CN110850467A - Digital low-frequency seismic sensor - Google Patents
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- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/16—Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
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Abstract
The invention provides a digital low-frequency seismic sensor, which solves the problems that the existing seismic detection system cannot directly output digital signals, or has high manufacturing cost, complex structure, large power consumption and cannot detect low-frequency seismic signals in the deep part of the earth crust. The sensor comprises a pendulum system, an electromagnetic transducer, a detection stage circuit, a multi-stage integrator, a quantizer, a driving stage circuit, a PID controller and a DAC; the pendulum system induces vibration to generate a vibration signal, and the vibration signal is converted into a voltage signal through the electromagnetic transducer; the voltage signal is reversely amplified by a detection stage circuit, enters a multi-stage integrator and is subjected to sampling holding and integral filtering; performing analog-to-digital conversion on the filtered voltage signal by a quantizer; the DAC is used for generating pulse width modulation voltage from the digital bit stream output by the quantizer, the pulse width modulation voltage is conditioned into control voltage through the PID controller, the control voltage is converted into coil current of the electromagnetic transducer through the driving stage circuit, and the coil current is converted into electromagnetic force through the magnetic field transducer and used for balancing the motion trend of the pendulum body system.
Description
Technical Field
The invention relates to the field of sensors, in particular to a digital low-frequency seismic sensor.
Background
The existing exploration seismic detection system mainly comprises a geophone and a data acquisition unit, and is structurally characterized in that the geophone is used as a sensing unit to pick up seismic signals and output analog voltage, and the data acquisition unit converts the voltage signals into digital quantity. The detection system can not directly output digital signals, and the digital acquisition of the detection system depends on an analog-digital conversion chip, so that the detection system has the problems of high manufacturing cost, complex structure, large power consumption and the like; in addition, the conventional moving-coil geophone adopts a speed type electromagnetic transduction principle, is of a non-feedback open-loop structure, limits the lower cut-off frequency to be 4 Hz-50 Hz, cannot detect low-frequency seismic signals reflected and transmitted from the deep part of the earth crust, and influences the detection precision and depth of underground medium structures and oil and gas resources.
Disclosure of Invention
The invention provides a digital low-frequency seismic sensor, aiming at solving the technical problems that the existing seismic detection system can not directly output digital signals, or an analog-digital conversion chip has high manufacturing cost, complex structure and large power consumption, and can not detect low-frequency seismic signals reflected and transmitted in the deep part of the crust, thereby influencing the detection precision and depth of underground medium structures and oil-gas resources.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a digital low-frequency seismic sensor is characterized in that: the digital feedback control device comprises a signal pickup unit and a digital feedback control unit; the signal pickup unit comprises a pendulum system, an electromagnetic transducer, a detection stage circuit, a multi-stage integrator and a quantizer;
the pendulum body system induces vibration to generate a vibration signal, and the vibration signal is converted into a voltage signal through the electromagnetic transducer; the voltage signal is reversely amplified by a detection stage circuit, enters a multi-stage integrator and is subjected to sampling holding and integral filtering; the analog-to-digital conversion is carried out on the filtered voltage signal by a quantizer, and if the voltage signal is greater than a threshold value, the quantizer outputs a digital high level + 1; if the voltage signal is less than or equal to the threshold value, the quantizer outputs a digital low level-1;
the digital feedback control unit comprises a driving stage circuit, a PID controller and a DAC.
The DAC is connected with the output of the quantizer and used for generating pulse width modulation voltage from the digital bit stream output by the quantizer; the pulse width modulation voltage is conditioned into control voltage through a PID controller, the control voltage is converted into coil current of an electromagnetic transducer through a driving stage circuit, and the coil current is converted into electromagnetic force through a magnetic field transducer and is used for balancing the movement trend of the pendulum body system.
