RF Circuit Design, 2nd Edition

Chapter 9: Layout

9.1 Difference in Layout between an Individual Block and a System

The difference in layout between an individual block and a system can probably be summarized as follows:

First, the size of the PCB (printed circuit board) or the IC substrate for an individual block is usually smaller than that for a system. Therefore, the ground surface for an individual block is usually equipotential if the maximum dimension of the PCB or IC substrate is much shorter than the quarter wavelength corresponding to the operating frequency. Consequently, fewer grounding problems arise. On the contrary, the large ground surface of a system is usually not equipotential, so forward and return current coupling may take place. Coercive grounding is absolutely necessary and must be taken care of seriously.

Second, the number of metallic layers of the PCB or the IC substrate is different. Very often, a PCB or an IC substrate with two metallic layers is applied to lay out an individual block, whereas a PCB or an IC substrate with multiple metallic layers is applied to lay out a system. The conductive via is applied in both layouts. Via study is more important in the layout for a system than for a block because more vias with more complicated configurations are applied in the layout of a system.

Another remarkable difference is the number of DC power supplies. Multiple DC power supplies are usually required in the layout for a system, whereas a single power supply is usually sufficient in ...