Bjt And Fet Basics Practice Questions

An NMOS transistor operating in the linear region has $I_{D S}$ of $5 \mu \mathrm{A}$ at $V_{D S}$ of $0.1 \mathrm{~V}$ . Keeping $V_{G S}$ constant, the $V_{D S}$ is increased to $1.5 \mathrm{~V}$ . Given that $\mu_{n} C_{o x} \frac{W}{L}=50 \mu \mathrm{A} / \mathrm{V}^{2}$ , the transconductance at the new operating point (in $\mu \mathrm{A} / \mathrm{V}$ , rounded off to two decimal places) is ________

Which of the following statements is/are true for a BJT with respect to its DC current gain $\beta$ ?

An ideal MOS capacitor (p-type semiconductor) is shown in the figure. The MOS capacitor is under strong inversion with $V_G=2V$ . The corresponding inversion charge density $Q_{IN}$ is $2.2\mu C/cm^2$ . Assume oxide capacitance per unit area as $C_{OX}=1.7\mu F/cm^2$ . For $V_G=4V$ , the value of $Q_{IN}$ is ______ $\mu C/cm^2$ (rounded off to one decimal place).

In the circuit shown in the figure, the transistors $M_{1}$ and $M_{2}$ are operating in saturation. The channel length modulation coefficients of both the transistors are non-zero. The transconductance of the $\text{MOSFETs} M_{1}$ and $M_{2}$ are $g_{m1}$ and $g_{m2}$ , respectively, and the internal resistance of the $\text{MOSFETs} M_{1}$ and $M_{2}$ are $r_{01}$ and $r_{02}$ , respectively. Ignoring the body effect, the ac small signal voltage gain $\left ( \partial V_{out}/\partial V_{\in} \right )$ of the circuit is

For the transistor $M_{1}$ in the circuit shown in the figure, $\mu_{n} C_{\text{ox}} = 100\:\mu A/V^{2}$ and $(W/L)=10$ , where $\mu_{n}$ is the mobility of electron, $C_{\text{ox}}$ is the oxide capacitance per unit area , W is the width and L is the length. The channel length modulation coefficient is ignored. If the gate-to-source voltage $V_{\text{GS}}\text{ is } 1\:V$ to keep the transistor at the edge of saturation, then the threshold voltage of the transistor (rounded off to one decimal place) is _______ V.

For an n-channel silicon $\text{MOSFET}$ with $10\:nm$ gate oxide thickness, the substrate sensitivity $\left ( \partial V_{T}/\partial \left | V_{BS} \right | \right )$ is found to be $50\:mV/V$ at a substrate voltage $\left | V_{BS} \right |=2V$ , where $V_{T}$ is the threshold voltage of the $\text{MOSFET}$ . Assume that, $\left | V_{BS} \right | \gg 2\Phi _{B}$ , where $q\Phi _{B}$ is the separation between the Fermi energy level $E_{F}$ and the intrinsic level $E_{i}$ in the bulk. Parameters given are Electron charge $(q) = 1.6 \times 101^{-19}\:C$ Vacuum permittivity $(\varepsilon _{0}) = 8.85 \times 10^{-12}\: F/m$ Relative permittivity of silicon $(\varepsilon _{Si}) = 12$ Relative permittivity of oxide $(\varepsilon _{ox}) = 4$ The doping concentration of the substrate is

The band diagram of a p-type semiconductor with a band-gap of 1 eV is shown. Using this semiconductor, a MOS capacitor having $V_{TH}$ of $-0.16 V, C'_{ox}$ of 100 $nF/cm^2$ and a metal work function of 3.87 eV is fabricated. There is no charge within the oxide. If the voltage across the capacitor is $V_{TH}$ . the magnitude of depletion charge per unit area (in $C/cm^2$ ) is

The base of an npn BJT T1 has a linear doping profile $N_B(x)$ as shown below. The base of another npn BJT T2 has a uniform doping $N_B$ of $10^{17} cm^{-3}$ . All other parameters are identical for both the devices. Assuming that the hole density profile is the same as that of doping, the common-emitter current gain of T2 is

