novice for nourishment

[electronics_kumar]

i a novice in FET devices.

why there are large hue and cry over threshold voltage(Vt) and W/L ratio and the parameter called λ.
i want answer that can ram me

 

[methisherenow]

The FET is basically a resistor (called channel) between the source and drain terminals, that is controlled by the gate terminal. So, if the gate voltage level creates carriers in the channel, then the resistance between source and drain is small. IF the gate voltage does not create the carriers in the channel, the resistance is very high.

So, the threshold voltage is the GATE voltage (measured from the source terminal) at which the channel just starts to have significant carriers (thus conducts or has low resistance).

The W/L ratio is the ratio of the width of the channel to the length between the Source and the Drain. This ratio determines how much current flows for a given gate voltage (i.e if the Width is large, then more current flows).

Lambda is a parameter that expreses the dependence of the current through the channel on the voltage between the source and the drain. Although ideally the resistance in the channel is independent of the voltage between the source and the drain (only depending on the gate voltage), in reality the resistance is also dependent on the source to drain voltage, the dependence is marked by lambda. So if lambda is large, there is more dependence on Source-Drain voltage.

HOpe it helps.

 

[nzahirov]

Lambda is called the channel-length modulation parameter and realistically is only present with the FET transistor operating in saturation with pinch-off occuring in the inversion layer below the gate oxide.

Simply put as you increase the drain-source voltage the effective length of the gate changes causing a dependence of the transistor current on the drain-source voltage.