You can tell when something isn’t as clear as it should be. The same questions come up time and again. You ask three experts and get three different answers. Routing differential pairs can be like that. Why? Because “it depends” – on exactly what signals those pairs are carrying and what kind of PCB you’re creating.
If we look inside the box of any electronic product around us, many would find a programmable device, such as a field programmable gate array (FPGA), implemented within the design. These programmable devices allow designers to control the functional behavior of that product easily. Such FPGA devices have changed the environment of electronic product design by giving the designers greater flexibility in providing a tailored solution for their customers. But all this comes at a price that is paid for during product development.
Luckily, where signals need return vias, component vendors often do most of the work for you. Let’s look at a PCI Express differential pair. First, the standard connector, showing its pinout but not its body; I’ll cover the connector body in a moment. The signal pin assignments are also standardized.
Although we’ve been talking about it for years, in PCB design it has yet to catch on in quite the same way despite there being a host of benefits to be reaped from modular design practices. So in the first of this two-part series I’d like to challenge you to ask yourself a few questions about how you reuse designs.
Incorporating FPGAs into PCBs designs can be tricky and involves a constant dialog of communication between the FPGA designer and design and PCB/layout designer throughout the process – which can be tiresome, tedious and, worst of all, time-consuming.
Are you one of the many designers developing today’s complex PCBs? Those containing high pin count ICs like FPGAs or new microprocessors sharing multiple voltage rails? If you’re anything like the people I’ve been talking to recently, you might be suffering from time-consuming and costly problems in supplying the chips with power over the required frequency range. Yep – you’ve got a Power Integrity problem.