Resistor degrading phase noise of VCO..

[haadi20]

I have two tuning voltages for the varactors to tune the LC-VCO.

I notice that when i connect these nodes through a large resistor (~5k) to the supplies...my simulated phase noise degrades by 5-6 dB at 1 MHz offset as compared to the case when i connect the nodes directly to the supplies.

My question is, whether it is important to use these resistors for connecting the nodes to external power supply...? or the nodes can directly be connected to bond pads and the pads can be connected to an external supply....In the second case doesnt the supply variation and noise affect the VCO phase noise..??


Kind Regards

 

[khouly]

sure the resistor will affect the phase noise, try to add a capacitor to the ground to filter out some noise from the resistor

i don't know if it is important to put this or not , but i think u put it to make this path high impedance for the RF signal in the varactor

sure the supply variation will affect so u need to filter this supplu by useing some decoupling caps

Khouly

 

[rfmems]

the resistors contributes noise which are converted to phase noise by am-fm conversion

 

[Lance_RFdude.com]

I wrote an article on phase noise... primarily to cover the topic of phase noise caused by the resistors in loop filters.

you can find it at my website if you want to take a look (rfdude.com -- on the tools/PLL analysis, and also linked on my resume I think). Pretty simplistic and not too hard to follow.

Lance