Chap.2-opamp-Handout

Chap.2-opamp-Handout - Operational Amplifiers - Covered are...

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1 Operational Amplifiers 1 - Covered are Sections 2.1-2.4 and 2.7 - Skipped are Sections 2.5, 2.6 and 2.8 Chapter expectations Use opamp to learn and apply the amplifier concepts: gain, i/o resistances, circuit model,. . Apply opamp properties to analysize and design various application circuits
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An ideal Volt.Amp has R i =( ) R o =( ) A vo = ( ) 2 In this chapter, we will study a most typical voltage amplifier – the opamp Opamp possesses characteristics that are very close to an ideal voltage amplifier: infinite R i , zero R o , and infinite gain . Again, what are the properties of an ideal voltage amplifier ??? 0 >> R s << R L Performance depends on Source & Load
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3 The Circuit Symbol: Opamp is an integrated circuit made of many transistors (For example, uA741 has 20 Trs, 10 Rs and 1 C) and possesses an almost ideal voltage amp property! Terminals: 1=Inverting input 2=Noninverting input 3=Output showing DC supplies 4, 5=DC supply terminals if more than one opamp are in the package, then the DC supply pins are shared by all opamps.
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4 14-pin 5-pin 8-pin IC Opamp Packages How many opamps in each chip ?? Note DC supplies lines are shared by different opamps 1 opamp 2 opamps 4 opamps 3 for i/o + 2 for DC 2 x3 for i/o + 2 for DC 4 x3 for i/o + 2 for DC
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5 Ideal Opamp Property : (1) R i = ∞ (2) R o = 0 (3) A cm = 0 [ Common-mode input: v cm = ½ (v 1 +v 2 ) ] (4) A = ∞ [ Differential-mode input: v d = v 2 -v 1 ] (5) Infinite Bandwidth Equivalent circuit showing the ideal properties Common-mode & Differential-mode: v cm d Ideal Property means : (1) Input terminals take in 0 Amp (2) v o is indept. of R L (3) (4) v d =0 v 1 = v 2 ( virtual short-circuit ) (5) v o = A cm v cm + A v d ideal voltage amp Input v i is composed of v cm and v d Opamp amplifies v cm and v d , differently Ideal opamp model
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6 Example: TV signal in Coaxial Cable center conductor to one input ( + ) shield to the other input ( - ) V d = V center V shield = V signal The noise V noise is the same in the center conductor and the shield V center = V noise + V signal V shield = V noise V center -V shield = V signal common-mode = noise differential-mode = signal V o = A cm V cm + A V d
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Note: When there are two inputs, v 1 and v 2 , they can always be reduced to Common-mode and Differential-mode Common-mode : v cm = ½ (v 1 + v 2 ) = average of the two amplitudes Differential-mode : v d = v 2 v 1 = difference in the amplitudes You can show that v 1 = v cm ½ v d v 2 = v cm + ½ v d How v d is generated in op amp.
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Chap.2-opamp-Handout - Operational Amplifiers - Covered are...

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