirped.

2. The signal processing device according to claim 1 , wherein the resonant frequency measurement unit is configured to obtain the resonant frequency of the acoustic wave transmitting device from an average of the first frequency and the second frequency.

3. The signal processing device according to claim 2 , wherein the average is a simple average of the first frequency and the second frequency.

4. The signal processing device according to claim 3 , wherein a frequency change rate in the down-chirp is the same as a frequency change rate in the up-chirp.

5. The signal processing device according to claim 2 , wherein the average is a weighted average of the first frequency and the second frequency.

6. The signal processing device according to claim 5 , wherein a frequency change rate in the down-chirp and a frequency change rate in the up-chirp are different from each other.

7. 2. The signal processing device according to claim 1, wherein the resonant frequency measurement unit is configured to determine the resonant frequency of the acoustic wave transmitting device from either the first frequency or the second frequency and an output signal of a sensor configured to detect a surrounding environment.

8. The signal processing device according to claim 1 , further comprising an attenuation unit configured to attenuate a secondary voltage of the transformer.

9. A signal processing device according to any one of claims 1 to 8; The transformer; and the acoustic wave transmitting device.

10. A vehicle comprising the sonic system of claim 9.