Transfer Characteristic of JFET

The transfer characteristic of a JFET (Junction Field Effect Transistor) is the relationship between the input voltage (VGS) and the output current (ID). This characteristic curve is an important parameter for understanding the behavior of the JFET in different circuit configurations.

Shape of Transfer Characteristic

The shape of the transfer characteristic of a JFET is very nearly a hyperbola. A hyperbola is a curve that has two branches that are asymptotic to two intersecting lines. The transfer characteristic of a JFET is almost symmetric about the origin, and the two branches of the hyperbola represent the saturation and cutoff regions of operation.

Explanation

The transfer characteristic of a JFET can be derived from the basic equation that governs the operation of the device, known as the Shockley equation. This equation relates the drain current ID to the gate-source voltage VGS and the device parameters such as the threshold voltage Vp and the transconductance parameter gm.

ID = IDSS(1 - VGS/Vp)²

where IDSS is the maximum drain current that can flow through the device when VGS = 0.

When VGS is zero, the device is in the cutoff region and no current flows through the channel. As VGS increases, the channel resistance decreases, and the drain current ID starts to increase. When VGS reaches a certain value known as the pinch-off voltage VP, the channel resistance becomes very small, and the drain current ID reaches its maximum value IDSS.

As VGS continues to increase beyond VP, the channel resistance remains constant, and the drain current ID remains at its maximum value. This region is known as the saturation region.

The transfer characteristic of a JFET is almost symmetric about the origin, and the two branches of the hyperbola represent the saturation and cutoff regions of operation. The slope of the curve in the saturation region is determined by the transconductance parameter gm, which is a measure of the device's ability to amplify an input signal.

Conclusion

In conclusion, the transfer characteristic of a JFET is very nearly a hyperbola, and it is an important parameter for understanding the behavior of the device in different circuit configurations. The shape of the characteristic curve is determined by the basic equation that governs the operation of the JFET and its device parameters such as the threshold voltage and the transconductance parameter.

Answer is not A but C , It is clearly seen as a parabolic , I don't get it why People just assume every word of JB gupta objective book as truth . Look at the curve , its parabolic  , other wise study what is parabolic again . Anyways , It is mentioned in foreign author book  and B P Singh book on electronics (pearson publication) as well . Page 228