Bipolar Junction Transistor · Analog Circuits · GATE ECE

A cascade connection of two voltage amplifiers A1 and A2 is shown in the figure. The open-loop gain A_v0, input resistance R_in, and output resistance R₀ for A1 and A2 are as follows:
A1: A_v0 = 10,R_in = 10 kΩ ,R₀ =1 kΩ
A2 : A_v0 = 5,R_in = 5 kΩ , R₀ = 200 Ω
The approximate overall voltage gain $$\frac{{\mathrm V}_\mathrm{out}}{{\mathrm V}_\mathrm{in}}$$ is ______.

GATE ECE 2014 Set 2

The current i_b through the base of a silicon npn transistor is $$1\;+\;0.1\;\cos\left(10000\;\mathrm\pi\;\mathrm t\right)$$ mA . At 300 K, the $$r_\mathrm\pi$$ in the small signal model of the transistor is

GATE ECE 2012

In the circuit shown below, capacitors C₁ and C₂ are very large and are shorts at the input frequency. V_i is a small signal input. The gain magnitude $$\left|\frac{{\mathrm V}_0}{{\mathrm V}_\mathrm i}\right|$$ at 10 Mrad/s is

GATE ECE 2011

The amplifier circuit shown below uses a silicon transistor. The capacitors C_C and C_E can be assumed to be short at signal frequency and the effect of output resistance r₀ can be ignored. If C_E is disconnected from the circuit, which one of the following statements is TRUE?

GATE ECE 2010

In the silicon BJT circuit shown below, assume that the emitter area of transistor Q₁ is half that of transistor Q₂.The value of current I₀ is approximately

GATE ECE 2010

The input impedance (Z_i) and the output impedance (Z_o) of an ideal transconductance (voltage controlled current source) amplifier are

The cascode amplifier is a multistage configuration of

GATE ECE 2005

Assuming V_Cesat=0.2V and β = 50, the minimum base current (I_B) required to drive the transistor in the figure to saturation is

GATE ECE 2004

The current gain of a BJT is

GATE ECE 2001

Introducing a resistor in the emitter of a common amplifier, stabilizes the dc operating point against variations in

GATE ECE 2000

In a series regulated power supply circuit, the voltage gain A_v of the ‘pass’ transistor satisfies the condition:

The emitter coupled pair of BJT’s gives a linear transfer relation between the differential output voltage and the differential input voltage V_id only. When the magnitude of V_id is less than '$$\alpha$$' times the thermal voltage, where '$$\alpha$$' is

The circuit of Fig. is an example of feedback of the following type

From a measurement of the rise time of the output pulse of an amplifier whose input is a small amplitude square wave, one can estimate the following parameter of the amplifier:

A BJT is said to be operating in the saturation region if

GATE ECE 1995

A transistor having $$\alpha$$ = 0.99 and V_BE = 0.7 V, is used in the circuit of the figure.What is the value of the collector current?

GATE ECE 1995

In order to reduce the harmonic distortion in an amplifier, its dynamic range has to be _________

GATE ECE 1994

A common emitter transistor amplifier has a collector current of 1.0 mA when its base current is 25 $$\mu$$A at the room temperature. It's input resistance is approximately equal to (in K$$\Omega$$) _________ .

GATE ECE 1994

For the amplifier circuit of figure, the transistor has a $$\mathrm\beta$$ of 800. The mid-band voltage gain $$V_0/V_1$$ of the circuit will be

GATE ECE 1993

The bandwidth of an n-stage tuned amplifier, with each stage having a band width of B, is given by

GATE ECE 1993

Marks 2

A small signal source, $V_i(t)=A \cos \left(10^5 t\right)+B \sin \left(10^7 t\right)$ is applied to a BJT circuit as shown in the Figure.

Assume zero source resistance, $V_{B E}=0.7 \mathrm{~V}, \beta_{\mathrm{dc}}=99$, Early voltage $=100 \mathrm{~V}$ and Thermal voltage $=25 \mathrm{mV}$. Effect of internal parasitic capacitances of the BJT may be neglected. Which expression is the best approximation of the output voltage $V_o(t)$ ?

