Signal processing circuit and electronic device

Abstract

This application provides a signal processing circuit and an electronic device. The signal processing circuit includes: a charge amplifier circuit for receiving a differential charge signal output from a sensor; amplifying and converting the differential charge signal to output a first voltage signal; a non-inverting amplifier circuit connected to the charge amplifier circuit for receiving the first voltage signal; amplifying the first voltage signal to output a second voltage signal; a voltage-controlled filter circuit connected to the non-inverting amplifier circuit for receiving the second voltage signal; amplifying and filtering the second voltage signal to output a third voltage signal; and a hysteresis comparator circuit connected to the voltage-controlled filter circuit for receiving the third voltage signal and comparing it to obtain a stable square wave signal. The solution provided in this application can effectively suppress common-mode noise signals, has a fast response speed, is less affected by circuit impedance, and produces a better square wave signal output.

Description

Technical Field

[0001] This application relates to the field of low-frequency analog technology, and in particular to a signal processing circuit and electronic device. Background Technology

[0002] With the development of intelligent technology, various intelligent devices have become widespread. The realization of intelligent functions of these devices mainly relies on various sensors. These sensors detect signals from nature, such as light, electricity, pressure, and temperature, and convert these signals into digital signals (or square wave signals) that can be processed by computers.

[0003] Existing solutions often use dedicated chips when building signal circuits to process sensor outputs, which is costly; or they are built based on single-ended charge amplification principles or passive capacitor charging and discharging principles, which can easily lead to problems such as large common-mode noise in the circuit and poor conversion performance. Summary of the Invention

[0004] In view of the above problems, this application provides a signal processing circuit and electronic device that solves or at least partially solves the above problems.

[0005] In one embodiment of this application, a signal processing circuit is provided. The signal processing circuit includes:

[0006] A charge amplifier circuit is used to receive the differential charge signal output by the sensor; amplify and convert the differential charge signal to output a first voltage signal;

[0007] A non-inverting amplifier circuit, connected to the charge amplifier circuit, is used to receive the first voltage signal; amplify the first voltage signal, and output a second voltage signal.

[0008] A voltage-controlled filter circuit, connected to the non-inverting amplifier circuit, is used to receive the second voltage signal, amplify and filter the second voltage signal, and output a third voltage signal.

[0009] The hysteresis comparator circuit, connected to the voltage-controlled filter circuit, is used to receive the third voltage signal and compare and process the third voltage signal to obtain a stable square wave signal.

[0010] Optionally, the charge amplification circuit includes:

[0011] The first operational amplifier has an inverting input terminal and a non-inverting input terminal, which are respectively used to receive the positive charge signal and the negative charge signal in the differential charge signal; the output terminal of the first operational amplifier is connected to the input terminal of the non-inverting amplifier circuit to output the first voltage signal to the non-inverting amplifier circuit.

[0012] The first feedback unit is connected between the output terminal and the inverting input terminal of the first operational amplifier, and is used to provide feedback to the inverting input terminal of the first operational amplifier based on the first voltage signal.

[0013] The second feedback unit is connected at one end to the non-inverting input of the first operational amplifier to receive the negative charge signal, convert the negative charge signal into a fourth voltage signal, and output it from the other end.

[0014] A reference voltage unit, connected to the other end of the second feedback unit, is used to provide a reference voltage.

[0015] Optionally, the first feedback unit consists of a first feedback capacitor and a first feedback resistor connected in parallel; the second feedback unit consists of a second feedback capacitor and a second feedback resistor connected in parallel; wherein the first feedback capacitor and the second feedback capacitor have the same capacitive reactance, and the first feedback resistor and the second feedback resistor have the same resistance value;

[0016] The reference voltage unit includes a second operational amplifier, a first resistor, and a second resistor; one end of the first resistor is connected to a voltage source, and the other end is connected to the non-inverting input terminal of the second operational amplifier at a common connection point with one end of the second resistor; the other end of the second resistor is grounded; the inverting input terminal of the second operational amplifier is connected to the output terminal of the second operational amplifier and the other end of the second feedback unit; the first resistor and the second resistor have the same resistance value.

[0017] Optionally, the charge amplification circuit further includes: a first filter capacitor, a second filter capacitor, and a stabilizing resistor; one end of the first filter capacitor is connected to the inverting input terminal of the first operational amplifier, and the other end is used to receive the positive charge signal; the first filter capacitor is used to filter the positive charge signal and transmit it to the inverting input terminal of the first charge amplifier; one end of the second filter capacitor is connected to the non-inverting input terminal of the first operational amplifier, and the other end is used to receive the negative charge signal; the second filter capacitor is used to filter the negative charge signal and transmit it to the non-inverting input terminal of the first operational amplifier.

[0018] The two ends of the stabilizing resistor are respectively connected to the other ends of the first filter capacitor and the second filter capacitor; the stabilizing resistor is used to stabilize the input positive charge signal and the negative charge signal, so that the positive charge signal and the negative charge signal are kept in a state of opposite polarity and the same magnitude; wherein, the first filter capacitor and the second filter capacitor have the same capacitive reactance.

[0019] Optionally, the in-phase amplifier circuit includes: a third operational amplifier and a third feedback unit;

[0020] The non-inverting and inverting input terminals of the third operational amplifier are respectively connected to the output terminal of the first operational amplifier and one end of the third feedback unit; the output terminal of the third operational amplifier is connected to the input terminal of the voltage-controlled filter circuit to output the second voltage signal to the voltage-controlled filter circuit.

[0021] The other end of the third feedback unit is connected to the output terminal of the third operational amplifier, and is used to provide feedback to the inverting input terminal of the third operational amplifier based on the second voltage signal;

[0022] The third feedback unit consists of a third feedback capacitor and a third feedback resistor connected in parallel.

[0023] Optionally, the non-inverting amplifier circuit further includes: an adjustment unit, one end of which is connected to both the inverting input terminal of the third operational amplifier and one end of the third feedback unit, and the other end of which is connected to the input terminal of the voltage-controlled filter circuit; the adjustment unit is used to adjust the voltage signal at the inverting input terminal of the third operational amplifier to the reference voltage and then output it to the voltage-controlled filter circuit; wherein, the adjustment unit consists of a first resistor and a first adjustable resistor.

[0024] Optionally, the voltage-controlled filter circuit includes: an active voltage-controlled filter unit, whose input and output terminals are respectively connected to the output terminal of the third operational amplifier and the input terminal of the hysteresis comparator circuit, for amplifying and filtering the second voltage signal and outputting the third voltage signal to the hysteresis comparator circuit; and a limiting unit, whose two ends are respectively connected to the input and output terminals of the active voltage-controlled filter unit, for limiting the amplitude of the third voltage signal so that the amplitude of the third voltage signal is kept within an appropriate range.

[0025] Optionally, the active voltage-controlled filter unit includes: a fourth operational amplifier, a second resistor, a third resistor, a third capacitor, and a fourth feedback unit; the inverting input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier through the second and third resistors connected in series; the common junction of the second and third resistors is connected to one end of the third capacitor, and the other end of the third capacitor is connected to the non-inverting input terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier is connected to the input terminal of the hysteresis comparator circuit to output the third voltage signal to the hysteresis comparator circuit;

[0026] One end of the fourth feedback unit is connected to the common junction of the inverting input terminal of the fourth operational amplifier and the third resistor, and the other end is connected to the output terminal of the fourth operational amplifier. It is used to provide feedback to the inverting input terminal of the fourth operational amplifier based on the third voltage signal. The fourth feedback unit consists of a fourth feedback resistor and a fourth feedback capacitor connected in parallel.

[0027] Optionally, the limiting unit includes: a first diode, a second diode, and a fourth resistor;

[0028] The anode of the first diode and the cathode of the second diode are connected to the output terminal of the fourth operational amplifier at a common connection point. The cathode of the first diode, the anode of the second diode, and one end of the fourth resistor are connected to a common connection point. The other end of the fourth resistor is connected to the common connection point of the second resistor, the third resistor, and the third capacitor.

[0029] Optionally, the hysteresis comparator circuit includes: a fifth operational amplifier, a threshold adjustment unit, and a fifth feedback resistor; one end of the threshold adjustment unit is connected to the output terminal of the second operational amplifier, and the other end is connected to the non-inverting input terminal of the fifth operational amplifier; the inverting input terminal of the fifth operational amplifier is used to connect to the third voltage signal output by the output terminal of the fourth operational amplifier.

