Power Integrity

Abstract

Poor power integrity is one of the most common root causes of system-related problems. This is because there are too many things that could affect power delivery to multiple devices on a system. These include DC resistance of PCB traces or power/ground planes, AC impedance of PCB traces, power supply decoupling around the DSP, and or other surrounding circuits such as DDR, clocks, and analog-to-digital and digital-to-analog converters. One of the most challenging tasks for designers is to determine the best decoupling techniques to achieve low noise and high performance. In general, component manufacturers provide a conservative recommendation for power supply decoupling, but in many cases, it is not practical to follow this recommendation because of PCB space availability, power consumption, EMI, or safety requirements. Also, component manufacturers always provide development platforms for designers to evaluate and these platforms typically are a lot larger than the actual design and are not required to be FCC certified, so copying what was done on the development platform is not a guarantee that the design will be successful. This chapter will discuss five important topics for designers: (1) DC resistance of traces; (2) AC impedance; (3) a general rule-of-thumb decoupling method; (4) an analytic decoupling method; and (5) how to make design tradeoffs to achieve the best noise performance possible.