Bipolar Junction Transistor · Analog Circuits · GATE ECE
Marks 1
1
Consider the circuit shown in the figure. Assuming VBE1 = VEB2 = 0.7 volt, value of the dc voltage Vc2 (in volt) is _______
GATE ECE 2016 Set 3
2
Resistor R1 in the circuit below has been adjusted so that I1 = 1 mA. The bipolar transistor Q1 and Q2 are perfectly matched and have very high current gain, so their base currents are negligible. The supply voltage Vcc is 6 V. The thermal voltage kT/q is 26 mV.
The value of R2 (in $$\Omega $$ ) for which I2 = 100 $$\mu {\rm A}$$ is ________.
GATE ECE 2016 Set 2
3
If the emitter resistance in a common-emitter voltage amplifier is not bypassed, it will
GATE ECE 2014 Set 4
4
In the circuit shown, the PNP transistor has $$\left|{\mathrm V}_\mathrm{BE}\right|=0.7\;\mathrm V$$ and β = 50. Assume that RB = 100 kΩ.
For V0 to be 5 V, the value of RC ( in kΩ) is _____________.
GATE ECE 2014 Set 3
5
A cascade connection of two voltage amplifiers A1 and A2 is shown in the figure. The open-loop
gain Av0, input resistance Rin, and output resistance R0 for A1 and A2 are as follows:
A1: Av0 = 10,Rin = 10 kΩ ,R0 =1 kΩ
A2 : Av0 = 5,Rin = 5 kΩ , R0 = 200 Ω
The approximate overall voltage gain $$\frac{{\mathrm V}_\mathrm{out}}{{\mathrm V}_\mathrm{in}}$$ is ______.
A1: Av0 = 10,Rin = 10 kΩ ,R0 =1 kΩ
A2 : Av0 = 5,Rin = 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
6
The current ib 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
7
In the circuit shown below, capacitors C1 and C2 are very large and are shorts at
the input frequency. Vi
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
8
The amplifier circuit shown below uses a silicon transistor. The capacitors CC and
CE can be assumed to be short at signal frequency and the effect of output
resistance r0 can be ignored. If CE is disconnected from the circuit, which one of
the following statements is TRUE?
GATE ECE 2010
9
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
10
The input impedance (Zi) and the output impedance (Zo) of an ideal transconductance
(voltage controlled current source) amplifier are
GATE ECE 2006
11
The cascode amplifier is a multistage configuration of
GATE ECE 2005
12
Assuming VCesat=0.2V and β = 50, the minimum base current (IB) required to drive the transistor in the figure to saturation is
GATE ECE 2004
13
The current gain of a BJT is
GATE ECE 2001
14
Introducing a resistor in the emitter of a common amplifier, stabilizes the dc operating point against variations in
GATE ECE 2000
15
In a series regulated power supply circuit, the voltage gain Av of the ‘pass’
transistor satisfies the condition:
GATE ECE 1998
16
The circuit of Fig. is an example of feedback of the following type
GATE ECE 1998
17
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:
GATE ECE 1998
18
The emitter coupled pair of BJT’s gives a linear transfer relation between the
differential output voltage and the differential input voltage Vid only. When the
magnitude of Vid is less than '$$\alpha$$' times the thermal voltage, where '$$\alpha$$' is
GATE ECE 1998
19
A BJT is said to be operating in the saturation region if
GATE ECE 1995
20
A transistor having $$\alpha$$ = 0.99 and VBE = 0.7 V, is used in the circuit of the figure.What is the value of the collector current?
GATE ECE 1995
21
In order to reduce the harmonic distortion in an amplifier, its dynamic range has
to be _________
GATE ECE 1994
22
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
23
The bandwidth of an n-stage tuned amplifier, with each stage having a band
width of B, is given by
GATE ECE 1993
24
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
Marks 2
1
Which of the following statements is/are true for a BJT with respect to its DC current gain $\beta$?
GATE ECE 2024
2
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 Vo/Vs
in the
mid-band frequency range is _____________ (up to second decimal place).
