VCO Varactor Bank Control Logic Noise

[yi_demon]

Hi all,

Has anyone ever encounter the problem that huge amount of noise brought by varactor bank control logic? I tried to switch on/off the AMOS varactor bank by changing the S/D node voltage between 0 and Vdd directly. So the control logic is directly connect to varactor S/D node, not switch is used. The logic worsens my phase noise by 5dBc.

Is there any way to solve this problem??

Thanks a lot.



Yi.

 

[jiripolivka]

VCO tuning voltage is usually low-pass filtered to make VCO generate a stable frequency. In your case I would try to use a series R and parallel C for such low-pass filter.