Further, the electromagnetic transducer comprises an induced voltage Vcoil and a coil resistance Rcoil, wherein one end of the induced voltage Vcoil is connected with one end of the coil resistance Rcoil;
the detection stage circuit comprises a detection stage operational amplifier and a feedback resistor R1;
the other end of the induced voltage Vcoil is connected to the negative input end of the detection-stage operational amplifier through an input resistor R2, two ends of a feedback resistor R1 are respectively connected to the negative input end of the detection-stage operational amplifier and the output end of the detection-stage operational amplifier, the positive input end of the detection-stage operational amplifier is connected to the other end of a coil resistor Rcoil, the other end of the coil resistor Rcoil is connected to one end of a matching resistor R3, and the other end of the matching resistor R3 is grounded.
Further, the matching resistor R3 is equal to the coil resistor Rcoil, and the feedback resistor R1 is equal to the input resistor R2.
Further, the multistage integrator adopts a 3-order distributed feedback structure or a 2-order distributed feedback structure.
Further, the 3 rd order distributed feedback structure comprises a first-stage filter, a second-stage filter and a third-stage filter;
the first-stage filter comprises a first subtracter, a feedforward amplifier K1 and a first integrator, the second-stage filter comprises a second subtracter, a feedforward amplifier K2 and a second integrator, and the third-stage filter comprises a third subtracter, a feedforward amplifier K3 and a third integrator;
the first subtractor, the feedforward amplifier K1, the first integrator, the second subtractor, the feedforward amplifier K2, the second integrator, the third subtractor, the feedforward amplifier K3 and the third integrator are sequentially connected, the positive input end of the first subtractor is connected with the output end of the detection-stage operational amplifier, the output end of the third integrator is connected with the input end of the quantizer, and the negative input end of the first subtractor, the negative input end of the second subtractor and the negative input end of the third subtractor are respectively connected with the output end of the quantizer.
Further, the 2 nd order distributed feedback structure comprises a first stage filter and a second stage filter;
the first-stage filter comprises a first subtracter, a feedforward amplifier K1 and a first integrator, and the second-stage filter comprises a second subtracter, a feedforward amplifier K2 and a second integrator;
the first subtractor, the feedforward amplifier K1, the first integrator, the second subtractor, the feedforward amplifier K2 and the second integrator are sequentially connected, the positive input end of the first subtractor is connected with the output end of the detection-stage operational amplifier, the output end of the second integrator is connected with the input end of the quantizer, and the negative input end of the first subtractor and the negative input end of the second subtractor are respectively connected with the output end of the quantizer.
Further, the DAC comprises an analog switch, and the input end of the analog switch is connected with the output end of the quantizer;
when the input digital signal is +1, the analog switch connected with the positive control voltage + Vfb is conducted; when the input digital signal is-1, the analog switch connected with the negative control voltage-Vfb is conducted.
Furthermore, the PID controller comprises an addition circuit and three amplification branches connected in parallel, wherein the three amplification branches are respectively a proportional amplifier, an integral amplifier and a differential amplifier;
one ends of the proportional amplifier, the integral amplifier and the differential amplifier are all connected with the output end of the analog switch, and the other ends of the proportional amplifier, the integral amplifier and the differential amplifier are all connected with three positive input ends of the addition circuit.
Further, the driving stage circuit comprises a control stage operational amplifier;
the positive input end of the control-stage operational amplifier is connected with the output end of the addition circuit, the negative input end of the control-stage operational amplifier is connected with the other end of the coil resistor Rcoil, and the output end of the control-stage operational amplifier is connected with the other end of the induced voltage Vcoil.
Further, the quantizer is a 1-bit quantizer or a lower-bit quantizer; the DAC and the quantizer correspond to a 1-bit DAC or a low-bit DAC.
Compared with the prior art, the invention has the advantages that:
1. the digital low-frequency seismic sensor has the advantages that digital signals are directly output, an analog-digital mixed circuit system is adopted for sampling and quantifying, an analog-digital conversion chip is not needed, and the digital low-frequency seismic sensor has the characteristics of good low-frequency response, compact structure, low power consumption, large dynamic range and good linearity;
the pendulum body system and the electromagnetic transducer are connected into the detection stage circuit and the driving stage circuit, so that the pendulum body can realize the detection of the movement of the pendulum body by relying on the original coil, the ground movement speed is converted into induced electromotive force, the feedback electromagnetic force is applied, the movement trend of the pendulum body is balanced, the low-frequency bandwidth of the mechanical system is expanded, and the closed-loop feedback is realized.
