Preliminary Data Sheet #: TM012

Page 2 of 16

Rev: P06

Date: 05/20/ 02

General Description

Stratum 3E synchronization for a complete system clock

solution in a single module in accordance with GR-1244-

CORE Issue 2, GR-253-CORE Issue 3, and ITU-T G.812

Option III.

The STM-S3E provides a reliable network

element clock reference to line cards used in TDM, PDH,

SONET, and SDH application environments. Typical

applications include digital cross talks, DSLAMs, ADMs,

multiservice platforms, switches and routers.

The STM-S3E meets 12 ppb Hold Over requirements over

0° – 70°C temperature range. The 5V power requirement

will draw a maximum of 1.2 A during an initial start-up period

and then drop to a typical current of 800 mA during normal

operating conditions. It accepts two 8 kHz input references

and can be manufactured to supply a fixed frequency from

1.544 MHz to 38.88 MHz.

The STM-S3E offers 4 user selectable modes of operation,

Reference 1, Reference 2, Hold Over and Free Run. Mode

of operation is selected by two control pins (Table 6). The

current mode of operation is also indicated by two status

pins (Table 7). Free Run is the default mode if no control

signals are asserted on the control pins.

Reference 1 mode and Reference 2 mode are the two

primary operating modes. When the module is locked to a

valid reference, any time after initial power up or reset, the

module is considered to be in the normal operating mode.

During normal operation the output frequency is phase

locked to the input reference frequency. The offset between

the input and output is dependant upon the amount of noise

that is present on the reference signal. For input tolerances,

refer to Table 4.

Hold Over mode provides a stable frequency that is

guaranteed to be within ±0.012 ppm over the entire

temperature range for the first 24 hours after entry into Hold

Over. Hold Over is valid 701 seconds after a reference is

selected and continues to do a running average every 8

seconds for the next 1049 seconds. Long-term Hold Over

values are based on a 1049 second moving window

average. Hold Over values are not updated during LOR or

during Fast Acquisition mode.

Hold Over values are

buffered for at least 32 seconds to allow enough time to

respond to the RFL alarm.

Free Run is a mode of operation in which the module is not

locked to a reference and its output frequency is solely

dependent on the initial frequency setting of the internal

oscillator. The output frequency in Free Run is guaranteed

to be ±4.6ppm of the nominal frequency.

A fifth, automatic mode of operation is Fast Acquisition

mode.

Fast Acquisition mode is entered whenever

Reference 1 or 2 has been selected. After a new reference

has been selected, the module uses internal filtering that

limits the frequency movement to less than 2.9 ppm/sec. By

600 seconds the module switches to a slower 0.001Hz filter.

While in normal mode, if the phase error is greater than 20

µs, Fast Acquisition mode will be initiated. Fast Acquisition

mode is further described as fast start mode in GR-1244-

CORE, Issue 3, sec 3.6.

The STM-S3E may be reset by asserting a logic low signal

to the Reset pin or cycling the power. Using the Reset pin

for a manual reset is the recommend method for resetting the

module. Resetting the module by cycling the power requires

more time due to the restablization of the internal ovenized

oscillator.

The STM-S3E provides the user with non-interruptive Tri-

State capabilities. By asserting a logic high signal to the Tri-

State pin, the user is able to Tri-State all outputs. While in

Tri-State, the module continues normal operations and

accepts all normal inputs. When the module is released from

Tri-State, all output signals are valid.

The STM-S3E module provides three output frequencies.

The Sync_Out is the primary synchronized output. It is

phase locked to the input reference during normal operation

and is set to a fixed frequency when operating in Hold Over

or Free Run. Clock_Out provides a frequency output that

comes from an independent, undisciplined, free running

oscillator that is ±4.6 ppm from the nominal frequency. This

output is typically used for reference frequency qualification.

The 8 kHz output is derived from the Sync_Out output.

The STM-S3E module provides a variety of alarm indicators

to alert the user to multiple conditions that may affect the

overall performance of their system. The LOR (Loss of

Reference) alarm indicates that the active reference has

been lost. RFL (Reference Frequency Limit) indicates that

the Sync_Out frequency is 15 ppm or more from the Free

Run frequency. The PBO (Phase Build Out) pin indicates

that a phase transient greater than 3.4

µs over any 0.1

second interval has occurred. The PBO indicator will remain

high as long as the phase transient condition exists.

The Mode Alarm pin is used to indicate that the module is not

in a normal operating mode. Conditions that will cause the

Mode Alarm to go high are Hold Over, Free Run, Fast

Acquisition Modes or when Phase Build Out has been active

for more than 0.4 seconds. During the latter condition, both

the Mode Alarm indicator and the PBO indicator will be high.

See Table 8 for a full description of input control pins and

output indicator pins.

The Hold Over Good pin indicates that an initial average has

been acquired to provide a qualified Hold Over frequency.

The module requires approximately 700 seconds from any

reference switch or mode switch to a new reference to

reacquire a valid average before the indicator goes high (Fig.

17). Initially, entry into Hold Over prior to this will result in a

Free Run frequency.

After the first Hold Over Good

indication, entry into Hold Over will be the last valid Hold Over

frequency.

The

STM-S3E

meets

the

requirements

for

wander

generation and wander transfer as required by GR-1244,

sections 5.3 and 5.4. Figures 4, 5 and 6 show typical results.

It also complies with phase transient requirements during

Reference Rearrangement, Entry into Hold Over, and 1

µs

transient. See figures 7-9 for typical performance results and

requirement masks. Input jitter is attenuated at about 20 dB/

decade to minimize jitter noise from being passed to other

network elements or clocks. Figure 10 illustrates the STM-

S3E’s typical roll off of attenuated jitter.