Active filter, system, chip and electronic device
By combining passive and active filter networks and employing a combination of RC filter modules, voltage followers, and flip-flop voltage follower modules, the problem of poor filtering performance of active filters in high-frequency scenarios is solved, achieving good filtering performance in high-frequency environments.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHUHAI JIELI TECH
- Filing Date
- 2022-10-17
- Publication Date
- 2026-07-10
AI Technical Summary
Existing active filters cannot work effectively in high-frequency scenarios, especially in the wireless signal transmission and reception of communication equipment, where the filtering effect is poor.
By combining passive and active filtering networks, and employing a combination of RC filter modules, voltage follower modules, flip-flop voltage follower modules, and positive feedback modules, efficient filtering of the signal to be filtered is achieved. This includes passive filtering of the signal by the RC filter module, active filtering of the signal by the voltage follower module and the flip-flop voltage follower module, and providing gain through the positive feedback module to suppress unwanted frequencies.
The operating frequency of the active filter was increased to make it suitable for high-frequency environments, ensuring that signals within the passband can pass through without obstruction, while out-of-band signals are effectively suppressed, forming a flat Butterworth curve and improving the filtering effect.
Smart Images
Figure CN116781036B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of signal processing technology, and more particularly to active filters, systems, chips, and electronic devices. Background Technology
[0002] In signal processing tasks such as information processing, data transmission, and interference suppression in electronic devices, filtering is a common operation, and filters are common filtering components. Based on their working principle, filters can be divided into active filters and passive filters.
[0003] Passive filters are mainly composed of passive components such as inductors, capacitors, and resistors. They are designed to have extremely low impedance at a specific frequency to shun harmonics of that frequency. Passive filters often have poor filtering performance and can only filter out one or more specific frequency harmonics. Therefore, passive filters are mainly used for tuned filtering and high-pass filtering.
[0004] Active filters mainly consist of RC components and operational amplifiers. Their working principle is to allow signals within a certain frequency range to pass through, while suppressing or drastically attenuating signals outside that frequency range. Compared to passive filters, active filters offer significantly better filtering performance.
[0005] However, because the operating frequency of active filters is limited by the bandwidth of operational amplifiers, existing active filters are often only usable in the low-frequency range. When the operating frequency is very high (30–300 MHz) or higher, active filters cannot be used.
[0006] Especially in the field of communications, when communication equipment transmits and receives wireless signals, it usually requires VHF or higher operating frequencies. In the current technology, only passive filters can be used, which results in poor filtering effect.
[0007] Therefore, how to enable active filters to operate in high-frequency scenarios has become an urgent technical problem to be solved. Summary of the Invention
[0008] Based on the above situation, the main objective of this invention is to provide an active filter, system, chip, and electronic device to solve the technical problem of how to prevent active filters from working in high-frequency scenarios.
[0009] Therefore, according to a first aspect, embodiments of the present invention disclose an active filter, including a passive filter network and an active filter network. The signal to be filtered is filtered by the passive filter network and then output to the active filter network for active filtering. The passive filter network includes an RC filter module; the active filter network includes a voltage follower module, a flip-flop voltage follower module, and a positive feedback module, wherein:
[0010] The input terminal of the RC filter module is the signal input terminal of the active filter, which is used to receive the signal to be filtered by the active filter, so as to perform passive filtering on the signal to be filtered to obtain a passive filtered signal.
[0011] The voltage output of the voltage follower module rises and falls in tandem with the rise and fall of the passive filter signal to obtain a voltage follower signal;
[0012] The flip-type voltage follower module receives a voltage follower signal and causes the voltage output from the filter output terminal of the flip-type voltage follower module to rise and fall in accordance with the rise and fall of the voltage follower signal, so as to obtain an active filter signal; the filter output terminal is the output terminal of the active filter;
[0013] The positive feedback module is connected between the filter output and the RC filter module. When the frequency of the signal to be filtered falls within the preset cutoff range, the positive feedback module is used to feed the active filter signal back to the RC filter module to provide positive gain for the active filter signal and weaken the active filter signal.
