While-drilling azimuth electromagnetic wave nanovolt-level high-Q-value multi-frequency signal detection circuit

Abstract

The invention relates to the technical field of oil and gas drilling, in particular to a while-drilling azimuth electromagnetic wave nanovolt-level high-Q-value multi-frequency signal detection circuit. The invention provides a nanovolt-level high-Q-value multi-frequency signal detection pre-amplification circuit which is suitable for all while-drilling azimuth electromagnetic wave resistivity instruments and is simpler in structure. The method is suitable for solving the problem of multi-frequency-point multi-group parallel matching in antenna inductance sensor open-loop voltage signal acquisition preprocessing, and the signal-to-noise ratio of the whole acquisition circuit is effectively improved. The method is suitable for a frequency-selecting filter which has the requirement for amplitude-frequency response characteristic stability near a center frequency point in a narrow-band-pass filter. The multi-frequency signal high-dynamic-range measuring circuit can be independently used as a sensor pre-amplification circuit, a segmented program control gain circuit containing a crossing interval is adopted, the measuring dynamic range spans four orders of magnitude to reach 80dB, and multi-frequency signal high-dynamic-range measuring is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas drilling, and particularly relates to a downhole azimuth electromagnetic wave nano-volt level high-Q value multi-frequency signal detection circuit. Background Art

[0002] A weak signal does not only mean a small signal amplitude, but mainly refers to the signal being submerged by noise. Only by amplifying the amplitude of the weak signal under the condition of effectively suppressing noise can the useful signal be extracted. The detection of analog weak signals mainly realizes the filtering and amplification of weak signals in the noise background. There are many weak signal detection circuits, and most of them adopt the phase-locked amplification technology to achieve. However, when using the phase-locked amplification technology to measure signals, especially when measuring nano-volt level AC voltages, the output voltage of the multiplier is very small, which causes serious zero drift of the subsequent DC amplifier and is not conducive to the measurement of nano-volt level voltages. The existing phase-locked amplifiers generally use the detection algorithm of digital phase-sensitive detector (DPSD) to extract the amplitude and phase of the input signal. The current digital extraction method is greatly affected by the sampling time length and is easily interfered by external noise, which affects the extraction quality of the signal. The existing analog phase-locked amplifiers generally have single-channel or dual-channel inputs. However, as the number of circuit frequency channels increases, the circuit complexity increases exponentially, making it difficult to meet some multi-channel and multi-frequency application scenarios, and the application flexibility is poor. Moreover, the problem of analog phase-locked amplification is that it realizes a 90° phase shift of the signal with an unchanged amplitude for the given frequency signal, and it is difficult to implement with analog circuits. Currently, most of the weak signal detection circuits at the front end of sensors still adopt the method of instrumentation amplifier and narrowband filter.

[0003] The weak signal of azimuth electromagnetic wave comes from the analog signal at the front end of the antenna sensor. Traditional downhole electromagnetic wave resistivity logging tools have different formation detection depths and formation interface detection resolutions at different transmitting frequencies. The traditional method is to match one antenna with one frequency. The method of downhole azimuth electromagnetic wave resistivity logging tool is to match one antenna with 2 or more frequencies simultaneously to improve the utilization rate of the antenna. For example, the conventional electromagnetic wave selects 400 kHz and 2 MHz dual-frequency resonance matching, which improves the utilization efficiency of the antenna. The dual-frequency resonance matching circuit realizes the matching of two frequency points. To realize the matching of more frequency points simultaneously, the circuit structure needs to be redesigned.

[0004] The existing multi-frequency weak signal detection has the following defects:

[0005] (1) The complex series-parallel resonance matching circuit exchanges the amplitude-frequency characteristics at the cost of circuit complexity. The more circuit frequencies there are, the more complex the circuit structure is, and the more types of transformers and the number of tuning inductors it contains are, and the process requirements are high.

[0006] (2) Existing filter circuits all adopt single-chip MFB band-pass filters, which have extremely high requirements for the gain bandwidth of integrated circuits. There are very few components that meet the high quality factor and appropriate gain bandwidth. For existing single-stage band-pass filter circuits, the flatness of the amplitude-frequency characteristic is poor under the condition of environmental temperature change.

[0007] (3) The measurement dynamic range of existing weak signal detection circuits is limited, and the weak signal detection accuracy is not high. Summary of the Invention

[0008] In view of the above problems, the present invention provides a downhole azimuth electromagnetic nano-volt high-Q multi-frequency signal detection circuit.

