Gain-adjustable QCM circuit system suitable for liquid-phase high-damping environment

Abstract

The invention relates to a gain-adjustable QCM circuit system suitable for a liquid-phase high-damping environment, and belongs to the technical field of sensor detection, the gain-adjustable QCM circuit system comprises a QCM adjustable capacitance compensation module, the QCM adjustable capacitance compensation module comprises an adjustable capacitor and an operational amplifier, the operational amplifier is arranged under a negative feedback condition, and the adjustable capacitor is connected with the operational amplifier; the adjustable capacitor and the quartz crystal oscillator are connected in parallel and then connected to the inverted input end of the operational amplifier. According to the invention, the operational amplifier is arranged under a negative feedback condition, and then the adjustable capacitor and the quartz crystal oscillator are connected in parallel and then are connected to the inverted input end of the operational amplifier, so that the influence of equivalent capacitance in a static branch of the quartz crystal oscillator on the oscillation frequency of the circuit is compensated through the adjustable capacitor; the effect of the dynamic equivalent resistance on the resonant frequency is enhanced through the differential amplification circuit, so that the problem that the quartz crystal oscillator is difficult to start oscillation stably in a liquid-phase high-damping environment is solved, and the adaptability of the quartz crystal oscillator in a liquid phase is remarkably enhanced.

Description

Technical Field

[0001] The invention belongs to the technical field of sensor detection, and in particular relates to a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment. Background Art

[0002] The origin of QCM (Quartz Crystal Microbalance) technology can be traced back to the discovery of the piezoelectric effect of piezoelectric quartz crystals. In 1880, the Curie brothers verified the piezoelectric effect. In 1959, German scientist Günter Sauerbrey first proposed an important conclusion that the mass change on the surface of the quartz crystal can cause the change of the resonant frequency, and gave the corresponding linear relationship between the mass change and the frequency change. In 1982, QCM was successfully applied in a liquid environment for the first time; in 1985, the quantitative equation of QCM in pure viscous liquid was born. These achievements show that QCM technology not only plays an important role in traditional precision measurement fields such as mass, thickness, density and gas detection, but also has great potential in the research of analytical chemistry, medicine, life sciences and other fields. As a result, the second wave of research and application of QCM technology was triggered, and this craze has continued to this day.

[0003] Compared with other detection methods, QCM has many significant advantages. It has high precision, and the detection accuracy can generally reach the nanogram level, which is extremely suitable for the detection of microscopic substances such as cells, viruses, microorganisms and macromolecules; and it is compact in size. QCM sensors are usually made into circular wafers with a diameter of about ten millimeters and a thickness of only a few hundred microns. They are composed of cut crystals and two upper and lower metal electrodes. In addition, the resonant frequency of the QCM sensor is extremely sensitive to changes in the mass, density and viscosity of the material it contacts. In terms of real-time detection, QCM also performs well. By embedding a quartz crystal into an oscillation circuit, a highly stable resonator can be made. With the help of frequency meters, oscilloscopes and other equipment, real-time detection of the frequency of the oscillation circuit can be achieved, and the detection results can be obtained quickly and conveniently.

[0004] The main methods for measuring the frequency of QCM include the frequency sweep measurement method using precision instruments such as network analyzers to perform spectrum analysis by measuring its impedance and admittance characteristics, the oscillator method using a chip as a resonator embedded in an oscillation circuit, and the QCM-D method (Quartz Crystal Microbalance with Dissipation Monitoring) for measuring the dissipation factor. The most classic method is the oscillator method. The principle of the oscillator method is to use the QCM as a frequency selection network and design it into a quartz resonator. This method can directly measure the frequency of the oscillation circuit through an oscilloscope, frequency meter, etc. Therefore, the design of the oscillation circuit is the key part of the oscillator method. The basic components of the oscillation circuit are generally the amplifier circuit, the frequency selection network, the positive feedback network, and the amplitude stabilization link. The frequency selection network and the positive feedback network can be combined, and the amplitude stabilization link can be combined with the amplifier circuit to adjust the amplification factor. Therefore, the amplifier circuit and the frequency selection network are the main components of the oscillation circuit. By rationally designing the circuits of each part, a complete oscillation circuit is formed.

