The application of spread spectrum techniques in IC EMC design

• Main Authors: Guo-Siang Hsiao, 蕭國祥
• Other Authors: Ming-Shing Lin
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/97959996485559700151

碩士 === 雲林科技大學 === 電機工程系碩士班 === 96 === In this study, a meander-line antenna and a spiral antenna were employed to perform the radiated emission (RE) measurement in a TEM cell and in the Yuntech 3m chamber. The measurement data acquired in these two environments were used to construct correlation factors, which, in conjunction with the correlation factors between a 3m and a 10 chamber, can be used to deduce the RE performance of a device under test (DUT) from the results measured using a TEM cell. The procedure established here for measuring the RE performance of an IC using a TEM cell was fully complied with the IEC 61967-2 standard. Clock circuits have been considered major sources of EMI from an IC. Hence, the reduction of EMI from the clock signals has been an active research topic in recent years. In this study, a spread spectrum technique was employed to modulate the frequency of a clock signal, leading to spreading each harmonic energy of the clock over a wider bandwidth. A TI CDCE-906 developing board with a built-in FM triangular modulating function was used as the spread spectrum clock generator (SSCG). In the experiment, a crystal-generated clock signal was first fed into the developing board, the output of which is then a spread clock signal. This spread clock signal is in turn used as the referenced clock of a microprocessor PIC-18F4420. The measured RE results of this microprocessor reveals that the RE levels with the spread clock signal are indeed smaller than those with a regular clock signal. That is, the EMI due to the microprocessor can be effectively reduced if the spread clock signal is employed. In short, this approach reduces the fundamental signal as well as the higher-order harmonic components, decreasing the EMI of the whole system.