What is the transconductance of a transistor?

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magnetra

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Transconductance

what is transconductance of a transistor?
What is it's physical significance?

Regards
M
 

Re: Transconductance

current=transconductance*voltage
 

Transconductance

hi magnetra,
transconductance has special significance when it comes to CMOS.
Almost all the amplifier gain characteristics is a function of transconductance of the MOSFET.

For example the gain of Common Source is = gm*rd
i.e gain is product of transconductance of the transistor multiplied by the load resistance.

This is because MOSFET is a voltage controlled current source in saturation region for given input signal (voltage) output drain current will vary. The amplification is due to this current flowing into the the load resistor(id *rd).

regards,
sudhir
 

Re: Transconductance

For a transistor transistor transconductance refers to the transistor equation


Ic = Iss e(Vbe/Vt) - 1


that means according to the units


[A] = [V] [1/R]
Ic Vbe Units of transconductance
 

Re: Transconductance

magnetra,
The transconductance of any device, transistor or otherwise, is the derivative of output current with respect to input voltage: g = d(iout)/dVin).
Regards,
Kral
 

Transconductance

transconductance 1. Symbol, gm. Unit, micromho.
In an electron tube, the extent to which
plate current (IP) changes in response to a change
in grid voltage (EG); gm = dIP/dEG. 2. Symbol,
gfs. Unit, micromho. In a field-effect transistor,
the extent to which drain current (ID) changes in
response to a change in gate-to-source voltage
(VGS); gfs = dID/dVGS.
 

Re: Transconductance

Mathematically, Transconductance is defined as d(iout)/dvin @ Vin = certain biased voltage, notice that the small letter implies small signal, hence in MOS active region, we have gm = d(id)/dvgs.
Physically in MOS, it is the ratio that relates the variation in vgs(t), which results variation in the shape of the inverted channel, and further results variation in the current, id(t) that has passed through the channel.
 

Re: Transconductance

transconductance is the most important parameter of a transistor. It is nothing but the voltage to current gain. If its an voltage amplifier, transconductance*load resistance gives your gain. it also determines your Gain Bandwidth Product(GBW). this votlage to current conversion is also responsible for introducing non-linearity in your ciruict.
 

Re: Transconductance

Transconductance is the device ability that can transfer input voltage into output current. In other words, if you invest amount of input voltage, the corresponding current amount is called "Transconductance".

Bigger transconductance has better ability to make bigger currents if inputs are the same.

Hope this is helpful
 

Re: Transconductance

resistance = resist conductance
just understand it in the same way:
transconductance= transfer conductance
so we have R = 1/S
Ohm = 1/Siemens
is it clear
 

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