ECE/CS 5780/6780: Embedded System DesignScott R. LittleLecture 19: Operati onal AmplifiersScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 1 / 29Introduction to Analog InterfacingMost embedded systems include components that measureand/or control real-world parameters.These include position, speed, temperature, etc.Usually exist in a continuous, or analog, form.We often need to amplify, filter, and convert these signals to adigital form.This chapter develops analog circuit bui ldi ng blocks for dataacquisition and control systems.Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 2 / 29Ideal Op AmpsVout= K (Vy− Vx)1Voltage ranges are bounded by the supply voltages, ±Vs.2Input currents, Ixand Iy, are zero.3Negative feedback drives Vxto equal Vy.4Positive or no feedback drives Voutto equal −Vsor +Vs.Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 3 / 29Various Op AmpsOp amp Description Open loop gain ±Vs±IsOPA4227 High Precision 160 dB ±5 to ±15 V ±3.8 mAOPA4132 High-Speed FET 130 dB ±2.5 to ±18 V ±4.8 mATLC2274 Rail-to-Rail 104 dB 0 to 5 or ±5 V 3 mAScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 4 / 29Input ImpedanceOp amp RcmRdiffOPA4227 1 GΩ 10 MΩOPA4132 1013Ω 1013ΩTLC2274 1012Ω 1012ΩScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 5 / 29Output ImpedanceScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 6 / 29Offset Voltage, Offset Current, and Bias CurrentOp amp VosIosIbOPA4227 0.075 mV 10 nA 10 nAOPA4132 0.5 mV 50 pA 50 pATLC2274 3 mV 100 pA 100 pAScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 7 / 29Noise DensityOp amp enOPA4227 3 nV/√HzOPA4132 23 nV/√HzTLC2274 50 nV/√HzScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 8 / 29Transient ResponseOp amp dV /dt, Slew rateOPA4227 2.3 V/µsOPA4132 20 V/µsTLC2274 3.6 V/µsScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 9 / 29Frequency ResponseOp amp f1OPA4227 8 MHzOPA4132 8 kHzTLC2274 2.18 MHzScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 10 / 29Power Gain (Adb)Combines voltage gain, input impedance, and output impedance.Pin=V2inRinPout=V2outRoutAdb= 10log10PoutPin= 20log10VoutVin+ 10log10RinRoutScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 11 / 29Threshold DetectorScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 12 / 29Simple Rules for Linear Op Amp CircuitsChoose quality components.Negative feedback required to create linear mode circuit.Assume no current flows into the op amp inputs.Assume negative feedback equalizes i npu t voltages.Choose resistor values in the 1kΩ to 1MΩ range.BW depends on the gain and the op amp performance.Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 13 / 29Simple Rules for Linear Op Amp Circuits (cont)Equalize the effective resistance to ground at the two op ampinput terminals.Input impedance is input voltage / input current.Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 14 / 29Simple Rules for Linear Op Amp Circuits (cont)Match input impedances to improve common-mode rejectionratio (CMRR).Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 15 / 29Inverting AmplifierScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 16 / 29Inverting Amplifier with -2.5V to 2.5V RangeScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 17 / 29Noninverting AmplifierScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 18 / 29Model for Linear Circuit DesignVout= A1V1+ A2V2+ . . . + AnVn+ BScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 19 / 29Linear Circuit DesignVout= 5V1− 3V2+ 2V3− 10Choose a reference voltage from available reference voltage chips.Vref= 5VRewrite the design equation in terms of the reference voltage, Vref.Vout= 5V1− 3V2+ 2V3− 2VrefAdd a ground input to the equation such that the sum of the gains is 1.Vout= 5V1− 3V2+ 2V3− 2Vref− VgChoose a feedback resistor, Rf, in range of 10 kΩ to 1 MΩ.Rf= 150k Ω R1= 30k Ω R2= 50k ΩR3= 75k Ω Rref= 75k Ω Rg= 150k ΩBuild the circuit: connect positive gain inputs to positive terminal andnegative gain inputs to the negative terminal.Scott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 20 / 29Linear Op Amp CircuitScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 21 / 29Instrumentation AmplifierScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 22 / 29Current-to-Voltage CircuitScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 23 / 29Voltage-to-Current CircuitScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 24 / 29Integrator CircuitScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 25 / 29Derivative CircuitScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 26 / 29HysteresisScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 27 / 29Voltage Comparators with HysteresisScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 28 / 29Analog IsolationScott R. Little (Lecture 19: Op Amps) ECE/CS 5780/6780 29 /
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