A fourth order current cross-coupled cancellation low pass filter
By designing a fourth-order current cross-coupling cancellation low-pass filter, and utilizing the cross-coupling current cancellation transistor to reduce the equivalent transconductance of the transconductance transistor, the problem of area occupation and power consumption of high-order filters is solved, realizing the design of low-power and small-area low-pass filters.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHONGQING INST OF INTEGRATED CIRCUIT INNOVATION XIDIAN UNIV
- Filing Date
- 2023-03-02
- Publication Date
- 2026-07-28
AI Technical Summary
The low-pass filters in existing biomedical simulation front-ends occupy a large chip area and consume a lot of power in high-order filters. Although the gm-C low-pass filter is suitable for high-order filters, its large capacitance value leads to an increase in circuit area and power consumption.
Design a fourth-order current cross-coupled cancellation low-pass filter. By using four series-connected single-stage filters and two bias current branches, the cross-coupled current cancellation transistors reduce the equivalent transconductance of the transconductance transistors, enabling multiple filters to share a single bias circuit.
Achieving a low cutoff frequency within a limited chip area reduces circuit power consumption while maintaining good process and mismatch robustness and minimizing capacitor area.
Smart Images
Figure CN116366025B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic components, specifically relating to a fourth-order current cross-coupling cancellation low-pass filter. Background Technology
[0002] Currently, cardiovascular and cerebrovascular diseases have become the leading causes of death and health threats to human life. Conditions such as arrhythmia, acute heart failure, and myocarditis are characterized by rapid onset and high mortality rates. However, effective intervention can significantly reduce the risk of death and increase patients' chances of survival. Pre-admission patient classification and identification based on biomedical signals helps in the timely diagnosis of related diseases and provides timely and effective medical treatment. Therefore, the Internet of Things (IoT) for healthcare has emerged, combining biomedical simulation front-ends, wireless communication systems, and medical application systems. It holds promise as a feasible solution for remote medical services.
[0003] Highly efficient low-pass filters play a crucial role in biomedical analog front-ends, effectively filtering out noise and ripple outside the analog front-end bandwidth. However, biological signals are characterized by low frequencies, and using on-chip multi-order RC low-pass filters to generate a low-frequency cutoff would occupy a significant chip area. Using OTA-C low-pass filters can greatly reduce chip area; however, the number of OTAs increases linearly with the filter order, leading to increased power consumption and complexity in the fully differential circuit structure.
[0004] GM-C low-pass filters are characterized by low power consumption and ease of cascading to increase order, making them ideal for multi-channel analog front-end (AFE) systems requiring high-order low-pass characteristics. In bio-analog front-end systems, to effectively acquire human biological signals, the low-pass filter needs to generate a cutoff frequency of less than 200Hz. Therefore, the capacitance values in GM-C low-pass filters are generally large. In multi-channel biosignal acquisition applications, multiple high-order GM-C low-pass filters occupy a large portion of the AFE chip area, resulting in a large circuit area and high power consumption. Summary of the Invention
[0005] To address the aforementioned problems in the prior art, this invention provides a fourth-order current cross-coupling cancellation low-pass filter. The technical problem to be solved by this invention is achieved through the following technical solution:
[0006] This invention provides a fourth-order current cross-coupling cancellation low-pass filter, comprising: four series-connected single-stage filters and two bias current branches, wherein the first-stage filter and the second-stage filter form a second-order gm-C low-pass filter, and the third-stage filter and the fourth-stage filter form another second-order gm-C low-pass filter, and the two bias current branches are connected to the two second-order gm-C low-pass filters respectively, so that the second-order gm-C low-pass filters are in normal working condition.
[0007] The single-stage filter includes a transconductance transistor, a capacitor, and a current-canceling transistor. The transconductance transistor and the current-canceling transistor are connected across the capacitor via cross-coupling. The current-canceling transistor is used to reduce the equivalent transconductance of the transconductance transistor.
