Part Number: 2N3958
Function: N-Channel dual silicon junction field-effect transistor
Package: TO-71 Type
Manufacturer: Vishay Semiconductors
Image and Pinouts:
Description
2N3958 is a monolithic dual N-channel JFET optimized for precision differential amplification. The two JFETs are fabricated on the same die, ensuring excellent matching characteristics, which is critical for low-offset, low-drift analog front-end designs.
Core Characteristics
- Device type: Dual N-channel JFET (matched pair)
- Monolithic construction → superior thermal tracking
- Designed for differential input stages
- Ultra-low gate leakage current
- Low noise and high dynamic range
Functional Description
- Contains two closely matched JFETs sharing the same substrate
- Typically used as a differential pair in analog circuits
- Provides high input impedance with minimal bias current
- Ensures stable operation over temperature due to matched thermal behavior
Why Dual Matched JFET Matters
- Minimizes offset voltage in differential amplifiers
- Improves gain symmetry and linearity
- Reduces need for trimming in precision circuits
- Enhances CMRR and PSRR in op-amp front ends
Design Insights
- Best used in long-tailed pair configurations
- Requires proper biasing (constant current source recommended)
- Thermal coupling improves matching → avoid asymmetric PCB layout
- Shield high impedance nodes to reduce noise pickup
- Gate protection may be needed in high-voltage environments
Typical Circuit Role
- Input stage of precision operational amplifiers
- Instrumentation amplifiers
- Low-noise preamplifiers (sensor interfaces)
- Sample-and-hold circuits
- Analog computation and filtering circuits
Typical Differential Pair Topology
- Sources connected together → constant current source
- Drains connected to load resistors or active loads
- Gates serve as differential inputs (Vin+ / Vin−)
Performance Advantages
- Very high input impedance → negligible loading
- Low noise floor → suitable for microvolt-level signals
- Excellent matching → minimizes offset and drift
- Wide dynamic range → handles both small and large signals accurately
Limitations
- Lower transconductance compared to bipolar input stages
- Limited current drive capability
- Requires careful bias design for optimal linearity
Equivalent / Alternative Devices
- LSK389 (modern low-noise dual JFET)
- MAT02 / MAT12 (precision matched transistor pairs, BJT alternative)
- 2N3954 / 2N3956 (same family variants)
- BF862 (single low-noise JFET alternative)
2N3958 Datasheet PDF Download