Consider a long-channel MOSFET with a channel length 1 $\mu m$ and width 10 $\mu m$ . The device parameters are acceptor concentration $N_A=5 \times 10^{16}cm^{-3}$ , electron mobility $\mu_n=800cm^2/V-s$ , oxide capacitance/area $C_{ox}=3.45 \times 10^{-7}F/cm^{2}$ , threshold voltage $V_T=0.7V$ . The drain saturation current ( $I_{Dsat}$ ) for a gate voltage of 5 V is _____mA(rounded off to two decimal places). $[\varepsilon _0=8.854 \times 10^{-14}F/cm,\varepsilon _{Si}=11.9]$

The figure shows the high-frequency C-V curve of a MOS capacitor (at T = 300 K) with $\Phi _{ms}=0V$ and no oxide charges. The flat-band, inversion, and accumulation conditions are represented, respectively, by the points

A MOS capacitor is fabricated on p-type Si (silicon) where the metal work function is 4.1 eV and electron affinity of Si is 4.0 eV. $E_{C}-F_{F}$ =0.9 eV, where $E_{C}$ and $E_{F}$ are the conduction band minimum and the Fermi energy levels of Si, respectively. Oxide $\in_{r}=3.9,\in_{o}=8.85 \times 10^{-14}$ F/cm, oxide thickness $t_{ox} = 0.1 \mu m$ and electronic charge $q =1.6 \times 10^{-19} C$ . If the measured flat band voltage of the capacitor is -1V, then the magnitude of the fixed charge at the oxide-semiconductor interface, in $nC/cm^{2}$ , is __________.

Two n-channel MOSFETs, T1 and T2, are identical in all respects except that the width of T2 is double that of T1. Both the transistors are biased in the saturation region of operation, but the gate overdrive voltage ( $V_{GS}-V_{TH}$ ) of T2 is double that of T1, where $V_{GS} \; and \; V_{TH}$ are the gate-to-source voltage and threshold voltage of the transistors, respectively. If the drain current and transconductance of T1 are $I_{D1} \; and \; g_{m1}$ respectively, the corresponding values of these two parameters for T2 are

Consider an n-channel MOSFET having width W, length L, electron mobility in the channel $\mu_{n}$ and oxide capacitance per unit area $C_{ox}$ . If gate-to-source voltage $V_{GS}$ =0.7V, drain-tosource voltage $V_{DS}=0.1V,(\mu_{n}C_{ox})=100\mu A/V^{2}$ ,threshold voltage $V_{TH}=0.3 V$ and (W/L)=50,then the transconductance $g_{m}$ (in mA/V) is ___________.

For a narrow base PNP BJT, the excess minority carrier concentration ( $\Delta n_{E}$ for emitter, $\Delta p_{E0}$ for base. $\Delta n_{c}$ for collector) normalized to equilibrium minority carrier concentration ( $n_{E0}$ for emmiter, $p_{B0}$ for base, $n_{C0}$ for collector) in the quasi-neutral emitter, base and collector regions are shown below. Which one of the following biasing modes is the transistor operating in ?

An npn bipolar junction transistor (BJT) is operating in the active region. If the reverse bias across the base - collector junction is increased, then

A voltage $V_{G}$ is applied across a MOS capacitor with metal gate and p-type silicon substrate at T=300 K. The inversion carrier density (in number of carriers per unit area) for $V_{G}=0.8 V$ is $2\times 10^{11} cm^{-2}$ . For $V_{G}=1.3 V$ , the inversion carrier density is $4\times 10^{11}cm^{-2}$ . What is the value of the inversion carrier density for $V_{G}=1.8 V$ ?

Figures I and II show two MOS capacitors of unit area. The capacitor in Figure I has insulator materials X (of thickness $t_1 = 1$ nm and dielectric constant $\varepsilon _{1}$ = 4) and Y (of thickness $t_2 = 3$ nm and dielectric constant $\varepsilon _{2}$ = 20). The capacitor in Figure II has only insulator material X of thickness $t_{Eq}$ . If the capacitors are of equal capacitance, then the value of $t_{Eq}$ (in nm) is __________

The figure shows the band diagram of a Metal Oxide Semiconductor (MOS). The surface region of this MOS is in

The injected excess electron concentration profile in the base region of an npn BJT, biased in the active region, is linear, as shown in the figure. If the area of the emitter-base junction is 0.001 $cm^{2},\mu _{n}=800 cm^{2}/(V-s)$ in the base region and depletion layer widths are negligible, then the collector current $I_{C}$ (in mA) at room temperature is __________ (Given: thermal voltage $V_{T}$ = 26 mV at room temperature, electronic charge $q=1.6\times 10^{-19}C$ )