[0030] One end of the fifth feedback resistor is connected to the output terminal of the fifth operational amplifier, and the other end is connected to the common connection point of the non-inverting input terminal of the fifth operational amplifier and the threshold adjustment unit. The fifth feedback resistor is used to provide feedback to the non-inverting input terminal of the fifth operational amplifier based on the square wave signal output from the output terminal of the fifth operational amplifier, so that the fifth operational amplifier can determine the appropriate threshold voltage based on the feedback information, and compare and process the third voltage signal based on the threshold voltage to obtain the square wave signal. The threshold voltage is determined by the fifth operational amplifier based on the reference voltage output from the output terminal of the second operational amplifier connected to the threshold adjustment unit, the resistance value corresponding to the threshold unit, the resistance value of the fifth feedback resistor, and the voltage source.

[0031] In another embodiment of this application, an electronic device is provided. This electronic device includes the signal processing circuit described in the embodiments of this application.

[0032] The technical solution provided in this application includes a signal processing circuit comprising a charge amplifier circuit, a non-inverting amplifier circuit, a voltage-controlled filter circuit, and a hysteresis comparator circuit. The differential charge signal received from the sensor output is first amplified and converted by the charge amplifier circuit into a first collectable voltage signal. Since the first voltage signal is relatively weak, it is further amplified by the non-inverting amplifier circuit to obtain a corresponding second voltage signal, which is then output to the voltage-controlled filter circuit. The voltage-controlled filter circuit amplifies and filters the second voltage signal to obtain a corresponding third voltage signal, which is then output to the hysteresis comparator circuit. The hysteresis comparator circuit compares and processes the third voltage signal to obtain a stable square wave signal. The solution provided in this application can effectively suppress common-mode noise signals, has a fast response speed, is less affected by circuit impedance, and produces a better square wave signal output. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1a A schematic diagram of the structure of an ideal operational amplifier provided in an embodiment of this application is shown;

[0035] Figure 1b This invention provides a schematic diagram illustrating the voltage transfer characteristics of an operational amplifier according to an embodiment of the present application.

[0036] Figure 2a A schematic diagram of the signal processing circuit provided in one embodiment of this application is shown;

[0037] Figure 2b for Figure 2a A detailed structural diagram of the signal processing circuit is shown;

[0038] Figure 3a A schematic diagram of the structure of a conventional charge amplifier circuit provided in an embodiment of this application is shown;

[0039] Figure 3b A schematic diagram of the charge amplifier circuit provided in one embodiment of this application is shown;

[0040] Figure 4a A schematic diagram of the structure of a conventional inverting amplifier provided in an embodiment of this application is shown;

[0041] Figure 4b A schematic diagram of the structure of an in-phase amplifier provided in one embodiment of this application is shown;

[0042] Figure 5 A schematic diagram of the structure of a voltage-controlled filter circuit provided in an embodiment of this application is shown;

[0043] Figure 6 A schematic diagram of the hysteresis comparator circuit provided in one embodiment of this application is shown;

[0044] Figure 7a A schematic diagram illustrating the relationship between the input and output signals of a hysteresis comparator circuit provided in an embodiment of this application is shown.

[0045] Figure 7b A schematic diagram illustrating the relationship between the input and output signals of a hysteresis comparator circuit provided in another embodiment of this application is shown. Detailed Implementation

[0046] Currently, in the process of realizing intelligent functions in equipment, since natural phenomena such as light, electricity, temperature, and pressure cannot be directly processed by computers, sensors (such as pressure sensors, photoelectric sensors, and temperature sensors) are often used to detect information such as light, electricity, temperature, and pressure. Generally, sensors convert the detected light, electricity, and pressure information into charge signals for output. However, the charge signals output by sensors are weak signals. Therefore, these weak charge signals need to be amplified and converted into analog voltage signals (hereinafter referred to as voltage signals). Then, the voltage signals are filtered and converted from analog to digital to finally output a square wave signal for subsequent processing modules.

[0047] As mentioned in the background section, existing signal processing circuits suffer from high costs and significant common-mode noise during conversion when amplifying, converting, and filtering weak charge signals output from sensors. Therefore, this application optimizes existing signal processing circuits in terms of circuit structure, impedance matching, response speed, frequency, and load, providing a new signal processing circuit and electronic device.

[0048] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings.

[0049] In some processes described in the specification, claims, and accompanying drawings of this application, multiple operations appearing in a specific order are included. These operations may be executed out of order or in parallel. Operation numbers such as 101, 102, etc., are merely used to distinguish different operations and do not represent any execution order. Furthermore, these processes may include more or fewer operations, and these operations may be executed sequentially or in parallel. It should be noted that the terms "first," "second," etc., used herein are used to distinguish different messages, devices, modules, etc., and do not represent a sequential order, nor do they limit "first" and "second" to different types. The term "or / and" in this application is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A or / and B means that A can exist alone, A and B can exist simultaneously, or B can exist alone. The character " / " in this application generally indicates that the preceding and following related objects have an "or" relationship. It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system including said element. Furthermore, the following embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0050] Before introducing the technical solutions provided in the various embodiments of this application, a brief overview of the basic structure of an operational amplifier will be given. Specifically,

[0051] An operational amplifier (OPA) is a direct-coupled amplifier with dual-ended input (or differential-mode input), single-ended output, high gain voltage amplification, high input impedance, and low output impedance. Initially used primarily for analog operations such as addition and multiplication, it has gradually become a general-purpose gain device, widely used in various fields of analog electronic circuits. See also Figure 1a The schematic diagram of an ideal operational amplifier (hereinafter referred to as an ideal operational amplifier) ​​shows that it is generally a multi-terminal device, including a non-inverting input (port 3), an inverting input (port 2), an output (port 1), and power supply terminals (ports 4 and 5). It can detect the difference u between the signals applied to the two input terminals (ports 3 and 2). idAfter being amplified by a factor of its intrinsic gain Av, the signal is transmitted to the output terminal (i.e., port 1), i.e., u. out =Av*u id =A V* (u + -u - Where u+ and u- are the terminal voltages of the non-inverting and inverting input terminals of the operational amplifier, respectively. The two power supply terminals of the operational amplifier are used to connect the positive and negative DC voltage sources (Vcc+ and Vcc-) applied during operation. In addition to containing... Figure 1a In addition to the ports shown, it may also include terminals connected to the zero-adjustment potentiometer, idle terminals, etc., which are not limited here. For details on the specific ports that an operational amplifier may include, please refer to the existing content.

[0052] Figure 1a The ideal operational amplifier shown in the figure satisfies the following characteristics: infinitely large differential input impedance (i.e., Z). i =∞), open-loop output impedance equal to zero (i.e., Zo = 0), infinite open-loop voltage gain (or open-loop voltage amplification factor, Av = ∞), infinite common-mode rejection ratio KCMR (KCMR = ∞, not shown in the figure), and infinite open-loop bandwidth (i.e., BW = ∞, not shown in the figure).

[0053] Furthermore, the characteristics of an operational amplifier also include voltage transfer characteristics, which are curves representing the relationship between the output voltage and the input voltage of the operational amplifier. For an operational amplifier powered by dual voltage sources (i.e., positive and negative DC voltage sources), its voltage transfer characteristics are as follows: Figure 1b As shown, Figure 1b The left and right sides of the image show the voltage transfer characteristics of the operational amplifier under ideal and actual conditions, respectively. Figure 1b As shown on the right, the voltage transfer characteristics under actual conditions can be divided into a linear region (the area marked with diagonal lines in the figure) and a nonlinear region (the area outside the diagonal lines in the figure); in the linear region, the output voltage u out With input voltage u id The output voltage u changes with the change; in other words, the output voltage u out With input voltage u id There is a linear amplification relationship between them; in the nonlinear region, the output voltage u out There are only two possibilities, namely +U OH or -U OL , where +U OH This indicates the positive saturation voltage (close to the positive power supply voltage V). CC+ ), -U OL This indicates the negative saturation voltage (close to the negative power supply voltage V). CC- Regarding the voltage transfer characteristics of an ideal operational amplifier (e.g.) Figure 1b The linear and nonlinear regions shown on the left can be found in the above description. Figure 1b The right side shows a description of the voltage transfer characteristics under actual conditions.

[0054] Based on the description of the voltage transfer characteristics of operational amplifiers, it can be known that operational amplifiers can operate in the linear region or the nonlinear region.

