An active filter
By designing an active filter with a dual-ring hierarchical gain structure and combining it with a common-mode passive filter circuit, the contradiction between filtering effect and cost in traditional active filters is resolved, achieving better filtering effect and lower implementation cost, thus promoting the application of high-performance active filters.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- MORNSUN GUANGZHOU SCI & TECH
- Filing Date
- 2026-04-21
- Publication Date
- 2026-07-31
AI Technical Summary
Existing active filters struggle to balance filtering performance with implementation cost. Traditional topologies are limited by the upper limit of insertion loss and rely on high-performance operational amplifiers, resulting in high costs and hindering widespread application.
An active filter design employing a dual-loop hierarchical gain structure includes a common-mode noise detection circuit, a feedforward filter circuit, and a feedback filter circuit, forming a stable dual-loop filter structure. By utilizing a low-voltage, narrow-bandwidth operational amplifier and combining it with a common-mode passive filter circuit, the filtering effect is further improved and the cost is reduced.
It significantly improves the common-mode noise filtering effect, reduces the bandwidth requirement of the operational amplifier, enables the use of low-cost general-purpose operational amplifiers, reduces the overall implementation cost, and promotes the independent research and development and popularization of high-performance active filters.
Smart Images
Figure CN122496010A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of electronic circuit technology, and more specifically, relates to an active filter. Background Technology
[0002] Active power filters are an effective means of improving electromagnetic compatibility in the field of power electronics. Traditional active power filters mostly adopt a single-loop feedback structure design. This topology has the advantage of structural simplicity at the theoretical level, but in practical engineering applications, it suffers from the dual drawbacks of poor filtering performance and high device cost. In terms of filtering performance, single-loop feedback active power filters have a clear upper limit on insertion loss. Their filtering performance is constrained by multiple factors such as topology, passive filter device parameters, and operational amplifier performance, resulting in actual filtering performance far below design expectations. In terms of implementation cost, existing structures place stringent requirements on the performance of the core component, the operational amplifier. To ensure stable gain and linearity of the filter at higher frequencies, a wide-voltage, high-speed operational amplifier must be used. However, such high-end operational amplifier chips are expensive due to market conditions. For example, Analog Devices' AD828ARZ wide-voltage, high-speed operational amplifier costs as much as 63 yuan per piece, far exceeding that of general-purpose operational amplifiers (less than 3 yuan per piece). Therefore, the overall implementation cost of single-loop feedback active power filters using high-end operational amplifiers remains high, severely restricting the independent research and development and widespread application of high-performance active power filters.
[0003] To address the aforementioned issues, existing technologies propose two improvement schemes: one is a dual-loop active filter based on a dual-sampling, single-injection structure. This scheme can improve the overall insertion loss to some extent by optimizing the gain of the second sampling circuit and subsequent amplification circuit. However, it essentially only has one injection circuit, and its theoretical maximum insertion loss is still limited by the upper limit of the single-loop structure. Furthermore, it still requires the use of wide-voltage high-speed operational amplifiers, making it cost-inefficient. The other is an active filter based on a single-sampling, dual-injection structure. This scheme simplifies the structure and reduces some costs by using a shared current transformer between the two loops, achieving higher insertion loss. However, because the two loops do not form an effective dual-loop hierarchical gain structure, it still relies on wide-voltage high-speed operational amplifiers for implementation, failing to reduce the overall implementation cost of the active filter.
[0004] In summary, existing active filter topologies cannot simultaneously solve the technical challenges of insufficient filtering performance and excessively high implementation costs. There is an urgent need for a new type of active filter topology that can effectively improve filtering performance while reducing dependence on operational amplifier performance, lowering device costs, and promoting the research, development, production, and application of high-performance active filters. Summary of the Invention
[0005] To address the issue that existing high-performance active filter topologies cannot simultaneously balance filtering performance and implementation cost, this application provides an active filter.
[0006] In one embodiment, an active filter is provided, placed between an external power supply and an electronic device, for filtering out common-mode noise signals generated by the electronic device. The filter includes a common-mode noise detection circuit for detecting common-mode noise of the electronic device, a feedforward filter circuit for performing feedforward filtering of the common-mode noise, and a feedback filter circuit for performing feedback filtering of the common-mode noise.
[0007] The common-mode noise detection circuit is connected to the external power supply input line, the electronic device input line, and the feedforward filter circuit, with one end grounded. It is used to detect the common-mode noise emitted by the electronic device. The feedforward filter circuit is connected to the external power supply input line, the common-mode noise detection circuit, and the feedback filter circuit, with one end grounded. It is used to perform feedforward filtering on the common-mode noise and provide an input signal to the feedback filter circuit. The feedback filter circuit is connected to the electronic device input line and the feedforward filter circuit, with one end grounded. It is used to perform feedback filtering on the common-mode noise.
[0008] The common-mode noise detection circuit is not connected to the feedback filter circuit. The common-mode noise detection circuit provides the common-mode noise signal input to the feedforward filter circuit. The feedforward filter circuit amplifies the common-mode noise signal in a wide frequency band. The input signal of the feedback filter circuit is the common-mode noise signal amplified by the feedforward filter circuit, thus forming a dual-loop hierarchical gain structure. While improving the filtering effect, it can be implemented using a low-voltage, narrow-bandwidth, low-cost general-purpose operational amplifier.
