Ultra-low frequency sensor

Abstract

The utility model discloses a kind of ultralow frequency sensors, including vibration detection unit, power supply voltage stabilizing unit and signal conditioning unit, the power supply voltage stabilizing unit is equipped with low-dropout linear voltage regulator U20, voltage converter U19 and negative voltage stabilizer U21, the low-dropout linear voltage regulator U20 is stabilized as positive power supply VCC with external power supply;The voltage converter U19 converts external power supply positive voltage into negative voltage, and stable negative power supply VEE is exported by negative voltage stabilizer;The positive power supply VCC and negative power supply VEE are powered for signal conditioning unit;The signal conditioning unit includes high common-mode rejection differential amplifier, differential to single-ended amplifier, band-pass filter and differential output driver, the differential signal output by the vibration detection unit is successively output differential voltage signal after high common-mode rejection differential amplifier, differential to single-ended amplifier, band-pass filter, differential output driver, the utility model has the advantages of stability and reliability etc.

Description

Technical Field

[0001] This utility model relates to the field of earthquake monitoring and geophysical exploration technology, specifically an ultra-low frequency sensor. Background Technology

[0002] In fields such as earthquake monitoring and geophysical exploration, the requirements for measuring ground vibration signals are increasing, especially for high-sensitivity and high-stability detection in the ultra-low frequency band. Currently, moving-coil magneto-electric velocity sensors are widely used as vibration detection units in this field. However, the natural frequency of this type of sensor is usually designed to be above several Hz. When the measured frequency is close to or lower than its natural frequency, its sensitivity will drop sharply, making it impossible to effectively measure weak vibration signals in the lower frequency band. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide an ultra-low frequency sensor with high stability and reliability.

[0004] The technical solution adopted by this utility model to solve its technical problem is: An ultra-low frequency sensor is characterized by comprising a vibration detection unit, a power supply and voltage regulation unit, and a signal conditioning unit. The power supply and voltage regulation unit is equipped with a low-dropout linear regulator U20, a voltage converter U19, and a negative voltage regulator U21. The low-dropout linear regulator U20 stabilizes the external power supply to a positive power supply VCC. The voltage converter U19 converts the positive voltage of the external power supply into a negative voltage, and outputs a stable negative power supply VEE through a negative voltage regulator; The positive power supply VCC and the negative power supply VEE power the signal conditioning unit. The signal conditioning unit includes a high common-mode rejection differential amplifier, a differential-to-single-ended amplifier, a bandpass filter, and a differential output driver. The differential signal output by the vibration detection unit is sequentially passed through the high common-mode rejection differential amplifier, the differential-to-single-ended amplifier, the bandpass filter, and the differential output driver to output a differential voltage signal. The power supply regulator and signal conditioning unit work together to achieve high-quality extraction and reliable transmission of ultra-low frequency signals. The power supply regulator generates high-quality, stable, and low-noise dual positive and negative power supplies, providing a stable and clean voltage for the signal conditioning unit, thereby reducing additional noise and drift introduced by the power supply at the source. The signal conditioning unit is configured to suppress transmission common-mode noise at the source through a high common-mode rejection differential amplifier, convert the differential signal into a ground-referenced single-ended signal that is easy for subsequent circuits to process through a differential-to-single-ended amplifier, and then accurately filter out DC drift, ultra-low frequency drift, and high-frequency interference through a bandpass filter. Finally, the processed high-quality single-ended signal is converted into a differential signal with strong anti-interference capability for output through a differential output driver. This multi-stage collaborative operation ensures that weak vibration signals can be effectively amplified, extracted, and reliably transmitted without being drowned out by noise, effectively avoiding dynamic range compression, and ultimately achieving high sensitivity, high stability, and high reliability detection of the sensor in the ultra-low frequency band.

[0005] The input pin and enable pin of the low dropout linear regulator U20 described in this utility model are connected to an external power supply, the grounding pin is grounded, and the output pin is connected to the positive power supply VCC through resistor R1. The input pin of the low-dropout linear regulator U20 is grounded via parallel capacitors C147 and C149, and the output pin is grounded via parallel capacitors C148 and C150 to generate a stable voltage.

[0006] The input pin of the voltage converter U19 described in this utility model is connected to an external power supply and grounded through capacitor C151. The grounding pin is grounded. A flying capacitor C60 is connected between the positive and negative pins of the flying capacitor. The output pin is grounded through capacitor C61. The negative voltage input pin of the negative voltage regulator U21 is connected to the output pin of U19 via parallel capacitors C156 and C158. The negative power supply reference ground pin is connected to the output pin of U19. The negative voltage output pin is connected to the negative power supply VEE via parallel capacitors C159 and C157 and then via resistor R65. The output pin of U19 is connected to the junction of capacitors C159 and C157 and resistor R65. U19 and U21 work together to convert the positive voltage into a stable negative voltage to provide a high-quality negative power supply for the signal conditioning unit.

