Operational Amplifiers (Op Amps)

Operational Amplifiers (Op Amps)

Operational Amplifiers (Op Amps) Adnan Pandjou Hunter Moore Tyler Randolph Agenda

Background Ideal Op Amp Inverting Non-inverting Integrating Differential Summing

Applications Conclusion Background Originally designed to perform mathematical operations in 1940 using vacuum technology The first integrated op-amp to become widely

available was produced in the late 1960s by Fairchild Wide variety of applications, low cost, and easily manufactured Ideal Op Amp Ideal Op-Amp Typical Op-Amp Input Resistance

infinity 106 (bipolar) 109 - 1012 (FET) Input Current 0 10-12 10-8 A Output Resistance

0 100 1000 Operational Gain infinity 105 - 109 Common Mode Gain

0 10-5 Bandwidth infinity Attenuates and phases at high frequencies (depends on slew rate)

Temperature independent Bandwidth and gain Inverting Op Amp Non-inverting

Integrating Inverting op-amp feed back resistor replaced with a capacitor Input voltage is integrated by using a capacitor Smoothes out signals and helps to remove offset Used for PID controllers Differential If all of the resistors are equal, the differential op-amp becomes a difference amplifier Vout=V1-V2

If R4=R3 and R2=R1, then it becomes amplified difference op-amp Vout=(V2-V1)R3/R1 Summing Summing amplifiers combine signals by adding directly or scaling and then adding If all resistors are equal Vo = (V1 + V2 + V3 ) Audio mixers sum several signals with equal gains Digital-to-analog converters use different resistors to give a weighted sum LEDs use summing amps to apply a DC off set to AC voltage to keep it in

its linear operating range Applications Low Pass Filters High Pass Filters

Offset Comparator Data acquisition Low Pass Filter Used to filter frequencies above fc Second order Active 1 fc = 2 R1R2C1C2

High Pass Filter Used to filter frequencies below fc Second order Active C2 and R2 switched 1 fc = 2 R1R2C1C2 Offset Comparator If

U2 R2 R1 + R2 .U1 Output = 0V If U2

5.R1 + U1.R2 R1 + R2 Output = 5V Good for setting thresholds Offset Comparator Example Setting thresholds for IR detector

IR detector Op-amp R1 R2 Data acquisition Signal amplification Example (Lab 2) Amplification of strain gage signal

Example Data acquisition Differential Circuit Vout V 2 (R3 + R1 )R4 V1 R3 = ( R4 + R2 ) R1 R1

Where to get Op-amps for Free Companies give free samples www.national.com Where to get Op-amps for Free 5 (max 5 of each kind) samples per week Design tools Design tools

Design tools Design tools Parts List Design tools Design simulation Conclusion Wide range of application Lots of recourses

Look at other previous student presentations Questions? Appendix Inverting Assumptions Infinite gain (amplification factor) Large internal resistance

ii1a= i=02+ia iV1out = i= 2 K ( V V

) B A VK out = VB VA VVBB= V= A Vi1A=

= 0 i2 Derivation (Large internal res istance) i2 ia

i1 VA VB Vout R2 = Vin R1 K =Infinite gain, therefore

From , Vout VA VA Vin = Rf Rin 1 1 Vout Vin VA = Rin Rf Rf Rin

Vout = Vin Rf Rin Non-Inverting Assumptions Infinite gain (amplification factor) Derivation Vout=K(VinVA) Vout =V V K in A

Vout 0 = VA 0 R2 +R1 R1 Vout Vin = R2 +R1 R1 VA Vout

Vin= VA K = Infinite gain, therefore R2 = Vin 1+ R1

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