Microstrip line impedance matching method and structure for improving transmission performance deterioration

Abstract

The invention discloses a microstrip line impedance matching method and structure for improving transmission performance deterioration, and the method comprises the steps: S1, changing the impedance characteristic through adjusting the height between a microstrip line and a reference ground for the discontinuous impedance when a bonding pad larger than the microstrip line in width exists on the microstrip line; s2, hollowing out a reference ground layer part corresponding to the bonding pad, and determining the number of layers of the printed board which needs to be hollowing out below the bonding pad according to a microstrip line impedance calculation formula; and S3, changing part of the reference ground into a grounding layer located at the lower part, changing part of the corresponding dielectric thickness, adjusting the dielectric thickness by adjusting the number of hollowed-out layers, and improving microstrip line impedance matching of the whole circuit. The structure comprises a microstrip line, a bonding pad and a hollow area. The problem of impedance discontinuity at the connection position of the microstrip transmission line and the device is solved, particularly the problem of transmission performance deterioration caused by the influence of the size of a bonding pad of the device is solved, a simple, practical and high-flexibility solution is provided, and the method can be widely applied to radio frequency circuit board design.

Description

Technical Field

[0001] The invention relates to the field of microstrip line impedance matching, and in particular to a microstrip line impedance matching method and structure for improving transmission performance degradation. Background Art

[0002] In modern wireless communication systems and radar systems, millimeter wave technology has been increasingly widely used, and the use of various high-performance millimeter wave integrated circuits has also increased. Microstrip lines are a very important form of transmission lines in existing millimeter wave integrated circuits. Their outstanding advantages are that they are compact and lightweight, and can be made into complex microwave circuits in a small volume using processes such as stereotypes, photolithography, and corrosion. They are also easy to integrate with other microwave electrical devices to achieve the integration of microwave components and systems, so they are widely used.

[0003] With the increasing miniaturization of microwave components and systems, the volume and weight requirements of microwave circuits have become increasingly stringent. Microstrip transmission lines have increasingly replaced waveguides to form microwave circuits, forming various complex planar circuits on the same substrate. The width of microstrip lines has become narrower and narrower, so the matching problem of microstrip lines has become more and more important. In the design of microwave circuits and systems, whether it is a passive circuit or an active circuit, its impedance matching problem must be considered.

[0004] The real field in the microstrip line is a mixed TE-TM wave field, and its longitudinal field components are mainly caused by the fringe fields EX and HX at the dielectric-air interface, which are very small compared to the transverse field components between the conductor strip and the ground plane. Therefore, the characteristics of the transmission mode in the microstrip line are very similar to the TEM mode, which is called the quasi-TEM mode. When microwave signals are transmitted between different devices, due to the influence of the pad size of the device, if there is no good transition structure to achieve matching, the transmission performance will be deteriorated, for example, causing additional insertion loss, signal reflection, exciting high-order modes and generating radiation, and even causing abnormal operation of the entire circuit system and damage to the device.

[0005] Impedance matching is a technical measure to make microwave circuits or systems non-reflective, carry traveling waves or as close to traveling waves as possible. In microwave circuit design, impedance matching is one of the important issues that must be considered to ensure effective power transmission, reduce reflection losses, and improve system efficiency. Summary of the invention

[0006] The present invention aims to solve the technical problem that when microwave signals are transmitted between different devices, the transmission performance is deteriorated due to the influence of the pad size of the device, and proposes a microstrip line impedance matching method and structure for improving the deterioration of transmission performance.

[0007] A microstrip line impedance matching method for improving transmission performance degradation comprises the following steps: S1: When there is a pad on the microstrip line that is larger than the width of the microstrip line, the impedance is discontinuous. The impedance characteristics are changed by adjusting the height between the microstrip line and the reference ground. S2: Hollow out the reference ground layer corresponding to the pad. According to the microstrip line impedance calculation formula, determine the number of printed circuit board layers that need to be hollowed out below the pad. The formula is: in, represents the characteristic impedance of the microstrip line, Represents the dielectric constant of the PCB board, Represents the distance from the trace to the reference ground plane, represents the width of the microstrip line, Represents the thickness of copper foil, It is a unit; S3: Part of the reference ground is changed to the ground layer located further down, and the dielectric thickness of the corresponding part is changed. The dielectric thickness is adjusted by adjusting the number of hollowed-out layers to improve the microstrip line impedance matching of the overall circuit.

