EE 435 Lect 8 Spring 2010

EE 435 Lect 8 Spring 2010 - EE 435 Lecture 8: High-Gain...

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1 EE 435 Lecture 8: High-Gain Single-Stage Op Amps -folded cascode structures
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2 Telescopic Cascode Op Amp L m C g GB 2 1 = Single-ended operation m1 o o3 o7 o1 o5 m3 m7 g - 2 A= gg g + g This circuit is widely used !! (CMFB circuit not shown) Review from last lecture:
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3 Telescopic Cascode Op Amp Current-Mirror p-channel Bias to Eliminate CMFB Only single-ended output available V SS V B5 V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8 V B3 V OUT C L M 11 M 12 I B I T V DD Current Mirror Bias V DD V SS V B5 V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8 V B3 V OUT C L M 11 M 12 I B I T V DD Current Mirror Bias V DD Standard p-channel Cascode Mirror Wide-Swing p-channel Cascode Mirror Review from last lecture:
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4 Telescopic Cascode Op Amp + OUT V - OUT V + OUT V - OUT V n-channel inputs p-channel inputs Review from last lecture:
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5 High output impedance quarter-circuits Regulated Cascode Amplifier or “Gain Boosted Cascode” Quarter Circuit (A is usually a simple amplifier, often the reference op amp with + terminal connected to the desired quiescent voltage) Review from last lecture:
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6 High output impedance quarter-circuits Regulated Cascode Amplifier or “Gain Boosted Cascode” Output conductance has been decreased even more! Same GB as for previous two circuits () + A 1 g g g g m3 O3 O1 OEQ 1 m mEQ g g [] + + m3 O3 O1 L m1 V g A 1 g g sC g (s) A ( ) + O3 m3 O1 m1 0 g A 1 g g g A L m C g GB 1 Review from last lecture:
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7 Gain-Boosted Telescopic Cascode Op Amp Needs CMFB Circuit for Vb1 Either single-ended or differential outputs Can connect counterpart as current mirror to eliminate CMFB Use differential op amp to facilitate biasing of cascode device V DD V OU T C L V B2 V B3 V S V B5 M 1 1 V B1 A 1 A 2 A 3 A 4 I T V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8
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8 Gain-Boosted Telescopic Cascode Op Amp Single-ended operation g OQC = g OCC = g mQC =
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9 Gain-Boosted Telescopic Cascode Op Amp L m C g GB 2 1 = m1 o o3 o7 o1 o5 1m 3 3m 7 g - 2 A= gg g+ g A gA g This is modestly less efficient at generating GB because now power is consumed in both the cascode devices and the boosting amplifier V DD V OU T C L V B2 V B3 V S V B5 M 1 1 V B1 A 1 A 2 A 3 A 4 I T V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8
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10 Gain-Boosted Telescopic Cascode Op Amp m1 L g GB = C o o3 o7 o1 o5 1m 3 3m 7 -g A= gg g+ g Ag This is modestly less efficient at generating GB because now power is consumed in both the cascode devices and the boosting amplifier V DD V OU T C L V B2 V B3 V S V B5 M 1 1 A 1 A 2 A 3 A 4 I T V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8 Elimination of need for CMFB Circuit
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11 Gain-Boosted Telescopic Cascode Op Amp V DD C L V B2 V B3 V S V B5 M 11 A 1 A 2 A 3 A 4 I T V IN V IN M 1 M 2 M 3 M 4 M 5 M 7 M 6 M 8 V DSAT V OUT V DSAT V DSAT V DSAT V DSAT A minimum of 5 V DSAT drops between V DD and V SS Signal Swing and Power Supply Limitations This establishes a lower bound on V DD -V SS and it will be reduced by the p-p signal swing on the output
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This note was uploaded on 01/31/2012 for the course EE 345 taught by Professor Geiger during the Fall '11 term at Iowa State.

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EE 435 Lect 8 Spring 2010 - EE 435 Lecture 8: High-Gain...

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