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lecture23annotat - 6.012 - Microelectronic Devices and...

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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 23-1 Lecture 23 - Frequency Response of Amplifiers (I) Common-Source Amplifier December 1, 2005 Contents : 1. Introduction 2. Intrinsic frequency response of MOSFET 3. Frequency response of common-source amplifier 4. Miller effect Reading assignment: Howe and Sodini, Ch. 10, §§ 10.1-10.4
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 23-2 Key questions How does one assess the intrinsic frequency response of a transistor? What limits the frequency response of an amplifier? What is the ”Miller effect”?
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 23-3 1. Introduction Frequency domain is a major consideration in most ana - log circuits. Data rates, bandwidths, carrier frequencies all pushing up. Motivation: Processor speeds Traffic volume ↑⇒ data rates More bandwidth available at higher frequencies in the spectrum MMDS 3G Skybridge LMDS Spacewav WE Datacom Frequency 0 0 4 20 25 40 50 60 2 8 45 100 155 500 Video WirelessMAN Teledesic 'V Band' DOM Radio BW (MHz) Figure by MIT OCW.
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 23-4 2. Intrinsic frequency response of MOSFET 2 How does one assess the intrinsic frequency response of a transistor? f t short-circuit current- gain cut-off frequency -g [GHz] Consider MOSFET biased in saturation regime with small- signal source applied to gate: V DD i D =I D +i out i G =i in v s V GG v s at input i out : transistor effect i in due to gate capacitance | i i in |↓ out Frequency dependence: f ↑⇒ i in ↑⇒ i out f t frequency at which | | =1 i in
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6.012 - Microelectronic Devices and Circuits - Fall 2005 Lecture 23-5 Complete small-signal model in saturation: G S D + - v gs C gs C gd C db C sb g m v gs g mb v bs r o + v bs - i out v s + - i in B v bs =0 + + - - v gs g m v gs i out i in v s C gs C gd 1 2 node 1 : i in v gs jωC v gd =0 i in = v ( C + C ) node 2 : i out g m v + v
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lecture23annotat - 6.012 - Microelectronic Devices and...

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