AD9546SLASHPCBZ datasheet(54/205 Pages) AD

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AD9546

Data Sheet

Rev. 0 | Page 54 of 205

COMMON CLOCK SYNCHRONIZER COMPONENT

The common clock synchronizer provides a precision method

for assigning an epoch to the local time scale yielding the

common time scale. Essentially, the user provides a

synchronization trigger event, the rising edge of an external

analog input signal, which the device time stamps. The time

stamp serves as an internal trigger event. Immediately following

the trigger event (and before the next trigger event), the user

programs the device with a time code corresponding to the

time associated with the trigger event and asserts an IO update,

which aligns the common time scale with the programmed

time code. In this way, the common time scale carries the

proper time. By carrying out the synchronization process across

all nodes (with a distributed common clock as the time base for

every node) and properly accounting for time delay in the

system, the common time scale of every node increments at the

same rate and carries the same epoch. Thus, all nodes are time

aligned to a high degree of precision.

USER TIME STAMPER (UTS) AND INVERSE USER

TIMER STAMPER (IUTS) COMPONENTS

A typical digitized clocking system can use one AD9546 as a

master time unit with various nodes synchronized to the

master. Thus, a means of transporting numeric time codes

between nodes is essential for transporting clocks and

correcting time errors throughout the system. Such is the role

of the UTS and IUTS. The AD9546 possesses nine UTS units

and two IUTS units.

A UTS converts internal time stamps to time codes (numeric

time values based on the common time scale) and provides the

user with a means to read the corresponding time codes.

Because time codes relate to the common time scale, the UTS

provides a means to export a digitized clock signal to remote

digitized clocking nodes.

An IUTS provides the user with a means to send a digital clock

signal to a node (a digital clock signal being a continuous series

of uniformly increasing numeric time codes). An IUTS

converts the digital clock signal to time stamps (based on the

common time scale), which can be distributed internally as

needed.

A DIGITIZED CLOCKING NODE EXAMPLE

Figure 49 shows the interaction of the various digitized clocking

components as applied to a single node in a hypothetical

digitized clocking system. The analog input signals consist of

the common clock (CC), a synchronization source (SS), and a

local user clock (LUC). The local user clock is any analog clock

signal intended for transport to another node or for local use as

a local analog clock output signal.

The three analog input clock signals route through their

respective physical clock converters, which convert the analog

clock signals to time stamps. The common clock time stamps

route to the common clock DPLL, which is responsible for

regulating the local time scale. The synchronization source time

stamps route to the common clock synchronizer, which allows

the user to translate the local time scale to a common time scale

with a known epoch. The local user clock time stamps route to

a UTS, allowing an external processor to capture local user

clock time codes related to the common time scale.

The local user clock time codes captured by the external

processor exist as a digitized clock signal. Thus, the processor

can transport the digitized clock signal in the form of data

packets to remote nodes.

Alternatively, the processor can route the local user clock time

codes from a local UTS to a local IUTS, which converts the

local user clock time codes back into time stamps. The time

stamps are then available to a physical clock generator for

conversion to an analog output signal. This basic example of

translating input clock edges to numeric values (time codes)

and reconstituting an analog clock signal from the time codes

within a single chip demonstrates the concept of digitized

clocking.

The local user clock time codes can be transported to a remote

node (via the processor) and then converted to an analog signal

at the far end. Assuming the remote node shares the same

common clock (a requirement for digitized clocking), and the

processor at the remote node properly synchronizes the remote

common time scale, then it is possible to replicate the local user

clock at remote nodes in the native time domain of the local

user clock.

AD9546/PCBZ 数据表(PDF) 54 Page - Analog Devices

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