TABLE OF CONTENTS Multipage schematics can be used to organize and simplify large circuit designs and to incorporate PSpice simulations into a PCB Layout design. The mixed analog/digital circuit from the last example (see the schematic in Fig. 9-59) is reused in this example but is modified to demonstrate how to route a single PCB from a multipage schematic project and add PSpice simulation capabilities. The example also demonstrates two methods used to establish isolated ground planes using blind vias and a buried chassis shield. The technique allows quiet circuits to be placed on one side of the board and shielded from noisy digital circuits, which are placed on the other side of the board.
In the previous example a single plane layer was used to produce a digital ground and an analog ground even though there was really only one ground net. The two ground systems were produced by physically segregating the parts on the board and removing a strip of copper from the one plane (creating a split plane) between the two circuit areas.
In high-density, high-frequency digital designs multiple ground planes are often used even when there is only one type of circuit ground (as demonstrated in the Example 4 below). This helps reduce loop inductance when using multiple routing layers and control trace impedance (see Chap. 6 for details). When two plane layers are used for a single net, connections are made to both planes simultaneously through...