[0005] Existing QCM detection is mainly used in gas phase environment, and the oscillation circuit is designed based on the resonant frequency of QCM. In the liquid phase environment, due to changes in factors such as damping, the quartz crystal will have a greater impact, causing its frequency characteristics to change, which will cause the oscillator to stop oscillating, or the oscillation frequency to jump from the fundamental frequency to the harmonic frequency, resulting in a mode hopping phenomenon. Therefore, the general QCM oscillation circuit used in the gas phase will make it difficult for the QCM to stably oscillate when used in the liquid phase. Therefore, there is a need for an oscillation circuit that enables the QCM to stably oscillate in the liquid phase. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a gain-adjustable QCM circuit system suitable for a liquid phase high damping environment. The technical problem to be solved by the present invention is achieved through the following technical solutions: The present invention provides a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment, comprising: a QCM adjustable capacitance compensation module, wherein the QCM adjustable capacitance compensation module comprises: an adjustable capacitor C1 and an operational amplifier U1, the operational amplifier U1 being set under a negative feedback condition, the adjustable capacitor C1 being connected to the inverting input terminal of the operational amplifier U1 after being connected in parallel with a quartz crystal oscillator Y1, and being used to compensate for the influence of the equivalent capacitance in the static branch of the quartz crystal oscillator Y1 on the circuit oscillation frequency.

[0007] In one embodiment of the present invention, the second electrode plate of the adjustable capacitor C1 is respectively connected to the quartz crystal oscillator Y1 and the inverting input terminal of the operational amplifier U1, and an adjustable resistor R3 is connected between the inverting input terminal and the output terminal of the operational amplifier U1.

[0008] In one embodiment of the present invention, the QCM adjustable capacitor compensation module further includes: an operational amplifier U2, a fixed resistor R1 and a fixed resistor R2, wherein the first end of the fixed resistor R1 is connected to the first plate of the adjustable capacitor C1; the second end of the fixed resistor R1 is connected to the first end of the fixed resistor R2, and the second end of the fixed resistor R2 is grounded; the non-phase input end of the operational amplifier U2 is respectively connected to the non-phase input end of the operational amplifier U1 and the second end of the fixed resistor R1, and the inverting input end of the operational amplifier U2 is connected to its output end.

[0009] In one embodiment of the present invention, it also includes: a differential amplification module; the differential amplification module is connected in series with the QCM adjustable capacitance compensation module, and is used to amplify the oscillation signal of the quartz crystal oscillator Y1 to enhance the influence of the equivalent resistance in the dynamic branch of the quartz crystal oscillator Y1 on the circuit gain.

[0010] In one embodiment of the present invention, the differential amplifier module includes: an operational amplifier U3, a resistor R4, a resistor R5, a resistor R6 and a resistor R7, wherein the first end of the resistor R4 is connected to the output end of the operational amplifier U1, and the second end of the resistor R4 is connected to the inverting input end of the operational amplifier U3; the resistor R5 is connected between the inverting input end and the output end of the operational amplifier U3; the non-inverting input end of the operational amplifier U3 is connected to the second end of the resistor R7; the first end of the resistor R7 is connected to the output end of the operational amplifier U2; the first end of the resistor R6 is connected to the first end of the resistor R7, and the second end of the resistor R6 is grounded.

[0011] In one embodiment of the present invention, a bandpass filter module is provided after the differential amplifier module; the bandpass filter module is used to filter out noise and interference signals in the oscillation signal of the quartz crystal oscillator Y1 after amplification by the differential amplifier module to obtain a filtered signal.

[0012] In one embodiment of the present invention, an AGC amplitude stabilization module is disposed after the bandpass filtering module, and the AGC amplitude stabilization module is used to adjust the gain and perform gain amplification on the filtered signal.

[0013] In one embodiment of the present invention, the AGC amplitude stabilization module includes: a variable gain amplifier and a true root mean square to direct current converter, the variable gain amplifier is used for gain amplification, the filtered signal after gain amplification is converted into a direct current root mean square voltage signal in the true root mean square to direct current converter, and then connected to the gain control terminal of the variable gain amplifier to adjust the gain.