2. The digital low-frequency seismic sensor has good low-frequency response, and the low-frequency band of the pendulum system is expanded by adopting a force balance technology;
3. the digital low-frequency seismic sensor has strong compatibility, and a circuit system can be directly connected to the existing moving-coil geophone or a similar pendulum body and energy conversion system, so that the low-frequency response is expanded, and a digital signal is output.
4. The multi-stage integrator in the sensor can adopt a 3-order distributed feedback structure, and the 3-order structure has the advantages of high-order noise shaping characteristic and small quantization noise;
the multistage integrator can also adopt a 2-order distributed feedback structure, a third pole filter in the 3-order distributed feedback structure is omitted by the structure, the structure is simpler, the power consumption is lower, and the system is easy to stabilize.
Drawings
FIG. 1 is a schematic diagram of a digital low frequency seismic sensor of the present invention;
FIG. 2 is a schematic circuit diagram of the detection stage circuit, the driving stage circuit and the PID controller of the digital low frequency seismic sensor of the invention;
FIG. 3 is a schematic circuit diagram of a multi-stage integrator, quantizer and DAC of a first embodiment of a digital low frequency seismic sensor of the present invention;
FIG. 4 is a schematic circuit diagram of a multi-stage integrator, quantizer and DAC of a second embodiment of the digital low frequency seismic sensor of the present invention;
wherein the reference numbers are as follows:
1-an electromagnetic transducer, 2-a PID controller, 21-an adder circuit, 22-an amplification branch, 3-an operational amplifier, 31-a negative input terminal of a detection-stage operational amplifier, 32-a positive input terminal of a detection-stage operational amplifier, 33-an output terminal of a detection-stage operational amplifier, 4-a control-stage operational amplifier, 41-a negative input terminal of a control-stage operational amplifier, 42-a positive input terminal of a control-stage operational amplifier, 43-an output terminal of a control-stage operational amplifier, 5-a circuit reference point, 6-a first-stage filter, 61-a first subtractor, 62-a first integrator, 7-a second-stage filter, 71-a second subtractor, 72-a second integrator, 8-a third-stage filter, 81-a third subtractor, 82-third integrator, 9-quantizer, 10-analog switch.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments.
Example one
As shown in fig. 1, a digital low frequency seismic sensor includes a signal pickup unit and a digital feedback control unit; the signal pickup unit comprises a pendulum system, an electromagnetic transducer detection stage circuit, a multi-stage integrator and a quantizer 9, and the digital feedback control unit comprises a driving stage circuit, a PID controller 2 and a DAC; the conventional moving-coil type geophone can be used as a pendulum body system and an electromagnetic transducer 1 and is connected with a detection-stage circuit and a driving-stage circuit, so that the pendulum body can realize the detection of the motion of the pendulum body by depending on the original single coil, the ground motion speed is converted into induced electromotive force, the feedback electromagnetic force is applied, the motion trend of the pendulum body is balanced, and the low-frequency bandwidth of a mechanical system is expanded; in addition, the digital feedback control unit changes an analog circuit system adopted in the prior art into an analog-hybrid circuit system, the working frequency of a quantizer 9 in the sensor is far higher than the Nyquist frequency, oversampling quantization of low-speed seismic signals is realized, quantization noise is shaped to be out of the frequency band of the seismic signals, and high-precision digital acquisition of the seismic signals is completed.
