FREQUENTLY ASKED QUESTIONS/ASSIGNMENT

BTEEE 303 – ANALOG ELECTRONICS

ANSWER ALL QUESTIONS
MODULE I
1. DC Load Lines in Transistors
Explana on: A DC load line is a graphical representa on of the constraints imposed by the external
circuit on the transistor. It is plo ed on the transistor’s characteris c curves to determine the opera ng
point or Q point of the transistor.
| Ic
|
| /
| /
| /
|/
|/_________ Vce
Significance of Q Point: The Q point (quiescent point) represents the steady-state opera ng condi on of
the transistor when no signal is applied. It is crucial for ensuring that the transistor operates in the
desired region (ac ve, cutoff, or satura on) and maintains linearity and stability.

2. h-Parameter Small Signal Low Frequency Model for BJT

Diagram:
+Vcc
|
Rc
|
Cb
|
|------+
| |
| Re
| |
| |
Vce Ic
|
Ce
|
GND

(hie = input impedance, hre = reverse voltage gain, hfe = forward current gain, hoe = output
admi ance)

Explana on:
 h_ie: Input impedance of the transistor.
 h_re: Reverse voltage gain.
  h_fe: Forward current gain (current gain).
 h_oe: Output admi ance.
The small-signal model uses these parameters to simplify analysis of the transistor's behavior in small
signal condi ons.

3. Design of Zener Voltage Regulator

Design Steps:
1. Select Zener Diode: Choose a Zener diode with the desired voltage (Vz) and power ra ng.
2. Calculate Series Resistor (Rs):
o Given: Input Voltage (Vin), Zener Voltage (Vz), and Load Resistance (RL).
o Use the formula: Rs=Vin−VzIz+ILRs = \frac{Vin - Vz}{Iz + I_{L}}Rs=Iz+ILVin−Vz
where ILI_{L}IL is the load current and IzIzIz is the Zener current.
3. Verify Power Ra ngs: Ensure the Zener diode and series resistor can handle the power
dissipa on.

4. Drawing DC Load Line and Fixing Q Point

Procedure:
1. Determine Load Line: Plot the load line on the transistor’s output characteris cs using:
VCE=VCC−IC⋅RCV_{CE} = V_{CC} - I_C \cdot R_CVCE=VCC−IC⋅RC
2. Fix Q Point: The Q point is where the load line intersects the transistor’s characteris c curve.
Choose a Q point that ensures opera on in the ac ve region.
Factors Affec ng Stability:
 Thermal Effects: Temperature changes can shi the Q point.
 Varia ons in β: Changes in transistor beta (current gain) affect stability.
 Power Supply Varia ons: Fluctua ons in supply voltage can alter the Q point.

5. Bias Compensa on Techniques

Diode Compensa on:
 A diode is placed in the base circuit to provide nega ve temperature coefficient compensa on.
As temperature rises, the diode's voltage drop decreases, which compensates for the increase in
base-emi er voltage.
Thermistor Compensa on:
 A thermistor (temperature-sensi ve resistor) is used to provide temperature compensa on by
adjus ng the biasing network. As temperature changes, the resistance of the thermistor changes
to counteract the effect on the transistor.
6. AC Equivalent Circuit of CE Amplifier
Diagram:
Vin
|
C1
|
|----> Base
|
Re
|
C2
|
Vout
Role of Capacitors:
 C1: Bypass capacitor, used to couple AC signals while blocking DC.
 C2: Emi er bypass capacitor, used to stabilize the gain by bypassing the AC signal around the
emi er resistor.

