A filter circuit

Abstract

The present invention discloses a filter circuit, wherein the first PCB layer is composed of a power line, a power interface, a second filter capacitor, and a first filter capacitor; the power line includes a power network and a GND network; the second PCB layer is provided with a conductor plane; the power interface is connected to the GND network, and the power interface is also connected to the conductor plane; the GND network, the second filter capacitor, and the conductor plane are connected in sequence; the power network, the first filter capacitor, and the conductor plane are connected in sequence. The circuit design of the circuit structure of the present invention and the overall layout design idea have a good suppression effect on common mode noise, differential mode noise, radiation noise, and conduction noise.

Description

Technical Field

[0001] The invention relates to filtering technology, in particular to a filtering circuit. Background Art

[0002] There are very strict testing requirements for the conducted noise and radiated noise at the power interface of electronic products with external power supplies. If the noise exceeds the standard, it will affect the normal operation of other electronic products and will also affect the performance and stability of their own circuits.

[0003] Commonly used filter circuits include passive filtering and active filtering. The main forms of passive filtering include capacitor filtering, inductor filtering and compound filtering (L-type, LC filtering, RC filtering, etc.). The main form of active filtering is active RC filtering, also known as electronic filtering.

[0004] The noise in the power supply part includes differential mode noise and common mode noise. Ordinary filtering circuits are generally only effective for differential mode noise and cannot solve the impact of common mode noise.

[0005] Common mode inductors, also called common mode chokes, are often used to suppress common mode noise, but they are large and expensive. Especially for electronic devices with relatively high power, common mode inductors are large and expensive to ensure current flow capacity, which is not conducive to circuit design and system integration. Summary of the invention

[0006] The object of the present invention is to provide a filtering circuit to solve the problem that the existing filtering circuit is difficult to suppress common mode noise.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A filter circuit comprises a first PCB layer and a second PCB layer;

[0009] The first PCB layer includes a power line, a power interface, a second filter capacitor, and a first filter capacitor; the power line includes a power network and a GND network;

[0010] The second PCB layer includes a conductor plane;

[0011] The power interface is connected to the GND network, and the power interface is also connected to the conductor plane;

[0012] The GND network, the second filter capacitor, and the conductor plane are connected in sequence;

[0013] The power supply network, the first filter capacitor and the conductor plane are connected in sequence.

[0014] The circuit design and overall layout design concept of the circuit structure of the present invention have a good suppression effect on common mode noise, differential mode noise, radiation noise and conduction noise.

[0015] Preferably, an intermediate layer is provided between the first PCB layer and the second PCB layer, and a plurality of via holes are provided on the intermediate layer.

[0016] Preferably, the second filter capacitor is connected to the conductor plane through a via hole in the middle layer; the first filter capacitor is connected to the conductor plane through a via hole in the middle layer; and the power interface 107 is connected to the conductor plane through a via hole in the middle layer.

[0017] Preferably, a third filter capacitor is further included, one end of the third filter capacitor is connected to the power supply network 106, and the other end is connected to the GND network.

[0018] Preferably, it further comprises a first filtering module and a second filtering module, the first filtering module is arranged on the power supply network, and the second filtering module is arranged on the GND network.

[0019] Preferably, the first filtering module and the second filtering module are inductors or magnetic beads or common-mode chokes.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] A filter circuit, the first PCB layer is composed of a power line, a power interface, a second filter capacitor, and a first filter capacitor; the power line includes a power network and a GND network; the second PCB layer is provided with a conductor plane; the power interface is connected to the GND network, and the power interface is also connected to the conductor plane; the GND network, the second filter capacitor, and the conductor plane are connected in sequence; the power network, the first filter capacitor, and the conductor plane are connected in sequence. The circuit design of the circuit structure of the present invention and the overall layout design concept have a good suppression effect on common mode noise, differential mode noise, radiation noise, and conduction noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the Layout structure of the present invention.

[0023] Figure 2 Schematic diagram of the circuit principle of Example 1.

