有效测量Cardinal时钟振荡器稳定性

有效测量Cardinal时钟振荡器稳定性，小有名气的Cardinal公司，通过自身的努力为世界创造独特的价值，也因此赢得无数的好评，同时Cardinal Components也是一家面向服务的垂直集成供应商，提供高混频频率控制和RF产品解决方案。我们投资于石英晶体技术，为那些需要频率控制设备的客户提供最新的大批量产品。我们成立了合资企业和子公司，以提供最高频率、最高质量的零件。Cardinal Components致力于通过提高产量、降低成本、提高客户满意度以及满足员工对培训、安全和士气的期望来持续提高质量。

振荡器表现出许多频率/周期不稳定性。制造商通常规定他们的振荡器长期和环境频率稳定性。

环境稳定性反映温度、振动、电源变化的影响，和其他环境因素取决于振荡器的输出频率或相位。图1是时钟稳定性示例振荡器在从冷启动。实际石英晶体振荡器输出显示在跟踪2中。这个较低的轨迹（轨迹B）是趋势平均内部温度（1mV=1°C）。这表明在启动过程中，内部温度升高约8°C在2000秒的时间段内。在此期间，平均振荡器周期的变化是大约±25 ps。读取轨迹C，包含平滑测量时间间隔误差的趋势水准仪(tie@lv)。

时间间隔级别上的错误衡量时间振荡器的差，从理想测量的周期时期轨迹A，平局的趋势@lv，覆盖在平滑的查出它显示了峰对峰变化略大于±100 ps.温度变化，对长期稳定性，如图2涉及一个逐渐漂移振荡器定时。长期稳定性通常包括振荡器老化，但不包括环境引起的漂移。晶体振荡器老化通过各种机电机制。

长期稳定性通常以每百万或ppm。10 ppm的典型规格意味着在1毫秒的时间间隔内，时钟周期可以改变10ns：

Dt=1ms*（10/1000000）=10ns

短期稳定性是一个函数振荡器内的噪声信号，并表示相位振荡器输出的调制。短期稳定性可以在时域中指定为抖动。最大的缺点这种指定short的方法项稳定性是指它与测量间隔有关。测量观察时间越长峰间抖动幅度。

图3显示了一个典型的抖动测量400MHz声表面波振荡器。平均值周期为2.4999 ns，均方根7 ps的抖动（西格玛）和峰值至35ps的峰值抖动（范围）。请注意这个振荡器指定峰值测量的峰值抖动1000个循环的持续时间。有效测量Cardinal时钟振荡器稳定性.

许多制造商将观测时间相关性通过指定振荡器短路阿尔兰方差的项稳定性。阿伦方差使用频率差相邻频率之间测量，通常使用频率计数器，用于计算OSC晶振输出的方差频率短期稳定性也可以在频域中指定作为相位噪声。相位噪声表征振荡器的频谱。典型的相位噪声规格为–100 dbC，温度为10kHz从载波偏移。相位噪声可以使用窄带FFT频谱进行测量分析器（12-16位振幅分辨率）或专用阶段噪声测量系统。
LeCroy抖动和时序分析软件包的最大优势是能够进行研究长期和短期振荡器定时的变化。长内存和智能触发器使获取和显示这些数据变得容易专用抖动与测量和关联温度或电源电压等其他参数影响的能力是评估环境稳定性的理想选择.

Environmental stability reflects the effects of temperature, vibration, power supply variations, and other environmental factors on an oscillator’s output frequency or phase. Figure 1 is an example of the stability of a clock oscillator during warmup from a cold start. The actually oscillator output is shown in Trace 2. The lower trace (trace B) is the trend of mean internal temperature (1mV = 1° C). It shows that during startup the internal temperature increases by about 8° C over a period of 2000 seconds. During that time the average change in the oscillators period is about ±25 ps. This is read in trace C which contains the smoothed measurement of the trend of time interval error at level (tie@lv) . Time interval error at level measures the time difference of an oscillator’s measured period from an ideal period. Trace A, the trend of tie @lv, is overlaid on the smoothed trace. It shows a peak to peak variation of slightly more than ±100 ps. Temperature variation has little effect on this oscillator.

Long term stability, illustrated in figure 2, involves a gradual drift in oscillator timing. Long term stability generally includes oscillator aging but excludes environmentally induced drift. Aging, in crystal oscillator is caused by a variety of electromechanical mechanisms. Long term stability is usually expressed in parts per million or ppm. A typical specification of 10 ppm means that over a 1 ms interval the clock period can change by 10 ns: Dt=1ms*(10/1,000,000) =10 ns Short term stability is a function of noise signals within the oscillator and represents a phase modulation of the oscillator output. Short term stability can be specified in the time domain as jitter. The greatest drawback to this method of specifying short term stability is that it is dependent of the measurement interval. The longer the measurement observation time the greater the peak to peak jitter magnitude. Figure 3 shows a typical jitter measurement of a 400 MHz Surface Acoustic Wave (SAW) oscillator. The mean or average period is 2.4999 ns with an rms jitter (sigma) of 7 ps and a peak to peak jitter (range) of 35 ps. Note that the manufacturer of this oscillator specifies that peak to peak jitter for a measurement duration of 1000 cycles.

Many manufacturers minimize the observation time dependency by specifying the oscillator short term stability in terms of the Al-lan Variance. The Allan Variance uses the frequency difference between adjacent frequency measurements, usually made with a frequency counter, to compute the variance of oscillator output frequency. 

Short term stability can also be specified in the frequency domain as phase noise. Phase noise characterizes the shape of the frequency spectrum of the oscillator. A typical phase noise specification is –100 dbC at 10 kHz offset from the carrier. Phase noise can be measured using a narrowband FFT spectrum analyzer (12-16 bit amplitude resolution) or a dedicated phase noise measurement system.

The greatest strength of the LeCroy jitter and timing analysis package is the ability to study both long term and short term variations in oscillator timing. Long memory and SmartTriggers make it easy to acquire and display this data Specialized jitter measurements combined with the capability to measure and correlate the effects of other parameters such as temperature or supply voltage are ideal for evaluating environmental stability.