[0007] The high common-mode rejection differential amplifier of this invention includes operational amplifiers U28.1 and U28.2. The positive power supply pins of U28.1 and U28.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. The inverting input pin of U28.1 is connected to the inverting terminal of the differential voltage output by the vibration detection unit, and the non-inverting input pin of U28.2 is connected to the non-inverting terminal of the differential voltage output by the vibration detection unit. The output pin of U28.1 is connected in series with resistor R69 and gain resistor R. g Resistor R71 is connected to the output pin of U28.2; The output pin of U28.2 is grounded via resistors R72 and R75 connected in series. The non-inverting input pin of U28.1 is connected to resistor R69 and gain resistor R. g At the node, the inverting input pin of U28.2 is connected to resistor R71 and gain resistor R. g At the node; U28.1 and U28.2 work together to form a cross-coupled differential amplifier, providing an extremely high common-mode rejection ratio to resist environmental interference and initially amplify the weak differential signal output by the vibration detection unit.

[0008] The resistors R69 and R71 described in this invention have the same resistance value. The gain of the amplifier is determined by the formula G=1+2*R69 / Rg. By changing the value of the gain resistor Rg, the amplification factor of the entire preamplifier can be easily adjusted. Resistors R69 and R71 together with the gain resistor Rg form a gain setting network.

[0009] The differential-to-single-ended amplifier of this invention includes an operational amplifier U27, whose positive power supply pin is connected to the positive power supply VCC and negative power supply pin is connected to the negative power supply VEE. The inverting input pin of U27 is connected to the output pin of U28.1 via resistor R70, and the end of resistor R70 away from the output pin of U28.1 is connected to the output pin of U27 via resistor R74. The non-inverting input pin of U27 is connected to the output pin of U28.2 via resistor R72, and the end of resistor R72 away from the output pin of U28.2 is grounded via resistor R75; U27, as the second-stage differential amplifier, converts the two differential signals output from the first-stage amplifier into a single-ended output signal with ground as the reference point.

[0010] The bandpass filter of this utility model includes operational amplifiers U23.1 and U23.2. The positive power supply pins of U23.1 and U23.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. The non-inverting input pin of U23.1 is grounded, and the inverting input pin is connected to the output pin of U27 via resistor R82. The inverting input pin of U23.1 is connected to the output pin via resistor R59. At the same time, the inverting input pin is connected to the output pin via capacitor C152 and R83 in series. The output pin of U23.1 is connected to the non-inverting input pin of U23.2 via capacitor C154, and the non-inverting input pin of U23.2 is grounded via resistor R56; The inverting input pin of U23.2 is directly connected to the output pin, and is also connected to the output pin via capacitor C166; U23.1 and U23.2 work together. U23.1 inverts and amplifies the signal from U27 and filters out unwanted high-frequency noise. Capacitor C154 and resistor R56 work together to effectively filter out DC offset and extremely low-frequency drift. U23.2 acts as a voltage follower, providing isolation buffer and driving capability for the filter network. Working together, they precisely shape the frequency response of the system, ensuring that only useful signals within the target frequency band are extracted and output, greatly improving the signal-to-noise ratio and dynamic range.

[0011] The differential output driver of this utility model includes operational amplifier U30 and operational amplifier U22. The positive power supply pin of U30 is connected to the positive power supply VCC, and the negative power supply pin is connected to the negative power supply VEE. The non-inverting input pin of U30 is grounded; The inverting input pin of U30 is connected to the output pin of U23.2 via resistor R85; The inverting input pin of the U30 is connected to the output pin via resistor R60, and is also connected to the output pin via capacitor C153 and resistor R84 in series. The output pin of U30 is connected to the positive differential output pin via capacitor C155, and the end of capacitor C155 away from the output pin of U30 is grounded via resistor R57. The positive power supply pin of U22 is connected to the positive power supply VCC, and the negative power supply pin is connected to the negative power supply VEE. The non-inverting input terminal of U22 is grounded via capacitor C160, and is connected to the junction of capacitor C155 and resistor R57 via series resistors R67 and R66. The inverting input pin of U22 is directly connected to the output pin, and the inverting input pin is connected to the junction of resistor R66 and resistor R67 via capacitor C161. The output pin of U22 is connected to the negative differential output pin; U22 and U30 work together to convert the single-ended signal output from the front-end bandpass filter into a differential signal with a high common-mode rejection ratio, greatly enhancing the anti-interference capability and reliability of the output signal during long-distance transmission.