[0008] In one embodiment of the present invention, in the single-stage filter, the size ratio of the transconductance transistor to the current cancellation transistor is N:1, where N<1.
[0009] In one embodiment of the present invention, the first-stage filter includes transistors M11, M12, M16, and M17, and capacitor C3, wherein,
[0010] The drain terminals of transistors M11, M12, M16, and M17 are all connected to the ground terminal; the gate terminals of transistors M11 and M12 are connected and serve as the first signal input terminal of the first-stage filter; the source terminal of transistor M11 is connected to the positive terminal of capacitor C3, and the source terminal of transistor M12 is connected to the negative terminal of capacitor C3.
[0011] The gate terminals of transistors M16 and M17 are connected and serve as the second signal input terminal of the first-stage filter; the source terminal of transistor M16 is connected to the positive terminal of capacitor C3, and the source terminal of transistor M17 is connected to the negative terminal of capacitor C3.
[0012] In one embodiment of the present invention, the second-stage filter includes transistors M13, M14, M18, and M19, and capacitor C4, wherein,
[0013] The drain terminals of transistors M13 and M14 are connected and connected to the positive terminal of capacitor C3; the gate terminals of transistors M13 and M14 are connected and connected to the negative terminal of capacitor C3; the source terminal of transistor M13 is connected to the positive terminal of capacitor C4, and the source terminal of transistor M14 is connected to the negative terminal of capacitor C4.
[0014] The drain terminals of transistors M18 and M19 are connected together and connected to the negative terminal of capacitor C3; the gate terminals of transistors M18 and M19 are connected together and connected to the positive terminal of capacitor C3; the source terminal of transistor M18 is connected to the positive terminal of capacitor C4, and the source terminal of transistor M19 is connected to the negative terminal of capacitor C4.
[0015] The positive terminal of capacitor C4 serves as the first output terminal of the second-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal of the second-stage filter.
[0016] In one embodiment of the present invention, the third-stage filter includes transistors M1, M2, M6, and M7, and capacitor C1, wherein,
[0017] The drain terminals of transistors M1, M2, M6, and M7 are all connected to the power supply terminal; the gate terminals of transistors M1 and M2 are connected together and connected to the second output terminal of the second-stage filter; the source terminal of transistor M1 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M2 is connected to the negative terminal of capacitor C1.
[0018] The gate terminals of transistors M6 and M7 are connected and connected to the first output terminal of the second-stage filter; the source terminal of transistor M6 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M7 is connected to the negative terminal of capacitor C1.
[0019] In one embodiment of the present invention, the fourth-stage filter includes transistors M3, M4, M8, and M9, and capacitor C2, wherein,
[0020] The drain terminals of transistors M3 and M4 are connected together and connected to the positive terminal of capacitor C1; the gate terminals of transistors M3 and M4 are connected together and connected to the negative terminal of capacitor C1; the source terminal of transistor M3 is connected to the positive terminal of capacitor C2, and the source terminal of transistor M4 is connected to the negative terminal of capacitor C2.
[0021] The drain terminals of transistors M8 and M9 are connected together and connected to the negative terminal of capacitor C1; the gate terminals of transistors M8 and M9 are connected together and connected to the positive terminal of capacitor C1; the source terminal of transistor M8 is connected to the positive terminal of capacitor C2, and the source terminal of transistor M9 is connected to the negative terminal of capacitor C2.
[0022] The positive terminal of capacitor C2 serves as the first output terminal of the fourth-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal of the fourth-stage filter.
[0023] In one embodiment of the present invention, the two bias current branches include a first bias current branch and a second bias current branch, wherein,
[0024] The first bias current branch includes transistors M15 and M20, wherein the source terminals of transistors M15 and M20 are both connected to the power supply terminal; the gate terminals of transistors M15 and M20 are connected and connected to the first node of the applied bias voltage; the drain terminal of transistor M15 is connected to the positive terminal of capacitor C4; and the drain terminal of transistor M20 is connected to the negative terminal of capacitor C4.