[0055] Specifically, see Figure 1b The left side shows the voltage transfer characteristics of an ideal operational amplifier. When the ideal operational amplifier operates in the linear region, since the voltage amplification factor Av is infinite and the output voltage is a finite value, u... + -u - =u out / Av=0, therefore, the voltages at the two input terminals of the operational amplifier are equal, i.e., u + =u - This phenomenon, where the voltages at the two input terminals of an operational amplifier are equal under ideal conditions, is called the "virtual short" phenomenon of the operational amplifier. Furthermore, due to the input impedance Z of an operational amplifier under ideal conditions... i The curve approaches infinity; therefore, the input current i at the two input terminals of the operational amplifier at this point... b =Zero (i.e., i) b+ =i b- =0). This phenomenon, where the input current at the two input terminals of the operational amplifier is zero under ideal conditions, is called the "virtual open circuit" phenomenon of the operational amplifier. Correspondingly, when the operational amplifier operates in the linear region, the output voltage of the operational amplifier is: u out =A V (u + -u - ).

[0056] When an ideal operational amplifier operates in the nonlinear region, the output voltage no longer increases linearly with the input voltage, but reaches saturation (i.e., close to the supply voltage). Therefore, an ideal operational amplifier operating in the nonlinear region has the following two characteristics: when the operational amplifier's u... + ≠u - When u reaches its saturation value, specifically: when u + >u - At this time, the operational amplifier operates in the positive saturation region, and the output voltage is the positive saturation voltage +U. OH , that is u out =+U OH ; when u + - At this time, the operational amplifier operates in the negative saturation region, and the output voltage is the negative saturation voltage value -U. OL , that is u out ​=-U OL ;u + =u - These are merely the possible transition points between the two operating states mentioned above. Additionally, when the ideal operational amplifier operates in the nonlinear region, u... + ≠u - Therefore, there is no "virtual short" phenomenon, but there is a "virtual open" phenomenon, that is, the input current at the two input terminals of the ideal operational amplifier is zero (i.e., i... b += i b -=0).

[0057] Based on the above description of the characteristics of operational amplifiers under ideal conditions, it is not difficult to deduce the characteristics of operational amplifiers under actual conditions. For a detailed description of the characteristics of operational amplifiers under actual conditions, please refer to the existing content or draw an analogy with the characteristics of operational amplifiers under ideal conditions; further details will not be elaborated here.

[0058] Typically, when operational amplifiers are used in operating circuits to achieve signal amplification and filtering functions, they operate in the linear region; while for comparison functions (such as analog-to-digital conversion), they operate in the nonlinear region. For specific implementations of how to make operational amplifiers operate in the linear and nonlinear regions, please refer to existing materials. In the technical solution provided in this application, a signal processing circuit including a charge amplification circuit, a non-inverting discharge circuit, a voltage-controlled filter circuit, and a hysteresis comparator circuit is constructed based on the characteristics of the operational amplifier, combined with resistors, capacitors, etc., to process the charge signal output by the sensor. For ease of description, the operational amplifier will be simply referred to as an op-amp in the following text; furthermore, voltage signals (such as first voltage signal, second voltage signal, etc.) mentioned below, unless otherwise specified, refer to analog voltage signals.

[0059] The signal processing circuit provided in this application will be described below.

[0060] Figure 2a and Figure 2b A schematic diagram of a signal processing circuit according to an embodiment of this application is shown. Figure 2a and Figure 2b As shown, the signal processing circuit provided in this application includes: a charge amplifier circuit 100, a non-inverting amplifier circuit 200, a voltage-controlled filter circuit 300, and a hysteresis comparator circuit 400. Among them,

[0061] The charge amplifier circuit 100 is used to receive the differential charge signal output by the sensor; amplify and convert the differential charge signal to output a first voltage signal;

[0062] A non-inverting amplifier circuit 200 is connected to the charge amplifier circuit and is used to receive the first voltage signal; amplify the first voltage signal, and output a second voltage signal.

[0063] The voltage-controlled filter circuit 300 is connected to the non-inverting amplifier circuit and is used to receive the second voltage signal, amplify and filter the second voltage signal, and output the third voltage signal.

[0064] The hysteresis comparator circuit 400 is connected to the voltage-controlled filter circuit and is used to receive the third voltage signal and compare and process the third voltage signal to obtain a stable square wave signal.

[0065] In the above description, the differential charge signal received by the charge amplifier circuit 100 is output by the sensor. The sensor can be, but is not limited to, a pressure sensor (such as a piezoelectric impact sensor), a photoelectric sensor, a temperature sensor, etc. The sensor exhibits the piezoelectric effect of crystals; when it detects natural signals such as pressure, temperature, or light, its internal crystal undergoes polarization, generating oppositely polarized charges on its surface, thus converting the natural signals into charge signals. When the external natural signal is removed, it returns to its uncharged state. For a detailed explanation of the sensor's principle of converting natural signals into charge signals, please refer to existing content; it will not be elaborated upon here.

[0066] Because sensors often output weak charge signals, which are difficult to display and record directly, it is necessary to amplify and convert these weak charge signals into voltage signals using a pre-amplifier circuit. The operational amplifier in the charge amplifier circuit is an amplifier with deep capacitive negative feedback; its output voltage is proportional to the input charge. In the process of amplifying and converting the charge signal, the charge amplifier circuit does not actually amplify the charge signal, but rather converts a high-impedance charge source into a low-impedance voltage source; it can be considered an impedance transformation process.

[0067] Existing solutions for converting charge signals into voltage signals mostly employ methods such as... Figure 3a The single-ended charge amplifier circuit with reversed direction is shown. Figure 3a As can be seen from the diagram, the input charge signal passes through the feedback capacitor C at the inverting input terminal of operational amplifier A. f Transmitting to the output, utilizing the "virtual open circuit" characteristic of the op-amp operating in the linear region, we can obtain the following equation:

[0068]

[0069] Among them, R Cs R Cf These represent the capacitance C. s and capacitor Cf Capacitive reactance; u o u is the output voltage of op-amp A. A- The voltage at the inverting input terminal of op-amp A; u s and capacitor C s These are the sensor's equivalent voltage source and equivalent capacitance, respectively.

[0070] Furthermore, by utilizing the "virtual short" (i.e., u) of the operational amplifier... A+ =u A- Because the non-inverting input of op-amp A is grounded, u A+ =0) and the capacitive reactance R of the combined capacitor C =1 / (jwC), transforming the above equation (1), we can obtain the output voltage uo of this charge amplifier circuit as:

[0071]

[0072] In the formula, Q S This indicates the amount of charge output by the sensor.

[0073] Combining the output voltage transfer function (2) of the charge amplifier circuit shown above, it can be seen that because the operational amplifier A has a high input impedance, there is almost no input current at its two input terminals (i.e., i... b+ =i b- ≈0), the charge Q output by the sensor S Only for the feedback capacitor C f Charging, feedback capacitor C f The voltage drop across the two terminals is approximately equal to the output voltage of op-amp A, i.e., u o =-Q S / C f It should be noted that: Figure 3a In the illustrated conventional charge amplifier circuit, capacitor C represents the parasitic capacitance formed between electronic components or circuit modules due to their proximity. This parasitic capacitance C significantly increases the high-frequency noise gain of the operational amplifier, potentially causing instability in the charge amplifier circuit. Here, short-circuiting the parasitic capacitance C reduces its impact on the charge amplifier circuit, thereby improving the circuit's conversion accuracy.

[0074] In the above-mentioned solutions, the existing solutions use a single-ended input charge amplifier circuit to process the charge signal output by the sensor. Although this can reduce the influence of parasitic capacitance C on the charge amplifier circuit, because it is a single-ended input, the existing charge amplifier circuit cannot suppress common-mode noise, and the presence of common-mode noise will reduce the circuit conversion accuracy. Therefore, the solution provided in this embodiment uses a dual-ended input, differential structure charge amplifier circuit to amplify and convert the charge signal.

[0075] Figure 3bA schematic diagram of the charge amplifier circuit 100 provided in this embodiment is shown. Figure 3b (or Figure 2b As shown in the figure, the charge amplifier circuit 100 includes: a charge amplification unit 101 and a reference voltage unit 102; wherein,

[0076] The charge amplification unit 101 has two input terminals and one output terminal. One input terminal of the charge amplification unit 101 is used to receive the positive charge signal in the differential charge signal, and the other input terminal is used to receive the negative charge signal in the differential charge signal. The output terminal of the charge amplification unit 101 is connected to the input terminal of the non-inverting amplifier circuit 200 so that after the charge amplification unit 101 amplifies and converts the received differential charge signal, it is output to the non-inverting amplifier circuit 200 via the output terminal.

