Mumbai University > EXTC > Sem 3 > Analog Electronics 1

Marks: 5 M

Year: Nov 2013

• FET operates in four region

1.Ohmic Region: The Ohmic Region of a FET transistor (also called the linear region) is the region where the drain current $(I_D)$ has a linear response to changes in the drain-source voltage $(V_{DS})$ and the FET acts like a voltage controlled resistor

2.Pinch-off region: It is the region where the drain-source channel resistance is at its maximum and there is no drain current, $I_D$. The transistor is off. Gate voltage $(V_{GS })$ is sufficient to cause the FET to act as an open circuit as the channel resistance is at maximum. This gate voltage is called as Cut-off voltage because it turns off FET.

3.Saturation region: The FET becomes a good conductor and ID is controlled by the Gate-Source voltage, $(V_{GS})$ while the Drain-Source voltage, $(V_{DS})$ has little or no effect. Current ID flowing from drain to source is maximum thus it is referred as saturation region. It is also called as active region and transistor is in ON state.

Fig1 Characteristics of FET

4.Breakdown region: The voltage between the Drain and the Source $(V_{DS} )$ is very high which causes a drastic increase in drain current $(I_D)$ due to breakdown of drain-source channel.

• The voltage $V_{GS}$ is applied between gate and source.$V_{GS}$ controls the current flowing between drain and source $(I_D)$. The voltage $V_{GS}$ refers to the voltage applied between drain and source. Graph shown in Fig1 is output characteristics of FET.