Differential-line-scheme of clock and signal bus of high-speed digital circuits and systems for minimizing electromagnetic radiated emission

Abstract

Even though the electromagnetic radiated emission due to the ground and power line fluctuation of the integrated circuit (IC) and printed circuit board (PCB) is minimized, the additional reduction of the radiated emission from the clock and the signal lines are not easy. In this paper, we introduce a new clock and signal line scheme to suppress the radiated emission from the fast transition of the clock and data signals. We proved that the proposed differential-line-scheme (DLS) could reduce the radiated emission by more than 10 dB compared to the conventional single-line-scheme (SLS). First, we report the necessity and the usefulness of the differential-line-scheme and explain the operation of the inverter circuit for the differential-line-scheme using HSPICE simulation. Test ICs and PCBs were designed and fabricated, to verify the effect of differential-line-scheme with the proposed inverter circuit. The electromagnetic radiated emission due to the device under test (DUT) is measured using a gigahertz transverse electromagnetic (GTEM) cell. The measured result has shown that the differential-line-scheme with the proposed inverter circuit achieves more than 10 dB suppression of the electromagnetic radiated emission. The results confirm that the clock and signal line is fundamental source of the radiation. The proposed differential-line-scheme with the proposed inverter circuit will be useful for both high-speed digital IC and PCB design.