# Small Signal Analysis

 Question 1
For an ideal MOSFET biased in saturation, the magnitude of the small signal current gain for a common drain amplifier is
 A 0 B 1 C 100 D infinite
GATE EE 2022   Analog Electronics
Question 1 Explanation:
For ideal MOSFET, $i_G=0$
Therefore, Current gain, $A_I=\frac{i_s}{i_G}=\infty$
 Question 2
The magnitude of the mid-band voltage gain of the circuit shown in figure is (assuming $h_{fe}$ of the transistor to be 100)
 A 1 B 10 C 20 D 100
GATE EE 2014-SET-1   Analog Electronics
Question 2 Explanation:
AC model,

$\; \; \; \; Z_{i}=10\, k\Omega$
Mid band voltage gain $\; \; \; \; A_{v}=\frac{A_{I}R_{L}}{Z_{i}}$
$\; \; \; \; A_{v}=\frac{-h_{fe}R_{L}}{Z_{i}} =\frac{-100\times 10\, k\Omega }{10\, k\Omega }=-100$
$\; \; \; \; \left | A_{v} \right |=100$
 Question 3
In the single-stage transistor amplifier circuit shown in figure, the capacitor $C_{E}$ is removed. Then, the ac small-signal midband voltage gain of the amplifier
 A increases B decreases C is unaffected D drops to zero
GATE EE 2001   Analog Electronics
Question 3 Explanation:
$\frac{A_{V_1}}{A_{V_1}}=1+\left ( \frac{1+h_{fe}}{h_{ie}} \right )R_{e}$
$\frac{A_{V_{1}}}{A_{V_{2}}}> 1$
$\Rightarrow \; A_{V_{2}} \lt A_{V_{1}}$
There are 3 questions to complete.