A circuit device for eliminating baseline drift

Abstract

The present invention discloses a circuit device for eliminating baseline drift, comprising: a pre-stage processing circuit, a differential amplifier circuit, a low-pass filter, a nonlinear limiting stage circuit and an integral feedback circuit; wherein the pre-stage processing circuit converts and amplifies an input current pulse signal to obtain a voltage signal, and the voltage signal and a feedback signal output by the integral feedback circuit are simultaneously input into the differential amplifier circuit, and an output signal is obtained after passing through the differential amplifier circuit and the low-pass filter; in addition, an integral feedback circuit is added to the entire circuit to form a high-pass filter, thereby eliminating DC offset in the circuit, and on the basis of introducing the integral feedback, a nonlinear limiting stage circuit is added to the entire circuit, thereby eliminating baseline drift caused by AC coupling.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear electronic technology, and more particularly, relates to a circuit device for eliminating baseline drift. Background Art

[0002] In recent years, amidst the rapid development of electronics, nuclear electronic testing technology has also continued to advance, demonstrating its unique advantages in areas such as neutron logging while drilling (LWD). As a key component of well logging technology, LWD neutron logging enables simultaneous drilling and logging operations, thereby improving the efficiency of oil exploration and development. Currently, the oil exploration and development industry is gradually shifting to reservoirs with more complex geological structures. Neutron logging while drilling, with its inherent advantages, plays a vital role in the exploration and development of these reservoirs.

[0003] In the spectrum acquisition board, the current pulse signal output by the gamma-ray detector is pre-processed by a preamplifier before entering the density acquisition circuit. This circuit, consisting of an analog forward channel and a digital processing circuit, amplifies and shapes the nuclear pulse signal, calculates its pulse height, and then plots the formation energy spectrum, thereby obtaining formation density information. Therefore, accurate measurement of pulse signals is paramount in nuclear well logging technology. In the analog circuit test channel of the spectrum acquisition module, baseline drift can affect test accuracy.

[0004] Traditionally, baseline drift is eliminated mainly by software, such as sliding average filtering, interpolation fitting, wavelet transform and other methods. However, sliding filtering easily causes the loss of low-frequency components, resulting in distortion of the filtered signal; interpolation fitting has relatively weak processing capabilities for severe baseline drift; and wavelet transform has a large amount of computational complexity when applied. These methods all have defects such as poor removal effect, inability to effectively improve accuracy, and inability to process signals in real time, which are not conducive to subsequent signal processing. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a circuit device for eliminating baseline drift. A nonlinear limiting stage is added to a feedback loop. The overall circuit device can quickly and effectively eliminate baseline drift, making it easier for subsequent circuits to accurately obtain its pulse height value.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a circuit device for eliminating baseline drift, characterized by comprising: a pre-stage processing circuit, a differential amplifier circuit, a low-pass filter, a nonlinear limiting stage circuit, and an integral feedback circuit;

[0007] The pre-stage processing circuit adopts two-stage amplification, wherein the first stage adopts a charge amplifier and the second stage adopts a voltage amplifier. The input current pulse signal is converted into a voltage signal by the charge amplifier, and the voltage signal is amplified by the voltage amplifier and then input into the differential amplifier circuit.

[0008] The reverse input terminal of the differential amplifier circuit receives the voltage signal processed by the pre-stage processing circuit, and the positive input terminal receives the feedback signal output by the integral feedback circuit. The voltage signal and the feedback signal are combined to obtain a differential signal through the differential amplifier circuit.

[0009] The low-pass filter performs pseudo-Gaussian shaping processing on the differential signal to obtain an output signal;

[0010] The nonlinear limiting stage circuit has an input terminal connected to the output signal, and an output terminal connected to the input terminal of the integral feedback circuit; the nonlinear limiting stage circuit adopts a slew rate limiting stage, and its slew rate is limited to Ic / C, where Ic is the current flowing through the capacitor in the slew rate limiting circuit, and C is the capacitance of the capacitor in the slew rate limiting circuit; the nonlinear limiting stage circuit reduces the area of ​​the output signal before being processed by the integral feedback circuit to obtain a zero-area pulse signal;

[0011] The integral feedback circuit uses an inverting integrator, the input end of the inverting integrator is connected to the output end of the slew rate limiting stage circuit, and the zero-area pulse signal is integrated by the inverting integrator to output a constant DC signal and fed back to the differential amplifier circuit, thereby realizing baseline elimination of the entire circuit.

