전자파 연구실 1 5. Ground planes and layer stacking

전자파 연구실 2 Provide stable reference voltages for exchanging digital signals Distribute power to all logic devices Control crosstalk between signals Ground and power planes perform three critical functions 5.1 High speed current follows the path of least inductance

전자파 연구실 3 Return current density underneath a signal trace

전자파 연구실 Crosstalk in solid ground planes Crosstalk between two conductors depends on L m and C m. In digital problems, inductive crosstalk is as big or larger than capacitive crosstalk.

전자파 연구실 Crosstalk in slotted ground planes

전자파 연구실 6 Ground slots also happen on dense backplanes. Always make sure the ground clear-outs around each pin have ground continuity between all pins.

전자파 연구실 7 For a long line the ΔI ≈ ΔV/Z 0. For a short line driving a heavy capacitive load C

전자파 연구실 8 Crosstalk in slotted ground planes Fengchao Xiao, Yohei Nakada, Kimitoshi Murano, and Yoshio Kami,“Crosstalk Analysis Model for Traces Crossing Split Ground Plane and Its Reduction by Stitching Capacitor,” Electronics and Communications in Japan, Part 2, Vol. 90, No. 8, 2007

전자파 연구실 9 Crosstalk reduction using stitching capacitors

전자파 연구실 10 Fig. 9. The near-end (a), S 21, and far-end (b), S 41, crosstalk characteristics between the two traces while the stitching capacitor is between the two traces.

전자파 연구실 Crosstalk in cross-hatched ground planes Power and ground grid saves board area, but at the expense of increased mutual inductance. Does not require separate power and ground plane layers. (Two layer board) Appropriate for small low-speed CMOS and ordinary TTL design. Inadequate for high-speed logic.

전자파 연구실 12 Cross-hatched ground planes Adequate for high impedance transmission lines. Crosstalk between two lines over a cross- hatched ground planes.

전자파 연구실 Crosstalk with power and ground fingers Don’t use this. Massive amount of self and mutual inductance is introduced.

전자파 연구실 Guard traces Guard traces appear extensively in analog design. At audio frequencies, on a two layer board having no solid ground plane, a pair of grounded traces running parallel to a sensitive input circuit can reduce crosstalk by an order of magnitude. In digital circuit, a solid ground plane provides most of the benefits of grounded guard traces.

전자파 연구실 How to stack printed circuit board layers Power and ground planning Specify signal rise time, number of the signals, physical dimensions of the board Make a guess as to the track width. Estimate self and mutual inductance using solid, hatched, and power-ground fingers. If you use a solid ground plane, plan on using ground and power planes in pairs to prevent warping in the circuit board.

전자파 연구실 Chassis layer

전자파 연구실 Selecting trace dimensions High density signal line decrease PCB cost. High density traces increase crosstalk, increase power handling capacity. Minimum trace width is limited by production processes Routing density vs. number of routing layers

전자파 연구실 Classic layer stacks

전자파 연구실 19