Electronics and Communication Engineering (EC) 1991 GATE Paper without solution

# Electronics and Communication Engineering (EC) 1991 GATE Paper without solution PDF Download

Page 1

GATE EC - 1991

1.1 An excitation is applied to a system at t = T and its response is zero for
. t T -8 < < Such a system is
(a) non-causal system
(b) stable system
(c) causal system
(d) unstable system
1.2 In a series RLC high Q circuit, the current peaks at a frequency
(a) equal to the resonant frequency
(b) greater than the resonant frequency
(c) less than the resonant frequency
(d) none of the above
1.3 The voltage across an impedance in a network is ( ) ( ) ( ), V s z s I s = where V(s) ,
Z(s) are the Laplace transforms of the corresponding time function
( ) ( ) ( ) , and . v t z t i t The voltage ( ) v t is:
(a) ( ) ( ) ( ) . t z t t ? ? = (b) ( ) ( ) ( )
1
0
. t i t z t d ? t t = -
?
(c) ( ) ( ) ( )
1
0
. t i t z t d ? t t = +
?
(d) ( ) ( ) ( ) t z t i t ? = +
1.4 Two two-port networks are connected in cascade. The combination is to be
represented as a single two-port network. The parameters of the network are
obtained by multiplying the individual
(a) z-parameter matrix (b) h-parameter matrix
(c) y-parameter matrix (d) ABCD parameter matrix
1.5 The pole-zero pattern of a certain filter is shown in the figure below. The filter
must be of the following type.
(a) low pass (b) high pass
(c) all pass (d) band pass
x(t)
t=T
t
×
×
×
jw
-1
+1
-j1
-j2
+j1
+j2
Page 2

GATE EC - 1991

1.1 An excitation is applied to a system at t = T and its response is zero for
. t T -8 < < Such a system is
(a) non-causal system
(b) stable system
(c) causal system
(d) unstable system
1.2 In a series RLC high Q circuit, the current peaks at a frequency
(a) equal to the resonant frequency
(b) greater than the resonant frequency
(c) less than the resonant frequency
(d) none of the above
1.3 The voltage across an impedance in a network is ( ) ( ) ( ), V s z s I s = where V(s) ,
Z(s) are the Laplace transforms of the corresponding time function
( ) ( ) ( ) , and . v t z t i t The voltage ( ) v t is:
(a) ( ) ( ) ( ) . t z t t ? ? = (b) ( ) ( ) ( )
1
0
. t i t z t d ? t t = -
?
(c) ( ) ( ) ( )
1
0
. t i t z t d ? t t = +
?
(d) ( ) ( ) ( ) t z t i t ? = +
1.4 Two two-port networks are connected in cascade. The combination is to be
represented as a single two-port network. The parameters of the network are
obtained by multiplying the individual
(a) z-parameter matrix (b) h-parameter matrix
(c) y-parameter matrix (d) ABCD parameter matrix
1.5 The pole-zero pattern of a certain filter is shown in the figure below. The filter
must be of the following type.
(a) low pass (b) high pass
(c) all pass (d) band pass
x(t)
t=T
t
×
×
×
jw
-1
+1
-j1
-j2
+j1
+j2
GATE EC - 1991

1.6 The necessary and sufficient condition for a rational function of s. T(s) to be
driving point impedance of an RC network is that all poles and zeros should be
(a) simple and lie on the negative axis in the s-plane
(b) complex and lie in the left half of the s-plane
(c) complex and lie in the right half of the s-plane
(d) simple and lie on the positive real axis of the s-plane
1.7 In the signal flow graph of Figure, the gain c/r will be
(a)
11
9
(b)
22
15
(c)
24
23
(d)
44
23
1.8 A second order system has a transfer function given by
( )
2
25
8 25
G s
s s
=
+ +
If the system, initially at rest is subjected to a unit step input at t = 0, the
second peak in response will occur at
(a) p sec (b) sec
3
p
(c)
2
sec
3
p
(d) sec
2
p
1.9 The open loop transfer function of a feedback control system is:
( ) ( )
( )
3
1
1
G s H s
s
=
+
The gain margin of the system is:
(a) 2 (b) 4 (c) 8 (d) 16
1.10 A unity feedback control system has the open loop transfer function
( )
( )
( )
2
4 1 2
2
s
G s
s s
+
=
+
If the input to the system is a unit ramp, the steady state error will be
(a) 0 (b) 0.5 (c) 2 (d) infinity
-1
-1 -1
1
1 C
5
T
2 3 4
Page 3

