Biasing for Transister Circuits

Why we need biasing for Transister, FET and MOSFET.?
What is the importance of the biasing in transister circuits.

Questions by kkumawat82

Editorial / Best Answer


  • Member Since Oct-2009 | Dec 25th, 2009

Biasing of transistor circuits is done for making it work in the desired region of operation. 

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Basically transister contains active region, saturation, cut off region. In saturation and cutt of region transister is used as a switch. To use transister as amplifier the operating point should be in exact middle of the active region. 

As transistor is using as amplifier the operating point should be stable, in operating transister the temperature can fluctuate operating point, there by to avoid operating point fluctuation some mechnism must be used, this mechanism can be called as biasing.


  • Oct 7th, 2010

Biasing means operationg the transistors in a particular region it could be either active(linear),cuttoff(off swith),saturation(nonlinear)
*active region it acts as an amplifier EB jn is FB and CB jn is RB
*saturation region of switch CB and EB forward biased acts as a constant current source
*cutt off both Jn RB acts as a off switch
It is a current controlled device
For Mosfet
*if Vgs<Vth acts in cutt of i.e off switch
*if VGs>Vth and Vds<(Vgs-Vth)..acts in linear region acts as a Resistor
*if Vgs>Vth and Vds>(Vgs-Vth) ..acts in saturation region which is most times a Const Current Source

**Vgs-gate to source Vtg
**Vth-minimum threshold Vtg
**Vds-Drain to source Vtg
**CB-collector Base
**EB-emitter Base
FB fwd bias RB-reverse Bias

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