Diodes Incorporated ZTX325STOA

Overview

ZTX325STOA from Diodes Incorporated is an NPN silicon planar RF transistor optimized for VHF/UHF amplification, featuring f_T = 1.3 GHz, noise figure < 5 dB at 500 MHz, and 175 mW output power at 500 MHz under 13.5 V_CE/22.5 mA bias. It operates with V_CEO = 15 V, V_CBO = 30 V, and P_tot = 350 mW in TO-92 package, commonly used in FM receiver front-ends and low-power RF driver stages.

For engineers reviewing the ZTX325STOA datasheet, ZTX325STOA pinout, ZTX325STOA application, or ZTX325STOA equivalent, key selection criteria include verified 500 MHz noise performance (N = 5.0 dB), transition frequency consistency across I_C = 2–25 mA, thermal stability up to +200°C junction temperature, and TO-92 mechanical compatibility with legacy E-line layouts.

Technical Context

This device employs a planar epitaxial structure with low base spreading resistance and optimized emitter geometry to achieve high f_T and low noise simultaneously. Its C_re = 0.85 pF and r_bb'C_b'c = 2–12 ps support stable gain above 400 MHz while maintaining intermodulation distortion of –53 dB at 217 MHz.

The transistor is characterized with fixed V_CE = 5 V and 13.5 V test conditions, and its h_FE ranges from 25 to 150 depending on I_C, enabling flexible biasing in Class-A or Class-AB small-signal amplifier configurations without external neutralization.

Key Specifications

Pinout & Package

Supplied in TO-92 package (E-Line compatible), with standard lead configuration: Emitter (pin 1), Base (pin 2), Collector (pin 3), as confirmed by Diodes Incorporated's ZTX325 series mechanical drawings and footprint reference 3-161.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN RF transistor applications.

Compared with ZTX213 and MPSH10, ZTX325STOA delivers superior 500 MHz noise and power performance in TO-92, making it optimal for compact FM/VHF amplifiers where thermal margin and gain flatness are critical.

Availability

ZTX325STOA is available at Aetrix Electronics and suitable for FM receiver front-ends, VHF transceiver drivers, and IF amplifier stages requiring stable component supply with consistent TO-92 mechanical fit and RF electrical performance.

Supply support for ZTX325STOA 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

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in China, Taiwan, and the US.

ZTX325STOA belongs to the ZTX series of general-purpose RF transistors developed for cost-sensitive, high-volume consumer radio and communications equipment requiring reliable small-signal amplification up to 1 GHz.

FAQ

What is the maximum safe collector-emitter voltage for ZTX325STOA?

The absolute maximum V_CEO is 15 V, verified per Diodes Incorporated's Issue 2 datasheet (March 1994). Operation above this voltage risks avalanche breakdown even with limited current. Derating to ≤12 V is recommended for long-term reliability in thermally constrained PCB layouts.

Can ZTX325STOA be used in common-base configuration?

Yes - its low C_re (0.85 pF) and high f_T make it well-suited for common-base RF amplifiers. The emitter must be AC-grounded via bypass capacitor, and input applied to emitter while output taken from collector, preserving wideband response up to 500 MHz.

Is thermal derating required for continuous operation at 25°C ambient?

Yes - although P_tot is rated at 350 mW at T_amb = 25°C, actual dissipation must be limited to ≤200 mW when mounted on standard FR-4 without copper pour due to TO-92's high thermal resistance (R_θJA ≈ 200°C/W). Use thermal vias or local ground plane for >250 mW operation.

Does ZTX325STOA require external neutralization for stability at 500 MHz?

No - measured C_re = 0.85 pF and r_bb'C_b'c = 2–12 ps ensure unconditional stability in common-emitter configuration up to 500 MHz with proper layout (short leads, grounded emitter pad, decoupled V_CC). Neutralization is unnecessary unless gain >20 dB is targeted beyond 600 MHz.