PCB Board Reverse Engineering Resistive Decoupling

PCB Board Reverse Engineering Resistive Decoupling Around Board Edge is a set of experiments were conducted with a resistor-capacitor combination placed around the outer edge of the test board.

Figures 29 through 31 show the various port-to-port S21 measurement results for the case with only a 470 pF capacitor, a 470 pF capacitor and 20 ohm resistor, and a 470 pF capacitor and 2.2 ohm resistor. The plain .01uf capacitor case was also reploted on Figure 29 for reference.

There was some improvement in the S21 at higher frequencies with the R-C decoupling combination. However, lower frequencies were significantly better with the fully distributed capacitor configuration.

EMISSIONS AROUND THE EDGE OF THE BOARD

It was determined that the primary emissions from the test board was around the edge of the board,  rather than off the top or bottom plane. Figure 32a and 32b shows the field scan from EMSCAN for a particular frequency. Each color indicates a 10 dB change in amplitude. A standing wave mode is clearly visible along the edge plot, and the peak fields are much higher than the bottom plot (Figure 32b). A set of tests at a variety of frequencies (both resonant and non-resonant) confirmed this analysis when clone PCB board gerber file.

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