Using oscilloscope X-Y displays

文章：亚瑟·皮尼（Arthur Pini）

X-Y显示器（也称为散点图或横图）提供了一种将一个痕迹绘制在另一个轨迹上的方法。这种类型的显示显示了两个波形之间的比较和关系。可以通过将其添加为二维图的颜色或强度变化来引入第三个参数，例如发生频率。

The X-Y display mode finds many classical and current applications. From the classic Lissajous pattern to measure phase or frequency ratios, to state transition diagrams for modern quadrature communications systems. X-Y plots can show if there is a relationship between two variables. If such a relationship is found it can show if the relationship is linear or nonlinear and the direction of the relationship. This article will look at some of these applications.

Lissajous Patterns

X-Y情节的经典介绍是Lissajous情节。两次正弦波相互绘制。对于相同频率的正弦波，该图用于测量正弦波之间的相位差。使用现代示波器，只需使用测量参数读取相对阶段就更加容易。如果正弦波处于不同的频率，则可以确定其频率之比如图1所示。

图1An X-Y plot of two harmonically related sine waves the ratio of the number of horizontal peaks to the number of vertical peaks shows the frequency ratio of the inputs in this case 2 to 5.

该图显示了两个输入的频率之间的关系为2至5。测得的频率为1和2.5 MHz。

Curve tracer

Using an oscilloscope along with an arbitrary waveform generator (AWG) you can characterize semiconductor device using the X-Y display to plot their V-I characteristics. Figure 2 shows the result of measuring a silicon diode.

图2基于AWG生成的十二个施加的电压值以及通过设备产生的最终电流的硅二极管的V-I曲线。

AWG生成的十二个脉冲，电压振幅从-5伏特到+5伏特，该脉冲施加到二极管上。使用示波器的序列模式以每个序列段为一个脉冲，从二极管上的电压和电流通过二极管。测量电压和电流参数汇总在趋势图中，每个点一个参数值。电压趋势应用于X-y显示水平输入，比例因子每次分裂1伏，而当前趋势则以每分划分为12.4 mA。所得的X-Y显示屏显示二极管V-I特征。这样的快速测试对于匹配组件之类的东西很有用。

Quadratic signal measurements

Quadratic signal generation uses two signals with a ninety-degree phase difference to generate a signal with a variable phase. Two signals added in quadrature define a vector with a magnitude and a phase. The magnitude of the input signals determines both vector attributes. X-Y plots, supported by X-Y cursors allow you to view and measure the vector phase and magnitude as it is generated by the quadrature inputs as shown in Figure 3.

图3两个正交信号的X-Y显示屏显示了为信号的二次总和生成的向量的相轨迹。X-Y光标读取矢量幅度（半径）和相位（角度）以及笛卡尔坐标。

X-Y显示屏使您可以通过由两个指数加权的RF脉冲的二次总和定义的旋转向量可视化所追踪的路径。除了通道1和2中的源样品点中的电压外，X-Y光标读取了矢量幅度（半径）和相对于正X轴的相对于正X轴。这意味着同时测量所有光标测量向量的源组件。401MV矢量幅度是349.6MV X分量和196.9 mV y组件的结果。此信息在使用二次信号生成（例如雷达和数字通信）的应用程序中很有用，在这些应用程序中，可以轻松地将矢量参数中的错误追溯到源组件。

x - y显示也可以呈现为persistence display which retains multiple traces overlaid on the display. Persistence displays show the frequency of occurrence of the displayed pixels either using displayed intensity or color. Figure 4 shows the in-phase(I) and quadrature (Q) components of a 16QAM signal along with the X-Y display showing I plotted against Q, the state transition diagram. Monochrome persistence is used on the X-Y display.

图4Rendering the X-Y display in monochrome persistence shows the data states of the state transition diagram as brighter dots while the multiple transitioned phase paths also are shown as brighter.

The state transition diagram shows the data states at the end of each transition path as well as marking the path between data the states. The waveform spends more time at each data state than on the transition path and therefore the data states are shown as brighter points on the X-Y display. The four phase states at 45, 135, 225, and 315 degrees are written over twice with two different vector amplitudes and also appear brighter. Persistence thus provides additional information about this measurement including more clearly showing the overlapping vectors.

Power related X-Y measurements

X-Y显示器还用于测量开关模式电源设备。一个示例绘制了电源FET与电流的电压，以确保该设备在其安全操作区域内运行（SOA），如图5所示。

图5X-Y显示器用于通过绘制排水电流与流量到源电压来测量功率FET的SOA。通过/失败测试将X-Y显示屏与掩模进行比较，红色圆圈表示故障。

The drain to source voltage (V_DS) across the FET is applied to the horizontal axis and the drain current is applied to the vertical axis. The vertical section of the X-Y display represents the FET in conduction, the V_DS当电流增加时，几乎是恒定的。水平回路显示FET关闭的时间，电流为零，电压为振荡。之间的迹线表示设备耗尽功率的开关转换。测试可以验证设备电压，电流和电源限量不超过。

蓝色区域是通行/故障蒙版，用于监视测量。X-Y痕迹不应与面膜相交。如果确实如此，则表示失败，它将被红色圆圈标记为故障。此外，通过/失败测试具有多种响应选项，包括硬件和软件，以指示响应操作的测试状态。

另一个相关的X-Y测量是测量电感设备的磁性。图6显示了电感器的磁性磁滞图。

图6The magnetic hysteresis plot plots magnetic flux density as a function of magnetic field strength.

磁滞图输入是磁场强度和通量密度。磁场强度是从电流通过电感器计算得出的，而通量密度是从施加电压的积分得出的。本文中使用的示波器具有用于功率测量的软件选项，该软件根据知识线圈几何（横截面区域和磁路径长度），电压和电流执行这些计算。磁滞回路内部的区域是每个周期损失的能量，称为磁滞损失。

Mechanical measurements

X-Y displays can be used to analyze mechanical devices. This requires appropriate transducers to convert mechanical parameters into proportional electrical signals. An example of an X-Y display of a mechanical device is a pressure-volume plot for an engine as shown in Figure 7.

图7X-Y显示器绘制压力随内燃机中的气缸体积的函数。

使用圆柱体的火花塞移植的压力传感器读取压力。使用旋转编码器根据测量的曲柄角度计算体积。两种换能器都使用示波器的恢复功能来允许在这种情况下以压力和体积的标准单位进行测量。PV图中有两个循环。上部，一个代表动力冲程，较低的是排气笔。发动机每个周期生成的机械工作与光伏图回路内的区域成正比。动力中风是积极的工作，排气中风是负面的。

结论

显而易见的是，X-Y显示器是解释测量值的非常有用的工具。它允许您比较信号，显示绘制变量之间的关系，并以图形方式显示二次输入的向量幅度和相位。它还可以提供循环过程中能源贡献或损失的信息。您应该牢记它用于研究双重跟踪应用程序的工具。

本文最初发表在EDN。

亚瑟·皮尼is a technical support specialist and electrical engineer with over 50 years experience in electronics test and measurement.