[0025] The second bias current branch includes transistors M5 and M10, wherein the source terminals of transistors M5 and M10 are both connected to the ground terminal; the gate terminals of transistors M5 and M10 are connected and connected to the second node of the applied bias voltage; the drain terminal of transistor M5 is connected to the positive terminal of capacitor C2; and the drain terminal of transistor M10 is connected to the negative terminal of capacitor C2.
[0026] In one embodiment of the present invention, the transistors of the first-stage filter, the second-stage filter, and the first bias current are all PMOS transistors;
[0027] The transistors of the third-stage filter, the fourth-stage filter, and the second bias current are all NMOS transistors.
[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0029] 1. The fourth-order current cross-coupling cancelling low-pass filter of the present invention realizes that multiple filters share a single bias circuit, which greatly reduces the power consumption of the circuit. By adding a current cancelling transistor, the equivalent transconductance of the transconductance transistor can be effectively reduced, thereby obtaining a larger time constant and achieving a lower cutoff frequency within a limited chip area.
[0030] 2. The fourth-order current cross-coupling cancellation low-pass filter of the present invention has good process robustness and mismatch robustness.
[0031] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description
[0032] Figure 1 This is a structural diagram of a fourth-order current cross-coupling cancellation low-pass filter provided in an embodiment of the present invention;
[0033] Figure 2 This is a structural diagram of a second-order gm-C LPF without a current-canceling transistor, provided in an embodiment of the present invention.
[0034] Figure 3 This is a small-signal circuit diagram of a second-order gm-C LPF without a current-canceling transistor, provided in an embodiment of the present invention.
[0035] Figure 4 This is the cutoff frequency distribution histogram obtained by Monte Carlo simulation of the fourth-order current cross-coupling cancellation low-pass filter provided in this embodiment of the invention. Detailed Implementation
[0036] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description of a fourth-order current cross-coupling cancellation low-pass filter proposed according to the present invention is provided in conjunction with the accompanying drawings and specific embodiments.
[0037] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.
[0038] Example 1
[0039] The fourth-order current cross-coupling cancellation low-pass filter of this embodiment includes four series-connected single-stage filters and two bias current branches, including a first bias current branch and a second bias current branch. The first-stage filter and the second-stage filter form a second-order gm-C low-pass filter, and the third-stage filter and the fourth-stage filter form another second-order gm-C low-pass filter. The two bias current branches are connected to the two second-order gm-C low-pass filters respectively, so that the second-order gm-C low-pass filters are in normal working condition.
[0040] In this embodiment, the single-stage filter includes a transconductance transistor, a capacitor, and a current-canceling transistor. The transconductance transistor and the current-canceling transistor are connected across the capacitor via cross-coupling. The current-canceling transistor is used to reduce the equivalent transconductance of the transconductance transistor. In the single-stage filter, the size ratio of the transconductance transistor to the current-canceling transistor is N:1, where N < 1.
[0041] Please refer to the above. Figure 1 The diagram shown is a structural diagram of a fourth-order current cross-coupling cancellation low-pass filter provided by an embodiment of the present invention. Figure 1 As shown, the first-stage filter includes transistors M11, M12, M16, and M17, and capacitor C3. The drains of transistors M11, M12, M16, and M17 are all connected to ground (GND). The gates of transistors M11 and M12 are connected and serve as the first signal input terminal VI+ of the first-stage filter. The source of transistor M11 is connected to the positive terminal of capacitor C3, and the source of transistor M12 is connected to the negative terminal of capacitor C3. The gates of transistors M16 and M17 are connected and serve as the second signal input terminal VI- of the first-stage filter. The source of transistor M16 is connected to the positive terminal of capacitor C3, and the source of transistor M17 is connected to the negative terminal of capacitor C3.
[0042] In this embodiment, the source terminals of transistors M11 and M16 are connected to the same node, and the source terminals of transistors M12 and M17 are connected to the same node. The biological signal requiring filtering is input from the first signal input terminal VI+ and the second signal input terminal VI- of the first-stage filter to the fourth-order current cross-coupling cancellation low-pass filter.
