AD9546SLASHPCBZ datasheet(156/205 Pages) AD

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AD9546

Data Sheet

Rev. 0 | Page 156 of 205

TAGGED TIME STAMPS

A tagged time stamp is a time stamp with a unique marker, or

tag, attached to it. Tagged time stamps allow the AD9546 to use

a lower frequency clock embedded within a higher frequency

clock. For example, by tagging every 10th edge of a clock signal,

there is a carrier signal (that is, the original clock signal) and a

divide by 10 version of the carrier embedded within the signal

resulting from the tagged time stamps.

The various time stamp sources within the AD9546 can

generate tagged time stamps (the auxiliary NCOs, for example).

Likewise, certain time stamp destinations within the AD9546

are capable of processing only tagged time stamps while

ignoring untagged time stamps (the user time stamp

processors, for example, described in the User Time Stamp

Processor (UTSP) section). However, the two DPLLs are the

most important of the time stamp destinations capable of using

tagged time stamps (see the Time Stamp Tagging Options

section).

Tagged Auxiliary NCO Time Stamps

The auxiliary NCOs generate time stamps coincident with the

expiration of each period defined by the programmed auxiliary

NCO frequency (that is, at the rollover point of the phase

accumulator). For example, an NCO frequency of 100 Hz

results in the generation of time stamps at a 100 Hz rate with

each time stamp 10 ms greater than the previous one.

The time stamp generator gives the user the option of tagging

auxiliary NCO time stamps via Bits[15:0] in Register 0x280B to

The value, N, represented by Bits[15:0] (tag ratio) results in every

Nth time stamp being tagged. For example, Bits[15:0] = 1 decimal

means every other time stamp is tagged. Similarly, a decimal

value of 2 means every third time stamp is tagged. Likewise, a

decimal value of 3 means every fourth time stamp is tagged.

This pattern continues to 65,535. A decimal value of 0 (default)

disables time stamp tagging (no tags).

The user can also shift the time position of the tagged flags

Bits[15:0] in Register 0x280D to Register 0x280E (for Auxiliary

NCO 0) and Register 0x284D to Register 0x284E (for Auxiliary

NCO 1). Bits[15:0] are an autoclearing bit field. The value, K,

represented by Bits[15:0], is a signed integer (twos complement)

indicating a number of fundamental periods of the auxiliary

NCO. Thus, for K = −3, the time stamp processor tags time

stamps three time stamps earlier than the Nth time stamp

locations indicated by the tag ratio described previously. K is

effectively a phase shift of the tagged time stamp period, where

K < N.

Note that when the auxiliary NCO is the reference to the DPLL

for an active translation profile (see the Translation Profiles

section), shifting the time position of a tag is not valid and must

be avoided. When using the tag shift feature, be sure that any

translation profiles using the auxiliary NCO as a DPLL

reference are not enabled, or if they are enabled, that the

associated DPLL is in freerun or holdover mode.

Tagged Reference Time Stamps

Tags associated with time stamps originating from the reference

TDCs are the result of demodulating an embedded clock (see

the Reference Demodulator section). Synchronization events

associated with demodulation generate tagged time stamps.

The user can program the DPLL to use the tagged time stamps

from a reference TDC.

Tagged Feedback Time Stamps

Tagged time stamps originating from the DPLL feedback path

are the result of synchronization events associated with the

modulation controller (see the Modulation section). The user

can program the DPLL to use the tagged time stamps from a

feedback TDC.

AD9546/PCBZ Datasheet(PDF) 156 Page - Analog Devices

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