When performing analysis on acquired waveforms, multiple processing steps are often required to extract information from the data. As the complexity of waveform analysis increases and the applications become more demanding in the analog, digital, and RF domains, the number of processing steps required to extract measurements from acquired data can increase dramatically. In order to gain more insight into these measurement problems, block diagrams and flow charts are valuable tools to model the processing steps. LeCroy’s Processing Web Editor feature enables a graphical approach to problem solving by allowing users to develop math and measurement processing chains using familiar block diagram/flowchart formats as shown in the example in Figure 1.
The processing web supports using multiple math and measurement operations within a single math trace.
WaveRunner 6Zi series oscilloscope
Displays shown in the tutorial are based on the following initial setup on a WaveRunner 6 Zi scope:
- Connect a coaxial cable from channel 1 to the Aux connector on the front panel.
- Recall the default setup: File pull down > Recall Setup> Recall Default.
- Turn off channel 2.
- Set the input coupling on Channel 1 to be 50 Ohms: Touch or click the channel 1 annotation box>touch or click on the coupling field >select DC 50 Ω.
- Set up the Aux output to be the Fast Edge signal. Utilities pull down > Utilities Setup >Aux Output Tab>touch or click on Fast Edge. The Fast Edge signal is a 5 MHz, 450 mVp-p, square wave.
- Auto Setup the scope: Press Scope Setup then select Auto Setup from the fly-out menu.
- Set the channel 1 signal amplitude using the C1 dialog box. Set the vertical scale to variable gain by checking the Var Gain checkbox. Adjust the vertical scale of channel 1 to maximize the C1 signal amplitude on the display. It should be 90% of full scale.
- This completes the initial setup. The scope display should be similar to Figure 2.
Accessing the Processing Web
Open the Math Setup dialog box (Math>Math Setup). Touch or click the F1 tab on the math setup dialog. This will open the F1 dialog box as shown in Figure 3.
Press the WebEdit button on the left side of the F1 dialog box. Check the Trace On check box.
Press the Show Processing Web button to open the Processing Web Editor as shown in Figure 4.
The Processing Web Editor uses a graphic interface to allow a user to create complex math and measurement parameter functions that use multiple single operations combined in various ways. The Web Editor dialog has buttons that will add math, measurements, or parameter math functions as shown in the left side in Figure 4. There is also a button which adds Previews, these are viewing windows that show the waveform or measured value at the output of any operation.
The Math tab allows the user to set the function of any other the math traces to single operator, dual operator, histogram, or web edit. Note that we have already set F1 to be the output from the processing web. This is indicated by the F1 terminal being on the right had side of the Web Editor in Figure 4. Open and look at the Math Tab.
The Measure tab similarly allows the user to set the function of any of the measurement parameters to be a simple measurement, parameter math, or the web edit. Open and look at the Measure tab.
A Processing Web Calculation Example
LeCroy oscilloscopes include a digital low pass filter math function called Enhanced Resolution (ERES). ERES applies a finite impulse response (FIR) digital low pass filter with the bandwidth of the filter set by a user selection of the number of bits of enhancement in a range of 0.5 to 3 bits in 0.5 bit steps. In our example we will use the ERES filter and some simple math to create a high pass filter in the F1 math trace.
From the Web Editor tab press the add math button. The math operator scroll list should appear. Scroll to the ERES entry and touch or click on it to open the ERES math function in the Web Editor as shown in Figure 5.
Touch or click the ERES math icon in the Web Editor. It will be highlighted and the right hand tab of the Web Editor dialog box will show the controls for the ERES math function as shown in Figure 5.
Use the Add Math button again to add the Sparse function. The sparse function is used to reduce the effective sampling rate of a waveform. The bandwidth of the ERES filter is a function of the effective sample rate and we want to reduce the 20 GS/s sample rate to 100 MS/s to reduce the bandwidth to the range of the 5 MHz fast edge signal we are using as a source.
Use the Add Math button to add the Difference function. These are the three math functions we need to create the high pass filter. Note, that unlike the math function traces which are limited to at most two operators, the processing web has no limit on the number of operators as long as you have enough processing memory.
Touch or click on each of the math operator icons and drag them to the approximate positions shown in Figure 6.
Touch or click on the blue output arrow on the terminal C1 in the upper left corner of the Web Editor. The arrow will turn green, drag from the C1 output arrow to the In terminal of the Sparse math operator. Note that a blue ‘wire’ will follow and establish a connection between C1 and Sparse. Repeat the process connection the following terminals:
Once you have ‘wired’ up the math operation you can drag the operator icons wherever you want to keep the Web Editor space neat. The screen should look like Figure 7.
Touch the output arrow of the ERES icon, it will turn green. Press the Add Preview button in the Web Editor dialog box. A preview box will open attached to the ERES output. It is showing a view of the waveform coming from the ERES function. Repeat this to add a preview to the output of the difference icon.
Adding a Measurement to the Operation
The processing web also supports measurements. Touch or click the Measurement tab on the Web Editor. Touch or click the web edit icon associated with parameter P1. The web edit icon will be highlighted and the P1 terminal will appear on the right of the Web Editor display. Touch or click on the Web Editor tab. Press the Add Measure button. The Measurement scroll box should appear. Select the amplitude measurement. The amplitude measurement icon will appear on the Web editor. Move the amplitude icon to a convenient location. Make a connection from the output of the difference operator to the input of the amplitude icon. Make another connection from the output of the amplitude icon to the P1 terminal on the right side of the Web Editor.
Touch or click on the output arrow of the amplitude icon, it should turn green. Press the Add Preview button on the Web Edit dialog box. A numeric readout preview box will appear showing the amplitude reading as shown in Figure 8.
Setting Up The math Operation Arguments
We have completed setting up the math processes we will need. We now have to set up the arguments for each math process.
Click or touch the Sparse icon. The Spare tab will appear on the Web Editor dialog box. Set the Sparsing factor to 200. This means the Sparse function will only keep one sample from each 200 raw data samples.
Click or touch the ERES icon. The ERES tab will appear, set the bits field to 1, note that the -3dB bandwidth of the FIR low pass filter is 12 MHz.
Press the close button on the Wed Editor dialog box. The screen should return to a normal waveform display. Use the measure setup to turn on the parameter P1. The screen should look like Figure 9.
The trace F1 is the high pass filtered version of the input C1. Adjust the Amplitude scale of F1 so that it matches that of C1 (60 mV/div in this example) using the zoom tab on the F1 dialog box. The high pass filtered signal contains only the edges of the waveform because the low frequency component has been attenuated.
So you can see that the processing web allows you more flexibility in setting up complex math and measurement operations using a large number of operations within a single math function trace.
This completes the tutorial.