[0009] A downhole azimuth electromagnetic nano-volt high-Q multi-frequency signal detection circuit includes:

[0010] A first frequency selection and filtering module, a first instrumentation amplifier module, a first single-ended to differential module, a second instrumentation amplifier module, a programmable gain module, a second frequency selection and filtering module, and a second single-ended to differential module connected in series in sequence;

[0011] The first frequency selection and filtering module is used to perform frequency selection and filtering on the nano-volt signal received by the downhole azimuth sensor;

[0012] The first instrumentation amplifier module is used to condition the nano-volt signal output by the first frequency selection and filtering module to the micro-volt level;

[0013] The first single-ended to differential module is used to differentially amplify the micro-volt signal output by the first instrumentation amplifier module and remove the differential common-mode voltage;

[0014] The second instrumentation amplifier module is used to further amplify the micro-volt signal output by the first single-ended to differential module and convert it into a single-ended signal;

[0015] The programmable gain module is used to further amplify the output signal of the second instrumentation amplifier module to reach the measurement range of the A / D acquisition circuit;

[0016] The second frequency selection and filtering module is used to filter out out-of-band noise from the output signal of the programmable gain module and retain the useful signal;

[0017] The second single-ended to differential module is used to convert the polarity of the single-ended voltage signal output by the second frequency selection and filtering module and filter out the noise introduced during transmission.

[0018] Furthermore, the first frequency selection and filtering module includes: a first group of MOSFET switches and capacitor arrays, a second group of MOSFET switches and capacitor arrays, and third to Nth group of frequency selection and filtering capacitor arrays;

[0019] The first frequency selection and filtering module is specifically configured to use the frequency control signal given by the system controller to perform selective control on the antenna receiving frequency, so that the receiving antenna cyclically receives signals of multiple known frequencies.

[0020] Furthermore, the first frequency selection and filtering module includes input connection ports VIN1 and VIN2 connected to the input of the external working electrode circuit, and field effect transistors Q1 and Q2;

[0021] Among them, the input connection port VIN1 is connected to the source S2 of the field effect transistors Q1 and Q2, and the input connection port VIN2 is connected to the source S1 of the field effect transistors Q1 and Q2; a capacitor bank C1 is directly connected in parallel to the input connection ports VIN1 and VIN2, a capacitor bank C2 is connected in parallel to the drains D1 and D2 of the field effect transistor Q1, and a capacitor bank C3 is connected in parallel to the drains D1 and D2 of the field effect transistor Q2;

[0022] When the first frequency selection and filtering module A1 and A2 are 0V and 0V, 0V and 3.3V, and 3.3V and 0V in sequence, frequencies 1 (4kHz), frequency 2 (10kHz), and frequency 3 (40kHz) are respectively selected and passed;

[0023] Furthermore, the field effect transistors used in the first frequency selection and filtering module are dual N-channel junction field effect transistors, which are used for selecting the capacitor array combination.

[0024] Furthermore, the first instrumentation amplifier module includes an instrumentation amplifier U1 with extremely low noise and high common mode rejection ratio;

[0025] The negative input terminal of the instrumentation amplifier U1 is connected to the input connection port VIN1, and the positive input terminal of the instrumentation amplifier U1 is connected to the input connection port VIN2;

[0026] A gain control resistor R1 is connected in parallel between the positive input terminal and the negative input terminal of the instrumentation amplifier U1; the positive input terminal of the instrumentation amplifier U1 is grounded through a DC discharge resistor R2;

[0027] The output terminal VOUT1 of the instrumentation amplifier U1 is grounded through a DC discharge resistor R3;

[0028] The instrumentation amplifier U1 is a multi-channel low-noise amplifier with adjustable amplification factor, and the equivalent input noise voltage of the amplifier is less than It is the unit of power spectral density, which is volts per square root hertz.

[0029] Furthermore, the input terminal of the first single-ended to differential module is connected to the output terminal of the first instrumentation amplifier module;

[0030] A DC blocking capacitor R4 is connected in series at the input terminal of the first single-ended to differential module, and R4 is connected to the non-inverting input terminal of the amplifier U2 through a resistor R5; a resistor R7 is connected in parallel between the non-inverting input terminal and the inverting output terminal of the amplifier U2;

[0031] The inverting input terminal of amplifier U2 is grounded through resistors R4 and R6, where R4 is the input current balancing resistor; a resistor R8 is connected in parallel between the inverting input terminal and the non-inverting output terminal of amplifier U2;

[0032] A passive first-order low-pass filter composed of a resistor R9 and a capacitor C5 is connected to the non-inverting output terminal of amplifier U2, and a passive first-order low-pass filter composed of a resistor R10 and a capacitor C7 is connected to the inverting output terminal of amplifier U2; an output terminal VOUT_N1 is connected between R9 and C5; an output terminal VOUT_P1 is connected between R10 and C7; a capacitor C6 is connected in series between VOUT_N1 and VOUT_P1;

[0033] The first single-ended to differential module uses a very low-noise and high common-mode rejection ratio fully differential operational amplifier U2, and adopts the in-phase input mode. To maintain circuit balance, a current adjustment resistor is used at the reverse end to make its input impedance the same as that of the in-phase input of the operational amplifier; a first-order low-pass filter circuit is simultaneously adopted at the differential output end to remove high-frequency noise.

[0034] Further, the second instrumentation amplifier module uses a very low-noise and high common-mode rejection ratio instrumentation amplifier U3 and its bias adjustment circuit. A symmetric first-order high-pass filter is adopted at the input end to remove low-frequency noise, and a first-order high-pass filter is connected after connecting a resistor at the output end to suppress the DC voltage.

