I am building a SDR (Software defined radio) and I am trying to clock my 16 bit 130 MS/s ADC. At this speed, the jitter of the clock is very important and a bad jitter can reduce the SNR of my ADC a lot. For instance clocking with a standard Xtal which does not have excellent phase noise characteristics induces a jitter into the clock that adds so much noise in the ADC that its effective SNR is not better that a 14 bit ADC! The only way to have access to the full range of the ADC is the have a jitter on the clock of around 80 fs. (according to the chosen ADC chip that adds 70fs by itself)
Of course I could buy an OCXO which has an excellent phase noise, but I cannot afford to spend 300$ for an oscillator. Especially if the board could have multiple ADC...
I have read some app notes that explain the usage of PLL to remove the phase noise from a clock. Ok, but then it's the VCO of the PLL that needs to be expensive as far as I understand. And the PLL chip adds phase noise also. Even with a perfect VCO, the jitter induced by the output driver of the PLL is around 100 fs. Thus it doesn't seem to be the solution.
Thus my question is multiple :
How to clean up the clock from a reasonably good oscillator? I thought about using discreet filters, but the phase noise energy that creates the jitter is very close to the oscillator nominal frequency. I would have to use a band pass filter with a bandwidth of ~10khz at 130Mhz! Is it possible to do ? (bellow 200$ otherwise it would be cheaper to buy the OCXO)
If there is no way to achieve this level of jitter of ~80fs (phase noise from 10Hz to 260MHz) by myself, where can I buy oscillators that have this level of performances with reasonable cost? The problem is that OCXO are extremely stable over time ( years ) and are usually used for that. But here I don't care, it's the phase noise that is relevant to me. Is there oscillators technologies that are very clean, but that drift over years?
How you, amateur radio guy who have a SDR system, or engineers that design high speed ADC, solved the problem?
As you can see, I have spent a LOT of time reading app notes on the subject on the web, thus I have a deep understanding on how it works. I am a bit pessimistic about this and start to believe that there is no way to obtain a low jitter clock without getting a ~100$+ OCXO...