Unit 4 Part – C

🔷 UNIT 4 – Oscillators & Feedback

Q1. Crystal Oscillator

1️⃣ Uses quartz crystal → piezoelectric effect.
2️⃣ When voltage applied → crystal vibrates → produces fixed frequency.
3️⃣ Amplifier with feedback sustains oscillation.
4️⃣ Frequency depends on physical size of crystal.
5️⃣ High frequency stability, low drift.
6️⃣ Applications: Clocks, microprocessors, communication transmitters.

Q2. Hartley Oscillator

1️⃣ Tank circuit: Two inductors (L1, L2) + one capacitor (C).
2️⃣ Feedback taken from tap between L1 & L2.
3️⃣ Transistor amplifier provides phase shift 180°; LC network adds 180° → total 360°.
4️⃣ Frequency: f=12π(L1+L2+M)Cf = \frac{1}{2\pi\sqrt{(L1 + L2 + M)C}}f=2π(L1+L2+M)C​1​

5️⃣ Output: Continuous sine wave.
6️⃣ Applications: RF oscillators.

Q3. Colpitts Oscillator

1️⃣ Tank circuit: One inductor (L) + two capacitors (C1, C2).
2️⃣ Feedback from junction of C1–C2.
3️⃣ Phase shift = 360°, oscillation sustained.
4️⃣ Frequency: f=12πLC1C2C1+C2f = \frac{1}{2\pi\sqrt{L\frac{C1C2}{C1+C2}}}f=2πLC1+C2C1C2​​1​

5️⃣ Applications: Audio, RF generators.

Q4. Wien Bridge Oscillator

1️⃣ RC bridge network (one series RC + one parallel RC).
2️⃣ Uses op-amp/transistor amplifier.
3️⃣ Produces low-distortion sine wave.
4️⃣ Frequency: f=12πRCf = \frac{1}{2\pi RC}f=2πRC1​

5️⃣ Applications: Audio frequency generators, function generators.

Unit 4 Tamil

Q1. Crystal Oscillator – Construction, Working & Frequency Stability

Definition:
Crystal Oscillator என்பது ஒரு piezoelectric crystal (quartz) பயன்படுத்தி fixed frequency oscillations generate பண்ணும் oscillator ஆகும்.

1️⃣ Construction:

• Quartz crystal இரண்டு metal plates-க்கு இடையில் mount பண்ணப்படும்.
• Crystal-இல் piezoelectric effect பயன்படுத்தப்படும் (mechanical stress → electrical voltage).
• Amplifier section transistor / op-amp பயன்படுத்தப்படும்.

2️⃣ Working Principle:

1. Crystal amplifier-இன் feedback path-இல் connect பண்ணப்படும்.
2. DC supply apply பண்ணும்போது, crystal அதன் mechanical resonance frequency-யில் vibrate ஆகும்.
3. Amplifier அந்த oscillations sustain பண்ணும் (Barkhausen condition satisfy).
4. Output pure sinusoidal waveform கிடைக்கும்.

3️⃣ Frequency Stability:

• Frequency mainly crystal dimension & cut-ஐ சாரும்.
• Temperature, supply variation-க்கு மிகக் குறைவு response.
• Highly stable frequency source.

4️⃣ Applications:

• Microprocessors / Microcontrollers clock circuit.
• Radio transmitters, frequency counters.
• Communication systems.

Q2. Hartley Oscillator – Construction & Working

Definition:
Hartley oscillator ஒரு LC oscillator, இதில் feedback inductive divider மூலம் கிடைக்கும்.

1️⃣ Circuit:

• Tank circuit: Capacitor (C) + two inductors (L1, L2).
• Transistor amplifier positive feedback கொடுக்கிறது.
• Feedback point → L1, L2 junction.

2️⃣ Working Principle:

1. DC supply ON ஆனதும், transistor noise small signal generate பண்ணும்.
2. Tank circuit (L1 + L2 + C) resonate ஆகி oscillation produce பண்ணும்.
3. Feedback 180° phase shift கொடுக்கும்; amplifier-இன் 180° combine ஆகி 360° (Barkhausen condition).
4. Continuous sinusoidal output கிடைக்கும்.

3️⃣ Frequency of Oscillation: f=12π(L1+L2+M)Cf = \frac{1}{2\pi\sqrt{(L_1 + L_2 + M)C}}f=2π(L1​+L2​+M)C​1​

4️⃣ Applications:

• RF oscillators.
• Signal generation circuits.

Q3. Colpitts Oscillator – Construction, Working & Frequency Expression

Definition:
Colpitts oscillator ஒரு LC oscillator, இதில் feedback capacitive divider மூலம் கிடைக்கும்.

1️⃣ Circuit:

• One inductor (L), two capacitors (C1, C2) series-ஆ connect பண்ணப்படும்.
• Feedback → junction of C1 & C2.
• Transistor amplifier oscillation sustain பண்ணும்.

2️⃣ Working Principle:

1. Transistor amplify பண்ணும் small noise signal.
2. Tank circuit (L, C1, C2) charge–discharge ஆகி oscillation maintain பண்ணும்.
3. Phase shift 360° maintain பண்ணும் → sustained oscillation.

3️⃣ Frequency of Oscillation: f=12πL(C1C2C1+C2)f = \frac{1}{2\pi\sqrt{L\left(\frac{C_1C_2}{C_1 + C_2}\right)}}f=2πL(C1​+C2​C1​C2​​)​1​

4️⃣ Applications:

• RF signal generators.
• Oscillator circuits in transmitters.

Q4. Wien Bridge Oscillator – Construction & Operation

Definition:
Wien Bridge Oscillator ஒரு RC network oscillator, pure sine wave produce பண்ணும்.

1️⃣ Circuit:

• Series RC + parallel RC combination form Wien Bridge network.
• Op-amp / transistor amplifier feedback provide பண்ணும்.

2️⃣ Working Principle:

1. AC signal amplifier-இல் generate ஆகும்.
2. RC bridge network frequency selective feedback கொடுக்கும்.
3. Loop gain = 1 மற்றும் phase shift = 0° ஆனால் oscillation sustain ஆகும்.
4. Output = low distortion sine wave.

3️⃣ Frequency of Oscillation: f=12πRCf = \frac{1}{2\pi RC}f=2πRC1​

4️⃣ Applications:

• Audio frequency generators.
• Function generators.
• Testing equipment.