Electronic Devices & Circuits II MUHAMMAD OBAIDULLAH OUTLINE - - PowerPoint PPT Presentation

Electronic Devices & Circuits II MUHAMMAD OBAIDULLAH

OUTLINE Chapter – 11: Feedback • General Feedback Structure • Feedback Topologies Chapter – 12: Power Amplifiers • Understanding Amplifiers • Different Classes of Amplifiers Chapter – 13: Waveform Generators • Phase Shift Oscillators • Comparators • Multivibrators

CHAPTER 11 FEEDBACK

BASIC FEEDBACK Feedback Loop Gain Open Loop Gain ∑ Source Amplifier Load Feedback Feedback Gain

CALCULATING GAINS 𝑊𝑗𝑜 + 𝑊𝑝𝑣𝑢 A Source ∑ Load − β Open Loop Gain = A 𝑊𝑝𝑣𝑢 = 𝐵(𝑊𝑗𝑜 − 𝑊𝑝𝑣𝑢. 𝛾) Closed Loop Gain = β 𝑊𝑝𝑣𝑢 = 𝐵. 𝑊𝑗𝑜 − 𝐵𝛾. 𝑊𝑝𝑣𝑢 𝑊𝑝𝑣𝑢 𝐵 Feedback Loop Gain = A f = 𝑊𝑗𝑜 = 𝑊𝑝𝑣𝑢 + 𝐵𝛾. 𝑊𝑝𝑣𝑢 = 𝐵. 𝑊𝑗𝑜 1+𝐵 β 𝑊𝑝𝑣𝑢(1 + 𝐵𝛾) = 𝐵. 𝑊𝑗𝑜 𝑊𝑝𝑣𝑢 𝐵 𝑊𝑗𝑜 = 1 + 𝐵 β

GAIN SENSITIVITY 𝑊𝑗𝑜 + 𝑊𝑝𝑣𝑢 A Source ∑ Load − β Δ𝐵𝑔 A𝑔 = Δ𝐵 1 A ( 1 + 𝐵 β )

EXAMPLE 100 ± 30 A 𝑊𝑗𝑜 S 𝑊𝑝𝑣𝑢 10 𝐿Ω 1 𝐿Ω Calculate Feedback Loop Gain ∴ Af = 10 ± 0.3 Step 1: Step 2: Step 3: 𝑆1 Δ𝐵𝑔 A𝑔 = Δ𝐵 1 𝐵 β = A ( 1 + 𝐵 β ) Af = 𝑆1 + 𝑆2 1 + 𝐵 β 𝛦𝐵𝑔 = 30 1 1𝐿 1 100 1𝐿+10𝐿 = × 10 β = Af = = 10 1 + 100 100 11 1 + 100 × 1 11 11 𝛦𝐵𝑔 = 0.3

BANDWIDTH EXTENSION 𝐵𝑝 Normal Open Loop Amplifier Gain: 𝐵 𝑃𝑀 = 1 + 𝑘 𝑔 𝑔𝑑 𝐵 𝑃𝑀 Feedback Gain: Af = 1 + β𝐵 𝑃𝑀 𝐵 𝑃 Af = 1 + 𝑘 𝑔 𝑔𝑑 + β𝐵 𝑃 𝐵 𝑃 Af = 𝑔 1 + β𝐵 𝑃 1 + 𝑘 1 + 𝛾𝐵𝑝 𝑔𝑑 𝐵 𝑃 1 Af = × 𝑔 1 + β𝐵 𝑃 1 + 𝑘 1 + 𝛾𝐵𝑝 𝑔𝑑

CURRENT CAPTURE AND SUPPLY Sampling Side Mixing Side Source Load Ammeter Current Source Load Source

VOLTAGE CAPTURE AND SUPPLY Sampling Side Mixing Side Source Voltmeter Load Source Load Voltage Source

VOLTAGE CAPTURE VOLTAGE SUPPLY Output Resistance Input Resistance

CURRENT CAPTURE CURRENT SUPPLY Output Resistance Input Resistance

CURRENT CAPTURE VOLTAGE SUPPLY Output Resistance Input Resistance

VOLTAGE CAPTURE CURRENT SUPPLY Output Resistance Input Resistance

CHAPTER 12 POWER AMPLIFIERS

WHY USE POWER AMPLIFIERS ? Source Load Signal Source Power Load Signal Amplifier

CLASS A Conducts for the whole cycle • Output is shifted by some DC value • Always biased to operate in active mode by Iss •

CLASS B Each transistor conducts for half the cycle • Output is not shifted by some DC value • No output voltage is produced when Vi<0.7 •

CLASS AB Conducts for the whole cycle • Output is not shifted by some DC value • Always biased to operate in active mode by V GG •

CLASSES OF POWER AMPLIFIERS CLASS A CLASS B CLASS AB S.NO. CLASS EFFICIECY CONDUCTION ANGLE DISTORTION 1 A 25% Θ = 360 NO 2 B 78.5% Θ = 180 YES 3 AB 25%↔78.5% 360> θ >180 NO 4 C >78.5% Θ < 180 YES

CHAPTER 13 WAVEFORM GENERATORS

CONDITIONS FOR OSCILLATIONS Barkhausen Stability Criterion Loop Gain = |A β | = 1 Phase Shift = 0 or 2 Π n

PHASE SHIFT OSCILLATIOR 1 𝑔 𝑝𝑡𝑑𝑗𝑚𝑚𝑏𝑢𝑗𝑝𝑜 = 2𝜌𝑆𝐷 6 𝑆 𝑔𝑐 = 29 R

COMPARATORS

MULTIVIBRATORS Astable The circuit is not stable in either state — it continually switches from one state to the other. It functions as a relaxation oscillator. Monostable One of the states is stable, but the other state is unstable (transient). A trigger pulse causes the circuit to enter the unstable state. After entering the unstable state, the circuit will return to the stable state after a set time. Bistable The circuit is stable in either state. It can be flipped from one state to the other by an external trigger pulse.

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