Two-Capacitor를 이용한 PCB 기판에서 발생하는 방사노이즈의 저감에 관한 연구

Abstract

According to the rapid development of the electric and electronic industry, the interests in the EMI (Electromagnetic Interference) / EMS (Electromagnetic Susceptibility) are gradually increasing as electromagnetic environment problems.

Recently, to solve the problem on mal-functions of digital equipments with high clock frequency, which are operated in low power and wide frequency band. In addition, the international regulations e.q., IEC, CISPR, FCC, ITU-T, etc. for the EMI/EMC have suggested. Therefore, it is necessary to perform countermeasure for EMI/EMC satisfying the international regulations.

A PCB may act as an antenna to radiate RF energy through free space or couple through a cable interconnect. Because PCBs can be major source that produce radiated emission. It has been proved and verified that due to high speed clock and pulsed data signals, currents of these signals in PCBs can produce strong coducted emission and radiated emission in a wide scope of frequency. So most PCBs act as an unintentional radiator and are regulated by international EMC requirements unless design requirements include it as being a transmitter.

To minimize the effects of an unwanted antenna existing in a PCB, EMC design and suppression techniques are required. These include establishing a good ground system in the layout in addition to the use of a Faraday cage (to contain RF emission). RF filters also reduce unwanted RF signals with minimal effects on the desired data, as long as the filter is properly chosen for its intended function. In this thesis, EMI suppression techniques for radiated emissions from PCB trace, source suppression using 2-capacitor Low Pass Filters is adopted.

Firstly, the RF energy from a simple 2 mm × 50 mm micro-strip transmission line was measured by using HITACHI company EMV-200. This tester using a magnetic near field prove shows a spatial distribution of electromagnetic noise on a PCB or an IC . From the transmission line with input 10 dBm signal of 100, 300, 500, 1000 MHz. A radiation was observed 59 ~ 76 as a maximum value.

Then, it was simulated using ADS and found optimal design using 2-capacitor. According by the experimental results, it has been clearly proved that the radiated emission from PCB is reduced 4.8 ~ 13.2 dB by using 2 capacitors.