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Operational Amplifiers

Operational Amplifiers. David Lomax Azeem Meruani Gautam Jadhav. What is an Op-Amp. Low cost integrating circuit consisting of: Transistors Resistors Capacitors Able to amplify a signal due to an external power supply Name derives from its use to perform operations on a signal.

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Operational Amplifiers

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  1. Operational Amplifiers David Lomax Azeem Meruani Gautam Jadhav

  2. What is an Op-Amp • Low cost integrating circuit consisting of: • Transistors • Resistors • Capacitors • Able to amplify a signal due to an external power supply • Name derives from its use to perform operations on a signal.

  3. Applications of Op-Amps • Simple Amplifiers • Summers • Comparators • Integrators • Differentiators • Active Filters • Analog to Digital Converters

  4. +V Inverting Input Terminal Non-Inverting Input Terminal -V Symbol for an Op-Amp

  5. IC Circuit

  6. What do they really look like?

  7. Ideal Op-Amps I- V- • Infinite input impedance • I+ = I- = 0 • Infinite gain • V+ = V- • Zero output impedance • Output voltage is independent of output current Vout I+ V+

  8. RF iout R iin C Vin Inverting Amplifier

  9. RF iout iin R C Vin Non-Inverting Amplifier

  10. Summing Circuits • Used to add analog signals • Voltage averaging function into summing function Calculate closed loop gain for each input If all resistors are equal in value:

  11. Difference Circuit • Used to subtract analog signals • Output signal is proportional to difference between two inputs If all resistors are equal:

  12. Integrating Circuit • Replace feedback resistor of inverting op-amp with capacitor • A constant input signal generates a certain rate of change in output voltage • Smoothes signals over time

  13. Differentiating Circuit • Input resistor of inverting op-amp is replaced with a capacitor • Signal processing method which accentuates noise over time • Output signal is scaled derivative of input signal

  14. Filters • Low Pass Filters • High Pass Filters • Band Pass Filters

  15. Low Pass Filter • Used to filter out signals above a specified frequency • Example: Noise Frequency range is governed by: Where R = R2 C = C2

  16. High Pass Filter • Filters out frequencies below a specified frequency • Reverse locations of resistors and capacitors in a low pass filter

  17. Band Pass Filter • Created by combining a high and low pass filter • Only allows signals within frequency ranges specified by the low and high pass filters to pass

  18. Comparator Circuit V1 is Vref V2 is Vin • Determines if one signal is bigger than another • No negative feedback, infinite gain and circuit saturates • Saturation: output is most positive or most negative value

  19. OR Gate If U1 or/and U2 = 5V, U3 = 5V If U2 and U1 = 0V, U3 = 0V

  20. If U3 = 0V If U3 = 5V Offset Comparator

  21. Real Vs Ideal Op Amp

  22. Non-Ideal Op-Amps • Gain Bandwidth • Falloff Frequency • Slew Rate (ΔV/ΔT) • Rise Time

  23. Gain Bandwidth • Gain Bandwidth Product (GBP)- is the product of the open-loop gain and the bandwidth at that gain. • For practical purposes the actual gain should only be 1/10 to 1/20 of the open loop gain at a given frequency to ensure that the op-amp will operate without distortion.

  24. Open and Closed Loop Response

  25. Important Parameters for Op-Amps • Input Parameters • Voltage (Vicm) • Offset voltage • Bias current • Input Impedance • Output Parameters • Short circuit current • Voltage Swing • Open Loop Gain • Slew Rate

  26. Where to buy Op-Amps • Newark Electronics • Radio Shack • DigiKey • Jameco

  27. References • David G Alciatore & Michael B. Histand, Introduction to Mechatronics and Measurement Systems • http://www.elexp.com/t_gain.htm • http://allaboutelectronics.com • Electronics book

  28. Questions ?

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