2024年4月18日发(作者：一加7pro防水吗)

Stratum 3与Stratum 3E有何区别

最近看了看两者的定义,大概的理解是:

1. 同样的精度 +/- 4.6PPM/20years;

2. 不一样的稳定度: Stratum 3达到3.7*10E-6; Stratum 3E达到1*10E-8;

Drift是漂移，以10Hz为界限与Jitter抖动相区分，时钟测试中的MTIE/TDEV参数就是针对

它的。具体的区别应该在G.813上有吧

STRATUM 3 and 3E OSCILLATOR REQUIREMENTS

Overview

Stratum 3 and Stratum 3E oscillators have two frequency stability specifications (Free Run and

Holdover). Bellcore has somewhat defined a third requirement, Drift. The Drift requirement is

not per say a Bellcore specification. However Bellcore suggests that the Drift be used for

calculating the Holdover specification and suggests Drift values.

Free Run (±4.6 ppm/20 years Stratum 3 and 3E)

Holdover (±0.37 ppm/24 hours for Stratum 3 and ±0.01 ppm/24 hours for Stratum 3E)

Drift (in a lab environment: ±0.04 ppm/24 hours for Stratum 3 and ±0.001 ppm/24 hours

for Stratum 3E)

Free Run

The Free Run requirement is easily obtainable for any precision oscillator. However part of the

system requirement is that any Stratum 3 and 3E system must be able to lock to any other

stratum 3 or 3E system. The reference signal into the system may be from an operating free

running system that can be off as much as ±4.6 ppm. Further clarifying the lock requirement,

a Stratum 3E system must be able to lock to a Stratum 3 system. This means that a system

where the VCO input of the oscillator in used to lock the frequency in the system, the oscillator in

that system must be able to adjust ±4.6 ppm plus the stability of the oscillator. It is very

difficult to design and build a Stratum 3 oscillator to pull ±9.2 ppm ( ±4.6 ppm for the

oscillator in the system plus ±4.6 ppm for the reference signal into that system).

Holdover

Holdover is the next easiest requirement. The Holdover requirement is defined to be over all

possible conditions. These conditions include aging, temperature, voltage, and initial offset.

Initial offset is how close the unit was locked to the reference signal at the time the signal was

lost; not the initial frequency accuracy of the oscillator. Bellcore break down the Holdover

requirement into 3 major components: Initial offset, Temperature, and Drift. Drift is explained

in the next section. Bellcore suggests adding the Initial offset, Temperature and Drift to obtain

the Holdover requirement. Their suggestion does not account for voltage changes, but alludes

to it in the Drift calculation. If one is not concerned about the recommended Drift requirement

and the temperature range is limited, then a TCXO could be used the Stratum 3 requirement.

System designers have some flexibility in this area because:

The temperature range is not fully defined. They can specify it in their system

specification.

The designer can choose a power supply circuit to reduce voltage effects.

The designer can control the lock accuracy (initial offset) by careful design.

Drift

The suggested Drift value ids the most difficult to satisfy but is not a requirement. The

temperature range is pseudo defined (Bell core suggest the temperature change in a lab

environment of ± 5°F). The voltage change is alluded to because the Drift value is to include

other effects along with aging and temperature. Since Drift is the tightest specification; aging,

temperature, and voltage characteristics of the oscillator are large factors in this stability value.

Usually TCXOs will not meet this value, because they usually do not have a frequency versus

temperature characteristic that is as linear as an oven oscillator. Like the Holdover requirement,

the system designer has some flexibility:

In controlling the oscillator voltage by choice of power supply.

Specifying the temperature change for the Drift.

Conclusions

The system manufacturer has some flexibility in specifying the conditions of the Holdover and

Drift values. Since Drift is not a requirement, it can be overlooked in the system specification.

A limited temperature range for the Holdover could also be specified. The purchaser of system

for end use should take into account the conditions of Holdover and Drift to determine the best

value that will meet their requirements.