[0024] Figure 3 Schematic diagram of the circuit principle of Example 2.

[0025] Figure 4 Schematic diagram of the circuit principle of Example 3.

[0026] Figure 5 The test results of conducted noise without using the circuit of the present invention.

[0027] Figure 6 Conducted noise test results using the circuit of the present invention.

[0028] Figure 7 Radiated noise test results using the circuit of the present invention.

[0029] Figure 8 The radiation noise test results of the circuit without using the present invention.

[0030] Markings in the figure: 101A-first PCB layer, 101B-middle layer, 101C-second PCB layer, 102-second filter capacitor, 103-first filter capacitor, 104-power line, 105-GND network, 106-power network, 107-power interface, 108-first metal via, 109-conductor plane, 110-air avoidance area, 111-third filter capacitor, 112-first filter module, 113-second filter module, 114-second metal via, 115-third metal via. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0033] Example 1

[0034] like Figure 1A filtering circuit shown includes a first PCB layer 101A and a second PCB layer 101C; the first PCB layer includes a power line 104, a power interface 107, a second filter capacitor 102, and a first filter capacitor 103; the power line 104 includes a power network 106 and a GND network 105; the second PCB layer 101C includes a conductor plane 109; the power interface 107 is connected to the GND network 105, and the power interface 107 is also connected to the conductor plane 109 through a first metal via 108; the GND network 105 is connected to one end of the second filter capacitor 102, and the other end of the second filter capacitor 102 is connected to the conductor plane 109 through a third metal via 115; the power network 106 is connected to one end of the first filter capacitor 103, and the other end of the first filter capacitor 103 is connected to the conductor plane 109 through a second metal via 114. An intermediate layer is also provided between the first PCB layer 101A and the second PCB layer 101C. The intermediate layer 101B is provided with a plurality of vias, and the vias are used to pass through metal vias. The intermediate layer can be a dielectric layer or an electrical layer plus a dielectric layer. The second filter capacitor 102 is connected to the conductor plane 109 through the vias of the intermediate layer 101B; the first filter capacitor 103 is connected to the conductor plane 109 through the vias of the intermediate layer 101B; and the power interface 107 is connected to the conductor plane 109 through the vias of the intermediate layer 101B.

[0035] Combination Figure 2 The circuit schematic diagram shows that the filtering effect of the present invention has a significant effect on the noise reduction of differential mode noise and common mode noise. Specifically:

[0036] For differential mode noise, path 1 of the differential mode noise current on the power network is GND network 105->second filter capacitor 102->third metal via 115->conductor plane 109->first metal via 108->power interface 107->GND network 105; path 2 of the differential mode noise current is power network 106->first filter capacitor 103->second metal via 114->conductor plane 109->first metal via 108->power interface 107->GND network 105; after the differential mode noise enters the PCB from the power line 104, it passes through a loop and then returns to the power line 104, effectively blocking the noise outside the PCB. Common mode noise exists on both the power supply network and the GND network. The path of common mode noise is GND network 105->second filter capacitor 102->third metal via 115->conductor plane 109->first metal via 108->power interface 107->GND network 105 and power supply network 106->first filter capacitor 103->second metal via 114->conductor plane 109->first metal via 108->power interface 107->GND network 105. After the common mode noise enters the PCB from the power line 104, it also passes through a loop and returns to the power line 104, effectively blocking the noise outside the PCB. Although the common mode noise and differential mode noise are the same in terms of path, the filtering principles are different.

[0037] Example 2

[0038] The difference between the second embodiment and the first embodiment is that the third filter capacitor 111 is further included. One end of the third filter capacitor 111 is connected to the power supply network 106, and the other end is connected to the GND network 105. Figure 3 shown.

[0039] The third filter capacitor 111 is added to further optimize the filtering effect of the differential mode noise, because the third filter capacitor 111 provides another noise current path for the differential mode noise, and the specific path is GND network 105->third filter capacitor 111->power supply network 106 or power supply network 106->third filter capacitor 111->105GND network. The third filter capacitor 111 can be one filter capacitor or multiple filter capacitors, and the capacitance value of the capacitor can be selected according to the required filtering frequency, such as 1nF or 100pF.

