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| + | ====== Simulation Software For PLL ====== | ||
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| + | //This was contributed originally by Grant Hodgson, October 1, 2007 on the Microwave mailing list// | ||
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| + | // http://www.valinet.com/mailman/listinfo/microwave // | ||
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| + | ---- | ||
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| + | There are some free PLL simulation tools that allow you to see the effect of any changes on the loop components before you warm up the soldering iron. | ||
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| + | For serious PLL design work it is well worth using these tools as they can predict all sorts of things that are difficult, if not practically impossible to measure. | ||
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| + | Two of the best ones are EasyPLL from National Semiconductors and ADIsimPLL from Analog Devices - and they are both free. | ||
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| + | Both tools are superb. Easy PLL has a nice feature that displays the noise contribution from each resistor in the loop filter. This allows you determine how low the resistor for the final pole should be, and it also shows what will happen if the resistor is made too small - you will lose the extra 6dB/octave benefit of the 3rd pole. But more importantly, you can see the effect on the loop's phase margin which is a good measure of loop stability. | ||
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| + | There may well be a trade-off between getting the lowest phase noise and the lowest levels of spurs, but you can simulate the effect of changing something in the loop which is usually a lot quicker than changing Rs and Cs. | ||
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| + | Choosing the reference frequency - this should be as high as possible to reduce both spurs and phase noise, but if you increase the reference frequency then you may need to increase the loop bandwidth to get the lowest overall phase noise. | ||
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| + | EasyPLL: | ||
| + | http://webench.national.com/appinfo/wireless/webench/easypll.html | ||
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| + | ADISimPLL: | ||
| + | http://forms.analog.com/form_pages/rfcomms/adisimpll.asp | ||