[0077] A reference voltage unit 102, connected to an input terminal of a charge amplifier unit 101, is used to provide a reference voltage. This reference voltage unit 102 can boost a fourth voltage signal received from an input terminal of the charge amplifier circuit 100 to the reference voltage before outputting it.

[0078] In the above, the positive and negative charge signals in the differential charge signal are charge signals with opposite polarities and equal magnitudes. For a detailed description of the differential charge signal, please refer to existing content; it will not be repeated here. In specific implementation, considering that the differential charge signal is often mixed with some common-mode noise charge signals due to various environmental factors such as temperature during the sensor's acquisition process, the common-mode noise charge signals input to the two input terminals of the charge amplification unit 101 have the same polarity and equal magnitude. To ensure that the charge amplification unit 101 has good amplification of the differential charge signal and suppression of common-mode signals, the charge amplification unit 101 provided in this embodiment specifically includes: a first operational amplifier A1, a first feedback unit 1011, and a second feedback unit 1012. Among them,

[0079] The inverting input and non-inverting input of the first operational amplifier A1 are used to receive the positive charge signal and the negative charge signal in the differential charge signal, respectively; the output of the first operational amplifier A1 is connected to the input of the non-inverting amplifier circuit 200 to output the first voltage signal to the non-inverting amplifier circuit 200.

[0080] The first feedback unit 1011 is connected between the output terminal and the inverting input terminal of the first operational amplifier A1, and is used to provide feedback to the inverting input terminal of the first operational amplifier A1 based on the first voltage signal.

[0081] One end of the second feedback unit 1012 is connected to the non-inverting input of the first operational amplifier A1 to receive the negative charge signal, convert the negative charge signal into a fourth voltage signal, and output it from the other end.

[0082] For specific implementation, please refer to Figure 3b As shown, when the first feedback unit 1011 implements the feedback function, it extracts part or all of the first voltage signal Uout1 output from the output terminal of the first amplifier A1 as a feedback signal (not shown in the figure) and feeds it back to the inverting input terminal of the first amplifier A1 to interact with the original input positive charge signal V. S+ The signal is then superimposed (e.g., added or subtracted) and applied to the inverting input of the first amplifier A1. Here, extracting part or all of the first voltage signal Uout1 means processing the first voltage signal Uout1 according to a certain feedback coefficient to obtain the feedback signal. In other words, the feedback signal is proportional to the first voltage signal Uout1. That is, if the feedback signal and the feedback coefficient corresponding to the first feedback unit 1011 are respectively denoted as U... f And F, then U f =F*Uout1; and the original first voltage signal Uout1 will continue to be transmitted to the next stage non-inverting amplifier circuit 200. For a detailed introduction and calculation of the above feedback coefficient, please refer to the existing content, which will not be repeated here. Similarly, when the second feedback unit 1012 implements the feedback function, it takes part or all of the fourth voltage signal Uout4 output from its other end as the feedback signal and feeds it back to the non-inverting input terminal of the first amplifier A1 to interact with the original input negative charge signal V. S- Superimposed; while the original fourth voltage signal Uout4 will be transmitted to the reference voltage unit 102, and after being raised by the reference voltage unit 102, it will be output to the corresponding circuit, such as Figure 2b or Figure 6 The hysteresis comparator circuit 400 shown in the figure is provided so that the corresponding circuit can be used.

[0083] In constructing the first feedback unit 1011 and the second feedback unit 1022, the first feedback capacitor C14 and the first feedback resistor R13 connected in parallel form the first feedback unit 1011, and the second feedback capacitor C13 and the second feedback resistor R12 connected in parallel form the second feedback unit 1012. Since the charge amplifier circuit provided in this embodiment has no "virtual ground," the selection of the first operational amplifier A1 must ensure that the first operational amplifier has a high common-mode rejection ratio. Furthermore, to ensure that the charge amplifier unit 101 has a good common-mode noise suppression effect, the charge amplifier unit 101 provided in this embodiment adopts a completely symmetrical structural design, making the capacitors and resistors in the first feedback unit 1011 the same as the corresponding capacitors and resistors in the second feedback unit 1012. Specifically, the first feedback capacitor C14 and the second feedback capacitor C13 have the same capacitive reactance, and the first feedback resistor R13 and the second feedback resistor R12 have the same resistance value.

[0084] As can be seen from the above, the charge amplification unit 101 in the charge amplification circuit 100 provided in this embodiment uses capacitive feedback (e.g., the first feedback unit 1011 is a negative capacitor feedback and the second feedback unit 1012 is a positive capacitor feedback). Because capacitive feedback is equivalent to an open circuit for DC operating power, it is relatively sensitive to cable noise, etc., and the first operational amplifier A1 has a large zero drift, which can easily cause circuit errors. To reduce zero drift and make the first operational amplifier A1 work stably, the resistors in the first feedback unit 1011 and the second feedback unit 1012 need to have high resistance values. And to ensure good capacitive feedback, the capacitors in the first feedback unit 1011 and the second feedback unit 1012 need to have small capacitive reactance. Therefore, in selecting the resistors and capacitors in the first feedback unit 1011 and the second feedback unit 1012, this embodiment preferably selects a capacitor with a capacitive reactance of 180pF and a resistor with a resistance of 6.4MΩ. That is, the capacitive reactance of the first feedback capacitor C14 and the second feedback capacitor C13 is 180pF, and the resistance of the first feedback resistor R13 and the second feedback resistor R12 is 6.8MΩ. The above-mentioned selection of resistors and capacitors in the first feedback unit 1011 and the second feedback unit 1012 can also ensure that the first operational amplifier A1 has a good common-mode rejection ratio. For a detailed introduction to the common-mode rejection ratio of operational amplifiers, please refer to the existing content, which will not be described in this embodiment.

[0085] It should be further explained here that in the aforementioned first feedback unit 1011 and second feedback unit 1012, the parallel connection of a resistor to the capacitor (e.g., a first feedback resistor R13 in parallel with the first feedback capacitor C14) also serves to protect the first operational amplifier A1. This is because, at high frequencies, when the capacitive reactance of the capacitor approaches zero, if a resistor is not connected in parallel with the capacitor, a short circuit will occur in the branch containing the capacitor, causing the first operational amplifier A1 to malfunction. Furthermore, when selecting the first operational amplifier A1, in addition to ensuring that it has a high rejection ratio, because the input electrical signal usually changes rapidly, the output requirements of the operational amplifier are high. Therefore, it is also necessary to ensure that the first operational amplifier A1 has a high slew rate. The slew rate refers to the slew rate of the operational amplifier's output voltage.

[0086] The reference voltage unit 102 is connected to one input terminal of the charge amplification unit 101 via the second feedback unit 1012. In a specific feasible technical solution, the reference voltage unit 102 includes a second operational amplifier A2, a first resistor R15, and a second resistor R16; one end of the first resistor R15 is connected to a voltage source, and the other end shares a common connection point with one end of the second resistor R16 (e.g., ...). Figure 3bThe contact shown in the figure is connected to the non-inverting input of the second operational amplifier A2; the other end of the second resistor R16 is grounded; the inverting input of the second operational amplifier A2 is connected to the output of the second operational amplifier A2 and the other end of the second feedback unit 1012; the first resistor R15 and the second resistor R16 have the same resistance value.

[0087] In practice, the resistance values ​​of the first resistor R15 and the second resistor R16, and the voltage of the voltage source connected to one end of the first resistor R15, can be flexibly determined according to the actual situation. For example, the voltage source can be 3V, 5V, 8V, etc. In this embodiment, it is preferred to select a voltage source of 5V; the resistance values ​​of the first resistor R15 and the second resistor R16 can be, but are not limited to, 154MΩ.

[0088] By introducing a reference voltage unit 102, the loss of useful voltage signals below ground potential due to the operational amplifier being grounded can be avoided. Furthermore, in this reference voltage unit 102, a DC voltage is further introduced through a first resistor R15 and a second resistor R16 connected in series to provide voltage to the second operational amplifier A2, effectively preventing voltage signal clipping during transmission. In addition, the reference voltage unit 102 can also provide a voltage standard for the signal processing circuit provided in this embodiment, facilitating accurate measurement of unknown voltages and output of standard voltages. Moreover, the reference voltage unit 102 also serves to amplify the amplitude of the fourth voltage signal output by the second feedback unit 1012.

