Self-frequency-modulation filter circuit and weak signal detection system
By designing a self-frequency modulation filter circuit, using a voltage-controlled oscillator and a driving module to adjust the comb tooth range, it automatically adjusts the filter frequency, which solves the problem that existing filters cannot automatically adjust the cutoff frequency, and improves circuit design flexibility and signal reading accuracy.
Patent Information
- Application Number
- CN202411465887.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-21
- Publication Date
- 2025-03-21
AI Technical Summary
Existing filters cannot automatically adjust the cutoff frequency, resulting in insufficient circuit design flexibility. In weak signal detection circuits, closed-loop control is prone to oscillation, affecting output stability.
A self-frequency modulation filter circuit is designed to adjust the range of the comb teeth according to the amplitude of the input signal through a voltage-controlled oscillator and a driving module, thereby automatically adjusting the frequency of the filter to form a closed-loop control circuit.
Automatically adjust the filter bandwidth, improve circuit design flexibility, reduce circuit area and cost, and improve driving force sensitivity through frequency control, and enhance frequency reading accuracy of weak signal detection system.
Smart Images
Figure CN119675626A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of filters, and in particular to a self-frequency modulation filter circuit and a weak signal detection system. Background Art
[0002] Converting weak capacitance into voltage and obtaining accurate CV output signal is a basic task in high-precision weak signal detection circuit. The analog front-end circuit in the weak signal detection circuit requires a high signal-to-noise ratio, and the noise and signal are often coupled and superimposed, which requires the front-end circuit to decouple the noise from the signal through modulation and demodulation, and filter out the noise through the filter. Therefore, the design of the filter is the focus of the front-end circuit design.
[0003] Filters include active filters and passive filters. Traditional RC filters are the most common type of passive filters and are widely used because of their simple structure and mature design theory. However, passive filters have defects such as cutoff frequency drift and poor filtering depth, which makes passive filters a bottleneck for improving system integration. In contrast, active filters can overcome the above defects, but they also have disadvantages such as complex structure, high power consumption, and signal-to-noise distortion ratio that is highly dependent on active devices.
[0004] However, neither passive filters nor active filters can achieve automatic adjustment of the cutoff frequency. If the filter bandwidth can be automatically adjusted, it can save circuit area and cost while improving circuit design flexibility.
[0005] Moreover, in weak signal detection circuits, closed-loop control is a common means of increasing linearity and improving detection dynamic range, which is often achieved by PID control or SDM control, and control is achieved through voltage amplitude feedback. However, loop voltage control is prone to oscillation, resulting in unstable output or a long time to reach steady state; and closed-loop drive and detection often require multiple signal sources to have corresponding functions, such as a drive signal source for driving and a carrier signal source for detection. At this time, two signal sources are required to realize capacitance readout, which will bring multiple constraints to device design. Summary of the invention
[0006] In order to solve at least one of the above problems, the present application proposes a self-frequency modulation filter circuit and a weak signal detection system.
[0007] According to the first aspect of the present application, at least one embodiment of the present application provides a self-frequency tuning filter circuit, including: a self-frequency tuning filter module, used to receive a first input signal at a signal input end, including: a first transistor, a gate connected to the signal input end, and a source connected to ground; a second transistor, a gate connected to the drain of the first transistor, and a source connected to the source of the first transistor; a first resistor, one end of which is connected to a DC power supply, and the other end is connected to the drain of the first transistor; a second resistor, one end of which is connected to the DC power supply, and the other end is connected to the drain of the second transistor; a comb tooth, one end of which is connected to the drain of the first transistor, and the other end is connected to the drain of the second transistor; a voltage-controlled oscillator, connected to the self-frequency tuning filter module, and used to output a second output signal of a corresponding frequency according to the amplitude of the first output signal of the self-frequency tuning filter module; a driving module, connected to the self-frequency tuning filter module and the voltage-controlled oscillator respectively, and used to receive the second output signal, and adjust the range of the comb teeth according to the amplitude of the second output signal to adjust the frequency of the self-frequency tuning filter module.
