Sunday 9 February 2014

ECA unit wise bits

   

                                            ECA

                                                     JNTUH OBJECTIVE EXAM

                                             UNIT-1: (SINGLE STAGE AMPLIFIERS)
SECTION-I : Choose the correct answers

1.  Which of the following amplifier has high power gain [ b]
(a) CB (b) CE (c) CC (d) both CB and CE

2.  The slope of ac load line is _________ that of dc load line. [b  ]
(a) same as (b)more than (c) less than (d) None of the above

3.  In a RC coupled amplifier, which of the following component is mainly responsible for harmonic distortion of the signal [   a]
(a) Transistor (b) Biasing resistor (c) coupling capacitor (d) power supply

4.  The voltage gain of well designed single stage CB amplifier is essentially determined by ac collector load and [C ]
A. Emitter resistor Re B. ac alpha C. Input resistance emitter diode D.ac beta.


5.  The emitter of a CE amplifier has no AC voltage because of the [c ]
A. DC voltage unit B. Bypass Capacitor C. Coupling capacitor D. load resistance


6.  Typical value of hie is [ ]
A. 1k B. 25k C.50k D.100k

SECTION-II: Fill in the blanks

7. The parameter h22 has units of  SEIMENS

8. A CC Amplifier has highest current gain but lowest power gain

9. The current gain of single stage CE amplifier is nearly equal to Beta

10. The input impedance Rof a CE amplifier in terms of hie, hoe, hre and load resistance. ___________________.

11. The phase difference between output and input voltages of a CB amplifier is 0


12. According to Miller’s theorem, the feedback capacitance when referred to input side with gain A is _Cin = C(1-A)

13. Trans conductance gin hybrid - π model is defined as  gm = ΔIc / ΔVBE when VCE=Constant



                                             UNIT-2: (Multi stage amplifiers)

1.  The most desirable feature of transformer coupling is its [c]
A. Higher voltage gain B. wide frequency range C.ability to provide impedance matching D. ability to eliminate hum from the output

2.  For matching a circuit of output impedance 200Ω with a load of 8 Ω the turn ratio of the two winding transformer should be [d ]
A. 25 B.1/25 C.1/5 D.5

3.  In the initial stages of a multi stage amplifier, we use [a ]
(a) RC coupling (b) transformer coupling (c) direct coupling (d) None
4.  The bandwidth of a single stage amplifier is ___ that of a multi stage amplifier. [ a ]
(a) more than (b) less than (c) same as (d) none
5.  The Darlington pair consists of the following two stages [ d ]
(a) CE,CC (b)CE,CB (c)both CE (d) both CC
6. Transformer coupling is generally used when Ris Small

7. In a two stage cascaded amplifier, each of two cascaded stages has a voltage gain of 30 then the overall gain is _900

8. Why do we go for multi stage amplifiers? for high gain
9. Direct coupled amplifiers are especially suited for amplifying extremely LOW frequency signals.

10. The DC resistance of transformer coupling is Low so it is more efficient


                            
                                   UNIT-3 (BJT amplifiers-frequency response)

1.  The gain bandwidth product of a two stage amplifier is [ c   ]
(a) same as that of single stage (b) greater than that of single stage
(c) less than that of single stage (d) product of two gain bandwidth products of each stage


2.  How does the amplifier behave for high frequencies? [   b   ]
(a) high pass filter (b) low pass filter (c) band pass filter (d) None


3.  The bandwidth of an amplifier can be increased by [b   ]
A. decreasing the capacitance of its bypass capacitors B.minimizing the stray capacitance
C.increasing the input signal frequency D. cascading it

4.  Lower cutoff frequency of an amplifier is primarily determined by the [D ]
A.Internal capacitance of the active device
B.Stray capacitance between its wiring and ground
C.ac beta(β) value of its active devices
D.Capacitances of coupling and bypass capacitor

5.  The main reason for the variation of amplifier gain with frequency is [A ]
A. the presence of capacitance internal and external B. due to interstage transformation
C. the logarithmic increase in its output power D. miller effect

6. The alpha (α) cut off frequency of a transistor is higher than is beta (β) cut-off frequency
7. The alpha (α) of the transistor Decreases with the increase in frequency

                                              UNIT-IV (MOS amplifiers)

1.  A source follower using FET usually has a voltage gain of _____. [b ]
(a) -1 (b) >100 (c) about -10 (d) less than 1 but positive

2.  For the operation of enhancement only N- Channel MOSFET , value of gate voltage has to be [  a]
A. High positive B. high negative C. low positive D. zero

3. In depletion mode and N- Channel DE MOSFET conducts with Vgs is ZERO
4. A MOSFET can be easily destroyed by any Stray voltage on its gate.
5. The positive gate operation of a N- Channel Depletion MOSFET is known as  Enhancement mode.

