04_-_opamp (1)

04_-_opamp (1) - Operational Amplifier (Chapter 4) s s s s...

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1 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights Operational Amplifier (Chapter 4) Basic Information Input-output Voltage Relationship Open-loop vs. Closed-loop (Feedback) Operation Standard Behavioral Op Amp Model Idealized Op Amp Model Canonical Op Amp Circuits Other Op Amp Circuits Multi-stage Amplifiers Saturation and Using the Op Amp as a Comparator General Summing Amplifiers
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2 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights 3 terminal (2 input, 1 output) circuit element that is an integral part of nearly all “analog” and “mixed- signal” electronic systems Output is basically equal to the difference between the two input terminals, amplified significantly Op amps need to be powered by external voltage sources (e.g. ± 15 V) Schematic Representation 5 connections (pins) per op amp V cc and –V EE power connections are often suppressed on schematics Op amps are typically packaged in an 8-pin IC containing 2 op amps In lab, we will use the National Semiconductor LF412 dual op amp package The term “operational” amplifier stems from the fact that early on these devices were used in analog computers to implement mathematical operations such as addition, subtraction, integration, etc. Operational Amplifier (op amp) - + inverting input non-inverting input output + V CC - V EE
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3 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights Internal Schematic of the Op Amp Although the internal circuitry of an op amp is fairly complex, the input/output behavior can be represented using a fairly simple equivalent circuit model Simplified Schematic of LF412 Op Amp Detailed Schematic of LF412 Op Amp
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4 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights Open-Loop (no feedback yet) Input-output Voltage Relationship ) v v ( v in - + - = [V] v out slope = A + V cc “head room” typically a few volts down to a few tenths of a volt - + v - v out v + v in “open-loop gain” - V EE + V sat - V sat Linear (active) Region typically in the range of 10 5 to 10 7 ) v v ( A v A v in out - + - = = v in [V] (within linear region)
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5 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights Caveats Regarding the Open-Loop Voltage Gain A Two op amps of the same make/model may have different values of open-loop voltage gain A due to slight differences in manufacturing conditions. The actual value of open-loop voltage gain A for any real op amp may vary during operation due to such factors as: The open-loop voltage gain A actually depends upon the frequency of the input voltage signal and tends to “roll off” as frequency is increased.
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6 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights 0 50 100 -0.1 0 0.1 v in = v + - v - [mV] 0 -20 0 20 out [V] 0 0 0 0 0 0 t [ms] 0 0 t
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7 op amps EE 210 © Jeffrey Mayer 2003-2006, David Salvia 2006. All rights Closed-Loop “Feedback” Operation Generally, we do not use op amps in an open-loop configuration because: By introducing a properly designed feedback network or “closing the loop around the op amp”, we obtain a closed-loop configuration that features:
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04_-_opamp (1) - Operational Amplifier (Chapter 4) s s s s...

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