As shown in fig. 2, the electromagnetic transducer 1 is equivalent to an induced voltage Vcoil and a coil resistance Rcoil, one end of the induced voltage Vcoil being connected to one end of the coil resistance Rcoil;
the detection stage circuit is an inverting amplifier formed by an operational amplifier 3, the output voltage is the negative value of the coil induced voltage, and the detection stage circuit comprises the detection stage operational amplifier 3 and a feedback resistor R1; the other end of the induced voltage Vcoil is connected to the negative input end 31 of the detection-stage operational amplifier through the input resistor R2, two ends of the feedback resistor R1 are respectively connected to the negative input end 31 of the detection-stage operational amplifier and the output end 33 of the detection-stage operational amplifier, the positive input end 32 of the detection-stage operational amplifier is connected to the other end of the coil resistor Rcoil, the other end of the coil resistor Rcoil is connected to one end of the matching resistor R3, and the other end of the matching resistor R3 is grounded.
The working principle of the detection stage circuit is as follows: the electromagnetic transducer 1 is equivalent to an induced voltage Vcoil series coil resistor Rcoil, is connected to the negative input end 31 of the operational amplifier of the detection stage through an input resistor R2, a feedback resistor R1 is connected across the negative input end and the output end to form a reverse amplification circuit, a reverse circuit reference point 5 is connected to the positive input end of the operational amplifier 33 and is connected with a matching resistor R3, and a matching resistor R3 is grounded GND (ground potential) wherein the circuit reference point 5 represents that when the circuit is calculated, the two operational amplifiers and the transducer can be used as a circuit reference point; the matching resistor R3 is equal to the coil resistor Rcoil, the feedback resistor R1 is equal to the input resistor R2, and the output resistor of the detection stage circuit is a negative value of the induced voltage, that is, Vout is-Vcoil, according to the characteristics of the operational amplifier 3.
As shown in fig. 3, the multi-stage integrator adopts a 3-order distributed feedback structure, and the 3-order distributed feedback structure includes a first-stage filter 6, a second-stage filter 7 and a third-stage filter 8; the first stage filter 6 comprises a first subtracter 61, a feedforward amplifier K1 and a first integrator 62, the second stage filter 7 comprises a second subtracter 71, a feedforward amplifier K2 and a second integrator 72, and the third stage filter 8 comprises a third subtracter 81, a feedforward amplifier K3 and a third integrator 82;
the first subtractor 61, the feedforward amplifier K1, the first integrator 62, the second subtractor 71, the feedforward amplifier K2, the second integrator 72, the third subtractor 81, the feedforward amplifier K3 and the third integrator 82 are connected in sequence, the positive input end of the first subtractor 61 is connected to the output end 33 of the detection-stage operational amplifier, the output end of the third integrator 82 is connected to the input end of the quantizer 9, and the negative input end of the first subtractor 61, the negative input end of the second subtractor 71 and the negative input end of the third subtractor 81 are respectively connected to the output end of the quantizer 9.
The working principle of the multistage integrator is as follows: the sampling holder converts the voltage Vout output by the detection stage circuit into a discrete time signal under the synchronization of the clock, the discrete time signal sequentially enters a first subtracter 61, a feedforward amplifier K1, a first integrator 62, a second subtracter 71, a feedforward amplifier K2, a second integrator 72, a third subtracter 81, a feedforward amplifier K3 and a third integrator 82, the cascade output outputs a digital bit stream +1 or-1 through a 1-bit quantizer 9, and the digital bit stream is fed back through a distributed feedback branch at the first subtracter 61, the second subtracter 71 and the third subtracter 81 respectively. The 3-order structure has high-order noise shaping characteristics, has the advantages of low quantization noise and the like, but has high power consumption, and needs to teach system parameters specially to ensure the closed loop stability of the system.
The quantizer 9 can be implemented by a 1-bit quantizer or a low-bit quantizer, and this embodiment adopts an implementation manner of the 1-bit quantizer, and the 1-bit quantizer can be implemented by a comparator circuit synchronized with a clock, and outputs a digital high level +1 when an analog signal of an input ground is greater than a reference voltage, and otherwise outputs a digital low level-1, which is a digital bit stream output by the seismic sensor of this application.