GATE ECE 2017 Set 2
3
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 VT = 25mV, VBE = 0.7V, and the BJT output r0 is practically infinite. Under these conditions the midband
voltage gain magnitude, av = $$\left| {{v_0}/{v_i}} \right|\,\,\,V/V,$$ is _____
GATE ECE 2017 Set 1
4
In the figure shown, the npn transistor acts as a switch.
For the input vin(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 VCE(sat) = 0.2V and base-to-emitter voltage VBE = 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
5
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
6
In the circuit shown, I1 = 80 mA and I2 b= 4mA. Transistors T1 and T2 are identical. Assume that the thermal voltage VT is 26 mV at 27oC. At 50oC, the value of the voltage V12 = V1 - V2 (in mV) is _______.
GATE ECE 2015 Set 1
7
For the amplifier shown in the figure, the BJT parameters are VBE = 0.7 V, $$\beta $$ = 200, and thermal voltage VT = 25 mV. The voltage gain (Vo/Vi of the amplifier is ______.
GATE ECE 2014 Set 1
8
A BJT is baised in forward active mode Assume VBE = 0.7 V, kT/q = 25 mV and reverse saturation current Is = 10-13A. The transconductance of the BJT (in mA/V) is
GATE ECE 2014 Set 1
9
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 IC be the collector
current, VBE be the base-emitter voltage and VT be the thermal voltage. Also, 𝑔m and 𝑟o 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 RE?
GATE ECE 2014 Set 4
10
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 _____.
GATE ECE 2014 Set 4
11
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 ______.
GATE ECE 2014 Set 4
12
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
13
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 Ic = 1mA is
GATE ECE 2013
14
The voltage gain Av of the circuit shown below is
GATE ECE 2012
15
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
16
For a BJT, the common-base current gain $$\alpha = \,\,0.98$$ and the colector base junction reverse bias saturation current Ico = 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 IB = 20$$\mu {\rm A}$$. The collector current Ic for this mode of operation is
GATE ECE 2011
17
A small signal source Vi(t) = A cos 20t + B sin 106 t, is applied to a transistor Amplifier as shown in fig. The transistor has $$\beta $$ = 150 and hie = 3k$$\Omega $$ , which expression best approximates $${V_0}\left( t \right)$$ ?
GATE ECE 2009
18
In the following transistor circuit, VBE = 0.7V, re = 25m/IE, $$\beta $$ and all the capacitances are very large.
The Value of DC current IE is
GATE ECE 2008
19
In the following transistor circuit, VBE = 0.7V, re = 25m/IE, $$\beta $$ and all the capacitances are very large.
The mid-band voltage gain of the amplifier is approximately
GATE ECE 2008
20
In a transconductance amplifier , it is desirable to have
GATE ECE 2007
21
For the BJT circuit shown, assume that the $$\beta $$ of the transistor is very large and VBE = 0.7 V. The mode of operation of the BJT is
GATE ECE 2007
22
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 CC can be assumed to be infinite.
If $${\beta _{DC}}$$ is increased by 10%, the collector-to emitter voltage drop
GATE ECE 2006
23
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 CC can be assumed to be infinite.
Under the DC conditions, the collector-to emitter voltage drop is
GATE ECE 2006
24
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 CC can be assumed to be infinite.
The small-signal gain of the amplifier $${{{V_c}} \over {{V_s}}}$$ is
GATE ECE 2006
25
For an npn transistor connected as shown in the figure, VBE = 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
26
The circuit using a BJT with β = 50 and VBE = 0.7 V is shown in the figure. The base current IB and collector voltage VC are respectively
GATE ECE 2005
27
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 (gm) and the input resistance ($${r_\pi }$$) of the transistor in the common emitter configuration, are
GATE ECE 2004
28
In the amplifier circuit shown in the figure, the values of R1 and R2 are such that the transistor is operating at VCE = 3V and IC = 1.5 mA when its $$\beta $$ is 150. For a transistor with $$\beta $$ of 200, the operating point (VCE, IC) is
GATE ECE 2003
29
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
30
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 Ic is
GATE ECE 2000
31
Match the following.