[0035] The second instrumentation amplifier module includes a very low-noise and high common-mode rejection ratio instrumentation amplifier U3;

[0036] The negative input terminal of instrumentation amplifier U3 is connected to the output terminal VOUT_N1 of the first single-ended to differential module, and the positive input terminal of instrumentation amplifier U3 is connected to the output terminal VOUT_P1 of the first single-ended to differential module;

[0037] A gain control resistor R12 is connected in parallel between the positive input terminal and the negative input terminal of instrumentation amplifier U3; the positive input terminal of instrumentation amplifier U3 is grounded through a DC discharge resistor R11; the negative input terminal of instrumentation amplifier U3 is grounded through a DC discharge resistor R13;

[0038] The output terminal VOUT2 of instrumentation amplifier U3 is grounded through a DC discharge resistor R14.

[0039] Further, the programmable gain module includes an adjustable gain amplifier composed of an operational amplifier U4, analog switches and resistors. The feedback loop enters one end of the analog switch through 4 groups of RC resistor-capacitor networks respectively, and the other end of the analog switch outputs; the programmable gain module uses analog switches to cooperate with a gain matching network to form an adjustable gain amplifier;

[0040] The negative input terminal of the operational amplifier U4 is connected to the output terminal VOUT2 of the second instrumentation amplifier module through the resistor R15; the positive input terminal of the operational amplifier U4 is grounded through the resistor R16;

[0041] The output terminal VOUT3 of the operational amplifier U4 serves as the output terminal of the programmable gain module; resistors R17, R18, R19, and R20 are connected in parallel between the output terminal VOUT3 of the operational amplifier U4 and the negative input terminal.

[0042] Furthermore, the input terminal of the second frequency selection and filtering module is connected to the output terminal VOUT3 of the programmable gain module, and the output VOUT4 is obtained after passing through the cascaded first band-pass filter and second band-pass filter;

[0043] VOUT3 is connected to the input resistor R1 of the first band-pass filter. After R1 is connected to C2, it enters the non-inverting input terminal of A1. The other end of C2 is grounded. A resistor R2 is connected across the non-inverting input terminal of A1 and the output terminal of A2. A resistor R3 is connected across the output terminal of A1 and the inverting input terminal of A2. A capacitor C1 is connected across the output terminal of A2 and the inverting input terminal of A1. A resistor Rx is connected across the output terminal of A1 and the non-inverting input terminal of A2. Another resistor Rx is connected across the non-inverting input terminal of A2 and the ground; the second band-pass filter has the same structure as the first band-pass filter;

[0044] The first band-pass filter and the second band-pass filter form a second-order second-order band-pass filter, and the cascaded combination forms a fourth-order high-Q narrow-band pass filter. The frequency selection and filtering module uses dual operational amplifiers to form a narrow-band filter with a single frequency point, and then uses the same circuit to form another narrow-band filter with a single frequency point. Two dual operational amplifiers are cascaded to form a complete staggered filter bank. A1 and A2 in the first band-pass filter are one dual operational amplifier, and B1 and B2 in the second band-pass filter are another dual operational amplifier; in the frequency range of 1 kHz - 2 MHz, the received signal is amplified and denoised.

[0045] Furthermore, the input terminal of the second single-ended to differential module is connected to the output terminal of the second frequency selection and filtering module;

[0046] The input terminal of the second single-ended to differential module is connected to the non-inverting input terminal of the amplifier U5 through the resistor R21; resistors R23 are connected in parallel between the non-inverting input terminal and the inverting output terminal of the amplifier U2;

[0047] The inverting input terminal of the amplifier U2 is grounded through the resistors R22 and R27; resistors R24 are connected in parallel between the inverting input terminal and the non-inverting output terminal of the amplifier U2;

[0048] The non-inverting output terminal of amplifier U2 is connected to a passive first-order low-pass filter composed of resistor R25 and capacitor C10, and the inverting output terminal of amplifier U2 is connected to a passive first-order low-pass filter composed of resistor R26 and capacitor C12; there is an output terminal VOUT_N2 connected between R25 and C10; there is an output terminal VOUT_P2 connected between R26 and C12; a capacitor C11 is connected in series between VOUT_N2 and VOUT_P2;

[0049] The second single-ended to differential module uses a very low-noise and high common-mode rejection ratio fully differential operational amplifier U5, and uses the in-phase input mode. To maintain circuit balance, the reverse terminal uses a current adjustment resistor to make its input impedance the same as that of the in-phase input of the operational amplifier; the differential output terminal simultaneously uses a first-order low-pass filter circuit to remove high-frequency noise.

[0050] The present invention has at least the following beneficial effects:

[0051] The present invention effectively reduces the input noise of the signal. In the circuit structure, the first-stage amplifier circuit selects an independent operational instrumentation amplifier with better noise characteristics to build an instrumentation differential amplifier circuit, replacing the commonly used instrumentation operational amplifier, so that the low-noise advantage of the independent operational amplifier is reflected in the circuit design.

