Optimized virtual ground fence for power delivery filtering of mixed-signal systems

In this paper, an efficient noise isolation technique in mixed-signal systems using semi-lumped element resonators is presented. The resonators act as a filter which can be implemented between the power delivery networks of RF and digital circuits. The power filtering is accomplished due to a short circuit that can be induced between the ground and power planes of the RF domain at the designed resonant frequency. Each resonator is consisted of a high-impedance micro-strip trace, acting as an inductor and a low-impedance open-circuited line providing a desired capacitor. As an array of the resonators surrounds the sensitive analog section of a mixed-signal system, a virtual ground fence (VGF) can be provided. It is shown that the semi-lumped element based VGFs require less PCB area compared to the ones implemented by quarter-wavelength open-circuited stubs. To show the effectiveness of the proposed method, a fast semi-analytical technique using a physics-based via model is employed. To this end, the semi-analytical method is altered accordingly to fit the problem of the plane-pair with the vias and the VGFs. To compare the simulated results, a full-wave finite-element based solver is utilized.