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Lecture 9: High-Gain Single-Stage Op Amps PDF

52 Pages·2010·0.62 MB·English
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Preview Lecture 9: High-Gain Single-Stage Op Amps

EE 435 Lecture 9: High-Gain Single-Stage Op Amps - Regulated Folded Cascode Op Amp - Cu rrent-mirror op amps - OT A Applications 1 Textbook reference: Some of the material we have been discussing appears in Chapter 3, some in Chapter 5, and some in Chapter 6 of the Martin and Johns text In particular, the telescopic and folded cascode structures are referred to as advanced op amps and appear in later chapters of the text 2 Review from Last Time What circuit is this? I B1 B2 V OUT OUT V DD BB 3 I V M B1 B1 3 V IN 1 M 1 IN V SS SS Folded Cascode Amplifier Biased Folded Cascode 3 Review from Last Time Folded Cascode Op Amp (cid:131)Needs CMFB Circuit for V B4 (cid:131)Either single-ended or differential outputs (cid:131)Can connect counterpart as current mirror to eliminate CMFB (cid:131)Folding caused modest deterioration of A and GB energy efficiency V0 (cid:131)Modest improvement in output swing 4 Review from Last Time Folded Gain-boosted Telescopic Cascode Op Amp V DD V B1 g M M − m1 5 6 2 A ≈ o g g (g +g ) o3 +g o9 M3 A3 A4 M 4 O1 O5 o7 A g A g VB2 VOU 3 m3 1 m9 T V B3 M9 A1 A2 M1 CL g VI VI 0 V IN GB = m1 N M1 M2 N 2C M M L 7 8 V B4 I I T T2 VS VS S S (cid:131)Needs CMFB Circuit for V B4 (cid:131)Either single-ended or differential outputs (cid:131)Can connect counterpart as current mirror to eliminate CMFB (cid:131)Folding caused modest deterioration in GB efficiency and gain (cid:131)Modest improvement in output swing 5 Review from Last Time Operational Amplifier Structure Comparison Small Signal Parameter Domain Reference 1 g g I A = m1 GB = m1 SR = T Op Amp VO 2 g + g 2C 2C O1 O3 L L g Telescopic m1 2 g I Cascode A = GB = m1 SR = T o g g g o3 +g o5 2C 2C o1 g o7 g L L m3 m5 Regulated g m1 g I Cascode A ≈ 2 GB = m1 SR = T o g g 2C 2C g o3 +g o9 o1 g A o7 g A L L m3 1 m9 3 Folded g m1 I g Cascode A = 2 GB = m1 SR = T o g g 2C (g +g ) o3 +g o9 2C L o1 o5 g o7 g L m3 m9 Folded g m1 I g Regulated A = 2 GB = m1 SR = T o g g 2C Cascode (g +g ) o3 +g o9 2C L o1 o5 g A o7g A L m3 3 m9 9 6 Review from Last Time Summary of Folded Amplifier Performance • + Modest improvement in output signal s wing (from 5 V to 4V ) DS SAT DS SAT • - Deterioration in A (maybe 30% or V0 m ore) • - Deterioration in GB power efficiency ( can be significant) • - Minor increase in circuit size 7 Folded Gain-boosted Cascode Amplifier − g A ≈ m1 o g ( ) g o3 o1 A g m3 g GB = m1 2C L (cid:131) with ideal current source bias (cid:131) modest improvement in output swing 8 Folded Gain-boosted Cascode Amplifier V − g OUT ≈ m1 ( ) V g + g g IN sC + o1 o5 o3 L g A m3 − g g A A ≈ m1 m3 0 ( ) g + g g o1 o5 o3 g GB = m1 C L modest improvement in output swing 9 Basic Amplifier Structure Comparisons Small Signal Parameter Domain Common Source g g A = m GB = m VO g C O L Cascode g g g A = m1 m3 GB = m1 VO g g C O1 o3 L g Regulated g g GB = m1 A ≈ m1 m3 A Cascode VO g g C O1 o3 L g Folded Cascode g g GB = m1 A = m1 m3 VO ( ) C g +g g O1 O5 o3 L Folded Regulated g g g A = m1 m3 A GB = m1 Cascode VO ( ) g +g g C O1 O5 o3 L 10

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1 EE 435 Lecture 9: High-Gain Single-Stage Op Amps-Regulated Folded Cascode Op Amp -Current-mirror op amps-OTA Applications
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