Problem with: Digital down conversion and digital PLLs

digital down conversion implementation

Hi!

I have trouble to understand how a digital PLL for discrete valus work.
Say that we sample a 1 MHz sinus wave with an ADC 12bit/15 Msps.

Then we hava a bunch of values to do signal procesing on.

What I do not understand how each sample (dscrete value) should be
processed in a digital PLL.

The first sample will be multiplied with a discrete value
fed from an NCO operating at 1 MHz. The result will then be processed in a
low pass filter and then set the NCO with an error term.

When should the second sample enter the PLL the third one and so on.

I do not understand if one sample must be totally processed before
theh next sample will be latched into the PLL. Must I use somekind
of pipelining??

Please, have anyone an answer to this?

/Rikard

Hi,
I suggest you write a tracking code in Matlab and compare it with the implementation you have described or want to do. It will definitely solve your problem.

Second or third sample depends on the order of the filter being used.

BRMadhukar

the part you have mentioned is mixer or PLL? down conv. should be

input -> mixer -> output to next stage
^
|
ref. freq. (NCO) <- tuning data

using NCO as ref. freq. why require PLL or i misunderstand something?
or your are making direct conversion receiver (with FLL)?