[0009] Furthermore, the common-mode noise detection circuit includes a current transformer and a current-to-voltage conversion circuit.
[0010] The primary side of the current transformer is connected to the input lines of the external power supply and the electronic equipment, respectively; the secondary side of the current transformer is connected to the current-to-voltage conversion circuit; one end of the current-to-voltage conversion circuit is connected to the secondary side of the current transformer, and the other end is grounded; the signal output port of the current-to-voltage conversion circuit is connected to the feedforward filter circuit.
[0011] Furthermore, the feedforward filter circuit includes a first input impedance network, a first feedback impedance network, a first injection circuit, a first operational amplifier, and a first external power supply circuit.
[0012] In this circuit, one end of the first input impedance network is connected to the signal output port of the current-to-voltage conversion circuit, and the other end is connected to the first feedback impedance network and the first operational amplifier; one end of the first feedback impedance network is connected to the first input impedance network, and the other end is connected to the first injection circuit and the first operational amplifier; one end of the first injection circuit is connected to the first feedback impedance network and the first operational amplifier, one end is connected to the input line of the external power supply, and the other end is connected to the feedback filter circuit; the non-inverting input of the first operational amplifier is grounded, the inverting input is connected to the first input impedance network and the first feedback impedance network, the output is connected to the first feedback impedance network and the first injection circuit, and the power supply is connected to the first external power supply circuit.
[0013] Furthermore, the feedback filter circuit includes a second input impedance network, a second feedback impedance network, a second injection circuit, a second operational amplifier, and a second external power supply circuit.
[0014] In this circuit, one end of the second input impedance network is grounded, and the other end is connected to the second feedback impedance network and the second operational amplifier; one end of the second feedback impedance network is connected to the second input impedance network, and the other end is connected to the second injection circuit and the second operational amplifier; one end of the second injection circuit is connected to the second feedback impedance network and the second operational amplifier, and the other end is connected to the input line of the electronic device; the non-inverting input of the second operational amplifier is connected to the first injection circuit, the inverting input is connected to the second input impedance network and the second feedback impedance network, the output is connected to the second feedback impedance network and the second injection circuit, and the power supply is connected to the second external power supply circuit.
[0015] In one scheme, the active filter also includes a common-mode passive filter circuit; the common-mode passive filter circuit attenuates noise signals at the external power supply and / or electronic device terminals based on the impedance mismatch principle, further improving the overall insertion loss of the filter and achieving better filtering performance.
[0016] Furthermore, the common-mode passive filter circuit includes an external power supply passive filter; one end of the external power supply passive filter is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit.
[0017] The common-mode passive filter circuit may include a passive filter at the electronic device end; one end of the passive filter at the electronic device end is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit. Alternatively, the common-mode passive filter circuit includes an external power supply passive filter and an electronic device passive filter. One end of the external power supply passive filter is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit; one end of the electronic device passive filter is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit.
[0018] Furthermore, the passive filter at the external power supply end and / or the passive filter at the electronic device end consists only of an inductor; or the passive filter at the external power supply end and / or the passive filter at the electronic device end consists of an inductor and a capacitor, with the capacitor placed between the external power supply / electronic device and the inductor, one end of the capacitor connected to the input line of the external power supply end or the input line of the electronic device end, and the other end of the capacitor grounded.
[0019] The beneficial effects of this application are: The active filter disclosed in this application, through a unique structural design that rationally sets up a common-mode noise detection circuit, a feedforward filter circuit, and a feedback filter circuit—specifically, the common-mode noise detection circuit is not connected to the feedback filter circuit, and the input signal of the feedback filter circuit is the output signal of the feedforward filter circuit—forms a stable dual-loop hierarchical gain structure. This effectively breaks through the insertion loss limit of traditional single-loop and existing dual-loop active filters, significantly improving the common-mode noise filtering effect and solving the technical defect that the actual filtering effect of existing active filters is far lower than the design expectation. Simultaneously, since the input signal of the feedback filter circuit has been amplified by the feedforward filter circuit, the remaining gain requirement will be significantly less than that of traditional feedback active filters. Therefore, the bandwidth requirement of the operational amplifier will also be less than that of traditional solutions—that is, there is no need to use high-cost wide-voltage high-speed operational amplifiers; low-cost general-purpose operational amplifiers can be directly selected. This significantly reduces the overall implementation cost of the active filter, effectively solving the technical problem of balancing filtering effect and implementation cost in existing technologies. This promotes the independent research and development and widespread application of high-performance active filters, possessing good engineering application value and promotion prospects. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of the structure of an active filter in one embodiment of this application; Figure 2 This is a topology block diagram of an active filter in one embodiment of this application; Figure 3 This is a circuit diagram of an active filter in one embodiment of this application; Figure 4 This is a circuit diagram of an active filter in one embodiment of this application; Figure 5 This is a circuit diagram of an active filter in one embodiment of this application; Figure 6 This is a circuit diagram of an active filter in one embodiment of this application; Figure 7 This is a comparison diagram of the actual filtering effects of an active filter and a traditional single-loop feedback active filter in one embodiment of this application; Figure 8 This is a load impedance curve of an active filter in one embodiment of this application. Detailed Implementation
[0022] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application. Similarly, the following examples are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0023] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0024] In this application, the terms "one embodiment," "some embodiments," "an embodiment," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0025] To address the issue that existing high-performance active filter topologies cannot simultaneously achieve both filtering performance and implementation cost, this application provides an active filter, with specific embodiments as follows: In one embodiment, please refer to Figure 1 An active filter is provided, placed between an external power supply and an electronic device, for filtering out common-mode noise signals generated by the electronic device, including a common-mode noise detection circuit, a feedforward filter circuit, and a feedback filter circuit.