(b)Differential Amplifier
(c)Darlington pair common-collector Amplifier
(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
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
32
A Darlington stage is shown in the figure, if the transconductance of q1 is gm1 and q2 is gm2, 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
$$g\matrix{ c \cr m \cr } \left[ { \buildrel \Delta \over = {{{i_c}^c} \over {{v_{be}}^c}}} \right]$$ is given by
GATE ECE 1996
33
If the transistors in fig. has high value of β and a vBE of 0.65, the
current I flowing through the 2 kilo ohms resistance will be ______.
GATE ECE 1992
34
In figure, all transistors are identical and have a high value of beta. The voltage
VDC is equal to ______.
GATE ECE 1991
35
Which of the following statements are correct for basic transistor Amplifier configurations?
GATE ECE 1990
36
For good stabilized biasing of the transistor of the CE Amplifier of fig, we should have
GATE ECE 1990
37
Of the four biasing circuits shown in Fig. For a BJT, indicate the one which can have maximum bias stability:
GATE ECE 1989
38
Each transistor in the Darlington pair (see Fig. below) has hfe = 100. The overall hfe of the composite transistor neglecting the leakage current is
GATE ECE 1988
39
The quiescent collector current Ic, of a transistor is increased by changing resistance. As a result
GATE ECE 1988
40
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 hfe of the BIPOLAR = 99. The overall Transconductance gm of the composite transistor is
GATE ECE 1988
41
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
GATE ECE 1988
Marks 5
1
An emitter-follower amplifier is shown in the figure, Zi is the impedance looking into the base of the transistor and Z0 is the impedance looking into the emitter of the transistor
(a)Draw the small signal equivalent circuit of the amplifier.
(b)Obtain an expression for zi.
(c)Obtain an expression for z0.
GATE ECE 2001
2
For the amplifier of given figure,
$${I_C}\, = \,1.3\,mA,\,{R_C}\, = \,2\,k\Omega ,\,{R_E}\, = \,500\,\Omega ,$$
$${V_T}\, = \,26\,mV,\,\beta \, = \,100,\,{V_{CC}}\, = \,15V,$$
$${V_s}\, = \,0.01\,\sin \left( {\omega t} \right)\,V\,and\,{C_b}\, = \,{C_C}\, = \,10\,\mu F.$$
$${I_C}\, = \,1.3\,mA,\,{R_C}\, = \,2\,k\Omega ,\,{R_E}\, = \,500\,\Omega ,$$
$${V_T}\, = \,26\,mV,\,\beta \, = \,100,\,{V_{CC}}\, = \,15V,$$
$${V_s}\, = \,0.01\,\sin \left( {\omega t} \right)\,V\,and\,{C_b}\, = \,{C_C}\, = \,10\,\mu F.$$
(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
3
A bipolar junction transistor amplifier circuit is shown in the figure. Assume that the current source Ibias 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
4
In the circuit of fig. Determine the resistance Ro seen by the output terminals, ignore the effects of R1 and R2.
GATE ECE 1998
5
In the cascade amplifier circuit shown below, determine the values of R1, R2 and RL. Such that the quiescent current through the transistors is 1mA and the collector voltage Vc1 = 3V, and Vc2 = 6V. Tke VBE = 0.7V, Transistor $$\beta $$ to be hifgh and base currents to be negligible.
GATE ECE 1997
6
The transistor in the circuit shown in the figure. is so biased (dc biasing N/W is not shown) that the dc collector current IC = 1mA. Supply is VCC = 5V.
The N/W components have following values, RC = 2$$k\Omega $$,
RS = $$1.4k\Omega $$,
RE = $$100\Omega $$.
The transistor has specifications, $$\beta \,\, = \,\,100$$
and base spreading resistance $${r_{bb\,}}^1\, = \,100\Omega $$
Evaluate input resistance Ri for two cases. At a frequency of 10 kHz
(a)CE, the bypass capacitor across RE is 25 $$\mu F$$
(b)The bypass capacitor CE is removed leaving RE unbypassed.
GATE ECE 1997