Question about Vcont value in VCO design

[liushangpiao]

hi,everybody,
I want to ask that the control voltage Vcont from the
loop filter may vary 0 to supply voltage AVDD? In general
how much is it?
thx

 

[Prototyp_V1.0]

VCO design

That all depends of the design. A simple vco can have an input voltage from 0,7V and up, where the Vcc and the transistors characteristics limit the upper speed.

 

[Sadegh.j]

Re: VCO design

Hey

Its range depends on the design.

In general how much is it?

That again depends on the design. I have a fundamental problem with this question, there is not a general value.

 

[liushangpiao]

Re: VCO design

thank your replies...

I meant that i am doing the VCO design alone ,not to do PFD ,CP and LPF,under the condition of supply power 1.8v and .18um process. Then the Vcont comes from
the former part CP,and what is it? I assign it with a range of 0.3v to 1.5v,it can be gotten from the CP? And if it can do,then is the CP implemented easily?

Besides, the fosc corresponding Vcont is 1.8v/2 generally?

who can give me a farther guidance? THANKS!

 

[Nicholaes]

Re: VCO design

hi,everybody,
I want to ask that the control voltage Vcont from the
loop filter may vary 0 to supply voltage AVDD? In general
how much is it?
thx

practicaly to AVDD (ADF4xxx PLL series)

 

[Sadegh.j]

Re: VCO design

It all depends on how you design the circuit

 

[prashantbabu]

Re: VCO design

From the CP perspective:
While deciding the range of the control, you need to take care that the current sinks in the CP are maintained in saturation. Ex: If you are using NMOS sink in your CP, the lower limit for the control voltage is set by the Vdsat voltages needed to keep the NMOS sinks in saturation.
You can check any CP architecture to better understand what I am talking about.
Hope this helps.