[0052] The present invention uses a staggered structure two-stage dual-op amp band-pass filter to replace the single-stage band-pass filter, stabilizing the amplitude-frequency response characteristics near the center frequency band. Compared with the aforementioned MFB type, the stability is stronger, and the Q value is increased to 25, especially having the amplitude-frequency characteristic flatness under the condition of environmental temperature change. The present invention adds a DC discharge circuit between the two-stage amplifier circuits, which has a simple structure and suppresses the DC voltage component.

[0053] After using the instrumentation amplifier and the single-ended to differential amplifier, the present invention uses the instrumentation amplifier and the single-ended to differential amplifier again to transmit the signal, achieving a higher common-mode rejection ratio. The present invention uses multiple groups of mutually parallel resonant matching circuits to form multi-frequency resonant matching. Each resonant matching circuit only needs 1 to 2 groups of resonant capacitors and a common resonant inductor connected in parallel, and each resonant frequency point is independent and the adjustment does not affect each other. In the present invention, the programmable gain circuit adopts a segmented control method with a cross interval, so that the measurement dynamic range spans 4 orders of magnitude to reach 80 dB.

[0054] The circuit of the present invention is applied to the preamplification and filter amplification circuit of the electromagnetic wave resistivity logging while drilling far detection tool, and can work stably for a long time in an environment with a high temperature of 150 °C.

[0055] Other features and advantages of the present invention will be described in the following specification, and part of them will become obvious from the specification or be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the structure pointed out in the specification and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0057] Figure 1 It is a block diagram of a circuit module;

[0058] Figure 2 It is a schematic diagram of a first frequency selection and filtering module;

[0059] Figure 3 It is a schematic diagram of a first instrumentation amplifier module;

[0060] Figure 4 It is a schematic diagram of a first single-ended to differential module;

[0061] Figure 5 It is a schematic diagram of a second instrumentation amplifier module;

[0062] Figure 6 It is a schematic diagram of a programmable gain module;

[0063] Figure 7 It is a schematic diagram of a second frequency selection and filtering module;

[0064] Figure 8 It is a schematic diagram of a second single-ended to differential module;

[0065] Figure 9 It is a circuit schematic diagram of a first frequency selection and filtering module;

[0066] Figure 10 It is a schematic diagram of a programmable gain adjustment curve;

[0067] Figure 11 It is a schematic diagram of the overall circuit amplitude-frequency response 126.672 dB@10 kHz;

[0068] Figure 12 It is a schematic diagram of the overall circuit amplitude-frequency response 35.908 dB@1 kHz. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0069] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0070] The present invention provides a nano-volt level high-Q value multi-frequency signal detection pre-amplification circuit with a simpler structure applicable to all azimuthal electromagnetic wave resistivity while-drilling instruments; it is applicable to solving the multi-frequency point multi-group parallel matching problem in the acquisition and preprocessing of open-loop voltage signals of antenna inductive sensors, effectively improving the signal-to-noise ratio of the overall acquisition circuit; it is applicable to solving the frequency selection filter in a narrow band-pass filter with requirements for the stability of the amplitude-frequency response characteristic near the center frequency point; it can be used alone as a sensor pre-amplification circuit, adopting a segmented programmable gain circuit with a cross interval, enabling the measurement dynamic range to span 4 orders of magnitude up to 80 dB, and realizing high-dynamic range measurement of multi-frequency signals.

[0071] An azimuthal electromagnetic wave nano-volt level high-Q value multi-frequency signal detection circuit while drilling, comprising:

[0072] A first frequency selection filter module, a first instrumentation amplifier module, a first single-ended to differential module, a second instrumentation amplifier module, a programmable gain module, a second frequency selection filter module, and a second single-ended to differential module connected in series in sequence;

[0073] The first frequency selection filter module is used for frequency selection filtering of the nano-volt level signal received by the azimuthal sensor while drilling;

[0074] The first instrumentation amplifier module is used for conditioning the nano-volt level signal output by the first frequency selection filter module to the micro-volt level;

[0075] The first single-ended to differential module is used for differential amplification of the micro-volt signal output by the first instrumentation amplifier module and removing the differential common-mode voltage;

[0076] The second instrumentation amplifier module is used for further amplifying the micro-volt signal output by the first single-ended to differential module and converting it into a single-ended signal;

[0077] The programmable gain module is used for further amplifying the output signal of the second instrumentation amplifier module to reach the measurement range of the A / D acquisition circuit;

[0078] The second frequency selection filter module is used for filtering out out-of-band noise from the output signal of the programmable gain module and retaining the useful signal;

[0079] The second single-ended to differential module is used for polarity conversion of the single-ended voltage signal output by the second frequency selection filter module and filtering out the noise introduced during transmission.