[0012] The object of the invention of the present invention is achieved like this:

[0013] The present invention provides a circuit device for eliminating baseline drift, comprising: a pre-stage processing circuit, a differential amplifier circuit, a low-pass filter, a nonlinear limiting stage circuit, and an integral feedback circuit. The pre-stage processing circuit converts and amplifies an input current pulse signal to obtain a voltage signal, and the voltage signal and a feedback signal output by the integral feedback circuit are simultaneously input into the differential amplifier circuit, and an output signal is obtained after passing through the differential amplifier circuit and the low-pass filter. In addition, an integral feedback circuit is added to the entire circuit to form a high-pass filter, thereby eliminating DC offset in the circuit. On the basis of introducing the integral feedback, a nonlinear limiting stage circuit is added to the entire circuit, thereby eliminating baseline drift caused by AC coupling.

[0014] At the same time, the circuit device for eliminating baseline drift of the present invention also has the following beneficial effects:

[0015] (1) Compared with the prior art, the present invention eliminates baseline drift through hardware devices, which is not likely to cause the loss of low-frequency components and signal distortion. The entire circuit device can amplify and shape the nuclear pulse signal, eliminate baseline drift, and facilitate the subsequent circuit to accurately obtain its pulse height value. It has a simple overall solution, good real-time processing effect, and effectively improves the accuracy rate.

[0016] (2) The present invention designs an integral feedback circuit at the output end to form a high-pass filter. Compared with the traditional high-pass filtering method, it avoids the influence of the circuit composite transfer function caused by the creation of a single real pole due to its own RC constant, eliminates the DC offset caused by the leakage current of the detector and the non-ideal characteristics of the operational amplifier, and does not affect the function of the circuit itself.

[0017] (3) The present invention adds a nonlinear limiting stage circuit to the integral feedback circuit to eliminate the baseline drift caused by AC coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of a circuit device for eliminating baseline drift according to the present invention;

[0019] Figure 2 This is a circuit diagram of a circuit device for eliminating baseline drift according to the present invention;

[0020] Figure 3 This is the waveform diagram of the circuit eliminating DC bias signal;

[0021] Figure 4 It is the waveform of the circuit signal baseline drift;

[0022] Figure 5 This is the waveform of the circuit eliminating baseline drift. DETAILED DESCRIPTION

[0023] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0024] Example

[0025] Figure 1 This is a schematic diagram of a circuit device for eliminating baseline drift according to the present invention.

[0026] In this embodiment, if Figure 1 As shown, the present invention provides a circuit device for eliminating baseline drift, comprising: a pre-stage processing circuit, a differential amplifier circuit, a low-pass filter, a nonlinear limiting stage circuit, and an integral feedback circuit;

[0027] The pre-processing circuit adopts two-stage amplification, of which the first stage adopts a charge amplifier and the second stage adopts a voltage amplifier. The input current pulse signal is converted into a voltage signal by the charge amplifier, and the voltage signal is amplified by the voltage amplifier and then input into the differential amplifier circuit.

[0028] The inverting input terminal of the differential amplifier circuit receives the voltage signal processed by the preamplifier circuit, and the positive input terminal receives the feedback signal output by the integral feedback circuit. The voltage signal and the feedback signal are combined through the differential amplifier circuit to obtain a differential signal.

[0029] The low-pass filter performs pseudo-Gaussian shaping on the differential signal to obtain an output signal. In the loop composed of the differential amplifier circuit, the low-pass filter, the nonlinear limiting stage circuit, and the integral feedback circuit, the low-pass filter provides the necessary dominant pole for the stability of the loop. The gain of the feedback loop is dynamically reduced only when a large and fast signal appears. Due to the presence of the low-pass filter, the device is characterized by a very low bandwidth and essentially zero response to each pulse. Therefore, the low-pass filter is regarded as a flat gain block with a gain of 1 in the loop. In this embodiment, in order to meet the measurement requirements of the subsequent analysis equipment, the signal must have a narrow time width and a relatively flat top, which is achieved using a two-stage Sallen-Key filter.