[0014] Preferably, the RC filter module includes a first resistor, a second resistor, and a high-frequency conducting capacitor;
[0015] One end of the first resistor and one end of the second resistor are both connected to a common connection point. The other end of the first resistor is connected to the signal input terminal, and the other end of the second resistor is connected to the voltage follower module.
[0016] A high-frequency conducting capacitor is connected between the other end of the second resistor and ground so that the signal to be filtered with a frequency exceeding the maximum value of the cutoff range is transmitted to ground via the high-frequency conducting capacitor.
[0017] Preferably, the voltage follower module includes a first current source and a first transistor, wherein the first current source is connected between the first electrode of the first transistor and the power supply terminal to provide a stable current to the first transistor;
[0018] The second terminal of the first transistor is grounded, and the control terminal of the first transistor is connected to the other end of the second resistor to receive the passive filter signal. The first terminal of the first transistor is connected to the output terminal of the voltage follower module so that the passive filter signal controls the impedance of the first transistor, thereby changing the voltage output of the voltage follower module.
[0019] Preferably, the flip voltage follower module includes a seventh transistor, an eleventh transistor, and a twelfth transistor. The first terminal of the seventh transistor is connected to the power supply terminal, the second terminal of the seventh transistor is connected to the first terminal of the eleventh transistor through a high potential terminal, the second terminal of the eleventh transistor and the first terminal of the twelfth transistor are both connected to the filter output terminal, and the second terminal of the twelfth transistor is grounded.
[0020] The control electrode of the eleventh transistor is connected to the output terminal of the voltage follower module; so that changes in the voltage follower signal cause changes in the impedance of the eleventh transistor, which in turn cause changes in the voltage at the high potential terminal, which in turn cause changes in the voltage at the control electrode of the twelfth transistor, which in turn cause changes in the impedance of the twelfth transistor, which in turn cause changes in the voltage at the filter output terminal.
[0021] Preferably, it further includes: a bias module for providing a bias voltage to the flip voltage follower module, the magnitude of which is negatively correlated with the voltage follower signal, and the voltage at the filter output terminal is negatively correlated with the bias voltage, so that the voltage at the filter output terminal rises and falls in accordance with the rise and fall of the voltage follower signal.
[0022] Preferably, the biasing module includes a first biasing branch and a second biasing branch, the first biasing branch including an eighth transistor, a ninth transistor and a fourth transistor; the second biasing branch including a tenth transistor and a fifth transistor;
[0023] The eighth transistor and the seventh transistor are connected to form the first current mirror, the ninth transistor and the tenth transistor are connected to form the second current mirror, and the fourth transistor and the fifth transistor are connected to form the third current mirror.
[0024] The common connection point of the tenth transistor and the fifth transistor is connected to the control electrode of the twelfth transistor.
[0025] Preferably, it further includes: a reference current module, used to provide a stable current to the flip voltage follower module and the bias module, so that the output current flowing through the flip voltage follower module and the bias current flowing through the bias module remain stable.
[0026] Preferably, the reference current module includes a current source submodule and a mirror submodule. The current source submodule is used to provide a stable reference current, the mirror submodule mirrors the reference current to obtain the converted current, and the seventh transistor mirrors the converted current to obtain the output current.
[0027] Preferably, the current source submodule includes a second current source and a second transistor. The second current source is used to provide a stable reference current to the second transistor. The second transistor forms a current mirror with the fourth transistor and the fifth transistor, respectively, so as to keep the first bias current of the first bias branch and the second bias current of the second bias branch stable.
[0028] Preferably, the mirror submodule includes a third transistor and a sixth transistor, the third transistor and the second transistor forming a current mirror, and the sixth transistor and the seventh transistor forming a current mirror.
[0029] According to a second aspect, an embodiment of the present invention discloses a filtering system, which includes an active filter as disclosed in the first aspect, a signal input module, and a load module. The signal input module inputs a signal to be filtered to the active filter so that the active filter filters the signal to be filtered to obtain an active filtered signal. The load module receives the active filtered signal.
