Amplifier Challenge

1. Design an inverting amplifier with a gain of -20. Use an LF411 op-amp, or similar. Build your amplifier, and feed it with a .1V square wave, centered around 0V from a function generator or an RCX output, using Robolab. Where should you set the power rails, V+ and V-?

Hint: if you're using the RCX, the output swings between 0-5V. Use a voltage divider to get the output from 0-.2V, and use a blocking cap to center the output around 0V. Remember to consider the output impedance of your divider in relation to the input impedance of the amplifier.

Use a scope or RCX datalogging to verify the output of your amplifier. Try to overlay the input and output signals to verify that the amplifier inverts the signal. Then, if you have a scope, expand the time axis to look at the vertical edges of the square wave. Do the edges really rise straight up? What's happening?

2. Design a non-inverting amplifier, again using an LF411 or similar, with a gain of 10. Set the power rails at +5V/-5V, and drive the amp with a .2V sine wave if you have a function generator, or a .2V square wave from an RCX, voltage divider, and blocking cap, as above.

Watch the output on a scope or RCX with datalogging. Then, drive the amp with a .5V wave. Can you see the clipping? How would you get rid of it?

3. Design a non-inverting amplifier with a gain of exactly one. What use could this have?


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