Application Note Please read the Important Notice and Warnings at the end of this document V 0.1 www.infineon.com page 1 of 13 2025-07-23 AN171411 Design guide for low-noise transistors for 6 GHz in space application HiRel NPN Silicon RF Transistor Scope and purpose This application note provides application circuit design examples of Infineon’s HiRel NPN Silicon RF Transistor for low-noise amplifiers (LNAs). In this document, the transistor-based LNA schematics, printed circuit board (PCB) layouts and measurement results are shown. This document is relevant to the following HiRel devices: • BFY740B-02(ES) Product features • For L, S, C, X-frequency bands • Ideal for low noise amplifiers • Hermetically sealed microwave package Intended audience This document is intended for engineers who need to design LNAs. Table of contents Table of contents ............................................................................................................................ 1 1 Introduction .......................................................................................................................... 2 1.1 Radio front ends for space applications ................................................................................................. 2 1.2 Infineon HiRel NPN Silicon RF Transistor ............................................................................................... 2 2 6 GHz band LNA application circuits ......................................................................................... 3 2.1 Performance overview ............................................................................................................................ 3 2.2 Schematic ................................................................................................................................................ 4 2.3 Bill of materials........................................................................................................................................ 5 2.4 Evaluation boards and layout information ............................................................................................ 6 2.5 Measurement results of the 6 GHz band LNAs ....................................................................................... 7 3 Authors ................................................................................................................................ 11 Revision history............................................................................................................................. 12 Application Note 2 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz Introduction 1 Introduction 1.1 Radio front ends for space applications Infineon’s broad range of high-performance and high reliability silicon bipolar transistors are ideal for low noise and high-gain broadband amplifiers and are supplied in hermetically sealed microwave transistor packages as well as chips. Using Infineon’s radiation hard high reliability RF microwave technology, the diverse portfolio of microwave bipolar junction transistors is available in a range of frequencies and voltage classes and are qualified for use for applications in both space and aerospace industries. Filter SPDT SwitchAntenna LNA PA RX TX Figure 1 Example of radio front end block diagram 1.2 Infineon HiRel NPN Silicon RF Transistor With nearly 50 years of space heritage, Infineon’s radiation hard HiRel microwave transistors are offered in hermetically sealed ceramic packages and used in a wide range of space missions. Application examples are first and second stage LNA’s, oscillators, and mixers. Infineon’s HiRel silicon bipolar transistor product range covers different generations of RF microwave transistor technology from bipolar Si to SiGe based devices. RF bipolar transistors with different voltage classes, frequency ranges, and output power, are available and based on Infineon’s vast microwave bipolar transistor technical knowledge. With different bipolar transistor types to choose from, Infineon’s high reliability microwave bipolar junction transistor devices are available in different quality levels: Professional (P), which are designed for Engineering Modules and used for breadboards and circuit evaluation, and ESCC qualified (ES), which fulfills the requirements of the European Space Agency (ESA) for Flight Modules. Their optimized inner transistor cell structure leads to best-in-class power gain and NF at high frequencies, including 6 GHz bands. Application Note 3 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits 2 6 GHz band LNA application circuits 2.1 Performance overview The following table shows the performance of the 6 GHz band low-noise transistors. Table 1 Summary of measurement results for the 6 GHz band LNA Parameter Symbol Value Unit Notes Device