Discrete spread-spectrum sampling (DSSS) to reduce RF emission and beat frequency issues

Using spread spectrum clocking techniques with digital systems is quite commonly used to reduce RF emission at the higher harmonics, this to fulfill the existing EMC regulations. Results have been reported frequently. However, with analogue interfaces, fixed frequency sampling is still in place for the sake of signal reconstruction and processing algorithms. In this paper the use of discrete spread spectrum sampling is introduced which will not only reduce the RF emission from these analogue-to-digital or digital-to-analog interfaces but will also eliminate the effect of beat frequencies. The beat frequency signal resulting from fixed frequency sampling harmonics and fixed frequency RF interference, will be spread out as sideband noise in the baseband of the intended signal. A similar DSS technique has been introduced in a patented ABCD power conversion concept using 16 (2⁴) fixed frequencies selected randomly.