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Taken from Maxta Microelectronics:Interpretation of Clock Product Parameters

Oct 21,2024
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introduction:

Clock is a core component of modern communication and digital systems, and is crucial for data transmission and system synchronization. in order to

To evaluate the performance and stability of a clock, people usually focus on some key parameter indicators. This article will introduce the main parameters of clocks

Standards, including stability, frequency accuracy, and phase noise, are used to help readers better understand the evaluation and application of clock performance.

1、 Stability:

Stability is an important indicator for measuring the stability of clock signals, and frequency stability usually refers to temperature stability

Degree, also known as temperature frequency difference, is a measure of the short-term stability of the output frequency of an oscillator that may change due to temperature fluctuations during operation

Sexual indicators. If the frequency drift exceeds the expected range of the application, timing errors may occur. Higher stability means that the clock signal

Maintaining stability over a long period of time helps ensure the accuracy of data transmission and system synchronization.

Among all oscillators, the OCXO constant temperature oscillator has the highest frequency stability, reaching ppb level (10-9), while the TCXO temperature compensated oscillator

The stability of the oscillator is below 1ppm, while the stability of a regular oscillator is within 100ppm. The stability of atomic clocks is higher, generally around 10-

Above 11.

2、 Frequency accuracy:

Frequency tolerance refers to the output frequency fx and center nominal frequency of an oscillator at room temperature (+25 ℃)

Deviation between f0. It is usually expressed in parts per million (ppm). The higher the frequency accuracy, the closer the frequency of the clock signal is to the standard frequency

Rate helps ensure the accuracy and timing synchronization of data transmission.

Usually, the clock deviation corresponding to 1ppm is 0.0864 seconds per day

3、 Phase noise:

Phase noise is a frequency domain view of the surrounding noise spectrum of an oscillator signal. It describes the frequency stability of the oscillator. Frequency stability

It can be divided into two parts: long-term stability and short-term stability. Long term stability (such as accuracy, drift, and aging) measured in hours, days, and months

Expressed in units of years. Short term stability (such as phase noise) occurs within a few seconds or even shorter. Short term changes have a greater impact on the system

Large, especially for phase noise. From a mathematical perspective, the National Institute of Standards and Technology (NIST) in the United States defines it as a deviation from load

The ratio of the power of a single sideband signal within a unit bandwidth at the wave frequency to the total power of the carrier signal.

相位噪声测量单位：

最常用的相位噪声测量单位是与载波频率功率距离一个特定频率的1赫兹带宽内的单边带(SSB)功率。

£(f) = 1 Hz带宽内的噪声功率/总信号功率

其中，£(f) 的单位为 dBc/Hz.

图1 所示为 SSB 相位噪声测量结果。频率和幅度均为对数刻度。对数图显示的是由最小和最大偏

移频率指定的频率范围内的相位噪声测量值。黄色迹线为原始测量结果，蓝色迹线为平滑后的结果。

下表列出了十进制频率偏移和相应的噪声功率（归一化到 1 Hz 带宽）。

Main phase noise measurement techniques:

1. Direct spectrum technology

2. Phase detector technology

3. Reference signal source/PLL method

4. Frequency detector method

5. Heterodyne (digital) phase detector method

6. Dual channel cross-correlation technology

Interpretation of the significance of the main parameters and indicators of the clock:

Frequency accuracy and stability are important indicators for measuring the performance of clocks or oscillators. By using phase comparison method and frequency counting

Testing methods such as magic, Allan variance, and frequency difference can be used to evaluate the frequency accuracy and stability of clocks or oscillators.

When conducting testing, attention should be paid to the stability of the measurement environment, the accuracy of the measuring equipment, the selection of testing time, and multiple repetitions

Testing, data analysis, and interpretation. At the same time, a good signal source with very low phase noise, that is, very good frequency

Spectral purity can ensure better RF link indicators and performance throughout the entire system. If the local oscillator signal of a receiver

Excellent phase noise index means that the carrier modulation information can be accurately restored, improving the signal-to-noise ratio and achieving high efficiency

The ability to accept.

These tests and evaluations are crucial for selecting the appropriate clock or oscillator, as well as for clock synchronization, navigation positioning, communication transmission, and more

Scientific research and other applications have important guiding significance.