References: GR-1244-CORE, Clocks for the Synchronized Network: Common Generic Criteria,

Issue 1 ( Bellcore, June 1995)

Notes: This document is Fortiming’s interpretation of the Frequency Stability requirements as

outlined in Bellcore GR-1244-CORE; it does not endorse or disclaim any requirements set by

Bellcore.

STC3800 INTEGRATED - 地层3E 定时源

发布时间：2014-1-23 12:51:21

描述

该STC3800是一个集成的单芯片对同步定时源解决方案在SONET / SDH网络元素。该设备生成四个同步

时钟，包括位，完全符合符合Telcordia GR- 1244-CORE ， GR- 253-CORE和ITU-T G.812/G.813 。

该STC3800可以在自由运行操作，锁定或缓缴模式。在自由运行模式，它锁定在一个OCXO或TCXO 。

在

锁定模式，锁定在8个输入1参考时钟。每个频率输入参考时钟可以被用户选择或由设备自动检测。该积

极的参考可以自动通过基于优先级的设备所选表或由用户手动控制。所有参考开关命中少。在缓缴模式，

该设备产生基于输出在最后锁定的频率历史参考。该STC3800支持的硕士或操作的冗余从模式设计。在

主控模式下，器件工作在自由运行，锁定或缓缴。在从机模式下，输出时钟锁定到主的主SYNC_CLK或8

千赫同步时钟的输出，并相偏移量可调。并行或串行总线接口提供访问STC3800内部控制和状态寄存器。

主要业务能从任总线接口或执行外部硬件连接的引脚。

产品特点

•与Telcordia公司GR-1244-CORE符合，

GR-253-CORE和ITU-T G.812/G.813

•支持主/从操作

•支持自由运行，锁定和缓缴

模式

•接受8参考输入和一个交叉

每一个从8kHz参考77.76 MHz的

•连续输入参考质量监测

•输入参考频率是自动

检测

•自动或手动选择主动参考

•支持硬件连接引脚来选择有效的参考

•四个输出信号：一个可选高达155.52

兆赫，1固定为8千赫，一个复帧同步

固定在2 kHz和1.544 MHz或2.048 MHz

BITS输出

•输出阶段是可调的，从模式

•在参考切换频率匝道控制

•命中少参考切换

•优于1

PPB缓缴精度

•可配置带宽滤波器用于Stratum3或3E

•支持SPI和8位并行总线接口

•IEEE 1149.1 JTAG边界扫描

•提供FBGA144包

关于三级时钟的一些问题

发布时间：2007-05-21 10:46:49

技术类别：通信网络

1、什么是stratum 3 compliant

当我们说某个芯片符合三级钟的标准明确的表明这颗芯片达到了Telcordia GR-1244-CORE规范中所列出

的所有关于三级时钟的要求。与此同时，在大多数的情况下，它还意味着这颗芯片达到了GR-253-CORE

规范中关于时钟同步的要求。

GR-1244文档规定了北美电信应用中所有的时钟等级要求，包括1, 2, 3E, 3, 4E, 4 。而GR-253是关于

SONET设备的规范，它的5.4节（时钟同步）和5.6节（Jitter）适用于时钟同步设备。GR-253的大部分

参数参照GR-1244的要求，但是在有些情况下，GR-253按照自身需求定义了参数。由于大部分的三级钟

设备应用于SONET，所以芯片设计时会同时考虑两个标准的要求。

2、系统要求还是芯片要求

符合三级时钟是指整个系统达到要求而不是某颗芯片。达到三级需求主要考虑以下几个方面：时钟卡芯片

达到要求的同时还要求本地晶振达到要求；系统可以支持的时钟卡数目；当一个时钟卡错误后系统的响应；

如何处理从SONET网络到线卡的SSM（同步状态信息）；在所有的SONET出口上如何处理SSM。从

以上可以看出时钟卡上的一颗时钟芯片无法满足所有这些系统要求，所以在设计电路时要考虑整个系统的

指标，然后针对每个部分再计算各个参数的冗余量。