6. Cascade amplifier is combination of CB-CE

7. CD amplifieris called as source follower


8. CS amplifier produces a phase shift of 180˚

                                                                                              Prepared By
                                                                                               KAVITHA

PDC unit wise bits


                                                  PDC

                                   UNIT-1(Linear wave shaping)

1. The waveform which preserves its form when transmitted through a linear network is a___________. [  b    ]
(a)Sine wave (b) Step signal (c) impulse signal (d) ramp signal

2.  An RC high pass circuit has R= 1kΩ and C=0.5 μF. Its lower cutoff frequency is [   b]
(a) zero (b) 318.3 Hz (c) 1kHz (d) infinity

3.  For a integrator, if input is square wave then the output waveform is _____ [ a]
(a) Impulse (b) Sawtooth wave (c) Triangular wave (d) Both a and c

4.  A ringing circuit has a quality factor Q=24. This circuit will ring for how many number of cycles? [ c]
(a) 24 (b) 12 (c) 8 (d) 6

5.  The rise time of the output of a low pass RC circuit is given by [c ]
(a) 2.2 RC (b) 0.35/fH (c) 2.2τ (d) all the above

6.  What is the response of step input to a high pass RC circuit [  a ]
a) V e-t/RC b) V (1- et/RC) c) V et/RC d) V(1- e-t/RC )



7.  When RC high pass circuit act as a differentiator? [ a]
a) RC<<T b) RC>>T c)RC=T d)RC=0

8.  What is the name of the circuit which converts square wave in to spikes [ c]
a) Low pass RC b) Bi stable multi c) High pass RC d) Monoshot


section II:   fill in the blanks

9. For DC input signal capacitor C acts as a open circuit

10. The average value of the output value of an RC high pass circuit is Zero

11. In RC integrator circuit the output is taken across capacitor

12. -------------is the condition for an RC high pass circuit to acts as a differentiator.

13. Time constant of RL circuit is     L/R

14. The process of converting pulses into spikes is called  Tilt

15. Write the relationship between time constant and tilt? Linear wave shaping



                     UNIT-2 : Non linear wave shaping

1.  A comparator is a basic building block in a system used to analyze the -------- distribution of noise generated in active device [    b]
a) Both frequency and phase b) Amplitude c) Phase d) Frequency

2.  Zener diode has ---------- temperature coefficient [    b]
a) sometimes positive and sometimes negative b) Only negative.
c) Both positive and negative d) Only positive

3.  A clamping circuit is also called as ____________. [  c ]
(a) dc restorer (b) dc reinserter (c) both a and b (d) none of the above

4.  A clipping circuit consists of ___________. [ c]
(a) Resistor (b) Diode (c) both a and b (d) c and capacitor

section II:   fill in the blanks

5. The clamping theorem is given by  Af/Ar=Rf/R

6. When the diode is forward biased it acts as closed switch


UNIT-III: SWITCHING CHARACTERISTICS OF DEVICES


1.  Common base configurations is little used because [  C]
a) High voltage gain b) High current gain c) It has low input impedance d) High input impedance

2.  The Vce (sat) of Si n-p-n transistor at 27 c is [ B ]
a) 0.7 v b) 0.3 v c) 0.8 v d) 0.1 v

3.  Turn off time of the transistor is = ------- [A ]

a)   toff =tf +ts b) toff =tf +ton c) toff =tfd +ts d) toff =ton +ts


               

                                             Unit-IV: multivibrators

 Section-I:  Multiple choice questions

1.  Monostable multivibrators generates [ b  ]
a) Pulse wave form b) Ramp signal c) Sine wave d) Square wave

2.  A sinusoidal waveform can be converted to a square waveform by using _______ [ c  ]
(a) Astable multivibrator (b) Bitable multivibrator (c ) Schmitt trigger (d) None of the above

3.  A Schmitt trigger is a __________. [ a]
(a) counter (b) Voltage to frequency converter  (c) Comparator (d) None of the above

Section-I: Fill in the blanks:

1.     A bistable multivibrator is used for 0.5MHz

2.     The time constant of a monostable multivibrator is 2.2τ = 2.2RC = 0.35/f2

3.     _______________ circuit is used to generate the sequence of pulses which are regularly spaced in time

     4. No of quasi stable states of astable is    2

5. The expression of pulse width for monostable multivibrator is  (T/2RC) X 100




                                                                                           Prepared by                                                                                                                             G.swathi