Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13EE201 Lecture 26 P. 1Op Amp Basics8 lead dual in-line package for Op Amp12348765The operation amplifier is a high gain amplifier. Traditionally used to perform math “operations”, the op amp has many uses (e.g feedback). Below is a typical package for an op amp.Terminal designations1. Offset null 2. Inverting input3. Noninverting input 4. neg. power supply5. Offset null 6. Output 7. pos. power supply 8. no connectionOp Amp Symbol and Notation+_v+v-voutNoninverting Inverting OutputEE201 Lecture 26 P. 2Positive power supplyNegative power supplyNote: only 5 terminal leads are important and of those, we will primarily use 3 (inverting, noninverting, and output)EE201 Lecture 26 P. 3Op Amp Current Variables+_iovCC+_+_vCCi+ (ip)i- (in)iC+iC-Op Amp Voltage Variables+_v- (vn)vo+_vCC+_+_+_vCCv+ (vp)+_Note: Negative and positive power supplies do not have to be equalEE201 Lecture 26 P. 4Because the op amp is a high gain voltage amplifier, we are interested in the voltage transfer characteristics of the device, as shown below. The output voltage is plotted as a function of the difference in input voltage.(v+ - v-) vsatslope=vout-vsatLinear regionPositive Saturation regionNegative Saturation regionI IIIIILarge gain deviceA = 104 - 107Op Amp Model (two resistors, one VCVS)+_v-v+Rii-v+ - v-)voi+RoEE201 Lecture 26 P. 5Output voltage for regimes of operation-vsat = -vcc(v+ - v-) < -vcc/AA(v+ - v-) -vcc/A ≤ (v+ - v-) ≤ vcc/Avsat = vcc(v+ - v-) > vcc/A {vo =Typical input voltage differences:A = 104 ; vcc = 10 V (v+ - v-) = ±1 mV All attributes of vo are satisfied by dependent source model+_EE201 Lecture 26 P. 6Redrawing figure on p. 5+_v-v+Rini-v+ - v-)voi+RoutQuestion: how does the op amp know it is operating in its linear regime?Negative feedback! Connect the output voltage to the inverting input terminal. This causes input voltage difference to decrease.+_Op Amp with negative feedback+_v-v+Rinv+ - v-)voRfEE201 Lecture 26 P. 7RsRout+_Analysis of Inverting Op Amp +_v-v+Riv+ - v-)voRfEE201 Lecture 26 P. 8RsRo+_vsabStrategy: perform KCL analysis at nodes “a” and “b”, then solve for vo as a function of vs.+_EE201 Lecture 26 P. 9KCL @ a:0foissRvvRvRvvKCL @ b:0)(oofoRvAvRvvssoffisvRvRvRRR11)111( 0)11()1( ooffovRRvRRAsfoisiofsfoovRRRRRRARRRRAv)/()1/()/1)(/()/(EE201 Lecture 26 P. 10Analysis of noninverting Op Amp +_v-v+Riv+ - v-)voRfRsRo+_vgabStrategy: perform KCL analysis at nodes “a” and “b”, then solve for vo as a function of vs.Rg+_EE201 Lecture 26 P. 11KCL @ a:0foiggsRvvRRvvRvKCL @ b:0)(oofoRvvAvRvv)])(()[/1(]/)(1)[/(]/)[(gisfsfiigsosgiossfoRRRRRRARRRRARRvARRRRRvNote that,ggiggRvvRRvv Note that,Rearranging and solving for vo = f(vg),if i- 0EE201 Lecture 26 P. 12+_ voif+_+_viVdi-i+Buffer Amplifier/Voltage Follower+_viv+v-Equivalent circuit_+v+ - v-)EE201 Lecture 26 P. 13Analyze equivalent circuit vo = A v+ - v-) vi = v+ vo = v- Relating vo to vi, vo = A vi - vo)vo = [A / (A + 1)] vi vi vo is said to ‘follow’ vi. This is called a voltage follower. This circuit buffers or isolates vo from vi, so that circuits connected to the output do not adversely affect the input circuitry. A wire directly connecting outputs and inputs would not serve this
View Full Document