[0012] In this invention, the resistors R70, R74, R72, and R75 have equal resistance values; and the resistors R66 and R67 have equal resistance values.

[0013] The positive power supply VCC pin of the high common-mode rejection differential amplifier, differential-to-single-ended amplifier, bandpass filter, and differential output driver described in this invention is grounded via parallel capacitors, and the negative power supply VEE pin is grounded via parallel capacitors; this is used to filter out ripple and ensure the stability of the provided positive and negative power supplies.

[0014] The beneficial effects of this invention are as follows: the cooperation between the power supply regulator unit and the signal conditioning unit jointly achieves high-quality extraction and reliable transmission of ultra-low frequency signals; the power supply regulator unit generates high-quality, stable, and low-noise positive and negative dual power supplies, providing a stable and clean voltage for the signal conditioning unit, thereby reducing additional noise and drift introduced by the power supply from the source; the signal conditioning unit, through a high common-mode rejection differential amplifier, suppresses transmission common-mode noise at the source, converts the differential signal into a ground-referenced single-ended signal that is easy for subsequent circuits to process through a differential-to-single-ended amplifier, and then accurately filters out DC drift, ultra-low frequency drift, and high-frequency interference through a bandpass filter, and finally converts the processed high-quality single-ended signal into a differential signal with strong anti-interference capability for output through a differential output driver. This multi-stage collaborative work ensures that weak vibration signals can be effectively amplified, extracted, and reliably transmitted without being drowned out by noise, effectively avoiding dynamic range compression, and ultimately achieving high sensitivity, high stability, and high reliability detection of the sensor in the ultra-low frequency band. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the power supply voltage regulator unit circuit.

[0016] Figure 2 This is a schematic diagram of the positive and negative power supply filtering circuits of the signal conditioning unit.

[0017] Figure 3 This is a schematic diagram of the signal conditioning unit circuit.

[0018] Figure 4 yes Figure 3 A schematic diagram of the circuit in which U28.1, U28.2, and U27 work together.

[0019] Figure 5 yes Figure 3 A schematic diagram of the circuit where U23.1 and U23.2 work together.

[0020] Figure 6 yes Figure 3 Schematic diagram of the circuit where U30 and U22 work together.

[0021] Figure 7 This is the measured sensitivity curve of the sensor. Detailed Implementation

[0022] The present invention will now be described in conjunction with the accompanying drawings and embodiments.

[0023] An ultra-low frequency sensor includes a vibration detection unit, a power supply and voltage regulation unit, and a signal conditioning unit. The power supply and voltage regulation unit is equipped with a low-dropout linear regulator U20, a voltage converter U19, and a negative voltage regulator U21. The low-dropout linear regulator U20 stabilizes the external power supply to a positive power supply VCC. The voltage converter U19 converts the positive voltage of the external power supply into a negative voltage, and outputs a stable negative power supply VEE through a negative voltage regulator; The positive power supply VCC and the negative power supply VEE power the signal conditioning unit. The signal conditioning unit includes a high common-mode rejection differential amplifier, a differential-to-single-ended amplifier, a bandpass filter, and a differential output driver. The differential signal output by the vibration detection unit is sequentially passed through the high common-mode rejection differential amplifier, the differential-to-single-ended amplifier, the bandpass filter, and the differential output driver to output a differential voltage signal. The power supply regulator and signal conditioning unit work together to achieve high-quality extraction and reliable transmission of ultra-low frequency signals. The power supply regulator generates high-quality, stable, and low-noise dual positive and negative power supplies, providing a stable and clean voltage for the signal conditioning unit, thereby reducing additional noise and drift introduced by the power supply at the source. The signal conditioning unit is configured to suppress transmission common-mode noise at the source through a high common-mode rejection differential amplifier, convert the differential signal into a ground-referenced single-ended signal that is easy for subsequent circuits to process through a differential-to-single-ended amplifier, and then accurately filter out DC drift, ultra-low frequency drift, and high-frequency interference through a bandpass filter. Finally, the processed high-quality single-ended signal is converted into a differential signal with strong anti-interference capability for output through a differential output driver. This multi-stage collaborative operation ensures that weak vibration signals can be effectively amplified, extracted, and reliably transmitted without being drowned out by noise, effectively avoiding dynamic range compression, and ultimately achieving high sensitivity, high stability, and high reliability detection of the sensor in the ultra-low frequency band.

