GATE EC 2025 Set 1 Q20 — BJT and MOSFET Amplifiers

A simplified small-signal equivalent circuit of a BJT-based amplifier is given below. The small-signal voltage gain $V_{o} / V_{S}$ (in $\mathrm{V} / \mathrm{V})$ is $\_\_\_\_\_\_$

The ideal BJT in the circuit given below is biased in the active region with a $\beta$ of $100$. If $I_{B}$ is $10 \: \mu \mathrm{A}$, then $V_{C E}$ (in Volts, rounded off to two decimal places) is $\_\_\_\_\_\_\_\_$.

The identical MOSFETs $M_{1}$ and $M_{2}$ in the circuit given below are ideal and biased in the saturation region. $\mathrm{M}_{1}$ and $\mathrm{M}_{2}$ have a transconductance $g_{m}$ of $5$ mS. The input signals (in Volts) are: $$\begin{array}{l} V_{1}=2.5+0.01 \sin \omega t \\ V_{2}=2.5-0.01 \sin \omega t \end{array}$$ The output signal …

In the circuit shown, the identical transistors $\text{Q1}$ and $\text{Q2}$ are biased in the active region with $\beta=120$. The Zener diode is in the breakdown region with $\mathrm{V}_{\mathrm{Z}}=5 \mathrm{~V}$ and $\mathrm{I}_{\mathrm{Z}}=25 \mathrm{~mA}$. If $\mathrm{I}_{\mathrm{L}}=12 \mathrm{~mA}$ and …

​​​​In the circuit below, assume that the long channel $\text{NMOS}$ transistor is biased in saturation. The small signal trans-conductance of the transistor is $g_{m}$. Neglect body effect, channel length modulation and intrinsic device capacitances. The small signal input impedance $Z_{i n}(j \omega)$ is $\_\_\_\_\_\_$

​​​​For the closed loop amplifier circuit shown below, the magnitude of open loop low frequency small signal voltage gain is $40$. All the transistors are biased in saturation. The current source $I_{S S}$ is ideal. Neglect body effect, channel length modulation and intrinsic device capacitances. The closed loop low frequency small signal voltage gain …