[0008] For example, in some embodiments of the present application, the comb teeth are equivalent to a first capacitor and a second capacitor, wherein: the first capacitor is connected to the drain and source of the first transistor to form a first amplifier; the second capacitor is connected to the drain and source of the second transistor to form a second amplifier.
[0009] For example, in some embodiments of the present application, the amplification factor of the second amplifier is calculated according to the following formula:
[0010] Av=g m2 R2
[0011] Wherein, Av is the gain of the second amplifier, g m2 is the transconductance coefficient of the second transistor, and R2 is the resistance value of the second resistor.
[0012] For example, in some embodiments of the present application, the cutoff frequency of the self-frequency tuning filter module is calculated according to the following formula:
[0013]
[0014] Among them, f p is the cut-off frequency of the self-frequency tuning filter module, R1 is the resistance value of the first resistor, and C1 is the capacitance value of the first capacitor.
[0015] For example, in some embodiments of the present application, the capacitance value of the first capacitor is calculated according to the following formula:
[0016]
[0017] Among them, ε0 is the dielectric constant, hx is the range of the two plates of the first capacitor, and d is the distance between the two plates of the first capacitor.
[0018] For example, in some embodiments of the present application, the voltage-controlled oscillator is configured to: when the amplitude of the first output signal increases, adjust the frequency of the second output signal to increase; when the amplitude of the first output signal decreases, adjust the frequency of the second output signal to decrease.
[0019] For example, in some embodiments of the present application, the driving module is configured as follows: when the frequency of the second output signal decreases, the driving force of the driving module decreases so that the range of the comb teeth is reduced, the frequency of the self-frequency tuning filter circuit is increased, and the amplitude of the first input signal is increased; when the frequency of the second output signal increases, the driving force of the driving module increases so that the range of the comb teeth is increased, the frequency of the self-frequency tuning filter circuit is reduced, and the amplitude of the first input signal is attenuated.
[0020] For example, in some embodiments of the present application, the difference between the frequency of the first input signal and the cutoff frequency of the self-frequency tuning filter module is within a first preset range.
[0021] For example, in some embodiments of the present application, the first transistor and the second transistor are NMOS transistors or PMOS transistors.
[0022] According to the second aspect of the present application, at least one embodiment of the present application provides a weak signal detection system, comprising: a self-frequency tuning filter circuit as described in any one of the first aspect; a frequency reading module, connected to the self-frequency tuning filter circuit, for displaying the frequency of the self-frequency tuning filter circuit.
[0023] Through the above-mentioned example embodiments, the present application provides a self-frequency-modulating filter circuit and a weak signal detection system, which form a closed-loop control circuit, and can save circuit area and cost while realizing automatic adjustment of the filter bandwidth, thereby improving the design flexibility of the circuit; and controlling the magnitude of the driving force from a frequency perspective, the narrower the resonant frequency range of the voltage-controlled oscillator device, the higher the control sensitivity; and the present application only needs one input signal to realize circuit closed-loop driving and device capacitance reading; in addition, since the capacitance will be amplified, the frequency reading accuracy of the weak signal detection system is higher.
[0024] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] By describing in detail exemplary embodiments thereof with reference to the accompanying drawings, the above and other objects, features and advantages of the present application will become more apparent. The accompanying drawings described below are only some embodiments of the present application, and are not intended to limit the present application.
[0026] Figure 1 A schematic diagram showing a self-frequency tuning filter circuit according to an exemplary embodiment;
[0027] Figure 2 An equivalent schematic diagram of a self-tuning filter module of an exemplary embodiment is shown;
[0028] Figure 3 A schematic diagram of a weak signal detection system according to an exemplary embodiment is shown. DETAILED DESCRIPTION
[0029] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.
[0030] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices, etc. may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.
[0031] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.
[0032] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.
[0033] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of example embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing the present application, and therefore cannot be used to limit the scope of protection of the present application.