[0008] Furthermore, a microstrip line impedance matching method for improving transmission performance degradation also includes the following sub-steps when there are a large number of pads: I1: The sudden change in pad size causes the deterioration of transmission performance, resulting in signal reflection and insertion loss in the circuit, and hollowing out the corresponding position of the original reference ground layer, making the reference ground of the circuit become the original ground layer below; I2: Increase the corresponding dielectric thickness of some parts to improve the impedance matching of the microstrip line of the overall circuit, obtain the electromagnetic characteristics of the RF line through electromagnetic simulation software, and make subtle adjustments through feedback from the electromagnetic software.

[0009] A microstrip line impedance matching structure for improving transmission performance degradation, comprising a microstrip line, a pad, and a hollowed-out area; When the number of pads does not exceed 2, the reference stratum corresponding to the pads is partially hollowed out to form a hollowed-out area; When the number of pads exceeds 2, the corresponding position of the original reference stratum will constitute a hollowed-out area.

[0010] The beneficial effects of the present invention are: through a microstrip line impedance matching method and structure for improving the deterioration of transmission performance, the impedance discontinuity problem at the connection between the microstrip transmission line and the device is improved, especially for the problem of transmission performance deterioration caused by the influence of the pad size of the device, a simple, practical and flexible solution is provided, which can be widely used in radio frequency circuit board design. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the circuit structure diagram of Example 1.

[0012] Figure 2 Reference stratigraphic structure diagram for Example 1.

[0013] Figure 3 This is an example diagram of microstrip line impedance calculation.

[0014] Figure 4 This is the circuit structure diagram of Example 2.

[0015] Figure 5 Reference stratigraphic structure diagram for Example 2.

[0016] Figure 6 The S11 curve obtained by simulating Example Circuit 1.

[0017] Figure 7 The S11 curve obtained by simulating Example Circuit 2.

[0018] in, Figure 1 -microstrip line, 2-soldering pad, 3-hollow area, 4-capacitor and resistor. DETAILED DESCRIPTION

[0019] The present invention is further described below, but the protection scope of the present invention is not limited to the following description.

[0020] As attached Figures 1 to 3 As shown in the specific embodiment 1, when the number of pads 2 is 1: When there is a pad 2 on the 50Ω microstrip line 1, the pad 2 is equivalent to a distributed capacitor, which destroys the continuity of the characteristic impedance of the microstrip line 1. The ground plane under the pad 2 is hollowed out to form a hollowed-out area 3, which is equivalent to increasing the height of the medium under the pad 2. According to the microstrip line impedance calculation formula: The impedance of the pad 2 part can be adjusted to about 50Ω to achieve the design goal of impedance continuity. There is a pad 2 at the end of the microstrip line 1 that is larger than the width of the microstrip line 1. This part causes impedance discontinuity. In order to obtain a good match, for the part with discontinuous impedance, the impedance characteristics are changed by adjusting the height of the microstrip line 1 and the reference ground. The current microstrip line width is 0.173mm, the pad 2 width is 1.99mm, and the dielectric thickness of the first layer is 0.1mm. The reference ground layer corresponding to the pad is hollowed out, and the reference ground of this part becomes the ground layer located further below, so that the dielectric thickness corresponding to this part changes. The dielectric thickness can be adjusted by adjusting the number of hollowed-out layers, so that the matching problem of the overall circuit is improved. According to the microstrip line impedance calculation formula, a pad 2 with a width of 1.99mm requires a dielectric with a thickness of about 0.815 to achieve an impedance of 50Ω. Based on this data, the number of printed circuit board layers that need to be hollowed out below the pad 2 can be roughly determined.