[0024] As attached Figure 1 As shown, the input pin (VIN pin) and enable pin (CE pin) of the low dropout linear regulator U20 are connected to an external power supply, the ground pin (VSS pin) is grounded, and the output pin (VOUT pin) is connected to the positive power supply VCC through resistor R1. The input pin (VIN pin) of the low-dropout linear regulator U20 is grounded via parallel capacitors C147 and C149, and the output pin (VOUT pin) is grounded via parallel capacitors C148 and C150 to generate a stable voltage.

[0025] In this embodiment, capacitors C147 and C148 have a capacitance of 10 uF, and capacitors C149 and C150 have a capacitance of 1 uF. The combination of capacitors C147 and C149 achieves input filtering to ensure a clean and stable input voltage, while the combination of capacitors C148 and C150 achieves output filtering to ensure a clean and stable output voltage.

[0026] In this embodiment, resistor R1 has a resistance of 0Ω, which is used to facilitate circuit debugging and testing and as a reserved design feature.

[0027] In this embodiment, the low-dropout linear regulator U20 is model ME6212C50M5G.

[0028] The input pin (IN pin) of the voltage converter U19 is connected to an external power supply and grounded through capacitor C151. The ground pin (GND pin) is grounded. A flying capacitor C60 is connected between the positive pin (CFLY+) and the negative pin (CFLY-) of the flying capacitor. The output pin is grounded through capacitor C61. The negative voltage input pin (-VIN pin) of the negative voltage regulator U21 is connected to the output pin of U19 via parallel capacitors C156 and C158. The negative power supply reference ground pin (VSS pin) is connected to the output pin (OUT pin) of U19. The negative voltage output pin (-VOUT pin) is connected to the negative power supply VEE via parallel capacitors C159 and C157 and then via resistor R65. The output pin (OUT pin) of U19 is connected to the junction of capacitors C159 and C157 and resistor R65. U19 and U21 work together to convert the positive voltage into a stable negative voltage to provide a high-quality negative power supply for the signal conditioning unit.

[0029] In this embodiment, capacitor C60 has a capacitance of 1uF. The internal switch of the chip controls the flying capacitor C60 to switch between charging and discharging states, thus reversing the input voltage. Capacitor C151 has a capacitance of 1uF and performs input filtering to suppress current surges and noise from the input power supply. Capacitor C61 has a capacitance of 1uF and is used for output filtering to stabilize the original negative voltage generated by the voltage converter. Capacitors C156 and C157 have a capacitance of 10uF, while capacitors C158 and C159 have a capacitance of 1uF. Capacitors C156 and C158 work together to achieve input filtering, providing U21 with a low-impedance path from low frequency to high frequency, ensuring that the power supply remains stable and clean at different frequencies. The parallel connection of C159 and C157 achieves output filtering, providing the subsequent signal conditioning unit with a high-quality negative power supply VEE with extremely low output impedance from low frequency to high frequency.

[0030] In this embodiment, resistor R56 has a resistance of 0Ω, which is used to facilitate circuit debugging and testing and as a reserved design feature.

[0031] In this embodiment, the voltage converter U19 is model TPS60400DBVR; the negative voltage regulator U21 is model XC62KN3302PR-G.

[0032] In this embodiment, a connector CN6 is provided, model DF3A-2P-2DSA. Pin 1 of CN6 is grounded, and pin 2 is connected to the external power supply and connected to the VIN pin of U20 and the IN pin of U19.

[0033] As attached Figure 3 Appendix Figure 4 As shown, the high common-mode rejection differential amplifier includes operational amplifiers U28.1 and U28.2. The positive power supply pins of U28.1 and U28.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. This embodiment is illustrated in the attached diagram. Figure 2 As shown, the positive power supply pins of U28.1 and U28.2 are grounded via parallel capacitors C164 and C165; the negative power supply pin is grounded via parallel capacitors C162 and C163. This is used to filter ripple and ensure the stability of the provided positive power supply VCC and negative power supply VEE. In this embodiment, capacitors C164 and C162 have a capacitance of 100nF, and capacitors C165 and C163 have a capacitance of 10uF. C164 and C165 work together to achieve high-frequency decoupling and low-frequency filtering, further ensuring the stability and cleanliness of the positive power supply VCC. Similarly, C162 and C163 work together to further ensure the stability and cleanliness of the negative power supply VEE. The inverting input pin (pin 2) of U28.1 is connected to the inverting terminal of the differential voltage output by the vibration detection unit (pin 1 of plug CN2), and the non-inverting input pin (pin 5) of U28.2 is connected to the non-inverting terminal of the differential voltage output by the vibration detection unit (pin 2 of plug CN2); in this embodiment, the plug CN2 is model DF3A-2P-2DSA; The output pin (pin 1) of U28.1 is connected to the output pin (pin 7) of U28.2 via a series resistor R69, a gain resistor Rg, and a resistor R71. The output pin of U28.2 is grounded via resistors R72 and R75 connected in series. The non-inverting input pin (pin 3) of U28.1 is connected to the junction of resistor R69 and gain resistor Rg, and the inverting input pin (pin 6) of U28.2 is connected to the junction of resistor R71 and gain resistor Rg. U28.1 and U28.2 work together to form a cross-coupled differential amplifier, providing an extremely high common-mode rejection ratio to resist environmental interference and initially amplify the weak differential signal output by the vibration detection unit.