[0043] In this embodiment, transistors M11 and M17 are transconductance transistors, transistors M12 and M16 are current cancellation transistors, and the size ratio of transistors M11, M12, M16 and M17 is N:1:1:N.
[0044] like Figure 1 As shown, the second-stage filter includes transistors M13, M14, M18, and M19, and capacitor C4. The drains of transistors M13 and M14 are connected and then to the positive terminal of capacitor C3; the gates of transistors M13 and M14 are connected and then to the negative terminal of capacitor C3; the source of transistor M13 is connected to the positive terminal of capacitor C4, and the source of transistor M14 is connected to the negative terminal of capacitor C4; the drains of transistors M18 and M19 are connected and then to the negative terminal of capacitor C3; the gates of transistors M18 and M19 are connected and then to the positive terminal of capacitor C3; the source of transistor M18 is connected to the positive terminal of capacitor C4, and the source of transistor M19 is connected to the negative terminal of capacitor C4; the positive terminal of capacitor C4 serves as the first output terminal VA of the second-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal VB of the second-stage filter.
[0045] In this embodiment, transistors M13 and M19 are transconductance transistors, transistors M14 and M18 are current cancellation transistors, and the size ratio of transistors M13, M14, M18 and M19 is N:1:1:N.
[0046] The bias current branch of the second-order gm-C low-pass filter, composed of the first-stage and second-stage filters, is formed by transistors M15 and M20. The sources of transistors M15 and M20 are both connected to the power supply terminal VDD; the gates of transistors M15 and M20 are connected and connected to the first node of the applied bias voltage Vbp; the drain of transistor M15 is connected to the positive terminal of capacitor C4, and the drain of transistor M20 is connected to the negative terminal of capacitor C4.
[0047] In this embodiment, the drain of transistor M15 is connected to the source of transistors M13 and M18, and the drain of transistor M20 is connected to the source of transistors M14 and M19.
[0048] like Figure 1As shown, the third-stage filter includes transistors M1, M2, M6, and M7, and capacitor C1. The drain terminals of transistors M1, M2, M6, and M7 are all connected to the power supply terminal VDD; the gate terminals of transistors M1 and M2 are connected together and then connected to the second output terminal VB of the second-stage filter.
[0049] The source terminal of transistor M1 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M2 is connected to the negative terminal of capacitor C1; the gate terminals of transistors M6 and M7 are connected and connected to the first output terminal VA of the second-stage filter; the source terminal of transistor M6 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M7 is connected to the negative terminal of capacitor C1.
[0050] In this embodiment, the source terminals of transistors M1 and M6 are connected to the same node, and the source terminals of transistors M2 and M7 are connected to the same node.
[0051] In this embodiment, transistors M1 and M7 are transconductance transistors, transistors M2 and M6 are current cancellation transistors, and the size ratio of transistors M1, M2, M6 and M7 is N:1:1:N.
[0052] like Figure 1 As shown, the fourth-stage filter includes transistors M3, M4, M8, and M9, and capacitor C2. The drains of transistors M3 and M4 are connected and then to the positive terminal of capacitor C1; the gates of transistors M3 and M4 are connected and then to the negative terminal of capacitor C1; the source of transistor M3 is connected to the positive terminal of capacitor C2, and the source of transistor M4 is connected to the negative terminal of capacitor C2; the drains of transistors M8 and M9 are connected and then to the negative terminal of capacitor C1; the gates of transistors M8 and M9 are connected and then to the positive terminal of capacitor C1; the source of transistor M8 is connected to the positive terminal of capacitor C2, and the source of transistor M9 is connected to the negative terminal of capacitor C2; the positive terminal of capacitor C2 serves as the first output terminal VO- of the fourth-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal VO+ of the fourth-stage filter.
[0053] In this embodiment, transistors M3 and M9 are transconductance transistors, transistors M4 and M8 are current cancellation transistors, and the size ratio of transistors M3, M4, M8 and M9 is N:1:1:N.