[0034] Figure 1 A schematic diagram showing a self-frequency tuning filter circuit according to an exemplary embodiment is shown.
[0035] like Figure 1 As shown, the self-frequency modulation filter circuit includes: a self-frequency modulation filter module 101 , a voltage-controlled oscillator 102 and a driving module 103 .
[0036] Wherein, the self-frequency modulation filter module 101 is used to amplify the first input signal of the signal input terminal Fin. The self-frequency modulation filter module 101 includes: a first transistor Q1, a second transistor Q2, a first resistor R1, a second resistor R2 and a comb tooth C0. The gate of the first transistor Q1 is connected to the signal input terminal, and the source is grounded. The gate of the second transistor Q2 is connected to the drain of the first transistor Q1, and the source is connected to the source of the first transistor Q1. One end of the first resistor R1 is connected to a DC power supply, and the other end is connected to the drain of the first transistor Q1. One end of the second resistor R2 is connected to a DC power supply, and the other end is connected to the drain of the second transistor Q2. One end of the comb tooth C0 is connected to the drain of the first transistor Q1, and the other end is connected to the drain of the second transistor Q2.
[0037] According to an example embodiment, the comb tooth C0 is equivalent to the first capacitor C1 and the second capacitor C2 by Miller, such as Figure 2 As shown. The first capacitor C1 is connected to the drain and source of the first transistor Q1, thereby forming a first amplifier. The capacitance of the first capacitor C1 to ground is (1+Av)C1. The second capacitor C2 is connected to the drain and source of the second transistor Q2, thereby forming a second amplifier. The capacitance of the second capacitor C2 to ground is (1+Av -1 )C1. The first amplifier and the second amplifier form a filter.
[0038] Calculate the gain of the second amplifier according to the following formula:
[0039] Av=g m2 R2
[0040] Where Av is the gain of the second amplifier, g m2 is the transconductance coefficient of the second transistor, and R2 is the resistance value of the second resistor.
[0041] According to some embodiments, the magnification factor Av may be set to a value much greater than 1000.
[0042] Calculate the capacitance of the first capacitor according to the following formula:
[0043]
[0044] Wherein, ε0 is the dielectric constant, hx is the range of the two plates of the first capacitor, and d is the distance between the two plates of the first capacitor.
[0045] The principle of the self-tuning filter module is that the comb capacitance C0 determines the cut-off frequency of the filter, that is, f p =1 / 2πRC0, it can be seen that when the drain resistance R remains unchanged, the filter cutoff frequency changes with C0, and the equivalent capacitance C1 changes with the resonant frequency of the MEMS comb device, and the capacitance value of c1 will be equivalently amplified to Av times, so the bandwidth of the filter is constantly changing dynamically. Calculate the cutoff frequency of the self-tuning filter module according to the following formula:
[0046]
[0047] Among them, f p is the cut-off frequency of the self-frequency modulation filter module, and R1 is the resistance value of the first resistor.
[0048] The cutoff frequency of the filter will change with the movement of the comb teeth. When it is used as a filter capacitor, the cutoff frequency of the filter changes, thereby realizing the self-frequency adjustment function: when the movement range of the comb teeth becomes larger, the bandwidth of the filter decreases; when the movement range of the comb teeth becomes smaller, the bandwidth of the filter increases.
[0049] According to some embodiments, the first transistor and the second transistor are NMOS transistors or PMOS transistors. The present application takes the NMOS transistor as an example, but the present application is not limited thereto.
[0050] The voltage controlled oscillator 102 is connected to the self-frequency tuning filter module 101 , and is used to output a second output signal of a corresponding frequency according to the amplitude of the first output signal of the self-frequency tuning filter module 101 .
[0051] According to an example embodiment, the voltage controlled oscillator 102 is configured such that: when the amplitude of the first output signal increases, the frequency of the second output signal increases; and when the amplitude of the first output signal decreases, the frequency of the second output signal decreases.