[0034] The differential-to-single-ended amplifier includes operational amplifier U27. The positive power supply pin (V+ pin) of U27 is connected to the positive power supply VCC, and the negative power supply pin (V- pin) is connected to the negative power supply VEE. In this embodiment, as shown in the attached diagram... Figure 2 As shown, the positive power supply pin of U27 is grounded via capacitors C109 and C110 connected in parallel; the negative power supply pin is grounded via capacitors C97 and C98 connected in parallel. This is used to filter out ripple and ensure the stability of the provided positive power supply VCC and negative power supply VEE. In this embodiment, capacitors C97 and C109 have a capacitance of 100nF, and capacitors C98 and C110 have a capacitance of 10uF. C109 and C110 work together to achieve high-frequency decoupling and low-frequency filtering, further ensuring the stability and cleanliness of the positive power supply VCC. C97 and C98 work together in the same way to further ensure the stability and cleanliness of the negative power supply VEE. The inverting input pin (-IN pin) of U27 is connected to the output pin (pin 1) of U28.1 via resistor R70, and the end of resistor R70 away from the output pin of U28.1 is connected to the output pin (OUT pin) of U27 via resistor R74. The non-inverting input pin (+IN pin) of U27 is connected to the output pin (pin 7) of U28.2 via resistor R72, and the end of resistor R72 away from the output pin (pin 7) of U28.2 is grounded via resistor R75; U27, as the second-stage differential amplifier, converts the two differential signals output from the first-stage amplifier into a single-ended output signal with ground as the reference point.

[0035] In this embodiment, resistors R69 and R71 have the same resistance value of 1MΩ. The gain formula is G=1+2*R69 / Rg. The gain resistor Rg can be set so that the amplification factor of the entire preamp can be easily adjusted by changing the value of the gain resistor Rg. Resistors R69 and R71 together with the gain resistor Rg form a gain setting network. If amplification is not required, this resistor can be left unsoldered. In this embodiment, both resistors R70 and R74 have a resistance of 1MΩ. Resistor R70 serves as the input resistor, transmitting the output signal of the first-stage operational amplifier U28.1 to the inverting input pin of U27. Resistor R74 serves as the feedback resistor, and together with R70, they determine the gain of the inverting amplification channel of U27. In this embodiment, both resistors R72 and R75 have a resistance of 1MΩ. Resistor R72 serves as the input resistor, transmitting the output voltage signal of the first-stage operational amplifier U28.2 to the non-inverting input pin of U27. Resistor R75 serves as the reference resistor, grounding the non-inverting input pin of U27 through a resistor, and forming a voltage divider with R72.

[0036] In this embodiment, operational amplifiers U28.1 and U28.2 are of model OP2177ARZ-REEL7; operational amplifier U27 is of model OP1177ARMZ-R7.

[0037] As attached Figure 3 Appendix Figure 5 As shown, the bandpass filter includes operational amplifiers U23.1 and U23.2. The positive power supply pins of U23.1 and U23.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. This embodiment is illustrated in the attached diagram. Figure 2 As shown, the positive power supply pins of U23.1 and U23.2 are grounded via parallel capacitors C112 and C113; the negative power supply pins are grounded via parallel capacitors C100 and C101. This is used to filter ripple and ensure the stability of the provided positive power supply VCC and negative power supply VEE. In this embodiment, capacitors C100 and C112 have a capacitance of 100nF, and capacitors C101 and C113 have a capacitance of 10uF. C112 and C113 work together to achieve high-frequency decoupling and low-frequency filtering, further ensuring the stability and cleanliness of the positive power supply VCC. Similarly, C100 and C101 work together to further ensure the stability and cleanliness of the negative power supply VEE. The non-inverting input pin (pin 5) of U23.1 is grounded, and the inverting input pin (pin 6) is connected to the output pin (OUT pin) of U27 via resistor R82. The inverting input pin (pin 6) of U23.1 is connected to the output pin (pin 7) via resistor R59. At the same time, the inverting input pin (pin 6) is connected to the output pin (pin 7) via a series capacitor C152 and R83. The output pin (pin 7) of U23.1 is connected to the non-inverting input pin (pin 3) of U23.2 via capacitor C154, and the non-inverting input pin (pin 3) of U23.2 is grounded via resistor R56; The inverting input pin (pin 2) of U23.2 is directly connected to the output pin (pin 1), and is also connected to the output pin (pin 1) via capacitor C166; U23.1 and U23.2 work together. U23.1 inverts and amplifies the signal from U27 and filters out unwanted high-frequency noise. Capacitor C154 and resistor R56 work together to effectively filter out DC offset and extremely low-frequency drift. U23.2 acts as a voltage follower, providing isolation buffer and driving capability for the filter network. Working together, they precisely shape the frequency response of the system, ensuring that only useful signals within the target frequency band are extracted and output, greatly improving the signal-to-noise ratio and dynamic range.

