Looking inside the flatline to determine DC power integrity

Every engineer knows that a perfectly flat and stable IC power rail, at any voltage, exists only in fantasy. In practice, the ideal thin, straight line contains several types of fluctuations, or Periodic And Random Disturbance (PARD), including dynamic load responses, PSU output-voltage drift, and
interference signals such as power supply switching transients or clocks coupled onto the power lines from nearby sources.

Judicious placement of decoupling and filtering networks can counter these fluctuations. Accurate noise measurements are needed to guide their design and verify effectiveness. This is becoming increasingly difficult
given the complexity of today’s DC Power Distribution Networks (PDNs) and the tight tolerances on accuracy and ripple specified in IC datasheets. Today’s complex ICs can require multiple power domains to run various circuits like I/Os or on-chip analogue, as well as digital circuitry at core voltages
as low as 1.0V, or sometimes lower. As a result, even a relatively small system can require many different voltages: a typical solid-state drive (SSD) may require about 12 different power rails, within the confines of form factors as small as 54mm x 78mm x 5mm
for an industry-standard 1.8 inch drive. More complex systems, such as network switches, may have more than 50 rails, while the next generation of smartphones will contain more than 100 different power domains within their ultra-slim and compact dimensions. 

Read the full article in the August issue of DPA