GATE EC - 1991

1.1 An excitation is applied to a system at t = T and its response is zero for
. t T -8 < < Such a system is
(a) non-causal system
(b) stable system
(c) causal system
(d) unstable system
1.2 In a series RLC high Q circuit, the current peaks at a frequency
(a) equal to the resonant frequency
(b) greater than the resonant frequency
(c) less than the resonant frequency
(d) none of the above
1.3 The voltage across an impedance in a network is ( ) ( ) ( ), V s z s I s = where V(s) ,
Z(s) are the Laplace transforms of the corresponding time function
( ) ( ) ( ) , and . v t z t i t The voltage ( ) v t is:
(a) ( ) ( ) ( ) . t z t t ? ? = (b) ( ) ( ) ( )
1
0
. t i t z t d ? t t = -
?
(c) ( ) ( ) ( )
1
0
. t i t z t d ? t t = +
?
(d) ( ) ( ) ( ) t z t i t ? = +
1.4 Two two-port networks are connected in cascade. The combination is to be
represented as a single two-port network. The parameters of the network are
obtained by multiplying the individual
(a) z-parameter matrix (b) h-parameter matrix
(c) y-parameter matrix (d) ABCD parameter matrix
1.5 The pole-zero pattern of a certain filter is shown in the figure below. The filter
must be of the following type.
(a) low pass (b) high pass
(c) all pass (d) band pass
x(t)
t=T
t
×
×
×
jw
-1
+1
-j1
-j2
+j1
+j2
GATE EC - 1991

1.6 The necessary and sufficient condition for a rational function of s. T(s) to be
driving point impedance of an RC network is that all poles and zeros should be
(a) simple and lie on the negative axis in the s-plane
(b) complex and lie in the left half of the s-plane
(c) complex and lie in the right half of the s-plane
(d) simple and lie on the positive real axis of the s-plane
1.7 In the signal flow graph of Figure, the gain c/r will be
(a)
11
9
(b)
22
15
(c)
24
23
(d)
44
23
1.8 A second order system has a transfer function given by
( )
2
25
8 25
G s
s s
=
+ +
If the system, initially at rest is subjected to a unit step input at t = 0, the
second peak in response will occur at
(a) p sec (b) sec
3
p
(c)
2
sec
3
p
(d) sec
2
p
1.9 The open loop transfer function of a feedback control system is:
( ) ( )
( )
3
1
1
G s H s
s
=
+
The gain margin of the system is:
(a) 2 (b) 4 (c) 8 (d) 16
1.10 A unity feedback control system has the open loop transfer function
( )
( )
( )
2
4 1 2
2
s
G s
s s
+
=
+
If the input to the system is a unit ramp, the steady state error will be
(a) 0 (b) 0.5 (c) 2 (d) infinity
-1
-1 -1
1
1 C
5
T
2 3 4
GATE EC - 1991