[0052] The driving module 103 is respectively connected to the self-frequency modulation filter module 101 and the voltage-controlled oscillator 102. The driving module 103 is used to receive the second output signal and adjust the range of the comb teeth according to the amplitude of the second output signal to adjust the frequency of the self-frequency modulation filter module 101, and finally realize the self-frequency modulation function.
[0053] According to an example embodiment, the driving module 103 is configured as follows: when the frequency of the second output signal decreases, the driving force of the driving module decreases so that the range of the comb teeth decreases, the frequency of the self-frequency modulation filter circuit increases, and the amplitude of the first input signal is increased; when the frequency of the second output signal increases, the driving force of the driving module increases so that the range of the comb teeth increases, the frequency of the self-frequency modulation filter circuit decreases, and the amplitude of the first input signal is attenuated.
[0054] According to some embodiments, the difference between the frequency of the first input signal and the cut-off frequency of the self-frequency modulation filter module is within a first preset range. The first preset range can be set voluntarily. The present application takes the frequency of the first input signal as the cut-off frequency of the self-frequency modulation filter module as an example, but the present application is not limited thereto.
[0055] According to some embodiments, the capacitance variation range of the MEMS comb teeth is set to (cap-min, cap-max), and the amplification factor of the second amplifier is Av times, then the variation range of the equivalent capacitance C1 is (Av*cap-min, Av*cap-max), and the corresponding filter bandwidth range is (BW-min, BW-max). The control signal frequency is set to w, and w=BW-max.
[0056] When the range of the comb teeth increases, the equivalent capacitance increases, the corresponding filter bandwidth decreases, and the amplitude of the w signal is attenuated after input. The effective value of w directly controls the output of the voltage-controlled oscillator, the amplitude of the w signal is attenuated, deviates from the resonant frequency of the voltage-controlled oscillator, and causes the output frequency of the voltage-controlled oscillator to decrease. At this time, the driving force of the driving module decreases accordingly, and the range of the comb teeth movement decreases.
[0057] When the output of the device decreases due to deviation from the resonant frequency, the movement range of the comb teeth becomes smaller, the equivalent capacitance becomes smaller, and the corresponding filter bandwidth becomes larger. After the w signal is input, the amplitude becomes larger, deviating from the resonant frequency of the voltage-controlled oscillator, and causing the output frequency of the voltage-controlled oscillator to increase. At this time, the driving force of the driving module is correspondingly increased, and the movement range of the comb teeth becomes larger.
[0058] In summary, the frequency-shaped closed-loop feedback of the self-frequency modulation filter circuit can be realized.
[0059] According to some embodiments, the magnitude of the driving force is controlled from a frequency perspective. The narrower the resonant frequency range of the voltage-controlled oscillator device, the easier it is for the input signal to deviate from the resonant frequency of the voltage-controlled oscillator, and the higher the control sensitivity.
[0060] The present application also provides a weak signal detection system, such as Figure 3 The weak signal detection system includes the self-frequency modulation filter circuit and the frequency reading module 104 as described above. The frequency reading module 104 is connected to the self-frequency modulation filter circuit and is used to display the frequency of the self-frequency modulation filter circuit.
[0061] From the readout perspective, the frequency reading module is connected to the voltage-controlled oscillator. The frequency value output by the voltage-controlled oscillator also represents the capacitance of the device comb teeth, and this capacitance value will be amplified by Av times, which is more conducive to readout.
[0062] The present application provides a self-frequency-modulating filter circuit and a weak signal detection system, which form a closed-loop control circuit. It can save circuit area and cost while automatically adjusting the filter bandwidth, thereby improving the design flexibility of the circuit. The driving force can be controlled from a frequency perspective. The narrower the resonant frequency range of the voltage-controlled oscillator device, the higher the control sensitivity. The present application only requires one input signal to realize circuit closed-loop driving and device capacitance reading. In addition, since the capacitance will be amplified, the frequency reading accuracy of the weak signal detection system is higher.
[0063] It should be clearly understood that the present application describes how to form and use specific examples, but the present application is not limited to any details of these examples. On the contrary, based on the teaching of the content disclosed in the present application, these principles can be applied to many other embodiments.
