Analog PLL or Digital PLL

[hanikapa]

Hello,
many advantages are mentioned in the papers related to Digital PLL but I see also many designs that still use Analog PLL. Can anybody help me to know that why still analog PLLs are popular and what are their advantages?
Thanks

 

[daniel442]

Analog PLL's (LC-PLL) has the advantage of low Phase-Noise due to the use of analog LC-tank (instead of ring OSC in ADPLL).
although it address narrower frequencies than ADPLL because of the inductor which may work for a narrow frequency band as oppose to the ring OSC who has more wideband frequency response.

 

[hanikapa]

Analog PLL's (LC-PLL) has the advantage of low Phase-Noise due to the use of analog LC-tank (instead of ring OSC in ADPLL).
although it address narrower frequencies than ADPLL because of the inductor which may work for a narrow frequency band as oppose to the ring OSC who has more wideband frequency response.

But there are many ADPLL structures that use also LC-tank. In this case, what are the advantages of analog PLL?

 

[FvM]

But there are many ADPLL structures that use also LC-tank.

Originally, ADPLL means all-digital PLL and implements time discrete signal generation rather than analog oscillators (neither LC nor ring oscillators).

Please clarify about which PLL topology you are asking.

 

[hanikapa]

Originally, ADPLL means all-digital PLL and implements time discrete signal generation rather than analog oscillators (neither LC nor ring oscillators).

Please clarify about which PLL topology you are asking.

ADPLL I mean a divider less, TDC based design that all the blocks are digital except the oscillator which is analog but is controlled digitally (digital controlled oscillator).

 

[FvM]

Thanks for the clarification. According to the classical terminology, as introduced e.g. by Best, an ADPLL uses a pure digital oscillator (NCO). In so far, the shown topology isn't an ADPLL. But it has many features of an ADPLL. The time discrete phase detector e.g. introduces a phase quantization and respective phase noise.

 

[filip.amator]

Analogue PLLs may be useful to recover very weak signal - I used such a PLL as a tracking oscillator to increase SNR of a noisy signal. In that case using a digital detector is difficult because sine- to square-wave conversion will introduce additional noise.