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Design >> RF Design >> divider
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Message started by nxing on Jul 10^th, 2007, 6:20pm

Title: divider
Post by nxing on Jul 10^th, 2007, 6:20pm

Hi everybody,

I have a question regarding the divider: say I have a divider working at 2GHz, for some reason, there is another signal is added to this 2GHz, (say 2.1GHz), I am wondering whether or not this divider will divide this 2.1GHz? or can I see a signal of 1.05GHz at the output? what's the reason for that?

Thanks

nxing

Title: Re: divider
Post by chenyan on Jul 15^th, 2007, 8:15am

the prescaler, or divider you mentioned, normally has a frequency range of operation. I believe if it works at 2Ghz, it will work at 2.1Ghz as well.

Title: Re: divider
Post by SemiLeon on Jul 18^th, 2007, 10:57pm

Hi, nxing,
If there is a pair of spurious tone on both side of VCO output spectrum, the offset frequency will not be changed by divider. for example, the VCO frequency is 2GHz, and the spurious tone is at 2.1GHz, at the output of divider, you will see the main tone at 1GHz, and spurious tone at 1.1GHz.

Leon

Title: Re: divider
Post by imtired on Jul 19^th, 2007, 2:11pm

I agree with SemiLeon, that you will see the same offset tone at 1GHz, but it will be smaller. My reasoning is if you add 0.1 GHz to 2 GHz sinewave, and then limit the signal, what you have essentially is an FM signal (or PM). The same edge excursions at the input will show up on the output as well, with the same frequency, 0.1 GHz. Since the period at the output is twice the input, therefore the frequency (or phase) deviation will be 1/2 of the input. On the other hand, if AM is causing the tone, then the output tone will be basically a feed-through of the input tone, at 0.1 GHz offset, also a smaller amplitude, unless the isolation of the divider really sucks.