1.11 The characteristic equation of a feedback control system is given by
( )
3 2
5 6 0 s s K s K + + + + =
Where K > 0 is a scalar variable parameter. In the root loci diagram of the
system the asymptotes of the root locus for large values of K meet at a point in
the s-plane whose coordinates are
(a) (-3,0) (b) (-2,0) (c) (-1,0) (d) (2,0)
1.12  A linear second order single input continuous time system is described by the
following set of differential equations
( ) ( ) ( )
( ) ( ) ( ) ( )
1 1 2
2 1 2
2 4
2
x t x t x t
x t x t x t u t
= - +
= - +
Where ( ) ( )
1 2
and x t x t are the state variables and ( ) u t is the control variable.
The system is:
(a) controllable and stable (b) controllable but unstable
(c) uncontrollable and unstable (d) uncontrollable and stable
1.13 A linear time-invariant discrete-time system is described by the vector matrix
difference equation
( ) ( ) ( ) 1 x k FX k Gu k + = +
Where ( ) X k is the state vector, F is an n × n constant matrix, G is a
( ) n r × constant matrix and ( ) u k is the control vector. The state transition matrix
of the system is given by inverse Z-transform of
(a) ZI - F (b) (ZI – F) Z (c) ( )
1
ZI F G
-
- (d) ( )
1
ZI F Z
-
-
1.14 A silicon sample is uniformly doped with
16
10 phosphorous atoms/cm
3
and
16
2 10 × boron atoms/cm
3
. If all the dopants are fully ionized, the material is
(a) n-type with carrier concentration of
16 3
10 /cm
(b) p-type with carrier concentration of
16 3
10 /cm
(c) p-type with carrier concentration of
16 3
2 10 /cm ×
(d)
2
T will get damaged and
1
T will be safe
1.15 An n-type silicon sample, having electron mobility
n
µ = twice the hole mobility
,
p
µ is subjected to a steady illumination such that the electron concentration
doubles from its thermal equilibrium value. As a result, the conductivity of the
sample increases by a factor of …
Page 4

GATE EC - 1991

1.1 An excitation is applied to a system at t = T and its response is zero for
. t T -8 < < Such a system is
(a) non-causal system
(b) stable system
(c) causal system
(d) unstable system
1.2 In a series RLC high Q circuit, the current peaks at a frequency
(a) equal to the resonant frequency
(b) greater than the resonant frequency
(c) less than the resonant frequency
(d) none of the above
1.3 The voltage across an impedance in a network is ( ) ( ) ( ), V s z s I s = where V(s) ,
Z(s) are the Laplace transforms of the corresponding time function
( ) ( ) ( ) , and . v t z t i t The voltage ( ) v t is:
(a) ( ) ( ) ( ) . t z t t ? ? = (b) ( ) ( ) ( )
1
0
. t i t z t d ? t t = -
?
(c) ( ) ( ) ( )
1
0
. t i t z t d ? t t = +
?
(d) ( ) ( ) ( ) t z t i t ? = +
1.4 Two two-port networks are connected in cascade. The combination is to be
represented as a single two-port network. The parameters of the network are
obtained by multiplying the individual
(a) z-parameter matrix (b) h-parameter matrix
(c) y-parameter matrix (d) ABCD parameter matrix
1.5 The pole-zero pattern of a certain filter is shown in the figure below. The filter
must be of the following type.
(a) low pass (b) high pass
(c) all pass (d) band pass
x(t)
t=T
t
×
×
×
jw
-1
+1
-j1
-j2
+j1
+j2
GATE EC - 1991

1.6 The necessary and sufficient condition for a rational function of s. T(s) to be
driving point impedance of an RC network is that all poles and zeros should be
(a) simple and lie on the negative axis in the s-plane
(b) complex and lie in the left half of the s-plane
(c) complex and lie in the right half of the s-plane
(d) simple and lie on the positive real axis of the s-plane
1.7 In the signal flow graph of Figure, the gain c/r will be
(a)
11
9
(b)
22
15
(c)
24
23
(d)
44
23
1.8 A second order system has a transfer function given by
( )
2
25
8 25
G s
s s
=
+ +
If the system, initially at rest is subjected to a unit step input at t = 0, the
second peak in response will occur at
(a) p sec (b) sec
3
p
(c)
2
sec
3
p
(d) sec
2
p
1.9 The open loop transfer function of a feedback control system is:
( ) ( )
( )
3
1
1
G s H s
s
=
+
The gain margin of the system is:
(a) 2 (b) 4 (c) 8 (d) 16
1.10 A unity feedback control system has the open loop transfer function
( )
( )
( )
2
4 1 2
2
s
G s
s s
+
=
+
If the input to the system is a unit ramp, the steady state error will be
(a) 0 (b) 0.5 (c) 2 (d) infinity
-1
-1 -1
1
1 C
5
T
2 3 4
GATE EC - 1991

