karote
Member level 2
I have made some comparison measurement between (VCO / VCXO) based PLL synthesizers. I got a bit contradicting result. At the same operating frequency 400 MHz, the VCXO based synthesizer has much better close-in phase noise (as expected) BUT the phase noise analyzer claims that the VCXO based has much higher residual FM compared to the VCO based PLL synthesizer. The RMS jitter is better for the VCXO based PLL synthesizer. As I have understood, the RMS jitter relates to residual FM. At least you can find such integral equations describing how to calculate the residual FM from the measured phase noise curve.
Could this be related on the fact that the VCXO output is ~square wave and it has some duty-cycle variation 45/55? The VCO has sinewave output with duty cycle very close to 50%.
Any comments are welcome.
Could this be related on the fact that the VCXO output is ~square wave and it has some duty-cycle variation 45/55? The VCO has sinewave output with duty cycle very close to 50%.
Any comments are welcome.