[0014] In one embodiment of the present invention, a coupling module is provided between the band-pass filtering module and the AGC amplitude stabilization module, and the coupling module includes: a coupling capacitor C2, a coupling inductor L1 and a coupling resistor R8, wherein the first electrode plate of the coupling capacitor C2 is connected to the output end of the band-pass filtering module, and the second electrode plate of the coupling capacitor C2 is respectively connected to the first end of the coupling inductor L1 and the first end of the coupling resistor R8; the second end of the coupling inductor L1 is connected to the second end of the coupling resistor R8.

[0015] In one embodiment of the present invention, a coupling capacitor C3 is connected between the output end of the AGC amplitude stabilization module and the QCM adjustable capacitance compensation module.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment of the present invention sets an operational amplifier under a negative feedback condition, and then connects an adjustable capacitor to an inverting input terminal of the operational amplifier after being connected in parallel with a quartz crystal oscillator. The adjustable capacitor compensates for the influence of the equivalent capacitance in the static branch of the quartz crystal oscillator on the circuit oscillation frequency, and at the same time enhances the effect of the dynamic equivalent resistance, thereby solving the problem that the quartz crystal oscillator is difficult to stably start oscillation in a liquid phase high-damping environment, and significantly enhancing its adaptability in the liquid phase.

[0017] The present invention effectively optimizes the signal waveform, enhances signal stability, reduces electromagnetic interference, and improves detection accuracy by combining a differential amplifier module, a bandpass filter module, and an AGC amplitude stabilization module. By adjusting the signal amplitude through an adjustable resistor, the flexibility and stability of the quartz crystal oscillator in different liquid phase environments are further improved, providing a more reliable detection method for fields such as biochemical detection.

[0018] The present invention is also provided with a coupling module and a coupling capacitor, which reduce electromagnetic interference and further enhance the stability of the signal.

[0019] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following specifically cites a preferred embodiment and describes it in detail with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a block diagram of a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment provided by an embodiment of the present invention; Figure 2 is an equivalent circuit model diagram of a quartz crystal oscillator provided by an embodiment of the present invention; Figure 3 is a structural diagram of a QCM adjustable capacitance compensation module provided by an embodiment of the present invention; Figure 4 is a structural diagram of a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of a bandpass filter based on a resonance frequency of 6 MHz and a bandwidth of 1 MHz provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of a gain-adjustable QCM circuit system suitable for a liquid phase high damping environment proposed by the present invention in combination with the accompanying drawings and specific implementation methods.

[0022] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0023] Embodiment 1 The high damping in the liquid phase can easily change the frequency characteristics of the QCM, thereby causing the QCM to stop oscillating or experience frequency disorder. In view of this, this embodiment provides a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment to ensure that the QCM can oscillate stably in the liquid phase.

[0024] It should be noted that quartz crystal is an electronic component with piezoelectric effect. Its inherent resonant frequency is highly stable and is often used to build frequency references. One of the core applications based on quartz crystal is the quartz crystal microbalance (QCM), which realizes nanogram-level mass sensing by detecting the frequency shift caused by the change in the mass of the crystal surface. The realization of the QCM function depends on the QCM oscillation circuit. The QCM oscillation circuit drives the quartz crystal to oscillate continuously near its resonant frequency through feedback amplification and frequency adjustment, and outputs the frequency signal. The quartz crystal oscillator is a more general frequency source module, which is usually integrated with a quartz crystal and an oscillation circuit. The stability is further improved through temperature compensation or constant temperature control. It is widely used in communications, timing and other fields. In short, quartz crystal is the physical core, QCM is its sensing application branch, QCM oscillation circuit is the key module to realize the QCM function, and quartz crystal oscillator is a more general high-frequency signal generator.

[0025] like Figure 1 and Figure 3 As shown, Figure 1 is a structural diagram of a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment provided by an embodiment of the present invention; Figure 3 It is a structural diagram of a QCM adjustable capacitance compensation module provided in an embodiment of the present invention.

