NXP Semiconductors BF904A,215

Overview

BF904A from NXP Semiconductors is an N-channel dual-gate MOSFET designed for low-noise, high-gain RF amplification in VHF/UHF tuners and professional communications equipment. It operates at 5 V supply, delivers 25 mS forward transfer admittance, exhibits 2.2 pF input capacitance at gate 1, and achieves 2 dB noise figure at 800 MHz.

For engineers reviewing the BF904A datasheet, BF904A pinout, BF904A application, or BF904A equivalent, this page provides verified package mapping (SOT143B), validated pin functions, confirmed AGC-compatible cross-modulation performance, and real-world RF amplifier use cases up to 1 GHz.

Technical Context

The BF904A integrates two cascaded MOSFET gates-gate 1 for signal input and gate 2 for automatic gain control (AGC)-with source and substrate internally connected. Its enhancement-mode structure enables stable biasing without external gate resistors when used with a 120 kΩ RG1 network.

It supports pulsed operation up to 30 mA drain current and maintains 22–30 mS |yfs| across junction temperatures from −65 °C to 150 °C. The device's 25 fF Crss and 2.2 pF Cig1-s enable broadband matching while minimizing Miller effect in 50 Ω systems.

Key Specifications

Pinout & Package

SOT143B plastic surface-mounted package (3.0 × 1.4 × 1.1 mm), 4-lead, standard pinning (top view: Pin 1 = source, 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 BF904A, BF998,115 offers extended frequency response but demands layout changes and higher supply voltage, while NE85633 sacrifices AGC integration for higher power and simpler biasing-neither is pin-compatible nor functionally interchangeable without system-level redesign.

Availability

BF904A is available at Aetrix Electronics and suitable for television tuners, professional VHF receivers, UHF wireless microphone systems, and ISM-band sensor transceivers requiring stable component supply and long-term obsolescence management.

Supply support for BF904A 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 markets.

The BF904A belongs to NXP's legacy RF transistor product line, engineered specifically for high-fidelity, low-noise amplification in analog and digital broadcast receiver front-ends operating from VHF through low-UHF bands.

FAQ

What is the maximum drain-source voltage rating for the BF904A?

The BF904A has a maximum drain-source voltage (V_DS) rating of 7 V, as specified in the Absolute Maximum Ratings table. This rating ensures safe operation under transient conditions in 5 V RF amplifier circuits. Exceeding 7 V risks permanent damage. The BF904A is optimized for stable 5 V supply operation, and its internal structure supports this voltage range without derating. Always observe this limit in both DC bias and RF peak envelope conditions when designing with the BF904A.

How does the BF904A achieve low cross-modulation during AGC operation?

The BF904A achieves low cross-modulation during AGC by integrating an internal bias circuit that stabilizes the channel conductance relationship between gate 1 (RF input) and gate 2 (AGC control). Its dual-gate structure isolates gain control from signal path nonlinearity, enabling >100 dB unwanted signal rejection at 40 dB gain reduction. This behavior is verified in Fig.7 of the datasheet using the test setup in Fig.21. The BF904A maintains this performance across temperature and supply variations-key for broadcast tuner reliability.

What is the typical noise figure of the BF904A and at what frequency is it measured?

The BF904A has a typical noise figure (F) of 2 dB at 800 MHz, measured under standard conditions: V_DS = 5 V, V_G2-S = 4 V, I_D = 10 mA, and optimal source impedance (Γ_opt). This value is confirmed in Table 2 (Noise Data) and Fig.6 of the official NXP datasheet. At 200 MHz, the noise figure drops to 1 dB, making the BF904A especially effective in VHF tuner applications. The BF904A's 2 dB NF at UHF frequencies directly supports compliance with DVB-T and ATSC reception standards.

Which package type is used for the BF904A and how are its pins arranged?

The BF904A is housed in the SOT143B plastic surface-mount package (3.0 × 1.4 × 1.1 mm), with standard pinning: Pin 1 = source, Pin 2 = drain, Pin 3 = gate 2, Pin 4 = gate 1 (top view). This differs from the BF904AR (SOT143R, reversed pinout) and BF904AWR (SOT343R). The BF904A marking code is %M7. Correct identification is critical-using BF904A in a layout designed for BF904AR will result in functional failure due to gate/drain misconnection.

Can the BF904A be used in 3 V supply applications?

The BF904A is explicitly designed for 5 V operation per its Features section and Quick Reference Data, and its static characteristics (e.g., V_G1-S(th), I_DSX) are characterized at V_DS = 5 V and V_G2-S = 4 V. While limited functionality may occur at 3 V, gain, noise figure, and AGC linearity degrade significantly-datasheet parameters are not guaranteed below 4.5 V. For true 3 V operation, consider newer alternatives like the BGA2022. The BF904A should be deployed only in 5 V systems to ensure compliance with its published specifications.