Infineon BFS481H6327XTSA1 RF Transistor: Datasheet, Features, and Application Circuit Design

The Infineon BFS481H6327XTSA1 is a high-performance NPN silicon germanium carbon (SiGe:C) RF bipolar junction transistor (BJT) packaged in a lead-free SOT-343 (SC-70) surface-mount device (SMD). It is engineered to deliver exceptional gains at very high frequencies, making it a premier choice for a wide array of wireless communication applications.

Key Features and Specifications

This transistor is distinguished by its impressive set of characteristics, optimized for low-noise amplification in the UHF and microwave bands. Its primary features include:

High Gain Performance: It offers a very high transition frequency (fT) of 25 GHz and a maximum oscillation frequency (fmax) of 45 GHz. This ensures excellent signal amplification capabilities well into the microwave range.

Low Noise Figure: With a low noise figure (NF) of just 0.9 dB at 1.8 GHz, it is exceptionally effective at amplifying weak signals without adding significant noise, which is critical for receiver front-ends.

High Linear Performance: The device provides outstanding linearity, characterized by an output third-order intercept point (OIP3) of up to +36 dBm. This minimizes distortion and intermodulation products in demanding multi-carrier systems.

Low Current Operation: It is designed to operate efficiently at very low collector currents, making it ideal for battery-powered and portable devices where power consumption is a key concern.

Datasheet Overview

The datasheet for the BFS481H6327XTSA1 provides all necessary information for circuit design and integration. Key absolute maximum ratings include a collector-emitter voltage of 3.5 V and a junction temperature of 150 °C. The detailed S-parameters, noise parameters, and DC characteristics graphs supplied across various frequencies and bias conditions are indispensable for simulating and optimizing circuit performance in tools like ADS or SPICE.

Application Circuit Design

A primary application for the BFS481H6327XTSA1 is as a Low-Noise Amplifier (LNA) in receiver chains. A typical application circuit for a 2.4 GHz LNA is outlined below.

Design Considerations:

1. Biasing: The transistor requires a stable DC bias point for optimal performance. A common-emitter configuration is typically used. The collector current (Ic) is often set between 10 mA to 20 mA using a voltage divider network at the base and a collector resistor (or RF choke) to achieve the desired operating point (e.g., Vce ≈ 2.5 V, Ic ≈ 15 mA).

2. Input/Output Matching: To maximize power transfer and minimize the noise figure, the input must be matched to the source impedance (typically 50 Ω) using the noise parameters (e.g., Gamma_opt) provided in the datasheet. The output is matched for maximum gain or linearity, depending on the system requirement. This is achieved using microstrip lines and matching networks with capacitors and inductors.

3. Stability: Ensuring the amplifier is unconditionally stable across all frequencies is paramount. This can be achieved by analyzing the stability factors (Rollett's K-factor and B1) using the S-parameters. Series feedback (a small emitter inductor) or shunt resistors are often incorporated to enhance stability without severely degrading noise performance.

4. Decoupling: Proper RF decoupling is critical to prevent unwanted oscillation and ensure stability. Capacitors are placed on the bias lines to decouple RF signals from the DC supply.

A simplified circuit would include:

Input matching network (L_match/C_match) connected to the base.

A RF choke or inductor in the collector bias path.

DC blocking capacitors at the input and output.

Bypass capacitors on the bias lines to ground.

ICGOOODFIND

ICGOOODFIND: The Infineon BFS481H6327XTSA1 stands out as a superior RF transistor for modern wireless systems. Its blend of exceptionally low noise figure, high gain at microwave frequencies, and excellent linearity makes it an ideal core component for designing high-performance LNAs in applications like GPS, cellular infrastructure (4G/5G), IoT modules, and satellite communication receivers. Its SMD package further facilitates compact and efficient PCB design.

Keywords: Low-Noise Amplifier (LNA), Silicon Germanium Carbon (SiGe:C), S-Parameters, Microwave Frequency, RF Transistor.