[0026] In this embodiment, a gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment includes: a QCM adjustable capacitance compensation module, wherein the QCM adjustable capacitance compensation module includes: an adjustable capacitor C1 and an operational amplifier U1, the operational amplifier U1 is set under negative feedback conditions, and the adjustable capacitor C1 is connected to the inverting input terminal of the operational amplifier U1 after being connected in parallel with the quartz crystal oscillator Y1, so as to compensate for the influence of the equivalent capacitance in the static branch of the quartz crystal oscillator Y1 on the circuit oscillation frequency.

[0027] The principle is that the QCM adjustable capacitance compensation module is designed on the basis of the operational amplifier. The operational amplifier U1 is connected to negative feedback. The adjustable capacitor C1 is connected in parallel with the quartz crystal oscillator Y1 by utilizing the virtual short and virtual open characteristics of the operational amplifier. After parallel connection, it is connected to the inverting input terminal of the operational amplifier U1 to compensate for the influence of the static equivalent capacitance in the static branch of the quartz crystal oscillator Y1. At the same time, the non-inverting input terminal of the operational amplifier U1 can also provide a certain amount of bias voltage.

[0028] like Figure 4 As shown, Figure 4 It is a structural diagram of a gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment provided by an embodiment of the present invention.

[0029] In an optional embodiment, the gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment also includes: a differential amplifier module; the differential amplifier module is connected in series with the QCM adjustable capacitance compensation module, and is used to amplify the oscillation signal of the quartz crystal oscillator Y1 to enhance the influence of the equivalent resistance in the dynamic branch of the quartz crystal oscillator Y1 on the circuit gain.

[0030] In order to further illustrate the compensation effect of the adjustable capacitor C1 in the liquid phase, the following uses an equivalent circuit model to illustrate the change in the frequency characteristics of the quartz crystal oscillator in the liquid phase and the working principles of the QCM adjustable capacitor compensation module and the differential amplifier module.

[0031] like Figure 2 As shown, Figure 2 It is an equivalent circuit model diagram of a quartz crystal oscillator provided in an embodiment of the present invention.

[0032] In the equivalent circuit model of a quartz crystal oscillator, it can be equivalent to a dynamic branch and a static branch in parallel. The dynamic branch determines the resonance characteristics of the quartz crystal. When the external environment changes, such as mass adsorption, changes in liquid viscosity, etc., the dynamic parameters will change to varying degrees, causing changes in the resonance frequency and equivalent impedance of the quartz crystal. Although the static branch does not directly participate in the resonance process of the quartz crystal, it will affect the electrical characteristics of the entire equivalent circuit. In actual measurements, the presence of the static equivalent capacitance of the static branch will cause a certain offset in the resonance frequency of the crystal, and will also affect the input impedance and frequency response characteristics of the measurement system.

[0033] Specifically, the static branch has a static equivalent capacitor C0, and the dynamic branch is composed of an equivalent resistor Rm, an equivalent capacitor Cm and an equivalent inductor Lm. When the quartz crystal oscillator Y1 resonates, the dynamic branch is purely resistive, and its resistance is Therefore, the actual equivalent admittance of the quartz crystal oscillator Y1 is: 0(1); in, is the equivalent admittance of the dynamic branch; is the equivalent admittance of the static branch; is the equivalent resistance of the dynamic branch; is the equivalent admittance of the static branch; is the static equivalent capacitance of the static branch.

[0034] However, when the quartz crystal oscillator is in the liquid phase, the increased damping will lead to the dynamic equivalent resistance The value of increases, The value of will decrease, thereby increasing the influence of the equivalent capacitance of the static branch, which in turn causes the phase to shift and ultimately affects the resonant balance. Therefore, it is necessary to increase the capacitance to compensate for the influence of the equivalent capacitance of the static branch.

[0035] By setting the adjustable capacitor C1, the influence of the equivalent capacitance of the static branch can be compensated. According to the characteristics of virtual short and virtual open, this can be achieved through the following process: For the quartz crystal oscillator Y1, that is, the voltage at the inverting input of the operational amplifier U1 , you can have: (2); in, is the voltage at the inverting input of operational amplifier U1, ; is the input of the circuit; is an adjustable capacitor used for compensation; is the output of the circuit; is the negative feedback resistor of the operational amplifier U1; is the equivalent admittance of the quartz crystal oscillator.

