A new 'filtered Allan variance' and its application to the identification of phase and frequency noise sources

Digital noise generators are described as is their use to generate sample series that simulate frequency samples as given by a counter. Applying the Allan variance to the samples of six generators (white phase, flicker phase, white frequency, flicker frequency, frequency random walk, filtered flicker frequency) yields the expected theoretical slopes. The method used consists in filtering the f/sup -1/ and f/sup 0/ phase noise by means of a digital filter in the time domain, (using the Z transform), which yields f/sup -3/ and f/sup -2/ noises, which thus can be identified by Allan variances. The combination of the digital filter and the Allan variance corresponds to a novel variance, which is described and compared to the well-known modified Allan variance.<>