[0026] In this embodiment, the common-mode noise detection circuit is used to detect the common-mode noise emitted by the electronic device. It is connected to the external power supply input line, the electronic device input line, and the feedforward filter circuit, and is grounded at one end. The feedforward filter circuit is used to perform feedforward filtering on the common-mode noise and provide an input signal to the feedback filter circuit. It is connected to the external power supply input line, the common-mode noise detection circuit, and the feedback filter circuit, and is grounded at one end. The feedback filter circuit is used to perform feedback filtering on the common-mode noise. It is connected to the electronic device input line and the feedforward filter circuit, and is grounded at one end.
[0027] The common-mode noise detection circuit is not connected to the feedback filter circuit. The common-mode noise detection circuit provides the common-mode noise signal input to the feedforward filter circuit. The feedforward filter circuit amplifies the common-mode noise signal in a wide frequency band. The input signal of the feedback filter circuit is the common-mode noise signal amplified by the feedforward filter circuit, thus forming a dual-loop hierarchical gain structure. While improving the filtering effect, it can be implemented using a low-voltage, narrow-bandwidth, low-cost general-purpose operational amplifier.
[0028] Specifically, when the active filter of this application is working, the common-mode noise detection circuit collects the original noise current signal from the input lines of the external power supply and the electronic device. Simultaneously, the low-frequency portion of the original noise current signal is attenuated by the common-mode noise detection circuit, and after attenuation, the noise current signal is converted into a voltage signal. This signal serves as the output signal of the common-mode noise detection circuit and enters the feedforward filter circuit. The feedforward filter circuit is set to unity current gain over a wide frequency range and converts the output signal into a current signal, which is injected into the input line of the external power supply before the sampling point, thus achieving feedforward filtering. The output signal, amplified by the feedforward filter circuit, also serves as the input signal of the feedback filter circuit. After being amplified again over a wide frequency range by the feedback filter circuit, the output signal is converted into a current signal and injected into the input line of the electronic device after the sampling point, thus achieving feedback filtering.
[0029] Furthermore, since the input signal of the feedback filter circuit is the noise signal amplified by the feedforward filter circuit, rather than the original noise signal, its input signal amplitude has been amplified over a wide frequency range. Therefore, the amplification factor requirement in the feedback filter circuit is reduced. That is, under the condition of achieving the same current gain, compared with the requirement of a wide-voltage high-speed operational amplifier for a traditional feedback active filter, the bandwidth requirement of the active filter in this application is significantly reduced, and a general-purpose operational amplifier can be directly used to implement it.
[0030] In one embodiment, please refer to Figure 2Based on the aforementioned embodiments, the common-mode noise detection circuit includes a current transformer and a current-to-voltage conversion circuit. The primary winding of the current transformer is connected to both the external power supply input line and the electronic device input line; the secondary winding of the current transformer is connected to the current-to-voltage conversion circuit; one end of the current-to-voltage conversion circuit is connected to the secondary winding of the current transformer, and the other end is grounded; the signal output port of the current-to-voltage conversion circuit is connected to the feedforward filter circuit.
[0031] Furthermore, the feedforward filter circuit includes a first input impedance network, a first feedback impedance network, a first injection circuit, a first operational amplifier, and a first external power supply circuit. One end of the first input impedance network is connected to the signal output port of the current-to-voltage conversion circuit, and the other end is connected to the first feedback impedance network and the first operational amplifier. One end of the first feedback impedance network is connected to the first input impedance network, and the other end is connected to the first injection circuit and the first operational amplifier. One end of the first injection circuit is connected to the first feedback impedance network and the first operational amplifier, one end is connected to the input line of the external power supply, and the other end is connected to the feedback filter circuit. The non-inverting input of the first operational amplifier is grounded, the inverting input is connected to the first input impedance network and the first feedback impedance network, the output is connected to the first feedback impedance network and the first injection circuit, and the power supply is connected to the first external power supply circuit.
[0032] Furthermore, the feedback filter circuit includes a second input impedance network, a second feedback impedance network, a second injection circuit, a second operational amplifier, and a second external power supply circuit. One end of the second input impedance network is grounded, and the other end is connected to the second feedback impedance network and the second operational amplifier. One end of the second feedback impedance network is connected to the second input impedance network, and the other end is connected to the second injection circuit and the second operational amplifier. One end of the second injection circuit is connected to the second feedback impedance network and the second operational amplifier, and the other end is connected to the input line of the electronic device. The non-inverting input of the second operational amplifier is connected to the first injection circuit, the inverting input is connected to the second input impedance network and the second feedback impedance network, the output is connected to the second feedback impedance network and the second injection circuit, and the power supply is connected to the second external power supply circuit.
