Method of controlling the low speed single-ended signal interference to the RF bands

Low speed IO signals on single ended lines such as the low pin count (LPC), high definition audio (HDA), serial peripheral interface (SPI) and so forth, typically has low emission energy from 30MHz onwards and normally meeting the EMC radiated emission requirements. However, the harmonics of these low speed IO signals may still pose the risk of interfering the RF bands such as the 3G/LTE/WCDMA and WiFi. These harmonics noise increases the noise floor of the platform at the mentioned RF bands and de-sensitizing the receive sensitivity. One of the root causes identified is the fast slew rate on the clock that causes the high amount of harmonics content. In this paper, an example of the data signal slew rate control on a flexible printed circuit (FPC) cable simulation model was being studied and with careful control of the data signal slew rate, the platform noise interfering with the GSM 850 bands can be reduced.