Analogue Electronic Circuits

Analogue Electronic Circuits - 2 Feedback Amplifiers 2.1...

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Unformatted text preview: 2 Feedback Amplifiers 2.1 Feedback Concept S i S S o S fb Load Source +- o fb S S = feedback transfer function (feedback factor) S S A o = amplification factor (open loop gain) KCL : fb i S S S- = A A S S AS S S A fb i o f + = + = = 1 closed loop transfer function Where A is commonly known as the loop gain 2.1.1 Gain Stability A A A f + = 1 For A >> 1, 1 = A A A f 2.1.2 Gain Sensitivity A A A f + = 1 ( 29 ( 29 2 2 1 1 1 1 1 A A A A dA dA f + = +- + = ( 29 A dA A A dA A dA dA f f f + = + = 1 1 1 2 2.1.3 Bandwidth Extension An amplifier with high frequency response characterised by a single pole can be described by, + = H M s A s A 1 ) ( where A M mid-band gain H upper -3dB frequency with negative feedback, ( 29 M H M M M H M f A s A A A s A s A s A s A + + + = + + = + = 1 1 1 1 1 ) ( 1 ) ( ) ( ( 29 M H H A + = 1 ' the new upper -3dB frequency Similarly for the low frequency response it can be shown, ( 29 M L L A + = 1 ' the new lower -3dB frequency 2.1.4 Non-linear Distortion D D A D-...
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Analogue Electronic Circuits - 2 Feedback Amplifiers 2.1...

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