[0033] Specifically, the active filter operates as follows: the common-mode noise detection circuit acquires the original noise current signal from the input lines of the external power supply and the electronic device. This noise signal can be expressed in the frequency domain as a function of frequency. Meanwhile, the original noise current signal The low-frequency portion is attenuated by the common-mode noise detection circuit, and after attenuation, the noise current signal is converted into a voltage signal. Its current-voltage gain is expressed as a function of frequency. The final sampled voltage signal is represented as This signal will be used as the output signal of the common-mode noise detection circuit and will then enter the feedforward filter circuit.
[0034] The gain of the feedforward filter circuit is a function of frequency, and its gain is determined by the first input impedance network and the first feedback impedance network, expressed as follows: Therefore, the output signal of the feedforward filter circuit is expressed as The output signal of the feedforward filter circuit Feedforward filtering is achieved by converting the signal back into a current signal through the first injection circuit and injecting it into the input line of the external power supply before the sampling point.
[0035] Furthermore, the output signal of the feedforward filter circuit Due to its excellent flatness, it also participates in the gain process of the feedback filter circuit as the input signal. Therefore, the output signal of the feedback filter circuit can be described as... The output signal of the feedback filter circuit The signal is converted back into a current signal by a second injection circuit and injected into the input line of the electronic device after the sampling point, thereby achieving feedback filtering.
[0036] Ultimately, the overall insertion loss of this dual-loop active filter is... 、 、 、 、 、 、 、 The function is described as follows:
[0037] For example, based on the above embodiments, please refer to Figure 3 The common-mode noise detection circuit can be composed of a current transformer TX2 and a current-to-voltage conversion circuit R4. The primary side of the current transformer TX2 is connected to the input line of the external power supply and the input line of the electronic equipment, and the secondary side is connected to the current-to-voltage conversion circuit R4. One end of the current-to-voltage conversion circuit R4 is connected to the secondary side of the current transformer TX2, and the other end is grounded. It also has a signal output port connected to the input port of the feedforward filter circuit.
[0038] Specifically, the first input impedance network of the feedforward filter circuit includes resistor R6; the first feedback impedance network is formed by connecting resistor R19 and capacitor C22 in series, and then connecting them in parallel with resistor R11; the first injection circuit is formed by connecting capacitor C9 and capacitor C11 in parallel. One end of the first input impedance network is connected to the signal output port of the current-to-voltage conversion circuit, and the other end is connected to the first feedback impedance network and the first operational amplifier X3; one end of the first feedback impedance network is connected to the first input impedance network, and the other end is connected to the first injection circuit and the first operational amplifier X3; one end of the first injection circuit is connected to the first feedback impedance network and the first operational amplifier X3, one end is connected to the input line of the external power supply, and the other end is connected to the second operational amplifier; one input terminal of the first operational amplifier X3 is grounded, one input terminal is connected to the first input impedance network and the feedback impedance network, and the output terminal is connected to the first feedback impedance network and the first injection circuit.
[0039] In this embodiment, the gain objective of the feedforward filter circuit is to achieve unity current gain over a wide frequency range to meet the maximum insertion loss condition. Its insertion loss can be described as follows:
[0040] Will Change to the current gain in the actual design Described as:
[0041] Therefore, the maximum insertion loss condition of the feedforward filter circuit is: This means that the voltage gain of the feedforward filter circuit is relatively low, typically less than 20dB, and its operational amplifier has a smaller gain factor and a flatter gain curve. Since in an active filter, the actual effective bandwidth of the operational amplifier is equal to its -3dB bandwidth divided by the gain factor, i.e. Therefore, in the feedforward filter circuit Because of its relatively wide amplitude, the feedforward filter circuit does not require a high-speed operational amplifier, and because of its small amplification factor and small output signal swing, it can be implemented without a wide-voltage operational amplifier.
[0042] For example, please refer to Figure 3The second input impedance network of the feedback filter circuit includes resistor R9; the second feedback impedance network is formed by connecting resistor R26 and capacitor C23 in series, and then connecting them in parallel with resistor R8; the second injection circuit is formed by connecting capacitor C5 and capacitor C4 in parallel. One end of the second input impedance network is grounded, and the other end is connected to the second feedback impedance network and the second operational amplifier X4; one end of the second feedback impedance network is connected to the second input impedance network, and the other end is connected to the second injection circuit and the second operational amplifier X4; one end of the second injection circuit is connected to the second feedback impedance network and the second operational amplifier X4, and the other end is connected to the input line of the electronic device.
[0043] In this embodiment, the gain objective of the feedback filter circuit is to achieve high current gain over a wide frequency range in order to achieve the maximum insertion loss condition. Its insertion loss can be described as follows:
[0044] Will Change to the current gain in the actual design Described as:
[0045] Therefore, the maximum insertion loss condition of the feedback filter circuit is: This means that the feedback filter circuit needs high voltage gain to achieve high current gain over a wide frequency range. For traditional feedback active filters, this means a need for high-speed operational amplifiers with higher voltage and wider effective bandwidth to handle higher op-amp gain and higher output voltage swing.
[0046] The active filter in this application, because its input signal is the output signal of the feedforward amplifier circuit rather than the original noise current signal, has its input signal amplitude amplified once over a wide frequency range. Therefore, the amplification factor requirement at this stage is smaller, approximately 1 / 10 to 1 / 5 of that of a traditional feedback active filter. Furthermore, in an active filter, the actual effective bandwidth of the op-amp is equal to its -3dB bandwidth divided by the amplification factor, i.e. To achieve the same current gain, active filters only require 1 / 10 to 1 / 5 of the bandwidth of the operational amplifier in traditional feedback active filters. This directly eliminates the need for wide-voltage, high-speed operational amplification in traditional feedback active filters, allowing the use of general-purpose operational amplifiers. This significantly reduces costs, meets the requirements for domestic device substitution, and overcomes the cost constraints imposed by the long-standing reliance on foreign companies for high-end operational amplifier chips.
