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way for calculating lock time of a PLL in the design process

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elec350

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PLL lock time [hlp]

hello
is there any way for calculating lock time of a PLL in the design process?
 

Re: PLL lock time [hlp]

As far as I know,the setting time can be affected by the gain of PFD
 

Re: PLL lock time [hlp]

Hi

I attach a simple papers vs example to calculate LPF and of course lock time, please review.

David
 

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    elec350

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Re: PLL lock time [hlp]

hello
what's about a hybrid PLL (using DDS)?
 

Re: PLL lock time [hlp]

The lock-time is easy to calculate:

With good accuracy it is simply: TL≈2*Pi/ωn
(ωn=loop natural frequency)

But realize that the lock-time is defined with the assumption that lock-in occurs within one beat-period. With other words: The frequency displacement is within the lock range.
 

Re: PLL lock time [hlp]

elec350 said:
hello
is there any way for calculating lock time of a PLL in the design process?
Click to expand...

If you know the bandwidth of you loop filter,
For example 100KHz.
So the lock time will be close to 1/100K=10uS.
But the lock time will be affected by the initial dc level.
 

PLL lock time [hlp]

just some reference for you!
with LPF BW=100K,not too bad phase margin,Locktime can be reached 60us.

with LPF BW=200K,not too bad phase margin,Locktime can be reached 40us.
 

Re: PLL lock time [hlp]

iaman said:
just some reference for you!
with LPF BW=100K,not too bad phase margin,Locktime can be reached 60us.

with LPF BW=200K,not too bad phase margin,Locktime can be reached 40us.
Click to expand...

Why?This is your experence?
But it is not match with the theory！
 

Re: PLL lock time [hlp]

frankiebai said:
iaman said:
just some reference for you!
with LPF BW=100K,not too bad phase margin,Locktime can be reached 60us.

with LPF BW=200K,not too bad phase margin,Locktime can be reached 40us.
Click to expand...

Why?This is your experence?
But it is not match with the theory！
Click to expand...

The lock-time can be calculated with the following :

Lock time≈K/ωn ,where K can be range from 3~6
(ωn=loop natural frequency)

the LPF BW=200K is the 3dB corner freq, the ωn can be got with BW3db/1.6.

the calculation is not very accurate, but I think it's a guide to optimize the design.
 

Re: PLL lock time [hlp]

In the mean time I have confirmed myself that the formula as given in my reply dated 21st of may 2008

lock-in time TL≈2*Pi/ωn

is recommended by several authors (Best, Gardner) for normal loop damping properties.
 

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