[0040] Figure 5 The test result of the conducted noise of the filter circuit without using the circuit of the present invention but only the third filter capacitor 111 shows that the conducted noise of the low-frequency part below 1 MHz exceeds the standard seriously. Figure 6 This is the test result of the conducted noise using the circuit design of the second embodiment. The result shows that the noise within the test range does not exceed the standard, and the noise suppression effect is close to 30dBuV.

[0041] Figure 8 The test results of the radiation noise of the filter circuit with S6 structure are shown in Figure 1, which does not use the circuit of the present invention. The results show that the noise at 199MHz, 375MHz and 625MHz exceeds the standard seriously. Figure 7 This is the radiation noise test result of the circuit design of Example 2. The result shows that the radiation noise does not exceed the standard at all frequencies within the test range. The noise suppression effect is close to 30dBuV / m.

[0042] Example 3

[0043] The difference between the present embodiment 3 and the embodiment 2 is that it further comprises a first filter module 112 and a second filter module 113. The first filter module 112 is arranged on the power supply network 106, and the second filter module 113 is arranged on the GND network 105. The first filter module 112 and the second filter module 113 are inductors, magnetic beads or common mode chokes, such as Figure 4 shown.

[0044] The first filter module 112 and the second filter module 113 are added to further optimize the filtering effect of the common mode noise. The first filter module 112 and the second filter module 113 can be inductors, magnetic beads, and common mode chokes. The number of the first filter module 112 and the second filter module 113 can be multiple, and they are selected according to the current size of the actual circuit and the frequency desired to be filtered.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A filter circuit, characterized in that: Includes a first PCB layer and a second PCB layer; The first PCB layer includes a power line, a power interface, a second filter capacitor, and a first filter capacitor; the power line includes a power network and a GND network; A third filter capacitor, one end of the third filter capacitor is connected to the power network, and the other end is connected to the GND network; The second PCB layer includes a conductor plane; The power interface is connected to the GND network, and the power interface is also connected to the conductor plane; The GND network, the second filter capacitor, and the conductor plane are connected in sequence; the power supply network, the first filter capacitor, and the conductor plane are connected in sequence; The power interface is connected to the conductor plane through a first metal via; the GND network is connected to one end of the second filter capacitor, and the other end of the second filter capacitor is connected to the conductor plane through a third metal via; the power network is connected to one end of the first filter capacitor, and the other end of the first filter capacitor is connected to the conductor plane through a second metal via; Three noise current paths are formed: From the GND network through the second filter capacitor, through the third metal via, through the conductor plane, through the first metal via, through the power interface, and finally back to the GND network; From the power network through the first filter capacitor, through the second metal via, through the conductor plane, through the first metal via, through the power interface, and finally back to the GND network; From the GND network through the third filter capacitor and then through the power network or the GND network and then through the third filter capacitor and finally back to the GND network; The noise current enters the PCB from the power line 104 and then returns to the power line 104 through a loop, thereby isolating the noise outside the PCB.

2. A filter circuit according to claim 1, characterized in that: An intermediate layer is further arranged between the first PCB layer and the second PCB layer. The intermediate layer is a dielectric layer or a dielectric layer plus an electrical layer. A plurality of vias are arranged on the intermediate layer.

3. A filter circuit according to claim 2, characterized in that: The second filter capacitor is connected to the conductor plane through a via hole in the middle layer; the first filter capacitor is connected to the conductor plane through a via hole in the middle layer; and the power interface is connected to the conductor plane through a via hole in the middle layer.

4. A filter circuit according to claim 1, characterized in that: It also includes a first filtering module and a second filtering module. The first filtering module is arranged on the power supply network, and the second filtering module is arranged on the GND network.

5. A filter circuit according to claim 4, characterized in that: The first filtering module and the second filtering module are inductors, magnetic beads or common mode chokes.

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