[0030] The input of the nonlinear limiting stage circuit is connected to the output signal, and its output is connected to the inverting input of the integral feedback circuit. In this embodiment, after the integral feedback is introduced, the circuit has a high-pass characteristic, which will cause the problem that only AC coupling circuits will cause, that is, baseline drift. A nonlinear limiting stage circuit can be added to the integrator feedback loop to solve the problem of output waveform baseline drift. The specific method is as follows: the nonlinear limiting stage circuit uses a slew rate limiting stage, and its slew rate is limited to Ic / C, where Ic is the current flowing through the capacitor in the slew rate limiting circuit, and C is the capacitance of the capacitor in the slew rate limiting circuit; the nonlinear limiting stage circuit reduces the area of ​​the output signal before it is processed by the integral feedback circuit to obtain a zero-area pulse signal. For a specific input signal, the capacitance of the capacitor in the nonlinear limiting stage circuit can be changed to change the charging and discharging time of the capacitor, thereby adjusting the slew rate of the device so that the slew rate of the device is always lower than the slew rate of the differential operational amplifier.

[0031] Integral feedback circuits always carry a certain amount of DC offset in their output signals due to detector leakage current and the non-ideal characteristics of the operational amplifier. This has a certain impact on the subsequent pulse height detection system and needs to be filtered out. Using a technique called servo feedback circuit, an inverting integrator is added to the circuit where the DC offset needs to be filtered out as feedback. The input of the inverting integrator is connected to the output of the nonlinear limiting stage circuit. The zero-area pulse signal is integrated by the inverting integrator, outputting a constant DC signal that is fed back to the operational amplifier circuit, thereby achieving baseline elimination for the entire circuit.

[0032] In this embodiment, the transfer function of the entire circuit device satisfies:

[0033]

[0034] Where V0 is the output signal, V is the input signal, G(s) is the gain of the differential amplifier circuit, N(s) is the gain of the nonlinear limiting stage circuit, and φ(s) is the gain of the loop consisting of the differential amplifier circuit, low-pass filter, nonlinear limiting stage circuit, and integral feedback circuit.

[0035] The transfer function shows that when the input signal is small and slow, there is no slew rate limitation, and the gain of the nonlinear limiting stage circuit, N(s), is very small, maintaining the gain of the entire device at G(s). When the input signal is large and fast, the slew rate limitation causes attenuation, and the gain of the nonlinear limiting stage circuit, N(s), becomes very large, reducing the overall loop gain, φ(s). At this point, the input signal remains unaffected by the feedback path.

[0036] Figure 2 This is a circuit diagram of a circuit device for eliminating baseline drift according to the present invention;

[0037] In this embodiment, if Figure 2As shown, the VCC terminals of the operational amplifiers U1 to U8 are connected to an external positive power supply, and the VEE terminals are connected to an external negative power supply. The input current pulse signal enters the preamplifier circuit through the resistor R14, and is input to the operational amplifier circuit after passing through the first-stage charge amplifier U7 and the second-stage voltage amplifier U8; in the operational amplifier circuit, the voltage signal processed by the preamplifier circuit is input to the reverse input terminal after passing through the resistor R3, and the feedback signal is directly input to the positive input terminal. The operational amplifier U3 processes the voltage signal and the feedback signal and inputs them to the pseudo-Gaussian shaper through the resistor R5; in the pseudo-Gaussian shaper, the differential signal passes through the operational amplifiers U4 and U5 in sequence to obtain the output signal; in this embodiment, the differential signal passes through the operational amplifiers U4 and U5 in sequence to obtain the output signal. In this embodiment, the output signal is input to the slew rate limiting stage circuit, and the charging and discharging time of the capacitor C1 is changed by changing the capacitance of the capacitor C1, thereby adjusting the slew rate of the device so that the slew rate of the device is always lower than the slew rate of the differential operational amplifier; when the output signal passes through the operational amplifiers U1 and U2, the capacitor C1 is charged and discharged, and during the charging and discharging process, the slew rate limiting stage circuit outputs positive and negative pulse signals to the integral feedback circuit; in the integral feedback circuit, the input end of the operational amplifier U6 is connected to the output end of the slew rate limiting stage circuit through the resistor R9, and the positive and negative pulse signals are integrated to output a constant DC signal and fed back to the operational amplifier circuit, thereby realizing baseline elimination of the entire circuit.