BFY740B-02(ES) Bias voltage VCC 3.3 V Bias current ICC 26.4 mA Frequency f 6.0 GHz Gain G 14.0 dB NF NF 1.56 dB PCB and SMA loss subtracted: 0.15 dB Input return loss RLin 10.6 dB Output return loss RLout 12.8 dB Reverse isolation ISOrev 22.1 dB Output 1 dB compression point OP1dB 8.6 dBm Measured at 6.0 GHz Output third-order intercept point OIP3 15.3 dBm Input power: -30 dBm Tone 1: 6000 MHz Tone 2: 6001 MHz Stability K >1 Measured from 10 MHz to 15 GHz Application Note 4 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits 2.2 Schematic The following figure shows the schematic of the 6 GHz band LNAs with Infineon HiRel NPN Silicon RF Transistor BFY740B-02(ES). In the LNA circuit, resistors R1 and R2 stand for transistor voltage and current bias; meanwhile, they form a negative DC feedback mechanism to stabilize the transistor bias points in various conditions. Capacitors C3 and C4 serve as the RF bypass. Transistor input matching is achieved by C1, C2, and L1. The output matching network is formed by C5, L2, and R3. Resistor R3 also has the function of improving circuit stability. Figure 2 6 GHz band LNA schematic Application Note 5 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits 2.3 Bill of materials Table 2 BOM of the 6 GHz band LNAs Symbol Value Package/size Manufacturer Notes Q1 BFY740B-02(ES) Micro-X Infineon SiGe:C bipolar low-noise transistor C1 6.8 pF 0402 Murata Input matching and DC blocking C2 0.3 pF 0402 Murata Input matching C3 47 nF 0402 Murata RF decoupling C4 47 nF 0402 Murata RF decoupling C5 4.7 pF 0402 Murata Output matching and DC blocking R1 22 ohm 0402 Various DC bias and DC negative feedback R2 15 kohm 0402 Various DC biasing for transistor base R3 39 ohm 0402 Various Low-frequency stability improvement L1 6.8 nH 0402 LQW Murata RF choke and input matching L2 4.7 nH 0402 LQW Murata RF choke and output matching Application Note 6 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits 2.4 Evaluation boards and layout information The evaluation boards for the 6 GHz band LNAs: • PCB material: FR4 • PCB marking: − BFY740 Micro-X The detailed description of the PCB stack and photos of the 6 GHz band LNAs’ evaluation boards are shown in the following figures. Copper 35 μm Gold plated FR4 core, 0.2 mm FR4 preg, 1 mm Vias Copper 35 μm Gold plated Copper 18 μm Figure 3 PCB stack information for the evaluation board Figure 4 Photo of the evaluation board with marking Micro-X 6Hz LNA Application Note 7 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits 2.5 Measurement results of the 6 GHz band LNAs Figure 5 Small-signal gain of the 6 GHz band LNA Figure 6 Input return loss measurement of 6 GHz band LNA Application Note 8 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits Figure 7 Output return loss measurement of the 6 GHz band LNA Figure 8 Reverse isolation measurement of the 6 GHz band LNA Application Note 9 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits Figure 9 NF measurement of the 6 GHz band LNA Figure 10 Input 1 dB compression point measurement at 6 GHz Application Note 10 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz 6 GHz band LNA application circuits Figure 11 Output IMD3 measurement of the 6 GHz band LNA Figure 12 Stability K-factor plots of the 6 GHz band LNAs Application Note 11 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz Authors 3 Authors Ishrat Mahbub, Application engineer of business unit RF and sensors Markus Lehner, Product marketing Manager, HiRel Application Note 12 of 13 V 0.1 2025-07-23 Design guide for low-noise transistors in WLAN front ends for 6 to 7 GHz Revision history Revision history Document version Date of release Description of changes V1.0 10.07.2025 Release of application note Trademarks All referenced product or service names and trademarks are the property of their respective owners. Edition 2024-06-31 AN_171411 Published by Infineon Technologies AG 81726 Munich, Germany © 2025 Infineon Technologies AG. All Rights Reserved. Do you have a question about this document? Email: [email protected] Document reference IMPORTANT NOTICE The information contained in this application note is given as a hint for the implementation of the product only and shall in no event be regarded as a description or warranty of a certain functionality, condition or quality of the product. Before implementation of the product, the recipient of this application note must verify any function and other technical information given herein in the real application. Infineon Technologies hereby disclaims any and all warranties and liabilities of any kind (including without limitation warranties of non- infringement of intellectual property rights of any third party) with respect to any and all information given in this application note. 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