1.11 The characteristic equation of a feedback control system is given by
( )
3 2
5 6 0 s s K s K + + + + =
Where K > 0 is a scalar variable parameter. In the root loci diagram of the
system the asymptotes of the root locus for large values of K meet at a point in
the s-plane whose coordinates are
(a) (-3,0) (b) (-2,0) (c) (-1,0) (d) (2,0)
1.12  A linear second order single input continuous time system is described by the
following set of differential equations
( ) ( ) ( )
( ) ( ) ( ) ( )
1 1 2
2 1 2
2 4
2
x t x t x t
x t x t x t u t
= - +
= - +
Where ( ) ( )
1 2
and x t x t are the state variables and ( ) u t is the control variable.
The system is:
(a) controllable and stable (b) controllable but unstable
(c) uncontrollable and unstable (d) uncontrollable and stable
1.13 A linear time-invariant discrete-time system is described by the vector matrix
difference equation
( ) ( ) ( ) 1 x k FX k Gu k + = +
Where ( ) X k is the state vector, F is an n × n constant matrix, G is a
( ) n r × constant matrix and ( ) u k is the control vector. The state transition matrix
of the system is given by inverse Z-transform of
(a) ZI - F (b) (ZI – F) Z (c) ( )
1
ZI F G
-
- (d) ( )
1
ZI F Z
-
-
1.14 A silicon sample is uniformly doped with
16
10 phosphorous atoms/cm
3
and
16
2 10 × boron atoms/cm
3
. If all the dopants are fully ionized, the material is
(a) n-type with carrier concentration of
16 3
10 /cm
(b) p-type with carrier concentration of
16 3
10 /cm
(c) p-type with carrier concentration of
16 3
2 10 /cm ×
(d)
2
T will get damaged and
1
T will be safe
1.15 An n-type silicon sample, having electron mobility
n
µ = twice the hole mobility
,
p
µ is subjected to a steady illumination such that the electron concentration
doubles from its thermal equilibrium value. As a result, the conductivity of the
sample increases by a factor of …
GATE EC - 1991

1.16 The small signal capacitances of an abrupt
1
P n - junction is
2
1 / nF Cm at zero
bias. If the built in voltage is 1 volt, the capacitance at a reverse bias voltage of
99 volts is equal to …
1.17 Referring to the figure. The switch S is in position 1 initially and steady state
conditions exist from time t = 0 to
0
. t t = The switch is suddenly thrown into
position 2. The current 1 through the 10K resistor as a function of time t from t =
0, is …. (Give the sketch showing the magnitudes of the current at t = 0,
0
and t t t = = 8 )
1.18 Discrete transistors
1 2
and T T having maximum collector current rating of 0.75
amps are connected in parallel as shown in the figure. This combination is treated
as a single transistor to carry a total current of 1 ampere, when biased with self
bias circuit. When the circuit is switched on,
1
T draws 0.55 amps and
2
T draws
0.45 amps. If the supply is kept on continuously, ultimately it is very likely that
(a) both
1 2
and T T get damaged (b) both
1 2
and T T will be safe
(c)
1
T will get damaged and
2
T will be safe
(d)
2
T will get damaged and
1
T will be safe
20V
20V
10K
1
S
2
T 1 T 2
Page 5

GATE EC - 1991

1.1 An excitation is applied to a system at t = T and its response is zero for
. t T -8 < < Such a system is
(a) non-causal system
(b) stable system
(c) causal system
(d) unstable system
1.2 In a series RLC high Q circuit, the current peaks at a frequency
(a) equal to the resonant frequency
(b) greater than the resonant frequency
(c) less than the resonant frequency
(d) none of the above
1.3 The voltage across an impedance in a network is ( ) ( ) ( ), V s z s I s = where V(s) ,
Z(s) are the Laplace transforms of the corresponding time function
( ) ( ) ( ) , and . v t z t i t The voltage ( ) v t is:
(a) ( ) ( ) ( ) . t z t t ? ? = (b) ( ) ( ) ( )
1
0
. t i t z t d ? t t = -
?
(c) ( ) ( ) ( )
1
0
. t i t z t d ? t t = +
?
(d) ( ) ( ) ( ) t z t i t ? = +
1.4 Two two-port networks are connected in cascade. The combination is to be
represented as a single two-port network. The parameters of the network are
obtained by multiplying the individual
(a) z-parameter matrix (b) h-parameter matrix
(c) y-parameter matrix (d) ABCD parameter matrix
1.5 The pole-zero pattern of a certain filter is shown in the figure below. The filter
must be of the following type.
(a) low pass (b) high pass
(c) all pass (d) band pass
x(t)
t=T
t
×
×
×
jw
-1
+1
-j1
-j2
+j1
+j2
GATE EC - 1991