[0036] In order to eliminate the influence of the static equivalent capacitance, only consider , simplifying formula (2) to obtain: (3); in, is the negative feedback resistor of operational amplifier U1.

[0037] Also because ,when When , the influence of the equivalent capacitance of the static branch can be offset. At this time, considering the influence of the dynamic branch, we can get: (4); The output voltage at this time It has nothing to do with the equivalent capacitance of the static branch, but it will be affected by the dynamic branch. As the output voltage increases, will gradually tend to In this way, the influence of the quartz crystal oscillator on the oscillation frequency will be greatly weakened, which will also lead to incorrect measurement results.

[0038] Therefore, it is necessary to perform differential amplification through power amplifier U3 to remove the constant term and only retain the , that is, , after being amplified by the power amplifier U3, can be expressed as: (5); in, is the output voltage of operational amplifier U2; At this time, the output of the circuit has only is mutable, and therefore only Therefore, the quartz crystal oscillator can stably control the resonant frequency of the circuit. At the same time, the resistance value of the adjustable resistor R3 can be adjusted as needed, thereby flexibly adjusting the amplitude of the oscillation signal.

[0039] At this point, the quartz crystal oscillator, under the action of the adjustable capacitor and the compensation circuit composed of the operational amplifier, eliminates the influence of the static equivalent capacitance, and then after passing through the differential amplifier circuit, the effect of the dynamic resistance is enhanced, thereby enhancing the influence of QCM on the circuit resonance.

[0040] See also Figure 3In an optional embodiment, the QCM adjustable capacitor compensation module includes: an adjustable capacitor C1 and an operational amplifier U1. The second electrode plate of the adjustable capacitor C1 is respectively connected to a quartz crystal oscillator Y1 and an inverting input terminal of the operational amplifier U1. An adjustable resistor R3 is bridged between the inverting input terminal and the output terminal of the operational amplifier U1.

[0041] Furthermore, the QCM adjustable capacitor compensation module also includes: an operational amplifier U2, a fixed resistor R1 and a fixed resistor R2, wherein the first end of the fixed resistor R1 is connected to the first plate of the adjustable capacitor C1; the second end of the fixed resistor R1 is connected to the first end of the fixed resistor R2, and the second end of the fixed resistor R2 is grounded; the non-phase input end of the operational amplifier U2 is respectively connected to the non-phase input end of the operational amplifier U1 and the second end of the fixed resistor R1, and the inverting input end of the operational amplifier U2 is connected to its output end.

[0042] It is worth noting that the QCM can adapt to different liquid environments by dynamically adjusting the adjustable capacitor C1; at the same time, the gain can also be adjusted by using the adjustable resistor R3 in the gain link. Figure 4 , exemplarily, the differential amplifier module includes: an operational amplifier U3, a resistor R4, a resistor R5, a resistor R6 and a resistor R7, wherein the first end of the resistor R4 is connected to the output end of the operational amplifier U1, and the second end of the resistor R4 is connected to the inverting input end of the operational amplifier U3; the resistor R5 is connected across the inverting input end and the output end of the operational amplifier U3; the non-inverting input end of the operational amplifier U3 is connected to the second end of the resistor R7; the first end of the resistor R7 is connected to the output end of the operational amplifier U2; the first end of the resistor R6 is connected to the first end of the resistor R7, and the second end of the resistor R6 is grounded.

[0043] In addition, the differential amplifier module enhances the influence of the dynamic branch resistance of the QCM on the circuit oscillation frequency, that is, enhances the effect of the dynamic equivalent resistance of the QCM. The output of the QCM adjustable capacitance compensation module is connected to the inverting input of the operational amplifier U3, and the non-inverting input of the operational amplifier U3 is also connected to the bias voltage of the same magnitude as the QCM adjustable capacitance compensation module. Finally, the differential amplifier module provides a 180-degree phase shift.

[0044] The gain-adjustable QCM circuit system suitable for a liquid phase high-damping environment of the present invention sets an operational amplifier under a negative feedback condition, and then connects an adjustable capacitor to an inverting input terminal of the operational amplifier after being connected in parallel with a quartz crystal oscillator. The adjustable capacitor compensates for the influence of the equivalent capacitance in the static branch of the quartz crystal oscillator on the circuit oscillation frequency, and at the same time enhances the effect of the dynamic equivalent resistance, thereby solving the problem that the quartz crystal oscillator is difficult to stably start oscillation in a liquid phase high-damping environment, and significantly enhancing its adaptability in the liquid phase.