7. Voltage Divider Bias Circuit Design

Design Steps:
1. Choose Resistors:
o Given: VCE = VE = 6V, IC = 1.5mA, β = 90.
o Use the following rela ons: VE=VCE=6VVE = VCE = 6VVE=VCE=6V IC=VCERCIC =
\frac{VCE}{RC}IC=RCVCE RC=6V1.5mA=4kΩRC = \frac{6V}{1.5mA} =
4k\OmegaRC=1.5mA6V=4kΩ
o For the voltage divider: Use: VR1=VCC−VBE−VR2V_R1 = VCC - VBE - V_R2VR
1=VCC−VBE−VR2 R1=VR1IBR1 = \frac{V_R1}{I_B}R1=IBVR1 R2=VR2IBR2 =
\frac{V_R2}{I_B}R2=IBVR2
Stability Factor (S):
S=1+R2R1S = 1 + \frac{R2}{R1}S=1+R1R2

8. h-Parameters Calcula on for CE Amplifier

Given Parameters:
 hie=1000Ωh_{ie} = 1000 \Omegahie=1000Ω
 hre=2×10−4h_{re} = 2 \ mes 10^{-4}hre=2×10−4
 hfe=50h_{fe} = 50hfe=50
 hoe=25μΩh_{oe} = 25 \mu \Omegahoe=25μΩ
 Load and Source Resistance = 1 kΩ
Current Gain (β):
β=hfe=50\beta = h_{fe} = 50β=hfe=50
Voltage Gain (Av):
Av=hfe1+hoe⋅RL≈501+(25×10−6×1000)≈50Av = \frac{h_{fe}}{1 + h_{oe} \cdot RL} \approx \frac{50}{1 +
(25 \ mes 10^{-6} \ mes 1000)} \approx 50Av=1+hoe⋅RLhfe≈1+(25×10−6×1000)50≈50

9. Expressions for CE Amplifier

Current Gain (β):
β=hfe\beta = h_{fe}β=hfe
Input Impedance (Zi):
Zi=hieZi = h_{ie}Zi=hie
Voltage Gain (Av):
Av=hfe1+(hoe⋅RL)Av = \frac{h_{fe}}{1 + (h_{oe} \cdot RL)}Av=1+(hoe⋅RL)hfe
Output Impedance (Zo):
Zo=1hoeZo = \frac{1}{h_{oe}}Zo=hoe1

10. Collector to Base Circuit of Transistor Amplifier

Diagram:
Vcc
|
Rc
|
Cb
|
|------+
| |
| Re
| |
| |
Vce Ic
|
GND
Calcula ons:
1. Ic:
Ic=Vcc−VceRcIc = \frac{Vcc - Vce}{Rc}Ic=RcVcc−Vce
2. VCE:
VCE=Vcc−Ic⋅RcVCE = Vcc - Ic \cdot RcVCE=Vcc−Ic⋅Rc
DC Load Line Diagram: Same as described in ques on 1.
Significance of Q Point: Represents the transistor’s opera ng point ensuring it func ons properly in the
desired region.

