Q.Define the terms i. amplification factor, ii. trans conductance and iii. drain resistance.

These are three of the small-signal parameters of a JFET, each defined as a ratio of small changes read from its characteristic curves.

[!ANSWER]

i. Amplification factor $\mu = \Delta V_{DS}/\Delta V_{GS}$ at constant $I_D$. ii. Transconductance $g_m = \Delta I_D/\Delta V_{GS}$ at constant $V_{DS}$ (in siemen). iii. AC drain resistance $r_d = \Delta V_{DS}/\Delta I_D$ at constant $V_{GS}$ (in ohm).

[!TLDR]

Amplification factor $\mu = \Delta V_{DS}/\Delta V_{GS}$ (constant $I_D$); transconductance $g_m = \Delta I_D/\Delta V_{GS}$ (constant $V_{DS}$); drain resistance $r_d = \Delta V_{DS}/\Delta I_D$ (constant $V_{GS}$).

The behaviour of a JFET as an amplifier is described by three small-signal parameters obtained from its characteristic curves.

i. Amplification factor $(\mu)$: the ratio of a small change in drain-to-source voltage to the corresponding small change in gate-to-source voltage, the drain current being kept constant.

It is a pure number and indicates how effectively the device amplifies.

ii. Transconductance $(g_m)$: the ratio of a small change in drain current to the corresponding small change in gate-to-source voltage, the drain-to-source voltage being kept constant. Also called forward transconductance, it is expressed in siemen (S).

iii. Drain resistance $(r_d)$: the AC or dynamic drain resistance is the ratio of a small change in drain-to-source voltage to the corresponding small change in drain current, the gate-to-source voltage being kept constant. It is expressed in ohm $(\Omega)$.

[!ANSWER]

i. $\mu = \Delta V_{DS}/\Delta V_{GS}$ at constant $I_D$. ii. $g_m = \Delta I_D/\Delta V_{GS}$ at constant $V_{DS}$ (siemen). iii. $r_d = \Delta V_{DS}/\Delta I_D$ at constant $V_{GS}$ (ohm).