How can the Kvco affects the performance of PLL?

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hi all:
how can the Kvco effects the performance of pll? can the Kvco be very large like 2Ghz/v?

if i want to design a vco with frequency range from 250M to 1.7Ghz and the supply voltage is only 1.8v, the Kvco is inevitably large.
then how can i do ?
thx
 

Re: Kvco is too large?


hard to achieve this range, I think. But, why do you need this wide dynamic range?
 

Re: Kvco is too large?

hard to realize it?
i want to make a pll as a clock frequency multiplier for HDMI1.3
the data clock is 25M to 340Mhz, and the pll is used to 5 times the clock frequency

so how can i do it

thx
 

Re: Kvco is too large?


almost everything is possible... but not always what you want!
Very large Kvco will be bad for phase noise and stability of the loop.

Assuming you have a LC tank you should use banks of switchable capacitors like most people do... And leave only a fraction of the total capacitance variation to a varactor.

Search for wideband VCOs in google, you'll find several papers and thesis on it.
 
Re: Kvco is too large?


thanks for your advice^_^
 

Kvco is too large?

i have seen Ic's from big companies , when the PLL will be used in very wideband , they make a bank of vco's and everyone cover some part and they do a some logic to select which VCO will be used , so they will not affect the stability or phase noise , they pay a chip area

everything is a compromise

khouly
 
Re: Kvco is too large?

i see,thank you all, budies

to khouly:
i have read some of your posters, you are really a expert^_^
 

Kvco is too large?

Kvco is dependent on the requirement and the max achieveable range of variosions in the capacitance you can achieve with the applied voltage . again the linearity play a major roll as the cap variation is not linear also the variation of L is not possible . so take the factors in consideration .

with regars
 

Re: Kvco is too large?

Kvco affects out-of-band phase noise, fn, loop bandwidth, phase margin & spur gain
 

Re: Kvco is too large?


I think you can divied it to lots of bands. and each band Kvco is reduced.
 

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