[0080] During specific implementation, as Figure 1 shown. The first frequency selection and filtering module is composed of a MOSFET switch array and a capacitor array, and is used for frequency selection and filtering of the nanovolt-level signals received by the sensor; the first instrumentation amplifier module is composed of a very low-noise and high common-mode rejection ratio instrumentation amplifier, and is used for conditioning the nanovolt-level signals output by the frequency selection and filtering module to the microvolt level; the first single-ended to differential module is composed of a low-noise fully differential operational amplifier, and is used for differentially amplifying the microvolt signals output by the first instrumentation amplifier module and removing the differential common-mode voltage; the first single-ended to differential module is connected to the second instrumentation amplifier module through a shielded cable; the second instrumentation amplifier module is composed of a very low-noise and high common-mode rejection ratio instrumentation amplifier, and is used for further amplifying the microvolt signals output by the first single-ended to differential module and converting them into single-ended signals; the programmable gain module is used for further amplifying the output signals of the second instrumentation amplifier module to reach the measurement range of the A / D acquisition circuit; the second frequency selection and filtering module is composed of a fourth-order band-pass filter, and selects channels through an analog switch, and is used for filtering out out-of-band noise and retaining useful signals; the second single-ended to differential module is composed of a low-noise fully differential operational amplifier, and is used for polarity conversion of the single-ended voltage signals output by the frequency selection and filtering module and filtering out the noise introduced during transmission; the second single-ended to differential module is connected to the subsequent circuit module through a shielded cable.

[0081] The first frequency selection and filtering module includes a first group of MOSFET switches and capacitor arrays, a second group of MOSFET switches and capacitor arrays, and third to Nth groups of frequency selection and filtering capacitor arrays, as Figure 2 shown.

[0082] The frequency control signal given by the system controller is used to select and control the receiving frequency of the antenna, so that the receiving antenna cyclically receives signals of multiple known frequencies; preferably, the field effect transistor is a dual N-channel junction field effect transistor for capacitor array combination selection.

[0083] The first instrumentation amplifier module includes a very low-noise and high common-mode rejection ratio instrumentation amplifier U1 and its bias adjustment circuit, as Figure 3 shown. The output end of the instrumentation amplifier is connected to a resistor and then to a capacitor to suppress the DC voltage, and can provide high suppression performance when needed most. The amplifier is a multi-channel low-noise amplifier with adjustable amplification factor, and the equivalent input noise voltage of the amplifier is less than is the unit of power spectral density, which is volts per square root hertz.

[0084] The first single-ended to differential module includes a very low-noise and high common-mode rejection ratio fully differential operational amplifier U2, which uses the in-phase input method. To maintain circuit balance, a current adjustment resistor is used at the reverse terminal to make its input impedance the same as that of the in-phase input of the operational amplifier. The differential output terminal simultaneously uses a first-order low-pass filter circuit to remove high-frequency noise, such as Figure 4 shown.

[0085] The second instrumentation amplifier module includes a very low-noise and high common-mode rejection ratio instrumentation amplifier U3 and its bias adjustment circuit. The input terminal uses a symmetric first-order high-pass filter to remove low-frequency noise, and the output terminal is connected to a resistor and then to a first-order high-pass filter to suppress the DC voltage, such as Figure 5 shown.

[0086] The programmable gain module includes an adjustable gain amplifier composed of an operational amplifier U4, analog switches, and resistors. The feedback loop consists of 4 groups of RC resistor-capacitor networks that respectively enter one end of the analog switch, and the other end of the analog switch outputs. The programmable gain module uses analog switches in cooperation with a gain matching network to form an adjustable gain amplifier, such as Figure 6 shown.

[0087] The second frequency selection and filtering module includes a two-stage second-order band-pass filter, which is cascaded to form a fourth-order high-Q narrow-band pass filter. The frequency selection and filtering module uses two operational amplifiers to form a narrow-band filter with a single frequency point, and then uses the same circuit to form another narrow-band filter with a single frequency point. Two dual operational amplifiers are cascaded to form a complete staggered filter bank. A1 and A2 are one dual operational amplifier, and B1 and B2 are another dual operational amplifier. In the frequency range of 1 kHz - 2 MHz, the received signal is amplified and denoised, such as Figure 7 shown.

[0088] The second single-ended to differential module includes a very low-noise and high common-mode rejection ratio fully differential operational amplifier U5, which uses the in-phase input method. To maintain circuit balance, a current adjustment resistor is used at the reverse terminal to make its input impedance the same as that of the in-phase input of the operational amplifier. The differential output terminal simultaneously uses a first-order low-pass filter circuit to remove high-frequency noise, such as Figure 8 shown.

[0089] To enable those skilled in the art to better understand the present invention, the principle of the present invention is described below in conjunction with the accompanying drawings:

[0090] Figure 9It is the first frequency selection and filtering module circuit, including connection ports VIN1 and VIN2 to the external working electrode circuit, connection port AGND to the external reference electrode circuit, field effect transistors Q1 and Q2 respectively, and amplifiers U1 and U2 respectively. Among them, connection port VIN1 is connected to the source S2 of field effect transistors Q1 and Q2, and at the same time connected to the negative input terminal of amplifier U1. Connection port VIN2 is connected to the source S1 of field effect transistors Q1 and Q2, and at the same time connected to the positive input terminal of amplifier U1. A DC discharge resistor R2 is connected to the positive input terminal. Connection ports VIN1 and VIN2 are directly connected to capacitor bank C1. The drains D1 and D2 of field effect transistor Q1 are connected in parallel with capacitor bank C2, and the drains D1 and D2 of field effect transistor Q2 are connected in parallel with capacitor bank C3. Connection ports A1 and A2 are used to select one of the three frequencies as the control signal.

