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Reducing ripples in VCO

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Shans60

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Hi i am designing a PLL for 100mhz spec and i am using ring VCO in my design. i ve put some seven stages for my design and i ve used NMOS to control voltage.. I am gettin the spec frequency but the problem i face is tat ripples occur in waveform.. can anybody suggest me a method to reduc ethe ripples
 

HI

Try to reduce stage numbers in your design
 

can you reduce the number of stages. Ring oscillators are very noisy, specially seven stages of it.

What is your tuning range?
 

Try differential topology and add decoupling cap at the power node of the ring VCO.
 

to reduce the ripple on the control voltage size the capacitor to filter the ripple.In a second order loop filter the second pole should be sized to filter out the ripple.
 

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