The DAC is a digital-analog conversion circuit and completes the conversion from input digital quantity to pulse modulation analog voltage signals. The DAC selection should be matched to the quantizer 9, and adapted to the 1-bit quantizer described above, this embodiment provides an embodiment using a 1-bit DAC, where the quantizer is implemented by an analog switch 10, the analog switch 10 connected to the positive feedback voltage + Vfb is turned on and outputs the positive feedback voltage when the input digital signal is +1, and the analog switch 10 connected to the negative control voltage-Vfb is turned on and outputs the negative feedback voltage when the input digital signal is-1, and the output is a pulse width modulation voltage signal proportional to the digital bit stream.
The PID controller 2 is a proportional-integral-differential controller, and comprises a control branch and an adding circuit 21 which are formed by three amplifying branches 22 in parallel, wherein the three amplifying branches 22 are respectively a proportional amplifier, an integral amplifier and a differential amplifier; one ends of the proportional amplifier, the integral amplifier and the differential amplifier are all connected with the output end of the analog switch 10, and the other ends thereof are all connected with three positive input ends of the addition circuit 21.
The digital bit stream is the pulse width modulation voltage generated by the 1-bit DAC as the input signal of the PID controller 2, the PID controller 2 is composed of three paths in parallel, which are respectively proportional, differential and integral, the three paths of signals respectively calculate the pulse width modulation voltage, and the pulse width modulation voltage becomes the control voltage Vctrl through the adding circuit 21.
The driving stage circuit takes an energy conversion coil as a feedback resistor of the control stage operational amplifier 4, drives a coil current, the current is in direct proportion to the input voltage of the driving stage, and the driving stage circuit comprises the control stage operational amplifier 4;
the control voltage Vctrl is connected to the positive input end 42 of the control-stage operational amplifier, the negative input end 41 of the control-stage operational amplifier is connected with the other end (circuit reference point 5) of the coil resistor Rcoil, and the output end 43 of the control-stage operational amplifier is connected to the input resistor R2 of the detection-stage circuit and is connected with the electromagnetic transducer 1; according to the characteristics of the operational amplifier 3, the voltage of the circuit reference point 5 is equal to the control voltage Vctrl, the current Icoil flowing through the coil resistance Rcoil is Vctrl/R3, and the electromagnetic force is proportional to the coil current Icoil and the control voltage.
The digital low-frequency seismic sensor principle of the embodiment is as follows:
when the outside applies vibration to the pendulum body system, the pendulum body deviates from the balance position due to the inertia effect and is converted into a voltage signal through the electromagnetic transducer 1; the voltage signal is reversely amplified by the detection stage circuit, enters the multi-stage integrator, is subjected to sampling, holding, integrating and filtering, the filtered signal is compared by the 1-bit quantizer 9, and is greater than the threshold value and outputs +1 (if the voltage signal is greater than the threshold value, the quantizer 9 outputs digital high level +1), otherwise, the filtered signal outputs-1 (if the voltage signal is less than or equal to the threshold value, the quantizer 9 outputs digital low level-1), and the binary bit stream is digital output, is synchronous with the sampling clock and serves as an input signal of the feedback control part.
The 1-bit DAC is connected to an output of the quantizer 9, and is configured to generate a pulse width modulation voltage from a digital bit stream output by the quantizer 9, where specifically, when the bit stream is +1, the 1-bit DAC outputs a positive voltage, and otherwise, outputs a negative voltage; the digital pulse width modulation signal is conditioned into control voltage by the PID controller 2, and is converted into coil current of the electromagnetic transducer 1 by the driving stage circuit, and the coil current is transduced into electromagnetic force by a magnetic field for balancing the movement trend of the pendulum body, so that the pendulum body has extremely small movement relative to a static reference system. Under the action of the feedback force, the mechanical characteristics of the pendulum body system are changed, the lower cut-off frequency is expanded, the low-frequency response of the system is improved, and the maximum detectable vibration amplitude of the system is improved.
The implementation mode of the signal pickup part and the digital feedback control part adopts an analog-digital mixed high-order summation-increment modulator circuit system, and has more digital circuits than the prior art adopting an analog circuit system, and under the structure, the sensor has the advantage of directly outputting digital signals: the digital signal is easy to store, anti-interference and interchannel crosstalk, low attenuation and suitable for long-distance transmission.
