BioNB 440: Lab 3

Operational amplifier applications, part 1.

Introduction.

This assignment will cover some of the ways you can build useful circuits using a standard integrated amplifier circuit.

Download the Opamp1.ewb file by right-clicking over the link and saving it to your directory. You may need to add the ewb extension to the filename in the dialog box. Start EWB from the shortcut on the desktop and open the file you just saved. This link shows the schematic.

Note that the LM358 opamp which is shown in the circuits is also the type we will be using to actually build these circuits. Some of the data from the LM358 data sheet will be necessary in the lab. Don't print it. We will have copies in lab.

For most of the labs to follow, you will need to produce a circuit on the prototype board. Typically, you will have one or more integrated circuits, which require power, and many passive components. You will need to develop a style of wiring which is reliable and easy to follow. I like to use the top and bottom rows of connections to distribute power. Color coding the power wiring to match the connectors is useful. Two pictures showing the wiring of one LM358 opamp are shown: the whole circuit, and a little closer. The opamp is wired as an inverting amplifier with a resistor between the negative input and the output.

Note that in this and every lab assignment the verb build means to construct a circuit on the protoype board whith actual parts. The verb simulate means use Electronics Workbench mathematically simulate the circuit.

1. Simulate the frequency response of the two amplifiers. The data sheet suggests that the gain-bandwidth product should be about 1 MHz. Is it? Apply a square wave to the amplifiers and measure the rise time. Is the rise time constant for for different output amplitudes? the rise rate may be dominated by the gain-bandwidth product or slew-rate, depending on conditions.

2. Vary the feedback resistors in the inverting amplifier to verify that the gain is proportional to Rf/Rin.

3. Use the Bode plotter to get the frquency response of the two filters. Does the cutoff frequency of each of the filters match the calculated value?

4. Design, simulate, and build a voice-band amplifier with an overall gain of 10, a highpass cutoff at 100 Hz and a lowpass cutoff at 3000 Hz. Test it by connecting its input to the phone jack of the CD player and listening to the output with a speaker. Try varying the cutoff frequencies.

Be sure your lab notes have your design for the voice-band amplifier.