GATE ECE 2026

In the circuit shown, the identical transistors Q1 and Q2 are biased in the active region with $\beta=120$. The Zener diode is in the breakdown region with $V_Z=5 \mathrm{~V}$ and $I_Z=25 \mathrm{~mA}$. If $I_L=12 \mathrm{~mA}$ and $V_{E B 1}=V_{E B 2}=0.7 \mathrm{~V}$, then the values of $R_1$ and $R_2$ (in $\mathrm{k} \Omega$, rounded off to one decimal place) are ___________ , respectively.

GATE ECE 2025

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

GATE ECE 2024

The base of an $n p n$ BJT $T 1$ has a linear doping profile $N_B(x)$ as shown below. The base of another $n p n$ BJT $T 2$ has a uniform doping $N_B$ of $10^{17} \mathrm{~cm}^{-3}$. 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 $T 2$ is

GATE ECE 2020

In the voltage regulator shown below, $V_I$ is the unregulated input at 15 V . Assume $V_{B E}=0.7 \mathrm{~V}$ and the base current is negligible for both the BJTs. If the regulated output $V_0$ is 9 V , the value of $R_2$ is $\_\_\_\_$ $\Omega$.

GATE ECE 2020

For the BJT in the amplifier shown below, $V_{B E}=0.7 \mathrm{~V}, \frac{k T}{q}=26 \mathrm{mV}$. Assume that the BJT output resistance ( $r_0$ ) is very high and the base current is negligible. The capacitors are also assumed to be short circuited at signal frequencies. The input $V_i$ is direct coupled. The low frequency voltage gain $\frac{V_0}{V_i}$ of the amplifier is

GATE ECE 2020

In the figure shown, the npn transistor acts as a switch.

For the input v_in(t)as shown in the figure, the transistor switches between the cut-off and saturation regions of operation, when T is large. Assume collector-to-emitter voltage saturation V_CE(sat) = 0.2V and base-to-emitter voltage V_BE = 0.7V. The minimum value of the common-base current gain$$\left( \alpha \right)$$ of the transistor for the switching should be _________.

GATE ECE 2017 Set 1

For the DC analysis of the Common-Emitter amplifier shown, neglect the base current and assume that the emitter and collector current are equal. Given that V_T = 25mV, V_BE = 0.7V, and the BJT output r₀ is practically infinite. Under these conditions the midband voltage gain magnitude, a_v = $$\left| {{v_0}/{v_i}} \right|\,\,\,V/V,$$ is _____

GATE ECE 2017 Set 1

In the circuit shown, transistors Q₁ and Q₂ are biased at a collector current of 2.6 mA. Assuming that transistor current gains are sufficiently large to assume collector current equal to emitter current and thermal voltage of 26m V, the magnitude of voltage gain V_o/V_s in the mid-band frequency range is _____________ (up to second decimal place).

GATE ECE 2017 Set 2

In the circuit shown, I₁ = 80 mA and I₂ b= 4mA. Transistors T₁ and T₂ are identical. Assume that the thermal voltage V_T is 26 mV at 27^oC. At 50^oC, the value of the voltage V₁₂ = V₁ - V₂ (in mV) is _______.

GATE ECE 2015 Set 1

In the ac equivalent circuit shown, the two BJTs are biased in active region and have identical parameters with β >> 1. The open circuit small signal voltage gain is approximately _______.

GATE ECE 2015 Set 2

A BJT is baised in forward active mode Assume V_BE = 0.7 V, kT/q = 25 mV and reverse saturation current I_s = 10^-13A. The transconductance of the BJT (in mA/V) is

GATE ECE 2014 Set 1

For the amplifier shown in the figure, the BJT parameters are V_BE = 0.7 V, $$\beta $$ = 200, and thermal voltage V_T = 25 mV. The voltage gain (V_o/V_i of the amplifier is ______.

GATE ECE 2014 Set 1

In the circuit shown, the silicon BJT has $$\beta \,\,\,\,50.\,\,\,\,\,$$ Assume $${V_{BE}}\,\,\, = \,\,\,0.7$$ and $${V_{CE\left( {sat} \right)}}\, = \,0.2V.$$ Which one of the following statements is correct ?

GATE ECE 2014 Set 3

A BJT in common-base configuration is used to amplify a signal received by a $$50\,\Omega $$ antena. Assume kT/q = 25 mV. The value of the collector bias current ( in mA ) required to match the input impedance of the amplifier to the impedance of the antena is ______.