[0047] Furthermore, such as Figure 7The diagram shows a comparison of the actual filtering performance of the active filter of this application and a traditional single-loop feedback active filter. Notably, across a wide frequency range, the insertion loss of the active filter of this application is greater than that of the traditional single-loop feedback active filter. Furthermore, as... Figure 7 The active filter shown is implemented using a domestically produced general-purpose operational amplifier, while the traditional single-loop feedback active filter is implemented using a foreign wide-voltage, ultra-high-speed operational amplifier. A comparison of key parameters such as -3dB bandwidth, sampling rate, power supply range, and cost between the two types of operational amplifiers is as follows: Domestic general-purpose operational amplifier: gain-bandwidth product ; slew rate Power supply voltage Cost per IC ; Foreign wide-voltage ultra-high-speed operational amplifiers: gain-bandwidth product ; slew rate Power supply voltage Cost per IC .
[0048] Therefore, the active filter of this application achieves better filtering effect with lower device cost.
[0049] In one embodiment, based on the active filter of the aforementioned embodiments, the external power supply can be a single-phase power supply, and the primary side of the current transformer includes a first primary winding and a second primary winding. The input line of the external power supply terminal and the input line of the electronic device terminal each include a phase line and a neutral line. The first primary winding is connected in series on the phase / neutral line of the input line of the external power supply terminal and the input line of the electronic device terminal; the second primary winding is connected in series on the neutral / phase line of the input line of the external power supply terminal and the input line of the electronic device terminal.
[0050] In one embodiment, based on the active filter of the aforementioned embodiment, the external power supply can be a three-phase three-wire power supply, and the primary side of the current transformer includes a first primary winding, a second primary winding, and a third primary winding. The input lines of the external power supply and the electronic equipment each include three phase lines. The first, second, and third primary windings are connected in series on the three phase lines of the external power supply and electronic equipment input lines, respectively.
[0051] In one embodiment, based on the active filter of the aforementioned embodiment, the external power supply can be a three-phase four-wire power supply, and the primary side of the current transformer includes a first primary winding, a second primary winding, a third primary winding, and a fourth primary winding. The input lines of the external power supply and the electronic equipment each include three phase lines and one neutral line. The first, second, third, and fourth primary windings are connected in series on the three phase lines and one neutral line of the external power supply and electronic equipment input lines, respectively.
[0052] In one embodiment, based on the active filter of the aforementioned embodiment, the external power supply can be a three-phase four-wire power supply, and the primary side of the current transformer includes a first primary winding, a second primary winding, and a third primary winding. The input lines of the external power supply and the electronic equipment each include three phase lines and one neutral line. The first, second, and third primary windings are connected in series on the three phase lines of the external power supply and electronic equipment input lines, respectively.
[0053] In one embodiment, based on the common-mode noise detection circuit in the foregoing embodiments, the current-to-voltage conversion circuit of the common-mode noise detection circuit includes a resistor, and the non-grounded end of the resistor is used as the signal output port.
[0054] In one embodiment, based on the common-mode noise detection circuit in the foregoing embodiments, the current-to-voltage conversion circuit of the common-mode noise detection circuit includes a resistor and a capacitor connected in series, and the non-grounded point of the overall impedance formed by the series connection of the resistor and the capacitor is used as the signal output port.
[0055] Furthermore, based on the feedforward filter circuit in the foregoing embodiment, the first injection circuit includes a capacitor.
[0056] In one embodiment, based on the feedforward filter circuit in the foregoing embodiments, the first injection circuit further includes a high-pass filter network. One end of the capacitor is connected to the external power supply input line, and the other end is connected to the high-pass filter network; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the first feedback impedance network, the first operational amplifier, and the feedback filter circuit.
[0057] In one embodiment, based on the feedforward filter circuit in the foregoing embodiments, the first injection circuit further includes a characteristic impedance branch. One end of the capacitor is connected to the external power supply input line, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the characteristic impedance branch. One end of the characteristic impedance branch is grounded, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the capacitor.
[0058] In one embodiment, based on the feedforward filter circuit in the foregoing embodiments, the first injection circuit further includes a high-pass filter network and a characteristic impedance branch. One end of the capacitor is connected to the external power supply input line, and the other end is connected to the high-pass filter network and the characteristic impedance branch. One end of the high-pass filter network is connected to the capacitor, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the characteristic impedance branch. One end of the characteristic impedance branch is grounded, and the other end is connected to the high-pass filter network and the capacitor.
[0059] Furthermore, based on the feedback filtering circuit in the foregoing embodiments, the second injection circuit includes a capacitor.
[0060] In one embodiment, based on the feedback filter circuit in the foregoing embodiments, the second injection circuit further includes a high-pass filter network. One end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the high-pass filter network; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the second feedback impedance network and the second operational amplifier.
[0061] In one embodiment, based on the feedback filter circuit in the foregoing embodiments, the second injection circuit further includes a characteristic impedance branch. One end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the capacitor.