[0045] Embodiment 2 The difference between this embodiment and the first embodiment is that a bandpass filter module and an AGC amplitude stabilization module are further provided in the gain adjustable QCM circuit system suitable for a liquid phase high damping environment, wherein the QCM adjustable capacitance compensation module, the differential amplifier module, the bandpass filter module and the AGC amplitude stabilization module are sequentially connected to form a closed loop, that is, the output end of the AGC amplitude stabilization module is then connected to the input end of the QCM adjustable capacitance compensation module to form a closed-loop structure of the entire circuit.

[0046] See also Figure 4 In an optional embodiment, a bandpass filter module is provided after the differential amplifier module; the bandpass filter module is used to filter out the noise and interference signal in the oscillation signal of the quartz crystal oscillator Y1 after amplification by the differential amplifier module to obtain a filtered signal. The bandpass filter module effectively removes the high-frequency noise interference and low-frequency signal in the output signal of the power amplifier U3, so that the output signal can be better maintained near the resonant frequency.

[0047] For example, a high-frequency coupling capacitor is used in the bandpass filter module to realize the effective transmission of high-frequency signals. The capacitance of the high-frequency coupling capacitor can be selected according to the oscillation frequency of the actual circuit. A specific bandpass filter module structure is as follows: Figure 5 As shown, it is based on a signal frequency of 6 MHz and a bandwidth of 1 MHz. Selecting a bandpass filter with this bandwidth is beneficial for filtering out noise and interference outside the resonant frequency.

[0048] It can be understood that the bandpass filter module can determine the size of the lower cutoff frequency and the upper cutoff frequency according to the specific QCM resonant frequency, and select the order of the filter circuit, such as a third-order Bessel bandpass filter structure or a third-order Butterworth bandpass filter, and the parameters of the devices such as capacitors, inductors or resistors can also be determined according to the lower cutoff frequency and the upper cutoff frequency. Therefore, the specific structure of the bandpass filter module is not introduced or limited in this embodiment.

[0049] In an optional implementation, an AGC amplitude stabilization module is provided after the bandpass filtering module, and the AGC amplitude stabilization module is used to adjust the gain and perform gain amplification on the filtered signal.

[0050] Exemplarily, the AGC amplitude stabilization module includes: a variable gain amplifier (Variable Gain Amplifier, VGA) and a true root mean square to direct current converter (Root Mean Square to Direct Current Converter, RMS-DC converter). The variable gain amplifier is used for gain amplification. The filtered signal after gain amplification is converted into a DC root mean square voltage signal in the true root mean square to direct current converter, and then connected to the gain control terminal of the variable gain amplifier to adjust the gain, thereby achieving the effect of amplitude stabilization.

[0051] Specifically, the variable gain amplifier is an amplifier with gain, but the size of the gain will change according to the control voltage fed back, that is, the variable gain amplifier adjusts the gain size through the control voltage. The source of the control voltage is collected by the true root mean square DC converter, and then fed back to the variable gain amplifier to adjust the gain. After the AC signal passes through the coupling capacitor and enters the variable gain amplifier, it is output through the coupling capacitor C3, and the output will be connected to the input end again, thus forming a closed loop of the entire circuit. The true root mean square DC converter converts the AC signal output by the variable gain amplifier into a DC voltage, and then into a true root mean square voltage. The output of the true root mean square DC converter is connected to the gain control pin of the variable gain amplifier, which is used to adjust the gain of the variable gain amplifier and plays a feedback role.

[0052] Similarly, the structure of the AGC amplitude stabilization module and the variable gain amplifier and true root mean square direct current converter therein can also be set according to actual needs.

