confused about PLL Capture Range vs Lock Range

capture and tracking pll

What 's the difference between the Capture Range and Lock Range of PLL ? In order to track the frequency which is more important ?

pll capture range greater than lock range

Once the PLL is in lock, what is the input (or VCO) frequency range for which it can keep itself locked is the lock range. When the PLL is initially not in lock, what frequency range can make the PLL lock is the capture range. Lock range is the parameter you should be interested in if you are looking for it's tracking behavior. But in CP PLLs, both the lock and capture ranges are the same.., limited only by the VCO's tuning range.

pll-in range tracking range difference

desperado1 said:

What 's the difference between the Capture Range and Lock Range of PLL ? In order to track the frequency which is more important ?

Click to expand...

For my opinion, it´s not quite clear.
According to R. Best: "In most cases "capture range" is an alternative expression for "lock range", sometimes it is also used for "pull-in-range".

Therefore, be careful with terms which may be used for different parameters.
However, I think one point is clear (with reference to saro_k-82): The definition does NOT depend on the kind of PD/PFD you are using.

Added after 8 minutes:

Example: In his book Sergio Franco uses capture range as a synonym for pull-in range.

pull-in pll

LvW said:

For my opinion, it´s not quite clear.
According to R. Best: "In most cases "capture range" is an alternative expression for "lock range", sometimes it is also used for "pull-in-range".

Therefore, be careful with terms which may be used for different parameters.
However, I think one point is clear (with reference to saro_k-82): The definition does NOT depend on the kind of PD/PFD you are using.

Added after 8 minutes:

Example: In his book Sergio Franco uses capture range as a synonym for pull-in range.

Click to expand...

In modern PLLs capture range and lock range are the same. But by definition these are different and this relaxed usage in journals and books leads to these confusions.
Capture range and pull-in range are the same. Both refer to the ability of the system to acquire lock (from an unlocked state) to a frequency. Here the VCO is running at some arbitrary frequency and the disturbance required at the input to make it respond to the input disturbances thereafter is quantified as capture range.
While the VCO is responding to the input disturbance (in-lock), the amount of disturbance at the input that will cause the VCO to shun the input and run freely is quantified as lock range.
Always lock range is equal to or greater than the capture range.

Definitions from the web
Lock range is defined as the band of frequencies centered on the VCO’s natural frequency over which a PLL can maintain frequency lock with an external input signal.
Capture range is defined as the band of frequencies centered around the VCO natural frequency where the PLL can initially establish or acquire frequency lock with an external input signal from an unlocked condition.

pll capture and tracking

Quote1:In modern PLLs capture range and lock range are the same. But by definition these are different

Quote2:Capture range and pull-in range are the same.

Quote3:
Always lock range is equal to or greater than the capture range.

Sounds a bit confusing, does it not ?

definition lock range pll

LvW said:

Quote1:In modern PLLs capture range and lock range are the same. But by definition these are different

Quote2:Capture range and pull-in range are the same.

Quote3:
Always lock range is equal to or greater than the capture range.

Sounds a bit confusing, does it not ?

Click to expand...

OK LvW., see if this is fine
1. Always these two terms have different meaning. In older PLLs (Type 1 PLLs) it made sense to spec or ask for these two quantities separately. But in type-2 PLLs it so happens that these two ranges are always the same.., which is an advantage.

2. The initial question was about capture range and lock range, as the new term "pull-in range" was brought in, I said it is the same as capture range both by definition and value in all types of PLLs. Now as the capture and hold ranges are the same., this one term "pull-in" is used in most of the datasheets., but by definition again it is means capture range.

3. In older PLLs lock range is always greater than capture range., and for recent PLLs they are equal.

capture range lock-in range

Hello BIF44 !

As you are deeply involved in PLL design - what do you think about it ?[/b]

sweep circuit for pll

In My opinion, the LOCK RANGE is ability of the PLL the to accect input frequency and generate output clock.
Capture range is ability of the PLL to generate fast output settle for given input disturbance

Re: confused about PLL

For your typical modern frequency synthesizer, one that contains some sort of integrating function in the loop filter, they are probably the same.

I can think of some scenarios where they might be different, though.

Lets say I was using a PLL as a receiver, say for a satellite system. On first turn on, the PLL might simply sit there unlocked. Then you might deliberately sweep the local oscillator frequency, either in steps or with a saw tooth. As the LO frequency changes, eventually the desired signal comes within the loop bandwidth of the PLL, and the PLL locks to it. You then disable the sweep circuit, and it remains locked. I am not sure if this is 100% correct, but I would call the full band sweep range the "capture range", and when I got close enough for the PLL to acquire the signal tracking, I would say that I got within the "lock-in range".

In such receivers, there is another phenomenon. Once locked, they stay locked over a wider range of perturbations, but if they become unlocked, the will not relock until you get within a smaller range.

I have seen the same phenomenon with injection locked oscillators: Once locked you can tune them pretty far one way or the other, but once lock is broken, you have to get pretty close in frequency before they will relock. I believe they call this bigger bandwidth, once locked, as the "hold-in range".

In a frequency synthesizer, you might run into a similar scenario. Lets say you were using a comb generator as an LO for a mixer (or downconverting sampler). You might have to coarse tune the VCO to be near the desired signal before the PLL can automatically lock up. There, you might call the "lock in range" starting and ending halfway to the two adjacent comb teeth, where the capture range can, with coarse tuning, be the entire possible output bandwidth.

Rich

Re: pll capture range greater than lock range

saro_k_82 said:

Once the PLL is in lock, what is the input (or VCO) frequency range for which it can keep itself locked is the lock range. When the PLL is initially not in lock, what frequency range can make the PLL lock is the capture range. Lock range is the parameter you should be interested in if you are looking for it's tracking behavior. But in CP PLLs, both the lock and capture ranges are the same.., limited only by the VCO's tuning range.

Click to expand...

Thanks for this helpful info!