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h28_lecture20_2

# h28_lecture20_2 - Lecture 20 Slewing Boris Murmann Stanford...

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EE 214 Lecture 20 (HO#28) B. Murmann 1 Lecture 20 Slewing Boris Murmann Stanford University Copyright © 2004 by Boris Murmann EE 214 Lecture 20 (HO#28) B. Murmann 2 Overview Reading 9.6.1, 9.6.2, 9.6.5 (Slew Rate) Introduction Today we'll complete our discussion of transient behavior in OTA circuits with capacitive feedback. Aside from the feedforward artifact we've discovered last time, there exists another effect called "slewing". Whenever the differential input pair is driven outside its "linear range", the differential output current is limited by the available tail bias. In typical switched capacitor circuits, slewing can cause a significant speed reduction, and is therefore an important effect to consider.

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EE 214 Lecture 20 (HO#28) B. Murmann 3 Simulation Example from Last Lecture Using simple single stage OTA (See lecture 13, slide 9) Parameters – C s =C f =500fF, C L =10pF, β =0.48, G m =1mS, G m R o =85 10gig C L C L C f C f V id V ic Diffdrive Diffsense C s C s 10gig V od V oc 0 V idstep EE 214 Lecture 20 (HO#28) B. Murmann 4 Another Simulation Set V idstep =-1V (C L =10pF insignificant feedforward to output) What causes this discrepancy ? 0 50 100 150 200 0 200 400 600 800 1000 Time [ns] Voltage [mV] -V id V od (simulation) V od (theory?)