19 - 1 ECSE334 – Introduction to Microelectronics ECSE...

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Unformatted text preview: 1 ECSE334 – Introduction to Microelectronics ECSE 334 Introduction to Microelectronics Roni Khazaka Lecture #19 ECSE334 – Introduction to Microelectronics 2 Khazaka - 2008 Stability of Feedback Amplifiers Σ + − Source Load A β s x i x o x f x Unstable system Î Sustained or increasing output without an input 2 ECSE334 – Introduction to Microelectronics 3 Khazaka - 2008 Stability of feedback Systems Σ + − Load A β = s x i x o x f x Σ n x Injected noise surge at t=0 Case #1 > β A Negative Feedback Stable Amplifier ECSE334 – Introduction to Microelectronics 4 Khazaka - 2008 Stability of feedback Systems Σ + − Load A β = s x i x o x f x Σ n x Injected noise surge at t=0 Case #2 1 < < − β A Positive Feedback Stable Amplifier 3 ECSE334 – Introduction to Microelectronics 5 Khazaka - 2008 Stability of feedback Systems Σ + − Load A β = s x i x o x f x Σ n x Injected noise surge at t=0 Case #3 1 − = β A Positive Feedback Stable Oscillation ECSE334 – Introduction to Microelectronics 6 Khazaka - 2008 Stability of feedback Systems Σ + − Load A β = s x i x o x f x Σ n x Injected noise surge at t=0 Case #4 1 − < β A Positive Feedback Increasing Oscillation 4 ECSE334 – Introduction to Microelectronics 7 Khazaka - 2008 Stability of Feedback Amplifiers Σ + − Source Load A β s x i x o x f x β A A x x A s o f + = = 1 ECSE334 – Introduction to Microelectronics 8 Khazaka - 2008 Open Loop Transfer Function Key Assumption: Open Loop Transfer function is stable β A Stable Poles ) ( ) ( ) ( s s A s H β = 5 ECSE334 – Introduction to Microelectronics 9 Khazaka - 2008 Effect of Amplifier Frequency Response Open Loop Transfer Function: ) ( ) ( ) ( s s A s H β = ) ( s H i x f x ) cos( t a ω )) ( cos( ) ( ω ω ω j H t a j H ∠ + When 180 ) ( − = ∠ ω j H ) cos( ) ( )) ( cos( ) ( t a j H j H t a j H ω ω ω ω ω − = ∠ + In other words: β A is real and negative ECSE334 – Introduction to Microelectronics 10 Khazaka - 2008 Effect of Amplifier Frequency Response Open Loop Transfer Function: ) ( ) ( ) ( s s A s H β = 180 ) ( − = ∠ ω j H 1 ) ( < ω j H Stable in feedback configuration 180 ) ( − = ∠ ω j H 1 ) ( ≥ ω j H Unstable in feedback configuration Frequency Compensation is designed to ensure amplifier stability in feedback configuration. 6 ECSE334 – Introduction to Microelectronics 11 Khazaka - 2008 Direct Coupled Amplifier: one pole 10 10 1 10 2 10 3 10 4 10 5-30-20-10 10 20 Angular Frequency (rd/s) |H(s)| (dB) 10 10 1 10 2 10 3 10 4 10 5-100-80-60-40-20 Angular Frequency (rd/s) Phase Angle (degrees) ECSE334 – Introduction to Microelectronics 12 Khazaka - 2008...
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19 - 1 ECSE334 – Introduction to Microelectronics ECSE...

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