[0089] Furthermore, considering that due to environmental factors such as temperature, when the sensor generates charge signals in response to detected signals such as pressure and light, some interference noise signals are unavoidable. To filter out this interference noise, the charge amplification circuit 100 provided in this embodiment may further include: a first filter capacitor C11, a second filter capacitor C12, and a stabilizing resistor R11.

[0090] One end of the first filter capacitor C11 is connected to the inverting input terminal of the first operational amplifier A1, and the other end is used to receive the positive charge signal; the first filter capacitor C11 is used to filter the positive charge signal and transmit it to the inverting input terminal of the first discharger A11;

[0091] One end of the second filter capacitor C12 is connected to the non-inverting input of the first operational amplifier A1, and the other end is used to receive the negative charge signal; the second filter capacitor C12 is used to filter the negative charge signal and transmit it to the non-inverting input of the first operational amplifier A1.

[0092] The two ends of the stabilizing resistor R11 are respectively connected to the other end of the first filter capacitor C11 and the other end of the second filter capacitor C12; the stabilizing resistor R11 can be used to stabilize the input positive charge signal and the negative charge signal, so that the positive charge signal and the negative charge signal are kept in a state of opposite polarity and the same magnitude;

[0093] In the above description, the first filter capacitor C11 and the second filter capacitor C12 have the same capacitive reactance. Specifically, the capacitive reactance of the first filter capacitor C11 and the second filter capacitor C12 can be flexibly determined according to the actual situation. For example, the capacitive reactance of the first filter capacitor C11 and the second filter capacitor C12 can be, but is not limited to, 82nF. Regarding the stabilizing resistor R11, since the charge amplifier circuit provided in this embodiment is a differential structure, in order to ensure that the charge signals at the two input terminals of the first operational amplifier A1 in the charge amplifier circuit are in a balanced state of equal magnitude and opposite polarity, the stabilizing resistor R11 should be selected as a resistor with high resistance accuracy and low temperature drift coefficient. The value of the stabilizing resistor R11 is also flexibly determined according to the actual situation. In the scheme provided in this embodiment, the resistance value of the stabilizing resistor R11 is 6.8MΩ.

[0094] Based on the above description of charge amplifier circuits, and considering the "virtual short" and "virtual open" characteristics of operational amplifiers, this paper addresses the following: Figure 2b or Figure 4b The charge amplifier circuit 100 shown in this embodiment provides an output voltage U corresponding to the charge amplifier circuit 100. out1 for:

[0095]

[0096] In the formula, R 总1011 R 总1012 Rc represents the total impedance of the first feedback unit 1011 and the second feedback unit 1012, respectively. 11 、Rc 12 These represent the capacitive reactances of the first and second filter capacitors, respectively. Uref is the reference voltage provided by the reference voltage providing unit. V S+ V S- These are the positive and negative charge signals received at the two input terminals of the first operational amplifier A1, U out1 This is the first voltage signal output from the output terminal of the first operational amplifier A1. As described above, in the charge amplifier circuit 100 provided in this embodiment, R... 总1011 =R 总1012 And Rc 11 =Rc 12 The simplified formula (3) can be obtained as follows:

[0097]

[0098] As can be clearly seen from equation (4), the charge amplifier circuit 100 is a differential charge signal V id (V id =V S+ -V S- (The image is then enlarged.)

[0099] After the weak charge signal from the sensor is initially processed by the charge amplification circuit 100 and converted into a first voltage signal, the resulting first voltage signal is still relatively weak and needs further amplification for later use. Since the charge amplification circuit 100 has a relatively high output impedance in the low-frequency range, impedance matching must be considered when constructing the amplification circuit for further discharge processing of the first voltage signal. Because a non-inverting amplifier has infinite input impedance and relatively low output impedance, the technical solution provided in this embodiment utilizes a non-inverting amplifier circuit to further amplify the first voltage signal.

[0100] Figure 4b A schematic diagram of the non-inverting amplifier circuit 200 provided in this embodiment is shown. Specifically, as shown... Figure 4b and Figure 2b As shown, the in-phase amplifier circuit 200 includes: a third operational amplifier A3 and a third feedback unit 201. Wherein,

[0101] The non-inverting and inverting inputs of the third operational amplifier A3 are connected to the output of the first operational amplifier A1 and one end of the third feedback unit 201, respectively; the output of the third operational amplifier is connected to the input of the voltage-controlled filter circuit 200 to output the second voltage signal U. out2 To the voltage-controlled filter circuit 200;

[0102] The other end of the third feedback unit 201 is connected to the output terminal of the third operational amplifier A3, and is used to base the second voltage signal U out2 It provides feedback to the inverting input of the third operational amplifier A3.

[0103] In existing solutions, such as Figure 4a The existing non-inverting amplifier circuit shown often uses a single feedback resistor (such as feedback resistor R) as the feedback unit. fThe circuit consists of a feedback unit, which is a hysteresis loop. This feedback unit, combined with the hysteresis loop of the operational amplifier, satisfies the self-oscillation condition. Using only a single feedback resistor to form the feedback unit can easily lead to circuit instability. To improve circuit stability, this embodiment provides a solution by connecting a feedback capacitor with a small capacitive reactance in parallel with the feedback resistor to provide phase compensation and thus enhance circuit stability. Specifically, in this embodiment, the third feedback unit 201 in the non-inverting amplifier circuit 200 is composed of a third feedback capacitor C21 and a third feedback resistor R21 connected in parallel. In practice, the values ​​of the third feedback capacitor C21 and the third feedback resistor R21 can be flexibly determined according to the actual application and are not limited here. Specifically, for example... Figure 2b and Figure 4b As shown, the value of the third feedback capacitor C21 can be 1nF, and the value of the third feedback resistor can be 304Ω. For the specific implementation of the feedback function of the third feedback unit 201, please refer to the description of the implementation of the feedback function of the first feedback unit 1011, etc., which will not be repeated here. It should be noted that when selecting the third operational amplifier A3, it is still required that the third operational amplifier A3 has a high common-mode rejection ratio.

[0104] Furthermore, the aforementioned in-phase amplifier circuit 200 may further include: an adjustment unit 202, one end of which is connected to both the inverting input terminal of the third operational amplifier A3 and one end of the third feedback unit 201, and the other end of which is connected to the input terminal of the voltage-controlled filter circuit 300; the adjustment unit 202 is used to adjust the voltage signal at the inverting input terminal of the third operational amplifier A1 to the reference voltage and then output it to the voltage-controlled filter circuit 300; wherein, the adjustment unit 202 is composed of a first resistor R22 and a first adjustable resistor W21.

[0105] Furthermore, in some embodiments, the aforementioned in-phase amplifier circuit 200 may further include a third filter capacitor C22. One end of the third filter capacitor C22 is connected to the output terminal of the third operational amplifier A3, and the other end is connected to the output terminal of the voltage-controlled filter circuit 300; the second voltage signal Uout2 output from the output terminal of the third operational amplifier A3 is filtered by the third filter capacitor C22 and then output to the voltage-controlled filter circuit 300. For example, as Figure 4b As shown, after the third filter capacitor C22 filters the second voltage signal Uout2, it outputs the filtered second voltage signal Uout2' to the voltage-controlled filter circuit 300.

[0106] Based on the above description of the in-phase amplifier circuit 200, and considering the "virtual short" and "virtual open" characteristics of the op-amp, the following is addressed: Figure 2b Right now Figure 4b The output voltage Uout2 of the non-inverting amplifier circuit 200 shown can be obtained as follows:

[0107]

[0108] In the formula, U i1 This indicates the first voltage signal U connected to the non-inverting input of the third operational amplifier A3. out1 U out2 This represents the second voltage signal output from the output terminal of the third operational amplifier A3; R 22 、Rw 21 R 21 and R C21 These represent the resistance values ​​of the first resistor R22, the first adjustable resistor W21, the third feedback resistor R21, and the third feedback capacitor C21, respectively.