[0053] See also Figure 3 In an optional embodiment, a coupling module is provided between the bandpass filter module and the AGC amplitude stabilization module, and the coupling module includes: a coupling capacitor C2, a coupling inductor L1 and a coupling resistor R8, wherein the first plate of the coupling capacitor C2 is connected to the output end of the bandpass filter module, and the second plate of the coupling capacitor C2 is respectively connected to the first end of the coupling inductor L1 and the first end of the coupling resistor R8; the second end of the coupling inductor L1 is connected to the second end of the coupling resistor R8, and the inductor L1 and the resistor R8 are connected in parallel, which plays a role in resisting electromagnetic interference. In addition, the coupling capacitor C2 can effectively transmit high-frequency signals, and its specific capacitance value can also be set according to the oscillation frequency of the actual circuit.

[0054] In an optional implementation, a coupling capacitor C3 is connected between the output end of the AGC amplitude stabilization module and the QCM adjustable capacitance compensation module. Similarly, the coupling capacitor C3 is also used for coupling AC signals to achieve AC signal transmission while blocking DC components.

[0055] It is worth noting that the gain-adjustable QCM circuit system of this embodiment, which is applicable to a liquid phase high-damping environment, reduces electromagnetic interference through a coupling module and a coupling capacitor, and further enhances signal stability.

[0056] The working principle of the gain adjustable QCM circuit system in the liquid phase high damping environment of this embodiment is that the QCM adjustable capacitance compensation module eliminates the influence of the static equivalent capacitance through the adjustable capacitor C1; the differential amplifier module is mainly used to eliminate the influence of the feedback resistance of the QCM adjustable capacitance compensation module on the circuit gain, and the effect of the dynamic equivalent resistance of the QCM is enhanced by eliminating the constant term. The signal after differential amplification passes through the bandpass filter module to filter out the noise signal except the resonant frequency and enter the AGC amplitude stabilization module. The AGC amplitude stabilization module is composed of a variable gain amplifier and a true root mean square DC converter. The signal first enters the variable gain amplifier through capacitor coupling, and then after the gain amplification of the variable gain amplifier, the AC signal is converted into a DC root mean square voltage through a true root mean square DC converter, and the gain control end of the variable gain amplifier is connected to adjust the gain size to achieve the effect of amplitude stabilization, and finally output through the coupling capacitor C3, and the output will be connected to the input end of the QCM adjustable capacitance compensation module again to form a closed loop of the entire circuit.

[0057] It is worth noting that the gain-adjustable QCM circuit system applicable to the liquid phase high damping environment of the present embodiment is provided with an adjustable capacitor C1 connected in parallel with the quartz crystal oscillator Y1, and combined with the negative feedback characteristics of the operational amplifier, the influence on the static equivalent capacitance is realized. Different from other compensation methods, the gain-adjustable QCM circuit system applicable to the liquid phase high damping environment of the present embodiment is a structural design of an adjustable capacitor combined with an operational amplifier. On the basis of the operational amplifier, the compensation effect is achieved through the mechanism of negative feedback. The compensated signal passes through the differential amplifier module again to eliminate the influence of the constant term in the relationship between the input and output, which plays a role in enhancing the dynamic equivalent resistance, thereby further enhancing the influence of the QCM on the resonant frequency of the circuit. Then, the oscillation stability of the circuit and the accuracy of the resonant frequency are enhanced through a suitable bandpass filter module and an AGC amplitude stabilization module.

[0058] The present invention effectively optimizes the signal waveform, enhances signal stability, reduces electromagnetic interference, and improves detection accuracy by combining a differential amplifier module, a bandpass filter module, and an AGC amplitude stabilization module. By adjusting the signal amplitude through an adjustable resistor, the flexibility and stability of the quartz crystal oscillator in different liquid phase environments are further improved, providing a more reliable detection method for fields such as biochemical detection.

[0059] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant is intended to cover non-exclusive inclusion, so that the article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the article or device including the elements. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. The orientation or position relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0060] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A gain adjustable QCM circuit system suitable for use in a liquid phase high damping environment, characterized in that: include: QCM adjustable capacitor compensation module, where: The QCM adjustable capacitance compensation module includes: an adjustable capacitor C1 and an operational amplifier U1. The operational amplifier U1 is set under negative feedback conditions. The adjustable capacitor C1 is connected to the inverting input terminal of the operational amplifier U1 in parallel with the quartz crystal oscillator Y1, so as to compensate for the influence of the equivalent capacitance in the static branch of the quartz crystal oscillator Y1 on the circuit oscillation frequency.

