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Difference between BJT and FET
Short answer
BJT is current-controlled with low input resistance and uses both electrons and holes; FET is voltage-controlled with very high input resistance and uses majority carriers. FETs have lower noise, better thermal stability, and higher switching speed.
State the difference between BJT and FET.
| Point | BJT | FET |
|---|---|---|
| Type of device | Bipolar: both electrons and holes carry current | Unipolar: only majority carriers carry current |
| Control | Current controlled (IB controls IC) | Voltage controlled (VGS controls ID) |
| Input resistance | Low (about 1 to 10 kΩ) | Very high (10⁷ to 10¹⁴ Ω) |
| Terminals | Emitter, base, collector | Source, gate, drain |
| Noise | Higher | Lower |
| Thermal stability | Poor (thermal runaway possible) | Better (negative temperature coefficient of ID) |
| Transconductance (gain) | Higher gm | Lower gm, so lower gain at the same current |
| Size and fabrication | Larger, more complex | Smaller, simpler, used in VLSI |
| Switching speed | Slower (minority carrier storage) | Faster |
| Application | Analogue amplifiers, power circuits | Digital ICs (CMOS), high-impedance input stages, switches |
✓ Answer checked by Claude Opus 5.5 (high effort)
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