[0064] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present application, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.
[0065] The exemplary embodiments of the present application are specifically shown and described above. It should be understood that the present application is not limited to the detailed structures, configurations or implementations described herein; on the contrary, the present application is intended to cover various modifications and equivalent configurations included in the spirit and scope of the appended claims.
Claims
1. A self-frequency modulation filter circuit, characterized in that: include: The self-frequency modulation filter module is used to receive a first input signal at a signal input terminal, and comprises: A first transistor, a gate connected to the signal input terminal and a source grounded; a second transistor, having a gate connected to the drain of the first transistor and a source connected to the source of the first transistor; a first resistor, one end of which is connected to a DC power supply, and the other end of which is connected to a drain of the first transistor; a second resistor, one end of which is connected to the DC power supply, and the other end of which is connected to the drain of the second transistor; a comb tooth, one end of which is connected to the drain of the first transistor, and the other end of which is connected to the drain of the second transistor; A voltage-controlled oscillator, connected to the self-frequency tuning filter module, and configured to output a second output signal of a corresponding frequency according to the amplitude of the first output signal of the self-frequency tuning filter module; A driving module is connected to the self-frequency tuning filter module and the voltage-controlled oscillator respectively, and is used to receive the second output signal and adjust the range of the comb teeth according to the amplitude of the second output signal to adjust the frequency of the self-frequency tuning filter module.
2. The self-frequency modulation filter circuit according to claim 1, characterized in that: The comb teeth are equivalent to a first capacitor and a second capacitor, wherein: The first capacitor is connected to the drain and source of the first transistor to form a first amplifier; The second capacitor is connected to the drain and source of the second transistor to form a second amplifier.
3. The self-frequency modulation filter circuit as claimed in claim 2, characterized in that: The gain of the second amplifier is calculated according to the following formula: Off=g m2 ·R2 Wherein, Av is the gain of the second amplifier, g m2 is the transconductance coefficient of the second transistor, and R2 is the resistance value of the second resistor.
4. The self-frequency modulation filter circuit as claimed in claim 3, characterized in that: The cutoff frequency of the self-tuning filter module is calculated according to the following formula: Among them, f p is the cut-off frequency of the self-frequency tuning filter module, R1 is the resistance value of the first resistor, and C1 is the capacitance value of the first capacitor.
5. The self-frequency modulation filter circuit as claimed in claim 4, characterized in that: The capacitance value of the first capacitor is calculated according to the following formula: Among them, ε0 is the dielectric constant, hx is the range of the two plates of the first capacitor, and d is the distance between the two plates of the first capacitor.
6. The self-frequency modulation filter circuit according to claim 1, characterized in that: The voltage controlled oscillator is configured as: When the amplitude of the first output signal increases, the frequency of the second output signal is adjusted to increase; In the case where the amplitude of the first output signal decays, the frequency of regulating the second output signal decreases.
7. The self-frequency modulation filter circuit according to claim 1, characterized in that: The driver module is configured as follows: When the frequency of the second output signal decreases, the driving force of the driving module decreases, so that the range of the comb teeth decreases, the frequency of the self-frequency modulation filter circuit increases, and the amplitude of the first input signal is increased; When the frequency of the second output signal increases, the driving force of the driving module increases, so that the range of the comb teeth increases, the frequency of the self-frequency modulation filter circuit decreases, and the amplitude of the first input signal is attenuated.
8. The self-frequency modulation filter circuit according to claim 1, characterized in that: The difference between the frequency of the first input signal and the cutoff frequency of the self-frequency tuning filter module is within a first preset range.
9. The self-frequency modulation filter circuit according to claim 1, characterized in that: The first transistor and the second transistor are NMOS transistors or PMOS transistors.
10. A weak signal detection system, characterized in that: include: The self-frequency modulation filter circuit as claimed in any one of claims 1 to 9; The frequency reading module is connected to the self-frequency modulation filter circuit and is used to display the frequency of the self-frequency modulation filter circuit.