AD9545BCPZ datasheet(96/157 Pages) AD

96 / 157 page

AD9545

Data Sheet

Rev. A | Page 96 of 157

follows:

•

No tagging (default)

•

Reference tagging only

•

Feedback tagging only

•

Combined reference and feedback tagging with equal

carrier rates

•

Combined reference and feedback tagging with unequal

carrier rates

With respect to tagged time stamps, the carrier rate is the rate at

which the TDC generates time stamps (that is, the underlying

rate of the input clock to the TDC). The tagged rate is the rate at

which the TDC generates tagged time stamps. The tagged rate is

always an integer submultiple of the carrier rate.

The no tagging mode is the normal operating mode of the

DPLL. That is, the digital PFD processes every reference and

feedback time stamp whether or not the time stamp is a tagged

time stamp.

The reference tagging only mode tells the digital PFD to use

tagged reference time stamps for phase alignment purposes.

The user must ensure the reference is set up to provide tagged

time stamps. When the reference is one of the REFx inputs, the

reference demodulator is the source of tagged time stamps (see

the Reference Demodulator section). When the reference is an

auxiliary NCO, the auxiliary NCO is the source of tagged time

stamps (see the Auxiliary NCOs section).

The feedback tagging only mode tells the digital PFD to use

tagged feedback time stamps for phase alignment purposes. The

user must ensure the feedback path is set up to provide tagged

time stamps via output clock modulation (see the Distribution

Embedded Output Clock Modulation section).

The combined reference and feedback tagging modes tell the

digital PFD to use tagged time stamps from both the reference

and feedback TDCs. The user must ensure that the reference

and feedback paths are set up to provide tagged time stamps.

Furthermore, the user must ensure that the tag rate of the

reference path matches the tag rate of the feedback path.

There are two variants of the combined reference and feedback

tagging modes: equal and unequal carrier rates. The combined

reference and feedback tagging modes require equal tag rates on

both paths. There is no such requirement on the carrier rates

for both paths. However, to function properly, the DPLL

requires advance knowledge of the relationship between the

reference and feedback carrier rates. Thus, the reason for the

two variants. The user must select the appropriate variant based

on whether the reference and feedback TDC carrier rates differ.

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