[0030] According to a third aspect, embodiments of the present invention disclose a chip for signal processing, the chip including an active filter as disclosed in the first aspect.
[0031] According to a third aspect, embodiments of the present invention disclose an electronic device with signal processing function, the electronic device including an active filter as disclosed in the first aspect.
[0032] [Beneficial Effects]
[0033] In the active filter disclosed in this embodiment, the input signal is passively filtered by an RC filter module to obtain a passive filtered signal. The voltage follower module enables the voltage follower signal to rise and fall with the rise and fall of the passive filtered signal. Since a flip-flop voltage follower module is set after the voltage follower module, the output impedance of the active filter is effectively reduced. The operating frequency of the active filter is inversely proportional to the output impedance, thus greatly increasing the operating frequency of the active filter. Therefore, the active filter can be used in high-frequency scenarios. By sequentially setting a voltage follower module and a flip-type voltage follower module after the RC filter module, the voltage at the filter output of the flip-type voltage follower module rises and falls with the rise and fall of the voltage follower signal. When the frequency of the signal to be filtered falls within the passband of the active filter, the positive feedback module is disconnected, and the active filter signal equals the signal to be filtered. When the frequency of the signal to be filtered falls within the preset cutoff range, the positive feedback module feeds the active filter signal back to the RC filter module to provide a positive gain for the active filter signal, causing the active filter signal to weaken rapidly. In other words, the active filter can have a good out-of-band suppression effect in high-frequency environments. When the frequency of the signal to be filtered exceeds the maximum value of the cutoff range, the RC filter module completely suppresses the signal to be filtered. At this time, there is no signal output at the active filter output. As a result, the characteristic curve of the active filter becomes flatter near the inflection point (cutoff frequency), forming a Butterworth curve. That is, the active filter can allow signals within the passband to pass through unimpeded in high-frequency environments, while out-of-band signals can be efficiently suppressed, thus ensuring the filtering effect of the active filter in high-frequency environments.
[0034] Other beneficial effects of the present invention will be explained in detail through the introduction of specific technical features and technical solutions in specific embodiments. Those skilled in the art should be able to understand the beneficial technical effects brought about by these technical features and technical solutions through the introduction of these technical features and technical solutions. Attached Figure Description
[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0036] Figure 1 This is a schematic diagram of an active filter circuit disclosed in this embodiment. Detailed Implementation
[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0038] In the description of this invention, it should be noted that the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0040] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0041] To enable adaptive adjustment of the turn-on time of an active filter, this embodiment discloses an active filter. Please refer to [link / reference needed]. Figure 1 , Figure 1This is a schematic diagram of an active filter circuit disclosed in this embodiment. The active filter includes a passive filter network and an active filter network. The signal to be filtered is filtered by the passive filter network and then output to the active filter network for active filtering. The passive filter network includes an RC filter module 100; the active filter network includes a voltage follower module 200, a flip-flop voltage follower module 300, and a positive feedback module 600.
[0042] The input terminal of the RC filter module 100 is the signal input terminal Vin of the active filter, which is used to receive the signal to be filtered by the active filter, so as to perform passive filtering on the signal to be filtered to obtain a passive filtered signal.
[0043] The voltage output from terminal B of the voltage follower module 200 rises and falls in response to the rise and fall of the passive filter signal, thus obtaining a voltage follower signal. In a specific embodiment, the following current flowing through the voltage follower module 200 remains constant, so that the rise and fall of the voltage at terminal B of the voltage follower module 200 is only related to the passive filter signal, thereby ensuring the accuracy of the voltage follower signal.
[0044] The signal input terminal of the flip voltage follower module 300 is connected to the output terminal B of the voltage follower module 200 to receive the voltage follower signal. This allows the voltage output from the filter output terminal C of the flip voltage follower module 300 to rise and fall in accordance with the voltage follower signal, thus obtaining an active filter signal. In a specific embodiment, the filter output terminal C is the output terminal of the active filter. The output current flowing through the flip voltage follower module 300 remains constant, ensuring that the rise and fall of the voltage at the filter output terminal C is only related to the voltage follower signal, thereby guaranteeing the accuracy of the active filter signal.