[0062] In one embodiment, based on the feedback filter circuit in the foregoing embodiments, the second injection circuit further includes a high-pass filter network and a characteristic impedance branch. One end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the high-pass filter network and the characteristic impedance branch; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the high-pass filter network and the capacitor.
[0063] In one embodiment, based on the foregoing embodiments, the active filter of this application further includes a common-mode passive filter circuit. The common-mode passive filter circuit attenuates noise signals at the external power supply terminal and / or the electronic device terminal based on the impedance mismatch principle, further improving the overall insertion loss of the filter and achieving better filtering performance. The common-mode passive filter circuit can be applied separately at either the external power supply terminal or the electronic device terminal, or simultaneously at both terminals.
[0064] Specifically, when the common-mode passive filter circuit is applied independently at the external power supply terminal, the common-mode passive filter circuit includes an external power supply passive filter. One end of the external power supply passive filter is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit. That is, the noise signal emitted from the electronic device is sampled by the common-mode noise detection circuit and attenuated by the feedback filter circuit and the feedforward filter circuit, and then further attenuated by the external power supply passive filter before entering the external power supply.
[0065] Specifically, when a common-mode passive filter circuit is applied independently at the electronic device end, the common-mode passive filter circuit includes a passive filter at the electronic device end. One end of the passive filter at the electronic device end is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit. That is, after the noise signal is emitted from the electronic device end, it is first attenuated by the passive filter at the electronic device end, then sampled by the common-mode noise detection circuit and successively attenuated by the feedback filter circuit and the feedforward filter circuit, finally entering the external power supply.
[0066] Furthermore, when the common-mode passive filter circuit is applied simultaneously at both the external power supply and the electronic device, the common-mode passive filter circuit includes a passive filter at the external power supply and a passive filter at the electronic device. One end of the passive filter at the external power supply is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit. One end of the passive filter at the electronic device is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit. That is, the noise signal emitted from the electronic device is first attenuated by the passive filter circuit at the electronic device, then sampled by the common-mode noise detection circuit and successively attenuated by the feedback filter circuit and the feedforward filter circuit, and finally attenuated again by the passive filter circuit at the external power supply, so that the amplitude of the noise signal finally entering the external power supply is much smaller than the amplitude of the noise signal at the electronic device.
[0067] Furthermore, based on the active filter of the aforementioned embodiment, the passive filter at the external power supply end and / or the passive filter at the electronic device end consists only of an inductor; or the passive filter at the external power supply end and / or the passive filter at the electronic device end consists of an inductor and a capacitor, with the capacitor placed between the external power supply / electronic device and the inductor, one end of the capacitor connected to the input line of the external power supply end or the input line of the electronic device end, and the other end of the capacitor grounded.
[0068] In one embodiment, as a preferred implementation, please refer to... Figure 4 An active filter is provided, including the common-mode noise detection circuit, feedforward filter circuit, and feedback filter circuit of the aforementioned embodiments.
[0069] In this embodiment, the current-to-voltage conversion circuit of the common-mode noise detection circuit adds capacitor C16 to achieve second-order LC filtering, thereby attenuating the low-frequency components of the sampled signal; the first injection circuit of the feedforward filter circuit adds resistor R2 and capacitor C1 to perform high-pass filtering on the output signal of the feedforward filter circuit, thereby reducing the low-frequency components of the input signal entering the feedback filter circuit.
[0070] In this embodiment, when the active filter is in operation and applied to a low-frequency, high-noise electronic device system, the addition of capacitor C16, resistor R2, and capacitor C1 can prevent the feedback filter circuit from saturating due to excessively high amplitude of the low-frequency components of the input signal. Simultaneously, because the low-frequency components of the output signal of the feedback filter circuit attenuate synchronously, the second operational amplifier can be set to a larger amplification factor to achieve better filtering effects without worrying about its nonlinear operating region.
[0071] Furthermore, the active filter in this embodiment can also prevent the feedback filter circuit from saturating due to excessively high amplitude of low-frequency components of the input signal, while allowing the feedback filter circuit to set a larger amplification factor to improve the overall filtering effect.
[0072] In one embodiment, as a preferred implementation, please refer to... Figure 5 An active filter is provided, including the common-mode noise detection circuit, feedforward filter circuit, and feedback filter circuit of the aforementioned embodiments.
[0073] In this embodiment, the first injection circuit of the feedforward filter circuit adds resistor R25, capacitor C46, and resistor R45 to optimize the frequency characteristics of the injected current signal of the feedforward filter circuit and improve the filtering effect attenuation caused by phase deviation. The second injection circuit of the feedback filter circuit adds resistor R23, capacitor C21, and resistor R17 to optimize the frequency characteristics of the injected current signal of the feedback filter circuit and improve the filtering effect attenuation caused by phase deviation.
[0074] In this embodiment, when the active filter is working, both the feedforward filter circuit and the feedback filter circuit improve the frequency characteristics of the injected current signal by adding damping resistors and ground branches, which can be regarded as compensation for the nonlinear characteristics of the operational amplifier load. The actual load impedance characteristics at the output of the operational amplifier are as follows: Figure 8 As shown by the dashed line, the impedance abrupt change point is caused by LC resonance, which significantly deteriorates the frequency characteristics of the injected current signal, thereby introducing phase deviation, leading to a decrease in filtering effect, and may even cause resonance in the active filter. Adding a damping resistor and a ground branch alleviates the nonlinear characteristics of the operational amplifier load, as shown... Figure 8 As shown by the solid line, the resulting frequency response issues, filtering effect attenuation issues, and resonance issues are improved.