[0091] As Figure 3 shown in Figure 4 the figure, the gain control resistor R1 of amplifier U1, the output terminal of amplifier U1 is connected to DC discharge resistor R3, and the output signal passes through a DC blocking capacitor C4 to eliminate the DC component in the signal amplified by the first-stage instrumentation amplifier circuit. It is connected to the non-inverting input resistor R5 of amplifier U2. A resistor R7 is connected in parallel between the non-inverting input terminal and the inverting output terminal of amplifier U2. The inverting input resistors R4 and R6 of amplifier U2, where R4 is the input current balance resistor. A resistor R8 is connected in parallel between the inverting input terminal and the non-inverting output terminal of amplifier U2. The non-inverting output and inverting output terminals of amplifier U2 are simultaneously connected to a passive first-order low-pass filter composed of R9 and C5 and a passive first-order low-pass filter composed of R10 and C7 to form a differential output signal, which is directly connected to connection ports VOUT_N1 and VOUT_P1 for output.

[0092] Amplifiers U1 and U2 form a two-stage amplification circuit, and the total amplification factor is the product of the two-stage amplification factors.

[0093] The inductance values are L(f0 = 40kHz) = 608x10-6H, L(f0 = 10kHz) = 687x10-6H, L(f0 = 4kHz) = 762x10-6H; among the three groups of capacitors, C1 = 2.6065x10-8F, C1 + C2 = 3.69083x10-7F, C1 + C3 = 2.07972x10-6F. Among them, the three resonant points are:

[0094]

[0095]

[0096]

[0097] The three frequency points are 4kHz, 10kHz, and 40kHz respectively.

[0098] Specific description of the second frequency-selective filtering module. The second frequency-selective filtering module is a high-Q staggered signal filter circuit, as Figure 7 shown.

[0099] For the center frequency, there is a calculation formula:

[0100]

[0101] Calculation formula for the circuit quality factor:

[0102]

[0103] In a preferred embodiment of the present invention, taking the second frequency-selective filtering module with a center frequency of 10 kHz as an example for calculation.

[0104] According to the definition formula of the quality factor:

[0105] Q = f0 / B W

[0106] The set value is 25.

[0107] Definition formula of the band-pass filter:

[0108]

[0109] And the definition formula of the dual-frequency point band-pass bandwidth:

[0110] B W = f H - f L

[0111] Wherein, f0, f H f L are the center frequency, the upper and lower cut-off frequency points respectively. Solving gives f L = 9802 Hz, f H = 10202 Hz,

[0112] Let R = 1 kΩ, and the parameters of the first-stage filter are solved: C = 16.24 nF, R = 1 kΩ, R1 = 25 kΩ; the parameters of the second-stage filter are: C = 15.61 nF, R = 1 kΩ, R1 = 25 kΩ.

[0113] In a preferred embodiment of the present invention, taking the minimum signal of 10 nV as an example to elaborate the implementation method of nanovolt-level programmable gain. The input signal dynamic range is 10 nV - 100 μV, and the three-stage gain adjustment curve is as Figure 10 shown.

[0114] The fixed gain of the filter amplification board is 4, and the programmable amplification gains of the filter amplification board are 2.5, 25, and 250 respectively, corresponding to the G1 - G3 gears. The relative gain relationships with respect to the 10 - fold gain of the first gear are 1, 10, and 100 times respectively. After multiplying by the fixed gain of 2000 of the pre - amplification circuit, they are the three gears of G = 20000 times, G = 200000 times, and G = 2M times in the programmable gain adjustment curve.

[0115] After power - on, first detect with a magnification of 10 times. If the detected amplitude is greater than 300 mV, switch to a magnification of 1 time. If the detected amplitude is less than 15 mV, switch to a magnification of 100 times; if currently at a magnification of 100 times, and if the detected amplitude 25 mV < Vmax < 300 mV, switch to a magnification of 10 times; if the detected amplitude Vmax > 300 mV, switch the magnification to 1 time; if currently at a magnification of 1 time, and if the detected amplitude 15 mV < Vmax < 50 mV, switch to a magnification of 10 times; if Vmax < 15 mV, switch to a magnification of 100; the four thresholds are 15 mV, 25 mV, 50 mV, and 300 mV respectively. The lower limit of 15 mV is the critical value of the detection amplitude for accurately collecting the phase; the upper limit of 300 mV is 50% of the positive - bias fluctuation of the crossover voltage, which is the voltage after amplification in the intermediate gear. The voltage thresholds of 25 mV and 50 mV are set to stagger the intervals.

[0116] The overall circuit simulation test results are as Figure 11 、 Figure 12 shown. When the input - end selects a signal frequency of 10 kHz, a noise frequency of 1 kHz, and a signal - to - noise ratio of 1:100. The weak - signal detection circuit has a gain of 126.672 dB for a 10 - kHz signal and a gain of 35.908 dB for a 1 - kHz signal, with an inhibition of 90.7 dB.

