| Electronics > Beginners |
| strange output on CRO while measuring output of 45Mhz |
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| Vindhyachal.takniki:
I am measuring output of 45Mhz of programmable oscillator of: http://www.cardinalxtal.com/products/programmable-oscillator-3 1. When I measuring it on gwinstel gds-11028 DSO,. 2. Gnd loop is mimized, like this: https://goo.gl/images/QqHD2d 3. Probes are conencted directly on oscillator output pins 4. Vdd = 3.3V 5. When on 1x probe: Signal is sine wave riding on 1.6Vdc. Peaks of sine wave dont touch the 3.3V & 0V limtis. 6. When on 10x probe, signal is sine wave which seems to ride on dc also, but this time negative peak of sine goes below zero volt 7. Why is that so? 8. Also what is output of this oscillator, we have TTL version, is it sine wave? I thought it would be square wave. |
| Zero999:
I couldn't find the gwinstel gds-11028, using Google. Presumably you mean the GDS-1102B? https://www.testequity.com/documents/pdf/GDS-1000B-brochure.pdf It's a 100MHz oscilloscope and you're measuring a 45MHz squarewave. An ideal square wave only contains odd harmonics, so you have 45MHz, plus the 3rd, 5th, 7th etc. harmonics 135MHz, 225MHz, 315MHz, but your oscilloscope will have a filter blocking everything below 100MHz, so you just see the fundamental of 45MHz. In other words, this is exactly what you should expect. To see anything resembling a square wave you need a much wider bandwidth oscilloscope. |
| alsetalokin4017:
The short answer is that you can't really measure a 45 MHz square wave with a 100 MHz oscilloscope. |
| Mechatrommer:
--- Quote from: Vindhyachal.takniki on February 08, 2019, 03:17:56 pm ---5. When on 1x probe: Signal is sine wave riding on 1.6Vdc. Peaks of sine wave dont touch the 3.3V & 0V limtis. 6. When on 10x probe, signal is sine wave which seems to ride on dc also, but this time negative peak of sine goes below zero volt 7. Why is that so? --- End quote --- with unterminated 1X coax cable, so you probably looking at one point in standing wave. with 10X probe, no reflection in probe cable, there maybe a little bit of loading in the circuit though. it goes -ve i guess due to overshoot in square wave signal or a little reflection due to mismatched cable. without properly measuring it with the right tool, we are actually measuring a funny business... attached is an example of 5V 125MHz oscillator clock in not so good terminated transmission line. if we let loose the termination it will become haywire. ymmv.. |
| David Hess:
Check to make sure the x10 probe is compensated correctly or it can increase the amplitude of high frequency signals. |
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