[0075] Furthermore, the active filter in this embodiment can also improve the frequency characteristics, filtering effect attenuation, and resonance problems caused by the nonlinear characteristics of the load impedance in feedforward and feedback filter circuits.
[0076] In one embodiment, as a preferred implementation, please refer to... Figure 6 An active filter is provided, including the common-mode noise detection circuit, feedforward filter circuit, feedback filter circuit, and common-mode passive filter circuit of the above embodiments.
[0077] Specifically, the common-mode passive filter circuit may include an external power supply-side LC-type passive filter circuit, composed of Y capacitors C36 and C37 and a common-mode inductor TX7; simultaneously, the common-mode passive filter circuit may also include an electronic device-side LC-type passive filter circuit, composed of Y capacitors C34 and C35 and common-mode inductors TX5 and TX6. The addition of LC-type passive filter circuits at both the external power supply and electronic device sides forms an active-passive hybrid filter, which can further improve the overall insertion loss of the filter based on the active filter, achieving better filtering performance. In particular, either the external power supply-side LC-type passive filter circuit or the electronic device-side LC-type passive filter circuit can be used individually or both.
[0078] In the operation of the active filter in this embodiment, the common-mode passive filter circuit, by satisfying the "impedance mismatch" principle, can improve the overall insertion loss of the filter to a certain extent. The noise signal emitted from the electronic device is first attenuated by the passive filter circuit at the electronic device end, then sampled by the common-mode noise detection circuit and attenuated a second and third time by the feedback filter circuit and the feedforward filter circuit, and finally attenuated a fourth time by the passive filter circuit at the external power supply end. This four-stage attenuation design ultimately ensures that the amplitude of the noise signal entering the external power supply is much smaller than the amplitude of the noise signal at the electronic device end. That is, by adding an external power supply end LC-type passive filter circuit and an electronic device end LC-type passive filter circuit that conform to the impedance mismatch principle, the active filter in this embodiment can further increase the overall insertion loss of the filter and achieve a better filtering effect.
[0079] The above are merely optional embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An active filter disposed between an external power source and an electronic device for filtering a common mode noise signal generated by the electronic device, characterized by, It includes a common-mode noise detection circuit for detecting common-mode noise in electronic devices, a feedforward filter circuit for feedforward filtering of common-mode noise, and a feedback filter circuit for feedback filtering of common-mode noise. The common-mode noise detection circuit is connected to the external power supply input line, the electronic device input line, and the feedforward filter circuit, and one end of the common-mode noise detection circuit is grounded. The feedforward filter circuit is connected to the external power supply input line, the common-mode noise detection circuit, and the feedback filter circuit, and one end of the feedforward filter circuit is grounded. The feedback filter circuit is connected to the input line of the electronic device and the feedforward filter circuit, and one end of the feedback filter circuit is grounded. The common-mode noise detection circuit is not connected to the feedback filter circuit; the common-mode noise detection circuit provides a common-mode noise signal input to the feedforward filter circuit, the feedforward filter circuit amplifies the common-mode noise signal over a wide frequency band, and the input signal of the feedback filter circuit is the common-mode noise signal amplified by the feedforward filter circuit.
2. The active filter of claim 1, wherein, The common-mode noise detection circuit includes a current transformer and a current-to-voltage conversion circuit. The primary side of the current transformer is connected to the input line of the external power supply and the input line of the electronic device, respectively; the secondary side of the current transformer is connected to the current-to-voltage conversion circuit. One end of the current-to-voltage conversion circuit is connected to the secondary side of the current transformer, and the other end is grounded; the signal output port of the current-to-voltage conversion circuit is connected to the feedforward filter circuit.
3. The active filter of claim 2, wherein, The feedforward filter circuit includes a first input impedance network, a first feedback impedance network, a first injection circuit, a first operational amplifier, and a first external power supply circuit. One end of the first input impedance network is connected to the signal output port of the current-to-voltage conversion circuit, and the other end is connected to the first feedback impedance network and the first operational amplifier. One end of the first feedback impedance network is connected to the first input impedance network, and the other end is connected to the first injection circuit and the first operational amplifier; One end of the first injection circuit is connected to the first feedback impedance network and the first operational amplifier, one end is connected to the input line of the external power supply, and the other end is connected to the feedback filter circuit. The non-inverting input of the first operational amplifier is grounded, the inverting input is connected to the first input impedance network and the first feedback impedance network, the output is connected to the first feedback impedance network and the first injection circuit, and the power supply is connected to the first external power supply circuit.
4. The active filter of claim 3, wherein, The feedback filter circuit includes a second input impedance network, a second feedback impedance network, a second injection circuit, a second operational amplifier, and a second external power supply circuit. One end of the second input impedance network is grounded, and the other end is connected to the second feedback impedance network and the second operational amplifier. One end of the second feedback impedance network is connected to the second input impedance network, and the other end is connected to the second injection circuit and the second operational amplifier. One end of the second injection circuit is connected to the second feedback impedance network and the second operational amplifier, and the other end is connected to the input line of the electronic device. The non-inverting input of the second operational amplifier is connected to the first injection circuit, the inverting input is connected to the second input impedance network and the second feedback impedance network, the output is connected to the second feedback impedance network and the second injection circuit, and the power supply is connected to the second external power supply circuit.