[0038] In this embodiment, resistor R82 has a resistance of 100KΩ and serves as an input resistor, transmitting the output signal of the preceding stage U27 to the inverting input of U23.1. Resistor R59 has a resistance of 5MΩ and serves as a DC feedback resistor, which, together with resistor R82, determines the DC gain and low-frequency gain of this stage circuit. Capacitor C152 has a capacitance of 1uF, and resistor R83 has a resistance of 100KΩ. Capacitor C152 serves as a feedback capacitor, reducing high-frequency gain, while resistor R83 serves as a damping resistor, connected in series with C152, used to control the damping characteristics of the filter, preventing excessively sharp gain peaks at the cutoff frequency and making the frequency response smoother. Capacitor C154 has a capacitance of 1uF and acts as a coupling capacitor to block the DC component in the output signal of U23.1. Resistor R56 has a capacitance of 10MΩ and acts as a bias resistor to provide a defined DC reference potential for the non-inverting input pin of U23.2. Capacitor C154 and resistor R56 together form a passive high-pass filter. U23.2 directly connects the inverting input pin to the output pin to isolate the RC filter network of the preceding stage from the load of the following stage, ensuring that the filtering characteristics are not affected. The capacitor C166 has a capacitance of 20pF and acts as a feedback high-pass capacitor, forming a first-order high-pass filter. This stage ensures that the high-pass filtering characteristics are not affected by the load and provides current drive capability. Together with the interstage coupling circuit, it filters out DC offset and extremely low frequency components in the signal.

[0039] In this embodiment, the operational amplifiers U23.1 and U23.2 are of model AD8599ARZ.

[0040] As attached Figure 3 Appendix Figure 6 As shown, the differential output driver includes operational amplifier U30 and operational amplifier U22. The positive power supply pin (V+) of U30 is connected to the positive power supply VCC, and the negative power supply pin (V-) is connected to the negative power supply VEE. This embodiment is illustrated in the attached diagram. Figure 2As shown, the positive power supply pin of U30 is grounded via parallel capacitors C170 and C174; the negative power supply pin is grounded via parallel capacitors C169 and C173. This is used to filter ripple and ensure the stability of the provided positive power supply VCC and negative power supply VEE. In this embodiment, capacitors C169 and C170 have a capacitance of 100nF, and capacitors C173 and C174 have a capacitance of 10uF. C170 and C174 work together to achieve high-frequency decoupling and low-frequency filtering, further ensuring the stability and cleanliness of the positive power supply VCC. Similarly, C169 and C173 work together to further ensure the stability and cleanliness of the negative power supply VEE. The non-inverting input pin (+IN pin) of the U30 is grounded; The inverting input pin (-IN pin) of U30 is connected to the output pin (pin 1) of U23.2 via resistor R85; The inverting input pin (-IN pin) of the U30 is connected to the output pin (OUT pin) via resistor R60, and is also connected to the output pin (OUT pin) via a series capacitor C153 and resistor R84. The output pin of U30 is connected to the positive differential output pin (OUT+ pin of connector CN7) via capacitor C155, and the end of capacitor C155 away from the output pin of U30 is grounded via resistor R57. The positive power supply pin (V+ pin) of U22 is connected to the positive power supply VCC, and the negative power supply pin (V- pin) is connected to the negative power supply VEE; as shown in the attached figure in this embodiment. Figure 2 As shown, the positive power supply pin of U22 is grounded via parallel capacitors C168 and C172; the negative power supply pin is grounded via parallel capacitors C167 and C171. This is used to filter ripple and ensure the stability of the provided positive power supply VCC and negative power supply VEE. In this embodiment, capacitors C167 and C168 have a capacitance of 100nF, and capacitors C171 and C172 have a capacitance of 10uF. C168 and C172 work together to achieve high-frequency decoupling and low-frequency filtering, further ensuring the stability and cleanliness of the positive power supply VCC. Similarly, C167 and C171 work together to further ensure the stability and cleanliness of the negative power supply VEE. The non-inverting input pin (+IN pin) of U22 is grounded through capacitor C160, and is connected to the junction of capacitor C155 and resistor R57 through series resistors R67 and R66. The inverting input pin (-IN pin) of U22 is directly connected to the output pin (OUT pin), and the inverting input pin (-IN pin) is connected to the junction of resistor R66 and resistor R67 via capacitor C161; The output pin (-IN pin) of the U22 is connected to the negative differential output pin (OUT- pin of connector CN7); U22 and U30 work together to convert the single-ended signal output from the front-end bandpass filter into a differential signal with a high common-mode rejection ratio, greatly enhancing the anti-interference capability and reliability of the output signal during long-distance transmission.

