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Weixin Official Accounts Platform Heroes Lecture Hall | Infineon Discrete Amplifier Transistor Emitter Microstrip Line Design Considerations Original Infineon Infineon Official Microblog Infineon Official Microblog Infineon Technologies (China) Co., Ltd. Our technology makes consumption a little less and yields a little more, it is always by your side. We make people’s lives more convenient, safe, and environmentally friendly. As a globally leading semiconductor company, Infineon’s microelectronic products and solutions take you to a beautiful future. 750 original contents July 18, 2024 11:01 Shanghai Li Dandan Infineon Power & Sensor Systems Division Infineon’s discrete amplifier transistors are typically used as low-noise amplifiers for reception, capable of covering frequencies within 12GHz. Infineon provides a series of different types of amplifier transistors, featuring low noise, high gain, high linearity, and low power consumption, widely used in different types of applications such as automotive active antennas, walkie-talkies, LIDAR, UWB, 5.8GHz radar, set-top boxes, etc. For different applications, Infineon provides corresponding application notes for customer reference, which introduce the amplifier transistor circuit schematic design, layout design, test results, and detailed test data. Customers can easily implement the schematic and layout design based on the information from the application notes, achieving the required functional and performance requirements. For the link to the official website application notes, please refer here. Common applications such as GNSS, FM, UWB, SDARS, WLAN, and LIDAR are included. Figure 1 Infineon Discrete Amplifier Transistor Application Notes Although the application notes provide detailed layout information, due to the difference between the customer’s motherboard and Infineon’s motherboard, the design of the emitter microstrip line needs to be adjusted based on the actual usage of the motherboard. This article will detail the role and adjustment methods of the emitter microstrip line, using the GNSS SOT343 device package design as an example. For the link to the official website GNSS application notes, please refer here. 1.1 Application Notes Schematic and Layout Information The following is the detailed design information of EVB board on page 7 of the GNSS application notes. From the above information, it can be seen: The emitter port is not directly drilled to the ground, but is drilled to the ground after a small section of microstrip line. The EVB board is a three-layer board, with the second layer being the reference ground, and the reference ground distance to the surface layer is 0.2mm. Figure 2 SOT343 package LNA evaluation board and emitter detailed design Figure 3 EVB reference board stack-up information 1.2 Role of Emitter Microstrip Line The emitter microstrip line plays a very important role in system design, mainly in the following two aspects: Ensuring the system stability factor k>1. Affecting the input matching and noise figure, gain. 1.3 Adjustment Methods of Emitter Microstrip Line with Different Reference Grounds In practical applications, it is common to encounter situations where the PCB board and the EVB board have different reference grounds. A common situation is the two-layer board design, with the surface layer being the RF pathway and the backside being the reference ground, and the board thickness being 1mm. For situations with different reference grounds, one principle should be followed, that is, the inductance value corresponding to the emitter port design of the PCB board and the EVB reference board should be the same, which will be described in detail below. First, we simulate to obtain the equivalent inductance value of the EVB board emitter port. Figure 4 Emitter port microstrip line and ground hole ADS simulation – board thickness 0.2mm Figure 5 Emitter port equivalent inductance value calculation – board thickness 0.2mm From the above ADS simulation results, it can be seen that the inductance value formed by the emitter port microstrip line and ground hole is 0.186nH. Next, adjust the Msub to be the actual reference ground thickness and change the microstrip line length to obtain an approximate inductance value of 0.186nH. Figure 6 Emitter port microstrip line and ground hole ADS simulation – board thickness 1mm Figure 7 Emitter port equivalent inductance value calculation – board thickness 1mm (blue for simulation data in Figure 6) Figure 7 inductor2 blue line is the equivalent inductance value of a single ground hole at 1mm board thickness (the simulation accuracy of the ADS VIAGND model at 1mm board thickness will be slightly worse, although there is some deviation from the actual value, it can still be used as a reference), the red line inductor is the equivalent inductance value at 0.2mm board thickness in Figure 4. From the simulation results, it can be seen that when the board thickness is 1mm, the inductance effect of a single ground hole is already equivalent to the sum of the microstrip line and ground hole at 0.2mm board thickness. If the microstrip line design is still consistent with the reference board at 1mm board thickness, the inductance value will be relatively large, the system stability will not be a problem, but the gain will decrease. Therefore, if you want to obtain the same gain as the reference board, you need to shorten the length of the microstrip line or drill directly to the ground. Appendix: 1. ADS Ground Hole Inductance Simulation Model The reference article for the ADS ground hole simulation model is: M. Goldfarb and R. Pucel. ‘Modeling Via Hole Grounds in Microstrip,’ IEEE Microwave and Guided Wave Letters, Vol. 1, No. 6, June 1991, pp. 135-137. 2. Relationship Curve between Ground Hole Inductance Value and Thickness (hole diameter fixed at 0.3mm) Figure 8 Relationship Curve between Ground Hole Inductance Value and Thickness (hole diameter fixed at 0.3mm) Looking for more applications or product information? Want to contact us to purchase products? 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