Testing an RF oscillator
I need advice to find the best way to test my Rf oscillator. At the beginning I used this oscilloscope Agilent InfiniiVision 5000/6000/7000 Series Oscilloscopes with 10073C probes. The problem I found was that the parasitic capacitance of my probes modify the osicllator frequency so, to fix that, I built a buffer to isolate the tank part of the oscillator from the probe's part. With the buffer I hope that the parasite capacitance doesn't affect the frequency of operation but I don't know if I have solved the other problems.
My teacher recommended me to use SMA connectors and SMA cables to improve the signal but I found that those cables have a parasitic capacitance of 100pF/m (I have a 0.5m one) and when I introduce them in my simulation, I get the signal attenuated. The question is: Do I need another way to mesure the oscillator or just another SMA cable with low capacitance? What is the regular procediment to measure this kind of circuits?
The circuit here:
Ty very much!
whats your oscillation frequency?
yeah the probe does effect your measuring e.g. a probe of 10MHz will surely give different result then a probe of 1GHz when used for testing a 1GHz application circuit.
My oscillation frequency is 868MHz. Yes, I noticed this before I built the buffer. The question is: How do I test it now? Should I connect the SMA cable directly at oscilloscope? Is there any common way to measure those Rf circuits?
Ty very much for your advice!
the thing with RF is one need to have proper instrument to conclude a result. Sorry I don't get when you say connecting SMA cable directly to scope? you mean from the output of the oscillator through a SMA connector and cable you will connect it to the scope?
Perhaps for a test it just came in my mind, try reverse configuration of cable for measuring! I mean connect the probe (Needle part) of the cable with ground and the ground part(crocodile clip) at your measuring point.... I assume a slight difference would be there in your result ? give it a try!
Yes, when I say "connecting SMA cable directly to scope" I mean connecting a SMA cable from SMA connector to oscilloscope. I think that in this way I would avoid the parasite capacitance of the probe but not the one from the cable.