Why there is dc component in square signal

AI Thread Summary
A square wave signal sent to a digital oscilloscope can show a DC component due to factors like the internal resistance of the coaxial cable or the oscilloscope's input impedance. The observed DC offset of approximately 17 mV in a ±1 V signal suggests a small error, potentially from the signal generator. Adjustments such as using a large capacitor in series or selecting "AC input" can eliminate the DC component. Additionally, the rise time of the square wave may contribute to the DC offset. Overall, the discussion highlights the importance of understanding signal integrity and potential sources of error in measurements.
giulioo
Messages
7
Reaction score
0
hi!
when I send a square wave to a digital oscilloscope it detects the signal + dc signal. I wanted to know why. I was thinking about internal resistance of coaxial cable i was using.

signal got out of an oscilloscope/wave generator and in channel A of the same oscilloscope/wg. It was +-1 V, while dc component was something like 17 mV.
 
Engineering news on Phys.org
or probably it is due to internal impedance of the oscilloscope?
 
giulioo said:
hi!
when I send a square wave to a digital oscilloscope it detects the signal + dc signal. I wanted to know why. I was thinking about internal resistance of coaxial cable i was using.

signal got out of an oscilloscope/wave generator and in channel A of the same oscilloscope/wg. It was +-1 V, while dc component was something like 17 mV.
This sounds like a small error in the generator. You can remove all DC component by placing a large capacitor in series with the oscilloscope, or selecting "AC input". It is possible that the square wave is not exactly "50/50".
 
well the wave is for sure not exactly 50/50 because of rise time. I haven't thought about it anyway. I will meditate upon it, i mean, rise time could add a dc component.
Do you think input and output resistance could not affect signal in such way too?
I already removed the dc component using an offset.
thank you for your advice!
 
giulioo said:
It was +-1 V, while dc component was something like 17 mV.
17mV DC error in a signal of ±1V - that is an error of ≈ 1%. I would not be able to see that on an oscilloscope. And, as you said, the signal generator might easily give an error of that size.
 
Hi all I have some confusion about piezoelectrical sensors combination. If i have three acoustic piezoelectrical sensors (with same receive sensitivity in dB ref V/1uPa) placed at specific distance, these sensors receive acoustic signal from a sound source placed at far field distance (Plane Wave) and from broadside. I receive output of these sensors through individual preamplifiers, add them through hardware like summer circuit adder or in software after digitization and in this way got an...
I have recently moved into a new (rather ancient) house and had a few trips of my Residual Current breaker. I dug out my old Socket tester which tell me the three pins are correct. But then the Red warning light tells me my socket(s) fail the loop test. I never had this before but my last house had an overhead supply with no Earth from the company. The tester said "get this checked" and the man said the (high but not ridiculous) earth resistance was acceptable. I stuck a new copper earth...
Thread 'Beauty of old electrical and measuring things, etc.'
Even as a kid, I saw beauty in old devices. That made me want to understand how they worked. I had lots of old things that I keep and now reviving. Old things need to work to see the beauty. Here's what I've done so far. Two views of the gadgets shelves and my small work space: Here's a close up look at the meters, gauges and other measuring things: This is what I think of as surface-mount electrical components and wiring. The components are very old and shows how...
Back
Top