Example two
The difference from the first embodiment is that, as shown in fig. 4, the multistage integrator adopts a 2-step distributed feedback structure;
the 2-order distributed feedback structure comprises a first-stage filter 6 and a second-stage filter 7; the first-stage filter 6 comprises a first subtracter 61, a feedforward amplifier K1 and a first integrator 62, and the second-stage filter 7 comprises a second subtracter 71, a feedforward amplifier K2 and a second integrator 72;
the first subtractor 61, the feedforward amplifier K1, the first integrator 62, the second subtractor 71, the feedforward amplifier K2, and the second integrator 72 are connected in sequence, the positive input end of the first subtractor 61 is connected to the output end 33 of the detection-stage operational amplifier, the output end of the second integrator 72 is connected to the input end of the quantizer 9, and the negative input end of the first subtractor 61 and the negative input end of the second subtractor 71 are respectively connected to the output end of the quantizer 9.
The working principle of the multistage integrator is as follows: the sample holder converts the voltage Vout output by the detection stage circuit into a discrete time signal under the synchronization of the clock, the discrete time signal sequentially enters the first subtracter 61, the feedforward amplifier K1, the first integrator 62, the second subtracter 71, the feedforward amplifier K2 and the second integrator 72, the cascade output outputs a digital bit stream +1 or-1 through the 1-bit quantizer 9, and the digital bit stream is fed back through the distributed feedback branch at the first subtracter 61 and the second subtracter 71 respectively. The third-stage filter in the 3-order structure is omitted, so that the 2-order structure is simpler, the power consumption is lower, and the system is easy to stabilize.
The above description is only for the purpose of describing the preferred embodiments of the present invention and does not limit the technical solutions of the present invention, and any known modifications made by those skilled in the art based on the main technical concepts of the present invention fall within the technical scope of the present invention.
Claims (10)
1. A digital low frequency seismic sensor, comprising: the digital feedback control device comprises a signal pickup unit and a digital feedback control unit;
the signal pickup unit comprises a pendulum system, an electromagnetic transducer (1), a detection stage circuit, a multi-stage integrator and a quantizer (9);
the pendulum body system induces vibration to generate a vibration signal, and the vibration signal is converted into a voltage signal through the electromagnetic transducer (1); the voltage signal is reversely amplified by a detection stage circuit, enters a multi-stage integrator and is subjected to sampling holding and integral filtering; the analog-to-digital conversion is carried out on the filtered voltage signal by a quantizer (9), and if the voltage signal is greater than a threshold value, the quantizer (9) outputs a digital high level + 1; if the voltage signal is less than or equal to the threshold value, the quantizer (9) outputs a digital low level-1;
the digital feedback control unit comprises a driving stage circuit, a PID controller (2) and a DAC;
the DAC is connected with the output of the quantizer (9) and is used for generating pulse width modulation voltage from the digital bit stream output by the quantizer (9); the pulse width modulation voltage is conditioned into control voltage through the PID controller (2), and is converted into coil current of the electromagnetic transducer (1) through the driving stage circuit, and the coil current is converted into electromagnetic force through the magnetic field transducer and is used for balancing the motion trend of the pendulum system.
2. The digital low frequency seismic sensor of claim 1, wherein: the electromagnetic transducer (1) comprises an induced voltage Vcoil and a coil resistor Rcoil, wherein one end of the induced voltage Vcoil is connected with one end of the coil resistor Rcoil;
the detection stage circuit comprises a detection stage operational amplifier (3) and a feedback resistor R1;
the other end of the induced voltage Vcoil is connected to a negative input end (31) of the detection-stage operational amplifier through an input resistor R2, two ends of a feedback resistor R1 are respectively connected with the negative input end (31) of the detection-stage operational amplifier and an output end (33) of the detection-stage operational amplifier, a positive input end (32) of the detection-stage operational amplifier is connected with the other end of a coil resistor Rcoil, the other end of the coil resistor Rcoil is connected with one end of a matching resistor R3, and the other end of the matching resistor R3 is grounded.
