Odd Square Wave Behavior in Lab Experiment

In summary, the conversation discusses an experiment with a white noise and a square wave signal, run through a summing amplifier with different voltage ratios. The results showed spikes on the square wave, which was unexpected and the cause was unclear. Suggestions were made to try a noninverting configuration or reduce the rise time of the signal generator. The difference in the width of the spikes for different op-amp types was also mentioned.
  • #1
Feldoh
1,342
3
So the other day in a lab my group was working with a signal and some noise and the signal we got was a bit interesting...

Essentially we were using a white noise with 0.5 Vpp and a 1kHz square wave with the 10 times the amplitude (5V) running them through a 741 op-amp summing amplifier.

We were supposed to experiment with different ratios of approximate voltage and looking at FFTs of the data we collected. The first ratio was ~1/1 so we were dividing the square wave signal by a factor of 10.

However just running the signal (no noise) through the amplifier gave us an interesting display and I'm still not particularly sure why it is happening:

Here's are some simulations that show pretty much the same thing we observed in the lab
http://filer.case.edu/pal25/square%20wave.JPG -- Output on oscilloscope
http://filer.case.edu/pal25/circuit.JPG -- Schematic of circuit (essentially it's two function generators in a summing amplifier)

There are spikes on the square wave if we run it through the amplifier and I'm not particularly sure why we've tried using a better op-amp (OP42G) and we still get effectively the same display which leads me to believe it's something else.
 
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  • #2
I'm no expert, but it seems to me that this could more easily occur in your inverting summing amp than in a noninverting version?

I saying this because in your case, the input square wave is resistively coupled "directly" to the output of the amp, so any slowness in the amps feedback loop would result in an overshoot spike if the rise time of your signal generator is faster than the opamp.

Maybe you should try a noninverting configuration?:
http://www.allaboutcircuits.com/vol_3/chpt_8/8.html

Another possibility is to se if you can reduce the rise time of your square wave generator. Either on the apparatus, or by introducing a capacitor across the signal generator output? But please find out beforehand if this can cause damage to the generators output.

Did you notice a difference in the width of the overshoot spike for your two types of op-amp? I would expect it to be wider for the slower op-amp.

Torquil
 

Related to Odd Square Wave Behavior in Lab Experiment

1. Why did the square wave have an odd behavior in my lab experiment?

There could be several reasons for this odd behavior. It could be due to external factors such as temperature or interference from other equipment. It could also be a result of incorrect setup or malfunctioning equipment. It is important to carefully review your experimental setup and make any necessary adjustments.

2. Can the odd square wave behavior be caused by human error?

Yes, human error can also contribute to odd square wave behavior. This could include incorrect calibration, incorrect measurement techniques, or misinterpretation of data. It is important to carefully follow the experimental procedure and double-check all measurements and calculations.

3. Is it possible that the odd square wave behavior is a result of faulty equipment?

Yes, faulty equipment can also cause odd square wave behavior. This could be due to aging or wear and tear of equipment, or a malfunctioning component. It is important to regularly maintain and calibrate equipment to avoid any potential issues.

4. Are there any common mistakes that can lead to odd square wave behavior?

Yes, there are several common mistakes that can contribute to odd square wave behavior. These include incorrect wiring, incorrect voltage settings, and improper grounding. It is crucial to carefully follow the instructions and double-check all connections before conducting the experiment.

5. How can I troubleshoot odd square wave behavior in my lab experiment?

There are a few steps you can take to troubleshoot odd square wave behavior. First, check all connections and make sure they are secure. Next, review the experimental setup and make any necessary adjustments. You can also try replacing any potentially faulty equipment. If the issue persists, seek guidance from a colleague or supervisor.

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