NXP Semiconductors BF998WR,115

Overview

BF998WR from NXP Semiconductors is an N-channel dual-gate MOSFET designed for low-noise, high-gain RF amplification in VHF/UHF front-ends. It delivers 24 mS forward transfer admittance, 2.1 pF gate-1 input capacitance, and 1 dB noise figure at 800 MHz, operating with 12 V supply in television tuners and professional communications equipment.

For engineers reviewing the BF998WR datasheet, BF998WR pinout, BF998WR application, or BF998WR equivalent, this device is selected for gain-controlled amplifier stages requiring stable transconductance, low reverse transfer capacitance (25 fF), and integrated gate protection diodes - critical for tuner AGC loops and broadband RF preamplifiers.

Technical Context

The BF998WR employs a depletion-mode dual-gate structure with source and substrate internally connected, enabling independent bias control of gate 1 (signal input) and gate 2 (gain control). Its short-channel design achieves high y_fs/C_ig1-s ratio (11.4 mS/pF typical), optimizing gain-bandwidth trade-offs up to 1 GHz.

Integrated back-to-back diodes between each gate and source provide ESD protection without external components. The device operates in common-source configuration with fixed V_G2-S = 4 V and variable V_G1-S, supporting automatic gain control (AGC) over >10 dB range at both 200 MHz and 800 MHz.

Key Specifications

Pinout & Package

BF998WR is housed in a plastic microminiature SOT343R package (4-pin, reverse pinning), optimized for high-frequency PCB layout with minimal parasitic inductance. Source and substrate are internally bonded to Pin 1 (s,b), enabling simplified grounding in RF matching networks.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BF998WR, BF998W,115 offers identical RF performance but mandates PCB redesign for pinout compatibility, while MRF9011LT1 trades integrated protection and low C_rs for higher power - making BF998WR optimal for space-constrained, ESD-sensitive tuner modules where layout reuse and stability are prioritized.

Availability

BF998WR is available at Aetrix Electronics and suitable for television tuners, professional UHF transceivers, and VHF aircraft band receivers requiring stable component supply across long-lifecycle consumer and industrial programs.

Supply support for BF998WR 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 leader specializing in high-performance RF, analog, and mixed-signal solutions for automotive, industrial, and consumer markets.

The BF998WR belongs to NXP's legacy RF transistor product line, engineered specifically for low-noise, gain-controllable amplification in broadcast and communications front-ends operating from VHF through UHF.

FAQ

What is the maximum drain-source voltage rating for BF998WR?

The BF998WR has a maximum drain-source voltage (V_DS) rating of 12 V, as specified in the Limiting Values table. This rating is absolute maximum and must not be exceeded under any operating condition. Operation at 12 V is standard in television tuner applications, and the device is characterized for reliable performance at this voltage with V_G2-S = 4 V and I_D = 10 mA. Exceeding 12 V risks permanent damage per IEC 60134 Absolute Maximum Ratings.

Does BF998WR include built-in ESD protection?

Yes, the BF998WR integrates back-to-back diodes between each gate (g1 and g2) and the source (s,b), providing inherent protection against electrostatic discharge during handling and PCB assembly. This eliminates the need for external gate protection components in most tuner designs. The datasheet explicitly states this feature under "DESCRIPTION", and pinning diagrams confirm diode connections to pins 1 (s,b), 3 (g2), and 4 (g1). Static discharge protection remains effective only when gate-source voltage stays within ±10 mA current limits.

What is the typical noise figure of BF998WR at 800 MHz?

The typical noise figure (F) of BF998WR at 800 MHz is 1 dB, measured under conditions of G_S = 3.3 mS and B_S = B_Sopt, as documented in the DYNAMIC CHARACTERISTICS section. This value is confirmed in both the Quick Reference Data and detailed Dynamic Characteristics tables. The 1 dB figure reflects optimized low-noise performance for UHF digital TV reception and professional wireless links, and is achievable using the recommended test circuit in Figure 16 of the datasheet.

How does the dual-gate structure of BF998WR support automatic gain control (AGC)?

The BF998WR's dual-gate architecture enables AGC by applying a variable DC voltage to gate 1 (g1) while holding gate 2 (g2) at a fixed bias (typically 4 V). As shown in Figures 17 and 18, varying V_AGC across g1 produces >10 dB of gain reduction at both 200 MHz and 800 MHz. This direct transconductance modulation - confirmed by transfer characteristic curves (Figure 3) - allows analog AGC loop implementation without additional active components, making BF998WR ideal for tuner IC integration where g1 serves as the controlled input path.

What is the thermal resistance from junction to ambient (R_{th j-a}) for BF998WR?

The thermal resistance from junction to ambient (R_{th j-a}) for BF998WR is 350 K/W, specified with the device mounted on a printed-circuit board per note 1 in the THERMAL CHARACTERISTICS table. This value assumes standard FR-4 board construction and defines the worst-case thermal path for power dissipation up to 300 mW. For thermal design, junction temperature can be estimated as T_j = T_amb + (P_diss × 350), and must remain ≤150 °C. Derating begins above 45 °C ambient, as shown in Figure 2.