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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I have a simple two-stage RC low pass filter. Each stage is 0.33uf and 1kohms. I built this on a breadboard with through-hole components.
I am inputing a square wave of 4 kHz.
I have attenuated the signal by more than 100-fold, but I am getting these spikes at the transition state. If I connect the scope ground to the signal ground the spikes get much smaller, but they are still there. Is this the square-wave transitions being picked up by the component leads? Would it be less with surface mount components?
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
How is this hooked up right now, signal generator->RC filter->Scope, or is there anything else in the loop?
If the point where you connect the scope's ground matters, then your ground voltage is not stable. It could mean a lot of current is getting dumped to ground in one of the stages of the filter, probably the first stage. Decoupling your power supply can help, though that's not really an option if you don't have a power supply.
This is going as a VCO input right? If the spikes don't have any real width to them then they're not even really going to affect the VCO's output, so you might not need to worry about it.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Welcome to the real world! That noise may not even be in your circuit, it could be picking up on the scope probes. Then again, it might be in your circuit.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
If you are using two probes you need to connect both probe grounds to the signal ground or you will have all sorts of trouble. I got a similar scope and have had those exact problems.
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How do I get rid of these spikes?