[0054] In this embodiment, the first output terminal VO- and the second output terminal VO+ of the fourth-stage filter serve as the output terminals of the fourth-order current cross-coupling cancellation low-pass filter, outputting the filtered signal.
[0055] The bias current branch of the second-order gm-C low-pass filter, composed of the third and fourth stage filters, is formed by transistors M5 and M10. The sources of transistors M5 and M10 are both connected to ground GND; the gates of transistors M5 and M10 are connected and connected to the second node Vbn of the applied bias voltage; the drain of transistor M5 is connected to the positive terminal of capacitor C2, and the drain of transistor M10 is connected to the negative terminal of capacitor C2.
[0056] In this embodiment, the drain of transistor M5 is connected to the source of transistors M3 and M8, and the drain of transistor M10 is connected to the source of transistors M4 and M9.
[0057] In this embodiment, the transistors for the first-stage filter, the second-stage filter, and the first bias current, namely M11, M12, M13, M14, M15, M16, M17, M18, M19, and M20, are all PMOS transistors. The transistors for the third-stage filter, the fourth-stage filter, and the second bias current, namely M1, M2, M3, M4, M5, M6, M7, M8, M9, and M10, are all NMOS transistors.
[0058] Furthermore, the implementation method and principle of the fourth-order current cross-coupling cancellation low-pass filter in this embodiment are described in detail.
[0059] like Figure 1 As shown, for the second-order gm-C low-pass filter composed of the third and fourth stage filters in the right half, the substrates of all NMOS transistors are grounded, with transistors M5 and M10 providing bias current for the right half of the circuit. Transconductance transistors M1, M3, M7, and M9, along with capacitors C1 and C2, constitute a second-order gm-C low-pass filter. Current-canceling transistors M2, M4, M6, and M8 divert some of the small-signal current from the transconductance transistors, thus reducing the equivalent transconductance of the circuit. The size of the transconductance transistors is N times the size of the current-canceling transistors (N < 1), resulting in the following transistor size ratio:
[0060] (W / L)1:(W / L)2:(W / L)6:(W / L)7=N:1:1:N(1);
[0061] (W / L)3:(W / L)4:(W / L)8:(W / L)9=N:1:1:N(2);
[0062] Please refer to the above. Figure 2 and Figure 3 The diagram shows the structure and small-signal circuit of a second-order gm-C LPF without a current-canceling transistor, taking into account the bulk effect.
[0063] From the small-signal circuit diagram, the transfer function of this second-order low-pass filter is derived as follows:
[0064]
[0065] Among them, g ms1,3 =g m1,3 +g mb1,3 g m Indicates the transconductance of the MOSFET, g mb VO represents the back gate transconductance of the MOSFET, VI represents the output voltage signal, and C1 and C2 represent the capacitance values of capacitors C1 and C2, respectively.
[0066] The fourth-order current-cross-coupled cancelling low-pass filter proposed in this embodiment not only has the advantage of low power consumption, but also effectively reduces the equivalent transconductance of the transconductance transistor by adding a current-canceling transistor, thereby reducing the capacitor area. The cutoff frequency expression of the low-pass filter is:
[0067]
[0068] Here, τ = C / gm is the time constant. Qualitative analysis can be performed using the above expression: by using the current-canceling transistor, the equivalent transconductance of the transconductance transistor is reduced. While maintaining the cutoff frequency, this effectively reduces the capacitance in the circuit, thereby reducing the chip area.
[0069] The following is a quantitative analysis. Since the size ratio of the transconductance transistor to the current-canceling transistor is N:1, the transconductance of the transconductance transistor in the circuit becomes: (The original text contains some formatting errors and inconsistencies. A more accurate translation would require the full context.)
