low pass filter in viva/calculator

Dear David,

A couple of thoughts come to mind...perhaps you have already considered these...

1. In your schematic, you could include a low pass filter and hence could directly plot the low pass filter output with your unfiltered outputs. A coltage controlled voltage source might be used to prevent any loading of the output under test.

2. In ViVA's calculator, choose the dft function and take the dft of the signal of interest. Using the clip() function, select the portion of the resulting DFT corresponding to the frequency components you wanted to capture using a low pass filter. Finally, use the fourEval() function to determine the inverse DFT and hence the resulting time domain waveform.

3. Finally, although someone may have written a skill function to implement an IIR low pass filter, I've occasionally downloaded the time domain version of a waveform (using ViVA - Send To...Table and svae as csv format) or an ocean script) and, using an Excel workbook where I've implemented an IIR based low pass/bandpass/high pass filter, I can vary the low pass filter frequency and compare the filtered and unfiltered waveforms. If you are interested in the workbook, I'll gladly pass it along...but it is very basic and I am sure others have more elaborate versions.

I hope these help a bit...

Shawn

A couple of other options. One is to use the iinteg function to integrate it (probably not what you want). Another is to use the moving average function here

Another is to use the svcvsp component from analogLib which allows you to create a Laplace (s-domain) voltage controlled voltage source to define your filter. This is of course then in the simulator rather than post-processing.

Regards,

Andrew.

Hi Shawn,

Thank you very much for the reply.  I'll give these options a shot and see which one works out best.  I would be interested in taking a look at your basic excel file, if that's not too much trouble.

Again, thank you.

David

Hi Andrew,

Thank you very much for your reply as well. svcvsp option sounds interesting, I was not aware of it's existence.  I'll give it a shot.

I also tried to use the SKILL code, but did not get far (I'm a total beginner when it comes to SKILL).  I was able to "load(abMovingAgv.il)" in the CIW window, but could not get it to register in the calculator (i.e., I do not see abMovingAvg in the list of functions).  If you have a simple suggestion I can try to get it to load, I'd be much obliged.

Once again, thanks for the inputs.

David

Hi David,

> I would be interested in taking a look at your basic excel file,

> if that's not too much trouble.

Absolutely! I hope it helps and makes sense...I've uploaded a zip file containing the Excel file.

As I mentioned, the workbook is pretty simple. However, it can be used to compute a lowpass or highpass filtered signal in the time domain. I've added a few instructions to a sample lowpass filter at 5 MHz. The coefficients of the IIR filter are found using Excel's (now Frontline) Solver. The example illustrates the methodology. Let me know if you have any questions.

Shawn

Shawn500meg_lpf_080814.zip

HI David,

I just read your response to Andrew. I think I can help you.

If you load the SKILL code in the CIW using the load command with a path to the file as shown below:

load "<path_to_file>/abMovingAgl.il"

You then need to register the function in the calculator (Andrew includes this in the instructions in the comments header of the file) in the CIW:

abRegMovingAvgSpecialFunction()

Once the calculator is open, you can now utilize the function by providing a waveform followed by the period over which to compute the moving average. For example, I have a waveform called "qclkout_phase_lsb" whose x-axis spans 0 to 250 and the calculator entry to plot the moving average up to 200 is:

abMovingAvg(qclkout_phase_lsb 200)

The abMovingAvg()  function does not appear in the list of Calculator functions on my machine.

Shawn

(Thank you Andrew!)

"

Note that after calling abRegMovingAvgSpecialFunction, you'll have to change the cyclic field in the Functional Panel to "Skill User Defined Functions" to see it. If it's on "All" you won't see it. Here's what that panel should look like:

Note that to use the function (i.e. just type it into the buffer), there's no need to "register" it; the code just needs to be loaded. The registration is just so that you can click on it in the function panel and (dependent upon the function) have a form pop up.

Regards,

Andrew.

Shawn, Andrew,

Thank you both very much, really appreciate your help and inputs.  I'll play around with all these options and see how far I get!

David

Hi everyone,

I used the skill script - 'abMovingAvg.il', and it work perfectly fine in the ADE-L. Thank you Andrew Beckett for uploading this solution.

For some reason, ADE-XL had trouble finding the function moving average function and would report an error when I run corner simulations. I tried loading the function again in the CIW window with no success.

I came up with another way to calculate the moving average using the equations in the Calculator tool. Here is the equation - 

(((iinteg(((VT("/vrfp") - VT("/vrfm")) * IT("/I_rectifier/vrfp"))) - iinteg(lshift(((VT("/vrfp") - VT("/vrfm")) * IT("/I_rectifier/vrfp")) (10 / 9.15e+08)))) * -9.15e+08) / 10)

Here I'm trying to calculate the input power of my block. '(VT("/vrfp") - VT("/vrfm")' is the differential input voltage. ' IT("/I_rectifier/vrfp")'  is the input current. 

'(10 / 9.15e+08)' is the time period over which I want the average to be calculated. 

The waveform from the above equation matches with the waveform generated by the skill code. 

I wanted to share this equation here hoping it might be useful to someone else. 

Regards,

Ashwath

Ashwath,

You need to load the code from your .cdsinit so that the background virtuoso (known as the ICRP) picks it up OK. Otherwise it will not be visible in the background process which performs the calculations after simulation.

Regards,

Andrew.