[0045] The positive feedback module 600 is connected between the filter output terminal C and the RC filter module 100. When the frequency of the signal to be filtered falls into the preset cutoff range, the positive feedback module 600 feeds the active filter signal back to the RC filter module 100 to provide positive gain for the active filter signal, thereby weakening the active filter signal so that the signal to be filtered whose frequency falls into the cutoff range can be quickly suppressed. This allows the characteristic curve of the active filter disclosed in this embodiment to drop rapidly in the cutoff region, thus making the cutoff characteristics of the active filter better.
[0046] Therefore, in the active filter disclosed in this embodiment, the input signal is passively filtered by the RC filter module 100 to obtain a passive filtered signal. The voltage follower module 200 enables the voltage follower signal to rise and fall with the rise and fall of the passive filtered signal. Since a flip voltage follower module 300 is set after the voltage follower module 200, the output impedance of the active filter is effectively reduced. Since the operating frequency of the active filter is inversely proportional to the output impedance, the operating frequency of the active filter is greatly increased. Thus, the active filter can be applied to high-frequency scenarios.
[0047] Furthermore, by sequentially setting a voltage follower module 200 and a flip-type voltage follower module 300 after the RC filter module 100, the voltage at the filter output of the flip-type voltage follower module 300 rises and falls with the rise and fall of the voltage follower signal. When the frequency of the signal to be filtered falls within the passband range of the active filter, the positive feedback module is disconnected, and the active filter signal equals the signal to be filtered. When the frequency of the signal to be filtered falls within the preset cutoff range, the positive feedback module feeds the active filter signal back to the RC filter module 100 to provide a positive gain for the active filter signal, enabling the active filter signal to quickly... The active filter exhibits good out-of-band suppression in high-frequency environments. When the frequency of the signal to be filtered exceeds the maximum value of the cutoff range, the RC filter module 100 completely suppresses the signal. At this time, there is no signal output at the active filter output terminal. As a result, the characteristic curve of the active filter becomes flatter near the inflection point (cutoff frequency), forming a Butterworth curve. In other words, the active filter allows signals within the passband to pass through unimpeded in high-frequency environments, while out-of-band signals are efficiently suppressed, thus ensuring the filtering effect of the active filter in high-frequency environments.
[0048] It should be noted that the active filter disclosed in this embodiment can be a high-pass filter, a low-pass filter, or a band-pass filter. For ease of understanding, this solution is described using a low-pass filter as an example, but it does not mean that this solution is limited to the low-pass filter type.
[0049] In this embodiment, the active filter further includes a bias module 400, which provides a bias voltage to the flip-flop voltage follower module 300. The magnitude of the bias voltage is negatively correlated with the voltage follower signal, and the voltage at the filter output terminal C is negatively correlated with the bias voltage, so that the voltage at the filter output terminal C rises and falls with the voltage follower signal. In a specific embodiment, the bias current flowing through the bias module 400 remains constant, thereby ensuring that the magnitude of the bias voltage is only related to the voltage follower signal, thus guaranteeing the accuracy of the bias voltage.
[0050] In this embodiment, the active filter also includes a reference current module 500, which provides a stable current to the flip voltage follower module 300 and the bias module 400 so that the output current flowing through the flip voltage follower module 300 and the bias current flowing through the bias module 400 remain stable.
[0051] In a specific embodiment, the RC filter module 100 includes a first resistor R1, a second resistor R2, and a high-frequency on-state capacitor C2. One end of the first resistor R1 and one end of the second resistor R2 are both connected to a common connection point F. The other end of the first resistor R1 is connected to the signal input terminal Vin, and the other end of the second resistor R2 is connected to the voltage follower module 200. The high-frequency on-state capacitor C2 is connected between the other end of the second resistor R2 and ground, so that the signal to be filtered whose frequency exceeds the maximum value of the cutoff range is transmitted to ground via the high-frequency on-state capacitor C2.
