idealCircuit simulator

Andre Kesteloot andre.kesteloot at
Thu Jan 3 16:17:27 CST 2013


Very  promising results indeed.


On 1/3/2013 13:54 PM, Karl W4KRL wrote:
> Tacoistas,
> I ordered an AD9850 DDS Arduino shield on eBay for less than $6. It 
> should be here from Thailand at the end of the month.
> A quick reading of the application notes suggests that the output 
> should go through a 70MHz low pass filter for use in the 0 to 40MHz 
> range. There are several nice on-line filter designers:
> But after looking at the low-res circuit jpg on eBay it turns out that 
> it has an on-board filter. The values are vaguely similar to what the 
> on-line designers calculate for a 7-pole Butterworth Pi but each 
> inductor is shunted with a small capacitor. I thought it would be 
> interesting to figure out what the filter was supposed to do and 
> looked unsuccessfully for an on-line circuit simulator. There is a 
> fair one sponsored by Digi-Key at but 
> I found it so awkward to use that I gave up after drawing the circuit. 
> It did not produce any useful results.
> Then I came across idealCircuit at
> The download is only 1.4MB and is free. There are probably a lot of 
> limitations but it looks good enough for quick general use. One 
> obvious drawback is the lack of part IDs. Maybe there is a work around 
> in the manual.
> I drew the filter and got a voltage and phase graph in just a few 
> minutes with zero frustration. The circuit and results are attached. 
> It seems to be a 70MHz low pass with some ripple and peaks near 
> cutoff. _Comments on the design and performance of the filter are 
> welcome. Why did they shunt the inductors with caps?_
> Happy New Year
> Karl W4KRL
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