Coupling coefficients for signal lines separated by ground lines on PC boards

Signals propagating on PC (printed circuit) board traces are subject to overshoot and crosstalk, both of which increase as rise time decreases. Overshoot depends upon the ratio of self-inductance to capacitance to ground; crosstalk depends also upon mutual inductance between traces and trace-to-trace capacitance. Multilayer boards with ground planes close to traces are shown to decrease inductance and coupling capacitance, thereby tending to reduce overshoot and crosstalk. A similar reduction is obtained by placing grounded traces between signal traces. Equations which relate capacitive and inductive parameters to trace geometry, including intervening grounded traces, are presented. Examples of crosstalk, as calculated by a SPICE model using derived parameters, are shown