Non-coherentdemodulationisusuallyusedforFSKsignal,wherenarrowbandfilterwithgoodselectivityisnecessaryforextractionofbothsignalenvelopingandtiming.Thecomb-spectrumIIRfilterisusedhere.Inthispaper,anintroductionisgivenabouttheimplementationprincipleofthealldigital2FSKdemodulator,withanemphas