1.6 The necessary and sufficient condition for a rational function of s. T(s) to be
driving point impedance of an RC network is that all poles and zeros should be
(a) simple and lie on the negative axis in the s-plane
(b) complex and lie in the left half of the s-plane
(c) complex and lie in the right half of the s-plane
(d) simple and lie on the positive real axis of the s-plane
1.7 In the signal flow graph of Figure, the gain c/r will be
(a)
11
9
(b)
22
15
(c)
24
23
(d)
44
23
1.8 A second order system has a transfer function given by
( )
2
25
8 25
G s
s s
=
+ +
If the system, initially at rest is subjected to a unit step input at t = 0, the
second peak in response will occur at
(a) p sec (b) sec
3
p
(c)
2
sec
3
p
(d) sec
2
p
1.9 The open loop transfer function of a feedback control system is:
( ) ( )
( )
3
1
1
G s H s
s
=
+
The gain margin of the system is:
(a) 2 (b) 4 (c) 8 (d) 16
1.10 A unity feedback control system has the open loop transfer function
( )
( )
( )
2
4 1 2
2
s
G s
s s
+
=
+
If the input to the system is a unit ramp, the steady state error will be
(a) 0 (b) 0.5 (c) 2 (d) infinity
-1
-1 -1
1
1 C
5
T
2 3 4
GATE EC - 1991

1.11 The characteristic equation of a feedback control system is given by
( )
3 2
5 6 0 s s K s K + + + + =
Where K > 0 is a scalar variable parameter. In the root loci diagram of the
system the asymptotes of the root locus for large values of K meet at a point in
the s-plane whose coordinates are
(a) (-3,0) (b) (-2,0) (c) (-1,0) (d) (2,0)
1.12  A linear second order single input continuous time system is described by the
following set of differential equations
( ) ( ) ( )
( ) ( ) ( ) ( )
1 1 2
2 1 2
2 4
2
x t x t x t
x t x t x t u t
= - +
= - +
Where ( ) ( )
1 2
and x t x t are the state variables and ( ) u t is the control variable.
The system is:
(a) controllable and stable (b) controllable but unstable
(c) uncontrollable and unstable (d) uncontrollable and stable
1.13 A linear time-invariant discrete-time system is described by the vector matrix
difference equation
( ) ( ) ( ) 1 x k FX k Gu k + = +
Where ( ) X k is the state vector, F is an n × n constant matrix, G is a
( ) n r × constant matrix and ( ) u k is the control vector. The state transition matrix
of the system is given by inverse Z-transform of
(a) ZI - F (b) (ZI – F) Z (c) ( )
1
ZI F G
-
- (d) ( )
1
ZI F Z
-
-
1.14 A silicon sample is uniformly doped with
16
10 phosphorous atoms/cm
3
and
16
2 10 × boron atoms/cm
3
. If all the dopants are fully ionized, the material is
(a) n-type with carrier concentration of
16 3
10 /cm
(b) p-type with carrier concentration of
16 3
10 /cm
(c) p-type with carrier concentration of
16 3
2 10 /cm ×
(d)
2
T will get damaged and
1
T will be safe
1.15 An n-type silicon sample, having electron mobility
n
µ = twice the hole mobility
,
p
µ is subjected to a steady illumination such that the electron concentration
doubles from its thermal equilibrium value. As a result, the conductivity of the
sample increases by a factor of …
GATE EC - 1991