[0070] G m1 =(N-1)g m1 (5);
[0071] G m3 =(N-1)g m3 (6);
[0072] Substituting this into the transfer function of the second-order low-pass filter given above (Equation (3)), we can obtain: The DC gain, cutoff frequency, and quality factor of the second-order current cross-coupling canceled low-pass filter are respectively:
[0073] A(0)=G m1 G m3 / G ms1 G ms3 =g m1 g m3 / g ms1 g ms3 (7);
[0074]
[0075]
[0076] Here G ms1,3 =G m1,3 +G mb1,3 As can be seen from the formula above, the DC gain and quality factor of the low-pass filter remain unchanged. Due to the shunting effect of the current cancelling transistor, the equivalent transconductance is reduced, thereby reducing the low-pass cutoff frequency to (1-N) times its original value. Therefore, if the cutoff frequency of the filter remains unchanged, the capacitor area can be reduced to 1 / (1-N) of its original value, thus optimizing the chip area. At the same time, the multi-stage filter shares a single bias circuit, which greatly reduces the circuit power consumption.
[0077] Please see Figure 4 The histogram showing the cutoff frequency distribution of the fourth-order current cross-coupling cancelling low-pass filter obtained through Monte Carlo simulation is illustrated. The horizontal axis represents frequency, and the vertical axis represents the number of points. Number represents the number of simulation sampling points, μ represents the average value of the simulation results (i.e., the average value of the desired low-pass filter cutoff frequency), σ represents the standard deviation of the simulation data distribution, and 3σ / μ is used to represent the robustness (stability) of the circuit; a smaller value indicates greater stability. The 3σ / μ mismatch of the low-pass filter is typically around 20%. As can be seen from the figure, the cutoff frequency of the fourth-order current cross-coupling cancelling low-pass filter varies within ±20.4% of the average value of 201.4Hz, indicating that the fourth-order current cross-coupling cancelling low-pass filter of this invention has good process robustness and mismatch robustness.
[0078] This embodiment of the fourth-order current-cross-coupled cancelling low-pass filter enables multiple filters to share a single bias circuit, significantly reducing circuit power consumption. By adding a current-canceling transistor, the equivalent transconductance of the transconductance transistor is effectively reduced, resulting in a larger time constant (τ = C / gm), achieving a lower cutoff frequency within a limited chip area. Furthermore, this fourth-order current-cross-coupled cancelling low-pass filter exhibits good process robustness and mismatch robustness.
[0079] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect.
[0080] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.
Claims
1. A fourth-order current-cross-coupling cancelling low-pass filter, characterized in that, include: Four cascaded single-stage filters and two bias current branches are provided. The first-stage filter and the second-stage filter form a second-order gm-C low-pass filter, and the third-stage filter and the fourth-stage filter form another second-order gm-C low-pass filter. The two bias current branches are connected to the two second-order gm-C low-pass filters respectively, so that the second-order gm-C low-pass filters are in normal working condition. The single-stage filter includes a transconductance transistor, a capacitor, and a current-canceling transistor. The transconductance transistor and the current-canceling transistor are connected across the capacitor via cross-coupling. The current-canceling transistor is used to reduce the equivalent transconductance of the transconductance transistor. The first-stage filter includes transistors M11, M12, M16, and M17, and capacitor C3, wherein, The drain terminals of transistors M11, M12, M16, and M17 are all connected to ground (GND); the gate terminals of transistors M11 and M12 are connected and serve as the first signal input terminal (VI+) of the first-stage filter; the source terminal of transistor M11 is connected to the positive terminal of capacitor C3, and the source terminal of transistor M12 is connected to the negative terminal of capacitor C3. The gate terminals of transistors M16 and M17 are connected and serve as the second signal input terminal (VI-) of the first-stage filter; the source terminal of transistor M16 is connected to the positive terminal of capacitor C3, and the source terminal of transistor M17 is connected to the negative terminal of capacitor C3. The second-stage filter includes transistors M13, M14, M18, and M19, and capacitor C4, wherein, The drain terminals of transistors M13 and M14 are connected and connected to the positive terminal of capacitor C3; the gate terminals of transistors M13 and M14 are connected and connected to the negative terminal of capacitor C3; the source terminal of transistor M13 is connected to the positive terminal of capacitor C4, and the source terminal of transistor M14 is connected to the negative terminal of capacitor C4. The drain terminals of transistors M18 and M19 are connected together and connected to the negative terminal of capacitor C3; the gate terminals of transistors M18 and M19 are connected together and connected to the positive terminal of capacitor C3; the source terminal of transistor M18 is connected to the positive terminal of capacitor C4, and the source terminal of transistor M19 is connected to the negative terminal of capacitor C4. The positive terminal of capacitor C4 serves as the first output terminal (VA) of the second-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal (VB) of the second-stage filter.
