NXP Semiconductors BF998,235

Overview

BF998,235 from NXP Semiconductors is a silicon N-channel dual-gate MOSFET in SOT143B package, designed for VHF/UHF RF amplification with 24 mS forward transfer admittance, 2.1 pF gate-1 input capacitance, and 1 dB noise figure at 800 MHz. It operates at 12 V supply, delivers up to 30 mA drain current, and is used in television tuners and professional communications receivers.

For engineers reviewing the BF998,235 datasheet, BF998,235 pinout, BF998,235 application, or BF998,235 equivalent, this page provides verified pin configuration, noise performance at UHF frequencies, AGC capability via gate-2 control, thermal derating curves, and validated alternatives for RF front-end design.

Technical Context

The BF998,235 is a depletion-mode dual-gate MOSFET with source and substrate internally connected, featuring integrated back-to-back protection diodes between gates and source. Its gate-1 controls RF signal path while gate-2 enables automatic gain control (AGC) without external bias networks.

It exhibits low reverse transfer capacitance (25 fF), high y_fs/C_ig1-s ratio, and stable noise figure across 200–800 MHz - optimized for cascode or common-source amplifier stages in 12 V-powered tuners where isolation and gain linearity are critical.

Key Specifications

Pinout & Package

BF998,235 is housed in a plastic surface-mounted SOT143B package (4-lead microminiature outline), with dimensions D = 2.8–3.0 mm, E = 1.2–1.4 mm, and body height A = 0.9–1.1 mm. The device uses standard JEDEC SC-61 footprint with pin 1 = source/substrate, pin 2 = drain, pin 3 = gate 2, pin 4 = gate 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BF998,235, BF998R,215 offers identical RF parameters but mandates layout changes due to reversed pinning, whereas MRF901LT1 sacrifices AGC functionality for higher power dissipation and larger footprint - making BF998,235 the optimal choice for space-constrained, gain-controlled VHF/UHF amplifiers.

Availability

BF998,235 is available at Aetrix Electronics and suitable for television tuners, professional UHF receivers, and wireless microphone preamplifiers requiring stable component supply, consistent parametric performance, and long-term obsolescence management.

Supply support for BF998,235 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 specializing in high-performance RF, analog, and mixed-signal solutions for consumer, industrial, and communications markets.

The BF998,235 belongs to NXP's legacy RF transistor product line, engineered specifically for low-noise, gain-controllable amplification in VHF/UHF tuner and receiver applications - emphasizing compact size, ESD robustness, and stable high-frequency performance.

FAQ

What is the maximum drain-source voltage rating for BF998,235?

The BF998,235 has a maximum drain-source voltage (V_DS) rating of 12 V, as specified in both Quick Reference Data and Limiting Values sections of the official NXP datasheet. This rating applies under all operating conditions and must not be exceeded to prevent permanent device damage. The BF998,235 is intended for use in 12 V-powered RF amplifier stages such as TV tuners and UHF receivers.

Does BF998,235 support automatic gain control (AGC)?

Yes, BF998,235 supports AGC through its gate-2 terminal: applying a variable DC voltage (0–8 V) to pin 3 modulates gain over >40 dB range, as confirmed by Figures 19 and 20 in the datasheet. This function is intrinsic to the dual-gate structure and requires no external components - a key differentiator from single-gate alternatives like MRF901LT1. The BF998,235 thus enables compact, high-linearity AGC in tuner front-ends.

What package type is used for BF998,235?

BF998,235 uses the SOT143B surface-mount package - a 4-lead microminiature plastic outline with standard SC-61 footprint, measuring approximately 3.0 × 1.4 × 1.1 mm. Pin 1 is source/substrate, pin 2 is drain, pin 3 is gate 2, and pin 4 is gate 1. This differs from BF998R,215 which uses SOT143R with reversed pin order. The BF998,235 package is optimized for RF layout with low parasitic inductance and integrated ESD protection.

What is the typical noise figure of BF998,235 at 800 MHz?

The typical noise figure of BF998,235 is 1 dB at 800 MHz, measured under conditions of G_S = 3.3 mS and B_S = B_Sopt, as stated in the Dynamic Characteristics table on page 4 of the NXP datasheet. This value is validated across production lots and forms the basis for its use in low-noise amplifier stages of UHF receivers and digital TV tuners where signal integrity is critical. The BF998,235 maintains sub-1.5 dB noise figure up to 1 GHz.

How is the substrate connected in BF998,235?

In BF998,235, the substrate is internally connected to the source terminal (pin 1), as explicitly stated in the DESCRIPTION section: "source and substrate interconnected." This configuration simplifies biasing in common-source amplifier topologies and ensures predictable junction temperature behavior. No external substrate connection is required - the BF998,235 functions correctly with pin 1 grounded, and this internal tie is consistent across all SOT143B-packaged BF998 variants.