PLL without external loop filter

[GDF]

external loop filter

Why some PLL doesn't need loop filter? what kind of technique make
this idea work?

Thanks,

 

[rfsystem]

They have it integrated and take considerable effort to reduce the area of the passive components.

 

[elbadry]

I think some people also use switched Cap filters instead of the passive loop filter. This may be noisier though...

 

[cmos_dude]

They have it integrated and take considerable effort to reduce the area of the passive components.

Where is the loop filter integrated ????

 

[Yun Lin]

Some capacitor and resistor can be made in chip inside. So, they don't need outside.

 

[GDF]

If the loop bandwidth is around several MHz, the R and C of loop filter may
be implemented with on-chip passive components, but once the loop bandwidth
is around several KHz, how to do this on-chip?

Added after 1 minutes:

They have it integrated and take considerable effort to reduce the area of the passive components.

What's the so-called "considerable effor"?

 

[rfsystem]

Considerable effort mean that to integrate the loop filter the capacitor have to be small. If the first zero in the loop filter is defined by the resistor, capacitor combination a small capacitor have to combined with a large resistor value. That mean that the noise within the loop bandwidth could be more defined by the loop filter noise than instead of the VCO. So there is trade of cap size versus noise contribution. A big cap also mean higher chargepump currents. To come out of this constrain the VCO gain have be reduced. Because then you could not cover the hole frequency range and have to use digital tuning also.

Then the considerable effort beginns. But it is trade of pure cap size versus more control logic.

 

[bill_sun]

as i known,most PLLs have on-chip filters in them.

 

[rfsystem]

I would say that integrated synthesizers tend to have integrated loop filters. But integrated PLLs have mostly have external loop filters.

 

[GDF]

as i known,most PLLs have on-chip filters in them.

what kinds of application of the PLLs you ever see?

If the reference clock is small such as severl ten kilohertz, it's not
easy to integrate the loop filter on chip.

 

[GDF]

I would say that integrated synthesizers tend to have integrated loop filters. But integrated PLLs have mostly have external loop filters.

A trick in your statement, what's difference between "PLL" and "Synthesizer"?
Why integrated synthesizer ofent with integrated loop filter but integrated PLL
doesn't?

 

[rfsystem]

There is no trick.

1. Synthesizer mean all frequency multiplying components including the VCO.

2. PLL circuit mean only the RF divider, Reference divider, Phase/Frequency Detector and Charge-Pump circuit. That is found in the popular NSC series. The VCO is often excluded because of the variours frequencies and specs from applications which could not be integrated into one device.

 

[yankuangtu]

i think that when you design your protype, you'd better use a filter with off-chip device--so that you can easily adjust your bandwidth when you debug your design.
But when we do mass production,we would like to use on-chip filter for lower cost.

 

[jecyhale]

Why some PLL doesn't need loop filter? what kind of technique make
this idea work?

Thanks,

It can be design internal of chip.

 

[AMS2007]

There is no trick.

1. Synthesizer mean all frequency multiplying components including the VCO.

2. PLL circuit mean only the RF divider, Reference divider, Phase/Frequency Detector and Charge-Pump circuit. That is found in the popular NSC series. The VCO is often excluded because of the variours frequencies and specs from applications which could not be integrated into one device.

PLL based frequency Synthesizer is more exact expression!!!