MODULE II
1. Enhancement Type MOSFET (E-MOSFET)
Construc on:
  N-Channel E-MOSFET: Consists of a p-type substrate with two n-type regions forming the source
and drain. A thin layer of silicon dioxide (SiO2) is grown on the substrate with a gate electrode
deposited on top.
 P-Channel E-MOSFET: Consists of an n-type substrate with two p-type regions forming the source
and drain. The gate is also separated from the channel by a thin SiO2 layer.
Opera on:
 N-Channel: When a posi ve voltage is applied to the gate rela ve to the source, it a racts
electrons towards the gate region, forming a conduc ve channel between the source and drain.
 P-Channel: When a nega ve voltage is applied to the gate rela ve to the source, it a racts holes
towards the gate region, forming a conduc ve channel.
Diagram:
Gate
|
--------
| |
Source | | Drain
| |
--------
|
Substrate
2. Drain Characteris cs of JFET
Explana on: The drain characteris cs of a JFET show the rela onship between the drain current (IDI_DID
) and the drain-source voltage (VDSV_{DS}VDS) for various gate-source voltages (VGSV_{GS}VGS).
Diagram:
I_D
|
| _____
| /
| /
| /
| /
| /
|/
|/_________________ V_DS
V_P (Pinch-Off Voltage)
Pinch-Off Voltage: The pinch-off voltage (VPV_PVP) is the gate-source voltage at which the drain current
becomes constant despite further increases in VDSV_{DS}VDS.
3. Construc on and Working of JFET
N-Channel JFET:
 Construc on: N-type semiconductor material is used for the channel with P-type material
forming the gate. Source and drain are also made from N-type material.
 Working: When a nega ve voltage is applied to the gate rela ve to the source, the channel is
pinched off, reducing the current flow.
P-Channel JFET:
  Construc on: P-type semiconductor material is used for the channel with N-type material
forming the gate. Source and drain are also made from P-type material.
 Working: When a posi ve voltage is applied to the gate rela ve to the source, it pinches off the
channel, controlling the current.
4. Construc on and Working of E-MOSFET
N-Channel E-MOSFET:
 Construc on: Made of a p-type substrate with n-type source and drain regions. The gate is
isolated from the substrate by an oxide layer.
 Working: Applying a posi ve voltage to the gate creates an inversion layer that forms a
conduc ve channel between source and drain.
P-Channel E-MOSFET:
 Construc on: Made of an n-type substrate with p-type source and drain regions. The gate is
isolated from the substrate by an oxide layer.
 Working: Applying a nega ve voltage to the gate creates a conduc ve channel between source
and drain.
5. Drain and Transfer Characteris cs of FET
Drain Characteris cs:
 Plot: Drain current (IDI_DID) vs. Drain-Source voltage (VDSV_{DS}VDS) for different gate-source
voltages (VGSV_{GS}VGS).
Transfer Characteris cs:
 Plot: Drain current (IDI_DID) vs. Gate-Source voltage (VGSV_{GS}VGS) for a fixed drain-source
voltage (VDSV_{DS}VDS).
Diagrams:
1. Drain Characteris cs:
I_D
|
| _________
| /
| /
| /
| /
|/
|/_________________ V_DS

Transfer Characteris cs:

 I_D

| /

| /

| /

| /

| /

| /

|/

|/_________________ V_GS

6. CD and CS Amplifiers

Common Drain (CD) Amplifier:

 Diagram:

V_in

C1

|----> Source

R_D

V_out

GND

Explana on: Acts as a voltage follower. It has high input impedance and low output impedance. The
output voltage follows the input voltage with minimal gain.

Common Source (CS) Amplifier:

 Diagram:
 V_in

C1

|----> Gate

R_G

Source

|----> Drain

R_D

V_out

GND

 Explana on: Provides high voltage gain. The output is taken from the drain and the source is
usually grounded.

7. (a) Frequency Response Curve of RC Coupled Amplifier

Curve:

Gain
 |

| _________

| /

| /

| /

| /

|/

|/_____________ Frequency

Methods to Improve Gain-Bandwidth Product:

 Use of Mul ple Stages: Increases gain while maintaining bandwidth.

 Feedback Techniques: Enhances stability and bandwidth.

(b) JFET Parameters and Transconductance

Parameters:

1. IDSSI_DSSIDSS: Drain-source satura on current.

2. VPV_PVP: Pinch-off voltage.

3. VGS(off)V_GS(off)VGS(off): Gate-source cutoff voltage.

4. gmg_mgm: Transconductance.

Transconductance (gmg_mgm):

gm=∂ID∂VGSg_m = \frac{\par al I_D}{\par al V_{GS}}gm=∂VGS∂ID

8. (a) JFET Common Drain Amplifier Design

Voltage Divider Biasing:

1. Design: Use resistors to set the gate voltage. Connect a resistor between the source and ground
to set the source voltage.

2. Calcula on:

o Set VGSV_GSVGS using a voltage divider.

o Ensure the source resistor is chosen to provide the desired bias current.

(b) Internal Capacitances of BJT

Capacitances:

1. Base-Collector Capacitance (CbcC_{bc}Cbc): Determines high-frequency response.

 2. Base-Emi er Capacitance (CbeC_{be}Cbe): Affects the small-signal frequency response.

3. Collector-Emi er Capacitance (CceC_{ce}Cce): O en neglected in low-frequency models.

Incorpora on in Hybrid-π Model:

 CbeC_{be}Cbe is included between base and emi er.

 CbcC_{bc}Cbc is included between base and collector.

