EE 435 Lect 19 Spring 2010

EE 435 Lect 19 Spring 2010 - EE 435 Lecture 19 Gain...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
EE 435 Lecture 19 Gain Enhancement with Positive Feedback Linearity in Operational Amplifiers -- The differential pairs
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
g meq Enhancement with Driven Counterpart Circuit 3 1 3 1 0 o o m m V g g g g A + + = L m m C g g GB 3 1 + = Both gain and GB enhancement .• • • Review from last lecture .•
Background image of page 2
Other Methods of Gain Enhancement OCC OQC QC M V0 g g g A + = Two Strategies: 1. Decrease denominator of A V0 2. Increase numerator of A V0 Consider again decreasing the denominator Recall: OX OCC OQC QC M V0 g g g g A + = Is it possible to come up with circuits that will provide a subtraction of conductance in the denominator ? .• • • Review from last lecture .•
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
But - can we easily build circuits with this property? But – the inverting amplifier may be more difficult to build than the op amp itself! Gain Enhancement with Regenerative Feedback YES – simply by cross-coupling the outputs in a fully differential structure .• • • Review from last lecture .•
Background image of page 4
Gain Enhancement with Regenerative Feedback () s mF1 V0 L oF1 oP1 mP1 g A sC g g g = ++− If g mP1 = g oF1 +g oP1 , the dc gain will become infinite !! V0 A mP1 g oP1 oF1 gg + 0 mF1 oF1 oP1 g + .• • • Review from last lecture .•
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Gain Enhancement with Regenerative Feedback L mP1 oP1 oF1 C g g g - p + = () s mF1 V0 L oF1 oP1 mP1 g A sC g g g = ++− If g mP1 > g oF1 +g oP1 , the pole will be in the RHP !! This will make the op amp unstable This is the major reason most have avoided using the structure ! Positive Feedback is BAD !! .• • • Review from last lecture .•
Background image of page 6
Gain Enhancement with Regenerative Feedback L mP1 oP1 oF1 C g g g - p + = () s mF1 V0 L oF1 oP1 mP1 g A sC g g g = ++− If g mP1 > g oF1 +g oP1 , the pole will be in the RHP !! It can be shown that the feedback amplifier is usually stable even if the open-loop Op amp is unstable How? V0 1 V0 1 Ap As sp = + ± ± ( ) FB 1 1A s s p A p ββ == −+ ± ±± ( ) ( ) FB 1 1 pp 1 A p 1 A β = −− = ± ( ) 1V 0 1 FB 0 1 p i f p 0 p p i f p 0 + < = −> Since A V0 <0 for p 1 <0 and A V0 >0 for p 1 >0, it follows that .• • • Review from last lecture .•
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Gain Enhancement with Regenerative Feedback The feedback performance can actually be enhanced if the open-loop amplifier is unstable Why? -1 β OUT V t 1 p 0 < 1 p 0 > 1 p 0 = • Time required to get in settling window can be reduced with RHP pole • But, if pole is too far in RHP, response will exit top of window .• • • Review from last lecture .•
Background image of page 8
Existing Positive Feedback Amplifier Vout C L Q2 Q7 Q1 Q3 Q4 Vi- Vi+ V DD V b1 Q6 Q5 () ( ) 4 m6 m1 4 m6 06 o4 o2 m1 VO g g 1/2 g g g g g 1/2 A m m g g + + + = ( ) ] g g g [g sC g 1/2 A(s) 4 m6 o6 o4 o2 L m1 m g + + + + =
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

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.

Page1 / 33

EE 435 Lect 19 Spring 2010 - EE 435 Lecture 19 Gain...

This preview shows document pages 1 - 10. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online