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ECE410 Spring 2012

ECE410 Spring 2012. Lecture #21 Op Amps. Homework Due 3/12/2012. Chapter 5 – Problems 1, 3, 11, 14, 15, 16, 18, 20, 28, 36

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ECE410 Spring 2012

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  1. ECE410 Spring 2012 Lecture #21 Op Amps

  2. Homework Due 3/12/2012 • Chapter 5 – Problems 1, 3, 11, 14, 15, 16, 18, 20, 28, 36 • PSpice – Simulate an inverting amplifier with a gain of negative 10 and with supply voltages of +/- 10V. Use a sinusoidal input voltage with 2V amplitude and zero offset (i.e. centered at zero volts) and a frequency of 1kHz. Plot the output waveform (showing at least a few cycles of the waveform) as well as the input waveform on the same axes. Turn in the circuit schematic and printout of the output waveform. • Hint – to do this you will need to use transient analysis (make sure to set the final time to roughly 5ms), Vsinvoltage source, and set voltage probes at the input and output of the op amp. Use the LM741 opamp model for your opamp.

  3. The Inverting Amplifier Input Signal goes into the inverting input In the linear region: The inverting gain is:

  4. Summing Amplifier • An extension of the inverting amplifier is the summing amplifier

  5. Non-inverting Amplifier • Has similar function to inverting amplifier, but gain coefficient is positive

  6. Non-inverting Amplifier • Since no current flows into the input terminals, the feedback path from the output acts like a simple voltage divider: • Additionally, the voltage at vp is simply the signal voltage (vg in the circuit drawing)

  7. Non-inverting Amplifier In the linear region: The gain is: Input Signal goes into the non-inverting input

  8. Difference Amplifier Allows you to amplify the difference between two input voltages

  9. Difference Amplifier If we set Ra/Rb = Rc/Rd then the output will become:

  10. Voltage Follower (Buffer) • One very simple op amp circuit can be highly useful • What is the output vs. input relationship? • What is the point? • Ideal op amp has infinite input impedance. You can use a follower after a circuit to prevent the next circuit from loading it - Vout + Vin

  11. Follower - continued • Remember the voltage divider • A load resistor placed in parallel with R2 loads the circuit and changes the output voltage. • If a follower is placed between the output node of the divider and the load resistance, the divider will not experience loading

  12. Examples • Example 5.3 • Assessment Problems 5.4, 5.5

  13. Transient Analysis in PSpice • To do transient analysis in PSpice you must use a time dependent voltage source • Use Vsin and set frequency, amplitude, and offset • Set transient parameters such as final time • Set voltage or current probes • Run simulation and view plot

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