[0021] As attached Figures 4 and 5As shown in the specific embodiment 2, when the number of pads 2 is too large: For more complex circuits, this part of the circuit introduces more pads 2 of capacitors and resistors 4. The sudden change in the size of pads 2 during the period causes the deterioration of transmission performance, resulting in greater signal reflection and insertion loss in the circuit. For this circuit problem, the corresponding position of the original reference stratum can be hollowed out to form a hollowed-out area 3. The dielectric thickness corresponding to this part changes from the original h1 to h2. By adjusting h2 or adjusting the size of the hollowed-out area of ​​the ground layer 1, the matching problem of the overall circuit can be improved. Then, the electromagnetic characteristics of this section of the RF line can be easily obtained through electromagnetic simulation software, and fine adjustments can be made through the feedback of the electromagnetic software.

[0022] Specific Example 3 HFSS simulation results Achieve excellent transmission performance in the 0.1-20GHz frequency band. Using HFSS, you can get the impedance characteristics before and after the circuit optimization. In the simulation, the port settings of Pin1 and Pin2 are both lumped ports, the impedance is set to 50 ohms, and the solution frequency is set to 0.1-20GHz.

[0023] As attached Figure 6 As shown, the lower curve is the S11 result of the example circuit 1 without optimization, and the upper curve is the S11 result after optimization using the method of the present invention. The reflection coefficient of the structure input in the frequency band of 0.1-20GHz or even wider is below -20dB, and the matching is good, while the example circuit 1 has poor matching in the high frequency band.

[0024] As attached Figure 7 As shown, the lower curve is the S11 result of the example circuit 2 without optimization, and the upper curve is the S11 result after optimization using the method of the present invention. The reflection coefficient of the structure input in the frequency band of 0.1-20GHz or even wider is below -20dB, and the matching is good, while the example circuit 2 has poor matching in the high frequency band.

[0025] A microstrip line impedance matching method and structure for improving transmission performance degradation is used to improve the impedance discontinuity problem at the connection between the microstrip transmission line and the device, especially for the transmission performance degradation problem caused by the influence of the device pad size, a simple, practical and flexible solution is provided, which can be widely used in RF circuit board design.

[0026] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A microstrip line impedance matching method for improving transmission performance degradation, characterized in that: The following steps are involved: S1: When there is a pad (2) on the microstrip line (1) that is larger than the width of the microstrip line (1), resulting in impedance discontinuity, the impedance characteristics are changed by adjusting the height between the microstrip line (1) and the reference ground; S2: Hollow out the reference ground layer corresponding to the pad (2). According to the impedance calculation formula of the microstrip line (1), determine the number of printed circuit board layers that need to be hollowed out below the pad (2). The formula is: in, represents the characteristic impedance of the microstrip line (1), Represents the dielectric constant of the PCB board, Represents the distance from the trace to the reference ground plane, represents the width of the microstrip line (1), Represents the thickness of copper foil, It is a unit; S3: The reference ground of part is changed to the ground layer located further down, and the thickness of the corresponding dielectric is changed. The dielectric thickness is adjusted by adjusting the number of hollowed-out layers to improve the impedance matching of the microstrip line (1) of the overall circuit.

2. A microstrip line impedance matching method for improving transmission performance degradation according to claim 1, characterized in that: The method further includes the following sub-steps when there are a large number of pads (2): I1: The sudden change in the size of the pad (2) causes the transmission performance to deteriorate, causing signal reflection and insertion loss in the circuit, and hollowing out the corresponding position of the original reference ground layer, making the reference ground corresponding to the circuit become the original ground layer below; I2: Increase the corresponding dielectric thickness to improve the impedance matching of the microstrip line (1) of the overall circuit, obtain the electromagnetic characteristics of the RF line through electromagnetic simulation software, and make subtle adjustments based on the feedback of the electromagnetic software.

3. A microstrip line impedance matching structure for improving transmission performance degradation, implemented according to a microstrip line impedance matching method for improving transmission performance degradation according to any of claims 1 to 2, characterized in that: It includes a microstrip line (1), a pad (2), and a hollowed-out area (3); When the number of the pads (2) does not exceed 2, the reference stratum portion corresponding to the pads (2) is hollowed out to form a hollowed-out area (3); When the number of pads (2) exceeds 2, the corresponding positions of the original reference stratum are formed into a hollowing area (3).

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