9. Common Drain JFET Amplifier Parameters

Circuit Diagram:

V_in

C1

|----> Gate

R_S

Source

Drain

R_D

V_out

GND

Expressions:

1. Input Impedance (ZinZ_{in}Zin):

Zin=1gmZ_{in} = \frac{1}{g_m}Zin=gm1

2. Current Gain (β\betaβ):

β=IDVGS\beta = \frac{I_D}{V_{GS}}β=VGSID

3. Voltage Gain (Av):

Av=VoutVinA_v = \frac{V_{out}}{V_{in}}Av=VinVout

4. Output Impedance (ZoutZ_{out}Zout):

Zout=RDZ_{out} = R_DZout=RD

10. (a) Transfer Characteris cs of JFET

Explana on:

 Graph: Shows how the drain current (IDI_DID) varies with the gate-source voltage
(VGSV_{GS}VGS).

Equa on:

ID=IDSS(1−VGSVP)2I_D = I_{DSS} \le (1 - \frac{V_{GS}}{V_P}\right)^2ID=IDSS(1−VPVGS)2

(b) High Frequency Hybrid π Model of CE Transistor

Diagram:

____

| |

| | C_ie | |

|____|

Base

| | C_bc | |

|____|

Collector

Explana on:

 CbeC_{be}Cbe: Base-Emi er capacitance.

  CbcC_{bc}Cbc: Base-Collector capacitance.

MODULE III

 Advantages of Nega ve Feedback Amplifier:

 Improves Stability: Reduces sensi vity to component varia ons.

 Enhances Bandwidth: Increases bandwidth.

 Reduces Distor on: Minimizes harmonic distor on.

 Barkhausen’s Criterion of Oscilla on:

 Criterion: For sustained oscilla ons, the loop gain must be equal to 1 and the total phase shi
around the loop must be 360 degrees or 0 degrees.

 Mul stage Amplifiers and Coupling:

 Mul stage Amplifiers: Amplifiers connected in series to increase gain.

 Coupling Types: RC coupling, transformer coupling, direct coupling.

 Direct, RC, and Transformer Coupled Amplifiers:

Direct Coupling:

 Advantages: Simple, wide bandwidth.

 Disadvantages: DC level shi s can affect performance.

RC Coupling:

 Advantages: Good frequency response, easy to design.

 Disadvantages: Loss of gain at high frequencies.

Transformer Coupling:

 Advantages: High efficiency, impedance matching.

 Disadvantages: Bulkier, frequency response limited.

 Opera on of Power Amplifiers:

Class A:

 Opera on: Conduc on over the en re input signal cycle.

 Advantages: High linearity.

 Disadvantages: Low efficiency (~25%).

Class B:

 Opera on: Conduc on for half of the input signal cycle.

  Advantages: Higher efficiency (~50%).

 Disadvantages: Crossover distor on.

Class AB:

 Opera on: Conduc on for slightly more than half of the input signal cycle.

 Advantages: Good efficiency and linearity.

 Disadvantages: Complexity.

Class C:

 Opera on: Conduc on for less than half of the input signal cycle.

 Advantages: High efficiency (up to 80%).

 Disadvantages: Nonlinear opera on, used in RF amplifiers.

 Conversion Efficiency of Class A/Class B:

Class A Efficiency:

η=PoutPin=VCE⋅ICVCC⋅IC\eta = \frac{P_{out}}{P_{in}} = \frac{V_{CE} \cdot I_C}{V_{CC} \cdot I_C}η=Pin

Pout=VCC⋅ICVCE⋅IC ηmax=25%\eta_{max} = 25\%ηmax=25%

Class B Efficiency:

η=PoutPin=VCC⋅Iout2⋅VCC⋅Iout=50%\eta = \frac{P_{out}}{P_{in}} = \frac{V_{CC} \cdot I_{out}}{2 \cdot

V_{CC} \cdot I_{out}} = 50\%η=PinPout=2⋅VCC⋅IoutVCC⋅Iout=50%

 Crystal Oscillator Circuit:

Diagram:

+Vcc

C1

|----> Base

Re

C2

|
 GND

 Explana on: The crystal sets the frequency of oscilla on by providing a specific resonance frequency.