[0052] Therefore, when the frequency of the received signal to be filtered is higher than the maximum value of the cutoff range of the active filter, the high-frequency conducting capacitor C2 effectively short-circuits the voltage follower module 200, allowing the signal to be filtered to be directly conducted to ground through the high-frequency conducting capacitor C2. Consequently, there is no signal input at the signal input terminal of the voltage follower module 200, and therefore no voltage output at the filter output terminal C. Thus, when the frequency of the signal to be filtered is higher than the maximum value of the cutoff range of the active filter, the high-frequency conducting capacitor C2 completely suppresses the signal to be filtered by providing a short-circuit path to ground.
[0053] In a specific embodiment, the voltage follower module 200 includes a first current source I1 and a first transistor M1. The first current source I1 is connected between the first terminal of the first transistor M1 and the power supply terminal to provide a stable current to the first transistor M1. The second terminal of the first transistor M1 is grounded, and the control terminal of the first transistor M1 is connected to the other end of the second resistor R2 through the passive filter output terminal A to receive the passive filter signal. The first terminal of the first transistor M1 is connected to the output terminal B of the voltage follower module 200 so that the passive filter signal controls the impedance of the first transistor M1, thereby causing a change in the voltage output at the output terminal B of the voltage follower module 200.
[0054] When the frequency of the signal to be filtered received at the signal input terminal Vin is within the passband range of the active filter, the voltage at the passive filter output terminal A increases, causing the impedance of the first transistor M1 to increase. Since the first current source I1 keeps the current flowing through the first transistor M1 constant, the increase in voltage at the passive filter output terminal A will cause the voltage at the output terminal B of the voltage follower module 200 to increase, thereby obtaining a voltage follower signal.
[0055] In a specific embodiment, the flip voltage follower module 300 includes a seventh transistor M7, an eleventh transistor M11, and a twelfth transistor M12. The first terminal of the seventh transistor M7 is connected to the power supply terminal, and the second terminal of the seventh transistor M7 is connected to the first terminal of the eleventh transistor M11 through the high potential terminal D. The second terminal of the eleventh transistor M11 and the first terminal of the twelfth transistor M12 are both connected to the filter output terminal C, and the second terminal of the twelfth transistor M12 is grounded.
[0056] The control electrode of the eleventh transistor M11 is connected to the output terminal B of the voltage follower module 200; so that the change in the voltage follower signal causes a change in the impedance of the eleventh transistor M11, which in turn causes a change in the voltage at the high potential terminal D, which in turn causes a change in the voltage at the control electrode of the twelfth transistor M12, which in turn causes a change in the impedance of the twelfth transistor M12, which in turn causes a change in the voltage at the filter output terminal C.
[0057] In a specific embodiment, the bias module 400 includes a first bias branch 410 and a second bias branch 420. The first bias branch 410 includes an eighth transistor M8, a ninth transistor M9 and a fourth transistor M4; the second bias branch 420 includes a tenth transistor M10 and a fifth transistor M5.
[0058] In this embodiment, the eighth transistor M8 and the seventh transistor M7 are connected to form a first current mirror, the ninth transistor M9 and the tenth transistor M10 are connected to form a second current mirror, and the second electrode of the ninth transistor M9 is shorted to its control electrode; the fourth transistor M4 and the fifth transistor M5 are connected to form a third current mirror.
[0059] The common connection point E between the tenth transistor M10 and the fifth transistor M5 is connected to the control electrode of the twelfth transistor M12.
[0060] In this embodiment, the reference current module 500 includes a current source submodule 510 and a mirror submodule 520. The current source submodule 510 provides a stable reference current, the mirror submodule 520 mirrors the reference current to obtain the converted current, and the seventh transistor M7 mirrors the converted current to obtain the output current. This ensures that the output current remains constant and is not affected by the voltage at the output terminal B of the voltage follower module 200 or the load of the external circuit connected to the filter output terminal C. Consequently, it ensures that the voltage at the filter output terminal C is only related to the voltage follower signal, thus minimizing or eliminating attenuation of the signal to be filtered within the passband.