1.16 The small signal capacitances of an abrupt
1
P n - junction is
2
1 / nF Cm at zero
bias. If the built in voltage is 1 volt, the capacitance at a reverse bias voltage of
99 volts is equal to …
1.17 Referring to the figure. The switch S is in position 1 initially and steady state
conditions exist from time t = 0 to
0
. t t = The switch is suddenly thrown into
position 2. The current 1 through the 10K resistor as a function of time t from t =
0, is …. (Give the sketch showing the magnitudes of the current at t = 0,
0
and t t t = = 8 )
1.18 Discrete transistors
1 2
and T T having maximum collector current rating of 0.75
amps are connected in parallel as shown in the figure. This combination is treated
as a single transistor to carry a total current of 1 ampere, when biased with self
bias circuit. When the circuit is switched on,
1
T draws 0.55 amps and
2
T draws
0.45 amps. If the supply is kept on continuously, ultimately it is very likely that
(a) both
1 2
and T T get damaged (b) both
1 2
and T T will be safe
(c)
1
T will get damaged and
2
T will be safe
(d)
2
T will get damaged and
1
T will be safe
20V
20V
10K
1
S
2
T 1 T 2
GATE EC - 1991

1.19. The built-in potential of the gate junction of a n-channel JFET is 0.5 volts. The
drain current saturates at 4.0
DS
V = volts when 0.
GS
V = The pinch off voltage is
________.
1.20. In figure, all transistors are identical and have a high value of beta. The voltage
DC
V is equal to ______.
1.21. In figure, both transistors are identical and have a high value of beta. Take the
dc base-emitter voltage drop as 0.7 volt and KT/q = 25 mV. The small signal low
frequency voltage gain ( )
o i
V V is equal to _______
Q 1
Q 2 Q 3
Q 4
5mA 1kO
10 volts
V DC=?
V i
~
1kO
1.2kO
10 volts
-5.7 volts
V O/V=?

## FAQs on Electronics and Communication Engineering (EC) 1991 GATE Paper without solution

 1. What is Electronics and Communication Engineering (EC)?
Ans. Electronics and Communication Engineering (EC) is a branch of engineering that focuses on the design and development of electronic devices, circuits, and communication systems. It involves the study of electronic components, networks, and systems used for signal processing, data communication, and information transmission.
 2. What is the significance of GATE in Electronics and Communication Engineering?
Ans. GATE (Graduate Aptitude Test in Engineering) is an important exam for Electronics and Communication Engineering students. It serves as a qualifying examination for admission into postgraduate programs in prestigious institutes and universities. GATE scores are also used for recruitment in various government and private organizations.
 3. Can you provide some tips for preparing for the GATE exam in Electronics and Communication Engineering?
Ans. Sure! Here are some tips for GATE preparation in Electronics and Communication Engineering: - Understand the exam pattern and syllabus thoroughly. - Create a study plan and allocate time for each subject. - Refer to standard textbooks and study materials recommended for GATE. - Solve previous year question papers and take online mock tests to gauge your preparation level. - Practice numerical problems and focus on conceptual understanding. - Join coaching classes or online platforms for guidance and assistance. - Stay updated with current affairs and the latest developments in the field of Electronics and Communication Engineering.
 4. What are the career prospects for Electronics and Communication Engineering graduates?
Ans. Electronics and Communication Engineering graduates have a wide range of career opportunities. They can work in industries such as telecommunications, electronics manufacturing, consumer electronics, information technology, research and development, and defense. Job roles include electronics engineer, communication engineer, network engineer, embedded systems engineer, VLSI engineer, and research scientist. Additionally, they can pursue higher studies and research in specialized areas of Electronics and Communication Engineering.
 5. What are some popular specializations within Electronics and Communication Engineering?
Ans. Some popular specializations within Electronics and Communication Engineering include: - Digital Communication - VLSI Design - Signal Processing - Wireless Communication - Embedded Systems - Microwave Engineering - Optical Communication - Robotics and Automation - Telecommunication Engineering - Nanoelectronics and Nanotechnology These specializations offer in-depth knowledge and expertise in specific areas, opening up diverse career opportunities for graduates.
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