[0038] Figure 3 This is the waveform diagram of the circuit eliminating DC bias signal;

[0039] In this embodiment, if Figure 3 As shown, now Figure 2 The input signal of the circuit shown is superimposed with a DC signal. By observing the input and output waveforms with an oscilloscope, it can be seen that the DC signal has been filtered out of the output signal.

[0040] Figure 4 It is the waveform of the circuit signal baseline drift;

[0041] Figure 5 This is the waveform of the circuit eliminating baseline drift;

[0042] In this embodiment, if Figure 4 As shown in the figure, after the integral feedback is introduced, the circuit has a high-pass characteristic, which will cause the problem that only AC coupling circuits will cause, that is, baseline drift. When outputting a single pulse signal, the signal will drift in the opposite direction until the waveform area above and below the zero level is equal, that is, the charge and discharge balance is achieved. The faster the input pulse frequency, the more obvious the baseline drift phenomenon. In order to solve Figure 4To solve this problem, we can add a nonlinear limiting stage circuit to the integrator feedback loop. This nonlinear link will suppress the gain of the input spike signal, but it will not limit the low-frequency signal that should pass through the feedback loop. By adding a nonlinear limiting stage link, the entire circuit can still eliminate DC offset while also solving the problem of output waveform baseline drift. Figure 5 As shown, after the nonlinear limiting stage circuit, Figure 4 The pulse shown in the figure gradually shifts downward, and the circuit with a nonlinear limiting stage link eliminates the baseline drift.

[0043] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. A circuit device for eliminating baseline drift, characterized in that: include: Pre-stage processing circuit, differential amplifier circuit, low-pass filter, nonlinear limiting stage circuit and integral feedback circuit; The pre-stage processing circuit adopts two-stage amplification, wherein the first stage adopts a charge amplifier and the second stage adopts a voltage amplifier. The input current pulse signal is converted into a voltage signal by the charge amplifier, and the voltage signal is amplified by the voltage amplifier and then input into the differential amplifier circuit. The reverse input terminal of the differential amplifier circuit receives the voltage signal processed by the pre-stage processing circuit, and the positive input terminal receives the feedback signal output by the integral feedback circuit. The voltage signal and the feedback signal are combined to obtain a differential signal through the differential amplifier circuit. The low-pass filter performs pseudo-Gaussian shaping processing on the differential signal to obtain an output signal; The input end of the nonlinear limiting stage circuit is connected to the output signal, and the output end thereof is connected to the input end of the integral feedback circuit; the nonlinear limiting stage circuit adopts a slew rate limiting stage, and its slew rate is limited to Ic / C, where Ic is the current flowing through the capacitor in the slew rate limiting circuit, and C is the capacitance value of the capacitor in the slew rate limiting circuit; The nonlinear limiting stage circuit reduces the area of ​​the output signal before being processed by the integral feedback circuit to obtain a zero-area pulse signal; The integral feedback circuit uses an inverting integrator, the input end of the inverting integrator is connected to the output end of the slew rate limiting stage circuit, and the zero-area pulse signal is integrated by the inverting integrator to output a constant DC signal and fed back to the differential amplifier circuit, thereby realizing baseline elimination of the entire circuit.

2. A circuit device for eliminating baseline drift according to claim 1, characterized in that: The low-pass filter uses a two-stage Sallen-Key filter, the poles of the low-pass filter are at least ten times greater than the poles of the integral feedback circuit, and the low-pass filter is regarded as a flat gain block with a gain of 1 in the loop composed of the differential amplifier circuit, the low-pass filter, the nonlinear limiting stage circuit and the integral feedback circuit.

3. A circuit device for eliminating baseline drift according to claim 1, characterized in that: The transfer function of the entire circuit device satisfies: Among them, V0 is the output signal, V i is the input signal, G(s) is the gain of the differential amplifier circuit, N(s) is the gain of the nonlinear limiting stage circuit, and φ(s) is the gain of the loop consisting of the differential amplifier circuit, low-pass filter, nonlinear limiting stage circuit and integral feedback circuit.

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