Comparison of BJT with MOSFET

Comparison of BJT with MOSFET

1. Control element

BJT: Current controlled device. Input current I_B controls output current I_C.

MOSFET: Voltage Controlled device. Input voltage V_GS controls drain current I_D.

2. Device type

BJT: Current flows due to both majority and minority carriers and hence bipolar device.

MOSFET: Current flows only due to majority carriers and hence unipolar device.

3. Types:

BJT: n‒p‒n and p‒n‒p

MOSFET: a. n‒channel depletion type MOSFET b. p‒channel depletion type MOSFET. c. n‒channel enhancement type MOSFET d. p‒channel enhancement type MOSFET

4. Symbols:

BJT: 

MOSFET: 

5. Configurations:

BJT: CE, CB, CC

MOSFET: CS, CG, CD

6. Input resistance:

BJT: Less as compare to JFET

MOSFET: Very high

7. Size:

BJT: Bigger than MOSFET

MOSFET: Smaller in construction and hence can be used to design high density VLSI circuits.

8. Sensitivity:

BJT: Higher sensitivity to changes in the applied signals.

MOSFET: Less sensitivity to changes in the applied voltage

9. Thermal stability:

BJT: Less

MOSFET: More

10. Thermal Runway:

BJT: Exists

MOSFET: Does not exist

11. Relation between input and output

BJT: Linear

MOSFET: Non‒linear

12. Ratio of output to input

BJT: ΔI_C / ΔI_B = β

MOSFET: ΔI_D / ΔV_GS = g_m

13. Thermal noise

BJT: More

MOSFET: Less

14. Gain bandwidth product

BJT: High

MOSFET: Low

Review Question

1. Give the comparison between BJT and MOSFET.