Analog PLL vs Digital PLL

[shaikhsarfraz]

digital pll vs analog pll

Hi,
What is the differnce between Analog PLL and a Digital PLL.
Is this only regarding the use of XOR gate as phase/frequecy detector in Digital PLL and we use Charge Pumped PFD in Analog PLL

Thanks
Shaikh Sarfraz

 

[Vamsi Mocherla]

pll vs

Well, the major difference in an Analog and Digital PLL is that the PD in analog is a mixer, which generates the control voltage.

While in digital it is a PFD(Two D-flops and an AND gate)+ Charge pump which generate the control voltage

There is another concept called All digital PLL which uses a Delay locked loop rather than a VCO for its frequency generation. Hence the Control voltage generation can be a bit based. This is a bit more complicated than the normal Analog PLL. This PLL is useful for pure CMOS implementation

 

[zorro]

pll vs digital

Hi,

Please don't confuse a digital PLL with a PLL that uses digital circuitry in its phase detector (PD).
Certain types of PDs for analog PLLs are based on XOR gate or flip-flops, but these PLLs are still analog: VCO and loop filter are analog.
A digital PLL is all-digital. It is discrete-time (sampled) in nature. It has a NCO instead of a VCO, and a digital loop filter.
Regards

Z

 

[RFIC_guy]

wikipedia digital pll

HI, zorro, you are almost correct.
Remember that "analog" PLL's with digital Phase/frequency detectors are discrete time systems also. The main reason that they can be classified as analog is that the sample rate of the PLL system exceeds the bandwidth of the PLL by at least a factor of 10 to 15. If this condition is violated then discrete time methods must be employed to understand the PLL trajectory behavior.

 

[selina_wch]

analog pll mixer

RFIC_guy is right, while there is an ALL-Digital PLL, which is called DDS. It means direct digital synthesis and its theory is different to PLL.

 

[shaikhsarfraz]

hi,
Thanks for the responses
can anybody provide some documents that tells about analog vs digital PLL.

For that sake individual docs/notes on analog PLL and digital PLL will also do.

thanks
sarfraz

 

[tlihu]

There is a book entitled "DDS Demystified," if I remember correctly.

 

[Miguel Gaspar]

About DDS: wikipedia says
"Direct Digital Synthesis (DDS) is an electronic method for digitally creating arbitrary waveforms and frequencies from a single, fixed source frequency."
But a ADPLL is used for diferent kind of modulation techniques like Manchester, NRZ etc, in order to decode information, so there are a very specific ADPLL for every kind of codification.

 

[willywalker]

When you open a book about electronics there will almost always be a block-schematic af a PLL. What I really would like to find one day, is a circuit of an all analog PLL. With discrete components or opamps...no CMOS involved.

Thanks