Operational Amplifiers
Op-amps: high-gain differential amplifiers that, with feedback, build almost any analog function.
An op-amp amplifies the difference between its two inputs with a very large open-loop gain (often –). By adding a few resistors and capacitors as negative feedback, you get precise amplifiers, filters, integrators, comparators and converters.
Popular parts: LM358 (dual, single supply), TL072 (JFET input audio), LM741 (classic, outdated), MCP6002 (rail-to-rail, 1.8–6 V), OPA2134 (audio).
Sub-topics (8)
Ideal Op-Amp and Golden Rules
With negative feedback: no current flows into the inputs, and the output drives the inputs to equal voltages.
Inverting Amplifier
Gain = −Rf/Rin; the inverting input sits at a virtual ground.
Non-Inverting Amplifier
Gain = 1 + Rf/Rg with very high input impedance.
Summing and Difference Amplifiers
Add or subtract several signals with resistor networks around an op-amp.
Integrator and Differentiator
Put a capacitor in the feedback path to integrate, or at the input to differentiate.
Comparators and Schmitt Triggers
Compare two voltages and output a clean high/low decision, with hysteresis to reject noise.
Active Filters
Op-amps with RC networks make filters with gain, sharp roll-off and no inductors.
Real Op-Amp Limitations
Offset voltage, bias current, gain-bandwidth product, slew rate and output swing.
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