[0061] In a specific embodiment, the current source submodule 510 includes a second current source I2 and a second transistor M2. The second current source I2 provides a stable reference current to the second transistor M2. The second transistor M2 forms current mirrors with the fourth transistor M4 and the fifth transistor M5, respectively, to keep the first bias current of the first bias branch 410 and the second bias current of the second bias branch 420 stable. Furthermore, the first terminal of the second transistor M2 is short-circuited to its control terminal.
[0062] In a specific embodiment, the mirror submodule 520 includes a third transistor M3 and a sixth transistor M6. The third transistor M3 and the second transistor M2 form a current mirror, and the sixth transistor M6 and the seventh transistor M7 form a current mirror. Furthermore, the first terminal of the third transistor M3 is shorted to its control terminal.
[0063] Therefore, the second current source I2 keeps the current flowing through the second transistor M2 constant, while the third transistor M3, the fourth transistor M4, and the fifth transistor M5 form current mirrors with the second transistor M2 respectively. Thus, by controlling the width-to-length ratio of the third transistor M3, the fourth transistor M4, and the fifth transistor M5 with the second transistor M2, the magnitude of the current flowing through them can be precisely controlled, which in turn allows for precise control of the magnitude and stability of the switching current, the first bias current, and the second bias current.
[0064] Furthermore, since the sixth transistor M6 and the seventh transistor M7 form a current mirror, the stability of the conversion current is ensured, which in turn ensures the stability of the current flowing through the seventh transistor M7. This keeps the output current constant, so that the voltage at the filter output terminal C is only related to the impedance of the twelfth transistor M12.
[0065] In a specific embodiment, since the first bias current is a constant current, and the tenth transistor M10 and the ninth transistor form a current mirror, and the second terminal of the ninth transistor M9 is short-circuited to its control terminal, this ensures that the control terminal voltage of the tenth transistor M10 remains constant. That is, the impedance of the tenth transistor M10 and the second bias current flowing through it remain constant, thereby keeping the voltage drop across the tenth transistor M10 constant. In other words, the arrangement of the tenth transistor M10 ensures that the voltage at the control terminal of the twelfth transistor M12 rises and falls with the voltage at the high-potential terminal D, and the voltage at the high-potential terminal D rises and falls with the voltage follower signal. This ensures that the voltage at the filter output terminal C rises and falls with the voltage follower signal.
[0066] In this embodiment, the resistance values of resistors R1 and R2 can be adjusted according to actual needs. For ease of expression, the resistance values of resistors R1 and R2 are set to be equal, and the transfer function of the active filter can be obtained as follows:
[0067]
[0068] Where h(s) is the operating frequency of the active filter, Zo is the impedance of the flip-flop voltage follower module 300, C1 is the capacitance of the first capacitor C1, C2 is the capacitance of the second capacitor C2, R is the resistance of resistors R1 and R2, and S is the parameter after Laplace transform.
[0069] Compared to existing voltage followers, the output impedance of the flip voltage follower disclosed in this embodiment is greatly reduced, thereby enabling the active filter disclosed in this embodiment to operate in the VHF band or even higher operating frequencies.
[0070] In summary, in the active filter disclosed in this embodiment, the input signal is passively filtered by the RC filter module 100 to obtain a passive filtered signal. The voltage follower module 200 enables the voltage follower signal to rise and fall with the rise and fall of the passive filtered signal. Since a flip voltage follower module 300 is set after the voltage follower module 200, the output impedance of the active filter is effectively reduced. Since the operating frequency of the active filter is inversely proportional to the output impedance, the operating frequency of the active filter is greatly increased. Thus, the active filter can be applied to high-frequency scenarios.
[0071] Furthermore, by sequentially setting a voltage follower module 200 and a flip-type voltage follower module 300 after the RC filter module 100, the voltage at the filter output of the flip-type voltage follower module 300 rises and falls with the rise and fall of the voltage follower signal. When the frequency of the signal to be filtered falls within the passband range of the active filter, the positive feedback module is disconnected, and the active filter signal equals the signal to be filtered. When the frequency of the signal to be filtered falls within the preset cutoff range, the positive feedback module feeds the active filter signal back to the RC filter module 100 to provide a positive gain for the active filter signal, forming a Butterworth characteristic, that is, the active filter can have a good out-of-band suppression effect in high-frequency environments. When the frequency of the signal to be filtered exceeds the maximum value of the cutoff range, the RC filter module 100 completely suppresses the signal to be filtered, and at this time, there is no signal output at the active filter output. Thus, the characteristic curve of the active filter is a Butterworth curve, that is, the active filter can allow signals within the passband to pass through without obstruction in high-frequency environments, while out-of-band signals can be efficiently suppressed, thus ensuring the filtering effect of the active filter in high-frequency environments.
