Transistors - Bipolar (BJT)

Transistors - Bipolar (BJT) - RF

Image	Part Number	Description / PDF	Quantity	Rfq
	SD1274 STMicroelectronics	RF TRANS NPN 16V M135	0
	SD1275 STMicroelectronics	RF TRANS NPN 16V M135	0
	SD1446 STMicroelectronics	RF TRANS NPN 18V M113	0
	START499ETR STMicroelectronics	RF TRANS NPN 4.5V 1.9GHZ SOT343	0
	SD1405 STMicroelectronics	RF TRANS NPN 18V M174	0
	START499D STMicroelectronics	RF TRANS NPN 4.5V SOT89	0
	SD1274-01 STMicroelectronics	RF TRANS NPN 16V M113	0
	START405TR STMicroelectronics	RF TRANS NPN 4.5V SOT343	0
	SD1488 STMicroelectronics	RF TRANS NPN 16V M111	0
	SD1728 STMicroelectronics	RF TRANS NPN 55V M177	0
	SD1477 STMicroelectronics	RF TRANS NPN 18V M111	0
	SD1731 STMicroelectronics	RF TRANS NPN 55V M174	0
	SD1275-01 STMicroelectronics	RF TRANS NPN 16V M113	0
	SD1726 STMicroelectronics	RF TRANS NPN 55V M174	0
	SD1727 STMicroelectronics	RF TRANS NPN 55V M164	0
	SD1433 STMicroelectronics	RF TRANS NPN 16V M122	0

Transistors - Bipolar (BJT) - RF

1. Overview

Radio Frequency Bipolar Junction Transistors (RF BJTs) are three-layer semiconductor devices optimized for amplification and switching in high-frequency applications (typically >100 MHz). These transistors maintain stable performance in microwave and ultra-high frequency (UHF) ranges, characterized by high current gain-bandwidth product (f_T), low noise figures, and fast switching capabilities. Their importance in modern technology spans wireless communication infrastructure, radar systems, and RF test equipment, enabling efficient signal transmission and reception in 5G networks, satellite communications, and IoT devices.

2. Main Types & Functional Classification

Type	Functional Features	Application Examples
NPN RF BJT	High electron mobility, optimized for low-noise amplification	5G base station LNAs, GPS receivers
PNP RF BJT	Complementary design for power amplification	RF power modules, automotive radar
RF Darlington Pair	High (current gain), cascaded amplification	Antenna drivers, industrial RF heaters
Heterojunction Bipolar Transistor (HBT)	Compound semiconductor materials (SiGe/GaAs), ultra-high f_T	Optical communication transceivers, mmWave systems

3. Structure & Composition

Typical RF BJT structure includes:

Material: Silicon (Si), Silicon-Germanium (SiGe), Gallium Arsenide (GaAs)
Layer Architecture: Emitter (high doping), Base (thin layer), Collector (graded doping)
Package Types: Surface-mount (SOT-89, SOT-343), Through-hole (TO-18, TO-92)
Metallization: Gold/aluminum contacts for reduced parasitic resistance

Advanced designs incorporate air-bridge structures to minimize parasitic capacitance and epitaxial layers for improved frequency response.

4. Key Technical Parameters

Parameter	Description	Typical Range
f_T (Transition Frequency)	Current gain cutoff frequency	1 GHz - 100 GHz
G_UM (Max. Available Gain)	Power gain at optimal impedance	10 dB - 30 dB
P_out (Output Power)	RMS power capability	0.1 W - 500 W
NF (Noise Figure)	Signal-to-noise degradation	0.3 dB - 5 dB
V_CE0 (Breakdown Voltage)	Collector-emitter withstand voltage	5 V - 80 V
(Junction Temperature)	Thermal stability limit	150 C - 200 C

5. Application Fields

Telecommunications: 5G massive MIMO amplifiers, fiber optic transceivers
Defense: Phased array radar systems, electronic warfare jammers
Test & Measurement: RF signal generators, spectrum analyzers
Consumer Electronics: Bluetooth LE modules, Wi-Fi 6E front-ends
Industrial: Plasma generators, RFID readers

6. Leading Manufacturers & Products

Manufacturer	Representative Product	Key Specifications
Infineon Technologies	BFP740F	f_T=50 GHz, NF=0.8 dB, P_out=18 dBm
STMicroelectronics	STAG2141	2.7 GHz dual-stage amplifier, 32 dB gain
Skyworks Solutions	ASK24011	0.05-6 GHz, 50 W GaAs power transistor
ON Semiconductor	MRF151G	125 W, 880 MHz, 40% efficiency

7. Selection Guidelines

Key considerations:

Match f_T to application frequency with 20% margin
Verify load-line requirements for power applications
Select appropriate package for thermal dissipation (e.g., TO-220 for >50 W)
Derate V_CE0 by 30% in high-temperature environments
Consider integrated solutions (RFICs) for complex impedance matching

8. Industry Trends

Future development directions:

Transition to SiGe BiCMOS technology for 100+ GHz applications
Integration with GaN-on-SiC substrates for hybrid power amplifiers
Development of 5G NR direct-conversion transmitters using HBT arrays
Advancements in wafer-level packaging (WLP) for mmWave 5G devices
Adoption of AI-driven parameter optimization in production testing