Understanding Field Effect Transistor (FET) and MOSFET Principles

Explore the construction, principles, characteristics, and relationships among parameters of Junction Field Effect Transistors (JFET) through detailed explanations and diagrams. Dive into the equation of drain characteristics and the resemblance to a parabolic curve. Understand the differentiation process and implications on the characteristics.

• Transistors
• FET Principles
• JFET Construction
• MOSFET Characteristics
• Drain Characteristics

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1. Unit 6 Field Effect Transistor (FET) And MOSFET

2. CONSTRUCTION OF JFET Figure 1: Symbol of n-channel FET Figure 2: Symbol of p-channel FET

3. PRINCIPLE OF JFET (n-Channel) Drain characteristics of JFET

4. PRINCIPLE OF JFET (n-Channel) When ???= ? and ???= ? When ???= ? and ??? is decreased from zero When ???= ? and ??? is increased from zero When ??? is negative and ??? is increased Drain characteristics of JFET

5. CHARACTERISTICS PARAMETERS OF JFET 1. Mutual conductance or transconductance, ?? ??? ???? ??? 2. Drain resistance, ?? ???? ??? ??? 3. Drain conductance, ?? ??? ???? ??? 4. Amplification factor, ? ?? ??? ??= = ,??? ??? ???????? = ??? ?? ??= ,??? ??? ???????? ?? ??? ??= = ,??? ??? ???????? ???? ???? = ??? ??? ? = ,??? ?? ???????? ??

6. Relationship among FET parameters or Relation between ?,?? & ?? ??= ? ???,??? Using Taylor s theorem by considering fractional change in ???,??? & ?? ??? ???? ??? ??? ?? ???? ???? ??? ?? ??? ??? ???? ??? ? ?? ? = ?? ?? ??? ???? ??? ???? = ?? ??= ???+ ???? ??= ??? ??? ??? ???? ??? ???? ???? ??? = + ??= ??? ??? ???? ???? If ?? is constant, = 0 ? = ?? ???? ???? ??? ???? ? ?? 0 = + 0 = ? + ?? ???

7. ? ?? Shockley gives the equation of drain characteristics as: Show that ??= ??? ???? 2 ??? ???? This resembles equation of parabola = 1 ??? ?? Characteristic is parabolic Decreasing the gate voltage ??? from zero till ?? is reduced to zero Equation of Parabola is given as ? = ?2 2 ???= ???? 1 ??? ??

8. 2 2 ???= ???? 1 ??? ??? ???? = 1 ??? ?? ?? Differentiating above equation with respect to ???, ???? ???? ??? ???? = ? ??? ?? = ???? 2 1 ??? 1 ??= 2???? ??? ???? ?? ?? ?? = 2???? 1 ??? ? ?? ?? 2 ???? ??? ???? ??= ?? ???? ???? ??= 2 ??? = ???? ??? ?? ? ?? ??= 2???? ? ??? ??= ??? ???? ?? ??

9. 2 ??= ????? 1 ??? ??? ???? = 1 ??? ?? ?? ?? Let ??= ??0 when ???= 0 ??? ???? = 1 ??? ??0= 2???? 1 0 ?? ?? ?? ??= 2???? ??? ???? ??0= ????? ?? ?? 2 2 ???? ??? ???? ??= 1 ??? ?? ??= ??0 ?? 2 = ???? ??? ?? ? ?? ??? ???? ??= ??0 ??= ??? ????