[0109] After the first voltage signal is amplified by the in-phase amplifier circuit 200, the second voltage signal is output. Since this second voltage signal is generally uneven and may contain some unwanted high-frequency noise, further filtering is required to obtain the desired useful voltage signal within a specific frequency band. In other words, the second voltage signal output by the in-phase amplifier circuit 200 needs to be filtered to ensure that the voltage signal remains stable within the passband (i.e., the useful frequency signal passes through) and rapidly attenuates outside the passband (i.e., unwanted frequency signals are suppressed), thereby obtaining the desired voltage signal within a specific frequency band.

[0110] Currently, commonly used filtering methods include active power filters (APF) and passive filters (FC). Passive filters (FC) utilize the inherent impedance characteristics of capacitors and resistors to provide low impedance to harmonics of a specific frequency, offering a lower impedance path for the load's harmonic current. This creates a parallel current-splitting relationship with the system impedance, allowing most of the harmonic components of that specific frequency to flow through the filter system, thus achieving a filtering effect. Active power filters (APF), on the other hand, use power electronic devices to actively generate harmonics of equal magnitude but opposite phase to the system harmonics, thus "cancelling" the system harmonics and making them resemble a sine wave. In addition to filtering harmonics, active filters can also dynamically compensate for reactive power. Therefore, passive filters (FC) are parallel current-splitting, while active filters (APF) are active cancellation. Although passive filter circuits are simple in structure and easy to design, their passband gain and cutoff frequency vary with the load, making them unsuitable for applications with high signal processing requirements. Active power filters, however, are not affected by the load and are commonly used in applications with high signal processing requirements. However, since active filter circuits are generally composed of operational amplifiers, resistors, capacitors, etc., they can only be used when powered by a suitable DC power supply, and they also have the function of amplifying signals.

[0111] Based on the above analysis of the characteristics of active and passive filtering, the technical solution provided in this embodiment preferentially selects active filtering for the second voltage signal U.out2 After amplification and filtering, a third voltage signal with good stability and belonging to the required specific frequency is obtained. This third voltage signal can be, but is not limited to, a sine wave signal. In specific implementation, considering the stable circuit performance and easy gain adjustment of active voltage-controlled filter circuits, a voltage-controlled filter circuit was built to perform discharge filtering processing on the second voltage signal. Figure 5 A schematic diagram of the voltage-controlled filter circuit 300 provided in this embodiment is shown. Figure 5 As shown in Figure 2, the voltage-controlled filter circuit 300 includes: an active voltage-controlled filter unit 301 and a limiting unit 302. Wherein,

[0112] The active voltage-controlled filter unit 301 has its input and output terminals connected to the output terminal of the third operational amplifier A3 and the input terminal of the hysteresis comparator circuit 400, respectively, for amplifying and filtering the second voltage signal and outputting the third voltage signal Uout3 to the hysteresis comparator circuit.

[0113] The limiting unit 302 is connected to the input and output terminals of the active voltage-controlled filter unit 301, respectively, and is used to limit the amplitude of the third voltage signal so that the amplitude of the third voltage signal is kept within an appropriate range.

[0114] In practical implementation, if the output terminal of the third operational amplifier A3 is connected to the third filter capacitor C22, the second voltage signal input to the active voltage-controlled filter unit 301 is the second voltage signal after being filtered by the third filter capacitor C22 (i.e., as shown in the figure). Figure 4b and Figure 2b The second voltage signal Uout2' shown in the figure; conversely, if the output terminal of the third operational amplifier is not connected to the third filter capacitor C22, the second voltage signal input to the active voltage-controlled filter unit 301 is the second voltage signal Uout2 directly output from the output terminal of the third operational amplifier A3.

[0115] In one specific implementation, the active voltage-controlled filter unit 301 has a second-order filter network structure. Specifically, the active voltage-controlled filter unit may include: a fourth operational amplifier A4, a second resistor R30, a third resistor R31, a third capacitor C31, and a fourth feedback unit 3011; wherein,

[0116] The inverting input of the fourth operational amplifier A4 is connected to the output of the third operational amplifier A4 through a series connection of a second resistor R30 and a third resistor R31; the common junction of the second resistor R30 and the third resistor R31 (junction b shown in the figure) is connected to one end of the third capacitor C31, and the other end of the third capacitor C31 is connected to the non-inverting input of the fourth operational amplifier A4; the output of the fourth operational amplifier A4 is connected to the input of the hysteresis comparator circuit 400 to output the third voltage signal to the hysteresis comparator circuit 400.

[0117] One end of the fourth feedback unit 3011 is connected to the common junction of the inverting input terminal of the fourth operational amplifier A4 and the third resistor R31, and the other end is connected to the output terminal of the fourth operational amplifier A4. It is used to provide feedback to the inverting input terminal of the fourth operational amplifier A4 based on the third voltage signal. The fourth feedback unit 3011 consists of a fourth feedback resistor R35 and a fourth feedback capacitor C33 connected in parallel.

[0118] In the above description, the second resistor R30, the third resistor R31, the third capacitor C31, and the fourth feedback unit 3011 in the active voltage-controlled filter unit 301 form a second-order filter network. Similarly, for the implementation of the feedback function of the fourth feedback unit 3011, please refer to the description of the feedback function implementation of the first feedback unit 1011 in the charge amplifier circuit, which will not be repeated here.

[0119] Furthermore, the aforementioned limiting unit 302 may specifically include: a first diode D31, a second diode D32, and a fourth resistor R32; wherein,

[0120] The first diode D31 and the second diode D32 are connected in parallel. The anode of the first diode D31 and the cathode of the second diode D32 are connected to the output terminal of the fourth operational amplifier A4 at a common connection point. The cathode of the first diode D31, the anode of the second diode D32, and one end of the fourth resistor R32 are connected to a common connection point. The other end of the fourth resistor R32 is connected to the common connection point of the second resistor R30, the third resistor R31, and the third capacitor C31.

[0121] In specific implementations, the first diode D31 and the second diode D32 mentioned above can be, but are not limited to, silicon diodes, germanium diodes, etc. Diodes have unidirectional conductivity; current can only move from the anode to the cathode. After the diode is forward-biased, its forward voltage drop remains essentially constant (0.7V for silicon diodes and 0.3V for germanium diodes). Utilizing this characteristic of a essentially constant voltage drop, diodes can be used as limiting elements in circuits to limit signals within a certain range. Based on this, this embodiment uses the first and second diodes to limit the third voltage signal Uout3 output by the active voltage-controlled filter unit, thereby improving the waveform of the output third voltage signal. For example: See... Figure 5Taking a scenario where both diodes D31 and D32 are silicon diodes, the second voltage signal Uout2' received by the active voltage-controlled filter unit 301 is applied to the limiting circuit of the first diode D31 and the second diode D32 via the fourth resistor R32. The active voltage-controlled filter unit 301 amplifies and filters the second voltage signal Uout2' to output a third voltage signal Uout3. When the output third voltage signal increases positively to 0.7V higher than the input second voltage signal or decreases to 0.7V lower than the input second voltage signal, the first diode D31 or the second diode D32 will conduct, thus starting bidirectional limiting of the third voltage signal. The signal with a higher amplitude of the original third voltage signal is limited, while the signal with a lower amplitude continues to be amplified. This improves the output waveform, and the peak values ​​of each wave are all within the threshold value of the hysteresis comparator, thus preventing leakage. For a detailed explanation of the limiting principle of the diodes, please refer to the existing content.

[0122] It should be noted that when the diode is conducting, it has a small resistance, and current flows through the branch corresponding to the limiting unit. The fourth resistor R32 mentioned above can limit the current and protect the diode (such as the first diode D31 and the second diode D32) when the diode is conducting. However, when the diode is not conducting, its resistance is close to infinite, and almost no current flows through the limiting circuit. Generally, the diode in the limiting unit 302 is in the non-conducting state.

[0123] Further, see also Figure 5 or Figure 2b As shown, the voltage-controlled filter circuit 300 may further include a fifth resistor R40 and a fourth filter capacitor C40. One end of the fourth filter capacitor C40 is connected to the output terminal of the fourth operational amplifier A4, and the other end is connected to one end of the fifth resistor R40 and the output terminal of the hysteresis comparator circuit 400; the other end of the fifth resistor R40 is connected to the common connection point of the first adjustable resistor W21 and the non-inverting input terminal of the fourth operational amplifier A4. The feedback unit composed of the fifth resistor R40 and the fourth filter capacitor C40 forms a voltage-controlled voltage source with controllable gain. In addition, the feedback unit formed by the fifth resistor R40 and the fourth filter capacitor C40 can also serve as a first-order filter network to filter and process the third voltage signal output by the fourth operational amplifier before outputting it.

