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Lect2UP270_(100328)

Lect2UP270_(100328) - Lecture 270 High Speed Op Amps Page...

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Lecture 270 – High Speed Op Amps (3/28/10) Page 270-1 CMOS Analog Circuit Design © P.E. Allen - 2010 LECTURE 270 – HIGH SPEED OP AMPS LECTURE ORGANIZATION Outline Extending the GB of conventional op amps Cascade Amplifiers - Voltage amplifiers - Voltage amplifiers using current feedback • Summary CMOS Analog Circuit Design, 2 nd Edition Reference Pages 368-384 Lecture 270 – High Speed Op Amps (3/28/10) Page 270-2 CMOS Analog Circuit Design © P.E. Allen - 2010 INCREASING THE GB OF OP AMPS What is the Influence of GB on the Frequency Response? The unity-gainbandwidth represents a limit in the trade-off between closed loop voltage gain and the closed-loop -3dB frequency. Example of a gain of -10 voltage amplifier: 0dB 20dB | A vd (0)| dB Magnitude log 10 ( ω ) GB ω A ω -3dB Op amp frequency response Amplifier with a gain of -10 Fig. 7.2-1 What defines the GB ? We know that GB = g m C where g m is the transconductance that converts the input voltage to current and C is the capacitor that causes the dominant pole. This relationship assumes that all higher-order poles are greater than GB .
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