NXP Semiconductors BF908R,235

Overview

BF908R,235 from NXP Semiconductors is a depletion-mode dual-gate MOSFET in SOT143R package, designed for low-noise RF amplification up to 1 GHz. It delivers 43 mS typical forward transfer admittance, 3.1 pF input capacitance at gate 1, and 1.5 dB noise figure at 800 MHz - enabling high-gain, low-distortion VHF/UHF signal conditioning in 12 V TV tuners and professional comms equipment.

For engineers reviewing the BF908R,235 datasheet, BF908R,235 pinout, BF908R,235 application, or BF908R,235 equivalent, key selection criteria include its dual-gate architecture for gain control, integrated back-to-back gate protection diodes, thermal resistance of 550 K/W, and validated performance at 800 MHz with 15 mA drain current under 8 V drain-source bias.

Technical Context

The BF908R,235 operates as a common-source RF amplifier with independent DC biasing on gate 1 (control) and gate 2 (RF input). Its dual-gate structure enables stable transconductance over temperature and supply variation, supported by −2 V gate 1 cut-off voltage and 4 V gate 2-source bias point.

It features integrated back-to-back diodes between each gate and source for ESD protection, and exhibits 30 fF reverse transfer capacitance and 1.7 pF output capacitance at 1 MHz - critical for minimizing Miller effect and maintaining broadband stability in tuned amplifier stages.

Key Specifications

Pinout & Package

BF908R,235 is housed in a plastic microminiature SOT143R surface-mount package (2.8 × 1.4 × 0.95 mm), optimized for RF layout with short internal leads and defined thermal path.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BF908R,235, BF998,215 offers superior RF performance at the cost of thermal headroom, while NE85633 provides a lower-cost, single-gate alternative lacking gain control - making BF908R,235 the optimal balance of noise, controllability, and SMT compatibility for tuner-grade designs.

Availability

BF908R,235 is available at Aetrix Electronics and suitable for digital TV tuners, professional UHF transceivers, VHF aircraft communication receivers, and UHF RFID reader front-ends requiring stable component supply across extended production lifecycles.

Supply support for BF908R,235 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 headquartered in Eindhoven, Netherlands, specializing in secure connectivity solutions for automotive, industrial, and consumer applications.

The BF908R,235 belongs to NXP's legacy RF transistor product line, engineered specifically for high-performance, low-noise amplification in VHF/UHF broadcast and communications equipment operating from 50 MHz to 1 GHz.

FAQ

What is the maximum drain-source voltage rating for BF908R,235?

The absolute maximum drain-source voltage (V_DS) for BF908R,235 is 12 V, as specified in the limiting values table. This rating applies under all operating conditions and must not be exceeded to prevent permanent device damage. The BF908R,235 is typically operated at 8 V V_DS to optimize noise figure and forward transfer admittance, aligning with its intended use in 12 V-supplied tuner circuits with appropriate biasing.

How does the dual-gate structure of BF908R,235 improve amplifier design?

The dual-gate structure of BF908R,235 separates RF signal injection (gate 2) from gain control (gate 1), enabling stable transconductance adjustment without disturbing DC bias or noise performance. Gate 2 is biased at 4 V for optimal noise/gain trade-off, while gate 1 accepts a variable DC voltage (0 to −2 V) to modulate gain - eliminating external AGC components. This architecture is integral to BF908R,235's role in TV tuners and professional radios.

What package type is used for BF908R,235 and how does it differ from BF908?

BF908R,235 uses the SOT143R package, a plastic microminiature surface-mount outline with pin 1 at bottom-left in top view (s,b), pin 2 (d), pin 3 (g2), pin 4 (g1). It differs from the BF908's SOT143 package in leadframe geometry and thermal resistance: BF908R,235 has 550 K/W R_{th j-a} (rated to 40 °C ambient), whereas BF908 has 500 K/W (rated to 50 °C ambient). Both share identical pinout and marking code %M2.

Does BF908R,235 include built-in ESD protection?

Yes, BF908R,235 integrates back-to-back diodes between each gate and source to protect against excessive input voltage surges. These diodes clamp gate-source voltages to ±10 mA peak current, providing inherent ESD robustness without requiring external protection components. This feature is explicitly documented in the device description and is a defining characteristic of BF908R,235's suitability for tuner front-end applications exposed to handling and environmental transients.

What is the typical noise figure of BF908R,235 at 200 MHz and 800 MHz?

The typical noise figure of BF908R,235 is 0.6 dB at 200 MHz and 1.5 dB at 800 MHz, measured under standardized conditions (V_DS = 8 V, I_D = 15 mA, V_G2-S = 4 V). These values are confirmed in the dynamic characteristics section of the datasheet and reflect BF908R,235's optimized performance across the VHF and lower UHF bands - critical for BF908R,235's deployment in broadcast and communications receivers.