Op Amps Intro to ECSE Analysis K. A. Connor Mobile Studio Project Center for Mobile Hands-On STEM SMART LIGHTING Engineering Research Center ECSE Department Rensselaer Polytechnic Institute Intro to ECSE Analysis

Outline What is an Op-Amp? No Negative Feedback Negative Feedback Golden Rules Op-Amp Model Inverting Amp Non-Inverting Amp

Op Amp – No Feedback An op-amp produces an output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the potential difference between its input terminals. Open loop gain is very, very large. Output is limited by power supply voltages.

Op-Amp Negative Feedback If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to the inverting input.

Golden Rules of Op Amps If there is negative feedback In a closed loop the output attempts to do whatever is necessary to make the voltage difference between the inputs zero. The two inputs draw no current

Op-Amp Model A more realistic model of the op amp when the inputs draw a very small amount of current and there is a small output resistance.

LTspice Analysis Feedback, input & load resistors and source.

LTspice Analysis Vin vs Vout Transfer Function?

Inverting Op Amp V+ = V- = 0 Current in Rin = Current in Rf

Non-Inverting Op Amp V+ = V- = Vin Current in Rin = Current in Rf See also Voltage Divider Videos

Special Case Why do this?

Many More Possibilities Negative impedance convertor Also: Integrator Differentiator Differential Amp Instrumentation Amp …