lec23 - 6.012 Microelectronic Devices and Circuits Fall...

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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 23­1 Lecture 23 ­ Frequency Response of Ampli±ers (I) Common­Source Amplifier December 1, 2005 Contents : 1. Introduction 2. Intrinsic frequency response of MOSFET 3. Frequency response of common­source ampli±er 4. Miller effect Reading assignment: Howe and Sodini, Ch. 10, §§ 10.1­10.4
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 23­2 Key questions± How does one assess the intrinsic frequency response of a transistor? What limits the frequency response of an ampliFer? What is the ”Miller effect”? •±
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 23­3 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 ( ) 0 0 4 2 8 MMDS 3G Skybridge Video WirelessMAN LMDS Teledesic Spacewav WE Datacom 'V Band' DOM Radio BW MHz Frequency 20 25 40 50 60 20 40 45 100 155 500 Figure by MIT OCW.
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6.012 ­ Microelectronic Devices and Circuits ­ Fall 2005 Lecture 23­4 2. Intrinsic frequency response of MOSFET How does one assess the intrinsic frequency response of a transistor? f t short­circuit current­gain cut­off frequency [GHz] Consider MOSFET biased in saturation regime with small­ signal source applied to gate: V DD i G =i in i D =I D +i out v s V GG v s at input i out : transistor effect i in due to gate capacitance i out Frequency dependence: f ↑⇒ i in ↑⇒ | 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 23­5 Complete small­signal 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
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lec23 - 6.012 Microelectronic Devices and Circuits Fall...

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