8) Two-Stage RC Coupled Amplifier:

Diagram:

Stage 1:

Vin ----> C1 ----> Base

R1

Collector ----> C2 ----> Base of Stage 2

Stage 2:

Emi er of Stage 1 ----> Emi er of Stage 2

1. Output Rela on:

o Stage 1: Gain A1=Vout1VinA_1 = \frac{V_{out1}}{V_{in}}A1=VinVout1

o Stage 2: Gain A2=Vout2Vout1A_2 = \frac{V_{out2}}{V_{out1}}A2=Vout1Vout2

o Total Gain Atotal=A1×A2A_{total} = A_1 \ mes A_2Atotal=A1×A2

2. Two-Stage RC Coupled Amplifier Efficiency:

o Circuit: Use RC coupling for impedance matching and gain stages.

o Design: Ensure proper biasing and coupling capacitors.

Class B Push-Pull Efficiency:

η=PoutPin where Pout=VCC2π⋅RL\eta = \frac{P_{out}}{P_{in}} \text{ where } P_{out} =

\frac{V_{CC}^2}{\pi \cdot R_L}η=PinPout where Pout=π⋅RLVCC2

Class A Efficiency:

η=PoutPin\eta = \frac{P_{out}}{P_{in}}η=PinPout

Efficiency Comparison:

o Class B has higher efficiency due to reduced power dissipa on compared to Class A.

3. Posi ve vs. Nega ve Feedback:

Posi ve Feedback:
  Enhances: Gain.

 Usage: Oscillators, amplifiers.

Nega ve Feedback:

 Reduces: Gain but improves stability.

 Usage: Amplifiers, stabilizers.

RC Phase Shi Oscillator:

Diagram:

Vcc

C1

|----> Base

R1

C2

GND

Frequency of Oscilla on:

f=12πRCf = \frac{1}{2 \pi R C}f=2πRC1

MODULE IV

1. Ideal vs. Prac cal Characteris cs of Op-Amp:

Ideal Characteris cs:

o Infinite gain.

o Infinite input impedance.

o Zero output impedance.

Prac cal Characteris cs:

o Finite gain.

o High but finite input impedance.

 o Low but non-zero output impedance.

2. Three-Input Summing Amplifier Design:

Design:

o Gain: G1=2G_1 = 2G1=2, G2=3G_2 = 3G2=3, G3=5G_3 = 5G3=5

o Configura on: Use resistors to set these gains in the inver ng amplifier configura on.

3. Common Mode Rejec on Ra o (CMRR):

Concept:

o Defini on: Ability of an op-amp to reject common-mode signals.

o Diagram: Shows differen al vs. common mode signals.

4. Characteris cs of Ideal Opera onal Amplifier:

o Infinite open-loop gain.

o Infinite input impedance.

o Zero output impedance.

o Infinite bandwidth.

o Zero offset voltage.

o Zero noise.

5. Output Voltage of a Closed-Loop Non-Inver ng Amplifier:

Equa on:

Vout=(1+RfRin)⋅VinV_{out} = \le (1 + \frac{R_f}{R_{in}}\right) \cdot V_{in}Vout=(1+RinRf)⋅Vin

Design with Gain of 6:

o Choose Resistors: Set Rf=5⋅RinR_f = 5 \cdot R_{in}Rf=5⋅Rin.

6. Open-Loop vs. Closed-Loop Voltage Gain of Op-Amp:

Open-Loop Gain:

o High but varies with frequency and temperature.

Closed-Loop Gain:

o Controlled by external resistors; more stable.

Limi ng Value: Depends on supply voltage.

7. Output Voltage Calcula on:

Given:
 o Input = 3V.

o R1=10kΩR_1 = 10k\OmegaR1=10kΩ, Rf=10kΩR_f = 10k\OmegaRf=10kΩ.