[0041] In this embodiment, resistor R85 has a resistance of 100KΩ and serves as the input resistor, transmitting the output signal of the preceding stage U23.2 to the inverting input of U30; resistor R60 has a resistance of 5MΩ and serves as the DC feedback resistor, which, together with resistor R85, determines the DC gain and low-frequency gain of this stage of the circuit; capacitor C153 has a capacitance of 1uF and serves as the feedback capacitor. For high-frequency signals, capacitor C153 presents low impedance, feeding more of the output signal back to the input, greatly attenuating the high-frequency gain; resistor R84 has a resistance of 100KΩ, and resistor R... 84 acts as a damping resistor, connected in series with capacitor C153, to control the filter's characteristics near the cutoff frequency, preventing sharp peaks in the frequency response and smoothing the filtering characteristics. Capacitor C155 has a capacitance of 1uF and is used to transmit AC signals and block DC offset. Resistor R57 has a resistance of 10MΩ and provides a DC path, forming a high-pass filter with C155. Resistor R66 has the same resistance as resistor R67, 499KΩ, ensuring the symmetry of the two differential signal paths. Capacitor C160 has a capacitance of 10uF. Capacitor C161 has a capacitance of 10uF, and through AC coupling and feedback, the synergistic resistors ensure that U22 generates a signal inversely phase to the output of U30.

[0042] In this embodiment, U30 and U22 are model AD8597ARZ.

[0043] In this embodiment, the vibration detection unit uses a lossless detector as shown in patent CN2017214561693. The differential signal output by the coil inside the detector enters the signal conditioning unit for signal conditioning.

[0044] The sensor was tested at different frequency bands, and the measured sensitivity data of the sensor at different frequencies are recorded below: Appendix Figure 7 The graph shows the sensor sensitivity curve. It can be seen that the ultra-low frequency sensor has a sensitivity of 230V / m / s ±10% in the 0.1~100Hz frequency band. The sensor can still maintain a sensitivity that is basically the same as that in the high frequency band when it is as low as 0.1Hz, which solves the technical problem of the sharp drop in sensitivity of traditional sensors in the ultra-low frequency band.

Claims

1. An ultra-low frequency sensor, characterized in that: It includes a vibration detection unit, a power supply and voltage regulation unit, and a signal conditioning unit. The power supply and voltage regulation unit is equipped with a low dropout linear regulator U20, a voltage converter U19, and a negative voltage regulator U21. The low dropout linear regulator U20 stabilizes the external power supply as a positive power supply VCC. The voltage converter U19 converts the positive voltage of the external power supply into a negative voltage, and outputs a stable negative power supply VEE through a negative voltage regulator; The positive power supply VCC and the negative power supply VEE power the signal conditioning unit. The signal conditioning unit includes a high common-mode rejection differential amplifier, a differential-to-single-ended amplifier, a bandpass filter, and a differential output driver. The differential signal output by the vibration detection unit is sequentially passed through the high common-mode rejection differential amplifier, the differential-to-single-ended amplifier, the bandpass filter, and the differential output driver to output a differential voltage signal.

2. The ultra-low frequency sensor according to claim 1, characterized in that: The input pin and enable pin of the low dropout linear regulator U20 are connected to an external power supply, the ground pin is grounded, and the output pin is connected to the positive power supply VCC through resistor R1. The input pin of the low-dropout linear regulator U20 is grounded via capacitors C147 and C149 connected in parallel, and the output pin is grounded via capacitors C148 and C150 connected in parallel.