2. The fourth-order current cross-coupling cancellation low-pass filter according to claim 1, characterized in that, In the single-stage filter, the size ratio of the transconductance transistor to the current cancellation transistor is N:1, where N < 1.
3. The fourth-order current cross-coupling cancellation low-pass filter according to claim 1, characterized in that, The third-stage filter includes transistors M1, M2, M6, and M7, and capacitor C1, wherein... The drain terminals of transistors M1, M2, M6, and M7 are all connected to the power supply terminal (VDD); the gate terminals of transistors M1 and M2 are connected together and connected to the second output terminal (VB) of the second-stage filter; the source terminal of transistor M1 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M2 is connected to the negative terminal of capacitor C1. The gate terminals of transistors M6 and M7 are connected together and connected to the first output terminal (VA) of the second-stage filter; the source terminal of transistor M6 is connected to the positive terminal of capacitor C1, and the source terminal of transistor M7 is connected to the negative terminal of capacitor C1.
4. The fourth-order current cross-coupling cancellation low-pass filter according to claim 3, characterized in that, The fourth-stage filter includes transistors M3, M4, M8, and M9, and capacitor C2, wherein... The drain terminals of transistors M3 and M4 are connected together and connected to the positive terminal of capacitor C1; the gate terminals of transistors M3 and M4 are connected together and connected to the negative terminal of capacitor C1; the source terminal of transistor M3 is connected to the positive terminal of capacitor C2, and the source terminal of transistor M4 is connected to the negative terminal of capacitor C2. The drain terminals of transistors M8 and M9 are connected together and connected to the negative terminal of capacitor C1; the gate terminals of transistors M8 and M9 are connected together and connected to the positive terminal of capacitor C1; the source terminal of transistor M8 is connected to the positive terminal of capacitor C2, and the source terminal of transistor M9 is connected to the negative terminal of capacitor C2. The positive terminal of capacitor C2 serves as the first output terminal (VO-) of the fourth-stage filter, and the negative terminal of capacitor C4 serves as the second output terminal (VO+) of the fourth-stage filter.
5. The fourth-order current cross-coupling cancelling low-pass filter according to claim 4, characterized in that, The two bias current branches include a first bias current branch and a second bias current branch, wherein, The first bias current branch includes transistors M15 and M20, wherein the source terminals of transistors M15 and M20 are both connected to the power supply terminal (VDD); the gate terminals of transistors M15 and M20 are connected and connected to the first node of the applied bias voltage (Vbp); the drain terminal of transistor M15 is connected to the positive terminal of capacitor C4; and the drain terminal of transistor M20 is connected to the negative terminal of capacitor C4. The second bias current branch includes transistors M5 and M10, wherein the source terminals of transistors M5 and M10 are both connected to the ground terminal (GND); the gate terminals of transistors M5 and M10 are connected and connected to the second node (Vbn) of the applied bias voltage; the drain terminal of transistor M5 is connected to the positive terminal of capacitor C2; and the drain terminal of transistor M10 is connected to the negative terminal of capacitor C2.
6. The fourth-order current cross-coupling cancelling low-pass filter according to claim 5, characterized in that, The transistors for the first-stage filter, the second-stage filter, and the first bias current are all PMOS transistors; The transistors of the third-stage filter, the fourth-stage filter, and the second bias current are all NMOS transistors.