Analog PLL or Digital PLL

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hanikapa

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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
 

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?
 

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

FvM said:
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.
Click to expand...

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).
 

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.
 
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.
 
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