[0117] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A downhole azimuth electromagnetic nano-volt level high-Q multi-frequency signal detection circuit, characterized in that, Including: A first frequency selection and filtering module, a first instrumentation amplifier module, a first single-ended to differential module, a second instrumentation amplifier module, a programmable gain module, a second frequency selection and filtering module, and a second single-ended to differential module connected in series in sequence; The first frequency selection and filtering module is used to perform frequency selection and filtering on the nano-volt level signal of the azimuth sensor while drilling; The first instrumentation amplifier module is used to condition the nano-volt level signal output by the first frequency selection and filtering module to the micro-volt level; The first single-ended to differential module is used to differentially amplify the micro-volt signal output by the first instrumentation amplifier module and remove the differential common-mode voltage; The second instrumentation amplifier module is used to further amplify the micro-volt signal output by the first single-ended to differential module and convert it into a single-ended signal; The programmable gain module is used to further amplify the output signal of the second instrumentation amplifier module to reach the measurement range of the A / D acquisition circuit; The second frequency selection and filtering module is used to filter out the out-of-band noise of the output signal of the programmable gain module and retain the useful signal; The second single-ended to differential module is used to convert the polarity of the single-ended voltage signal output by the second frequency selection and filtering module and filter out the noise introduced during transmission.

2. The nano-volt level high-Q multi-frequency signal detection circuit for azimuth electromagnetic wave while drilling according to claim 1, characterized in that The first frequency selection and filtering module includes: a first group of MOSFET switches and capacitor arrays, a second group of MOSFET switches and capacitor arrays, and third to Nth group of frequency selection and filtering capacitor arrays; The first frequency selection and filtering module is specifically used to use the frequency control signal given by the system controller to perform selection control on the antenna receiving frequency, so that the receiving antenna cyclically receives signals of known multiple frequencies.

3. The nano-volt level high-Q multi-frequency signal detection circuit for azimuth electromagnetic wave while drilling according to claim 2, characterized in that The first frequency selection and filtering module includes input connection ports VIN1 and VIN2 connected to the input of the external working electrode circuit, and field effect transistors Q1 and Q2; Among them, the input connection port VIN1 is connected to the source S2 of the field effect transistors Q1 and Q2, and the input connection port VIN2 is connected to the source S1 of the field effect transistors Q1 and Q2; a capacitor group C1 is directly connected in parallel between the input connection ports VIN1 and VIN2, a capacitor group C2 is connected in parallel between the drains D1 and D2 of the field effect transistor Q1, and a capacitor group C3 is connected in parallel between the drains D1 and D2 of the field effect transistor Q2; When the output connection ports A1 and A2 of the first frequency selection and filtering module are 0 volts and 0 volts, the selected frequency is 4 kHz; when A1 and A2 are 0 volts and 3.3 volts, the selected frequency is 10 kHz; when A1 and A2 are 3.3 volts and 0 volts, the selected frequency is 40 kHz.

4. The nano-volt level high-Q multi-frequency signal detection circuit for azimuth electromagnetic wave while drilling according to claim 3, characterized in that The field effect transistors used in the first frequency selection and filtering module are double N-channel junction field effect transistors, which are used to select the capacitor array combination.

5. The nano-volt level high-Q multi-frequency signal detection circuit for azimuth electromagnetic wave while drilling according to claim 1, characterized in that The first instrumentation amplifier module includes an ultra-low noise and high common-mode rejection ratio instrumentation amplifier U1; The negative input terminal of the instrumentation amplifier U1 is connected to the input connection port VIN1, and the positive input terminal of the instrumentation amplifier U1 is connected to the input connection port VIN2; A gain control resistor R1 is connected in parallel between the positive input terminal and the negative input terminal of the instrumentation amplifier U1; the positive input terminal of the instrumentation amplifier U1 is grounded through a DC discharge resistor R2; The output terminal VOUT1 of the instrumentation amplifier U1 is grounded through a DC discharge resistor R3; The instrumentation amplifier U1 is a multi-channel low-noise amplifier with adjustable amplification factor, and the equivalent input noise voltage of the amplifier is less than which is the unit of power spectral density and is volts per root hertz.

6. The downhole azimuth electromagnetic wave nano-volt level high-Q value multi-frequency signal detection circuit according to claim 1, characterized in that The input terminal of the first single-ended to differential module is connected to the output terminal of the first instrumentation amplifier module; A DC-blocking capacitor R4 is connected in series at the input terminal of the first single-ended to differential module. R4 is connected to the non-inverting input terminal of the amplifier U2 through a resistor R5; a resistor R7 is connected in parallel between the non-inverting input terminal and the inverting output terminal of the amplifier U2; The inverting input terminal of the amplifier U2 is grounded through resistors R4 and R6, where R4 is the input current balancing resistor; A resistor R8 is connected in parallel between the inverting input terminal and the non-inverting output terminal of the amplifier U2; The non-inverting output terminal of the amplifier U2 is connected to a passive first-order low-pass filter composed of a resistor R9 and a capacitor C5, and the inverting output terminal of the amplifier U2 is connected to a passive first-order low-pass filter composed of a resistor R10 and a capacitor C7; An output terminal VOUT_N1 is connected between R9 and C5; an output terminal VOUT_P1 is connected between R10 and C7; a capacitor C6 is connected in series between VOUT_N1 and VOUT_P1; The first single-ended to differential module uses an ultra-low-noise, high common-mode rejection ratio fully differential operational amplifier U2, and uses the non-inverting input method. To maintain circuit balance, the inverting terminal uses a current adjustment resistor to make its input impedance the same as that of the non-inverting input of the operational amplifier; the differential output terminals simultaneously use a first-order low-pass filter circuit to remove high-frequency noise.