Consider the common-collector amplifier in the figure (bias circuitry ensures that the transistor operates in forward active region, but has been omitted for simplicity). Let I_C be the collector current, V_BE be the base-emitter voltage and V_T be the thermal voltage. Also, 𝑔_m and 𝑟_o are the small-signal transconductance and output resistance of the transistor, respectively. Which one of the following conditions ensures a nearly constant small signal voltage gain for a wide range of values of R_E?

For the common collector amplifier shown in the figure, the BJT has high $${V_{CE\left( {sat} \right)}},$$ and $${V_{BE}}$$ $$\, = \,\,0.7\,\,\,V$$. The maximum undistorted peak-to-peak output voltage $${V_o}$$ (in Volts) is _____.

In the circuit shown below, the silicon npn transistor Q has a very high value of $$\beta $$. The required value of R₂ in k$$\Omega $$ to produce I_c = 1mA is

GATE ECE 2013

The voltage gain A_v of the circuit shown below is

GATE ECE 2012

For a BJT, the common-base current gain $$\alpha = \,\,0.98$$ and the colector base junction reverse bias saturation current I_co = 0.6 $$\mu {\rm A}$$. This BJT is connected in the common emitter mode and operated in the active region with a base drive current I_B = 20$$\mu {\rm A}$$. The collector current I_c for this mode of operation is

GATE ECE 2011

For the BJT Q₁ in the circuit shown below, $$\beta = \infty ,\,\,\,\,{V_{BEon\,}}\, = \,0.7V,\,\,\,{V_{CEsat}}\, = \,0.7V.$$. The switch is initially closed. at time t = 0, the switch is opened. The time t at which q₁ leaves the active region is

GATE ECE 2011

A small signal source V_i(t) = A cos 20t + B sin 10⁶ t, is applied to a transistor Amplifier as shown in fig. The transistor has $$\beta $$ = 150 and h_ie = 3k$$\Omega $$ , which expression best approximates $${V_0}\left( t \right)$$ ?

GATE ECE 2009

In the following transistor circuit, V_BE = 0.7V, r_e = 25m/I_E, $$\beta $$ and all the capacitances are very large.

The mid-band voltage gain of the amplifier is approximately

GATE ECE 2008

In the following transistor circuit, V_BE = 0.7V, r_e = 25m/I_E, $$\beta $$ and all the capacitances are very large.

The Value of DC current I_E is

GATE ECE 2008

In a transconductance amplifier , it is desirable to have

GATE ECE 2007

For the BJT circuit shown, assume that the $$\beta $$ of the transistor is very large and V_BE = 0.7 V. The mode of operation of the BJT is

GATE ECE 2007

In the transistor amplifier circuit shown in the figure below, the transistor has the following parameters: $${\beta _{DC}}$$ = 60, $${V_{BE}}$$ = 0.7V, $${h_{ie}} \to \,\,\infty $$, $${h_{fe}} \to \,\,\infty $$. The capacitance C_C can be assumed to be infinite.

If $${\beta _{DC}}$$ is increased by 10%, the collector-to emitter voltage drop

Under the DC conditions, the collector-to emitter voltage drop is

The small-signal gain of the amplifier $${{{V_c}} \over {{V_s}}}$$ is

For an npn transistor connected as shown in the figure, V_BE = 0.7 volts. Given that reverse saturation current of the junction at room temperature $${300^0}$$ K is $${10^{ - 13}}\,{\rm A}$$, the emitter current is $$\left( {\eta \, = \,1} \right)$$

GATE ECE 2005

The circuit using a BJT with β = 50 and V_BE = 0.7 V is shown in the figure. The base current I_B and collector voltage V_C are respectively

GATE ECE 2005

A bipolar transistor is operating in the active region with a collector current of 1mA. Assuming that the 'β' of the transistor is 100 and the transconductance (g_m) and the input resistance ($${r_\pi }$$) of the transistor in the common emitter configuration, are

GATE ECE 2004

In the amplifier circuit shown in the figure, the values of R₁ and R₂ are such that the transistor is operating at V_CE = 3V and I_C = 1.5 mA when its $$\beta $$ is 150. For a transistor with $$\beta $$ of 200, the operating point (V_CE, I_C) is

GATE ECE 2003

Three identical amplifiers with each one having a voltage gain of 50, input Resistance of 1 KΩ and output resistance of 250Ω, are cascaded. The open circuit voltage gain of the combined Amplifier is

GATE ECE 2003

In the circuit shown in the figure assume that the transistor is in the active region. It has a large β and its base Emitter voltage is 0.74. The value of I_c is

GATE ECE 2000

Match the following.