5. The active filter according to claim 2, characterized in that, The external power supply is a single-phase power supply. The primary side of the current transformer includes a first primary winding and a second primary winding. The input line of the external power supply terminal and the input line of the electronic device terminal each include a phase line and a neutral line. The first primary winding is connected in series on the phase / neutral line of the input line of the external power supply terminal and the input line of the electronic device terminal. The second primary winding is connected in series on the neutral / phase line of the input line of the external power supply terminal and the input line of the electronic device terminal. Alternatively, the external power supply may be a three-phase three-wire power supply, and the primary side of the current transformer may include a first primary winding, a second primary winding, and a third primary winding; the input line of the external power supply terminal and the input line of the electronic device terminal may each include three phase lines; the first primary winding, the second primary winding, and the third primary winding may be connected in series on the three phase lines of the input line of the external power supply terminal and the input line of the electronic device terminal; Alternatively, the external power supply may be a three-phase four-wire power supply, and the primary side of the current transformer may include a first primary winding, a second primary winding, a third primary winding, and a fourth primary winding; the input line of the external power supply terminal and the input line of the electronic device terminal may each include three phase lines and one neutral line; the first primary winding, the second primary winding, the third primary winding, and the fourth primary winding may be connected in series with the three phase lines and one neutral line of the input line of the external power supply terminal and the input line of the electronic device terminal, respectively; Alternatively, the external power supply may be a three-phase four-wire power supply, and the primary side of the current transformer may include a first primary winding, a second primary winding, and a third primary winding; the input line of the external power supply terminal and the input line of the electronic device terminal may each include three phase lines and one neutral line; the first primary winding, the second primary winding, and the third primary winding may be connected in series on the three phase lines of the input line of the external power supply terminal and the input line of the electronic device terminal.
6. The active filter of claim 2, wherein, The current-to-voltage conversion circuit includes a resistor, and the non-grounded end of the resistor is used as the signal output port; Alternatively, the current-to-voltage conversion circuit may include a resistor and a capacitor connected in series, and the non-grounded point of the overall impedance formed by the series connection of the resistor and the capacitor may be used as the signal output port.
7. The active filter according to claim 3, characterized in that, The first injection circuit includes a capacitor.
8. The active filter according to claim 7, characterized in that, The first injection circuit further includes a high-pass filter network; one end of the capacitor is connected to the external power supply input line, and the other end is connected to the high-pass filter network; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the first feedback impedance network, the first operational amplifier, and the feedback filter circuit. Alternatively, the first injection circuit may further include a characteristic impedance branch; one end of the capacitor is connected to the external power supply input line, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the capacitor. Alternatively, the first injection circuit may further include a high-pass filter network and a characteristic impedance branch; one end of the capacitor is connected to the external power supply input line, and the other end is connected to the high-pass filter network and the characteristic impedance branch; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the first feedback impedance network, the first operational amplifier, the feedback filter circuit, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the high-pass filter network and the capacitor.
9. The active filter according to claim 4, characterized in that, The second injection circuit includes a capacitor.
10. The active filter according to claim 9, characterized in that, The second injection circuit further includes a high-pass filter network; one end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the high-pass filter network; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the second feedback impedance network and the second operational amplifier; Alternatively, the second injection circuit may further include a characteristic impedance branch; one end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the capacitor; Alternatively, the second injection circuit may further include a high-pass filter network and a characteristic impedance branch; one end of the capacitor is connected to the input line of the electronic device, and the other end is connected to the high-pass filter network and the characteristic impedance branch; one end of the high-pass filter network is connected to the capacitor, and the other end is connected to the second feedback impedance network, the second operational amplifier, and the characteristic impedance branch; one end of the characteristic impedance branch is grounded, and the other end is connected to the high-pass filter network and the capacitor.
11. The active filter according to any one of claims 1 to 10, characterized in that, The active filter also includes a common-mode passive filter circuit; the common-mode passive filter circuit attenuates noise signals at the external power supply terminal and / or electronic device terminal based on the impedance mismatch principle.
12. The active filter according to claim 11, characterized in that, The common-mode passive filter circuit includes an external power supply passive filter; one end of the external power supply passive filter is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit. Alternatively, the common-mode passive filter circuit may include a passive filter at the electronic device end; one end of the passive filter at the electronic device end is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit; Alternatively, the common-mode passive filter circuit may include an external power supply passive filter and an electronic device passive filter; one end of the external power supply passive filter is connected to the external power supply, and the other end is connected to the common-mode noise detection circuit; one end of the electronic device passive filter is connected to the electronic device, and the other end is connected to the common-mode noise detection circuit.
13. The active filter according to claim 12, characterized in that, The passive filter at the external power supply end and / or the passive filter at the electronic device end consist only of inductors; Alternatively, the passive filter at the external power supply end and / or the passive filter at the electronic device end may be composed of an inductor and a capacitor, with the capacitor placed between the external power supply / electronic device and the inductor, one end of the capacitor connected to the input line of the external power supply end or the input line of the electronic device end, and the other end of the capacitor grounded.