7. The downhole azimuth electromagnetic wave nano-volt level high-Q value multi-frequency signal detection circuit according to claim 1, characterized in that The second instrumentation amplifier module uses an ultra-low-noise, high common-mode rejection ratio instrumentation amplifier U3 and its bias adjustment circuit. The input terminal uses a symmetric first-order high-pass filter to remove low-frequency noise, and the output terminal is connected to a resistor and then to a first-order high-pass filter to suppress the DC voltage. The second instrumentation amplifier module includes an ultra-low-noise, high common-mode rejection ratio instrumentation amplifier U3; The negative input terminal of the instrumentation amplifier U3 is connected to the output terminal VOUT_N1 of the first single-ended to differential module, and the positive input terminal of the instrumentation amplifier U3 is connected to the output terminal VOUT_P1 of the first single-ended to differential module; A gain control resistor R12 is connected in parallel between the positive input terminal and the negative input terminal of the instrumentation amplifier U3; the positive input terminal of the instrumentation amplifier U3 is grounded through a DC discharge resistor R11; the negative input terminal of the instrumentation amplifier U3 is grounded through a DC discharge resistor R13; The output terminal VOUT2 of the instrumentation amplifier U3 is grounded through a DC discharge resistor R14.

8. The downhole azimuth electromagnetic wave nano-volt level high-Q value multi-frequency signal detection circuit according to claim 1, characterized in that The programmable gain module includes an adjustable gain amplifier composed of an operational amplifier U4, analog switches, and resistors. The feedback loop consists of 4 groups of RC resistor-capacitor networks that respectively enter one end of the analog switch, and the other end of the analog switch outputs; the programmable gain module uses analog switches in cooperation with a gain matching network to form an adjustable gain amplifier; The negative input terminal of the operational amplifier U4 is connected to the output terminal VOUT2 of the second instrumentation amplifier module through a resistor R15; the positive input terminal of the operational amplifier U4 is grounded through a resistor R16; The output terminal VOUT3 of the operational amplifier U4 serves as the output terminal of the programmable gain module; resistors R17, R18, R19, and R20 are connected in parallel between the output terminal VOUT3 of the operational amplifier U4 and the negative input terminal.

9. The downhole azimuth electromagnetic wave nano-volt level high-Q multi-frequency signal detection circuit according to claim 1, characterized in that The input terminal of the second frequency selection and filtering module is connected to the output terminal VOUT3 of the programmable gain module, and outputs VOUT4 after passing through a cascaded first band-pass filter and second band-pass filter; The first band-pass filter and the second band-pass filter form a two-stage second-order band-pass filter, which are cascaded to form a fourth-order high-Q narrow band-pass filter. The frequency selection and filtering module uses dual operational amplifiers to form a narrow band filter with a single frequency point, and then uses the same circuit to form another narrow band filter with a single frequency point. Two dual operational amplifiers are cascaded to form a complete staggered filter bank. A1 and A2 in the first band-pass filter are a pair of dual operational amplifiers, and B1 and B2 in the second band-pass filter are another pair of dual operational amplifiers; in the frequency range of 1 kHz - 2 MHz, the received signal is amplified and denoised.

10. The downhole azimuth electromagnetic wave nano-volt level high-Q multi-frequency signal detection circuit according to claim 1, characterized in that The input terminal of the second single-ended to differential module is connected to the output terminal of the second frequency selection and filtering module; The input terminal of the second single-ended to differential module is connected to the non-inverting input terminal of the amplifier U5 through a resistor R21; resistors R23 are connected in parallel between the non-inverting input terminal and the inverting output terminal of the amplifier U2; The inverting input terminal of the amplifier U2 is grounded through resistors R22 and R27; resistors R24 are connected in parallel between the inverting input terminal and the non-inverting output terminal of the amplifier U2; The non-inverting output terminal of the amplifier U2 is connected to a passive first-order low-pass filter composed of a resistor R25 and a capacitor C10, and the inverting output terminal of the amplifier U2 is connected to a passive first-order low-pass filter composed of a resistor R26 and a capacitor C12; an output terminal VOUT_N2 is connected between R25 and C10; an output terminal VOUT_P2 is connected between R26 and C12; a capacitor C11 is connected in series between VOUT_N2 and VOUT_P2; The second single-ended to differential module uses an ultra-low noise and high common-mode rejection ratio fully differential operational amplifier U5, and uses the in-phase input mode. To maintain circuit balance, the reverse terminal uses a current adjustment resistor to make its input impedance the same as that of the in-phase input of the operational amplifier; the differential output terminal simultaneously uses a first-order low-pass filter circuit to remove high-frequency noise.

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