L13 lecture - Output Stages Driving large (resistive) loads...

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EECS 240 Lecture 13: Output Stages B. Boser 1 Output Stages • Driving large (resistive) loads – RC-filters (anti-aliasing) – Off-chip loads – Line driver • Twisted pair: Ethernet, ISDN, ADSL, HPNA •Coax EECS 240 Lecture 13: Output Stages B. Boser 2 OTA • Transconductance amplifier (common-source) • Excessive power dissipation • Only appropriate for modest loads and multi-stage amplifiers μA 100 k 10 2 10 mV 200 mA 100 k 10 2 000 , 10 mV 200 mA 20 50 2 10 mV 200 A 20 50 2 000 , 10 mV 200 2 2 * * = × × = × × = × × = × × = = L v D L D L m v R A V I R V I R g A
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EECS 240 Lecture 13: Output Stages B. Boser 3 Source Follower • Impractical for V DD < 5V • Push-pull follower – Class (A)B – Cross-over distortion – Quiescent current control EECS 240 Lecture 13: Output Stages B. Boser 4 Class (A)B Common-Source • Essentially inverter • Very nonlinear – Need feedback – Local (error amplifiers) – Global •B ias ing –Dynam ic – Floating voltage source
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EECS 240 Lecture 13: Output Stages B. Boser 5 Floating Voltage Source M1 10 / 0.35 M=10 M2 20 / 0.35 M=10 M3 10 / 0.35 M4 20 / 0.35 M5 10 / 0.35 M6 10 / 0.35 I1 dc = 100uA M7 20 / 0.35 M8 20 / 0.35 I2 dc = 100uA I3 dc = 100uA I4 dc = 100uA Vout VDD VSS Vg1 Vg4 Vg3 Vg2 EECS 240 Lecture 13: Output Stages B. Boser 6 References D. M. Monticelli, "A quad CMOS single-supply op amp with rail-to-rail output swing," IEEE Journal of Solid-State Circuits, vol. 21, pp. 1026 - 1034, December 1986. Original idea. R. Hogervorst, J. P. Tero, R. G. H. Eschauzier, and J. H. Huijsing, "A compact power- efficient 3 V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries," IEEE Journal of Solid-State Circuits, vol. 29, pp. 1505 - 1513, December 1994.
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L13 lecture - Output Stages Driving large (resistive) loads...

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