[0124] Based on the above description of the voltage-controlled filter circuit 300, and considering the "virtual short" and "virtual open" characteristics of the operational amplifier and the characteristics of the diode, this paper addresses the following: Figure 5 Or, as shown in Figure 2, the voltage-controlled filter circuit 300 provided in this embodiment has the following relationship:

[0125]

[0126]

[0127] u 3C+ =U ref =2.5V; R C33 =1 / SC 33 R C31 =1 / SC 31

[0128] In the above formula, S = jw, where w is the angular frequency; U out3 The third voltage signal output from the output terminal of the fourth operational amplifier, R C33 R C31 Let R1, R2, and R33 represent the capacitive reactances of the third charge C31 and the fourth capacitor C33, respectively, and R30, R31, and R35 represent the resistances of the second resistor R30, the third resistor R31, and the fourth resistor R35, respectively. Simplifying the above equations, the transfer function of the voltage-controlled filter circuit 300 can be obtained as follows:

[0129]

[0130] In the formula, the cutoff angular frequency is: Based on this, we can obtain the cutoff frequency fc = w c / 2π.

[0131] After the second voltage signal is processed by the voltage-controlled filter circuit 300, it becomes a smoother, sinusoidal signal. In other words, the voltage-controlled filter circuit 300 outputs a smoother, sinusoidal third voltage signal. Further, a comparator circuit is needed to process the third voltage signal to extract the eddy current signal, remove unfiltered interference signals, and appropriately set a threshold voltage to convert the third voltage signal into a digital signal (such as a standard square wave pulse signal). The solution provided in this embodiment utilizes the method shown in Figure 2 and... Figure 6 The hysteresis comparator circuit 400 shown is used to implement this. Specifically, see Figure 2 and... Figure 6 As shown, the hysteresis comparator circuit includes: a fifth operational amplifier A5, a threshold adjustment unit 401, and a fifth feedback resistor R41;

[0132] One end of the threshold adjustment unit 401 is connected to the output terminal of the second operational amplifier A2, and the other end is connected to the non-inverting input terminal of the fifth operational amplifier A5; the inverting input terminal of the fifth operational amplifier A5 is used to connect the third voltage signal output by the output terminal of the fourth operational amplifier A4.

[0133] One end of the fifth feedback resistor R41 is connected to the output terminal of the fifth operational amplifier A5, and the other end is connected to the common connection point of the non-inverting input terminal of the fifth operational amplifier A5 and the threshold adjustment unit 401. The fifth feedback resistor R41 is used to provide feedback to the non-inverting input terminal of the fifth operational amplifier A5 based on the square wave signal output from the output terminal of the fifth operational amplifier A5, so that the fifth operational amplifier A5 can determine the appropriate threshold voltage based on the feedback information, and compare and process the third voltage signal based on the threshold voltage to obtain the square wave signal.

[0134] The threshold voltage is determined by the fifth operational amplifier A5 based on the reference voltage output by the second operational amplifier connected to the threshold adjustment unit, the resistance value corresponding to the threshold unit, the resistance value of the fifth feedback resistor, and the voltage source.

[0135] In specific implementation, the threshold adjustment unit 401 adopts an adjustable design to facilitate circuit adjustment according to actual conditions. Specifically, the threshold adjustment unit 401 is composed of a second adjustable resistor W41 and a sixth resistor R22. The function of the fifth operational amplifier A5 in the hysteresis comparator circuit 400 is configured to compare the input analog third voltage signal with the threshold voltage and output the corresponding comparison result. This comparison result is the square wave signal output from the output terminal of the fifth operational amplifier A5. That is, the output state of the fifth operational amplifier A5 only includes two output states: high level and low level, and the output is a binary signal. The input voltage that causes the output of the fifth operational amplifier A5 to jump is the threshold voltage. Corresponding to the output state of the fifth operational amplifier A5, the threshold voltage includes a high-level threshold voltage and a low-level threshold voltage. A threshold voltage only works in one direction. The specific determination of the threshold voltage can be calculated based on the hysteresis comparator circuit provided in this embodiment and combined with existing content, which will not be elaborated here. The threshold voltage U in the hysteresis comparator circuit 400 provided in this embodiment T With the output voltage U of the fifth operational amplifier A5 OZ The relationship between them is:

[0136] U ref =2.5V

[0137] The two threshold voltages of the hysteresis comparator circuit 400 provided in this embodiment are set as follows: high-level threshold voltage U TH and low-level threshold voltage U TL Its two output states are: high-level output voltage U ZH and low-level output voltage U ZL Combining Figure 7a and Figure 7b The third voltage signal U connected to the hysteresis comparator circuit 400 shown is... i3 (The signal is a sine wave) and the output signal U OZThe relationship between the third voltage signal U i3 Converted into a square wave signal (i.e., output signal U) OZ The process is as follows:

[0138] Assume U i3 If the voltage increases from negative infinity to positive infinity, then the initial high-level output voltage is U. ZH , when U i3 =U TH At that time, the sign of the net input voltage signal of the fifth operational amplifier changes from negative to positive, and the output voltage changes from U... ZH Jump to U ZL ;if U i3 If the voltage decreases in opposite phase from positive infinity, the initial output voltage U will be low. ZL , when U i3 =U TL At this time, the sign of the net input voltage signal of the operational amplifier changes from positive to negative, and the output voltage changes from U... ZL Jump to U ZH As can be seen from the above, for a hysteresis comparator circuit, as long as the resistor values ​​in the circuit are selected appropriately and the U is adjusted to a suitable value, the comparator can function reliably. T By setting the value, the sine wave signal can be converted into a square wave signal.

[0139] Furthermore, the aforementioned hysteresis comparator circuit also includes: a current-limiting resistor R42, one end of which is connected to the output terminal of the fifth operational amplifier A5, and the other end is used to connect to the subsequent working module; the current-limiting resistor R42 is used to limit the current of the square wave signal output from the output terminal of the fifth operational amplifier A5, so as to prevent the square wave signal from flowing into the subsequent working module (such as the processor) with a large current, which would damage the subsequent working module.

[0140] In summary, the signal processing circuit provided in this embodiment consists of a charge amplifier circuit, a non-inverting amplifier circuit, a voltage-controlled filter circuit, and a hysteresis comparator circuit. When processing the differential charge signal output from the sensor, the differential charge signal is first amplified and converted by the charge amplifier circuit with a differential structure, transforming it into a first collectable voltage signal. Since this first voltage signal is still relatively weak, it is further amplified by a non-inverting amplifier circuit built with operational amplifiers to increase the amplitude of the first voltage signal to the required level, thereby obtaining a second voltage signal which is output to the voltage-controlled filter circuit. The voltage-controlled filter circuit amplifies and filters the second voltage signal to remove high-frequency noise and retain the low-frequency useful signal, thereby obtaining a third voltage signal which is output to the hysteresis comparator circuit. The hysteresis comparator circuit compares and processes the third voltage signal, thereby outputting a square wave signal (i.e., high and low level frequency signals). Thus, the charge signal output from the sensor is converted into a computable digital signal. The signal processing circuit provided in this embodiment has the following beneficial effects:

[0141] 1) The first stage uses a charge amplifier circuit with a differential structure, which can effectively amplify differential signals and suppress common-mode signals;

[0142] 2) The second stage uses an operational amplifier to build a non-inverting amplifier circuit, which not only amplifies the signal but also provides impedance matching. This is because a non-inverting amplifier has a high input impedance and a low output impedance.

[0143] 3) The third stage uses an active voltage-controlled second-order filter, which has a fast response speed. Compared with passive filters, the cutoff frequency of active filters does not change with the load, is not affected by the system impedance, and does not have harmonic amplification or resonance.

[0144] One embodiment of this application also provides an electronic device (the corresponding structural diagram is not specifically shown in the accompanying drawings). This electronic device includes the signal processing circuits provided in various embodiments of this application. For details regarding the signal processing circuits, please refer to the detailed descriptions in the above embodiments; they will not be repeated here.

[0145] Furthermore, the electronic device may also include a memory and a processor. The memory may be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0146] Furthermore, the electronic device also includes other components such as communication components, power supply components, and displays. The specific structural form of the electronic device is not limited here, as long as it includes the signal processing circuit provided in the embodiments of this application.