Group - I

(a)Cascode amplifier
(b)Differential Amplifier
(c)Darlington pair common-collector Amplifier

Group - II

(1)does not provide current gain
(2)is a wide band Amplifier
(3)has very low input impedance Emitter Amplifier and very high current gain
(4)has very high input impedance and very high current gain
(5)Provides high common mode voltage Rejection

GATE ECE 1996

A Darlington stage is shown in the figure, if the transconductance of q₁ is g_m1 and q₂ is g_m2, then the overall transconductance
$$g\matrix{ c \cr m \cr } \left[ { \buildrel \Delta \over = {{{i_c}^c} \over {{v_{be}}^c}}} \right]$$ is given by

GATE ECE 1996

If the transistors in fig. has high value of β and a v_BE of 0.65, the current I flowing through the 2 kilo ohms resistance will be ______.

GATE ECE 1992

In figure, all transistors are identical and have a high value of beta. The voltage VDC is equal to ______.

GATE ECE 1991

Which of the following statements are correct for basic transistor Amplifier configurations?

GATE ECE 1990

For good stabilized biasing of the transistor of the CE Amplifier of fig, we should have

GATE ECE 1990

Of the four biasing circuits shown in Fig. For a BJT, indicate the one which can have maximum bias stability:

GATE ECE 1989

The amplifier circuit shown below uses a compostie transistor of a MOSFET and BIPOLAR in cascade. ALL capacitance are large. gm of the MOSFET = 2 mA/V , and h_fe of the BIPOLAR = 99. The overall Transconductance g_m of the composite transistor is

Each transistor in the Darlington pair (see Fig. below) has h_fe = 100. The overall h_fe of the composite transistor neglecting the leakage current is

The transistor in the amplifier shown below has following parameters: $$${h_{fe}}\, = \,100,\,{h_{ie}}\, = \,2k\Omega ,\,{h_{re}}\, = \,0,$$$ $${h_{oe}}\, = \,0.05\,\,m\Omega .\,\,C$$ is very large.

The output impedance is

The quiescent collector current I_c, of a transistor is increased by changing resistance. As a result

An emitter-follower amplifier is shown in the figure, Z_i is the impedance looking into the base of the transistor and Z₀ is the impedance looking into the emitter of the transistor

Marks 5

(a)Draw the small signal equivalent circuit of the amplifier.
(b)Obtain an expression for z_i.
(c)Obtain an expression for z₀.

GATE ECE 2001

For the amplifier of given figure,
$${I_C}\, = \,1.3\,mA,\,{R_C}\, = \,2\,k\Omega ,\,{R_E}\, = \,500\,\Omega ,$$
$${V_T}\, = \,26\,mV,\,\beta \, = \,100,\,{V_{CC}}\, = \,15V,$$
$${V_s}\, = \,0.01\,\sin \left( {\omega t} \right)\,V\,and\,{C_b}\, = \,{C_C}\, = \,10\,\mu F.$$

(a)What is the small-signal voltage gain, $${A_V} = {V_0}/{V_s}?$$
(b)What is the approximate $${A_{v,}}\,\,if\,\,{C_e}\,\,$$ is removed?
(c)What will $${V_0}\,be\,if\,{C_b}$$ is short circuited?

GATE ECE 2000

A bipolar junction transistor amplifier circuit is shown in the figure. Assume that the current source I_bias is ideal, and the transistor has very large$$\beta ,\,\,{r_{b\,\,}} = \,\,0,$$ and the $${r_0}\, \to \,\infty $$.

Determine the ac small-signal mid-band and voltage gain $$\left( {{V_o}/{V_s}} \right),$$ input resistance (R₁, and output resistance (R₀) of the circuit. Assume $${V_{T\,\,}} = \,\,26\,mV.$$

GATE ECE 1999

In the circuit of fig. Determine the resistance R_o seen by the output terminals, ignore the effects of R₁ and R₂.