EE 230 Lecture 15 Spring 2010

EE 230 Lecture 15 Spring 2010 - EE 230 Lecture 15 Basic...

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EE 230 Lecture 15 Basic Applications of Operational Amplifiers Differential Amplifiers Impedance Converters Nonideal Op Amp Characteristics (if time permits)
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Applications of integrators to filter design () 0 BP 22 0 0 Is Ts s+Is+ I α = Design Strategy ( ) 1 Tj ω 1 2 1 The 2 nd order Bandpass Filter 0 I s 0 I s + 1. Pick C (use some practical or convenient value) 2. Solve expression to obtain R 3. Solve expression to obtain α and thus R Q 0 1 I= RC P0 ω = I P 1 ω = RC BW= RC RC Assume BW and ω P are specified Review from Last Time
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Another 2 nd -order Bandpass Filter () 3 2 2 12 3 1 s RC Ts = - 21 s+s + R //R RC ⎛⎞ ⎜⎟ ⎝⎠ 1 2 BW = P 3 1 ω = R R //R C ( ) BP Tj ω K K 2 1 3 R K= 2R Design Strategy 1. Pick C to some practical or convenient value 2. Solve expression to obtain R 1 3. Solve expression to obtain α and thus R 3 4. Solve expression to obtain R 2 1 2 BW = Assume BW, ω P , and K are specified 1 3 R K= 2R P 3 1 ω = R R //R C Review from Last Time
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STAR 2 nd -order Bandpass Filter () ( ) 1 3 2 2 12 3 2 3 1 sH RC H -1 Ts = - 21 s+s + R C R //R H-1 R //R R C ⎛⎞ ⎜⎟ ⎝⎠ Works fine ! Reduces to previous bandpass filter at H gets large Note that the “H” amplifier has feedback to positive terminal Implementation: ??? If op amp ideal, OUT IN V = H V Will discuss why this happens later! Review from Last Time
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Differential Amplifiers Many applications exist for difference (differential) amplifiers Differential amplifiers are widely used Strain gage is one application that demonstrates some challenges http://www.omega.com/prodinfo/straingages.html Wheatstone Bridge http://en.wikipedia.org/wiki/Strain_gauge Metal foil strain gages V OUT is very small compared to V B and V D Assume V A is ground
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Differential Amplifiers Ideal differential amplifier ( ) OUT IN1 IN2 V= A V - V R OUT =0 R IN = All Ideally the output is not dependent upon the size of V IN1 or V IN2 but only upon their difference This creates a challenge when designing differential amplifiers
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Differential Amplifiers Differential amplifier application SG OUT EXC D SG SG R R V = V A - R+R R+R ⎛⎞ ⎜⎟ ⎝⎠ SG OUT EXC D SG RR = V A R+R Let SG R= R + Δ R OUT EXC D EXC D V = VA 2R+ R 2R ΔΔ Δ ± If Δ
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This note was uploaded on 02/01/2012 for the course EE 230 taught by Professor Mina during the Fall '08 term at Iowa State.

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EE 230 Lecture 15 Spring 2010 - EE 230 Lecture 15 Basic...

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