3. The digital low frequency seismic sensor of claim 2, wherein: the matching resistor R3 is equal to the coil resistor Rcoil, and the feedback resistor R1 is equal to the input resistor R2.
4. The digital low frequency seismic sensor of claim 3, wherein: the multistage integrator adopts a 3-order distributed feedback structure or a 2-order distributed feedback structure.
5. The digital low frequency seismic sensor according to claim 4, wherein: the 3-order distributed feedback structure comprises a first-stage filter (6), a second-stage filter (7) and a third-stage filter (8);
the first-stage filter (6) comprises a first subtracter (61), a feedforward amplifier K1 and a first integrator (62), the second-stage filter (7) comprises a second subtracter (71), a feedforward amplifier K2 and a second integrator (72), and the third-stage filter (8) comprises a third subtracter (81), a feedforward amplifier K3 and a third integrator (82);
the detection device comprises a first subtracter (61), a feedforward amplifier K1, a first integrator (62), a second subtracter (71), a feedforward amplifier K2, a second integrator (72), a third subtracter (81), a feedforward amplifier K3 and a third integrator (82) which are sequentially connected, wherein the positive input end of the first subtracter (61) is connected to the output end (33) of the detection-stage operational amplifier, the output end of the third integrator (82) is connected with the input end of the quantizer (9), and the negative input end of the first subtracter (61), the negative input end of the second subtracter (71) and the negative input end of the third subtracter (81) are respectively connected with the output end of the quantizer (9).
6. The digital low frequency seismic sensor according to claim 4, wherein: the 2 nd order distributed feedback structure comprises a first stage filter (6) and a second stage filter (7);
the first-stage filter (6) comprises a first subtracter (61), a feedforward amplifier K1 and a first integrator (62), and the second-stage filter (7) comprises a second subtracter (71), a feedforward amplifier K2 and a second integrator (72);
the first subtractor (61), the feedforward amplifier K1, the first integrator (62), the second subtractor (71), the feedforward amplifier K2 and the second integrator (72) are sequentially connected, the positive input end of the first subtractor (61) is connected to the output end (33) of the detection-stage operational amplifier, the output end of the second integrator (72) is connected with the input end of the quantizer (9), and the negative input end of the first subtractor (61) and the negative input end of the second subtractor (71) are respectively connected with the output end of the quantizer (9).
7. The digital low frequency seismic sensor according to claim 5 or 6, wherein: the DAC comprises an analog switch (10), and the input end of the analog switch (10) is connected with the output end of the quantizer (9);
when the input digital signal is +1, the analog switch (10) connected with the positive control voltage + Vfb is conducted; when the input digital signal is-1, the analog switch (10) connected with the negative control voltage-Vfb is conducted.
8. The digital low frequency seismic sensor of claim 7, wherein: the PID controller (2) comprises an addition circuit (21) and three amplification branches (22) connected in parallel, wherein the three amplification branches (22) are respectively a proportional amplifier, an integral amplifier and a differential amplifier;
one ends of the proportional amplifier, the integral amplifier and the differential amplifier are all connected with the output end of the analog switch (10), and the other ends of the proportional amplifier, the integral amplifier and the differential amplifier are all connected with three positive input ends of the addition circuit (21).
9. The digital low frequency seismic sensor of claim 8, wherein: the driving stage circuit comprises a control stage operational amplifier (4);
the positive input end (42) of the control-stage operational amplifier is connected with the output end of the addition circuit (21), the negative input end (41) of the control-stage operational amplifier is connected with the other end of the coil resistor Rcoil, and the output end (43) of the control-stage operational amplifier is connected with the other end of the induced voltage Vcoil.
10. The digital low frequency seismic sensor of claim 1, wherein: the quantizer is a 1-bit quantizer or a low-bit quantizer;
the DAC and the quantizer correspond to a 1-bit DAC or a low-bit DAC.
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