基于直方图的数字化束流位置处理器检测方法

Detection Method of Digital Beam Position Monitor Based on Histogram

  • 摘要: 数字化束流位置处理器(DBPM)是基于北京正负电子对撞机(BEPCⅡ)和高能同步辐射光源(HEPS)等工程需求研发的束流位置测量核心设备之一。针对DBPM模拟数字转换(ADC)模块的批量测试需求,提出了用直方图检验ADC性能的方法。直方图的形状可确定ADC的锁相功能和输入信号幅值。使用分离算法获取直方图中每个峰对应的数据,并计算统计量。建立每个峰的统计量与时钟抖动和信噪比(SNR)的映射关系。分别用仿真和实验的方式验证该方法的有效性。直方图法是一种简单、快速且准确的测量DBPMADC性能的方法,该方法已植入DBPM自动测试平台,成功应用于DBPM产品的批量检测。

     

    Abstract: The digital beam position monitor processer (DBPM) is one of the important beam diagnosis equipments in particle accelerator and it will be massproduced during the construction of Upgrade of Beijing Electron Positron Collider (BEPCⅡ) and high energy photon source (HEPS), which brings great challenges to the testing work. The analog to digital converter (ADC) module is an essential component of DBPM and its conversion accuracy determines the resolution of the beam position measurement. Therefore, in order to ensure that these two projects meet the design targets, it is necessary to test the ADC performance. Its main observation object includes the phaselocked loop, sampling clock jitter, signaltonoise ratio (SNR), etc. To meet the batch test requirements of the selfdeveloped DBPM ADC, a method of testing the sampling performance based on the histogram was proposed. The histogram’s test principle is that the shape of the histogram can detect whether the sampling clock is phaselocked to the input signal, the boundary value of the histogram reflects the amplitude of the input signal to judge if the ADC is saturated, and the average and standard deviation of the data peak on the histogram can be used to calculate the clock jitter that conforms to the normal distribution. In this paper, the mathematical relation between the statistics of each data peak, clock jitter, and SNR was simulated by MATLAB in the situation of phaselocking. The separation algorithm was designed to obtain the data corresponding to each peak of the histogram and compute the clock jitter and SNR. An integrated test platform was built and experiments were carried out to verify the testing effect of the histogram method. The experimental results show that when the amount of sampling data is appropriate, the histogram method can complete the test quickly and accurately, and the measurement result is close to that of the highperformance phase noise analyzer. The clock jitter measurement error is less than 200 fs, the SNR measurement error is less than 2 dB, and the entire test duration is less than 1 min, which fulfills large volume testing demands. Compared with the manual instrument measure method, the histogram approach is simpler and lower cost to test with the same order of magnitude accuracy and has been implemented by programming to reduce labor intensity. The test program has been implemented in the automatic test platform and used to batch detection of DBPM products successfully.

     

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