EE203-SUNYBuffalo-35-Chapter05-03

EE203-SUNYBuffalo-35-Chapter05-03 - SMALL for Big Things...

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Unformatted text preview: SMALL for Big Things University at Buffalo SMALL for Big Things University at Buffalo nanobioSensors & MicroActuators Learning Lab The State University of New York nanobioSensors & MicroActuators Learning Lab The State University of New York Recall: Inverting-Amplifier Circuit EE 203 Circuit Analysis 2 Lecture 35 Chapter 5.5 Noninverting-Amplifier Circuit Kwang W. Oh, Ph.D., Assistant Professor SMALL (nanobioSensors and MicroActuators Learning Lab) Department of Electrical Engineering University at Buffalo, The State University of New York 215E Bonner Hall, SUNY-Buffalo, Buffalo, NY 14260-1920 Tel: (716) 645-3115 Ext. 1149, Fax: (716) 645-3656 E-mail: kwangoh@buffalo.edu, http://www.SMALL.Buffalo.edu EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Assumption OP Amp is operating in its linear region OP Amp is ideal Components & Parameters Two resistances: Rf, Rs A voltage siignal source: vs A short circuit (vp = 0): between the noninverting input terminal (+) and the common node The output voltage is an inverted, scaled replica of the input replica Sign reversal from input to output Scaling factor, or gain A, = the ratio of Rf/Rs is + i f = in vs − vn vo − vn + = in Rs Rf vs − 0 vo − 0 + =0 Rs Rf ∴ vo = − Rf Rs vs Lecture 35 | Chapter 5 | 3/4 | 1/9 EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo SMALL for Big Things University at Buffalo SMALL for Big Things University at Buffalo nanobioSensors & MicroActuators Learning Lab The State University of New York nanobioSensors & MicroActuators Learning Lab The State University of New York Noninverting-Amplifier Circuit ip = vg − v p Rg if =0 is EE 203 Circuit Analysis 2 Lecture 35 Chapter 5.6 Difference-Amplifier Circuit in ∴ v g = v p ( = vn ) is + i f = in ip 0 − vn vo − vn + = in Rs Rf 0 − vg Rs + vo − vg Rf vo =0 1 1 1 = vg ( + ) Rf Rs R f vo = 1 Rs + 1 Rf 1 Rf vg = To operate in the linear region Rs + R f Rs R f 1 Rf Lecture 35 | Chapter 5 | 3/4 | 2/9 vg = Rs + R f Rs EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo vg Rs + R f Rs < Kwang W. Oh, Ph.D., Assistant Professor SMALL (nanobioSensors and MicroActuators Learning Lab) Department of Electrical Engineering University at Buffalo, The State University of New York 215E Bonner Hall, SUNY-Buffalo, Buffalo, NY 14260-1920 Tel: (716) 645-3115 Ext. 1149, Fax: (716) 645-3656 E-mail: kwangoh@buffalo.edu, http://www.SMALL.Buffalo.edu VCC vg Lecture 35 | Chapter 5 | 3/4 | 3/9 EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Lecture 35 | Chapter 5 | 3/4 | 4/9 SMALL for Big Things University at Buffalo SMALL for Big Things University at Buffalo nanobioSensors & MicroActuators Learning Lab The State University of New York nanobioSensors & MicroActuators Learning Lab The State University of New York Difference-Amplifier Circuit vn = v p = Difference-Amplifier Circuit – Another Perspective if is Rd vb Rc + Rd Differential Mode Input: Common Mode Input: is + i f = in va − vn vo − vn + = in Ra Rb va − Rd Rc + Rd vb Ra + vo − Rd Rc + Rd vb Rb R vo = =0 vo = R d d 1 1 R +R R +R = vb ( c d + c d ) − va vo Rb Ra Rb Ra vo = Rd Ra + Rb R ( )vb − b va Ra Rc + Rd Ra = Rd Rb Ra + Rb R ( )vb − b va Rc + Rd Ra Rb Ra R R + Rb R ∴ vo = d ( a )vb − b va Ra Rc + Rd Ra If set Ra Rc = Rb Rd 1 Ra Rd + Rb Rd R ( )vb − b va Ra Rc + Rd Ra = 1 Rb Rc + Rb Rd R ( )vb − b va Ra Rc + Rd Ra R R + Rd R = b( c )vb − b va Ra Ra Rc + Rd R vo = b ( vb − va ) Ra EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Rd Ra + Rb ( )b Ra Rc + Rd v− Rb Ra va 1 ( vcm + vdm ) − 2 1 ( vcm − vdm ) 2 = Rd Ra + Rb ( ) Ra Rc + Rd Rb Ra = Ra Rd + Rb Rd − Rb Rc − Rb Rd Ra ( Rc + Rd ) Ra Rd + Rb Rd + Rb Rc + Rb Rd 2 Ra ( Rc + Rd ) = Ra Rd − Rb Rc Ra ( Rc + Rd ) vcm + vcm + Rd ( Ra + Rb ) + Rb ( Rc + Rd ) 2 Ra ( Rc + Rd ) if is vdm vdm = Acm vcm + Adm vdm Differential Mode Gain Common Mode Gain Lecture 35 | Chapter 5 | 3/4 | 5/9 EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo SMALL for Big Things University at Buffalo SMALL for Big Things University at Buffalo nanobioSensors & MicroActuators Learning Lab The State University of New York nanobioSensors & MicroActuators Learning Lab The State University of New York Difference-Amplifier Circuit – Another Perspective (2) Differential Mode Input: zero common mode gain and non zero (and usually large) differentiall mode gain. on-zero (and usually large) differentia mode gain. Two factors have an influence on the ideal common mode gain If Rc = Ra, Rd = Rb An ideal difference amplifier would amplif only the voltage of interest (vdm) fy and would suppress the noise (vcm) Ra Rd − Rb Rc Ra ( Rc + Rd ) = (0)vcm + vcm + Rd ( Ra + Rb ) + Rb ( Rc + Rd ) 2 Ra ( Rc + Rd ) Common Mode Rejection Ratio (CMRR) (1) An An ideal difference amplifier has Common Mode Input: vo = Lecture 35 | Chapter 5 | 3/4 | 6/9 vdm resistance mismatches (that is, a non-ideal OP Amp (that is, if is Ra Rb = Rc Rd is not satisfied) or is not satisfied). We focus here on the effect of resistance mismatches on the performance of a difference amplifier. Rb vdm Differential Mode Input Ra Information of interest Common Mode Input (Acm = 0) the noise found in all electric signals EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Lecture 35 | Chapter 5 | 3/4 | 7/9 EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Lecture 35 | Chapter 5 | 3/4 | 8/9 SMALL for Big Things University at Buffalo nanobioSensors & MicroActuators Learning Lab The State University of New York Common Mode Rejection Ratio (CMRR) (2) The Common Mode Rejection Ratio (CMRR) can be used to measure how nearly ideal a difference amplifier is is defined as the ratio of the differential mode gain to the common mode gain Common Mode Input (Acm = 0) the noise found in all electric signals If By making the differential mode gain = large = very large EE 203 Circuit Analysis 2 | Spring 2008 | Prof. Kwang W. Oh | EE@SUNY-Buffalo Lecture 35 | Chapter 5 | 3/4 | 9/9 ...
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This note was uploaded on 10/19/2011 for the course EE 203 taught by Professor Staff during the Spring '08 term at SUNY Buffalo.

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