3. An ultra-low frequency sensor according to claim 1 or 2, characterized in that: The input pin of the voltage converter U19 is connected to an external power supply and grounded through capacitor C151. The grounding pin is grounded. A flying capacitor C60 is connected between the positive and negative pins of the flying capacitor. The output pin is grounded through capacitor C61. The negative voltage input pin of the negative voltage regulator U21 is connected to the output pin of U19 via parallel capacitors C156 and C158. The negative power supply reference ground pin is connected to the output pin of U19. The negative voltage output pin is connected to the negative power supply VEE via parallel capacitors C159 and C157 and then via resistor R65. The output pin of U19 is connected to the junction of capacitors C159 and C157 and resistor R65.

4. An ultra-low frequency sensor according to claim 1 or 2, characterized in that: The high common-mode rejection differential amplifier includes operational amplifiers U28.1 and U28.

2. The positive power supply pins of U28.1 and U28.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. The inverting input pin of U28.1 is connected to the inverting terminal of the differential voltage output by the vibration detection unit, and the non-inverting input pin of U28.2 is connected to the non-inverting terminal of the differential voltage output by the vibration detection unit. The output pin of U28.1 is connected in series with resistor R69 and gain resistor R. g Resistor R71 is connected to the output pin of U28.2; The output pin of U28.2 is grounded via resistors R72 and R75 connected in series. The non-inverting input pin of U28.1 is connected to resistor R69 and gain resistor R. g At the node, the inverting input pin of U28.2 is connected to resistor R71 and gain resistor R. g At the node.

5. The ultra-low frequency sensor according to claim 4, characterized in that: The resistors R69 and R71 have the same resistance value, and the gain of the amplifier is determined by the formula G=1+2*R69 / Rg.

6. The ultra-low frequency sensor according to claim 4, characterized in that: The differential-to-single-ended amplifier includes an operational amplifier U27, whose positive power supply pin is connected to the positive power supply VCC and its negative power supply pin is connected to the negative power supply VEE. The inverting input pin of U27 is connected to the output pin of U28.1 via resistor R70, and the end of resistor R70 away from the output pin of U28.1 is connected to the output pin of U27 via resistor R74. The non-inverting input pin of U27 is connected to the output pin of U28.2 via resistor R72, and the end of resistor R72 away from the output pin of U28.2 is grounded via resistor R75.

7. The ultra-low frequency sensor according to claim 6, characterized in that: The bandpass filter includes operational amplifiers U23.1 and U23.

2. The positive power supply pins of U23.1 and U23.2 are connected to the positive power supply VCC, and the negative power supply pins are connected to the negative power supply VEE. The non-inverting input pin of U23.1 is grounded, and the inverting input pin is connected to the output pin of U27 via resistor R82. The inverting input pin of U23.1 is connected to the output pin via resistor R59. At the same time, the inverting input pin is connected to the output pin via capacitor C152 and R83 in series. The output pin of U23.1 is connected to the non-inverting input pin of U23.2 via capacitor C154, and the non-inverting input pin of U23.2 is grounded via resistor R56; The inverting input pin of U23.2 is directly connected to the output pin, and is also connected to the output pin via capacitor C166.

8. The ultra-low frequency sensor according to claim 7, characterized in that: The differential output driver includes operational amplifier U30 and operational amplifier U22. The positive power supply pin of U30 is connected to the positive power supply VCC, and the negative power supply pin is connected to the negative power supply VEE. The non-inverting input pin of U30 is grounded; The inverting input pin of U30 is connected to the output pin of U23.2 via resistor R85; The inverting input pin of the U30 is connected to the output pin via resistor R60, and is also connected to the output pin via capacitor C153 and resistor R84 in series. The output pin of U30 is connected to the positive differential output pin via capacitor C155, and the end of capacitor C155 away from the output pin of U30 is grounded via resistor R57. The positive power supply pin of U22 is connected to the positive power supply VCC, and the negative power supply pin is connected to the negative power supply VEE. The non-inverting input terminal of U22 is grounded via capacitor C160, and is connected to the junction of capacitor C155 and resistor R57 via series resistors R67 and R66. The inverting input pin of U22 is directly connected to the output pin, and the inverting input pin is connected to the junction of resistor R66 and resistor R67 via capacitor C161. The output pin of U22 is connected to the negative differential output pin.

9. The ultra-low frequency sensor according to claim 8, characterized in that: The resistors R70, R74, R72, and R75 have the same resistance value; The resistance values ​​of resistor R66 and resistor R67 are equal.

10. An ultra-low frequency sensor according to claim 1, 2, 5, 6, 7, 8, or 9, characterized in that: The positive power supply VCC pins of the high common-mode rejection differential amplifier, differential-to-single-ended amplifier, bandpass filter, and differential output driver are grounded via parallel capacitors, and the negative power supply pin VEE is grounded via parallel capacitors.

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