壓制emi噪聲的技術(shù)-文庫(kù)吧資料
2025-03-08 15:17本頁(yè)面
【正文】 ced by reflection and absorption of unwanted noise. Reflection is the dominant factor for highfrequency band as is present in electromagic field radiation test. The basic shielding materials for this frequency band is aluminum or parable low impedance material. 38 Shielding of Case Making the shield case39。s inductance causes a potential difference developed between the grounds of IC1 and IC2. It is possible that the noise caused by this potential difference flows through the grounds and the interface circuit to the cable. The mon mode noise generated in this manner can be effectively suppressed by reducing the ground impedance, suppressing the signal current, or inserting an EMI suppression filter in the signal line. 14 2. Suppressing EMI Noise Emission ? Approaches to Suppression Emission of EMI Noise ? Principal Emission Suppressing Methods ? EMI Suppression Filters ? Improved Ground Patten ? Changing Component and Pattern Layout ? Shielding 15 Approaches to Suppression Emission of EMI Noise In typical electronics circuits, noise is radiated from both circuit patterns and connecting cables. 16 Approaches to Suppression Emission of EMI Noise EMI noise emission suppression model 17 Approaches to Suppression Emission of EMI Noise Guidelines to select noise suppressing point Level of direct emission StrongWeak from noise source Number of noise ManyFew transfer routes (cables) Number of noise FewMany sources (ICs) Suppress noise source Suppress noise at transfer route 18 Principal Emission Suppression Method 19 EMI Suppression Filters It is important to thinking about how to use EMI suppression filters from the design stage and not when the prototype board is pleted. More effective noise suppression can be achieved by installing the EMI filters at the potential noise source and conductive noise paths during the initial design stage and then removing unnecessary filters. 20 EMI Suppression Filters The basic rule of EMI suppression filter application is to locate it near the noise source or the noise receiving unit so that the effectiveness will not be degraded by coupling of the filter39。 otherwise, some even order harmonics are also included. 5 Radiated Noise from Digital Circuit Boards Noise generated by IC Radiated noise from patterns Effect of EMI suppression Filter 6 Noise Generated by IC Radiation of noise requires both a noise source where noise is generated and antenna from which noise can be received. In t
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