Tuned guard circuit for conductive transmission lines on a printed circuit board

摘要

The present application describes a tuned guard circuit device and method for controlling impedance levels of transmission lines on a printed circuit board having at least one ground plane and at least two circuit components coupled by a conductive transmission line. The guard circuit device of the present invention includes two etched conducting guard bands on the printed circuit board disposed on opposite sides of a selected transmission line and affixed in a spaced parallel relation to the transmission line. The guard bands are of substantially constant width and substantially constant distance from the ground plane and have substantially the same length as the transmission line, and each guard band has a first and a second terminal end. Also included is a capacitor connected to the ground plane and connected at each of the first and second terminal ends of each guard band wherein the guard bands are connected to ground through the capacitors. The guard circuit device controls the impedance level of the transmission line by varying the capacitance values of the capacitors to optimize the impedance level of the transmission line. The capacitance values of all the capacitors are, preferably, equal.