Grounding design for analog/digital mixed signal circuit

• Main Author: Teng, Gabrwyn Dao Yong.
• Other Authors: See Kye Yak
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Electronic circuits
• Online Access: http://hdl.handle.net/10356/53398
• Institution: Nanyang Technological University

For mixed signal circuit design, ensuring good noise immunity is as important as other design issues such as timing and power consumption. It is a common practice to split on a ground plane on a mix-signal circuit to ensure good noise isolation. However, from EMI point of view, a split ground design can cause discontinuity to the return path of the high frequency digital signal. In this report, we will investigate the effectiveness of split ground planes in mixed signal circuit to test on various design layouts. A simulation software is used to analyze the power distribution network (PDN) impedance, overall near-field and far-field emission and lastly the signal isolation and its impact on the analog input. Based on the simulation and analysis done in this research, a split on the ground plane will reduced the PDN impedance by 50% when compared to a common ground plane. A slight shift in the resonance frequency is also observed by splitting the plane but it is not affected by different split width used. In addition, it also provides a better signal isolation of up to 20 dB at 5 GHz when compared to common ground plane. The signal isolation will increase when the split width increases. However, the surface current on the split plane is higher than that of a common ground plane due to return current is being confined beneath the trace. This results in a higher far-field radiated emission. Hence, the use of split plane has to be done with care to ensure minimum radiated emission.