NXP Semiconductors BF909WR,135

Overview

BF909WR from NXP Semiconductors is an N-channel dual-gate MOSFET in SOT343R package, designed for low-noise RF amplification up to 1 GHz with 43 mS typical forward transfer admittance, 3.6 pF gate-1 input capacitance, and 2.0 dB minimum noise figure at 800 MHz - deployed in VHF/UHF TV tuners and professional communications equipment.

For engineers reviewing the BF909WR datasheet, BF909WR pinout, BF909WR application, or BF909WR equivalent, key selection criteria include its 5 V supply optimization, cross-modulation performance under AGC, dual-gate bias architecture, and SOT343R thermal resistance (R_{th j-a} = 350 K/W).

Technical Context

The BF909WR employs enhancement-mode dual-gate topology where Gate 1 serves as RF input and Gate 2 as AGC-controlled bias node, enabling gain control without degrading cross-modulation. Its internal substrate-source interconnection stabilizes operation across 3–7 V supply range.

Static characteristics specify VG1-S(th) = 0.3–1.0 V and VG2-S(th) = 0.3–1.2 V at ID = 20 µA, while dynamic performance is characterized at VDS = 5 V, VG2-S = 4 V, ID = 15 mA - yielding |y_fs| = 36–50 mS and C_ig1-s = 3.6–4.3 pF at 1 MHz.

Key Specifications

Pinout & Package

Package: SOT343R - plastic microminiature surface-mount package with reverse pinning (top view: Pin 1 = source/bulk, Pin 2 = drain, Pin 3 = gate 2, Pin 4 = gate 1), footprint 2.2 × 1.35 mm, 0.65 mm pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-gate MOSFET amplifier applications.

Compared with BF909WR, BF998,115 delivers extended bandwidth at the cost of pinout redesign and reduced ESD robustness, while MRF901T1 offers higher power handling but demands additional external bias components and increases BOM count.

Availability

BF909WR is available at Aetrix Electronics and suitable for VHF/UHF television tuners, professional communications equipment, RF signal generators, and lab-grade IF amplifiers requiring stable component supply across industrial and broadcast production cycles.

Supply support for BF909WR includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

NXP Semiconductors is a global semiconductor company specializing in high-performance RF, analog, and mixed-signal solutions for automotive, industrial, and consumer applications.

The BF909WR belongs to NXP's legacy RF transistor product line, engineered specifically for low-noise, dual-gate amplifier functions in broadcast and professional wireless infrastructure - emphasizing AGC linearity and 5 V system compatibility.

FAQ

What is the maximum drain-source voltage rating for the BF909WR?

The BF909WR has a maximum drain-source voltage (V_DS) rating of 7 V, as defined in the Absolute Maximum Ratings table. This limit applies under all operating conditions and must not be exceeded to prevent permanent device damage. The BF909WR is optimized for 5 V supply systems, and operation near the 7 V ceiling requires careful attention to transient voltage spikes and PCB layout parasitics.

How does the BF909WR achieve low cross-modulation during AGC operation?

The BF909WR achieves low cross-modulation during AGC through its internal bias circuit that interconnects source and substrate, combined with separate Gate 1 (RF input) and Gate 2 (AGC control) terminals. This architecture maintains channel charge stability during gain reduction, resulting in <60 dBµV unwanted voltage at 1% cross-modulation - a performance metric verified in the datasheet's Fig.3 under V_DS = 5 V and V_GG = 5 V conditions.

What is the thermal resistance from junction to ambient for the BF909WR?

The BF909WR has a thermal resistance from junction to ambient (R_{th j-a}) of 350 K/W when mounted on a standard printed-circuit board, as specified in the Thermal Characteristics section. This value assumes standard JEDEC test conditions and implies that at 15 mA drain current and 5 V drain-source voltage, the junction temperature rise will be approximately 52.5 °C above ambient - necessitating appropriate copper pour or thermal vias for sustained operation.

Can the BF909WR be used with a 3 V supply?

Yes, the BF909WR is rated for VHF and UHF applications with 3 to 7 V supply voltage, as stated in the Applications section. While its optimal noise figure and gain are characterized at 5 V, functional operation is confirmed down to 3 V - though |y_fs decreases and noise figure rises slightly. Designers should consult Fig.10 and Fig.11 in the datasheet to validate ID vs. V_DS and V_G2-S behavior at 3 V bias points.

What is the gate-1 input capacitance of the BF909WR at 1 MHz?

The gate-1 input capacitance (C_ig1-s) of the BF909WR is 3.6 pF typical and 4.3 pF maximum at 1 MHz, per the Quick Reference Data and Dynamic Characteristics tables. This low capacitance supports broadband impedance matching in 50 Ω RF designs and contributes to the device's ability to operate linearly up to 1 GHz without excessive loading of preceding stages.