2. The gain-adjustable QCM circuit system suitable for a liquid phase high damping environment according to claim 1, characterized in that: The second electrode plate of the adjustable capacitor C1 is connected to the quartz crystal oscillator Y1 and the inverting input terminal of the operational amplifier U1 respectively. An adjustable resistor R3 is connected between the inverting input terminal and the output terminal of the operational amplifier U1.

3. The gain-adjustable QCM circuit system suitable for use in a liquid phase high damping environment according to claim 2, characterized in that: The QCM adjustable capacitance compensation module further includes: an operational amplifier U2, a fixed value resistor R1 and a fixed value resistor R2, wherein: The first end of the fixed resistor R1 is connected to the first electrode plate of the adjustable capacitor C1; the second end of the fixed resistor R1 is connected to the first end of the fixed resistor R2, and the second end of the fixed resistor R2 is grounded; the positive input end of the operational amplifier U2 is respectively connected to the positive input end of the operational amplifier U1 and the second end of the fixed resistor R1, and the inverting input end of the operational amplifier U2 is connected to its output end.

4. The gain-adjustable QCM circuit system suitable for use in a liquid phase high damping environment according to claim 3, characterized in that: Also includes: Differential amplifier module; the differential amplifier module is connected in series with the QCM adjustable capacitance compensation module, and is used to amplify the oscillation signal of the quartz crystal oscillator Y1 to enhance the influence of the equivalent resistance in the dynamic branch of the quartz crystal oscillator Y1 on the circuit gain.

5. The gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment according to claim 4, characterized in that: The differential amplifier module includes: an operational amplifier U3, a resistor R4, a resistor R5, a resistor R6 and a resistor R7, wherein: The first end of the resistor R4 is connected to the output end of the operational amplifier U1, and the second end of the resistor R4 is connected to the inverting input end of the operational amplifier U3; the resistor R5 is connected between the inverting input end and the output end of the operational amplifier U3; the non-inverting input end of the operational amplifier U3 is connected to the second end of the resistor R7; the first end of the resistor R7 is connected to the output end of the operational amplifier U2; the first end of the resistor R6 is connected to the first end of the resistor R7, and the second end of the resistor R6 is grounded.

6. The gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment according to claim 4, characterized in that: A bandpass filter module is disposed after the differential amplifier module; the bandpass filter module is used to filter out noise and interference signals in the oscillation signal of the quartz crystal oscillator Y1 after being amplified by the differential amplifier module to obtain a filtered signal.

7. The gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment according to claim 6, characterized in that: An AGC amplitude stabilization module is arranged behind the bandpass filtering module, and the AGC amplitude stabilization module is used to adjust the gain and perform gain amplification on the filtering signal.

8. The gain-adjustable QCM circuit system suitable for use in a liquid phase high damping environment according to claim 7, characterized in that: The AGC amplitude stabilization module includes: a variable gain amplifier and a true root mean square to direct current converter. The variable gain amplifier is used for gain amplification. The filtered signal after gain amplification is converted into a direct current root mean square voltage signal in the true root mean square to direct current converter, and then connected to the gain control terminal of the variable gain amplifier to adjust the gain.

9. The gain-adjustable QCM circuit system suitable for use in a liquid phase high-damping environment according to claim 7, characterized in that: A coupling module is provided between the bandpass filtering module and the AGC amplitude stabilization module, and the coupling module includes: a coupling capacitor C2, a coupling inductor L1 and a coupling resistor R8, wherein: The first plate of the coupling capacitor C2 is connected to the output end of the bandpass filter module, and the second plate of the coupling capacitor C2 is respectively connected to the first end of the coupling inductor L1 and the first end of the coupling resistor R8; the second end of the coupling inductor L1 is connected to the second end of the coupling resistor R8.

10. The gain-adjustable QCM circuit system suitable for use in a liquid phase high damping environment according to claim 7, characterized in that: A coupling capacitor C3 is connected between the output end of the AGC amplitude stabilization module and the QCM adjustable capacitance compensation module.

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