[0072] This embodiment also discloses a filtering system, including an active filter, a signal input module, and a load module as disclosed in the above embodiments. The signal input module inputs the signal to be filtered to the active filter so that the active filter filters the signal to be filtered to obtain an active filtered signal. The load module receives the active filtered signal.
[0073] This embodiment also discloses a chip for signal processing, including an active filter as disclosed in the above embodiments.
[0074] This embodiment also discloses an electronic device with signal processing function, including an active filter as disclosed in the above embodiments.
[0075] In a specific embodiment, the electronic device can be an electronic device with wireless communication function. Before transmitting the wireless signal, the electronic device filters the signal to be transmitted through the active filter disclosed in this embodiment, so that the wireless communication signal emitted by the electronic device can comply with the provisions of communication protocols such as the FCC protocol, and minimizes the impact on wireless signals of other frequency bands.
[0076] Those skilled in the art will understand that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.
[0077] It should be understood that the above embodiments are merely exemplary and not restrictive. Various obvious or equivalent modifications or substitutions that can be made by those skilled in the art regarding the above details without departing from the basic principles of the present invention will be included within the scope of the claims of the present invention.
Claims
1. An active filter, comprising a passive filter network and an active filter network, wherein a signal to be filtered is filtered by the passive filter network and then output to the active filter network for active filtering, characterized in that, The passive filter network includes an RC filter module (100); the active filter network includes a voltage follower module (200), a flip-flop voltage follower module (300), and a positive feedback module (600), wherein: The input terminal of the RC filter module (100) is the signal input terminal (Vin) of the active filter, which is used to receive the signal to be filtered by the active filter, so as to perform passive filtering on the signal to be filtered to obtain a passive filtered signal. The voltage output from the output terminal (B) of the voltage follower module (200) rises and falls in accordance with the rise and fall of the passive filter signal to obtain a voltage follower signal; The flip voltage follower module (300) receives the voltage follower signal so that the voltage output by the filter output terminal (C) of the flip voltage follower module (300) rises and falls with the rise and fall of the voltage follower signal to obtain an active filter signal; the filter output terminal (C) is the output terminal of the active filter; The positive feedback module (600) is connected between the filter output terminal (C) and the RC filter module (100). When the frequency of the signal to be filtered falls within a preset cutoff range, the positive feedback module (600) is used to feed the active filter signal back to the RC filter module (100) to provide positive gain for the active filter signal, thereby weakening the active filter signal.
2. The active filter as described in claim 1, characterized in that, The RC filter module (100) includes a first resistor (R1), a second resistor (R2), and a high-frequency conducting capacitor (C2); One end of the first resistor (R1) and one end of the second resistor (R2) are both connected to a common connection point (F). The other end of the first resistor (R1) is connected to the signal input terminal (Vin), and the other end of the second resistor (R2) is connected to the voltage follower module (200). The high-frequency on-state capacitor (C2) is connected between the other end of the second resistor (R2) and ground, so that the signal to be filtered with a frequency exceeding the maximum value of the cutoff range is transmitted to ground via the high-frequency on-state capacitor (C2).
3. The active filter as described in claim 2, characterized in that, The voltage follower module (200) includes a first current source (I1) and a first transistor (M1). The first current source (I1) is connected between the first electrode of the first transistor (M1) and the power supply terminal to provide a stable current to the first transistor (M1). The second terminal of the first transistor (M1) is grounded, and the control terminal of the first transistor (M1) is connected to the other end of the second resistor (R2) to receive the passive filter signal; the first terminal of the first transistor (M1) is connected to the output terminal (B) of the voltage follower module (200) so that the passive filter signal controls the impedance of the first transistor (M1) so that the voltage output of the output terminal (B) of the voltage follower module (200) changes.
