LeCroy's XStream™ series oscilloscopes allow users to embed any of MATLAB's library of filter types right into the oscilloscope's processing path. In figure 1 we show an example of a 2-pole, 1 MHz, Butterworth low pass filter which has been applied to the acquired waveform using the MATLAB math function.

Figure 1:

The response of a MATLAB based 2 pole Butterworth filter (lower trace) to a swept sine input (upper trace).

The MATLAB math function allows the user to call the MATLAB program and execute a MATLAB script file right in the scopes processing path. The output from MATLAB is returned to the next processing stage and operations continue within the scope. Figure 1 shows the basic setup of the MATLAB math function. The function accepts one or two input signals and returns a single output. Selecting the MATLAB tab of the math dialog box allows the user to load an existing .m file or create a new one in the built-in editor, as shown in Figure 2.

Figure 2:

A view of the editing window in the WaveMaster MATLAB math function showing part of the MATLAB .m file being executed

The .m file used in this example is shown in Figure 3. The filter type used is a Butterworth lowpass filter. MATLAB offers a choice of some 7 filter types. This filter is a relatively slow cutoff second order filter. The command to create the filter coefficients is:

$$[b,a]=butter(2,1e6/(Fs/2))$$

Where b represents the numerator coefficients of the digital filter and a represents the denominator coefficients of the digital filter.

The arguments for the Butterworth filter are order (2 in this case) and the cutoff frequency (this must be normalized to Nyquist which is why we have divided by half of the sampling frequency, Fs).

The filter is implemented using the filter command:

$$WformOut = filter (b,a,WformIn1);$$

This applies the filter coefficients to the selected data, in this case the input waveform (WformIn1)

The following command queries the scope via Microsoft automation to obtain the sampling frequency.

% Interfacing the scope via automation
h=actxserver('Lecroy.XStreamDSO');
% Get Sample Frequency
Channel =
h.Object.Item('Acquisition').Object.Item
('C1').Out.Result; 1
Fs = 1/Channel.HorizontalPerStep;

% Interfacing the scope via automation
h=actxserver('Lecroy.XStreamDSO');
% Get Sample Frequency, Fs
Channel=h.Object.Item('Acquisition').Object.Item('C1').Out.Result;
Fs = 1/Channel.HorizontalPerStep;

In this example we implemented a simple low pass filter using MATLAB. You can extend this to use any of the available MATLAB functions or scripts.

WaveMaster also supports embedded math operations based on VBScripts, Mathcad, or Excel.

1Note this command is appropriate for MATLAB version 6.5 or higher.