lec24 - 6.012 Microelectronic Devices and Circuits Fall...

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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 24­1 Lecture 24 ­ Frequency Response of Ampli±ers (II) Open­Circuit Time­Constant Technique December 6, 2005 Contents : 1. Open­circuit time­constant technique 2. Application of OCT to common­source ampliFer 3. ±requency response of common­gate ampliFer Reading assignment: Howe and Sodini, Ch. 10, §§ 10.4.4­10.4.5. 10.6
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 24­2 Key questions Is there a fast way to assess the frequency response of an ampliFer? Do all ampliFers suffer from the Miller effect?
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 24­3 1. Open­Circuit Time­Constant Technique Simple technique to estimate bandwidth of an ampliFer. Method works well if ampliFer transfer function has: a dominant pole that dominates the bandwidth no zeroes, or zeroes at frequencies much higher than that of dominant pole Transfer function of form: V out A vo = V s (1 + j ω ω 1 )(1 + j ω ω 2 )(1 + j ω ω 3 ) ... with ω 1 ω 1 2 3 , ... log |A v | A vo log ω ω 1 ω 2 -1 -2
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 24­4 V out A vo = V s (1 + j ω ω 1 )(1 + j ω ω 2 )(1 + j ω ω 3 ) ... Multiply out the denominator: V out A vo = V s 1+ jωb 1 +( ) 2 b 2 +( ) 3 b 3 ... where: 1 1 1 b 1 = + + + ... ω 1 ω 2 ω 3 If there is a dominant pole, the low frequency behavior well described by: V out A vo A vo = V s 1+ jωb 1 1+ j ω ω H Bandwidth then: 1 ω H b 1
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 24­5
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lec24 - 6.012 Microelectronic Devices and Circuits Fall...

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