Operational Amplifier


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Operational Amplifier

  1. 1. Operational Amplifier<br />
  2. 2. What is an Operational Amplifier?<br />Differential amplifier - amplifies difference between two signals.<br />Can amplify very small voltage signals to a useful level.<br />3) Typically an 8 lead IC.<br />4) Op Amps can require one power supply (single supply) or a positive and a negative power supply (dual supply)<br />
  3. 3. Basic Op Amp Function<br />1) If (inverting input) &gt; (non-inverting input) output saturates towards -Vss<br />2) If (inverting input) &lt; (non-inverting input) output saturates towards +Vss<br />3) Without feedback maximum saturation occurs with the slightest difference between inputs.<br />4) Ideal op-amp has infinite impedance on the inputs, infinite gain, and zero resistance on output.<br />
  4. 4. Contnd….<br />5) In real life gain is limited to voltage present at +Vss/-Vss<br />6) For practical purposes there is no current flow from the inputs to the outputs. The input voltage serves only as a reference to control the output.<br />
  5. 5.
  6. 6. Feedback<br />1) Degree of amplification can be controlled using feedback.<br />2) Feedback can be applied to the inverting or non-inverting input.<br />3) Feedback applied to the inverting input is more common and is called negative feedback. <br />4) Gain (A) = 1 + (Rf/Rin)<br />
  7. 7. Feed back<br />
  8. 8. Voltage follower<br />1) Rf = 0, therefore no amplification. Gain = 1 + (Rf/Rin)<br />2) Output voltage is equal to input voltage. <br />3) Use to buffer/isolate circuit. Voltage is the same, but current is supplied by Vss rather than Vin<br />
  9. 9. Amplifies small difference between two signals.<br />Output voltage will &quot;switch&quot; whenever the input voltage (at the inverting input) reaches the reference voltage Vref (at the non-inverting input)<br />3) Very useful for comparing signals and working with sensors<br />Comparator<br />
  10. 10. 4) Note that R2 and R1 form a voltage divider. Use a potentiometer in place of R2 for an adjustable reference voltage.<br />5) Comparator cicuits can be built with opamps, but there are also comparator ICs with large slew rates and short propagation delays - good for high speed switching. <br /> <br />
  11. 11. Non-Inverting Amplifier<br />1) Inverting input is connected to ground + feedback.<br />2) Noninverting input serves as signal.<br />3) Output is in phase with input.<br />
  12. 12. Negative power supply<br />1) Some opamps need a dual power supply.<br />2) If we&apos;re only interested in getting positive output from opamp, -Vss can be connected to ground.<br />3) Dual power supply options include building a dual power supply, using two batteries, or purchasing a dual polarity power supply.<br />
  13. 13. Slew Rate<br />1) Slew rate defines how fast the opamp can react to changes at the inputs. Different opamps have different slew rates.<br />2) If voltage chages faster than opamp&apos;s slew rate, signal will be attentuated.<br />3) The higher the gain, the more deliterious effect from slow slew rate.<br />4) This is only an issue with high frequencey signals.<br />
  14. 14. Construction tips<br />1) Don&apos;t reverse the power leads. This will kill the opamp. A diode can be placed in series with -Vss to avoid this.<br />2) +Vss and -Vss must be greater than the noninverting and inverting inputs.<br />3) Couple signals and output to ground with caps (1.0uf - 0.1uf) if needed to filter noise and prevent oscillation. <br />4) Keep leads from power supply to +/- Vss short and direct.<br />
  15. 15. Thanking You!<br />