4. The active filter as described in claim 3, characterized in that, The flip voltage follower module (300) includes a seventh transistor (M7), an eleventh transistor (M11), and a twelfth transistor (M12). The first terminal of the seventh transistor (M7) is connected to the power supply terminal, and the second terminal of the seventh transistor (M7) is connected to the first terminal of the eleventh transistor (M11) through a high potential terminal (D). The second terminal of the eleventh transistor (M11) and the first terminal of the twelfth transistor (M12) are both connected to the filter output terminal (C). The second terminal of the twelfth transistor (M12) is grounded. The control electrode of the eleventh transistor (M11) is connected to the output terminal (B) of the voltage follower module (200) so that the change of the voltage follower signal causes the impedance change of the eleventh transistor (M11) to cause the voltage change of the high potential terminal (D) to cause the voltage change of the control electrode of the twelfth transistor (M12) to cause the impedance change of the twelfth transistor (M12) to cause the voltage change of the filter output terminal (C).
5. The active filter as described in claim 4, characterized in that, Also includes: A bias module (400) is used to provide a bias voltage to the flip voltage follower module (300). The magnitude of the bias voltage is negatively correlated with the voltage follower signal. The voltage of the filter output terminal (C) is negatively correlated with the bias voltage, so that the voltage of the filter output terminal (C) rises and falls with the rise and fall of the voltage follower signal.
6. The active filter as described in claim 5, characterized in that, The bias module (400) includes a first bias branch (410) and a second bias branch (420). The first bias branch (410) includes an eighth transistor (M8), a ninth transistor (M9), and a fourth transistor (M4). The second bias branch (420) includes a tenth transistor (M10) and a fifth transistor (M5). The eighth transistor (M8) and the seventh transistor (M7) are connected to form a first current mirror, the ninth transistor (M9) and the tenth transistor (M10) are connected to form a second current mirror, and the fourth transistor (M4) and the fifth transistor (M5) are connected to form a third current mirror. The common connection point (E) between the tenth transistor (M10) and the fifth transistor (M5) is connected to the control electrode of the twelfth transistor (M12).
7. The active filter as described in claim 6, characterized in that, Also includes: A reference current module (500) is used to provide a stable current to the flip voltage follower module (300) and the bias module (400) so that the output current flowing through the flip voltage follower module (300) and the bias current flowing through the bias module (400) remain stable.
8. The active filter as described in claim 7, characterized in that, The reference current module (500) includes a current source submodule (510) and a mirror submodule (520). The current source submodule (510) is used to provide a stable reference current. The mirror submodule (520) mirrors the reference current to obtain a converted current. The seventh transistor (M7) mirrors the converted current to obtain the output current.
9. The active filter as described in claim 8, characterized in that, The current source submodule (510) includes a second current source (I2) and a second transistor (M2). The second current source (I2) is used to provide a stable reference current for the second transistor (M2). The second transistor (M2) forms a current mirror with the fourth transistor (M4) and the fifth transistor (M5) respectively, so that the first bias current of the first bias branch (410) and the second bias current of the second bias branch (420) remain stable.
10. The active filter as described in claim 9, characterized in that, The mirror submodule (520) includes a third transistor (M3) and a sixth transistor (M6). The third transistor (M3) and the second transistor (M2) form a current mirror, and the sixth transistor (M6) and the seventh transistor (M7) form a current mirror.
11. A filtering system, characterized in that, The system includes an active filter, a signal input module, and a load module as described in any one of claims 1-10. The signal input module inputs a signal to be filtered to the active filter, so that the active filter filters the signal to be filtered to obtain an active filtered signal. The load module receives the active filtered signal.
12. A chip for signal processing, characterized in that, Including the active filter as described in any one of claims 1-10.
13. An electronic device with signal processing function, characterized in that, The electronic device includes an active filter as claimed in any one of claims 1-10.