Lab 4 - ECE 420
Using the datasheet, linked above, the gain bandwidth product of the opamp can be found which can be used to estimate the bandwidths of different gains.
Image 1: Gain bandwidth product from data sheet linked above.
To obtain the exact value of each BW you simplty take the 1.3MHz and divide that by the gain of the circuit you are using, meaning that the 1 gain will have a bandgap of 1.3MHz, 5 will have 260kHz, and 10 will hae 130Hz.After calculating the expected bandwidth for the differnt gains they were tested experimentaly witht the following three circuits, using a common mode coltage of 2.5V
Image 2: Circuit used to experiment non-inverting topology of gain 1.
Image 3: Circuit used to experiment non-inverting topology of gain 5.
Image 4: Circuit used to experiment non-inverting topology of gain 10.
In order to experimentally test these circuits for the bandwidth the first step is to use a low frequency to get an accurate gain that we expect, then to raised the frequency until the ouput is .707 of the original value, or dropped 3dB. The frequency where the output drops 3dB is the bandwidth of the opamp gain. For the Following table all of the blue signals are the input signals, where the purple signals are the output signals.
| Gain | Low Frequency | High Frequency | Estimated Bandwidth | Experimental Bandwidth |
| x1 |  |  | 1.3MHz | 2.36MHz |
| x5 |  |  | 260kHz | 500Mhz |
| x10 |  |  | 130kHz | 200kHz |
The experimental values were not very close at lower frequencies however the 3dB drop was still found for all of the circuits. Additionally the 10 gain high photo has a message that was not seen until we left the lab, but the values still can be seen below.
After creating the circuits for the non-inverting topology the next step was to test the inverting topology with the folowing circuits
Image 5: Circuit used to experiment the inverting topology of gain 1.
Image 6: Circuit used to experiment the inverting topology of gain 5.
Image 7: Circuit used to experiment the inverting topology of gain 10.
As previously mentioned all the blue signals are the input signals, where the purple are the output signals.
| Gain | Low Frequency | High Frequency | Estimated Bandwidth | Experimental Bandwidth |
| x-1 |  |  | 1.3MHz | 1.6MHz |
| x-5 |  |  | 260kHz | 200kHz |
| x-10 |  |  | 130kHz | 356kHz |
For the -10 gain the experimental value was not close to the theoretical value, this could be due to the length of our cables introducing noise into our cirucits and having no capacitors to reduce noise.
For any op amp the output can only change so much a given time, thirs rate of change is the slew rate given in the datasheet that is linked above.
Image 8: Slew Rate from LM324 data sheet, linked above.
In order to test the slew rate of the circuit we will use the circuit given in Image 2, the non inverting gain of one togology, and imput a square wave. The square wave will have such a fast change the op amp will be unable to keep up and we will see the slew rate.
Image 9: Square wave input to see slew rate.
After using the square input wave we can change the input to a sinusoid wave that changes fast enough that the output can not keep up with the input.
Image 10: Sinusoid wave measuring slew rate.