Output Voltage:

Vout=(1+RfR1)⋅3V=6⋅3V=18VV_{out} = \le (1 + \frac{R_f}{R_1}\right) \cdot 3V = 6 \cdot 3V = 18VVout

=(1+R1Rf)⋅3V=6⋅3V=18V

(b) CMRR and Slew Rate:

CMRR: Ra o of differen al gain to common-mode gain.

CMRR=AdAcm\text{CMRR} = \frac{A_{d}}{A_{cm}}CMRR=AcmAd

Slew Rate: Rate of change of output voltage.

Slew Rate=ΔVoutΔt\text{Slew Rate} = \frac{\Delta V_{out}}{\Delta t}Slew Rate=ΔtΔVout

8. Non-Inver ng Amplifier Voltage Gain Equa on:

Diagram:

Vin

R1

Inver ng Input

Rf

Vout

 Voltage Gain:

Av=1+RfR1A_v = 1 + \frac{R_f}{R_1}Av=1+R1Rf

Design for Gain of 6:

 Choose Resistors: Rf=5⋅R1R_f = 5 \cdot R_1Rf=5⋅R1.

 Differen al Amplifier Gain and CMRR:

Gain Calcula on:

 Common Mode Gain:

Acm=VoutVinA_{cm} = \frac{V_{out}}{V_{in}}Acm=VinVout
  CMRR:

CMRR=AdAcm\text{CMRR} = \frac{A_{d}}{A_{cm}}CMRR=AcmAd

Given: Gain = 100, Common Input = 5mV, Output = 18mV.

Acm=18mV5mV=3.6A_{cm} = \frac{18mV}{5mV} = 3.6Acm=5mV18mV=3.6

CMRR=1003.6≈27.78\text{CMRR} = \frac{100}{3.6} \approx 27.78CMRR=3.6100≈27.78

MODULE 5

1. Circuit Diagram of an Ideal Differen ator Using Op-Amp

Circuit Diagram:

_______

Vin ---->| - |

| |----- Vout

|+ |

|_______|

GND

Explana on:

 The input signal (VinV_{in}Vin) is applied to the inver ng terminal through a capacitor (CCC).

 The output (VoutV_{out}Vout) is taken from the output terminal, with a feedback resistor
(RfR_fRf) connected between the output and the inver ng input.

 The non-inver ng input is grounded.

Waveforms:

 Input (Vin): A ramp waveform or sine wave.

 Output (Vout): A square wave for a ramp input or cosine wave for a sine input.

2. Opera on of a Square Wave Generator Using Op-Amp

Explana on:

 The square wave generator uses an op-amp in an astable mul vibrator configura on.

 The circuit con nuously switches between high and low output states, genera ng a square
wave.

Circuit Diagram:

R
Vin -----> |----->|

| |

| C

|------|

GND |

Vout

Opera on:

 The capacitor charges and discharges through the resistor, causing the op-amp to switch states.

 The output is a square wave with a frequency determined by the resistor and capacitor values.

3. Zero Crossing Detector

Explana on:

 A zero-crossing detector is an op-amp comparator circuit used to detect the point at which the
input signal crosses zero volts.

 The output switches states each me the input crosses zero, resul ng in a sharp transi on
between high and low output levels.

Circuit Diagram:

_______

Vin ---->| - |

| |----- Vout

|+ |

|_______|

GND

Waveforms:

 Input (Vin): A sine wave.

 Output (Vout): A square wave that transi ons at every zero crossing of the input sine wave.

4. Opera on of Ideal Integrator Circuit Using Op-Amp

Explana on:
  The integrator circuit produces an output that is propor onal to the integral of the input signal.

Circuit Diagram:

_______

Vin ---->| - |

| |----- Vout

|+ |

|_______|

GND

Opera on:

 The capacitor in the feedback loop accumulates charge, causing the output voltage to increase
or decrease linearly, depending on the input signal.

 For a constant input, the output is a ramp waveform.

5. Non-Inver ng/Inver ng Schmi Trigger

Explana on:

 A Schmi trigger is a comparator circuit with hysteresis, meaning it has two different threshold
voltages for rising and falling input signals.