# Electronic Circuit Analysis Important Quetion Bank 2016

11 Feb 2016    07:06 pm

ECA QUESTION BANK

Part A:

UNIT_ I

1. h-parameter values are hie=1100 ohms, hfe= 50, hoe =25 uA/V, hoe=2.5x10-4 and RL=1k.Find

out Current gain in CE configuration?

2. Write equation for Rif and Rof, If Rf is miller element?

3. In Multistage amplifier Av1= 10, Av2=20 & Av3=30 find out overall gain of multistage

amplifier?

4. Mention the different types of coupling in amplifier?

5. Mention the importance of Darlington Pair?

6. Mention the different types of Distortions in amplifiers?

UNIT-II

1. Lower cut –off frequency 100 hz , find out the 3-stage amplifier lower Cut-off frequency ?

2. Write the expression of rb’c  and  r b’e   of  π-Model?

3. Define fT of an amplifier?

4. Mention the relationship between fT    and fβ     of an amplifier?

5. Write the expression for the Voltage gain of CE amplifier with short circuit?

6. Write the expression for the Voltage gain of CE amplifier with load resistance RL?

PART-B

UNIT-I

1. (a) State Millers Theorem and its duality?

(b) Derive the expressions for the voltage gain, input resistance and output

resistance of common collector circuit using simplified Hybrid Model.

2. (a)A transistor in CB circuit has the following set of hybrid parameters.

hib=20Ω,hfb=0.98,hrb=0.5*10-4,hob=1.5KΩ.Find the values, Ri,Ro,Ai &Av ,if Rs=600Ω and

RL=1.5KΩ.

(b) Using the h-parameter model, derive the expression for current gain ,     input

impedance, voltage gain and output impedance of a CE configuration.

3.  (a) Draw the CE amplifier with un bypassed emitter resistance and derive the

expression for its Ri and Av.

(b) Compare three types of coupling methods used in multistage amplifier.

4.  (a) Draw the circuit diagram of Darlington pair.

(b) Derive the expression for overall current gain and overall input impedance of

Darlington pair.

5.  (a) An amplifier consists of three identical stages in cascade, the bandwidth of

overall amplifier extends 20Hz to 20KHz.Calculate the bandwidth of individual

stages.

(b) When n-identical stages of Amplifiers are cascaded. Derive the expression for

overall lower and upper 3-dB frequencies.

6. Two BJT CE amplifiers in self biasing configuration are connected in cascade.

The following are the parameters of each circuit:

The biasing resistors are R1=10KΩ; R2=5KΩ ; Collector resistor RC=2KΩ ;

Emitter Resistor RE=2KΩ .hie=1KΩ ;hfe=100.Neglect the effect of hoe.

Calculate the Voltage gain, input impedance and output impedance of the cascade.

UNIT-II

1. Derive the Expressions for hybrid-π conductance elements in terms of low

2. (a) Prove that fT= fβ hfe.

3.  The following low frequency parameters are known for a given transistor at

frequency h-parameters.

(b) Draw the Hybrid- π model for a common emitter transistor.

room temperature(300K) at IC=10mA and VCE=8V. hie=500 ,hoe=2*10-4 µs,hfe=100 and

hre=10-4.At the same operating point fT=50MHz and cob=3PF.Calculate the values of

hybrid-π parameters.

4. Derive the expression for CE short circuit Current gain.

5.(a) Explain about Gain-bandwidth product of an amplifier.

(b) Derive the expression for CE current gain with Resistive load.

6.(a)Explain the Effect of Coupling Capacitor on  Frequency response of an

Amplifier?

(b) Draw the small signal model for common-source MOSFET amplifier.

UNIT-III

1. (a). The open loop gain of an amplifier is 100.What will be the overall gain

when a negative feedback of 0.5 is applied to the amplifier.

(b). what are the different mixing techniques used in any feedback system?

Explain.

2.  (a). Draw the circuit of a voltage series feedback amplifier and derive the

expressions for Rif and Rof.

(b). what are characteristics of an amplifier that are modified by negative

feedback. Draw the four types of feedback amplifiers naming them.

3.  (a). Expailn the concept of feedback system.

(b). Draw the block diagram of Current Shunt feedback system and derive the

expression for Rif and Rof.

4. (a). Derive an expression for frequency of oscillations of a RC phase-shift

oscillator using BJT.

(b) In a Hartely oscillator L2=0.04mH and C=0.004µF.If the frequency of

oscillations is 150KHz, find L1.Neglect mutual inductance.

5. (a). Give the two Barkhausen conditions required in order for sinusoidal

oscillations to be sustained.

(b). Draw the circuit diagram of Colpitts oscillator and derive the expression for

frequency of oscillations& conditions for sustained oscillations.

6. (a). Determine the frequency of oscillations when a RC phase-shift oscillator has

R=10KΩ,C=0.01µF and RC=2.2KΩ.Also the minimum current gain required for this.

(b). Draw the circuit diagram of wien bridge oscillator and derive the expression

for frequency of oscillations.

UNIT-IV

1. (a). Derive the maximum efficiency of Class-A transformer coupled amplifier.

(b). What is cross-over distortion? Explain

2. (a). A transistor supplies 0.8W to a 5K load .The zero signal dc collector current is

30mA, and the dc collector current with signal is 36mA.Determine the percentage

second-harmonic distortion.

(b). Derive the maximum efficiency of push-pull Class-B power amplifier.

3. (a). For a Class-B amplifier providing a 20V peak signal to a 16Ω load operates on

a power supply of VCC=30V.Determine the input power, output power and circuit

effieiciency.

(b). How amplifiers are classified based on the biasing conditions.

4. (a). What is class-B amplifier? Why is it designed? Give its circuits?

(b). In a class-A power amplifier ,VCEmax =15V,VCEmin= 1V.Find the overall efficiency

5. (a).What are the differences between Small signal amplifiers and Large signal

amplifiers.

(b). Calculate the transformer turns ratio required to match a 8Ω to speaker load to

an amplifier so that the effective load resistance is 3.2KΩ.

6. (a). Draw the circuit diagram of complementary-symmetry class-B power amplifier

and explain its working.

(b). Write short notes on Heatsink.

UNIT-V

1.(a). What is a tuned amplifier ? What are the various types of tuned amplifier.

(b). What are the advantages of Stagger tuned amplifier?

2. (a). Why parallel resonance circuits are used in tuned amplifies.?

(b). Draw the equivalent circuit of Double tuned amplifier and derive the

expression for gain at resonance.

3. Draw the equivalent circuit of a single tuned capacitive coupled tuned amplifier

and derive the expression for gain at resonance.

4. Draw the equivalent circuit of a single tuned inductive coupled tuned amplifier

and derive the expression for gain at resonance.

5. A tank circuit has a capacitor of 100PF and an inductor of 100µH.The resistance

of the inductor is 5Ω. Determine the (i) resonant frequency (ii) impedance at

resonance (iii) Q-factor, and (iv)bandwidth.

6. Compare different types of tuned amplifies.  