Which transistor has higher gain. BJT or MOS and why?

Device Physics doubts related to diode, transistor, BJT, MOSFET, JFET.
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Vijay
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Location: Bangalore, India

Which transistor has higher gain. BJT or MOS and why?

Post by Vijay » Sat Apr 19, 2014 10:36 am

Which transistor has higher gain. BJT or MOS and why?

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Narveer
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Location: Bangalore, INDIA

Re: Which transistor has higher gain. BJT or MOS and why?

Post by Narveer » Wed Apr 30, 2014 10:10 pm

BJT have more gain than MOSFET because MOSFET shows Quadratic I-V characteristics and BJT shows Exponential I-V characteristics and the change in exponential behavior is more as compared to Quadratic behavior.

In mathematical terms:

The Intrinsic Gain in BJT = Va/Vt
where Va is Early Voltage.
It is a process parameter and its value lies in between 35V to 130V. Vt is thermal voltage and its value is 0.025V at room temperature. So, its Intrinsic Gain ranges from 1000 V/V to 5000 V/V.

In MOSFET Intrinsic Gain is 2Va/(Vgs - Vth)
where Va is Early Voltage same as in BJT.
Vgs is Gate to Source Voltage
Vth is threshold voltage
(Vgs - Vth) is higher as compared to thermal voltage Vt.
Normally (Vgs - Vth) is considered in between (0.2 -0.4).

So, MOSFETs have lower intrinsic gain as compared to BJT.

manoj
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Joined: Sun May 18, 2014 9:32 pm

Re: Which transistor has higher gain. BJT or MOS and why?

Post by manoj » Thu Jul 24, 2014 9:09 am

The transconductance of BJT is higher than that of MOSFET which makes the gain of BJT higher than MOSFET.

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