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Understanding Op-Amps: Functions, Applications, and Components

Dive into the world of operational amplifiers (Op-Amps) - learn about their low-cost design, applications, historical background, characteristics of ideal Op-Amps, circuit configurations, filtering, and comparator circuits. Explore the differences between real and ideal Op-Amps, non-ideal characteristics, and important parameters to consider when working with Op-Amps.

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Understanding Op-Amps: Functions, Applications, and Components

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  1. LECTURE 10Operational Amplifiersor Op Amps for short

  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. Realistically

  8. Background • Originally invented in early 1940s using vacuum tube technology • Initial purpose was to execute math operations in analog electronic calculating machines • Shrunk in size with invention of transistor • Most now made on integrated circuit (IC) • Only most demanding applications use discrete components • Huge variety of applications, low cost, and ease of mass production make them extremely popular

  9. 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+

  10. RF iout R iin C Vin Inverting Amplifier

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

  12. 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:

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

  14. 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

  15. 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

  16. Filters • Low Pass Filters • High Pass Filters • Band Pass Filters

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

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

  19. 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

  20. 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

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

  22. Real Vs Ideal Op Amp

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

  24. 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

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