[0147] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions 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 this application.

Claims

1. A signal processing circuit, characterized by comprising: The signal processing circuit comprises: a charge amplification circuit configured to receive a differential charge signal output by a sensor; amplify and convert the differential charge signal to output a first voltage signal; a non-inverting amplification circuit connected to the charge amplification circuit and configured to receive the first voltage signal, amplify the first voltage signal, and output a second voltage signal; a voltage-controlled filter circuit connected to the non-inverting amplification circuit and configured to receive the second voltage signal, amplify and filter the second voltage signal, and output a third voltage signal; the voltage-controlled filter circuit comprises an active voltage-controlled filter unit and a limiting unit; the active voltage-controlled filter unit is configured to amplify and filter the second voltage signal to output the third voltage signal; and the limiting unit is configured to limit the amplitude of the third voltage signal to keep the amplitude of the third voltage signal within an adaptive range; a hysteresis comparison circuit connected to the voltage-controlled filter circuit and configured to receive the third voltage signal and perform a comparison process on the third voltage signal to obtain a stable square wave signal.

2. The signal processing circuit of claim 1, wherein, The charge amplification circuit comprises: a first operational amplifier having an inverting input and a non-inverting input configured to receive a positive charge signal and a negative charge signal in the differential charge signal, respectively; and an output connected to an input of the non-inverting amplification circuit to output the first voltage signal to the non-inverting amplification circuit; a first feedback unit connected between the output and the inverting input of the first operational amplifier and configured to provide feedback to the inverting input of the first operational amplifier based on the first voltage signal; a second feedback unit having one end connected to the non-inverting input of the first operational amplifier to receive the negative charge signal and output a fourth voltage signal after converting the negative charge signal; and a reference voltage unit connected to the other end of the second feedback unit and configured to provide a reference voltage.

3. The signal processing circuit according to claim 2, wherein: the first feedback unit comprises a first feedback capacitor and a first feedback resistor connected in parallel; and the second feedback unit comprises a second feedback capacitor and a second feedback resistor connected in parallel; the first feedback capacitor and the second feedback capacitor have the same capacitive reactance; and the first feedback resistor and the second feedback resistor have the same resistance value; the reference voltage unit comprises a second operational amplifier, a first resistor, and a second resistor; one end of the first resistor is connected to a voltage source, the other end of the first resistor is connected to the non-inverting input of the second operational amplifier via a common connection point, one end of the second resistor is connected to the non-inverting input of the second operational amplifier, and the other end of the second resistor is connected to ground; the inverting input of the second operational amplifier is connected to the output of the second operational amplifier and the other end of the second feedback unit; and the first resistor and the second resistor have the same resistance value.

4. The signal processing circuit of claim 3, wherein, The charge amplification circuit further comprises a first filter capacitor, a second filter capacitor, and a stabilizing resistor; one end of the first filter capacitor is connected to the inverting input of the first operational amplifier, and the other end of the first filter capacitor is configured to be connected to the positive charge signal; and the first filter capacitor is configured to filter the positive charge signal and transmit the filtered positive charge signal to the inverting input of the first operational amplifier. One end of the second filter capacitor is connected to the non-inverting input terminal of the first operational amplifier, and the other end is used to connect to the negative charge signal; the second filter capacitor is used to filter the negative charge signal and transmit it to the non-inverting input terminal of the first operational amplifier; The other ends of the first filter capacitor and the second filter capacitor are respectively connected to the other end of the first filter capacitor and the other end of the second filter capacitor; the stable resistor is used to stabilize the input positive charge signal and the negative charge signal, so that the positive charge signal and the negative charge signal remain in the state of opposite polarity and same size; wherein the first filter capacitor and the second filter capacitor have the same capacitive reactance.

5. A signal processing circuit according to claim 3 or 4, characterised in that, The non-inverting amplifier circuit comprises a third operational amplifier and a third feedback unit. The non-inverting input terminal and the inverting input terminal of the third operational amplifier are respectively connected to the output terminal of the first operational amplifier and one end of the third feedback unit; the output terminal of the third operational amplifier is connected to the input terminal of the voltage-controlled filter circuit, so as to output the second voltage signal to the voltage-controlled filter circuit; The other end of the third feedback unit is connected to the output terminal of the third operational amplifier, and is used to provide feedback to the inverting input terminal of the third operational amplifier based on the second voltage signal; wherein the third feedback unit is composed of a third feedback capacitor and a third feedback resistor connected in parallel.

6. The signal processing circuit of claim 5, wherein, The non-inverting amplifier circuit further comprises: An adjusting unit, one end of which is connected to the inverting input terminal of the third operational amplifier and one end of the third feedback unit, and the other end of which is connected to the input terminal of the voltage-controlled filter circuit; the adjusting unit is used to adjust the voltage signal of the inverting input terminal of the third operational amplifier to the reference voltage and then output it to the voltage-controlled filter circuit; wherein the adjusting unit is composed of a first resistor and a first adjustable resistor.

7. The signal processing circuit of claim 5, wherein, The voltage-controlled filter circuit comprises: An active voltage-controlled filter unit, the input terminal and the output terminal of which are respectively connected to the output terminal of the third operational amplifier and the input terminal of the hysteresis comparison circuit, and is used to amplify and filter the second voltage signal and output the third voltage signal to the hysteresis comparison circuit; An amplitude limiting unit, the two ends of which are respectively connected to the input terminal and the output terminal of the active voltage-controlled filter unit, and is used to limit the amplitude of the third voltage signal so that the amplitude of the third voltage signal remains within an adaptive range.

8. The signal processing circuit of claim 7, wherein, The active voltage-controlled filter unit comprises a fourth operational amplifier, a second resistor, a third resistor, a third capacitor and a fourth feedback unit; The inverting input terminal of the fourth operational amplifier is connected to the output terminal of the third operational amplifier through the second resistor and the third resistor connected in series; the common connection point of the second resistor and the third resistor is connected to one end of the third capacitor, and the other end of the third capacitor is connected to the non-inverting input terminal of the fourth operational amplifier; the output terminal of the fourth operational amplifier is connected to the input terminal of the hysteresis comparison circuit, so as to output the third voltage signal to the hysteresis comparison circuit; One end of the fourth feedback unit is connected to the common connection point of the inverting input terminal of the fourth operational amplifier and the third resistor, and the other end is connected to the output terminal of the fourth operational amplifier, for providing feedback to the inverting input terminal of the fourth operational amplifier based on the third voltage signal; wherein the fourth feedback unit is composed of a fourth feedback resistor and a fourth feedback capacitor connected in parallel.

9. The signal processing circuit of claim 8, wherein, The limiting unit comprises a first diode, a second diode and a fourth resistor; the anode of the first diode and the cathode of the second diode are connected to the output terminal of the fourth operational amplifier, and the cathode of the first diode and the anode of the second diode and one end of the fourth resistor are connected to the common connection point; the other end of the fourth resistor is connected to the common connection point of the second resistor, the third resistor and the third capacitor.

10. The signal processing circuit of claim 9, wherein, The signal processing circuit comprises: The hysteresis comparison circuit comprises a fifth operational amplifier, a threshold adjusting unit and a fifth feedback resistor; One end of the threshold adjusting unit is connected to the output terminal of the second operational amplifier, and the other end is connected to the non-inverting input terminal of the fifth operational amplifier; the inverting input terminal of the fifth operational amplifier is used to input the third voltage signal output by the output terminal of the fourth operational amplifier; One end of the fifth feedback resistor is connected to the output terminal of the fifth operational amplifier, and the other end is connected to the common connection point of the non-inverting input terminal of the fifth operational amplifier and the threshold adjusting unit; the fifth feedback resistor is used to provide feedback to the non-inverting input terminal of the fifth operational amplifier based on the square wave signal output by the output terminal of the fifth operational amplifier, so that the fifth operational amplifier determines an adaptive threshold voltage based on the feedback information, and performs comparison processing on the third voltage signal based on the threshold voltage, to obtain the square wave signal; Wherein, the threshold voltage is determined by the fifth operational amplifier based on the reference voltage output by the output terminal of the second operational amplifier connected by the threshold adjusting unit, the resistance value corresponding to the threshold adjusting unit, the resistance value of the fifth feedback resistor and the voltage source.

11. An electronic device, comprising: The signal processing circuit comprises any one of claims 1 to 10.

Images