how to reduce the gain of the VCO

[asicpark]

Hi all,

I want to reduce the gain of the VCO to make phase noise improve.
Power is 1.8V, center freq is about 500MHz and this is not a freq synthesizer
so that there is no need for wide range of freqency tuning range.

I use the differential amp with symmertric load as a delay cell and design the center frequency comes out at vdd=1V. In that case the resistor is so small
that the vco gain exceed over 1GHz/V. I just want to make it under 1~3 hundred
MHz. But I don't know how to make it.

Does anyone who know about this?

Thanks in advance.

 

[jfyan]

Hi all,

I want to reduce the gain of the VCO to make phase noise improve.
Power is 1.8V, center freq is about 500MHz and this is not a freq synthesizer
so that there is no need for wide range of freqency tuning range.

I use the differential amp with symmertric load as a delay cell and design the center frequency comes out at vdd=1V. In that case the resistor is so small
that the vco gain exceed over 1GHz/V. I just want to make it under 1~3 hundred
MHz. But I don't know how to make it.

Does anyone who know about this?

Thanks in advance.

hi,
try in this way:
as we know, Kvco~1/(NCload),and ~[1/(Ibias)]^1/2,so i think, increase the delay cell number and load capacitance, or increase the baising current if power is permitted.
good luck.
jeff.yan

 

[chenmy]

Hi, so ur VCO must have a voltage to current converter, maybe a diff pair,right?
Increasing the W/L of the diff pair to reduce the voltage to current gian will help!
Good luck!