Hi,
I intend to design a RF Circuit, So I required a Clock Oscillator at 45Mhz. As you might know, this is rather very high frequency, I might need a Impedance MAtching network. What is the OUTPUT IMPEDANCE OF OUT pin of CLOCK oscillators as I failed to find that information in any datasheets I referred. Can you provide the necessary data?
Thanks,
Praveen
PS : This is the first time I am designing a RF Circuit, forgive me for any trivial questions!
Disclaimer: I'm gong to assume you have a technical background when answering this question.
When determining if you need to consider the RF properties of a signal you need to calculate the wavelength of the signal in the material in which is travels. For example, let's assume the 45 MHz signal is traveling in the fiberglass of a standard FR4 circuit board. The wavelength will be:
where λ is the speed of light [3 x 10^8 m/s],
εr is the relative permittivity of the FR4 board [4],
μr is the relative permeability of the FR4 board [1],
and f is the frequency [45 MHz]
Note, I realize not all the signal is in the dielectric, but this serves as a good reference calculation. If you run these numbers, you see that the wavelength is 3.3 meters.
Now, here is the rule-of-thumb:
If the traces and combined parts length add up to more than 1/10 of a wavelength, you must consider the RF properties of the signal. That is, you must impedance match the trace because it becomes a transmission line. So, for your case, if the combined trace length and component lengths are more than 33.3 cm you will need to impedance match your lines. I doubt this is a concern for you, since 33 centimeters would be about a 1 foot trace, and that's a really, really, really long trace.
